THE CITRUS REENTRY PROBLEM: RESEARCH ON ITS CAUSES AND EFFECTS, AND APPROACHES TO ITS MINIMIZATION

RESIDUE REVIEWS VOLUME 67

The citrus reentry problem: Research on its causes and effects, and approaches to its minimization

RESIDUE REVIEWS The citrus reentry problem:

Research on its causes and effects, and approaches to its minimization

Editor

FRANCIS A. GUNTHER

Assistant Editor

JANE DAVIES GUNTHER

Riverside, California

ADVISORY BOARD F. BAR, Berlin, Germany· F. BRO-RAsMUSSEN, S.oborg, Denmark

D. G. CROSBY, Davis, California· S. DORMAL-VAN DEN BRUEL, Bruxelles, Belgius C. L. DUNN, Wilmington, Delaware • H. EGAN, London, England

H. FREHSE, Leverkeusen-Bayerwerk, Germany • K. FUKUNAGA, Saitama, Japan H. GEISSBUHLER, Basel, Switzerland· G. K. KOHN, Richmond, California

H. F. LINSKENS, Nijmegen, The Netherlands· N. N. MELKINOV, Moscow, U.S.S.R. R. MESTEES, Montipellier, France· P. DE PIETRI-TONELLI, Milano, Italy

I. S. TAYLOR, Melborne, Australia· R. TRUHAUT, Paris, France I. ZIEGLER, Miinchen, Germany

VOLUME 67

SPRINGER-VERLAG

NEW YORK HEIDELBERG BERLIN

1977

Coordinating Board of Editors

FRANCIS A. GUNTHER, Editor

Residue Reviews

Department of Entomology University of California

Riverside, California 92521

JOHN W. HYLIN, Editor

Bulletin of Environmental Contamination and Toxicology

Department of Agricultural Biochemistry University of Hawaii

Honolulu, Hawaii 96822

WILLIAM E. WESTLAKE, Editor

Archives of Environmental Contamination and Toxicology

P.O. Box 1225 Twain Harte, California 95383

All rights reserved. No part of this book may be translated or reproduced in any form without written permission from Springer-Verlag.

© 1977 by Springer-Verlag New York Inc. Softcover reprint of the hardcover 1st edition 1977

Library of Congress Catalog Card Number 62-18595.

The use of general descriptive names, trade names, trade marks, etc. in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as under­stood by the Tmde Marks and Merchandise Marks Act, may accordingly be used freely by any­one.

New York: 175 Fifth Avenue, New York, N.Y. 10010 Heidelberg: 6900 Heidelberg 1, Postfach 105280, West Germany

ISBN-13: 978-1-4684-7064-2 e-ISBN-13: 978-1-4684-7062-8 DOl: 10.1007/978-1-4684-7062-8

Preface

That residues of pesticide and other contaminants in the total environ­ment are of concern to everyone everywhere is attested by the reception ac­corded previous volumes of "Residue Reviews" and by the gratifYing en. thusiasm, sincerity, and efforts shown by all tve individuals from whom manuscripts have been solicited. Despite much propaganda to the contrary, there can never be any serious questions that pest-control chemicals and food-additive chemicals are essential to adequate food production, manufac­ture, marketing, and storage, yet without continuing surveillance and intel­ligent control some of those that persist in our foodstuffs could at times con­ceivably endanger the public health, Ensuring safety-in-use of these many chemicals is a dynamic challenge, for established ones are continually being displaced by newly developed ones more acceptable to food technologists, pharmacologists, toxicologists, and changing pest-control requirements in progressive food-producing economies.

These matters are of genuine concern to increasing numbers of gov­ernmental agencies and legislative bodies around the world, for some of these chemicals have resulted in a few mishaps from improper use. Adequate safety-in-use evaluations of any of these chemicals persisting into our foodstuffs are not simple matters, and they incorporate the considered judgments of many individuals highly trained in a variety of complex biologi­cal, chemical, food technological, medical, pharmacological, and toxicologi­cal disciplines.

It is hoped that "Residue Reviews" will continue to serve as an integrat­ing factor both in focusing attention upon those many residue matters requir­ing further attention and in collating for variously trained readers present knowledge in specific important areas of residue and related endeavors in­volved with other chemical contaminants in the total environment. The con­tents of this and previous volumes of "Residue Reviews" illustrate these ob­jectives. Since manuscripts are published in the order in which they are re­ceived in final form, it may seem that some important aspects of residue analytical chemistry, biochemistry, human and animal medicine, legislation, pharmacology, physiology, regulation, and toxicology are being neglected; to the contrary, these apparent omissions are recognized, and some pertinent manuscripts are in preparation. However, the field is so large and the in­terests in it are so varied that the editors and the Advisory Board earnestly solicit suggestions of topics and authors to help make this international book-series even more useful and informative.

viii Preface

"Residue Reviews" attempts to provide concise, critical reviews of timely advances, philosophy, and significant areas of accomplished or needed en­deavor in the total field of residues of these and other foreign chemicals in any segment of the environment. These reviews are either general or specific, but properly they may lie in the domains of analytical chemistry and its methodology, biochemistry, human and animal medicine, legislation, pharmacology, physiology, regulation, and toxicology; certain affairs in the realm of food technology concerned specifically with pesticide and other food-additive problems are also appropriate subject matter. The justification for the preparation of any review for this book-series is that it deals with some aspects of the many real problems arising from the presence of any "foreign" chemicals in our surroundings. Thus, manuscripts may encompass those matters, in any country, which are involved in allowing pesticide and other plant-protecting chemicals to be used safely in producing, storing, and shipping crops. Added plant or animal pest-control chemicals or their metabolites that may persist into meat and other edible animal products (milk and milk products, eggs, etc.) are also residues and are within this scope. The so-called food additives (substances deliberately added to foods for flavor, odor, appearance, etc., as well as those inadvertently added dur­ing manufacture, packaging, distribution, storage, etc.) are also considered suitable review material. In addition, contaminant chemicals added in any manner to air, water, soil or plant or animal life are within this purview and these objectives.

Manuscripts are normally contributed by invitation but suggested topics are welcome. Preliminary communication with the editors is necessary be­fore volunteered reviews are submitted in manuscript form.

Department of Entomology University of California Riverside, California March 1, 1977

F.A.G. J.D.G.

Foreword

Worldwide concern in scientific, industrial, and governmental com­munities over traces of toxic chemicals in foodstuffs and in both abiotic and biotic environments has justified the present triumvirate of specialized pub­lications in this field: comprehensive reviews, rapidly published progress re­ports, and archival documentations. These three publications are integrated and scheduled to provide in international communication the coherency es­sential for nonduplicative and current progress in a field as dynamic and complex as environmental contamination and toxicology. Until now there has been no journal or other publication series reserved exclusively for the diversified literature on "toxic" chemicals in our foods, our feeds, our geog­raphical surroundings, our domestic animals, our wildlife, and ourselves. Around the world immense efforts and many talents have been mobilized to technical and other evaluations of natures, locales, magnitudes, fates, and toxicology of the persisting residues of these chemicals loosed upon the world. Among the sequelae of this broad new emphasis has been an inescap­able need for an articlated set of authoritative publications where one could expect to find the latest important world literature produced by this emerg­ing area of science together with documentation of pertinent ancillary legis­lation.

The research director and the legislative or administrative advisor do not have the time even to scan the large number of technical publications that might contain articles important to current responsibility; these individuals need the background provided by detailed reviews plus an assured aware­ness of newly developing information, all with minimum time for literature searching. Similarly, the scientist assigned or attracted to a new problem has the requirements of gleaning all literature pertinent to his task, publishing quickly new developments or important new experimental details to inform others of findings that might alter their own efforts, and eventually publish­ing all his supporting data and conclusions for archival purposes.

The end result of this concern over these chores and responsibilities and with uniform, encompassing, and timely publication outlets in the field of environmental contamination and toxicology is the Springer-Verlag (Heidel­berg and New York) triumvirate:

Residue Reviews (vol. 1 in 1962) for basically detailed review articles con­cerned with any aspects of residues of pesticides and other chemical contaminants in the total environment, including toxicological consid­erations and consequences.

x Foreword

Bulletin of Environmental Contamination and Toxicology (vol. 1 in 1966) for rapid publication of short reports of significant advances and dis­coveries in the fields of air, soil, water, and food contamination and pollution as well as methodology and other disciplines concerned with the introduction, presence, and effects of toxicants in the total envi­ronment.

Archives of Environmental Contamination and Toxicology (vol. 1 in 1973) for important complete articles emphasizing and describing original experimental or theoretical research work pertaining to the scientific aspects of chemical contaminants in the environment.

Manuscripts for Residue Reviews and the Archives are in identical for­mats and are subject to review, by workers in the field, for adequacy and value; manuscripts for the Bulletin are not reviewed and are published by photo-offset to provide the latest results without delay. The individual editors of these three publications comprise the Joint Coordinating Board of Editors with referral within the Board of manuscripts submitted to one pub­lication but deemed by major emphasis or length more suitable for one of the others.

March 1, 1977 Coordinating Board of Editors

The citrus reentry problem: Research on its causes and effects, and approaches to its minimization

By

F. A. Cunther*, Y. Iwata*, C. E. Carman*, and C. A. Smith*

Contents

I. Introduction......................................................................................... 2 a) Physiological effects of OP pesticides on workers......... .......... .......... ... ....... 3 b) Routes of worker exposure to residues.................................................... 7 c) Dimensions of the reentry problem....................................................... 10 d) Legislative approaches to the reentry problem......................................... 12 e) Measurement of pesticide exposure....................................................... 15 f ) California citrus investigations.............................................................. 19

II. Foliar dislodgable residues....................................................................... 20 a) Background. .................. .... ........ ............................ ... .... ..... .... ........ ... 20 b) Methodology.................................................................................... 25 c) Effect of soil dust type on residue dissipation........................................... 33 d) Effect of climatic factors on residue dissipation......................................... 37 e) Effect of method ofapplication on residue dissipation................................. 62 f ) Effect offormulation on residue dissipation... ............. ........ ... ..... ....... .... ... 67 g) Effect of citrus variety on residue dissipation............................................ 69 h) Reduction ofresidues by tree washing.................................................... 73 i ) Reduction of residues by chemical degradation......................................... 76

III. Fruit rind residues................ ................................................................. 79 IV. Orchard soil dust residues........................................................................ 83

a) Methodology.................................................................................... 83 b) Residues from spray drift and runoff....................................................... 83 c) Sloughable residues........................................................................... 86 d) Effect of climatic factors on residue dissipation......................................... 91 e) Soil moisture and residue dissipation... ................................................... 91

V. Airborne residues .................................................................................. 103 a) Background.............. .......... .... ........ ..... ....... ...... ..... ..... ................ ...... 103 b) Vapor-phase residues.......................................................................... 103 c) Airborne particulate residues............................................................... 104

VI. Methods other than human exposure studies for assessing hazard in treated groves 107 a) Foliar residue estimation...... ..... ....... .... .............. ...... .... ............ .... ....... 110 b) Soil residue estimation..................................................... ................... III c) Odorants as pesticide residue warning indicators....................................... 119 d) Mathematical estimation methods......................................................... 119

Summary and conclusions.............. ....... ...... ...... .............. ..... .............. ... .... ...... 124 References.................. ......................................................... ....................... 127

'Department of Entomology, University of California, Riverside, CA 92521.

2 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

I. Introduction

The "reentry problems" arises from agricultural workers becoming ill as a result of entering and working in a field some time after a pesticide applica­tion has been made to a crop plant. Although sulfur, with its capacity to cause eye irritations, may be claimed to have caused the first reentry prob­lem in agriculture, the problem as currently evaluated is limited to the use of cholinesterase (ChE)-inhibiting organophosphorus (OP) pesticides. The definition of the problem in the future will likely extend to other compounds and other biological effects, such as conjuntivitis and dermatitis. Table I lists the reported cases of post-treatment illnesses to farm workers in California, where most of the incidents in the United States have occurred. A few iso­lated incidents have been reported from some of the cotton-and tobacco­growing states in this country; there are no documented reports yet from any other country. It is evident from this table that the problem is not a new one and that it appeared hand-in-hand with the introduction of OP pesticides to agriculture. The use of OP pesticides has increased greatly and will probably continue to increase as the use of organochlorine pesticides becomes more restricted. Production and usage of OP pesticides in the United States are expected to continue at a high level for the forseeable future, even though other approaches to pest controls such as biological control techniques, pheromones, and new classes of pesticides will be added to pest-control methods. More intensive farming methods, including OP pesticides, are being introduced to many other countries, and the same problems experi­enced in the United States will probably be experienced by these other us­ers. Although foods, fibers, and feedstuffs were grown successfully in the United States prior to the introduction of synthetic pesticides in the late 1940s, expectations have changed regarding both quality and quantity of agricultural production as a result of the effectiveness of chemical pest control. Increasing world population requires greater productivity and it is, therefore, unrealistic to halt the use of OP compounds as a solution to the reentry problem (TASK GROUP 1974).

QUINBY and LEMMON (1958) documented in detail 11 worker-poisoning episodes involving 70 workers engaged in thinning, picking, cultivating, or irrigating crops of apples, pears, grapes, oranges, and hops treated with one lb or more of parathion!/ A. QUINBYet al. (1958) reported on health hazards, including reentry hazards, due to the use ofOP pesticides, primarily methyl parathion and azinphosmethyl, in cotton culture in the delta area of Mississippi. Following an outbreak of illness among peach harvesters in 1963, MILBY et al. (1964) studied 186 peach orchard workers in relation to pesticide application practices and fruit harvesting procedures representative of the orchards in which they worked. Although parathion could be easily recovered from all elements of the orchard environment, it was not present in amounts deemed sufficient to account for the observed illnesses. The toxic parathion alteration product paraoxon was postulated as the prime cause of the outbreak. DAVIES et al. (1976) reported on the occurrence of systemic poisoning in 1970 when 20 workers became ill shortly

'Chemical designations of pesticides mentioned in text are listed in Table XXIII.

Citrus reentry problem 3

after entering a cornfield in Florida that had been sprayed the day before with a mixture of ethyl and methyl parathion. WARE and MORGAN (1976) have expressed concern for the cotton insect field checkers (cotton scouts) who may acquire up to ten hr of intermittent pesticide residue exposure/day and up to 40 hr/week.

Thus, reported problems involving injury or illness as a result of exposure to treated crops have been largely limited to tree fruits, grapes, tobacco, and cotton where hand labor is involved, resulting in continuous and extensive contact with treated foliage and other plant surfaces (PAYNTER 1976); however, one cannot rule out the possibility of risk in leafY vegetables such as cauliflower, Brussels sprouts, artichokes, cabbage, broccoli, celery, and lettuce (TASK GROUP 1974). This is supported by the 1970 Florida cornfield episode (DAVIES let al. 1976). The principal hand labor operations requiring contact with treated foliage and other plant surfaces include harvesting, fruit thinning, summer pruning, and propping (grapes). In addition, "scouting" to determine the cotton pest situation and the need for pesticide treatment may result in considerable contact with treated foliage. Cotton scouts, however, could be considered a special group of field laborers requiring special methods of protection (TASK GROUP 1974). While some exposure is unavoidable in each of these operations, harvest normally results in the greatest exposure of workers to treated crops (PAYNTER 1976). With all crops, parathion is the compound most often involved when episodes of worker poisoning occur. This may be coincidental with its extensive use in pest control or may be related to some special property associated with the compound, such as its high dermal toxicity. The heart of the reentry problem is not that workers become ill after entering a pesticide-treated grove several hours or days after application, as this might be anticipated, but rather arises from the fact that episodes are reported in groves several weeks or months after the last known pesticide application, during which time toxic residues should have dissipated to a safe level.

a) Physiological effects of OP pesticides on workers

The cause of the worker illnesses is attributed to exposure to the op pes­ticides and their alteration products. The primary mode of action of most of these pesticides is the inhibition of ChE enzymes throughout the body. Normally, acetylcholine liberated at the presynaptic endings and motor endplates by nerve impulses acts directly upon motor and autonomic effector cells to produce appropriate responses. The enzyme ChE terminates the re­sponse by hydrolyzing acetylcholine to choline and acetate ion. There is also a considerable quantity of the enzyme in the circulating blood, both in the red cells and in the plasma; physiologists have not yet given a satisfactory account of the role of these high concentrations in blood (GAGE 1967). op compounds entering the bloodstream may undergo a number of reactions. They may be hydrolyzed to relatively nontoxic products. Compounds con­taining the P=S group may be converted to p=o compounds (oxons) by mixed-function oxidase enzymes, making them much more toxic, but gener­ally also more susceptible to hydrolysis.

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6 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

Through a two-stage process, the second of which is irreversible, OP compounds can attach a phosphoryl group to ChE and thereby render the enzyme unable to perform its function. Excessive concentrations of acetyl­choline, therefore, accumulate in the endings of parasynaptic nerves to the smooth muscles of the iris, ciliary body, bronchial tree, gastrointestinal tract, blood and blood vessels, in the secretory glands of the respiratory tract, in cardiac muscle, and in the synaptic nerves of sweat glands. There is also in­creased accumulation of acetylcholine in motor nerves to voluntary muscles in the autonomic ganglia, and in the central nervous system (KRAMER 1972). SUMERFORD et al. (1953) postulated that the rate of fall in ChE rather than the level of ChE determines whether or not symptoms representing sys­temic effects of the toxicant could be expected.

The first definite symptoms of intoxication include nausea and loss of ap­petite which may be aggravated by smoking. Other effects such as vomiting, abdominal colic, diarrhea, sweating, and salivation then ensue. Central nervous system effects, which include restlessness, giddiness, apprehension, slurred speech, loss of coordination, and hyperventilation later become ap­parent (KRAMER 1972). QUINBY and LEMMON (1958) described symptoms reported for workers involved in poisoning episodes. Often-described com­plaints and observations, which varied with the degree of exposure and with individuals, were uncontrollable twitching of the eyelids, headache, vertigo, nausea, vomiting, retching, subnormal temperature, chills, excessive pers­piration, pallor, weakness, fast pulse, twitching of arm and leg muscles, chest pains, abdominal cramps, visual disturbance, and miosis (pinpoint pupils). Administration of atropine gave dramatic relief. MILBY et al. (1964) reported that the most consistent complaints described by clinically ill peach pickers were nausea, vomiting, headache, profound weakness, and extreme malaise. Other manifestations of parasympathetic stimulation including miosis, blurred vision, dizziness, excessive sweating, salivation, diarrhea, and abdominal cramping were reported, but not consistently so.

Large doses of OP pesticides lead ultimately to death, but the field worker is extremely unlikely to accumulate such dosages. The onset of symptoms whose severity increases with continued exposure should force the individual to cease working and thus to terminate continued exposure. No fatal cases of poisonings from pesticide residues related to reentry have been verified (TASK GROUP 1974). Thus, the reentry problem is concerned with the debilitating effects on the workers with the added burden of loss of income during the illness to a group which can least afford it. Following human exposure to OP compounds, plasma ChE levels return to normal within a few days; red blood cell (RBC) ChE levels, however, only return to normal as new red blood cells are produced and require much longer for complete recovery to pre-exposure levels. For the overall safety of workers, it would be desirable also to know whether inhibition of ChE is the sole toxic action of the OP compounds. While no gross or microscopic pathologies were observed after two one-year chronic feeding studies at 100 ppm of parathion in the total diet of rats (WILLIAMS et al. 1958), certain effects may not have been observable with the sample size used. All OP pesticides are alkylating agents and thus, in addition to the hazards of acute toxicity to

Citrus reentry problem 7

workers caused by the anti-ChE properties, there may be another hazard from the alkylating effects of these compounds on DNA (deoxyribonucleic acid). Several OP pesticides, including dichlorvos, trichlorfon, dimethoate, Bidrin, and oxydemeton-methyl, have been shown to be potentially mutagenic in some organisms (WILD et ai. 1975), raising the possibility of germ cell mutations and carcinogenicity in man. It should be strongly em­phasized that no evidence for mutagenic or carcinogenic activity of OP pes­ticides in man has ever been observed. All mammals have a variety of effec­tive defenses against potentially mutagenic chemicals in various organs and within the cells themselves. However, both dimethoate and trichlorfon have been reported to be carcinogenic in rats and mice (GIBEL et ai. 1973) when applied for long periods at high doses.

Little data exist on carcinogenicity and mutagenicity of OP pesticides in mammalian species, due at least partly to the time and expense of animal testing. KaLATA (1976) stated that an animal test program for carcinogenicity requires about $100,000 and three years' time. At least one other animal study, on dichlorvos, has been carried out, using mice and Chinese hamsters; no detectable effects were observed (DEAN and THORPE 1972). Other studies have been performed which indicate little or no effect from normally encountered concentrations of pesticides; WILD (1975) has ob­served that tissue concentrations in mammals following exposure to pesticides are lower by a factor of 103 to 105 than the lowest concentrations which are mutagenic for microbes in vitro. Although it may well be an insignificant hazard, the possibilities of mutagenicity and carcinogenicity are an argument for keeping exposure to OP pesticides as low as possible.

b) Routes of worker exposure to residues

There are three principal routes by which workers may be exposed to OP pesticides: respiratory, oral, and dermal. Pesticide applied to foliage can dis­sipate through volatilization and thus give a finite air concentration of pes­ticide; workers would then be exposed simply through breathing the air. Also, worker activity can disperse pesticide-bearing particulate matter into the air, and the workers could inhale the dust. Small particles «7 /-L) would penetrate into the respiratory tract, giving rise to respiratory exposure, while larger particles would be trapped by mucus which can be swallowed, resulting in oral exposure. The pesticide residing on the plant surface or sorbed to particulate matter on foliage or on the soil surface can be transfer­red to worker skin and clothing, resulting in dermal exposure.

CARMAN et al. (1952) were first to note that in Southern California, citrus tree surfaces are normally covered with dust and microdebris and that this condition coupled with the use of parathion formulated as wettable powders may lead to losses of parathion from the foliage as air dispersions of contami­nated particulate matter; their analytical data supported this contention. The most hazardous exposure to parathion residues was postulated to result from mechanical dislodgment of pesticide-bearing dust during operations involv­ing tillage, picking, pruning, and similar operations. Later, QUINBY and LEMMON (1958) also discounted vapor exposure to parathion; they attributed

8 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

illnesses to extensive contact with fruit and less extensive contact with foliage, a conclusion now reversed. MILBY et al. (1964), using alcohol swabs, confirmed the presence of parathion on the arms and trunk as well as on the palms and hands of peach harvesters and suggested that contact with leaves and tree surfaces contributed to total exposure. GUNTHER et al. (1973) con­sidered foliage to be a more important source of toxic material than fruit, due to the much greater area of foliage/tree; for the average 20-year-old orange tree, the leaf:fruit area ratio is 17:1 and for the average 10-year-old peach tree this ratio is 53:1 for freestone and 28:1 for cling peaches ..

WARE and MORGAN (1976) estimated that field checkers working for 30 min in a just-treated cotton field would accumulate parathion residues of3.5 mg on the hands, 1.1 /Lg by inhalation, and 18 mg on the clothing. Thus, the hands and clothing were the greatest sources of pesticide chemical exposure. Although the amount of trapped material was of sufficient quantity to have an effect on ChE activity if completely absorbed, exposure did not affect serum or RBC ChE levels and there was no detectable p-nitrophenol in urine col­lections from subjects up to 48 hr after exposure. WARE and MORGAN (1976) suggested that data on skin and clothing contamination by the toxicant are therefore inadequate for evaluation of pesticide absorption and effect. It is obviously difficult to estimate how much of the pesticide trapped by clothing ultimately penetrates the skin. MILBYet al. (1964) described peach harves­ters' clothing as being light in weight due to the heat and often sweat­impregnated. Shirts were open at the collar and often shirt sleeves were short or rolled above the elbow. Exposure of greater skin area would, of course, facilitate percutaneous pesticide penetration. The use of protective clothing in warm weather is impractical (PAYNTER 1976). Thus, at tempera­tures which prevail during harvest seasons in most parts of the United States, workers engaged in strenuous physical activities will not wear rubber garments, respirators, and other types of protective devices. The risk of heat prostration may well be greater than the risk from pesticide residues. Also QUINBY and LEMMON (1958) pointed out that most of the laborers who do thinning and similar agricultural tasks may wear their work clothing for a week or longer without laundering. Prolonged wearing of contaminated clothing was thought to increase the likelihood of poisoning. Personal hygiene involving bathing and frequent clothing changes can only be re­commended to workers since such a requirement cannot be practically en­forced. In addition, studies have shown that washing of skin exposed to pes­ticides lowers but does not prevent percutaneous pesticide exposure (TASK GROUP 1974).

A complex lipid mixture known as sebum covers and permeates the outer horny skin layer known as the stratum corneum. Sebum contains many lipids and has a high affinity for lipid-soluble, water-insoluble substances and thus is ideal for the acquisition of most toxic pesticide residues. The average adult skin area is about 17,000 cm2, and the area which is most likely to be directly exposed (face, neck, "V" of the chest, forearms, and hands) is about 2,100 cm2. There is little literature to allow prediction of the relationship between surface concentration and penetration. In the case of parathion, by increas­ing the surface dose from four to 2,000 /Lg/cm2, the percentage of the applied dose that was absorbed remained relatively constant (TASK GROUP 1974).

Citrus reentry problem 9

MAIBACH et al. (1971) reported on the percutaneous penetration of pes­ticides in human males in various regions of the body. The pesticides used were parathion, malathion, and carbaryl. The forearm was used as a frame of reference. A portion of their data is reproduced in Table II. The palm, of which the thick stratum corneum is allegedly almost impenetrable, allowed approximately the same penetration as the forearm. The abdomen and the back of the hand had twice the penetration of the forearm, whereas follicle­rich sites, including the scalp, angle of the jaw, and forehead had four-fold greater penetration. The armpit had a four- to seven-fold increase; the scrotum allowed almost total absorption. The authors concluded that all anatomic sites studied showed significant potential for pesticide penetration and, hence, systemic intoxication through dermal pesticide exposure. Of the dose applied to the forearm, 8.6% of the parathion and 6.8% of the malathion were absorbed. Carbaryl was almost completely absorbed when applied to the forearm. The angle of the jaw also allowed almost total penetration and allowed more rapid absorption. Thus, percutaneous toxicant absorption ap­pears to be dependent on the specific pesticide and its alteration products.

NABB et al. (1966) estimated the percutaneous absorption rates of para­thion and paraoxon in rabbits by comparison of the rate of plasma ChE inhibi­tion observed when the compound was infused intravenously with the rate observed when the compound was applied dermally. The average rates of dermal absorption were estimated to be 0.059 p.,g/min/cm2 of skin area for parathion and 0.32 p.,g/min/cm2 for paraoxon. If this five-fold faster rate of penetration of paraoxon into rabbit skin is also applicable to human skin, paraoxon as a dislodgable residue on parathion-treated plants is indeed a major factor in reentry illnesses, a conclusion amply supported later in this review. Paraoxon was found to be approximately ten times more toxic in­travenously and 55 times more toxic dermally than parathion, another major factor. The difference in ease with which the two compounds penetrated the skin was attributed to the fact that paraoxon is much more soluble in water than is parathion. The water solubilities of parathion and paraoxon at 25°C

Table II. Effect of anatomic region on the percutaneous absorption of topically applied pesticides ( MAIBACH et al. 1971).

Forearma Palm Foot, ball Abdomen

Anatomic region

Hand, dorsum (back) Scalp Jaw angle Postauricular (behind ear) Forehead Axilla (armpit) Scrotum

a Reference region.

Absorption ratio

Parathion

1.0 1.3 1.6 2.1 2.4 3.7 3.9 3.9 4.2 7.4

12

Malathion

1.0 0.9 1.0 1.4 1.8

3.4 4.2

10 F. A. GeNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

are 24 and 2,400 ILg/ml, respectively (WILLIAMS 1951). There was approxi­mately a ten-fold individual variation between rabbits in permeability of the skin by both compounds. The shaved skin of small mammals used in animal studies differs structurally and functionally from human skin, however, and care should be exercised in precisely extrapolating these results to man.

c) Dimensions of the reentry problem

The extent of the reentry problem is difficult to assess. When large groups of workers are involved, the pattern of illness often suggests food poisoning or water-borne gastroenteritis. When small groups are involved, heat stroke is sometimes suggested (QUINBY and LEMMON 1958). Blood ChE measurements can confirm exposure but facilities may not be available to make such measurements. Measurements when made are difficult to inter­pret without pre-exposure baseline values needed for comparison. Even with pre-exposure values comparison is questionable unless both samples have been analyzed under identical conditions (equipment, reagents, analyst) or in conjunction with a standard control sample of known ChE ac­tivity (SERAT and MENGLE 1973). Even identical samples analyzed by diffe­rent laboratories often give dissimilar results even if each laboratory uses the same method of analysis (SERAT and MENGLE 1972).

As stated earlier, the episodes of poisonings appear to be predominately a California problem. KAHN (1976), however, believes that the predominance of episodes in California results from the fact that California is the only state with any meaningful system of reporting and field investigation [California's pesticide safety program is described by MADDY (1976)]. This view is not shared by all, however. This disproportionate regional distribution is gener­ally believed to be due to the existence of other regional differences beside merely differences in official reporting (TASK GROUP 1974). DAVIES et al. (1976) reported that with the one exception involving entry into a treated cornfield, knowledge of the occurence of residue intoxication in groups of agricultural workers in Florida has been discounted by the Florida State De­partment of Health and Rehabilitative Services, the Florida State Depart­ment of Agriculture, and the Florida Citrus Commission. The average RBC and plasma ChE levels noted in 269 migrant Florida workers in 1972 were cited by DAVIES et al. (1976) to support the concept that residue intoxication is not a serious problem in Florida, since the workers were (presumably) fre­quently exposed to foliar residues2 . While it was admitted that milder cases not requiring hospitalization may have been missed, it was contended that had widespread pesticide-related illnesses occurred, these would have been drawn to the attention of the State. Thus, the reentry problem is a difficult one to deal with as its extent is open to debate and difficult to document to everyone's satisfaction.

MILBY et al. (1964), after extensively investigating the 1963 California peach orchard poisoning episode (Table I), postulated that, due to the preva­lence of ChE depression in the workers studied, the problem of significant

2As shown later herein, rainfall can significantly reduce both foliar and soil "dust" residues; compared to California, Florida is a high-rainfall state.

Citrus reentry problem 11

pesticide residue absorption extended beyond the few score cases reported by physicians or discovered by study of a highly selected group of pickers working in orchards in which illness had been reported. On the average, about 4.5 million people are engaged annually in farm employment in the United States (TASK GROUP 1974). At one time or another during the year, probably as many as eight or nine million people do some work in commer­cial agriculture. ~1any of these persons are exposed to OP pesticide residues, but the number who are exposed remains essentially unknown (TASK GROUP

1974). GUNTHER et al. (1973) concluded that since there are more than 300,000 field workers in California, the 28 authenticated incidences in Table I involving about 500 persons since 1949 represent a remarkable safety re­cord. KAHN (1976) believes, however, that the occurrences listed in Table I represent perhaps one % of the occupational illnesses caused by pesticide residues3 . Deaths rarely occur in California due to pesticide exposure of employed workers in agriculture (MADDY 1976 b). In the years 1973, 1974, and 1975, only two deaths were reported in employed agriculture workers due to exposure to pesticides or their residues. These deaths befell two sepa­rate structural pest-control employees (one in 1973 and one in 1975) who used cyanide indoors to kill bees without using gas masks and without standby persons available for safety as required by state regulations. Whereas no fatal cases of poisonings from pesticide residues related to reen­try have been verified (TASK GROUP 1974), just during the period 1970 to 1974 inclusive, a total of 347 agricultural workers met their deaths in job­related accidents, 74 in 1970, 59 in 1971, 62 in 1972, 66 in 1973, and 86 in 1974 (California Department of Industrial Relations 1972 and 1976). Table III lists the above types of accidents and numbers of fatalities involved in 1972, 1973, and 1974. Thus, although the reentry problem exists, other agriculture-related problems causing a vastly greater number of disabling in­juries and deaths have elicited greater priority from regulatory agencies. Ac­cording to physicians' reports, most illnesses due to pesticide exposure occur in persons who mix, load, and apply the material (MADDY 1976 b). Thus,

Table III. Fatal accidents for 1972,1973, and 1974 in California agriculture (California Department of Industrial Relations 1976).

Type of accident

Highway motor vehicle Farm tractors Electrocution Falls from elevations Agricultural machinery Aircraft Accidents in em ployer-provided housing Others

Total

No. of fatalities

1972 and 1973

33 30 10 20

8 12

6 9

128

1974

42 15

6 5 4 3 3 8

86

3Approximately 300,000/yr or 7,SOO,000/2S years; SOO illnesses/7,SOO,OOO workers 0.006% rate of illness. If KAH:-I (1976) is correct, this rate becomes 0.6o/c.

12 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

relatively few cases have been reported among field workers as a result of exposure to pesticide residues on crop plants and soil.

d) Legislative approaches to the reentry problem

Worker reentry safety is not a new concept. In the first reentry-related publication, CARMAN et al. (1952) noted that tillage, picking, pruning, and similar operations should be scheduled so as to avoid the necessity of expos­ing field workers during the immediate post-treatment period, particularly to airborne, residue-bearing particulate matter. These workers studied con­centrations of parathion in the vapor phase and on air-borne particulates (grove "dust") in parathion-treated groves; they found only traces of para­thion in the vapor phase but possibly significant amounts on trapped particu­lates. It was noted that a 30-day safety period was sufficient for citrus opera­tions but that perhaps longer periods might be required for other crops.

In the late fifties some members of a citrus picking crew working in the Riverside, California area reported illnesses while working and it was gener­ally concluded that exposure to OP pesticides was responsible. Orchard re­cords indicated that the last application, prior to the picking operation, was that of parathion at a relatively high dose completed over 55 days earlier. In recognition of the problem, a group at the University of California Citrus Re­search Center, Riverside, in consulation with State and Federal health officers, formulated a plan whereby a research group of the U. S. Public Health Service would be notified immediately at the time of any episode for the purpose of getting to the location promptly and conducting an in-depth study of what actually happened and of relatable factors. As no episodes were reported during the next several years the group dispersed (CARMAN 1976).

In 1970, in an effort to provide better protection for field workers from exposure to pesticide residues on crops, staff members of the University of California, the California Department of Health, and the California Depart­ment of Food and Agriculture analyzed a number of options. The options and the tentative conclusions that were reached are summarized by BAILEY (1972) and MADDY (1976 a). California's position, after the consideration of all alternatives, was that the most practical overall way to protect field work­ers was to establish "reentry intervals" for crops and pesticides with iden­tified problems (MADDY 1976 a). A "worker reentry period" is thus the time interval that must elapse between the date of application of a specific pes­ticide to a specific crop and the date when laborers can safely work in the treated fields. The reentry interval concept is based on the assumption that the potential for intoxication trom residues decreases with time. It is further assumed that the decay process varies so little that a single reentry interval can be applied to a given pesticide-crop combination regardless of regional or climatic variations (SPEAR et al. 1975 b). In June 1971, California estab­lished rather extensive reentry interval regulations specifying the time periods that workers be restricted from activities that involve substantial body contact with foliage in fields of grapes, citrus, peaches, and nectarines after these crops had been treated with anyone of 17 OP pesticides or with sulfur. The current California reentry intervals are given in Table IV. The

Citrus reentry problem

Table IV. California state safe reentry intervals in days after application (California Administrative Code 1976).

Peaches and Insecticide Citrus nectarines Grapes

Azinphosmethyl (Guthion) 30 14 21 Carbophenothion (Trithion) 14 14 14 Demeton (Systox) 5 7 7 Diazinon 5 5 5 Dimecron (Phosphamidon) 14 Dimethoate (Cygon) 4 4 Dioxathion (Delnav) 30 30 30 EPN 14 14 14 Ethion 30 14 14 Malathion 1 1 Methidathion (Supracide) 30 Mevinphos (Phosdrin) 4 4 4 Naled (Dibrom) 1 1 1 Parathion-ethyl 30a 21 21

45b Parathion-methyl 21 6 Phosalone (Zolone) 21 21 21 Imidan 5 5 Sulfur 1 1 TEPP 4 4 Torak 30

13

Apples

14

14

14

14

a Less than eight Ib of actual parathion/ A/application but no more than ten Ib/ A, in the past 12 months.

bMore than eight Ib of actual parathion/A/application or more than ten lb/A, in the past 12 months.

intervals were selected to take into account the toxicity of the pesticides, de­gradation rates, kinds of human exposure according to the cultural practices being employed, types of pesticide usage patterns, amounts of pesticides used, and the combination patterns of certain pesticides (MADDY 1976 a).

From June 1971, when the reentry intervals became effective in Califor­nia, until the present time, there have been few systemic illnesses resulting from exposure to pesticide residues where the required intervals have been adhered to (MADDY 1976 a).

A "Task Group on Occupational Exposure to Pesticides", chaired by Dr. Thomas H. Milby and operating under the aegis of the Federal Working Group on Pest Management, was established in the first quarter of calendar 1972. The National Institute for Occupational Safety and Health (NIOSH) was instrumental in its establishment (MAY 1976). The Task Group was charged to:

(1) Assemble and interpret all available information regarding the extent and severity of this occupational health problem in the United States.

(2) Prepare a report which would identify significant areas in which re­levant information was not available.

(3) Make recommendations for the development of standard research protocols to determine safe reentry intervals for the protection of ag­ricultural and forest workers.

14 F. A. CDITHER, Y. IWATA, C. E. CAR'dA~, A"iD C. A. S'dITH

(4) Suggest interim reentry standards, where possible, based upon .xist-ing knowledge.

The Task Group found that the lack of technical data and the lack of occupa­tional illness-reporting mechanisms in agriculture combined to make it im­possible to formulate interim national reentry standards.

NIOSH evaluated the evidence gathered by the Task Group as well as from other sources and concluded that the majority of reported episodes have been regional in nature with the majority occurring in California, and that it is currently impossible to assess the magnitude of the problem on a national scale (MAY 1976).

During the Occupational Safety and Health Act (OSHA) regional hearing held in Washington, D.C., in August, 1973, Dr. Jon R. May, as a spokesman for NIOSH, supported the concept of "reentry intervals" with flexibility in the form of regional standards (MAY 1976). CARMAN (1976), speaking for the Citrus Industry of California, accepted the reentry requirement as the most compatible and practical method for circumventing further episodes. He stated that the concept of biological tolerance and adaptability negate the view that exposure must be totally eliminated and support the view that re­strictions are needed so that workers are not exposed to unsafe levels of re­sidues. KAHN (1976) strongly criticized the chosen reentry intervals as being based upon unwarranted extrapolations of existing data and stated that not one principle employed in setting standards for consumer health protection is applied to the setting of reentry intervals for the protection of farm work­ers. He contended that economic interests and not worker health interests were foremost when the concept was accepted and that public health profes­sionals, who should be the prime architects for reentry regulations, were not consulted. Human exposure studies were recommended as the most impor­tant area of research. Thus, while reentry intervals have been adopted to protect workers, their role as a viable practical solution or as an interim emergency measure is subject to considerable controversy.

The reentry problem is concerned with the protection of a highly mobile labor force made up of workers who are frequently poorly educated and fre­quently non-English speaking. DAVIES et al. (1976) stated that limited qual­ity care is available to agricultural workers. The implementation of conven­tional health practices in agriculture was considered fragmentary at best and practically nonexistent in some areas. Since the worker cannot be controlled as in a factory situation, his health and safety depend upon the control of the environment in which he works. The first principle of environmental safety requires that the working environment be as free from hazardous conditions as possible (TASK CROUP 1974). The need to use new pesticides, new combi­nations of old pesticides, and new formulations gives rise to a large number of variables that will tax the adequacy of reentry intervals for the protection of workers. CULVER (1976) considered the best alternative to the reentry strategy to be that of preventive medical programs and medical supervision for workers, as currently required for commercial pest-control applicators. Such a program would include the arrangements necessary to insure proper treatment of work-related illnesses and injuries. Education of medical staaff to render correct treatment and arrangements for statewide treatment

Citrus reentry problem 15

facilities would be required. Worker selection would then be based upon pre-employment physicals and worker health would be under constant med­ical surveillance.

e) Measurement of pesticide exposure

Criteria by which to establish the reasonable safety of a given reentry in­terval have not been officially prescribed. Such criteria might be based upon (1) symptomology, (2) biochemical effects such as blood ChE depression, (3) rate of urinary excretion of pesticide metabolites, and (4) presence of pes­ticides in blood or urine (WARE and MORGAN 1976). Given the extreme sen­sitivity of modern techniques for detection of pesticides and their alteration products in blood and urine, a requirement that workers absorb no detecta­ble pesticide in the course of their task is probably incompatible with the continued use of OF pesticides in agriculture (WARE and MORGAN 1976).

Although the measurement of blood ChE activity is widely used in the control of occupational exposure to OF and carbamate pesticides, there does not appear to be any general agreement concerning the interpretation which should be placed on the results obtained from such analyses. In particular, no body of experts has established a threshold for the inhibition of blood ChE which, if exceeded, indicates unsatisfactory working conditions (GAGE 1967). From the available evidence, GAGE (1967) suggested that there is not the slightest risk of toxic effects when the RBC or plasma enzyme is reduced to 70% of its normal pre-exposure value and suggested that a compromise inhibition of 30% be taken as a biological threshold limit for both types of enzymes. It was emphasized that the removal of a worker from his employ­ment when either his RBC or plasma enzyme falls to 70% of its normal value is not required because the he<llth of the individual is thereby affected, but rather to ensure that further absorption does not lead to a deterioration of the worker's condition. WARE and MORGAN (1976) proposed a "no effect" level as a criterion for reentry for cotton scouts. This level could be defined as an absence of statistically Significant depression of ChE activity as a result of exposure, based upon an arbitrary minimum number of subjects. This criterion would provide a substantial safety factor for any anomalous situation that may occur. GAGE (1967), however, stated that any threshold value selected must be sufficiently large to be measurable with an acceptable de­gree of significance, but not so great as an inhibition likely to be associated with toxic manifestations. If a threshold value were established at a value en­compassed by the variability of a normal population, a number of normal in­dividuals would be classed as having been exposed to unsatisfactory working conditions. More seriously, the method would fall into disrepute if workers were too frequently taken off work or if there were an interruption of produc­tion when no clinical symptoms were apparent, nor any evidence of a break­down in safety precautions.

Several alternatives to the measurement of blood ChE levels have been described. The serum pesticide levels and the urinary metabolite levels of a group of pilots and loaders exposed to methyl parathion were compared to their serum and RBC ChE values by ROAN et al. (1969). They found a good correlation between the serum pesticide and the urinary p-nitrophenol

16 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

levels, and no significant correlation of either with ChE levels. It should be noted that these investigators were measuring and reporting absolute values rather than decreases in blood ChE activity. Normal ChE levels can vary widely from one person to another, thus obscuring inhibition due to pesticides. Later, SHAFIK and BRADWAY (1976) reported that urinary p-nitrophenol excretion is significantly more sensitive than blood ChE in measuring absorption of parathion and proposed that urine analyses be used to investigate reentry problems. Collection of urine samples has the advan­tage over blood samples in that highly paid medical technologists are not re­quired, the ever-present risk of infection from drawing blood is avoided, and there would be a greater cooperation from workers to give urine over blood samples. Worker resistance to volunteer more than a few blood samples has been noted by many investigators.

BURNS and PARKER (1975) monitored the plasma and RBC ChE levels and the p-nitrophenol urinary excretion of a group of 12 cotton scouts through an entire growing season. Methyl parathion was the most commonly used pesticide. They observed an initial drop in ChE levels, which returned to normal in about three weeks, although the p-nitrophenollevels indicated continuing exposure to pesticides. The authors suggested that there may be some feedback mechanism in the body which counteracts low ChE levels. DAVIES et al. (1976) suggested that, where large numbers of workers are in­volved, the use of enzymes as a biological index of exposure on a routine basis is impractical. The urinary metabolites were thought to be a preferable biological index of exposure; however, if worker exposure is to be monitored and limited, urine collection and analysis for pesticide metabolites may be too slow. SHAFIK et al. (1973) reported that one chemist can analyze only 25 to 30 samples/week using the diazopentane alkylation method developed for analysis of alkyl phosphate OP metabolite fragments in urine. More rapid methods of metabolite analysis are undoubtedly feasible, and would make this approach more attractive for worker monitoring.

It should be noted that there is a basic philosophical difference between the measurement of blood ChE and the other methods which measure pes­ticides or their metabolites in blood and urine. The ChE measurement de­termines response of a physiological variable to the pesticides, while the other methods measure dosage of the person. Since the ChE response of in­dividuals to OP psesticides varies widely, and is affected by a multitude of factors other than OP pesticides, it is not nearly as accurate a measure of exposure as are the other methods. On the other hand, the physiological ef­fect rather than the exposure is the important factor in the reentry problem. A disadvantage of all the above methods should be noted: none actually mea­sures the crucial physiological effect, which is the reduction of ChE available at the junctions of the parasympathetic nervous system.

The TASK GROUP (1974) believed that there is only one method for setting worker reentry periods which achieve the primary purpose of protecting ag­riculturallaborers, and that method is to study the effect of a known amount of pesticide residue on a known physiological response, with distorting vari­ables held constant insofar as it is possible to do so. This group contended there is no substitute for basing the reentry intervals on carefully designed

Citrus reentry problem 17

field studies involving human beings, at least until sufficient base data and experience permit wider latitude of design of reentry experiments. The TASK GROUP (1974) considered certain elements fundamental to reentry-interval research: measurement and the fate of a pesticide and its breakdown pro­ducts on foliage, measurements of a physiological response (blood ChE) in a group of human volunteers, and attention to climate and other possible re­levant variables. Six reentry-interval projects were described which were considered to meet the minimum requirements essential to a reentry study, and the strengths and weaknesses of each project were discussed. The studies were regarded as initial efforts forced to proceed without well­grounded precedents, and their value was regarded as methodological rather than substantive. In its summary, the Task Group noted that perhaps the most valuable single lesson to be learned from these investigations is that OP residues often retain ChE-inhibiting properties longer than anticipated. In five of the six studies, statistically significant ChE depression resulted, al­though the studies were designed, in every case, to test a reentry period thought to be sufficient to prevent such depression.

Designing and carrying out a satisfactory reentry experiment to establish a safe reentry interval for an OP pesticide is an extremely complex task. Dr. E. Kahn (KAHN 1975 a) of the California Department of Health has prepared a guide for the performance of these studies which should be invaluable to persons responsible for them. A short summary of this guide is given below:

General considerations and study design. A reentry interval is an occupa­tional health standard, and the rationale and industrial hygiene philosophy underlying such standards apply here as well. Since the study involves human subjects, it must be conducted in a manner conforming to the ethical requirements for such studies.

Advance planning and preparation, including thorough testing of laboratory techniques, will require at least three months; subsequent studies may require a shorter lead time.

Dosage applied must be the maximum intended usage. Other variables, such as formulation, dilution applied, work duration, speed of work, and type of work must be chosen to give the maximum dosage to workers.

A test plot must be used which is free of ChE-inhibiting pesticides. The pesticide being tested must be applied by skilled and experienced persons. Dislodgable foliar residues should be sampled before and after application and at standard intervals and at the time of work exposure. Pertinent en­vironmental variables such as humidity, maximum and minimum tempera­tures, and precipitation, if any, should also be recorded.

The work force should be large enough to give results which are statisti­cally significant. Care must be taken that the workers do not have ChE de­pression due to previous exposure at the time of the test.

A suitably long reentry interval should be chosen for the test. Application schedules should be planned so that a second shorter interval can be tested if the first one is found to give no ChE depression.

There should be two ChE determinations before the test to establish the worker's baseline level; during the test a sample should be obtained at the end of each work day, followed by another the day following the test to check

18 F. A. GC~THER, Y. IWATA, G. E. CARMAl'O, A~D C. A. SMITH

for delayed effect. In tests of a new compound the first day of work exposure should be limited to four hr and blood samples taken at the end of that period.

Ethical considerations. The purpose of the experiment must be explained carefully to the workers before they are asked to sign a consent form. There must be medical superivsion of the workers, with a pre-exposure physical examination. During the test an individual must be removed from the test if his RBC ChE level shows a 30% decrease or if his plasma ChE level shows a 40% drop. For the overall group a 15% decrease in the average RBC ChE level or 20% in the plasma ChE level must cause termination of the test.

KAHN (1975 a) also presented a sample schedule for a test of a 30-day reentry interval; this schedule is reproduced in Table V. The complexity of the overall effort is obvious. The schedule is designed to test one reentry

Table V. Schematic possible time frame for reentry study to testa 30-day interval" (KAH:\ 1975 a).

Day 1 - 30:

Day 20 - 60:

Day 50 - 80:

Day 60:

Day 60 - 80:

Day 60 - 93:

Day 82 (or 83):

Day 84 (or 85):

Day 86 (and 88):

Day 89 (Afternoon):

Day 90:

Days 90,91, and 92:

Day 93:

Selecting staff. Consultation with State agencies. Arranging for laboratory support.

Obtaining consultants and medical supervisor. Arranging for use of test plots. Arranging for pesticide application. Arranging to recruit study subjects. Calibration of spray equipment. Obtaining equipment for environmental measurements. Obtaining pre-application foliar and soil samples.

Laboratory determination of precision in ChE measurement and variance of D,ChE in unexposed subjects.

Application of test material. Study subjects (work force) come on board. Last day for any possible exposure of subjects.

Subjects kept free from exposure. Orientation of subjects. Pre-exposure medical examination.

Foliar residues sampled at standard intervals. Environmental measurements.

First baseline blood test.

Second baseline blood test.

Repeat baseline blood tests, if needed.

Final baseline blood test.

"Reentry" begins.

Work-exposure and daily afternoon blood tests.

Final post-exposure blood test.

aTo test a second shorter interval (if first is safe), days 96 - 100 would follow pattern of days 89 - 93. For a third interval, same pattern would be followed on days 103 - 107. Statis­tical analysis and laboratory determinations on the environmental and foliar samples might require an additional month. Preparation of the final report will probably take a second additional month.

Citrus reentry problem 19

interval; it is relatively simple to spray additional plots, so that if the first interval is found to be safe one or two additional tests with shorter intervals can be carried out.

This synopsis ofKHA~'S outline guide is greatly condensed from the orig­inal 25-page document, and anyone contemplating reentry tests will do well to obtain the complete document. The description and critique of reentry­interval tests by the TASK GROUP (1974) should also be invaluable for this purpose.

Worker reentry research inescapably has social, and even political, di­mensions. No useful purpose is served by debating whether this should or should not be so. It is a fact, springing from the very nature of the society in which we operate. Social forces concerned with protecting the well-being of its members exist and, invoking the specter of "human experimentation", some members propose that worker reentry intervals be based only on ex­trapolation from residue and animal toxicity data. The TASK GROUP (1974) felt that the choice is not between human experimentation and no human ex­perimentation but between sound, ethical, controlled studies and the kind of "study" which takes place every time a crew of workers enters a treated field without well-founded assurance of safety. The fundamental concept central to the formulation of a safe, workable reentry interval is the concept of "no response" in the test population during the period of controlled exposure. It is absolutely vital for the investigator to differentiate clearly between "no re­sponse" and "no exposure". The Task Group asserted that reentry studies in­volving human subjects are necessary and, if carried out properly, fully com­ply with all canons of medical ethics.

In August 1975 the California Department of Health and the California Department of Food and Agriculture announced it to be improper to use farm workers as subjects in experimental studies. This policy was based on the determination that under present conditions in California agriculture it was impossible to achieve the two necessary prerequisites for using human experimental subjects: (1) truly informed consent and (2) truly voluntary con­sent, free from any duress (KAH~ 1975 b). Published reentry studies involv­ing human subjects which have been conducted since the California an­nouncement have utilized either the authors or university students and have been conducted with OP pesticide-treated cotton (WARE et al. 1973, 1974 b, and 1975 a), apple trees (WOLFE et al. 1975), tobacco (GUTHRIE et al. 1976), and citrus trees (SPEAR et al. 1975 b).

f) California citrus investigations

The fact that some workers become ill due to pesticide residue exposure is not disputed. The environmental factors and toxic agents responsible for the occurrence of poisoning episodes are less clearly defined. In a study fol­lowing an outbreak of illness among peach harvesters in 1963, MILBY et al. (1964) found the only ChE-inhibiting compound used in every illness­producing orchard was parathion. Yet, it was apparent that application of parathion, in itself, was not the determining factor in the causation of illness because 40 of the 43 orchards without associated illness also applied it. Al­though the mean parathion content of the foliage of the illness-producing or-

20 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

chard was greater than no-illness orchards, considerable overlap between the two orchard groups rendered impractical any attempt to use residue levels as an indicator of worker risk. Weather was not a variable as all or­chards were in the same area. QUINBY and LEMMON (1958) considered temperature to playa role in precipitating the episodes. It was speculated that sweating in response to high temperatures produced a layer of moisture on the skin which made parathion-containing dust adhere more easily and perhaps facilitated absorption of the compound (however, see Introduction). It was noted that high temperatures and humid working conditions did cause some workers to remove their shirts and otherwise disregard protective clo­thing, thus increasing the area of skin exposed. The evidence for unusual temperature effects could be circumstantial, as most crop operations from which poisoning episodes ensued are normally conducted during the rela­tively warm summer months.

The exact set of circumstances that requires one group of workers to seek medical attention while similar groups do not has been the concern of a number of investigators. Reported here are results of work conducted on re­sidues in citrus plantings. Citrus differs from other crops with OP pesticide poisoning episodes in that it has wax-coated leaves and is nondeciduous. Cit­rus trees are also a difficult spray target because of the frequently dense peripheral shell structuring. The bulk of the foliage, twigs, and fruit is in this area (CARMAN and JEPPSON 1974). Although the emphasis here will be on citrus, pertinent concepts and data obtained from other crops will be discus­sed when appropriate.

For a greater in-depth discussion of some aspects of the reentry problem the reader is referred to the "Report to the Federal Working Group on Pest Management" from the Task Group on Occupational Exposure to Pesticides chaired by Dr. Thomas H. Milby (TASK GROUP 1974) and to Volume 62 (1976) of Residue Reviews, which gives eight reports on the reentry problem pre­sented as part of a symposium, 167th National Meeting, American Chemical Society, Los Angeles, California, April 3, 1974.

II. Foliar dislodgable residues

a) Background

CARMAN et al. 1952) postulated that a worker hazard results from worker exposure to parathion residues which are mechanically dislodged from tree surfaces through worker operations involving tillage, picking, pruning, and similar activities. QUINBY and LEMMON (1958) attributed worker illnesses to extensive contact with fruit and less extensive contact with foliage. POPEN­DORF and SPEAR (1974) conducted a survey in the Central Valley of Califor­nia during late August 1972 among harvesters of grapes, peaches, and oranges and described the work procedures and working conditions of har­vesters which might affect their exposure to pesticide residues. For orange pickers, oddly enough, minimal direct skin contact with foliage was noted, and it was concluded that poisoning incidents would most probably be as­sociated with either respiratory (later disproved) or indirect dermal exposure

Citrus reentry problem 21

to the heavy foliar aerosols generated during picking. Soil "dust" as a possible means of exposure was not mentioned. It was also noted that the accumula­tion of (airborne and foliar) dust on the exposed parts of the body was aided by perspiration on skin. Since poisoning episodes have been associated with crops such as cotton, grapes, and some tree fruits where extensive contact of workers with foliage does occur, foliage is currently suspected as being the prime source of toxicants to workers. As shown later in this review, soil "dust" is the other major source. However, the relationship between foliar residues and the adverse biochemical response of workers has not been clearly established (SPEAR et al. 1975 a). Experience is the major type of evi­dence (PAYNTER 1976). The complexity of the problem has been illustrated by POPENDORF and SPEAR (1974). They graphically described the various environmental, toxicological, and intervening factors influencing the expo­sure to and abosrption of pesticide residues by agricultural workers (see Fig. 1). The variables and functional relationships shown on their diagram elabo­rately denne the interface between the worker and his environment and be­tween the residue and its biological impact.

Parathion is the pesticide most implicated in worker poisoning episodes. This may be a result of its very extensive use in agriculture or it may be due to some special chemical or physical property of the compound; probably a combination of these factors is responsible. For example, whereas parathion and azinphosmethyl have comparable oral LD50 values for rats (GAINES 1960) oflO to 17 and 12 to 14 mg/kg, respectively, the dermal LD50 value (GAINES

-- Pesticide transport

---- Functional relation

,.------...,: I ,

Physical variables

rl-i ,- -.---------------------~--, I , 1 , I 1 1/' I , Dermal dose I Dermal

:ContactTexposure Clothing r ~,', _~barrier ,! prote~t ion Contamination , 1 I , ,I I Agricultural Wor k I I I

,: ;r:cklices -.- - - - physiology --6-----~:;-t-Job reqmts. and I G.T.

: personal : barrier I Wor ker Ihygiene , I -~ :~. '----,--....Jposi lion 'L '

I _! 1 ungl : FOliar 1 ICI~:arce I disturbance ii' ............

',' Aeroso'l lAirborne: Respirotory : Resp. exposure dose : exposure r : Vapor exposure

'" barrier

~ '--____ -'1 ,

Environment: Interface

Absorbed I dermal dose I

Human toxicological processes

I Response variables

WlbsorbedJ G.I dose

~bsorbed I resp. dose

Mon

Fig. 1. Factors affecting residue intoxication. Redrawn from SPEAR et al. (1975 a).

1\

22 F. A. GVNTHER, Y. IWATA, G. E. CARMAN, A:'oID C. A. SMITH

1960) of 14 to 34 mg/kg for parathion is ten-fold less than the 183 to 264 mg/kg for azinphosmethyl. Extrapolation from laboratory animal studies to a man in the field has its limitations, since factors such as perspiration may alter the degree of percutaneous exposure (see Introduction).

It is not completely certain whether the worker illnesses result from ex­posure to the parent insecticide, to a compound derived from it, or, most likely, to a combination of these. MILBY et al. (1964) investigating a worker posioning in peach orchards felt that the amount of parathion recovered from the environment was insufficient to account for the episode. As discussed earlier and in more detail below, the alteration product paraoxon was postu­lated as the causative agent and is considered by many to be the principal toxic constituent of weathered residues (SPEAR et al. 1975 a, ADAMS et al. 1976).

Thus, SPEAR et al. (1974 b) followed the decay of parathion on citrus foliage in the Central Valley of California for 16 days and reported that paraoxon comprised a Significant fraction of the foliar residues in all groves and that paraoxon decayed more slowly than parathion, a finding confirmed by others (e. g., ADAMS et al. 1976). WINTERLIN et al. (1975) found that on peach foliage paroxon was lowest when trees were sprayed with an EC for­mulation rather than with a WP or an encapsulated formulation; oddly, the rate of paraoxon degradation was similar to that of parathion. With grape leaves treated with ethion, LEFFINGWELL et al. (1975) reported that, in dis­lodgable residues, the ethion monooxon appeared at the time of pesticide application, possibly as a contaminant in the formulated material, and per­sisted at that level for approximately three days, then began to decay in a first-order fashion. Almost immediately after pesticide application, ethion di-oxon appeared, increasing in concentration to between seven and 14 days post-application and thereafter slowly decreasing in concentration. The same authors recovered phosalone-oxon from grape foliage treated with phosalone, MILBY et al. 1964) also suggested that the S -ethyl and S -phenyl parathion isomers (O,S-diethyl O-p-nitrophenyl and O,O-diethyl S-p­nitrophenyl phosphorothioate, respectively) also needed to be searched for in the agricultural environment as they are ChE inhibitors. JOINER and BAETCKE (1973) found trace amounts of both isomers along with paraoxon in methanol extracts of cotton leaves treated with radiolabeled parathion. It was stated that evidence suggestive of the formation of other toxic metabolites of parathion on plant material was not present, however. WINTERLIN et al. (1975) detected the S -ethyl isomer of parathion in only very small quantities the first few days after application to peach trees of WP and encapsulated parathion formulations and none at all was detected after an EC application. Using the encapsulated formulation, the residue of S-ethyl parathion de­clined from 0.11 ppm the day of application to 0.04 ppm three days post­application. With the WP formulation, the residue declined from 0.28 ppm to 0.05 ppm during the same period. WINTERLIN et al. (1975) concluded that residues ofS -ethyl parathion were low enough to be excluded from consider­ation in further studies involving parathion on peaches. GRUNWELL and ERIKSON (1973) obtained O,O,S-triethyl-thiophosphate as the major photo­lysis product of parathion in aqueous tetrahydrofuran and aqueous ethanol

Citrus reentry problem 23

solutions. It was suggested that worker poisonings might occur through a buildup ofO,O,S-triethylthiophosphate on trees from repeated spraying of parathion and its potentiation of the toxicity of parathion. Photolysis exper­iments conducted in the laboratory are excellent tools in producing candi­date compounds to be searched for in the environment. However, care should be exercised not to imply that they will be present. Due to the appli­cation of several pesticides to a crop over the growing season, potentiation of toxicity among the OP pesticides present has also been suggested (SERAT and BAILEY 1974). The potentiation of toxicity between pesticides was reviewed by DURHAM (1967).

DAUGHTON et ai. (1976) compared the inhibition of human plasma ChE in vitro by parathion, paraoxon, and their hydrolysis products diethyl phos­phate, diethylthiophosphate, and p-nitrophenol: paraoxon was 1,000 times more inhibitory than parathion, diethylthiophosphate was as inhibitory as parathion, diethylphosphate was less inhibitory than parathion by an order of magnitude, and p-nitrophenol showed no inhibition relative to the control sample. In a similar vein, SHAFIK et al. (1971) noted ChE depression in rats fed diethylthiophosphate. WALKER and STOJANOVIC (1973) reported that dimethylthiophosphate is not inhibitory to bovine true ChE, however. The OP esters produce a two-stage inhibition; initially this is slowly reversible but later it becomes completely irreversible. With the dimethyl OP esters the initial reversible stage leads to a more rapid recovery of activity than oc­curs with the diethyl OP esters such as parathion, which more readily lead to an irreversible inhibition (GAGE 1976).

Although many hypotheses have been advanced as to the identity of the toxic agents that cause the worker-poisoning episodes, all proposals are still largely speculative; however, the preponderance of evidence indicts paraoxon which, as will be shown, can be formed in surprising amounts on parathion­treated dusty foliage and on soil dust and is surprisingly stable thereon, especially in the presence of clay materials (see later).

Aside from parathion, studies of foliar dislodgable OP pesticide residues on citrus foliage have been limited to phosphamidon (WESTLAKE et al. 1973 b), dioxathion (WESTLAKE et al. 1973 a), and phenthoate (IWATA et al. 1977).

WESTLAKE et al. (1973 b) conducted a limited study on the dissipation of phosphamidon from field-treated orange leaves. Trees were treated at 1.0 lb a.i. of ph os ph amidon 8EC/200 gal/A. Foliar dislodgable residues 1, 3,7,14, 21, and 28 days after spraying were 1.17, 0.73. 0.47, 0.04, 0.05, and 0.06 p,g/cm2 , respectively. Thus, phosphamidon residues dropped to <0.1 p,g/cm2 level within two weeks after application. The half-life of the rapid initial decay processes was about 2.5 days. The residues penetrated into the leaf were 0.16,0.10,0.02, and <0.01 p,g/cm2 after 1,3,7, and 14 days, re­spectively, post-application. WESTLAKE et al. (1973 a) gave detailed data for the diSSipation of dislodgable foliar residues of dioxathion on citrus trees. Dissipation was slow with a half-life of two to four weeks for several dosages; foliar dust residues were transferred in large amounts to hands and arms of citrus pickers at the rate of several g/day/picker. IWATA et al. (1977) reported that phenthoate dissipated rapidly from orange foliage, especially down to the 0.05 p,g/cm2 level. The time intervals after spraying which were required

24 F. A. GC:-;THER, Y. IWATA, G. E. CARMAI\, AI\D C. A. SMITH

to reach the 0.01 p.,g/cm2 1evel were 10, 17, and 30 days for the 1. 9, 3.8, and 7.5 Ib a.i./1,500 gal/A treatments, respectively, and 30 days for the 7.5 Ib a. i./100 gallA treatment. The approximate times required to reach 0.01 p.,g/cm2 for lemon foliage were 11, 19, and 33 days after treatment with 1.6, 3.1, and 6.31b a.i./1,250 gal/A, respectively, and 46 days after treatment at 6.3 Ib a.i./lOO gal/A. Dislodgable residues on grapefruit leaves were 0.05, 0.01, and <0.01 p.,g/cm2 4, 11, and 18 days, respectively, after spraying with 3.8 Ib a.i./1,500 gal/A. Half-lives for foliar dislodgable residues for all three citrus varieties were 2.5 to 3.0 days for the initial rapid pesticide loss.

Table VI lists the OP pesticides used on oranges in California in 1975 (California Department of Food and Agriculture 1975). This table shows the relative importance of these pesticides. The compounds most extensively used were dimethoate, parathion, and malathion. Table VII gives the oral and dermal toxicities to male rats for the OP pesticides listed in Table VI. Table VIII gives the California pesticide usage pattern for materials with State-assigned reentry restrictions in terms of pest, pesticide(s) recom­mended for its control, range for rates of application, citrus variety, and probable application period. Table IX gives the harvest periods for citrus in California. The latter two tables can be used to assess the degree of hazard that might exist between a pesticide-crop combination. For example, navel orange harvests generally occur during the winter months and parathion ap­plications are generally made during the summer months, thus incidences of worker poisoning episodes for this combination should be fewer than for Val-

Table VI. Important OP compounds for California oranges (California Department of Food and Agriculture 1975).

Chemical structure Reported Total pounds Total

Compound P=S P=O applications of active acres ingredients

dimethoate (Cygon) x 2,310 117,722 76,955 parathion x 1,554 124,049 45,189 malathion x 689 74,059 18,248 azinphosmethyl (Guthion) x 495 28,264 14,923 methidathion (Supracide) x 442 28,222 11,820 phosphamidon (Dimecron) x 192 6,161 4,084 trichlorfon (Dylox) x 147 5,855 2,333 naled (Dibrom) x 117 5,814 4,691 ethion x 72 10,783 1,759 dioxathion (Delnav) x 59 6,664 2,148 phosalone (Zolone) x 34 1,753 543 mevinphos (Phosdrin) x 28 447 1,363 demeton (Systox) x 19 620 1,043 diazinon x 13 678 1,022 monocrotophos (Azodrin) x 8 154 121 carbophenothion (Trithion) x 6 389 84 oxydemeton-methyl (Meta-

Systox) x 2 9 21 TEPP x 40 50

Citrus reentry problem 25

encia oranges which are generally harvested during the summer months (see Table I for confirmation).

Decay of foliar dislodgable OP residues from cotton foliage has been the subject of a number of papers. QUINBY and LEMMON (1958) studied the decay of methyl parathion and azinphosmethyl following application to cot­ton. WARE et ai. (1973) studied the disappearance of foliar residues of methyl parathion and ethyl parathion, and measured the foliar concentrations of methyl paraoxon and ethyl paraoxon following spraying with methyl and ethyl parathion, respectively. WARE et ai. (1974 a), and CAHILL et ai. (1975) measured decay rates of monocrotophos, methyl parathion, ethyl parathion, azinphosmethyl, and a number of additional pesticides. WARE et al. (1975 a) studied the behavior of residues of methyl and ethyl parathion and monocrotophos on cotton foliage, and observed sufficient transfer of leaf juices to cotton scouts' clothing to stain them green thus indicating foliar penetrated insecticides may be a reentry hazard with cotton. WARE et al. (1975 b) studied the rate of disappearance from cotton foliage of methyl parathion alone and with toxaphene, as well as the disappearance of several non-OP pesticides. They observed that toxaphene appeared to stabilize the dislodgable methyl parathion residues considerably.

b) Methodology

1. Collection and extraction of foliar residues-GuNTHER et al. (1973) described a technique for collecting leaf samples and for removing the dis-

Table VII. Oral and dermal toxicities ofOP compounds used on California citrus.

Chemical

Azinphosmethyl (Guthion) carbophenothion (Trithion) demeton (Systox) diazinon dimethoate (Cygon) dioxathion (Delnav) ethion malathion methidathion (Supracide) mevinphos (Phosdrin) monocrotophos (Azodrin) oxydemeton-methyl (Meta-Systox) naled (Dibrom) parathion phosalone (Zolone) phosphamidon (Dimecron) TEPP trichlorfon (Dylox)

Toxicity as LD, 0 (mg/kg) for male ratsa

Oral Dermal

13 30

6.2 lOS 215

43 65

1,375 25-4S b

6.1 20b

lS0b 450b

13 USb

23.5 1.05

630

220 54 14

900 400 235 245

> 4,444

4.7

21

143 2.4

> 2,000

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p

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n

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Citrus reentry problem 29

lodgable residues thereon for analysis. Modifications and additional informa­tion were later developed (GUNTHER et al. 1974). Any technique to evaluate total dislodgable residues must accommodate statistical size and appropriate field representation requirements, be as simple as possible and yet provide adequate reproducibility and standardizability, and be adaptable to a variety of pesticides and types offoliage. The technique must not be so tedious that the operator becomes bored and careless during the collection of large num­bers of samples resulting from replicate sampling of replicated field plots. Both surface areas and weights of the samples need to be easily determined as large numbers of samples are often involved; measuring areas of large numbers of entire leaves is difficult. Collection of leaf disc samples of fixed diameter was determined to be a feasible procedure. The leaf punch should have a strongly concave cutting sUi"face to avoid disturbances of the foliar sur­face. The excised disc should fall into a container without operator handling and a stroke-activiated counter should record the number of disc samples collected. Field experience has demonstrated that the cutting edge needs to be cleansed with a tissue moistened with water or acetone after each batch sample to remove plant juices that prevent easy operation of the punch. Further, the number of leaf discs collected should be confirmed in the laboratory after the dislodgable residue removal step is completed. Photo­graphs of leaf punches which have been found satisfactory are shown in Fig­ure 2.4

An adequate sample is recommended to be 40 2.5-cm diameter leaf discs per sample for mature citrus foliage and 200 1.8-cm diameter leaf discs for grape and peach foliage. Three field replicates are recommended; variability among replicates was reported to be ± 15% for dislodgable residues of dioxathion, parathion, and phosphamidon (GUNTHER et al. 1973).

One sampling procedure (GUNTHER et al. 1973) for obtaining 40 discs is to punch at 45° intervals around eight trees at shoulder height, with five discs/tree as follows to afford five discs/sampling position:

Tree 1 0° 45° 90° 135° 180° Tree 2 45° 90° 135° 1800 225 0

Tree 3 900 135° 1800 225 0 2700

Tree 4 135 0 1800 225 0 2700 315 0

Tree 5 180 0 225 0 270° 315 0 0 0

Tree 6 225 0 2700 315 0 0 0 45 0

Tree 7 2700 315 0 00 45 0 900

Tree 8 315 0 0 0 450 90° 1350

Any sampling procedure can be substituted provided that the entire circum­ference of the tree is properly and reproducibly represented.

WINTERLIN et al. (1975) pointed out that leaf discs removed from the center of the leaf may not be representative of the total leaf; residues on peach leaves appear to have their greatest deposition on the periphery of

'Available from Birkestrand Co., 129 Casuda Drive, Monterey Park, CA 91754. Punch dif­fers in appearance but not in function from those shown in Fig. 2.

30 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

the leaf; particularly the tip. Comparison of dislodgable parathion residue values from leaf discs and whole leaves showed that leaf disc samples gave higher values. This was attributed, however, to differences in stripping pro­cedures in that a greater ratio of surfactant to leaf area was used for the discs.

Fig. 2. Photograph ofJeaf punches.

Citrus reentry problem 31

In any event, the discs should be cut from standard positions on the leaves, preferably between center and tip.

To avoid unnecessary complications, storage of leaf discs in any manner should be avoided, with immediate processing. If discs must be stored, as undoubtedly they will, preliminary tests should be made to determine whether there may be adverse storage effects. KAWAR et ai. (1973) reviewed the cold-storage stability of OP pesticides in plant parts; of 12 pesticides studied, only six were stable under a variety of conditions. Tables X and XI show little, if any, effect on the recoveries of parathion, ethion, and azin­phosmethyl after six days of refrigerator storage and 90 days of frozen storage (GmnHER et ai. 1974). Propargite was adversely affected after six days under both types of storage.

The revised procedure proposed by GUNTHER et ai. (1974) involves mechanical dislodgment of surface residues via thorough water-washing of leaves. Despite some published procedures, organic solvents are to be avoided as they can carry external insecticides into the leaf tissue or, perhaps more seriously, extract field-penetrated residues, unless clearly de­monstrated otherwise. The procedure for removal of dislodgable residues is to mechanically shake the leaf disc sample with 100 ml of water containing four drops of a 1 :50 dilution of Sur-Ten wetting agent (70% sodium dioctyl­sulfosuccinate) on a reciprocating shaker at 200 cycles/min for 20 min. The stripping "solution" is poured into a 500-ml separatory funnel or a temporary holding bottle, retaining the discs in the jar. The procedure is repeated two more times, adding the succeeding strippings to the first. Care is taken to transfer all particulate matter in the aqueous strippings into the separatory funnel or holding bottle to avoid loss of pesticides sorbed on the particles. The pesticide in this aqueous mixture is then transferred to an appropriate organic solvent such as chloroform or hexane using the following procedure: add 50 ml of solvent and shake 20 sec; transfer the organic solvent phase into a sample storage bottle. Repeat this extraction twice more, combining the three extracts; add 20 g of anhydrous Na2S04, cap the bottle, and store at 4°C. The partitioning process should be checked for each compound sought by fortifYing a stripping mixture with appropriate levels of each sought com­pound and verifYing that satisfactory amounts are transferred into the or­ganic solvent. This is particularly necessary when the sought compound has appreciable water solubility as with many of the OP pesticide oxons.

The adequacy of the method has not been extensively tested for obtain­ing extra-surface residues of micro-encapsulated OP pesticide residues. WINTERLIN et ai. (1975) used the original GUNTHER et ai. (1973) procedure

Compound

Parathion

Table X. Effect of refrigerator storage (4°C) on dislodgable foliar residues on orange leaf discs ( GUNTHER et al. 1974).

Residue (J.ig/cm 2 ) after

o day 3 days

1.2 1.3 Azinphosmethyl 1.2 1.4 Ethion 1.3 1.5 Propargite 2.1 2.4

6 days

1.1 1.3 1.5 0.4

32 F. A. GDITHER, Y. IWATA, G. E. CARMA~, A~D C. A. SMITH

Table XI. Effect of frozen storage (_10°C) on dislodgable foliar residues on orange leaf discs (GuNTHER et al. 1974)

Compound

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with peach leaves and reported that once the encapsulated product has been removed, the pesticide contained in the capsule is nearly all retrieved by the organic solvent used for the partitioning step. The plastic capsule did not act as a barrier between pesticide and solvent. Due to the limited use of the method for encapsulated OP pesticides, more information should be ob­tained before the revised method ofGuNTHERet al. (1974) is adopted for this general use.

Since the removal of foliar dislodgable residues by water washing and its subsequent partitioning into a suitable organic solvent is time-consuming and can lead to losses of appreciably water-soluble compounds, a methanol rinse method was tested to see if dislodgable residues could be obtained without simultaneous extraction ofleaf-penetrated residues (GUNTHER et al. 1976 b). Three replicate samples of 40 leaf discs were collected from parathion-sprayed trees and each disc was hand-washed with water to re­move surface residues and dried with a paper towel. Each 40-leaf sample was shaken with 50 ml of 4°C methanol four successive times. Each methanol rinse was decanted and separately stored over Na2S04 prior to analysis. The methanol rinses were analyzed by gas chromatography without any further manipulation except concentration. Four successive methanol rinses of2, 5, 10, and 15 min removed 40, 8, 7, and 6 f.Lg of parathion, respectively. Thus, even a rapid two min rinse gave a false dislodgable residue of 0.10 f.Lg of parathion/cm2 ofleaf area. SERAT (1973) used a benzene rinse to obtain foliar residues of an OP compound (unspecified). A sample of20 leaf discs was sha­ken with 20 ml of benzene for 15 min in a four-oz jar. The procedure was repeated by GUNTHER et al. (1976 b) using field-treated leaf discs which were handwashed with water to remove surface residues of parathion and dried with a paper towel. The benzene rinse was analyzed without any further manipulation except concentration. The mean of three replicate samples was 25 f.Lg of parathion corresponding to a false dislodgable residue of 0.12 f.Lg of parathion/cm2 ofleaf area. Thus, organic solvents are unsuitable for obtaining 'strictly dislodgable residues from citrus leaves, as mentioned earlier.

For leaves other than citrus, however, the organic-solvent rinse method may occasionally be a viable procedure even though the carry-in and extrac­tion question remains. For example, WARE et at. (1974 a) used a two-min leaf rinse of 100 cotton leaf discs with benzene for ethyl and methyl parathion and aZinphosmethyl; water, with a subsequent chloroform partitioning step, was used for monocrotophos. WARE et al. (1975) used 30-sec leaf rinses with benzene for ethyl and methyl parathion on cotton leaf discs and, this time,

Citrus reentry problem 33

acetone for monocrotophos. GUTHRIE et ai. (1976) adopted the monoc­rotophos method used by WARE et ai. (1974 a) for monocrotophos-treated tobacco leaves. Neither set of workers clearly demonstrated absence of "carry-in" of surface insecticide or "carry-out" of penetrated insecticide.

2. Analyses of dislodgable residues-Analyses of residue samples are generally performed by gas chromatography (GLC). In conjunction with al­kali flame or flame photometric detector, good response to ng quantities of OP pesticides is often achievable. The parent compounds are generally eas­ily gas chromatographed but their corresponding oxons often show less GLC stability and alternate methods of quantitation may be required which can be conducted at ambient temperatures to avoid thermal decomposition. MIRER et al. (1975) quantitated paraoxon in a set of samples by using both GLC and ChE inhibition and obtained comparable results by both techniques; the anti-ChE technique was more rapid and conventient than the GLC method for paraoxon under their GLC conditions. STAIFF et al. (1975) reported much lower detectability for paraoxon with the ChE method than with the GLC method, however. Where both techniques could be used, results for paraoxon were in good agreement. KVALV AG et al. (1977 a) analyzed samples for parathion and paraoxon by both GLC and liquid chromatography (LC) and obtained good agreement for the two compounds, demonstrating no GLC decomposition of the paraoxon under the conditions utilized. LC gave excel­lent resolution of parathion and paraoxon. Relative to GLC, LC was slower and the minimum detectability was poorer. \Vhile GLC is thus an adequate tool for quantitation of paraoxon, and also of ethion and phosalone oxons (LEFFINGWELL et al. 1975), it has not been as satisfactory for other oxons. Azinphosmethyl oxon analysis by GLC, though possible, is difficult to ac­complish due to decomposition at the temperatures required. However, an improved method for this compound has been published by IVES and GIUF­FRIDA (1970); in their procedure Carbowax 20M, a polyethylene glycol, is vapor deposited on the chromatographic column, thus covering up or inac­tivating the sites responsible for decomposition of the compound.

In order that all researchers working on the reentry problem have com­parable data, dislodgable residues should be expressed as J.Lg of com­pound/cm2 of leaf surface area, not ng/cm2 ; ng/cm 2 signal too many significant figures.

c) Effect of soil dust type on residue dissipation

WESTLAKE et al. (1973 a) determined the amounts of dislodgable particu­late matter on leaf surfaces by gravimetric analysis. The leaf disc samples were washed with water containing a wetting agent and the dislodged par­ticulate matter was obtained by filtration. The weights of the dislodgable dust on the leaves averaged 222 J.Lg/cm 2 for the samples collected two days after the dioxathion application, while the dioxathion content of the dust was 1.4 J.Lg/cm2 . Accordingly, the calculated pesticide content of this dust was 0.63%. POPENDORF et al. (1975) developed a vacuuming technique for col­lecting foliar dust samples. As with the leaf disc method, this procedure was designed to collect that fraction of the foliar residue that can become air­borne due to the activity of workers engaged in harvesting or thinning crops.

34 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

The procedure requires careful clipping of leaves prior to vacuuming off the foliar dust. The leaves must then be sized to obtain the surface area sampled. The foliar dust levels measured by this procedure were shown to be highly correlated with the airborne dust concentrations collected while simulating worker activity; however, the leaf disc washing technique of GUNTHER et al. (1974) is more efficient at removing dislodgable residues from the leaf sur­faces. This vacuuming technique was used to collect foliar dust in an orange grove in the Central Valley of California. The dust level data collected over a five-month period showed increasing levels offoliar dust with time, as shown in Figure 3. Actual dust levels were likely much higher than those found, since the described technique was not designed to collect dislodgable dust that could be transferred to workers through contact with worker skin and clothing. POPENDORF et al. (1975) collected foliar dust using the vacuuming technique and the gravimetric technique of WESTLAKE et al. (1973 a) and con­currently collected aerosols generated by a simulated picking exercise. They concluded that the vacuuming technique was a better predictor of airborne dust levels than the gravimetric technique.

The chemical and physical characteristics of the foliar dust will be related to the orchard soil where most of it originates. Each orchard soil could exhibit differences from other, even nearby, orchard soils and these differ­ences will also be manifested in the foliar dust. Another source of foliar dust will be the solid carrier for WP pesticide formulations

ADAMS et al. (1976) investigated the influence of six different soils (dusts) resident on orange leaves on the dissipation rate of parathion, the rate of conversion of parathion to paraoxon, and the dissipation rate of the paraoxon formed. Included among the soils used was a Visalia silt loam collected from a citrus grove which was the site of a 1974 worker-poisoning episode and a Pike's Peak clay used in some insecticidal WP formulations. The semi­logarithmic plots of the dislodgable residue data obtained by ADAMS et al. (1976) for both parathion and paraoxon with respect to time are reproduced in Figure 4. For all six soils the graphs were linear initially with Laveen loamy sand exhibiting the highest parathion dissipation rate. For the other soils, the initial rate varied slightly but was about half of that for Laveen soil. Except forPike's Peak clay, the initial parathion dissipation rate changed to a lower rate at about ten days. The occurrence of the two first-order rate pro­cesses with dissimilar rate constants is identical to that observed with dis­lodgable foliar residue dissipation in field experiments. The parathion re­sidue level at which the rate change occurred was dependent upon the soil. The parathion dissipation rate after the rate change was low and did not vary greatly among the soils; thus it was the initial parathion dissipation process which was important in reducing residue levels. The total result of the effects was that after 30 days, 4% of the applied parathion remained on the Laveen soil, 15% on Santa Lucia, 20% on Windy, 8% on Madera, 14% on Visalia, and 2% on Pike's Peak clay. Certain foliar dusts can retard parathion dissipa­tion and may serve as a hazard to workers, as indicated by the wide variation in initial rates of parathion dissipation and the residue level at which a rate change occurred depending on the soil involved.

Dislodgable residues of paraoxon were not present in detectable quan-

Citrus reentry problem 35

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tities until at least the second day and then rose to a maximum about the eighth day. This time interval coincided approximately to the rate change in the parathion dissipation. Paraoxon levels in some soils exceeded those of parathion. Paraoxon levels then diminished at a rather low rate for all six soils which was of the same order of magnitude as the dissipation rate for para­thion. At the 30th day the paraoxon levels corresponded to a parathion con­version of 17% for Laveen, 11% for Santa Lucia, 5% for Windy, 3% for Mad­era, 15% for Visalia, and 34% for Pike's Peak clay, respectively. Soils can thus influence the conversion of parathion to paraoxon. Paraoxon levels dif­fered greatly with the type of soil and were highest with Pike's Peak clay. Thus, its use in a parathion formulation could produce relatively high levels of paraoxon dislodgable residues. The use of surfactants and other additives in the formulation, however, will likely modifY the activity of the clay sur­face.

Combining the parathion and paraoxon residue values at 30 days showed that 21 % of the toxicant remained with Laveen, 26% with Santa Lucia, 25% with Windy, 11 % with Madera, 29% with Visalia, and 36% with Pike's Peak clay. Second to Pike's Peak clay, the highest total dislodgable residue level was found with Visalia silt loam which was collected from a grove where a worker-poisoning episode had occurred in 1974.

Subsequently ADAMS et al. (1977) conducted another study using the same soils, but using paraoxon rather than parathion, so that the behavior of

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Citrus reentry problem 37

paraoxon could be studied without the complications of formation from the parathion. The persistence behavior of paraoxon was similar to that observed in their earlier paper, and is shown in Figure 5. It was calculated that during the last 20 days of the experiment the paraoxon half-life was over 22 days.

SPEAR et al. (1975 b) monitored the decay of parathion on citrus foliage for 16 days post-application in 32 groves in Central California. In terms of half-lives the median parathion half-life was three days and the median paraoxon half-life was six days. Thus, here also paraoxon dissipated more slowly than parathion. Paraoxon production occurred principally during the first few days after applications when high levels of parathion were present. Thereafter, paraoxon levels were largely independent of the decay of para­thion. The paraoxon/parathion ratio increased from 0.2 on day two to 0.6 and 0.8 on days nine and 16, respectively. By day 16, 30% of the groves showed greater foliar residues of paraoxon than the parent compound with the maximum observed ratio in excess of four. No clear associations of high paraoxon/parathion ratio with application rate, irrigation practices, gallon­age, or the variety of additives in the spray mixture were found.

GRU~WELL and ERICKSON (1973) through solution photolysis deter­mined that neither singlet oxygen nor the interaction of the ground state triplet oxygen with parathion was responsible for the formation of paraoxon. Water, either reacting with photo-excited parathion or some intermediate generated from excited parathion, was the source of the oxygen of the p=o bond of paraoxon. GU~THER et al. (1970) demonstrated that ozone can con­vert parathion in aqueous ethanol solution to paraoxon with 20 to 40% ef­ficiency. SPEAR (1976 a) proposed that ozone and other oxidants in air may be responsible for the parathion-to-paraoxon conversion on foliage. Sub­squently SPEAR (1976 b) carried out a series of tests of dislodgable residues on citrus under conditions where the atmosphere and the radiation could be controlled. He found that either radiation or ozone converted parathion to paraoxon, and that if neither was present there was no detectable formation of paraoxon. It is possible that the binding of parathion to soil catalyzes, or at least facilitates, this conversion.

d) Effect of climatic factors on residue dissipation

A broad study was conducted to determine the effect of climatic factors on the dissipation of parathion residues from foliage (GUNTHER et al. 1976 a). Seven monthly applications, May through November (July through November 1974, May and June 1975), were made on mature Valencia orange trees located on the Irvine Ranch, Tustin, California. A 25% WP formulation was applied at four and ten lb a.i./1,600 gal/A using an oscillating boom (di­lute spray) and at ten lb a.i./lOO gal/A using a Kinkelder machine (low­volume spray). Each treatment on 16 to 23 sub-plots was replicated three times. The applications were made during the latter half of the month and samples for residue analysis were collected for two months after each appli­cation.

A plot of the daily maximum air temperature for the experimental period is shown in Figure 6. The sampling interval for each monthly application is also shown in this figure.

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y 1

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ly

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. 6.

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aily

max

imum

air

tem

pera

ture

at T

usti

n, C

A.

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int

erva

ls d

enot

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y (1

---1

) ind

icat

e th

e 60

-day

sam

plin

g pe

riod

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er a

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, 19

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(GU

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. 19

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).

(j ::;: ., !;; @

(1) ::I ~

'0 a cr

rn­ a W

rD

40 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

The foliar residues resulting from the May, June, and July treatments were subjected to the warmest weather with average daily maximum tem­peratures generally ranging from the low seventies to the high eighties. The residues from the September, October, and November applications experi­enced a much cooler weather pattern with temperatures ranging from the mid-seventies to the mid-fifties.

Inspection of the parathion dissipation curves shown in Figure 7 for the ten lb a.i.l100 galJA treatment represented by the top curve (closed circles of each figure) for the seven monthly applications shows that parathion dissipa­tion is much more rapid for the residues exposed to warmer climatic condi­tions. The 17 -day residue levels for the seven monthly applications, May through November, were 0.3,0.1,0.8,1.0,3.5,5.3, and 4.2f.Lg/cm2 , respec­tively. The 59-day residue levels for the six monthly applications, May through November were 0.3,0.1,0.8, 1.0,3.5,5.3, and 4.2 f.Lg/cm2 , respec­f.Lg/cm2 , respectively. Assuming that the vaporization rate of a residue is proportional to the gross surface area of spray deposit and using the potential volatilization rate of parathion, SPENCER et al. (1973) estimated that 50 g of parathion distributed uniformly over a mature citrus tree would vaporize within one day. Temperature influences volatilization rates mainly through its effect on vapor pressure (SPENCER et al. 1973). This relationship could account in part for the more rapid decline in dislodgable foliar residues dur­ing warmer weather, although it would be expected that parathion-paraoxon conversion would also be accelerated under these conditions. These calcula­tions do not take into account the effective decrease in vapor pressure caused by sorption on to particulate matter (dust) discussed earlier.

The study on the effect of climatic factors on residue dissipation from foliage was repeated with azinphosmethyl applications (GUNTHER et al. 1976 a). Three monthly applications, October and November 1975 and April 1976, were made on mature Valencia orange trees located on the Citrus Research Center, Riverside, California. A 2EC formulation was applied at one and two lb a.i. /500 gallA and six lb a.i. at 100 and 1,200 gal/A. The applications were made during the latter half of the month and samples for residue analysis were collected for two months each time.

A plot of the daily maximum air temperature for the experimental period is shown in Figure 8. The sampling interval for each monthly application is also shown in this figure. The maximum air temperature for the October to January experimental period was extremely irregular but there appears to be a trend towards lower temperatures during this period. The maximum air temperature for the April application sampling period is extremely irregular with no definite trend. Proposed guidelines for conducting human reentry field studies invariably stress the need to collect climatic data (TASK GROUP 1974, KAHN 1975 a). Figure 8 clearly demonstrates that it is far easier to gather the data than to use it to make any meaningful interpretation.

The azinphosmethyl dissipation curves for the six lb a. i. /100 gall A treat­ment represented by the top curve (closed triangles) of Figure 9 show that initial azinphosmethyl dissipation is possibly slightly more rapid during warmer weather. The 17-day residues for the October and November appli­cations were 5.4 and 6.1 f.Lg/cm 2 , respectively. However, the corresponding

'­o o

'+-

Q)

Ll o CTl

"'0 o (/)

o

10 f--

\

o 10

Citrus reentry problem

July

.......... ---

I I

20 30 40 50

Elapsed days

41

60

Fig. I. Dissipation curves for dislodgable foliar residues of parathion (closed symbols) and paraoxon (open symbols) after a 25'7c \VP parathion application to orange trees at four (-) and ten (A) lb a.i./l,600 gallA using an oscillating boom and at ten (e) lb a.i./l00 gallA using a Kinkelder (low-volume) machine, Irvine Ranch, Tustin, CA, July-:-.1ovember 1974 and May-June 1975 (GL"TIIER et al. 1976 a).

42 F. A. CDITHER, Y. IWATA, C. E. CAR~AN, AND C. A. S~ITH

10

\ August

5

-C\J

E (J

""-01

~ (l) :::J ~

(/) (l) ~

~ 0.5 0

0 ~

(l)

.D 0 01 ~ 0

'"i -

~ (/) 0.1

0 '" , , ,

0.05

~ f~ \ ~ , , ,

0 10 20 30 40 50 60

Elapsed days

Fig. 7. (Continued)

'-o o -<J)

..0 o 0'1

"'0 o (f)

o 0.1

0.05

o 10

Citrus reentry problem

September

20 30

I Rain .14mm

40

Elapsed days

Fig. 7. (Continued)

50

43

60

44 F. A. GU:-.iTHER, Y. IWATA, G. E. CAR~Al';, AND C. A. SMITH

!~ October 14mm

10

5

N

E 1 Rain u 64 mm "-01

~I\ ::l Q) ::J

"0 en Q) ..... I

I

..... 0.5 I

~ I

C

~ 0 - ---Q) 1 ------4l .0 c 01

t "0 0 en 0.1

0 \ t 0.05 \ \ \ --l!r

\ \ \ \ \

0 10 20 30 40 50 60

Elapsed days

Fig. 7. (Continued)

Citrus reentry problem

I Rain t 64mm

"-C\I '

E \ U I

'- ' 0'1 :

November

..... \ I Rain o 0.5 \ t 31 mm

o '+-

..0 o 0'1 "0 o (/) 0.1

o

0.05

o 10

...... ~ . .... ..... , .......... \ -..... \ ..... , ..........

~ --I

20 30 40 50

Elapsed days

Fig;. 7. (Continued)

45

60

46 F. A. GL'~THER, Y. IWATA, G. E. CAR~AN, AND C. A. S~[TH

10 May

5

N

\ E u

" 01

~ <I> ~

"'0 (/)

<I> I...

I... 0.5 0

0 -<I> ..c 0 01

"'0 0 (/) 0.1

0

0.05

'\

0 10 20 30 40 50 60

Elapsed days

Fig. 7. (Continued)

C\J

E u

""­Cl

:::l Q)

:l "'0 II) Q) ~

~

o '0 -Q)

..0 o Cl

"'0 o II) .-o

o

problem Citrus reentry

20 30

Elapsed days

. 7 (Continued) Fig ..

47

June

60

48

100

90

1L.. 0 80

~ ~ -~ 70 Q) a. E Q)

f-60

50

F. A. Gl':-ITHER, Y. IWATA, G. E. CARMA:-;, A:-ID C. A. SMITH

\

• • • • • • • • • • • •• • •

• . . \ • - •• • • . -.. • • • • •• • • • . ' ... ..... , ,

• , • • • • • . .. -.. • \ • •• •

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•

• • • •

10ctober I November

Oct. Nov. Dec. Jan.

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. , . , • • • • • • , . •

• •••• •

I April

• •

May

.-.. \ .. \ .. ••

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•

Jul

Fig. 8. Daily maximum air temperature at Riverside, CA. The intervals denoted by (1--1) indicate the 60-day sampling period after an azinphosmethyl application, 1975-1976 (Gl':-;THER et al. 1976 a).

59-day residue levels were 3.6 and 2.8 p.,g/cm2 . The initial degradation curve changed to the persistence curve within ten days in October but was pro­longed for 30 days in November and thus reduced residue levels much more. Azinphosmetyl dislodgable residues appear overall to be quite persistent, yet only rarely is azimphosmethyl implicated (circumstantially) in worker poisoning episodes. This may be because of the much lower dermal LD50 of azinphosmethyl, as compared to parathion (see Table VII).

LEFFINGWELL et al. (1975) observed a rapid decay of ethion leaf and soil residues on grape foliage in California's Central Valley between time of ap­plication to three days post-application when air temperatures were quite high. Temperatures decreased four days post-application and both the ethion leaf extract and soil data indicated a simultaneous lessening of ethion decay rates. Temperature effects on the levels of phosalone residues in leaf extracts were not as great as for ethion. It was concluded that rapid ethion dissipation resulted from the high air temperatures. This may have been a coincidental relationship as it is generally observed that pesticide residue dissipation is more rapid during the first few hours or days after spraying (GUNTHER and BLINN 1955).

DURHAM et al. (1972) reported that spraymen, after dermal exposure to parathion, had greater excretion of p-nitrophenol with higher temperature. This effect was shown not only in connection with diurnal variations but also in connection with seasonal variations in temperature. As dermal absorption of parathion is both slow and incomplete (as discussed earlier), the higher temperature was thought to increase the rate of absorption.

Citrus reentry problem 49

10 ~\ October

5 t-t--t_ _-6 -. -C\J

E

\-I u ......... 0" :i.

'-'

t I-I~~---~ Q) :::)

"0 en

\ --------I --------I Q) 0.5 ~

~

0

8 ---t --------I 0 '+-

Q)

.0 0 g-----01

"0 0 0.1 II)

0

! _-!---~------tt-0.05 ! Rain " ------- ~ Ilmm --- · · , · ,

I · L~

0.01 0 10 20 30 40 50 60

Elapsed days

Fig. 9. Dissipation curves for dislodgable foliar residues of azinphosmethyl after a 2EC azin­phosmethyl application to orange trees at six lb a. i. per 100 (A) and at 1,200 (0) gal/A and at one (0) and two (e) lb a.i./500 gal/A. Azinphosmethyl oxon (~) residues were de­termined only for the six lb a.i.l100 gallA treatment. Citrus Research Center, Riverside, CA, October-November 1975 and April 1976 (GL'NTHER et al. 1976 a).

50

-(\J

E o

........ C' :l -.-

(I'J

<1> ~

~

o

.E <1> :0 o C' "0 o

AND C. A. SMITH E CARMAN, Y IWATA, G .. F. A. GUSTHER, .

10 l~t November

5 ~I~t~t~t

I Rain ,llmm

-~~~~~o- ·40 20 30

E lapsed days

. 9 (Continued) Fig ..

50 60

C\I

E u

......... Ol

10

problem Citrus reentry

April

: I I"" .g t8~ I I ~ 0.5 1\1 ~"--- ___ ___ Q)

..0 o .g 0.1 o en

o 05 O. "----------! t -----1------~

I-----r--- -f 1 50 60 L~~-20 ~30 40 01 20 S

o. 0 Elapsed day

. 9 (Continued) FIg ..

51

52 F. A. GV!IITHER, Y. IWATA, G. E. CARMAN, A!IID C. A. SMITH

Climate, of course, involves much more than maximum air temperature and includes such factors as wind velocity, incident radiation, and relative humidity. The residue data in Figure 7 demonstrate the large effect of over­all climatic factors on parathion residue levels, however. 5 Thus, the same application made in May and October yielded a 9O-fold difference in foliar residues after 59 days (GUNTHER et al. 1976 a). It follows that the same ap­plication made on the same calendar day but to trees located in two different growing regions such as along the Pacific coast and on the edge of the desert will yield different residue levels after a specific time interval after applica­tion. Parathion residues appear to persist longer when applied during cool climatic conditions, but it should be noted that due to decreased pest activ­ity, applications are less likely to be made under these circumstances (see Table IX).

Rainfalls of 3,14, 31, and 64 mm are noted on Figure 7. Only the 64-mm (2.5-in) rainfall gave a demonstrable drop in the foliar residue level of para­thion. The 64-mm rainfall over a 24-hr period is not a common occurrence in Southern Califronia. The reduction of foliar residues by rainfall supports the hypothesis that this is one factor that has prevented episodes of worker poisonings in Florida, as mentioned earlier. Clearly, in establishing national reentry standards, variation in the environmental variables must be consi­dered and rainfall is the most important of these. Thus, GUTHRIE et al. (1976) also showed that reentry periods for tobacco may be altered appreci­ably when rainfall occurs, especially when water-soluble insecticides such as monocrotophos are involved6 . ChE depression in mice maintained in cages over treated tobacco leaves was different when the experiment was con­ducted with leaves collected in the absence of rain (75% depression) and with leaves collected after 1.1 in. rainfall (40% depression). Thus, when OSHA established temporary reentry intervals effective June 18, 1973, for citrus (oranges, lemons, and grapefruits), peaches, grapes, tobacco, and apples for 21 OP pesticides (Federal Register 1973), as shown in Table XII, reentry in­tervals for areas receiving moderate rainfall were less than for arid areas (see Section II h for the effect of field-washing of citrus trees as a means of remov­ing pesticides from foliage).

Although rainfall less than 3 mm (0.12 in.) is not shown on the graphs, its occurrence should not be dismissed lightly. WARE and MORGAN (1976) ex­posed volunteer cotton scouts to parathion-treated foliage. The 24-hr para­thion residues had no effect on either RBC or plasma ChE while there was a detectable drop in subjects entering the field after 48-hr. A very light rain before daybreak of the 48-hr reentry had left the leaves wet. The subject's pants were soaked immediately on entering the field, remained wet for ap­proximately one hr, and were dry within the second hr. It was postulated

5It has been suggested that the increased parathion residue persistence may be more sig­nificantlya result of foliar dust buildup over the successive months (SPENCER and SPEAR 1976).

6But not excluding so-called water-insoluble insecticides. Thus, parathion-with a water solubility of about 24 ppm at 25°C (WILLIAMS 1951) and with an acre-inch of rain equal to about 27,000 gallA-could be dissolved to the extent of about 2.5 kg by one in. of rainfaIVA of citrus grove.

Tab

le X

II.

l'ie

ld-r

ee"t

ry s

afe

ty i

nter

vals

in

da

ys f

or

crop

s tr

eate

d w

ith

org

an

op

ho

sph

oru

s p

esti

cid

es (

Fed

eral

Reg

iste

r 1

97

3).

Ora

nges

·, In

sect

icid

e le

mo

ns,

an

d

Pea

ches

G

rap

es

To

bac

co

Ap

ple

s g

rap

efru

its

Dry

W

et

Dry

W

et

Dry

W

et

Dry

W

et

Dry

W

et

a a

a a

a a

rea

ar

ea

area

ar

ea

area

ar

ea

area

ar

ea

area

ar

ea

Azi

np

ho

smct

hy

l (G

uth

ion

) 14

5

10

5 14

5

5 5

5 5

Car

bo

ph

eno

thio

n (

Tri

thio

n)

14

5 14

5

14

5 5

5 D

emet

on

(S

yst

ox

) 5

5 5

S 5

S 5

S D

iazi

non

2

2 2

2 2

2 2

2 2

2 D

imct

ho

ate

(Cyg

on)

2 2

2 2

2 2

D. D

iox

ath

ion

(D

elna

v)

2 2

2 2

2 2

2 2

::r D

isu

lfo

ton

(D

iSy

sto

n)

3 3

~ E

PN

14

S

10

5 10

S

S 5

... ("!)

Eth

ion

14

5

8 S

8 S

5 S

("!) '"

Imid

an (

Pro

late

) 2

2 2

2 2

2 ::r "<

M

alat

hio

n

2 2

2 2

2 2

2 2

2 2

'0 ...

Met

hy

l p

arat

hio

n

10

5 14

S

S 5

S S

0 u M

cvin

ph

os

(Ph

osd

rin

) 5

S 5

S 5

S 5

S "

Mo

no

cro

top

ho

s (A

zod

rin

) 5

5 S

Nal

ed (

Dib

rom

) 2

2 2

2 2

2 2

2

Ox

yd

emet

on

met

hy

l (M

eta-

Sy

sto

x R

) 5

5 5

5 5

5 P

arat

hio

n

14

5 10

5

14

S 7

Ab

5A

b S

S 5

Be

SB

c P

ho

salo

ne

(Zo

lon

e)

]0

5 5

S P

ho

sph

amid

on

(D

imec

ron

) 14

S

5 S

TE

PP

3

3 3

3 3

3 T

rich

lorf

on

(D

ylo

x)

2 2

a A

n ar

ea w

her

e m

od

erat

e ra

infa

ll h

as o

ccu

rred

, o

r a

mo

der

ate

was

h h

as b

een

ap

pli

ed,

afte

r p

esti

cid

e ap

pli

cati

on

. b

A =

pla

nt

bed

to

bac

co.

c 13

=

fie

ld t

ob

acco

. f:}

54 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

that the additional contact with residues carried to the skin with leaf mois­ture was the probable route of additional exposure sufficient to depress blood ChE activity. Thus, not only light rain but morning dew on the leaves or heavy fog are climatic variables that need to be considered. .

Figure 7 shows that parathion dissipation is quite similar regardless of the rate or method of application so that the dissipation curves tend to be paral­lel. In Florida, parathion was never used in the amounts of eight to ten lb a. i. / A, as is common in California for the control of the California red scale, and in recent years its usage in Florida has virtually disappeared (sPEARet al. 1975). This is another of the reasons (see earlier) cited for the lack of worker poisoning episodes in Florida.

Paraoxon levels on foliage tended to be higher when parathion levels re­mained high, according to GUNTHER et al. (1976 a). Slower parathion dissi­pation may give greater opportunity for the parathion-to-paraoxon conver­sion to occur. All paraoxon levels in that study were below 0.05 f-tg/cm 2 of leaf surface. The overall data indicate that hot climatic conditions represent decreased hazard in that parathion dissipation is more rapid and due to its dissipation decreases the time available for the parathion-to-paraoxon con­version. The actual hazard at any time, of course, is the result of the parath­ion and paraoxon residues present. The most striking feature in Figure 7 is the generally slower rate of paraoxon dissipation from foliage as noted by SPEAR et al. (1975 b) for paraoxon on foliage in the Central Valley of Califor­nia. Potentially, paraoxon levels would be cumulative if there were multiple parathion applications in a single growing season with the qualification that the gallonage of spray / A is kept low so that existing residues are not washed off the leaves. The earlier mentioned rainfall of 64 mm was effective in reduc­ing paraoxon as well as parathion foliar residues.

STAIFF et al. (1975) found no apparent increase in the levels of parathion, paraoxon, or other ChE-inhibiting material (e.g., S-ethyl parathion) on apple or peach foliage as a result of repeated weekly applications, 12 for apples and five for peaches, made with 25% WP parathion as a 0.03% spray solution applied to the trees to run-off, indicating no cumulative buildup of residues.

Foliar dislodgable levels of azinphosmethyl oxon are shown in Figure 9 for the six lb a.i.ll00galJA application (KUALUAG et al. 1977 b). Quantitation was by LC (liquid chromatography). Oxon formation was quite low, similar to paraoxon. Unlike paraoxon, azinphosmethyl oxon appeared to dissipate faster when rainfall of II mm occurred, but further confirmation is needed.

The solubility of parathion in orange leaf wax at 25°C is 0.5g/g of wax which is equivalent to approximately a 30% solution (OKAMURA et al. 1977). This high solubility and the possible frictional transfer of parathion-bearing leaf waxes to fruit pickers' arms, hands, and clothing were postulated as being another important factor in citrus picker reentry safety. This possibil­ity is supported by the observation of WARE et al. (1975 a) that cotton scouts' clothing was stained chlorophyll green from contact with the plants. In order to obtain a complete picture of the behavior of foliar pesticide residues, dis­sipation curves for penetrated parathion residues were also determined and are given in Figure 10 (GUNTHER et al. 1976 a). These data are valuable in that they give a reference value for checking foliar dislodgable residue val-

Citrus reentry problem 55

July

100

E 50 0... 0...

Q)

::J ""0 (/) I Q) '-

'- ---I v 10

0 '+-

""0 1-----t Q) 5 +-0 ----1---1 '- 1,--+-Q)

c Q)

CL 1-----1 ____ . .. ---o 10 20 30 40 50 60

Elapsed days

Fig. 10. Dissipation curves for penetrated foliar residues of parathion after a 25% WP parathion application to orange trees at four (-) and ten (.4) lb a.i. 11,600 gallA using an oscillating boom and at ten (e) lb a.i. 1100 gallA using a Kinkelder machine, Irvine Ranch, Tustin, CA, July-November 1974 and May-June 1975 (GC:-HHER et af. 1976 a)

56 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

1\ August

100

E 50

t 1\1 0.. 0..

Q)

:::J I:J (j) Q) '-

'- 1----1 a 0 I -

f ----f I:J Q) - 5 a '-

~f~ -Q)

c Q)

0..

! ...

a 10 20 30 40 50 60

Elapsed days

Fig. 10. (Continued)

E 0. 0.

Q)

:::J "0 (j')

Q) ~

~

o

o '+-

"0 Q) -o ~ -Q)

c Q)

CL

o

problem Citrus reentry

\ .

September

I Rain .14mm

\ I--f_J--f \t -------

10 20 30 40 50 60

Elapsed days

. 10 (Continued) FIg. .

57

58 ND C A. SMITH G E. CARMAN, A . Y IWATA, . F. A. GUNTHER, .

October

10 20 40 50

Elapsed days

. 10 (Continued) FIg. .

~

o

o '+-

-Q)

c Q)

0..

Problem Citrus reentry

November

I Rain + 31 mm

----1 ____

10 --:;;:;--3300 40 l....- 20

Elapsed days

. 10 (Continued) Fig. .

59

60

100

E 50 a. a.

"-'

~

.~ 10 o

'+-

"0

2 5 C ~ -Q)

C Q)

a..

I .

o

F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND t. A. SMITH

10 20 30 40 50 60

Elapsed days

Fig. 10. (Continued)

Citrus reentry problem 61

June

100

E 50

! 0. 0.

f Q)

::J -0 • (/) Q) ~

~

I\I-0

f 10

0 --0 Q)

0+-5 0

~

fL 0+-Q)

f c Q)

Q...

o 10 20 30 40 50 60

Elapsed days

Fig. 10. (Continued)

62 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

ues. The penetrated residue dissipation shows no discontinuity for the Oc­tober and November applications in spite of the 64-mm rainfall, as would be expected. However, the same rainfall decreased foliar dislodgable residue levels. The data for the penetrated residues therefore assure that the occur­rence of sampling error or mixup during processing were unlikely. Degrada­tion and persistence half-lives for the low-volume treatment are given in Table XIII. The penetrated foliar azinphosmethyl residue data are shown in Figure 11.

In California, the appropriate reentry time is given as a function of crop, the type of pesticide, and, in one case (parathion), the amount of pesticide applied. Different geographical or climatological areas of the state are not distinguished. The TASK GROUP (1974) guidelines for human exposure reen­try studies heavily emphasize the collection of environmental data in parallel with dislodgable pesticide residue data and human response data. One of the greatest difficulties in assessing the results of these studies is the extent to which their results can be extrapolated from one environment to another. It is much easier to quantifY the important variables associated with the en­vironmental factors and the toxicological processes than it is to relate them through a well-defined exposure mechanism (SPEAR et al. 1975 a).

e) Effect of method of application on residue dissipation

Spraying procedures used for pest control on citrus are discussed by CARMAN (1975). Due to increasing labor costs and a pronounced shift to the use of more toxic pesticides, fully mechanized spraying of citrus trees has been utilized extensively in many producing areas. The most effective mechanical sprayers are ground units; for the most part, those used on citrus crops fall into one of the following categories:

(1) Vertical boom arrangement, preferably oscillated, and dependent on hydraulic pressure to form and project relatively large droplets for di­lute spray distribution.

(2) Air-blast sprayers which utilize a movement of air to distribute rela­tively large droplets of dilute spray.

(3) Low-volume sprayers which form and distrubute, primarily with the movement of air, relatively small droplets from a limited amount of concentrated spray mixture.

There is a developing trend towards a substantial use of low-volume spraying on citrus. The use of low-volume applications offers tangible ben­efits. The equipment is less costly than comparable mechanical spray units for dilute applications and maintenance needs are minimized. Labor costs are also less, largely relatable to the handling of greatly reduced volumes of spray. Also to the extent that less material/A may be applied, pesticide costs are reduced. It is apparent that personnel applying concentrated spray mix­tures in low-volume applications will experience more hazardous contamina­tions from spillages and direct spray or diiffexposures. From a reentry view­point the residues on the foliage from these different tYpes of commonly used applications should be systematically investigated; work in this area is in progress, some of which is reported below.

Citrus reentry problem

Table XIII. Half-life values for parathion residues penetrated into orange leaves ( GUNTHER et al. 1976 a) a

Application date

July August September October November May June

Degradation

(days)

4 6 4

13 12

8 3

Half-life

a Treated with 25% WP at ten lb a.i./l 00 gallA. bpretreatment value was ten ppm.

Persistence

(days)

53 43 63 27 36 46

>200

59-Day penetrated leaf residue

(ppm)

11 7.1

11 11

9.2 34b 34b

63

Low-volume in its current state of development for use on California cit­rus is taken to mean an application of about 100 gal of spray/A. This amount is in contrast to gallonages ranging from several hundred to over 3,500 gal of dilute spray/A, depending primarily on tree size, amount of foliage, nature of pest-control problem, material being used, and cost of water and labor in­volved. CARMAN et al. (1972) recognized the need for residue studies for comparison of low-volume and corresponding dilute (high-volume) applica­tions. Their data clearly demonstrated that low-volume applications of a rep­resentative selection of pesticides commonly in use on California citrus gen­erally result in significantly higher7 residues on and in fruit and leaves than applications of the same amount of a. i. /A in the currently used dilute gallon­ages. The low-volume application also gave higher fruit and leaf residues on surfaces close to the operating spray unit and thus less uniform coverage than the corresponding dilute application.

Figure 7 showed the foliar dislodgable parathion residue levels from a ten lb a.i./llOO gallA low-volume application and from a ten lb a.i./1,600 gallA dilute application (GUNTHER et al. 1976 a). In all cases, the low-volume ap­plication method left greater amounts of dislodgable parathion and paraoxon residues, indicating that from a worker reentry standpoint greater hazard may be anticipated after a low-volume spray application than from the con­ventional dilute spray application.

WESTLAKE et al. (1971 b) reported that, with dialifor, concentrate spray applications gave higher initial deposits and somewhat longer persisting re­sidues on fruit than did dilute sprays. The point was raised that differences in deposits may be due in part, at least, to the sampling technique used. Fruits were collected at about shoulder height, the area where the air-blast sprayer used for the low-volume sprays is centered and where the maximum deposit would be encountered. All samples taken for residue analysis and reported

7U P to 10 x on foliage and 6 x on fruit from the materials evaluated to date (CARMAN et al. 1972).

64 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

October

10 - i E a. a. - 5 ~ Q) -B ::I -a :-en Q) ~ -, ~

~ 0 -t-o '+-

-~ -a Q) -0 ~ -0.5 Q)

c Q)

a..

o 10 20 30 40 50 60 Elapsed days

Fig. 11. Dissipation curves for penetrated foliar residues of azinphosmethyl after a 2EC azin­phosmethyl application to orange trees at six lb a.i./l00 (.a.) and/l,200 (0) gallA and at one (0) and two (e) lb a.i./500 gaVA, Citrus Research Center, Riverside, CA, October­November 1975 and April 1976 (GUNTHER et al. 1976 a).

problem Citrus reentry

November

. 11 (Continued) Fig. .

40

days 50

65

60

66 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

April

10

E Q. Q.

- 5 Q) ::J

"C ·in

I Q) ~

~

0

0

! -"C Q) .... 0 ~ .... Q) c ~ .5

o 10 20 30 40 50 60 E lapsed days

Fig. 11. (Continued)

Citrus reentry problem 67

herein were also taken at shoulder height and may represent excessively high residues on a total tree basis. However, these residue levels are present after a low-volume application for potential worker contact.

WOODHAM et al. (1974) studied the deposition and disappearance of di­methoate and its oxygen analog on and in citrus leaves following a helicopter treatment of an orange grove. Heavy rainfall during the two-day sampling period probably removed much of the dislodgable residues and their data primarily represent residues penetrated into the leaf waxes. Residues of di­methoate and its oxygen analog on and in leaves from trees treated with one lb a. i. of dimethoate /three pints/ A were significantly higher than those from the one lb a. i. of dimethoate/five gal/A treatment. This was generally true for all segments of the tree. A more uniform deposition was reported for the three pint/ A treatment, but this difference may be due to variations in appli­cation technique rather than to differences in the application volume.

f) Effect of formulation on residue diSSipation

Pesticides which are applied to crops are generally available in either emulsifiable concentrate (EC) or wettable powder (WP) formulations. The fraction of the pesticide is generally, but not invariably, 25 to 50% of the total formulation weight in WP formulations but may exceed both limits in EC formulations. Both types oHormulations contain emulsifiers which result in a relatively stable suspension or mixture when the formulation is added to wa­ter. In addition, there may be adjuvants which help to improve wetting or sticking of the pesticide to the fruit and foliage. A discussion oHormulations and adjuvants may be found in EBELING (1963).

Certain pesticides may also be obtained in microencapsulated form, where the pesticide is contained in a capsule 30 to 50 micrometers in diame­ter. The capsules are supplied suspended in water, and the suspension is di­luted and applied as if it were an emulsifiable concentrate. In water suspen­sion the pesticide can diffuse through the capsule until a saturated solution in the water results. When the capsules are applied to the plant and become dry, pesticide can slowly diffuse out, maintaining a more even concentration of pesticide than with other types of formulations. Tests to date indicate that microencapsulated pesticides are much less hazardous to persons exposed to them, either orally or dennally (Penn walt Corp. 1974), as also mentioned earlier in this review and discussed in more detail below.

WOLFE et al. (1975) reported that in studies of a volunteer, hand­thinning apples under controlled conditions 1, 24, 48, 72, 96, 168, and 240 hr after application of a conventional 0.03% parathion spray, both dermal and respiratory exposure were greater when a WP formulation was used than when an EC formulation was used. The difference was attributed to the ease with which the dried residue from a WP formulation application dislodged from the foliage during contact or agitation by the worker. 8 Total foliar

HAs discussed later in this review, a major factor was probably the sloughing of the initial deposit from the WP formulation (GUNTHER and BLINN 1955).

68 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

parathion residues from the two types of applications were approximately the same over ten days with the loss of one-half the original residue within ap­proximately 48 hr after application. Only trace amounts of paraoxon could be detected one and seven days after application, in contrast to the behavior of parathion on citrus discussed earlier. Urinary p-nitrophenol excretion by the volunteers indicated slightly more absorption following exposure in WP ex­perimental plots than in EC plots.

WINTERLIN et al. (1975) treated peach trees with WP, EC, and encapsu­lated parathion formulations. The percentages of dislodgable residues in the EC formulation from punched-leaf samples ranged between 17 and 33% with an average of 25% for seven sampling periods. The WP formulation gave a higher percent of dislodgable residue and ranged between 43 and 61 % with an average of 47% for seven sampling periods. The dissipation of encapsu­lated parathion from peach foliage was much slower than for WP and EC parathion applications, as expected. The percentage of dislodgable parathion compared to the remaining residue was considerably higher for the encapsu­lated parathion. About two-thirds of the total residue was dislodgable. It was emphasized that dislodgable residues include both capsulated and noncapsu­lated material, and thus do not represent the same hazard to workers as they would if noncapsulated. Paraoxon residues were lowest with the EC applica­tion and were below the detectable limit the second day of sampling. Sam­ples prayed with WP and encapsulated formulations contained considerably higher levels of paraoxon than did the EC formulation; the rate of degrada­tion of paraoxon was similar to parathion, particularly after the third post­application day.

To determine the effect of formulation on parathion dissipation on citrus leaves, trees were sprayed at 12.51b a.i./2,000 gallA using both an EC and a WP formulation (GUNTHER et al. 1976 b). Two applications were made, one on November 14, 1975 and one on May 20, 1976, at the Citrus Research Center, Riverside, California. To obtain dislodgable foliar residues, dupli­cate leaf disc samples were collected and each sample was stripped of surface dislodgable parathion residues by four successive aqueous strippings fol­lowed by four successive partitionings into hexane using the procedure of GUNTHER et al. (1974) described earlier. Hexane extracts were stored at 4°C over Na2S04 prior to analysis. To obtain penetrated residues, a sample of 40 leaf discs was extracted by blending in a semi-micro Waring Blendor for two min at high speed with about 15 g of Na2S04 and 100 ml of acetone. The mixture was filtered through a coarse sintered-glass funnel at reduced pres­sure. The solid residue was reextracted with 100 ml of acetone. The filtrates were combined, the volume was recorded, and the extracts were stored over Na2S04 at 4°C prior to analysis. Temperature data for the initial 12 days of the experiment are given in Figure 12.

Figure 13, for the application on November 14, 1975, shows that under identical conditions, the dislodgable parathion residues present dissipated faster after application with the EC than with the WP formulation. The re­sults of a replicate application on May 20, 1976 shown in Figure 14, although less definitive, also indicate a somewhat faster dissipation from an EC appli­cation.

Citrus reentry problem 69

90 90 • • • • • • • 80 •• • 80 •• ~ • 0

Q) • •• • '- •• 2- • 0 70 • 70 • a:; • a. E Q) • f-

60 60 •

50 50

Nov. 14 Nov.21 Nov.28 May20 May27 JUN.3

1975 1976

Fig. 12. Daily maximum temperatures at the Citrus Research Center, Riverside, CA (Gl':-;THER

et al. 1976 a).

In Figure 13 dislodgable paraoxon levels increased over a two-to-three­day period and than remained constant over the experimental period. The increase in the paraoxon level for both formulations ceased when the persis­tence curve changed to the degradation curve. In Figure 14 there was no increase in the paraoxon level after one day and residues then declined very slowly with a half-life of seven to ten days. These results from field experi­ments are in agreement with the greenhouse experiments of ADAMS et al. (1976) earlier cited in this review. The WP seems to yield more paraoxon residues than the EC formulation. Figure 15 shows the decline in penetrated and total parathion (penetrated and dislodgable) residues. After 15 days both residue dissipation curves merge indicating that of the total residues, dis­lodgable residues are a minor component.

g) Effect of citrus variety on residue dissipation

The emergency temporary standard for exposure to OP pesticides estab­lished by the U. S. Department of Agriculture (Federal Register 1973) gives reentry intervals for "oranges, lemons, and grapefruits." Numerous citrus varieties exist within the category of "oranges, lemons, and grapefruits" and also many outside this category, for example, limes and tangerines.

GUNTHER et al. (1976 a) determined the dependence of foliar residues on citrus variety. Twelve citrus varieties located in a single field plot at the Cit­rus Research Center of the University of California, Riverside, were used. The use of a single plot insured that climatic factors were identical for all varieties. The clean (dust-free) trees were treated with parathion thoroughly and uniformly, using manual spray equipment, with 1.5 lb of 25% WP/IOO gal of water. The application was made on September 16, 1974, and 1-, 3-,

70 F. A. Gl'NTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

November,1975

- ~. (\J '\~ E • • ~ 1.0 J,o". Ol

::l "'~ - 0, (/) o~ ._ Q.) 0.5 e-e ::J o 0 --e WP

""C

~o (/)

Q) ~

~ ~

o EC 0

0 -Q.) 0.1 -..c 0 Ol

""C 0.05 • 0 • • • • (/)

./ • 0 • • •

r e

0 0_ 0 _°-0 0 0

0.01 0 0

5 10

Elapsed days

Fig. 13. Dislodgable residues of parathion (top) and paraoxon (bottom) on orange leaves after an application of 12.5 lb a.i./2,OOO gallA using a 25WP (e) or 4EC (0) formulation (GuNTHER et ai. 1976 a).

Citrus reentry problem

5r e May,I976

C\I ~\

E. '\\ ~ 0' e\ ::L In

0.5.& e\ Q) ::l

"U (/) e Q) -- ~ e ... ~--o __

--~ 0 ... .& 0 0

o -Q) 0.1

g, 6 --~--~-:\6 -g 005 6 :. -~---6 EC

WP

.................... _...Q --

. ~--

~ .~-------.& ~--

--- -~

----.&~.&

71

5 10 15

Elapsed days

Fig. 14. Dislodgable residues of parathion (closed symbols) and paraoxon (open symbols) on orange leaves resulting from a parathion application ofWP (0) and EC (~) formulations (GeNTHER et al. 1976 a).

72 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. ~. SMITH

~ • E 100~ ." a. g. • ~ 50 ~,,~ ".

-6 \0 -.;:~ ~ ~ ~,~"~.

May,1976

, .'\::." ,t:. ,,0--0--0 W P t:.' --'. ----o - 10 t:.- _

"t:." ...... :~----t:. ---

--.-- --t:. --__ .~ ------EC -o -Q) 5 c Q)

a..

5 10 15

Elapsed days

Fig. 15. Total (closed symbols) and penetrated (open symbols) foliar parathion residues reco­vered from orange trees sprayed with WP (0) and EC(Ll) parathion formulations (GUNTHER et al. 1976 a).

Citrus reentry problem 73

and lO-day leaf samples were taken. The residue data are in Table XIV. All varieties exhibited a definite decline of parathion dislodgable residues over the ten-day period. Foliar residues varied from 1.03 to 0.25, 0.25 to 0.07, and 0.08 to 0.01 f-Lg/cm 2 on days 1, 3, and 10, respectively. The mean para­thion values for all varieties were 0.51,0.16, and 0.04 f-Lg/cm 2 for days 1, 3, and 10, respectively, and yielded a half-life of about 2.5 days. The dislodgable paraoxon residue values were quite low, being 0.03 to 0.02 f-Lg/cm 2 on day one and 0.01 f-Lg/cm 2 on day ten. All varieties also exhibited a definite de­cline in penetrated foliar residues. This experiment was repeated on May 6, 1975, and the second set of residue data are in Table XV. Probably due to warmer weather, residues dissipated slightly more rapidly. The means for all varieties were 0.26, 0.09, and 0.01 f-Lg/cm 2 for days 1, 3, and 10, respec­tively, and again yielded a parathion half-life of about two days.

As the climatic factors were identical for all these citrus varieties, any var­iation in the residue values found would be a characteristic of the foliage of the variety exhibiting the variation. Without exception, there was a very sig­nificant decline in the foliar dislodgable parathion residues within ten days and no significant buildup of paraoxon residues for any variety. The results of the two applications on dust-free foliage (except for the inerts in the formula­tion) show that all varieties behave quite similarly with the tangelos possibly retaining higher parathion residues than other varieties.

h) Reduction of residues by tree washing

The field washing of citrus trees for pesticide residue removal has been studied to obtain background for procedure and efficacy if a grower elected to wash his trees as a means of reducing the dislodgable residues on fruit and foliage and qualifYing for an earlier picking than would be permitted by reen­try standard requirements. It appears that the economics of a tree washing operation could render its use by growers impractical except when unique marketing situations prevailed.

WESTLAKE et at. (1973) washed dioxathion-treated orange trees with a hand-gun with water containing a wetting agent using 30 gal/tree, approxi­mately 3,000 gal/A. Different sets of trees were washed 4, 10,38, and and 46 days post-application and the average dislodgable residue reductions achieved at these times were 56,37,30, and 30%, respectively. Dislodgable foliar residue levels had ceased to decline after about 17 days post­application. Manually operated spray guns are now wholly impractical for grower use, but these data demonstrated that foliar residue reduction could be achieved.

IWATA et ai. (1977) spray washed phenthoate-treated orange trees with water containing a wetting agent using an oscillating boom sprayer deliver­ing 3,000 gal/A. Residues before and after washing were 0.34 and 0.11 f-Lg/cm 2 , respectively, for trees washed three days post-treatment and 0.07 and 0.02 f-Lg/cm 2 , respectively, for trees washed ten days post-treatment. Thus, approximately 70% of the foliar dislodgable residues was removed each time. Phenthoate-treated lemon trees were similarlv field washed at 2,500 gallA. Residue values before and after washing we're 0.07 and 0.06

~

Tab

le X

IV.

Fol

iar

disl

odga

ble

and

pene

trat

ed p

arat

hion

and

par

aoxo

n re

sidu

es o

n ci

trus

var

ieti

es (

Gu

NT

HE

R

et a

l. 19

76 a

).a

Dis

lodg

able

res

idue

s (/

lg/c

m2

)b a

fter

P

enet

rate

d re

sidu

es (

ppm

)b a

fter

~

?-V

arie

ty

Par

athi

on

Par

aoxo

n P

arat

hion

G

i

1 3

10

1 3

10

1 3

10

~ ~ da

y da

ys

days

da

y da

ys

days

da

y da

ys

days

t'l

.?'

L

isbo

n le

mon

0.

64

0.19

0.

05

0.03

0.

02

0.03

48

9

3 ~

Sat

sum

a m

anda

rin

0.27

0.

17

0.08

0.

02

0.02

0.

01

42

7 2

.....

$J K

ara

man

dari

n 0

.34

0.

10

0.01

0.

02

0.02

0.

01

33

11

1 ~

Kin

now

man

dari

n 0.

44

0.14

0.

02

0.02

0.

02

0.01

28

6

1 '?

D

ancy

tan

geri

ne

0.52

0.

19

0.0

4

0.03

0.

04

0.01

27

6

1 G

i T

empl

e or

ange

0.

38

0.13

0.

02

0.02

0.

03

0.01

18

4

1 ~

Was

hing

ton

nave

l 0.

56

0.20

0.

06

0.03

0.

02

0.01

28

8

1 C

l F

rost

nuc

ella

r na

vel

0.25

0.

07

0.02

0.

02

0.02

0,

01

20

5 1

>

Ree

d gr

apef

ruit

0.

51

0.14

0.

03

0.03

0.

02

0.01

24

6

1 ~

Bea

rss

lim

e 0.

58

0.15

0.

02

0.02

0.

03

0.01

43

10

3

.~ M

inne

ola

tang

elo

0.6

4

0.21

0.

06

0.02

0.

02

0.01

44

8

2 ~

Orl

ando

tan

gelo

1.

03

0.25

0

.04

0.

03

0.04

0.

01

50

9

3 I:

) 0 a

App

lica

tion

dat

e S

epte

mbe

r 1

6,

1974

; tr

eatm

ent

1.5

lb o

f 25

% W

P/1

00 g

al,

thor

ough

cov

erag

e w

ith

man

ual

spra

y eq

uipm

ent,

Riv

ersi

de,

CA

. ?-

bEac

h va

lue

is t

he m

ean

of

four

sam

ples

(tw

o sa

mpl

ers

each

col

lect

ed d

upli

cate

sam

ples

).

'" ~ ::j

:I:

Citrus reentry problem 75

Table XV. Dislodgable foliar parathion and paraoxon residues on citrus varieties (GUNTHER et al. 1976 a).a

Dislodgable residue (llg/cm 2 ) after Variety Parathion b Paraoxon c

1 day 3 days 10 days 1 day 3 days

Lisbon lemon 0.25 0.06 0.01 <0.01 0.01 Satsuma mandarin 0.27 0.08 0.01 0.01 0.01 Kara mandarin 0.20 0.06 0.01 0.01 0.01 Kinnow mandarin 0.31 0.08 0.01 <0.01 0.01 Dancy tangerine 0.35 0.15 0.01 <0.01 0.02 Temple orange 0.15 0.07 0.01 <0.01 0.01 Washington navel 0.18 0.07 <0.01 <0.01 0.01 Frost nucellar navel 0.12 0.08 0.01 <0.01 0.01 Reed grapefruit 0.22 0.08 <0.01 <0.01 0.01 Bearss lime 0.31 0.10 0.01 0.01 0.01 Minneola tangelo 0.37 0.17 0.01 0.01 0.02 Orlando tangelo 0.33 0.11 0.01 0.01 0.01

a Application date May 6, 1975; treatment 1.5 lb of25% WP/100 gal, thorough coverage with manual spray equipment, Riverside, CA.

bEach value is the mean of four samples (two samplers each collected duplicate samples). c < 0.01 Ilg/cm 2 after ten days for all varieties.

f.Lg/cm 2, respectively, for trees washed four days post-treatment and 0.03 and 0.02 f.Lg/cm 2 for trees washed 11 days post-treatment. Residue reduction was not as great as anticipated but because of the low residues present these data were difficult to interpret.

CARMAN et al. (1976) conducted tree washing tests using water alone to establish optimum conditions for an oscillating boom sprayer. Trees sprayed with 8.75 lb a. i. of parathion/2,500 gal! A were washed three to five days post-treatment and gallons of water used/A, boom oscillations/min, nozzle delivery pressure, spray cone angle, and vehicle speed were each individu­ally altered while keeping the other parameters constant. As expected, the amount of foliar dislodgable residue removed increased with the quantity of water used. Amounts of residue removed were 59, 65, 75, and 81 % with 1,500,2,000,2,500, and 3,000 gal/A, respectively. Boom oscillation was not critical as average amounts of residue removed were 71, 72, and 67% at 29, 53, and 78 oscillations/min, respectively. Nozzle pressure was not critical as amounts of residue removed were 59, 77, 60, and 65% at 300, 400, 500, and 600 psi, respectively. Spray cone angle was not critical as reductions were 70, 72, and 71 % at 16, 32, and 48 degrees. Vehicle speeds of O. 9, 1.4, and 1. 9 mph coupled with boom oscillations of 39, 60, and 78 oscillations/min, re­spectively, gave reductions of 29, 46, and 44%, respectively. Low vehicle speed coupled with a low boom oscillation rate gave a lower washing ef­ficiency. The overall conclusion was that the volume of water applied is the single important factor in reducing foliar dislodgable residues by washing with an oscillating boom sprayer. Cost of the tree-washing procedure also increases with the volume of water applied because of increased costs of water and labor required.

76 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

One set of parameters was selected by GUNTHER et al. (1976 a) to evaluate the repetitive efficiency of foliar dislodgable residue reduction. Trees were sprayed with 25% WP parathion at ten lb a.i./1,600 gallA and three days post-treatment the trees were washed with an oscillating boom spray rig. A No. 10 nozzle operated at 46 oscillations/min delivered 4,000 gal of water / A at 550 psi; ground speed was 0.9 mph. Six replicate leaf samples were taken before the washing operation and again the same day when the washed trees had dried. This experiment was repeated seven times through­out the year. Results are in Table XVI. The foliar dislodgable parathion re­sidues present before washing varied almost ten-fold as the rate of dissipa­tion over the three-day post-application period was dependent on the exist­ing environmental conditions. Reduction varied from a low of 20% to about 80% with the average reduction for the seven trials being 60±20%. Foliar dislodgable paraoxon levels were too low «0.06lLg/cm2) to give meaningful results but residues when present were reduced by washing. It is likely that paraoxon residues were removed just as effectively as parathion residues. Washing tests were also conducted by GUNTHER et al. (1976 a) with other trees sprayed with azinphosmethyl. Mature trees were sprayed with an EC formulation at six lb a.i./1,200 gallA or at six lb a.i./100 gal/A. Trees were washed three days post-application at 3,600 gallA and tests were conducted at three different times. Table XVII gives the results which show that dis­lodgable foliar residues were reduced by 59±14%. Reduction varied from a low of39 to a high of 74% for six tests. Reduction by washing did not appear to be dependent on the gallonage of spray used for the application, i. e., whether dilute (high-volume) or concentrate (low-volume).

Although penetrated foliar parathion residues are probably not sig­nificant from a worker reentry perspective, these residues were determined in these tests and are also given in Table XVI. Without temperature consid­erations (month), the penetrated parathion residue present before washing varied only two-fold in contrast to the dislodgable residues, which varied more than ten-fold. The washed foliage often showed a 30 to 60% reduction in penetrated parathion residues. The water contained a wetting agent (16 ml ofVatsol/100 gal) and this was probably capable of removing residues from the leaf wax surface.

Studies conducted in two vineyards by Kmo et al. (1975) showed that the effect of overhead sprinkler irrigation reduced methyl parathion residues only slightly more than from nonirrigated vines, and then only if the treated vines were irrigated (1.5 in. over 12 hr) on the night following the insecticide application. The results are probably due to the normal rapid methyl parath­ion dissipation from grape leaves (90% of surface residues lost in one day).

i) Reduction of residues by chemical degradation

Since the use of large volumes of water for removing foliar residues is uneconomical because of water and labor costs involved, the use of lime as a chemical degradant for pesticide residues was evaluated by CARMAN et al. (1976). Lime suspension was applied to parathion- and dioxathion-treated citrus trees to determine if the alkaline solution would enhance pesticide dis-

Dat

e ap

pli

edb

19

74

July

26

Aug

. 23

S

ep.

20

O

ct.

18

N

ov.

15

19

75

May

24

Ju

ne

20

Tab

le X

VI.

P

arat

hion

res

idue

s o

n a

nd

in

oran

ge l

eave

s b

efo

re a

nd

aft

er w

ashi

ng o

f tr

ees

wit

h w

ater

plu

s a

wet

tin

g

agen

t th

ree

days

po

st-t

rea

tmen

t us

ing

an o

scil

lati

ng b

oo

m s

pray

ing

rig

(GU

NT

HE

R

et a

l. 1

97

6 a

) a

Dis

lodg

able

res

idue

s (l

lg/c

m2

) P

enet

rate

d r

esid

ues

(pp

m)

Pre

-was

h P

ost

-was

h

Cha

nge

Pre

-was

h P

ost-

was

h ('Y

o)

1.0

0 ±

0.

15

0.2

3 ±

0

.07

-7

7

43 ±

6

21 ±

1

0.80

± 0.

18

0.18

± 0

.02

-7

8

37 ±

4

14

± 1

0.8

3±

0.1

8

0.2

7 i

0.1

2

-67

5

3 i

11

28 ±

8

2.6

± 0

.3

1.2

± 0

.1

-54

30

± 6

32

± 6

4.

0 ±

0.4

1.

7 ±

0.2

-5

8

44 ±

13

29 ±

17

0.6

6±

0.1

0

0.53

± 0

.12

-2

0

46 ±

6

47 ±

8

0.4

2 ±

0.0

7 0

.13

± 0

.02

-6

9

26 ±

3

17 ±

1

-6

0 ±

20

Ch

ang

e ('Y

o)

-51

-6

2

-47

+6

-3

4

+2

-35

-32

± 2

6

a A

No.

10

no

zzle

op

erat

ed a

t 46

osc

illa

tio

ns/

min

del

iver

ed 4

,00

0 g

al/A

at

55

0 p

si a

nd

80

gal

/min

; ve

hicl

e sp

eed

was

0.9

mp

h.

Eac

h re

sid

ue

valu

e is

th

e m

ean

of

the

valu

es f

rom

six

rep

lica

te s

ampl

es.

b A

pp

lica

tio

n t

o V

alen

cia

oran

ges

was

40

lb o

f 25

% W

P/1

,600

gal

/A,

Irvi

ne R

anch

Co.

, T

ust

in,

CA

.

Q

... '" '" ... to

to ;:;. ... '<

"Cl ... 0 g;

to 3 :::j

Dat

e ap

plie

d

19

75

Oct

. 3

Nov

. 7

19

76

Apr

. 23

Tab

le X

VII

. A

zin

ph

osm

eth

yl r

esid

ues

on

and

in o

rang

e le

aves

bef

ore

and

afte

r w

ashi

ng o

f tr

ees

wit

h w

ater

plu

s w

etti

ng a

gent

thr

ee d

ays

post

-tre

atm

ent

usin

g an

osc

illa

ting

bo

om

spr

ay r

ig (

GU

NT

HE

R

et a

l. 19

76a)

a.

Dis

lodg

able

res

idue

s (l

lg/c

m2

)b

Pen

etra

ted

resi

dues

(pp

m)

Pre

-was

h P

ost-

was

h %

Cha

nge

Pre

-was

h P

ost-

was

h

2.04

± 0

_18

0.63

± 0

.04

-6

9

9.8

4±

1.5

6 2.

52 ±

0.3

7 -7

4

1.88

± 0

.34

0.

73 ±

0.1

0 -6

1

6.89

± 0

.93

2.49

± 0

.29

8.80

± 0

.46

2.

94 ±

0.3

8

-67

11

.9 ±

2.6

4.

45 ±

0.7

7

1.06

± 0

.19

0.65

± 0

.05

-39

5

.94

± 1

.47

3.28

± 0

.62

-4

5

-59

± 1

4

% C

hang

e

-64

-6

2

o;J

"l ?­ (") c:: ~ t'1

J' ~ '? ~ .> o t'1

(') ~ ~ ~

a A

No

.9 n

ozzl

e o

per

ated

at

46 o

scil

lati

ons/

min

del

iver

ed 3

,600

gal

/A a

t 50

0 ps

i an

d 69

gal

/min

; ve

hicl

e sp

eed

was

0.9

mph

; ea

ch r

esid

ue v

alue

is

0 th

e m

ean

of

the

valu

es f

rom

six

rep

lica

te s

ampl

es.

?-bA

ppli

cati

on t

o V

alen

cia

oran

ges

wit

h G

uth

ion

(az

inph

osm

ethy

l) (

two

lb/g

al)

EC

at

six

lb a

.i./

1,20

0 ga

l/A

(to

p va

lue)

and

six

lb

a.i.

/100

gal

/A ~

(bo

tto

m v

alue

); C

itru

s R

esea

rch

Cen

ter,

Riv

ersi

de,

CA

. ~

Citrus reentry problem 79

sipation through hydrolysis. No enhanced pesticide degradation resulted from a 25 or 50 Ib/l00 gallA low-volume lime application. A 50% enhanced reduction of parathion occurred with a lime application of 50 Ib/2,500 gallA and essentially little or no reduction of dioxathion occurred with a 25 Ib/l,250 gallA lime application. It was concluded that the total amount of water used/tree was the main factor in reducing foliar residues and not the presence of lime in the spray solution.

Some metal ions catalyze the hydrolysis ofOP compounds and cupric ion is the most active of them. Catalytic hydrolysis by copper ion is much more effective on phosphorothionate esters than on their oxygen analogs. Thus, the hydrolysis ofEPN and parathion is accelerated by the presence of copper ion 47.6 and 20 times, respectively, whereas that of paraoxon is only 1.7 times (KETELAAR et al. 1956). The use of Bourdeaux mixture (1:1 copper sul­fate:lime) or copper chelates may hold some promise as chemical degradants for reducing foliar thionophosphate pesticide residues (CARMAN et al. 1976).

III. Fruit rind residues

Dissipation of pesticide residues from fruit has been extensively investi­gated (GUNTHER and BLINN 1955, GUNTHER 1969) due to its importance in consumer protection. As discussed earlier, QUINBY and LEMMON (1958) at­tributed worker poisoning to the extensive contact between harvesters and pesticide-treated fruit, leading to percutaneous pesticide penetration; this route of exposure is now felt to be relatively unimportant, as also discussed earlier and again discounted below. POPENDORF and SPEAR (1974), in their survey of orange harvesters in the Central Valley of California, noted that experienced orange pickers wear gloves to protect themselves from thorns and sharp branches and to prevent skin abrasion from the orange rind. It has been reported that the wearing of canvas gloves for picking operations in­creased the penetration of parathion from the hand from 11 to 31% (TASK GROUP 1974). Although pesticide residue exposure to workers through fruit contact is not discounted, it is currently believed that foliage is the greater source of toxicants to workers. For an average 20-year-old orange tree, GUNTHER et al. (1973) calculated that the leaf:fruit area ratio is 17: 1. WOLFE et al. (1975) noted in an apple hand-thinning study that collection of pes­ticides on the forearm from leaf contact is almost twice as much/hr of work as on the hands which come into firm contact with residues on the small apples. WESTLAKE et al. (1973 a) studied the accumulation of dust and pesticide re­sidues on workers by washing pickers' arms and hands at ten-minute inter­vals. Dust accumulated ranged from 0.6 to 1. 7 mglcm2 of skin area/ten min.

As part of the study described in Section II(d) on the effect of seasonal climatic variations on pesticide dissipation from foliage, fruit samples were also taken when available (GUNTHER et al. 1976 a). Parathion residues on and in rind are plotted in Figure 16 for the trees sprayed November 15, 1974, May 24, 1975, and June 20, 1975. The latter two experiments have pre-treatment residue values which resulted from July 1974 and August 1974 applications, respectively. The dissipation rate from rind is essentially the

80 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

same regardless of the method (dilute versus low-volume) or rate (four or ten lb a.i./A) of application as demonstrated by the parallel lines for the dissipa­tion curves. The degradation half-life calculated from the first three data points for the low-volume application is about 15 days for all three applica­tions. The persistence half-life for the May and June applications is about 48 days and for the November application is about 110 days. Sixty-day rind re­sidues after a low-volume application of ten lb a. i./l00 gallA were 5.7, 3.7, and 7.5 ppm for the May, June, and November applications, respectively. Rainfall on November 19 (64 mm) and again on December 14 (31 mm) did not remove any significant amounts of these stabilized 19-day-old and 44-day-old residues. GUNTHER et al. (1963) noted reduction of azinphosmethyl residues from fruit due to only a few tenths of an inch of rainfall.

1"'" "'" I ~~nm November

~ Rain

"'" "",1",-r 31 mm

E 10 Cl. Cl.

f - -1 -Q)

5 :::J

I"", -

"0 en Q) I", ~

"0 1- -1- -r c: 0::

o ~r L........----J. ~---L--...I.---.L....-I . 0 10 20 30 40 50 60

Elapsed days

Fig. 16. Parathion residues on and in Valencia orange rind after treatment with a 25% WP for­mulation at (e) ten Ib a.i./100 gal/A (low-volume), (.A.) ten Ib a.i./1,600 gal/A, and (.) four Ib a.i./1,600 gal/A; trees were located on the Irvine Ranch, Tustin, CA; each data point is the mean of three replicate field plot samples and duplicate laboratory sam­ples; November 1974 and May-June 1975 (GC~THER et al. 1976 a).

Citrus reentry problem 81

Three days post-application parathion-treated trees were washed with an oscillating boom spray rig at 4,000 gallA (GUNTHER et ai. 1976 a). Data for the rind residues for months when fruit were available (July, November, May, and June) before and after washing show that residue levels remained unchanged by washing in the field. Foliar dislodgable residue levels for the same trees were lowered by 56% (see Table XVI). It is likely that the dislodg­able fruit residue constitutes such a minor portion of the total rind residue that its removal was not significant in terms of a change in total residues. Alternatively, it may be that washing of trees is not as effective in removing dislodgable residues from fruit as it is for removing dislodgable residues from leaves.

Shaking of parathion-treated trees three days post-application with an OMC "Shock-Wave" tree shaker for one min did not lead to any demonstra­ble change in the rind residue level (GUNTHER et ai. 1976 a). This result does not imply that residues cannot be removed by handling the fruit. WESTLAKE et ai. (1973) washed dioxathion-treated trees with a hand-gun delivering 30

May

-I", "::l----f------E 10

a. a.

....-Q) 5 ----- ----~

~I--f ------i~ -----0 en <V ~

-0 ! c --------I __________ : 0::

0.5~~------~------~------~----~------~------~--o 10 20 30 40 50 60

Elapsed days Fig. 16. (Continued)

82 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

gal of water containing a wetting agent/tree. Different trees were washed 4, 10, 38, and 46 days post-treatment. Whereas dislodgable foliar residues were reduced by 56, 37, 30, and 30%, respectively, fruit rind reductions were 11, 0, 24, and 15%, respectively. Reduction of residue on fruit was thus less than for leaves, if indeed any actual reduction occurred at all.

IWATA et al. (1977) reported that little if any reduction of phenthoate rind residues occurred from laboratory washing of lemons and oranges, although GUNTHER (1969) reported that laboratory washing of lemons and orange:, treated in the field with 18 other insecticides removed from traces up to nearly 100% of rind residues, depending upon the compound, its rate of penetration into rind, and the citrus variety. Laboratory washing of grape­fruit, however, removed about 50% of the residue from fruit sampled four days after treatment and from 25 to less than ten % thereafter. Field washing with a wetting-agent spray at 2,500 gallA was also ineffective in reducing re­sidues of phenthoate on lemon fruit; thus, rind residues before and after

-E 0.. 0.. -Q)

::l -0 (J)

Q) ~

-0 C

0::

10

5

June

t i ____

f I--l----T ·----1----1

0.5~~------~------~------~----~------~------~--o 10 20 30 40 50 60

Elapsed days

Fig. 16. (Continued)

Citrus reentry problem 83

washing with an oscillating boom sprayer were 3.5 and 4.0 ppm, respec­tively, for trees washed four days post-treatment and 2.6 and 2.8 ppm, re­spectively, for trees washed 11 days post-treatment. Similarly, laboratory washing was ineffective in removing residues of dialifor from oranges (WESTLAKE et al. 1971 b).

In contrast, WESTLAKE et d. (1973 b) reported that phosphamidon re­sidues on fruit remained largely on the surface. Laboratory washing of oranges removed 77,75, and 72% of the total residue for fruit sampled 3,14, and 28 days after field-spraying with phosphamidon 8EC. WESTLAKE et al. (1971 a) also reported that laboratory washing of oranges reduced propargite residues by 12 to 30% in samples picked seven and 28 days after spraying, respectively, but had no effect at the 75-day interval; no reduction of re­sidues by washing lemons was observed at any sampling interval.

IV. Orchard soil dust residues

a) Methodology

SPENCER et al. (1975) reported a procedure for collecting soil dust from the orchard floor. Samples of loose dust were obtained by vacuuming through a 100-mesh screen installed on the bottom of an 18- X 25-cm wooden frame. The frame was held on the soil surface and a stainless steel nozzle attached to a portable vacuum cleaner was passed over the screen. Dust samples were extracted with an azeotropic mixture of hexane (41 %) and acetone (59%) for five hr in a Soxhlet extractor for the determination of parathion and paraoxon soil dust residues. LEFFINGWELL et al. (1975) used a soil scoop designed to remove the top six mm of the soil surface. The soil sample was screened through a six-mesh sieve to remove sticks, stones, and plant material and 250 g of the soil was extracted with 300 ml ofCHC13 in a one-quart Waring Blendor. SMITH and GUNTHER (1977) developed a rapid field method for the estimation of OP soil residues prior to worker reentry (see Section VI b ).

b) Residues from spray drift and runoff

Considerable loss of pesticide spray mixture is evident during application to citrus trees. As a result of mechanized spraying operations, some losses occur during issuance of spray suspension or solution between target trees. Losses also occur from the target trees through runoff when the amount of spray exceeds the retentive capacity of the tree surfaces. The waxy composi­tion of the citrus fruit and leaf surfaces is also not conducive to the retention oflarge amounts of aqueous spray mixture. In principle, the amount of runoff could be limited by maintaining the gallons of spray/tree low. The amount applied, however, is dictated by requirements of the pest-control situation. Gallonage can be minimized if pests reside on the exterior foliage (lepidopte­ran larvae, aphids, katydids) or the pest is active (mites, thrips) and would be likely to contact treated foliage even if not directly exposed to the spray. If

84 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

the pest is sessile or resides in the interior of the tree (scales), increased gallonage is required to penetrate the exterior barrier of foliage to wet the foliage, twigs, and branches within the canopy of the tree. Runoff losses of pesticides are acceptable because of this need for a thorough wetting of the tree.

Aside from the economic disadvantage due to nonuniform distribution of pesticides, the OP pesticide reaching the soil surface, particularly between trees, has been suggested (SPENCER et al. 1975) as a source of toxicants to workers entering a treated field. Others (e.g., GUNTHER et al. 1974) have postulated that contaminated soil at the tree drip line would be a more likely source of toxicant transferrable to pickers' lower extremities as the pickers moved around vigorously, reaching into the trees. A study was therefore conducted to estimate the magnitude and distribution of spray mixture reaching the orchard floor as a result of various gallonages of spray applied (CARMAN et al. 1976 b). Navel orange trees were sprayed, using an oscillat­ing boom sprayer, with varying amounts of water, ranging from 1,520 to 3,650 gal/A. The water from drift and runoff was collected in one-pint jars positioned at one-foot intervals in racks under the trees, and the amount col­lected was determined by weight. It was found that the soil surface within the tree canopy received the greatest portion of the runoff, as shown in Fi­gure 17, which is a composite for the five different gallonages applied. The percentage of the liquid applied which ran off varied from 20% at the low gallonages to 40% at the high. These results do not necessarily mean that these percentages of pesticide would also run off, since there may be a grea­ter deposition of the pesticide from the spray mixture. EBELING (1963) dis­cussed spray oil deposits as a function of quantity of emulsion applied to leaves, and suggested that oil continues to deposit from an emulsion into a film of oil. It seems likely that hydrophobic pesticides would exhibit similar behavior, so that the above percentages for drift and runoff should be re­garded as maximum possible values for pesticide deposition on soil. For example, at 3,650 gal/A, the maximum spray volume used, a ten lb a.i./A application of pesticide will deposit four lb a. i.I A of soil if the maximum amount of pesticide (40% of the amount applied) were lost by drift and runoff.

SPENCER et al. (1975) determined the persistence of parathion and paraoxon on dry soil under treated citrus trees near Lindcove, California. Residues in dust obtained at the drip line of trees treated at rates of 2, 4, and 8 lb of parathion in 500, 1,000, and 1,500 gal/A, respectively, were deter­mined. The four-day parathion concentration in dust after the eight-Ib treatment was very high, about 700 ppm. Its oxidation to paraoxon was appa­rent even at this initial sampling. The paraoxon level which was about 100 ppm after four days rose to a maximum ofl60 ppm at 11 days and decreased very slowly thereafter while still remaining above 100 ppm over the 46-day period examined. Parathion decreased steadily to about 100 ppm at day 46. The parathion and paraoxon concentrations were higher in dust obtained from the dripline than in dust from the middle of the row. The ratio of paraoxon to parathion was greater from the row middle, however, than from the dripline. It was concluded that paraoxon formation was a soil surface phenomenon caused by the action of sunlight. It should be noted that SPEAR

5

4

'-0

"- 3 0>

"0 <I>

u <I>

0 u

>. 2 0 ~

0-(f)

15

Citrus reentry problem

\ \ \ \ \ \ \ \ \ \ \ \ \ \ \

I..

Tree periphery

3.5 5.5

Distance from

7.5

tre e

9.5 11.5

trunk (ft)

85

.... ... .... .... .,. .,. .... .,. ......

middle

13.5

Fig. 17. Amounts of spray collected in jars positioned at various distances from the tree trunk; composite of five different gallonages of spray/A is shown: dotted line represents the diagonals of the plots which extend out to the row middle (CAR~AN et al. 1976 b).

86 F. A. CU:-ITHER, Y. IWATA, C. E. CARMAN, AND C. A. SMITH

(1976 b) and coworkers found that ozone also can convert parathion to paraoxon, as did GUNTHER et al. (1970) in laboratory experiments.

c) Sloughable residues

Toxicant losses from fruit and leaf surfaces after a pesticide application were considered by GUNTHER and BLINN (1955) to be composed of three separate steps. The first step occurring immediately after the pesticide spray had dried was postulated to be a rapid loss within a few hours to a few days of the loosely adhering deposits consisting of pesticide sorbed to formulation carrier and adhering to natural dust on the plant, probably in built-up de­posits (EBELING 1963). The following step was a dissipation of toxicant from the more tenaciously adhering deposits through volatilization and decompos­ition of the compound by the action of sunlight, moisture, and through in­teraction with the dust to which toxicant was sorbed. The duration of this step could be several days to several weeks. The final step was dissipation of the persisting foliar residues at a greatly reduced rate through a combined action of dislodgment, volatilization, chemical degradation, and penetration into subsurface tissues. The occurrence of the second and the final steps, de­signated on semi-logarithmic plots of pesticide dissipation as the degradation and the persistence curves, respectively, was recapitulated by GUNTHER (1969) for 26 insecticides and acaricides on citrus fruits. WESTLAKE et al. (1973) demonstrated this phenomenon on both citrus fruit and citrus foliage for the insecticide dioxathion.

To evaluate the initial step of toxicant loss (sloughed residues) from foliage as a potential problem for worker safety, tests were made to deter­mine the significance, if any, of this initial loss as a contributor to soil dust residues (GUNTHER et al. 1976 b). Thus, estimations of the magnitude and distribution of sloughed residues over the orchard floor for three parathion formulations were made. Parathion was applied to Valencia orange tree plots located at the Citrus Research Center, Riverside, California. For the study involving the comparison of sloughed residues from trees after dilute and low-volume applications, plots were sprayed with a 25WP parathion formu­lation on September 26, 1975 at a high-volume rate of 12.5 lb a.i.l2,OOO gall A with an oscillating boom and a low-volume rate of 12.5 lb a. i.l100 gall A with a Kinkelder® sprayer. For the study involving the comparison of sloughed residues from trees after dilute applications of three different for­mulations, plots were sprayed with a 25WP, 4EC, or two lb/gal Penncap® E (encapsulated) formulation. High-volume applications were made on November 14, 1975. In all experiments, sprays were applied to plots of trees so as to duplicate the normal spraying conditions employed in a commercial citrus grove. The formulation study was repeated on May 20, 1976 with the 25WP and 4EC formulations: application was by manually spraying the trees to give thorough coverage. This time the concentration of the spray mixture was 0.63 lb a.i.llOO gal. Each tree selected for the sloughed residue study was located near the center of the treated plot. For the September applica­tion, the tree selected for the dilute application sampling was 15.7 ft in height and had an in-row dimension of 16.5 ft and an across-row dimension of

Citrus reentry problem 87

15.0 ft. The tree selected for the low-volume application was 15.3 ft in height and had an in-row dimension of 15.8 ft and an across-row dimension of 16.3 ft. Trees used for the formulation studies were located in the same field and had similar dimensions.

The sloughed residues were collected using the same technique used to collect spray drift and runoff described in Section IV(b). The trees chosen were symmetrical and of uniform density. After parathion application, the trees were allowed to dry for approximately two hr and the Mason jars were placed in racks under a selected tree for a five-day period. The jars were then capped, collected, and stored at 4°C. Prior to analysis, each jar interior was thoroughly rinsed (extracted) with ten ml of acetone and the parathion pre­sent was quantitated by CLC.

The mean parathion content in the jars located at one-ft intervals from the trunk for three experiments is shown in Figures 18, 19, and 20. The trees were approximately 8.5 ft in radius. As the data obtained for the individual racks were essentially identical, only the composite picture is presented. Paraoxon was not detected «0.1 p.g) in the jars.

Figure 18 shows the parathion profile resulting from low-volume (100 gal/A) and dilute (2,000 gal/A) applications of a 12.5 lb a.i. /A 25WP formula­tion. As the low-volume application would leave more residues on the tree (CARMAN et al. 1972), the siough-offfrom this application was somewhat great­er than that from a corresponding dilute application. Figures 19 and 20 show the parathion profiles resulting from a dilute application (12.5 lb a. i. /2,000 gall A) using encapsulated, WP, and EC formulations. As ex­pected, the most slough-off was obtained with the encapsulated formulation due to the dislodgment of capsules containing high levels of parathion. In all cases the amount of slough-off was less than one % of the total amount of pesticide applied. The WP formulation gave more sloughed residues than the EC due to dislodgment of parathion-containing solids from the formula­tion. CARMAN et al. (1952) recorded complete kills with houseflies kept in or under the trees sprayed with parathion as a WP, whereas somewhat lower

4.0

~

.~ 3.0 "-0>

.::t. c 2.0 0 I

.r: I

~ 0 0.

1.0

o 1.5 3.5 5.5 7.5 9.5 II. 5

Distance from tree trunk (ft.) 13.5

Fig. 18. Mean parathion contents of jars placed under an orange tree at various distances from the trunk; canopy radius w,,"s about 8.5 ft. Jars were placed in position about two hr post-application and left for five days. Treatment was 12.5 lb a.i. of parathion 25WP!A using 100 gal (low-volume) or 2,000 gal (dilute) of spray (GVNTHER et al. 1976 b).

88 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

20

18

Encapsulated

16

14

..... . 2. 12 "-Ol

::L c 10 0

£: 0 .....

8 0 a..

6 EC

4

2

----" /" "-/" '-

....... , /', " " \ " ' / '\.... \ / --, ... - ... _---..,,,/

'"",,- ........ --------o 1.5 3.5 5.5 7.5 9.5 11.5 13.5

Distance from tree trunk (ft.)

Fig. 19. Mean parathion contents of jars placed under an orange tree at various distances from the trunk; canopy radius was about 8.5 ft. Jars were placed in position about two hr post-application and left for five days. Application was 12.5 lb a. i. of parathion/2,OOO gallA using 25 WP, 4EC, or two lblgal Penncap E (encapsulated) formulations (GUNTHER et al. 1976 b).

mortalities occurred among flies stationed in or under trees sprayed with liquid formulations containing parathion.

WINTERLIN et al. (1975) treated peach trees with WP, EC, and encapsu­lated parathion. Of total parathion foliar residues, dislodgable residues con­stituted 25% for EC, 47% for WP, and 67% for encapsulated parathion treatments, data in agreement with those above for citrus. WOLFE et al. (1975) reported that in studies of a volunteer hand-thinning of apples at vari­ous intervals after parathion application, both dermal and respiratory expo­sure were greater when a WP formulation was used than an EC. The differ­ence was attributed to the ease with which the dried residue from a WP ap­plication dislodged from the foliage during contact or agitation by the worker. Urinary p-nitrophenol excretion by the volunteer indicated slightly

.... o

20

18

16

14

'- 12 0>

::i.. c 10 o ~

a o 8 a..

6

4

2

o

Citrus reentry problem

I I I I I I I I I I I I I I I I I I I I I I I I I

\ Wp \ ......... '\

'., /\ I' \ I \ \ I , \ I , , I \

\/ \ \ , , , , , , ,

EC /"\ , /,' \ \,

\ / \,--", \ \ / \ \ /'

1.5

\ / \ '\,' \ 'v \ '\,/ \

3.5 5.5

\ '. ',-- \ " /~ "v ""'\------__ _

7.5 9.5 11.5 13.5

Distance from tree trunk (ft.)

89

Fig. 20. Mean parathion contents of jars placed under an orange tree at various distances from the trunk; canopy radius was about 8.5 ft. Jars were placed in position about two hr post-application and left for five days. Application was 12.5 lb a.i. of parathion/2,OOO gal/A using 25WP or 4EC formulations (Gl':-.!THER et al. 1976 b).

more absorption following exposure in WP experimental plots than EC plots. These findings are also in agreement with those for citrus.

All these slough-off profiles show that the naturally dislodged material is predominantly deposited on the soil and detritus within the tree canopy; re­latively little is deposited on the soil surface between the trees, in accor­dance with the findings of SPENCER et ai. (1975). The second characteristic feature of the profiles is the low quantities of parathion collected. They do not approach normal soil residue levels such as reported by SPENCER et ai. (1975) from another citrus growing area and show that soil residues result from spray drift and runoff during pesticide application. Table XVIII gives the amounts of sloughed residue estimated to have fullen on to the orchard floor within a 15-ft radius of the tree trunk. For the November 1975 applica-

90 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

Table XVIII. Estimation of sloughed parathion residues per tree over a five-day period for an .orange tree treated with 12.5 Ib a.i. of parathion/A ( GUNTHER et al. 1976 b).

Application

Application Parathion (mg)a date Formulation GallA

Sept. 26, 1975 WP 100 16 WP 2,000 8.4

Nov. 14,1975 WI' 2,000 66 EC 2,000 33

encapsulated 2,000 96

May 20, 1976 WP full coverage 45 EC full coverage 21

14 aTree located in center of plot of 15-ft radius. Total mg. = ~ Cn n [n2 - (n - 1)2]

n = 2 where Cn is the soil surface residue in mg/ft 2 for the area between (n - 1) and n ft from the trunk; Cn is estimated from the average residue in the jars located (n - Y2) ft from the trunk.

tion, parathion and paraoxon foliar dislodgable residues were determined, as earlier shown in Figure 12. If the initial parathion loss is extrapolated back to 2.5 hr for the EC formulation, parathion loss was 2.1p.,g/cm2 ofleaf area from 2.5 hr after application to the break in the curve at 32.5 hr [(3.0-0.9) p.,g/ cm2 of leaf area). Combining this value with the estimated total surface area of a 20-year-old orange tree of5 X 106 cm2 (GUNTHER et al. 1973), a total loss of 10.5 g of parathion in the 30-hr time period is obtained. A similar treat­ment for the WP application data gives 7.5 g of parathion lost in a 66-hr time period. This compares with a parathion loss over five days of 0.033 and 0.066 g/tree for the EC and WP sloughed residues, respectively. As only about one % of the material was collected as sloughed parathion residues, the results indicate that the major initial loss of parathion is due to a process other than sloughing of foliar dislodgable residues. It must be remembered, however, that these sloughed residues can initially be very high in insecticide content (250,000 jLg of parathion/g ofWP formulation). The dislodgable foliar parath­ion and paraoxon levels after WP and EC applications in May 1976 were plotted in Figure 13. Penetrated and total parathion residue data were shown in Figure 14. The total residue curve was obtained by extracting.un­washed leaf discs whereas the penetrated residue curve was obtained by ex­tracting leaf discs after having removed the dislodgable residues for separate quantitation. Although absent in Figure 12, Figure 13 showed the three-step dissipation curve predicted by GUNTHER ;md BLINN (1955).

Figure 14 showed that there is a high level of parathion, 140 to 340 ppm, present in the total leaf sample immediately after spray application. The val­ues indicate that rapid partitioning of parathion into the leaf waxes occurs and could account for the initial rapid loss of foliar residues. Volatilization

Citrus reentry problem 91

may also account for this loss. Thus, SPENCER et al. (1973) calculated that a 50-g parathion application distributed over a mature orange tree would be lost within one day based on volatilization rates; this prediction is not borne out by the present field residue data probably because vapor pressures are affected by sorption.

It is concluded that soil residues result predominantly from pesticide reaching the orchard floor through drift and runoff during application and only trace amounts result from post-treatment slough-off; slough-off residues can be heavily contaminated with insecticide, however.

d) Effect of climatic factors on residue dissipatiun

In Section II(d) the effects of seasonal climatic variation on the dissipation of parathion residues from foliage were described. Seven monthly pesticide applications, ~ay through ~ovember, were made on mature orange trees. In addition to leaf samples, soil dust samples were also collected using the procedure of SPENCER et al. (1975) from the drip line of trees treated at ten Ib a.i./l,600 gallA and at ten lb a.i./100 gal/A. The parathion and paraoxon soil residue data are shown in Figure 21 (GUNTHER et al. 1976 a). Soil re­sidues can result from spray runoff, drift, and slough-off. As dilute applica­tions result in a large amount of runoff, soil dust residues are consistently higher with this type of application than after a low-volume application which deposits pesticides on soil solely through spray drift and slough-off. Initial deposits of parathion residues after a dilute application can exceed 1,000 ppm. Generally there appears to be a rapid first-order loss of parathion within the first ten days after application followed by a much slower loss which is also first-order. The rate ofloss during the second step is similar for all tests. Paraoxon soil dust residues do not increase but either remain rela­tively constant or decrease slowly. A rainfall of64 mm was effective in reduc­ing both parathion and paraoxon soil dust residues (GUNTHER et al. 1976 a).

Figure 22 (GUNTHER et al. 1976 a) shows the residues of azinphosmethyl in the soil dust resulting from a six-Ib a.i./A application using 100 and 1,200 gal/A. Similar to parathion applications, more soil residues result from a di­lute than from a low-volume application. Azinphosmethyl residues in soil appear to decline in a first-order fashion, also. The oxon in the soil appeared for form after application and then decline very slowly. KVALV AG et al. (1977b) gives the analytical methodology for azinphosmethyl oxon by Le.

e) Soil moisture and residue dissipation

Soil moisture can accelerate OP pesticide disSipation by providing water for hydrolytic decomposition and by providing an environment favorable for the existence of microorganisms that can degrade OP pesticides. A detailed discussion of the behavior of pesticides in soil is beyond the scope of this review, but wetting of orchard soil through irrigation has often been suggested as a method of accelerating pesticide dissipation.

IWATA et al. (1975) obtained degradation curves in soil for ethion, dioxathion, azinphosmethyl, phenthoate, and parathion and demonstrated

92 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

July

1000

500

E i~ a. a.

100 Q) I :=I "0 Cf) : Q) 50 ~ -- --t------Cf) r----:=I

"0

0 ~ (f)

~ 10 1----- ----~~ 5

o~----~----~~----~----~------~----~---o 10 20 30 40 50 60

Elapsed days

Fig. 21. Dissipation curves for parathion (solid symbols) and paraoxon (open symbols) in the surface soil dust beneath sprayed trees after a 25% WP parathion application to orange trees at ten (e) lb a.i./l,600 gallA using an oscillating boom and at ten (.a.) lb a.i./l00 gallA using a Kinkelder machine, Irvine Ranch, Tustin, CA, July-November 1974 and May-June 1975 (GuNTHERet al. 1976 a).

10

t problem Citrus reen ry

August

days

. 21 (Continued) Fig. .

93

94 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

September 1000

!"1 J~~;~ 500

~! 1 Rain 14mm

"'" E I" a.

~ a. 100

Q)

:J "0

~ (J) 50

1>" Q) ....

" ' ~ (f) , " :J " , "0 "

, , " , , , 0

, , Cf) " "-

"- "-10 , , , , "-, , , 5 "

O~----~----~----~~----~-----L----~---o 10 20 30 40 50 60

E lapsed days

Fig. 21. (Continued)

+-(/)

:::J -0

'0 (f)

Problem Citrus reentry

October

30 40

days

. 1 (Continued) Fig. 2 .

Rain ~ 64mm

I I

" " I, I, " I, " " \~ I I I I

~

-I I I , , , I , , I , , , , , , , , ,

L. __ _

50

95

96 F. A. GUNTHER, Y. IWATA, G. E. CAR..>.fA..'1, AND C. A. SMITH

November 1000 ira;' ~ 64mm

500 \ 1 l"r -....\ 'I

"

E \~ a. I , a. 100

~ Q)

::J 'U

CJ) 50 Q)

------i, '--CJ)

::J 'U

I

0 (f)

10 , I I I

5 I l.. ..... ...... ......

...... ........

........ ...... ...... .....

OL-----~----~------~--__ ~ ____ _L ____ ~~_

o 10 20 30 40 50 60

Elapsed days

Fig. 21. (Continued)

Citrus reentry problem 97

May 1000

10

5

10 20 30 40 50 60

Elapsed days

Fig. 21. (Continued)

98 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

June 1000

500 \ E f t~f a. a.

Q) 100 :::J

-0 (f)

Q) .... 50

0+-(f)

---f-J~ --:::J -0

0 (f) - -~!~

10

5

oL-____ ~ ____ ~ ____ ~ ____ _L ____ _L ____ ~ ___

o 10 20 30 4 50 60

Elapsed days

Fig. 21. (Continued)

300

200

100 -E 0-0- 50 --Q)

:::J "'0 en Q) ~ -en :::J

"'0 10

0 en

o

Citrus reentry problem

October

/A--_ / A-_ / -_ A

If' --_

~--~- --------- f:l. --- --f:l. -- -_ --

10

-_ A --

20 30

Elapsed 40

days

-------50 60

99

Fig. 22. Dissipation curves for azinphosmethyl (circles) and azinphosmethyl oxon (triangles) in the surface soil dust beneath sprayed trees after a 2EC azinphosmethyl application to orange trees at six lb a.i. per 100 (0, ~ for oxon) and per 1,200 (e, ... for oxon) gal/A, Citrus Research Center, Riverside, CA, October-November 1975 and April 1976 (GUNTHER et al. 1976 a).

100 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

150

100 -E c.. ~50 Q) ::J

"'Q

en Q) ~ -en ::J

"'0

o Cf)

10

o

• November

10 20 30 40 50

EI apsed days

Fig. 22. (Continued)

60

Citrus reentry problem 101

April

100

-E a. a. 50 -Q) :J

"'0 (J) Q) ~ -(J)

:J "'0 10

A---- ____________ _ / A A

/ 0 /

C/) / t:. t:. ----------------------

t:.

o 10 20 30 40 50 60

Elapsed days

Fig. 22. (Continued)

102 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

that under identical conditions they degrade at vastly different rates in soil dust. Figure 23 shows the degradation curves for these compounds in a silty clay loam maintained at 30°C and a soil moisture of 40% of maximum reten­tive capacity. Half-lives for degradation for phenthoate, azinphosmethyl, dioxathion, and ethion are 10, 15, 55, and 420 days, respectively, and show that hydrolytic decomposition for these pesticides even under favorable con­ditions is not a rapid process occurring within a matter of hours or days. In an arid region such as Southern California where soil dries out within a few days, hydrolytic pesticide decomposition would be a slow, intermittent pro­cess occurring for a few days after each irrigation or rainfall. WESTLAKE et ai. (1973) sampled the top cm of soil beneath dioxathion-treated orange trees and did not observe any decrease in the residue level over the rainless 59-day experimental period. IWATA et ai. (1977) found no decrease in phen­thoate levels in dry soil under orange trees over the 59-day experimental period. The soil was in cake pans and except for the brief moisture resulting from the spray runoff, the soil remained air-dry.

The situation is different for some compounds, such as para.thion (LICHTENSTEIN and SCHULTZ 1964), which are susceptible to rapid biodeg­radation. [In a recent publication KATAN et ai. (1976) reported that under moist soil conditions parathion is reduced to aminoparathion by microor­ganisms, and this is then adsorbed tightly by the soil.] In the silty clay loam used in Figure 23 (IWATA et ai. 1975), over 98% of the parathion was de­graded within ten days. In contrast, in distilled water (pH 5 to 6, 25°C) both parathion and paraoxon would show less than one % hydrolysis after 62 days

r 500 -

\~-o- ~ _ ___ CI_ - -_ -0- ___ _ --0_

."" "

E ,00 c. c.

"<> 50 <II

0; > o u ~

c: • :J , o 10 I

~ ~ , 5 \

"', , ),." , ,

\ , '\, , , ,

" " "',

, , , \ \

phenthooh

a

\ . porofhion

, , \ oz inphosmett'liyl , ,

'~

90 120

Days

e.'hion

Fig. 23. Recovery of five OP pesticides from the silty clay loam dust which was maintained at 30°C with a moisture content of 40% of maximum retentive capacity (IWATA et al. 1975).

Citrus reentry problem 103

(WILLIAMS 1951). SPENCER et ai. (1975) reported that parathion and paraoxon concentrations were much lower in orchard soil from irrigation fur­rows than from dry sampling sites; residue concentrations in dust and soil were extremely low following an unspecified amount of rain that fellUO days after parathion application. Figure 21 showed that a 64 mm (2.5 in.) rainfall resulted in a decrease of parathion and paraoxon levels in soil dust; lesser amounts of rain were ineffective.

V. Airborne residues

a) Background

One route by which workers may be exposed to pesticides on reentry is through airborne residues; these may be in the form either of vapors or of aerosols (liquid or solid particles). Aerosols may have a very high concentra­tion of pesticide, as with drift from a spraying operation, or they may be mostly materials other than pesticides, such as soil or foliar dust. Analytical methods which are suitable for sampling pesticide vapors are usually not suitable for sampling particulates, and methods suitable for sampling particu­lates probably will not suffice for vapor sampling.

Methods for sampling pesticides in air have been reviewed by VAN DYK

and VISHWESWARIAH (1975). They noted that the use of two similar sampling devices in series is not a satisfactory means of determining the efficiency of one of them. They stated that the fact that little or no material is collected in the second device is not necessarily an indication that the first unit is highly effective, because the same uncollected fraction which passed the first unit will probably also pass the second one.

The collection limitations for a sampling device must be evaluated before the start of an experiment. In the case of samplers which segregate particles into different size fractions, a particle distribution smaller or larger than that for which they are designed may result in incorrect indications of the size distribution or even of the total quantity of material, thus giving an incorrect indication of the respiratory hazard.

The problems involved in the estimation of respiratory exposure from air concentrations were earlier discussed by DURHAM and WOLFE (1962). Res­piratory exposure cannot be separated completely from oral or from dermal exposure in the sense that some material retained on the mucous membrane of the upper respiratory tract will be absorbed through these membranes or swallowed and made available for absorption by the gastrointestinal tract. It is practically impossible to duplicate mechanically the aerodynamics of inha­lation and exhalation through a pliable nostril. Generally the tidal character of respiratory air flow is not taken into account in air sampling and, fre­quently, even the relation of air velocity in the intake of the sampler to air velocity in the nares is ignored.

b) Vapor-phase residues

SPENCER et ai. (1973) reviewed pesticide volatilization at length, discus­sing mechanisms and factors influencing volatilization rates, their prediction,

104 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

and field and laboratory methods for the measurement of volatilization rates. They concluded that volatilization is an important pathway for loss of applied pesticides from plant, water, and soil surfaces.

GUNTHER et al. (1976 a) measured parathion and paraoxon vapor con­centrations in citrus plots treated with ten lb a. i. of parathion 25WP /100 gal/A, to determine if this route of pesticide exposure was significant in worker reentry. Two Greenburg-Smith impingers connected in tandem and containing ethylene glycol were operated at an air flow rate of five L/min, with the intake 45 cm above ground level. Table XIX gives the parathion and paraoxon air concentrations which were found; as expected, parathion air concentrations are highest when samples are taken within several hours after the spraying operation. After ten days the maximum air concentration found was less than four /-tg/m3 • Using the average value for lung ventilation in man given by SPECTOR (1956) of 3,600 L/hr (3.6 m3 /hr) during heavy work and four /-tg of parathion/m3 , the respiratory exposure is estimated at 0.1 mg/eight-hr day assuming complete pesticide retention. Thus, with a cur­rent California 45-day reentry interval for an application of more than eight lb/A, respiratory exposure of parathion in grove air should be insignificant to workers: the maximum permissible concentration of parathion in air is 0.05 mg/m3 (MELNIKOV 1971).

c) Airborne particulate residues

Particulate pesticide residues may be produced by agitation of foliage or soil surface dust by wind or by worker activity. Since the degree of respira­tory penetration and retention is a function of the aerodynamic particle size, information on the particle size distribution of dislodged pesticide-bearing dust is important to assess the inhalation health hazard. Particles larger than about five /-tm (different workers report from three to seven /-tm) do not ordi­narily penetrate into the alveoli; BROWN et al. (1950) demonstrated that upper respiratory retention decreases in an orderly fashion from about 80% retention for particles with a five /-tm diameter to zero for particles slightly above one /-tm in diameter. Alveolar retention, calculated as a percentage of the number of particles reaching the alveoli, remained between 90 and 100% for all sizes down to about one /-tm below which it began to decrease rapidly to about 50% for 0.25-/-tm particles.

Using personal air samplers on a small number of professional pickers, POPENDORF and SPEAR (1974) found mean airborne dust levels of 13.5 mg/m3 in grapes, 28.6 mg/m3 in peaches, and 40.2 mg/m3 in orange groves. The geometric mean particle size of these dusts ranged from 1.8 to 3.1 /-tm. It was concluded that while the majority of the particles were well within the respiratory range, that the potential respiratory dose of a pesticide carried on such dust is quite small. The ratio of paraoxon to parathion on the dust was a function of particle size with higher ratios associated with smaller particle sizes. Aside from inhalation, it was speculated that this would have impor­tant implications with regard to the penetration of the pesticide-laden dust through the clothing of workers.

Citrus reentry problem 105

Table XIX. Vapor concentrations of parathion and paraoxon in grove air (GUNTHER et al. 1976 a).a

Date Day Concentration (Ilg/ m 3)

applied sampled Parathion Paraoxon

July 1974 4 3.3 < 0.1 10 0.9 < 0.1

Aug. 1974 5 2.3 0.2 11 0.9 0.1

Sep. 1974 0 23 0.2 7 1.3 < 0.1

10 1.2 < 0.1

Oct. 1974 0 27 0.2 3 6.8 0.3

12 1.1 < 0.1

Nov. 1974 0 13 < 0.1 3 6.1 < 0.1

10 3.8 < 0.1

May 1975 0 11 < 0.1 3 2.3 < 0.1 9 0.9 < 0.1

June 1975 0 17 < 0.1 3 3.6 < 0.1

10 1.4 < 0.1

aTwo Greenburg-Smith impingers connected in tandem and each containing 200 ml of ethylene glycol were operated at an air flow rate of five L/min and with the air intake 45 cm above ground; sampling time varied from one to four hr.

In order to agitate leaves in simulation of worker activity, WESTLAKE et al. (1973 a) shook orange trees with an OMC "Shock Wave" tree shaker of the type used for shaking some fruits and nuts from trees for harvest. This machine grasps the tree trunk in a pair of rubber-covered jaws, and can shake the tree at an intensity chosen by the operator. The entire tree was agitated for one min, shaking the tree as violently as possible without severe damage to the trunk bark at the grasping points. Each of ten trees was shak­en while a current of air was directed into the tree using the fan of a high­velocity air-blast sprayer to carry dislodged material away from the tree. Six replicate leaf samples of 40 leaf discs/sample were taken immediately before and after the tree-shaking operation. Different sets of trees sprayed with five lb a.i. of dioxathion 8EC/IOO gallA were shaken 7, 13, 27, and 45 days post­application and the dislodgable residue reductions were 0, 45, 0, and 28%, respectively. The variable data suggested that residue reduction by this technique could not be demonstrated by measurements on leaf samples. It was quite evident visually that particulate matter was being shaken loose from the trees, but the portion being removed was evidently quite small compared to the total amount on the trees.

106 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

Similarly, IWATA et al. (1977) agitated each of five trees for one min with­out directing a current of air against the trees. The orange trees had been treated with 7.5 lb a.i. of phenthoate 4EC/l,500 gallA. The foliar dislodgable residues before and after shaking were 0.39 and 0.37 J-Lg/cm2 , respectively, for trees shaken three days post-treatment and 0.08 and 0.07 J-Lg/cm2 , re­spectively, for trees shaken ten days post-treatment. Similar to the results with dioxathion, the deposits, although sufficiently loosely adhering to per­mit their ready removal by washing, could not be shaken off in this manner in demonstrable quantities.

Virtually all of the dioxathion (WESTLAKE et al. 1973 a) was sorbed to par­ticulate matter in the larger size ranges which would be detained from enter­ing the lower trachea or alveoli of the lungs. It was thought that the bulk of the inhaled particulate matter would be trapped in the frontal nasal passages and that much of the accompanying pesticide would be passed into the blood stream through the nasal tissue or swallowed with sloughing of the mucus. Three volunteer pickers wearing air samplers near the face and working for one hr collected dioxathion residues on the sampler collectors equivalent to 0.8 mg/m3 . This was about 30 times the highest level found using the same samplers during the tests with the mechanical tree shaker, showing that mechanically shaking the tree is not equivalent to the combined shaking and rubbing action of a fruit picker.

Shaking tests were conducted to determine if measurable amounts of parathion foliar dislodgable residues could be dislodged from orange trees (GUNTHER et al. 1976 a). Trees were sprayed with parathion 25WP at ten lb a.i./l,600 gal/A and shaken three days post-treatment. The test was repli­cated seven times throughout the year using ten trees each time and shaking each tree for one min. The dislodgable foliar residues present varied over ll-fold as the rate of dissipation over the three-day period was dependent on existing environmental conditions. The average change in the foliar parath­ion residues resulting from the shaking operation was 0 ± 12% for the seven trials. Thus, no measurable change occurred. Foliar paraoxon levels were too low «0.06 J-Lg/cm 2) to give meaningful results. Shaking tests were also con­ducted with trees sprayed with aZinphosmethyl (GUNTHER et al. 1976 a). Trees were sprayed with an EC formulation at six lb a.i./l,200 gal/A and at six lb a.i./l00 gal/A. The trees were shaken three days post application and the tests were conducted at three different times. Similar to the parathion experiment, no demonstrable change in the dislodgable foliar residue levels of azinophosmethyl occurred as a result of vigorous tree agitation. The re­sults do not preclude frictional transfer of dislodgable and cuticular wax re­sidues to workers through contact with skin and clothing.

IWATA et al. (1977) operated Andersen nonviable particulate matter samplers and smaller personnel samplers (mini-sampler)9 while trees were agitated with the tree shaker. This sampler is specially designed for the quantitative determination of airborne particles and is suitable for determin­ing respiratory health hazards because it simulates the human respiratory

"Both samplers are available from Andersen 2000 Inc., P.O. Box 20769, Atlanta, GA 30320.

Citrus reentry problem 107

tract in collecting airborne particles (ANDERSEN 1966). Both the nonviable particulate sampler and the mini-sampler fractionate the airborne particulate matter into various size ranges. To evaluate the sample of air fully for dust hazard, the quantity of matter in each aerodynamic size category should be multiplied by a factor representing lung penetrability for that size. These values for the several categories added together give the total evaluation as regards penetration into the respiratory tract.

Over 80% of the phenthoate recovered from the particulate matter col­lected was in the largest particles (above 11 f-t in the standard sampler; above 4.7 f-t in the mini-type). The data for all the mini-samplers showed that less than 15% of the dislodged particulate matter could reach the trachea of the human respiratory system. It was evident that shaking the trees dis­lodged only the larger loosely-adhering particles and is probably not a good indicator of the exposure encountered by a worker moving about in a tree, vigorously brushing against foliage.

Ambient air was sampled with Greenburg-Smith impingers immediately after phenthoate was applied and at the three- and ten-day intervals. The impingers were placed with air intakes 45 cm above the ground inside the tree canopies. The vapor-phase levels of phenthoate detected were 21, 4.0, and 2.0 f-tg/m 3 at 0, 3, and 10 days after application, respectively.

To obtain an estimate of the size range of particulate matter dislodged from' trees during worker activity, trees were mechanically shaken with the OMC "Shock Wave" tree shaker to simulate worker activity and air samples were collected (GUNTHER et al. 1976 a). Tests were conducted using trees that three days previously had been treated with ten lb a. i. of parathion 25WP/1,600 gal/A. Each of ten trees was vigorously agitated for one min dur­ing which time air was sampled with an eight-stage nonviable Andersen with the air intake located 45 cm above ground level and personnel Andersens hand-held at various predetermined positions. Data are presented in Tables XX and XXI. The particles dislodged from the tree-shaking operation as de­termined by the Andersen nonviable sampler show that the distribution is predominately above the seven-f-t diameter and would be retained in the nasal passages. Due to the large particles being dislodged by the operation the personnel samplers probably do not truly reflect the correct values as they were forced to collect particles larger than they were meant to handle.

Actual worker activity would brush off particulate matter from the plant parts and would probably result in the respiration of greater amounts of smal­ler diameter particulate matter. Although particles are trapped in the nasal passages the insecticides present can result in dermal and oral exposure as earlier discussed.

VI. Methods other than human exposure studies for assessing hazard in treated groves

The current system of reentry intervals is required to assure safety under all conditions in citrus groves, even though the rates of pesticide dissipation vary widely owing to many different variables, including formulation, temp-

Tab

le X

X.

Par

athi

on a

nd

pa

rao

xon

res

idue

s o

n t

he d

islo

dgab

le p

arti

cula

te m

att

er c

oll

ecte

d d

urin

g .... 0

fiel

d s

haki

ng o

f tr

ees

thre

e da

ys p

ost-

appl

icat

ion

( G

UN

TH

ER

et

al.

19

76

a).

a 0

0

Par

ticl

e si

ze (

IL)

Tre

e >

4.7

4.

7 -

3.3

3.3

-2.

1 2.

1 -

0.65

D

ate

Tre

e he

ight

~

appl

ied

po

siti

on

b (m

) P

Sc

PO

c P

Sc

PO

c P

Sc

PO

c P

Sc

PO

c ?-

(lLg/

m 3

) (lL

g/m

3 )

(lLg/

m 3

) (lL

g/m

3)

(lLg/

m 3

) (lL

g/m

3)

(lLg/

m3

) (lL

g/m

3 )

C"l c z

July

26,

19

74

C

1.

8 7

8

6 3

4

< 0

.2

29

4 7

< 0

.2

o-j :z:

P 1.

2 28

3

45

< 0

.2

8 <

0.2

<

0.2

t'l

Jl

P

2.4

36

3 2

4

< 0

.2

5 <

0.2

2

< 0

.2

~

Aug

. 2

3,

19

74

C

1.

8 4

4

7 21

<

0.2

21

<

0.2

5

< 0

.2

~ P

1.2

77

5 1

00

5

14

<

0.2

4

< 0

.2

~ P

2.4

117

8 22

<

0.2

17

<

0.2

<

4

< 0

.2

1>

Sep

t. 2

0,

19

74

C

1.

8 25

<

0.

2 19

<

0.2

23

<

0.2

<

6

< 0

.2

C"l

P 1.

2 24

<

0

.2

13

< 0

.2

<

6 <

0.2

<

6

< 0

.2

t"l

P 2.

4 10

<

0

.2

9 <

0.2

22

<

0.2

<

6

< 0

.2

n ;.-

Oct

. 1

8,1

97

4

C

1.8

150

6 96

6

19

< 0

.2

9 <

0.2

~

P 1.

2 7

0

<

0.2

45

<

0.2

9

3

6 5

< 0

.2

"~ M

ay 2

4,

19

75

C

1.

8 7

3

<

0.2

24

<

0.2

24

<

0.2

16

<

0.2

~

P 1.

2 2

50

1

0

75

< 0

.2

23

< 0

.2

9 <

0.2

tI

P 2

.4

86

<

0

.2

9 <

0.2

4

< 0

.2

<

0.2

< 0

.2

0 Ju

ne

20

, 1

97

5

C

1.8

90

<

0

.2

44

<

0.2

11

<

0.2

7

< 0

.2

;..

P 1.

2 87

<

0

.2

29

< 0

.2

19

<

0.2

7

< 0

.2

'" ::: P

2.4

16

<

0.2

7

< 0

.2

<

0.2

<

0.2

<

0

.2

< 0

.2

::j :z:

a A

min

i-sa

mpl

er d

raw

ing

air

at 1

.4 L

/min

was

use

d to

col

lect

th

e di

slod

ged

part

icle

s b

y o

per

atin

g f

or o

ne

min

dur

ing

the

init

ial

shak

ing

per

iod

for

ea

ch o

f te

n tr

ees.

b

e f

or c

ente

r o

f tr

ee n

ear

the

tru

nk

an

d P

for

per

iph

ery

of

tree

ju

st o

uts

ide

the

can

op

y.

cpS

for

par

ath

ion

and

PO

for

par

aox

on

.

Tab

le X

XI.

P

arat

hion

an

d p

ara

oxo

n r

esid

ues

on

th

e di

slod

gabl

e pa

rtic

ulat

e m

att

er c

olle

cted

dur

ing

fiel

d

shak

ing

of

tree

s th

ree

days

pos

t-ap

plic

atio

n (

GU

NT

HE

R

et a

l. 1

97

6 a

).a

Par

ticl

e si

ze (

~)

> 1

] 11

-7

7 -

4.7

4.7

-3.

3 3.

3 -

2.1

2.1

-1.

1 1.

1 -

0.65

0.

65 -

0.4

3

Dat

e T

ree

appl

ied

..

b PS

c PO

c P

Sc

PO

c PS

c P

Oc

PSc

PO

c P

Sc

POc

PS

c P

Oc

PS

c P

Oc

PSc

PO

c p

osi

tio

n

(Qua

ntit

ies

in ~g/m3)

July

26,

19

74

C

1

30

6.

6 4.

9 <

0.2

0.

5 <

0.2

<

0.2

<

0.2

<

0.2

<

0.2

<

0.2

<

0.2

<

0.2

<

0.2

<

0.2

<

0.2

Aug

. 23

, 1

97

4

C

]20

7

.8

6.5

0.2

2.3

0.1

1.5

< 0

.2

1.2

< 0

.2

1.4

< 0

.2

1.4

< 0

.2

n O

ct.

18,

19

74

C

1

70

5.

8 8.

2 0.

4 1.

9 <

0.2

0.

8 <

0.2

1.

5 <

0.2

1.

4 <

0.2

0.

5 <

0.2

<

0.2

;:;

: .... P,

O°

130

5.3

52

1.6

4.6

< 0

.2

1.5

< 0

.2

0.6

<

0.2

0.

8 <

0.2

1.

9 <

0.2

<

0.2

<

0.2

:;;

P,9

0°

20

0

6.5

30

0.

9 4.

5 0.

3 5.

4 0.

2 3.

9 0

.3

1.2

< 0

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0.6

<

0.2

<

0.2

<

0.2

.... '" '" "

Nov

. 15

, 1

97

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C

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4.

8 <

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2.

1 <

0.2

0.

6 <

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0.

6 <

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].

4

< 0

.2

< 0

.2

:r P,

Oo

62

1.

6 16

<

0.2

3.

0 <

0.2

2.

1 <

0.2

1.

3 <

0.2

3.

1 <

0.2

1.

5 <

0.2

<

0.2

<

0.2

'<

'0

P

,90°

12

0 2.

3 1

4

< 0

.2

4.8

< 0

.2

2.4

<

0.2

1.

3 <

0.2

1.

0 <

0.2

0

.6

< 0

.2

< 0

.2

< 0

.2

.... 0 0-

May

24

, 1

97

5

C

34

0.

9 7.

1 <

0.2

3,

3 <

0.2

1.

5 <

0.2

0.

8 <

0.2

0.

8 <

0.2

2.

6 <

0.2

0.

8 <

0.2

rn

P,

Oo

46

1.1

16

0.6

6.9

< 0

.2

1.5

< 0

.2

1.0

< 0

.2

< 1

.0

< 0

.2

0.7

< 0

.2

0.8

< 0

.2

a P

,90°

3

3

0.7

9.7

<

0.2

7

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< 0

.2

2.7

< 0

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0.9

< 0

,2

1.3

<

0.2

2.

9 <

0.2

1.

2 <

0.2

Jun

e 2

0,1

97

5

C

26

0.8

9.7

0.5

4.7

0.5

3.1

0.2

3.4

0.5

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0.3

3.

0 0.

3 0.

9 <

0.2

P,

Oo

46

2.1

10

1.

0 3.

4 0

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1.9

0.4

1.

9 0

.6

1.3

0

.4

0.6

<

0.2

P

,90°

5

3

1.9

7.1

< 0

.2

1.8

< 0

.2

0.9

< 0

.2

0.8

< 0

.2

0.7

< 0

.2

1.5

< 0

.2

0.3

<

0.2

a A

sta

nd

ard

eig

ht-s

tage

And

erse

n sa

mpl

er d

raw

ing

air

at 2

8.4

L/m

in w

as u

sed

to c

olle

ct t

he

disl

odge

d pa

rtic

les

by

dra

win

g ai

r fo

r o

ne

min

dur

ing

the

init

ial

shak

ing

peri

od f

or e

ach

of

ten

tre

es;

air

inta

ke

was

at

gro

un

d l

evel

. b

e f

or a

ir i

nta

ke

loca

ted

nea

r th

e tr

ee c

ente

r, P

for

air

in

tak

e lo

cate

d o

n t

he

ou

tsid

e p

erip

her

y o

f th

e tr

ee c

ano

py

, 0°

an

d 9

0° i

ndic

ate

sam

plin

g p

osi

tio

n b

etw

een

th

e tr

ees

wit

hin

an

d b

etw

een

th

e ro

ws,

res

pect

ivel

y.

cpS

for

par

ath

ion

an

d P

O f

or p

arao

xo

n.

"" 0 co

llO F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

erature, type of application, amount and kind of dust on the leaves, and un­doubtedly other factors. An alternative approach to the problem of assuring worker safety is to measure foliar dislodgable and soil "dust" op pesticide residues in a grove prior to entry of workers to determine whether condi­tions are safe for extended exposure. Rapid and convenient techniques are desirable to enable an on-the-spot semi-quantitative determination of the level of these residues in order to assure safe working conditions for work­ers.l0 Reliable methods for this purpose would make shorter reentry inter­vals feasible in many cases, since the decision would be based on conditions actually existing in the grove in question. In addition, records of residue levels could be more eas4ly obtained using rapid measurement methods, and would indicate areas where hazardous conditions existed.

a) Foliar residue estimation

SMITH et al. (1976) reported the development of a rapid field method for the measurement of dislodgable foliar op residues on citrus. The method is based on the alkylation of 4-(p-nitrobenzyl)pyridine (NBP) by the op com­pounds, and appears to be sensitive to all op pesticides. The method con­sists of three steps:

(1) Using a specially designed sampler ( Fig. 24), dislodgable foliar re­sidues are transferred from one or more leaves to a porous paper strip. The sampler has a counter which indicates the surface area sampled.

(2) Using paper chromatography in a test tube, the sought compounds are separated from the dust and other material removed from the foliage.

(3) With suitable reagents, a color of an intensity proportional to the op compounds removed from the leaf is developed.

Step (3) is based on the formation of a blue product when an op compound (either P=S or P=O) and NBP are heated together and then treated with base. The minimum detectability of the method is about 0.05 JLg of total OP residues/cm2 of leaf surface sampled.

In the original paper a portable battery-operated refiectometer was used for the measurement of the intensity of the color produced by the NBP­pesticide reaction. Subsequently a visual color-comparison chart was de­veloped to replace the refiectometer (SMITH and GUNTHER 1976), in order to reduce the size, cost, and complexity of the complete system. To do this, a series of seven painted paper strips was chosen, primarily by visual trial and error, to be of suitable shades to give a reasonably linear response in com­parison with a series of developed paper test strips having a linearly increas­ing series of parathion concentrations. The color comparison standards are each approximately 3 x 12 mm (roughly the size of the colored zone on the paper strip), and the series is sandwiched between two sheets of glass which are securely taped together. Calibration curves were prepared for parathion, paraoxon, azinphosmethyl, and azinphosmethyl oxon, which were the insec­ticides and oxons of most interest in this work at the time.

l()This will be possible, however, only after public health professionals have established safe upper levels of dislodgable and soil "dust" residues for each OP compound.

Citrus reentry problem ill

Fig. 24. Photograph of dislodgable residue sampler (SMITH et al. 1976).

This foliar residue sampling method was used to monitor the concentra­tions of OP residues on two groups of four trees each which had been sprayed with parathion at the Citrus Research Center, Riverside, California. One group was sprayed with a dilute application (12.5 lb a.i ./2,OOO gal/A) using an oscillating boom sprayer; the other was sprayed with a concentrate application (12.5 lb a.i./lOO gal/A) using a Kinkelder low-volume sprayer. One sample of five cm2 was taken from each tree of each group at each sampl­ing time. The averages for each group are shown in Figure 25; the low­volume dislodgable residues are higher than those for the dilute application, in accordance with the findings of CARMAN et al. (1972). Considerable varia­tion was shown by the individual values, primarily due to the normal varia­tion encountered in spray deposits on citrus leaves (GUNTHER and BLINN 1955).

b) Soil residue estimation

OP insecticide residues on and in orchard soil have been suggested as one of the main routes of exposure of workers to these residues (see earlier). The dust with absorbed residues can become airborne through wind or through worker activities, and can deposit on workers' clothing and skin, where the residues may be absorbed into the workers' bodies ; it is common knowledge, for example, tbat citrus pickers' lower extremities become heav­ily coated with orchard dust, inside the trousers and well above the knees. Alternatively, soil "dust" may settle on foliage , where it may also be picked up by workers .

A method for the measurement of OP residues in soils was developed by SMITH and GUNTHER (1977). The method is based on the reaction of the re­sidues with 4-(p-nitrohenzyl)pyridine, as in the previously described method for determination of foliar residues. It is sensitive to the OP insecticides themselves and to their oxons; both of these classes are important in a realis­tic assessment of worker hazard, as discussed earlier.

112 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

5 V>

~4 E ~ c

<; ~

3

u 2

(; (5 UI

"-" " --~ " - Dilute -", \

~t1 l:J. l:J. -- -~o

>0.18 _ c: Q)

C 0.18 '5

0-Q)

0.15

0.12

0.09

c: o :c_ - N e E o u a. .....

0> V> :l.. 0_

c 0.06 .2

~ C

0.03 ~ c o

U OL-~5--~IO---175--720~~25~~3~0--~3~5--~40~0

Days after application

Fig. 25. Field test results of dislodgable residue sampler; each point is a average of four sam­ples; right side of chart is parathion concentrations giving corresponding color chart numbers; ~ = low-volume application, - = dilute application (SMITH and GUNTHER

1976).

In order to measure residue concentrations in soil "dust", a method was developed by SPENCER et al. (1975), which was described in Section IV. While this method is suitable for residue studies, the total time required from soil sampling to final results is quite long, and large amounts of equip­ment are required, both in the field and in the laboratory. A rapid method, using easily portable equipment, was needed which could be used for analysis of OP residues in orchard soil shortly prior to worker entry into treated groves. The field method reported here (SMITH and GUNTHER 1977) is suitable for this purpose; it consists of the following steps:

(1) A small scraper is used to pick up approximately ten cm3 of soil from the top 0.5 cm of orchard Hoor under the tree dripline.

(2) The soil is sieved in a 100-mesh sieve. (3) A 0.20-cm3 volume of sieved soil in placed in a small filter funnel and

extracted with an acetone-hexane mixture. (4) The extractant solution is mixed with NBP and oxalic acid in a test

tube, then heated in a small battery-operated heater for 15 min. (5) The test tube is removed from the heater and 2.0 ml of a base solution

is added. The rose-red color is compared to a set of color standards to mea­sure the combined OP concentration.

The total time required from soil sampling to color measurement is ap­proximately 20 min. The following equipment and reagents are used in the procedure.

1. Equipment and reagents.-Scraper. A small scraper, constructed of stainless steel sheet, as shown in Figure 26, is used to sample the orchard soil under the dripline. The scraper removes the top nine mm of soil in a strip 37 mm wide. To use, the sampler is placed on the ground and pushed forward (toward the right in the figure) so that the sharpened lower edge of the 37 mm opening scrapes the top layer of soil into the trough behind it; the

Citrus reentry problem

~ ~ --- - -- - ------- -- - ---

( )

- - ----------- ------

c:(§? c:(§?

... 120 mm

...... -------- 90 mm -----....

t E E I'­rt)

1

E E rt)

113

Fig. 26. Top and side views of soil scraper for sampling top layer of orchard soil under tree dripline (S~IlTH and GC:'-ITHER 1977).

114 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

other end of the trough is closed off. The metal extensions on either side of the trough prevent sampling of soil at depths greater than nine mm.

Filter. Millipore XX30 012 40, 13 mm, stainless steel with Teflon gasket. Filter screen. A fine woven stainless steel screen of about 400 mesh is

used in the filter, rather than filter paper. This gives a faster extractant liquid flow rate than filter paper or membrane filters, and can be quickly rinsed free of soil and reused.

Heater. A small portable heater was designed and constructed for this application which could be operated from a car or truck battery, thus freeing it from requiring AC line current. The unit is thermostatically regulated, and the temperature can be adjusted from 100° to 150°C. Details of the heater construction are given in Figure 27, and an electrical schematic is given in Figure 28.

Measuring spoon. Capacity 0.10 cm3 of sieved soil, constructed from 0.25-in. o.d. copper tubing as shown in Figure 29.

Extracting solution. Acetone-hexane, 1:9 v/v. Base solution. Tetraethylenepentamine-toluene, 1:9 v/v. This solution is

stable indefinitely if air and moisture are excluded. Sieve. Standard 100-mesh testing sieve, eight-in. diameter. Color comparison chart. Prepared from a series of five painted paper

strips of graduated color intensity. The special rose-red paints were prepared by inspection.

7"

Test tube well

Heater on off

115 120 II 0 \ /

'~""'130 105-

-140

100/

.. 1 .. ----5"----~-1

rp -------, [ --- - -coppe;.--: l

____ .J1!.b~ ___ I I

Thermal I insulation I L.-_~. ________ •

/

..... I .. f---- 3"----.11 Fig. 27. Test-tube heater for single test tube, for operation from 12 v DC power source (SMITH

and GUNTHER 1977).

Citrus reentry problem 115

IN /' 2071

Fenwal 12V 300 G835P8 6A Thermistor 820

/. 5K 2.0. Heater

3 LED 59100

IN2071

Fig. 28. Schematic diagram of oven for heating of NBP-residue reaction mixture; potentiomet­ers marked Land H are to calibrate temperature scale; 3500 potentiometer is temp­erature setting on front of heater (S~IITH and Gl':-iTIIER 1977).

Prepared test tubes. Into a 15 X 125-mm borosilicate test tube place 0.10 ml of a five % solution of NBP in acetone, and 0.02 ml of a two % solution of oxalic acid in acetone. Allow the acetone to evaporate, then cork the tube until needed. The prepared test tubes are stable for at least three months.

2. Procedure.-Using the soil scraper, sample the top layer of soil under the drip line from an area of approximately 3.5 cm X 6.0 cm, and place the soil in the sieve. Sieve the soil by gently tilting it so the soil shifts to the side of the sieve; repeat this tilting nine times. Using the special spoon, place two spoonfuls of the sieved soil in the filter, and add 3.0 ml of extracting mixture, allowing the filtrate to flow into a prepared test tube. Place the test tube in the heater (130°C) for 15 min, remove the tube, cool it for about 30 sec, and add 2.0 ml of base solution. Mix and compare with the visual color chart. Results are expressed as p.,g of parathion/g of soil.

3. Results. -The response of the method is shown in Figure 30 as cali­bration curves prepared using parathion and paraoxon standards. The absor­bance values were obtained using a Beckman DB spectrophotometer, with a wavelength setting of 530 nm and one-cm cells.

The precision of the method was studied for an actual soil sample taken from an orchard which had received a spraying of parathion formulation. For a series of five replicate determinations having a mean absorbance of 0.200, the standard deviation was 0.013.

114 .. ---------7.5"----------.1-1 0.25 Copper tubing

~ __________________________ ~~Cup

Fig. 29. Measuring spoon: flatten cup end in vise, solder 0.25" length of 0.25"-diameter cop­per tubing on to flattened surface (S~ITH and GlJNTHER 1977).

116 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

0.8

•

Q) U C 0 0.4 .0 ... 0 III .0 <l: 0.3

0.2'

3 6 9 12 15

Insecticide (f-Lg)

Fig, 30, Response of soil residue measurement method to parathion and paraoxon: • = parath­ion, A = paraoxon (SMITH and GUNTHER 1977),

The extraction efficiency of the rapid procedure described here was com­pared to a much longer residue extraction procedure for laboratory use con­sisting of the following steps:

(1) Weigh out a 1.00-g sample of sieved soil and place in a 27 -mm diame­ter X 70-mm screw-cap vial with a TeHon liner.

(2) Add 2.0 ml of a water-acetone solution of 5.0 ml water in 100 ml of total volume.

(3) Shake at 200 cycles/min for 15 min. (4) Add 2.0 ml of hexane. (5) Shake 15 min more. (6) Place a folded 7.5-cm Whatman No.1 filter paper in a small funnel,

prewet it with 2.0 ml of hexane, and filter the contents of the vial into a I5-ml graduated tube with a glass stopper. Rinse the vial with 2.0 ml of hexane and filter; repeat. Finally, rinse the top edge of the filter with 2.0 ml of hexane.

(7) Place the tube in a water bath at 30° to 40°C and evaporate to near dryness with a slow stream of air.

(8) Add 1.5 ml of acetonitrile, and fill to the I5-ml mark with water. Following the above procedure the comparison samples were analyzed

for parathion and paraoxon by liquid chromatography. In Table XXII these results are compared to those from the rapid procedure. As would be ex-

Citrus reentry problem 117

Table XXII. Comparison of rapid soil extraction procedure using NBP procedure for total OP residue with laboratory extraction procedure (SMITH and GUNTHER 1977).

Rapid Laboratory extraction procedure Rapid Sample extraction extraction

no. (I-lg/g soil) Parathion Paraoxon Combined (% recovery)

1 75 157.5 10.5 168 45 2 100 168 13.5 181.5 55 3 85 102 9.0 111 77 4 165 231 10.5 241.5 68 5 50 126 4.5 130.5 38 6 165 261 4.5 265.5 62 7 68 85.5 12.0 97.5 70 8 58 120 17.2 137 42 9 138 196 33.8 230 60

10 70 124 21.0 145 48 11 69 110 16.5 126.5 55 12 82 148 19.5 167.5 49

pected, less residue is extracted by the rapid procedure than by the laborat­ory procedure. Assuming that the laboratory procedure extracts 100% of the residues, the rapid procedure extracts 56 ± 10%. This extraction efficiency gives adequate sensitivity for the intended field use.

Parathion levels in orchard soil were followed using the rapid extraction procedure and NBP color development. Color intensity was measured spec­trophotometrically, rather than with the color comparison chart. Residue concentrations after application of parathion as an EC formulation and as a WP formulation were followed. In both cases the application was at the Cit­rus Research Center, Riverside, California and was at the rate of 12.5 lb a. i. /A applied manually. Samples were taken at three locations under the tree dripline for each formulation and analyzed separately. Results for the two formulations are shown in Figure 31. The WP formulation shows consistently higher residue concentrations at all times following application; as discussed earlier, this higher level was also observed in foliar residue levels which were analyzed by conventional methods.

The heating step actually consists of two parts. In the first, the tempera­ture of the contents of the test tube remains nearly constant at about 70°C while the extracting solvents boil away and the reaction mixture is concen­trated; this requires about six min, and no significant reaction occurs during this time. When all solvents have evaporated, the temperature rises rapidly to 130°C, where the reaction of the OP residues with the NBP actually takes place.

The choices of 130°C as the heating temperature and 15 min as the heat­ing time gave the maximum color development with parathion. As alterna­tive conditions, a temperature of 100°C, using a boiling water bath, and a heating time of 20 min give adequate color development.

The use of a comparison chart to measure color intensity, as described

118 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

~ 2lJl Vl

150f--01 L

....... 01 • ::l 100 • • • • • Q.l • '0 • • u 50

-Vl Q.l

CL 0 5 10 15 20 25 30 35 40

250 D.

0 200 Vl

01 • ....... 01

150

::l ~ 100

Q.l

'0 U

-;;; 50 Q.l

CL

0 5 10 15 20 25 30 35 40

Days after application

Fig. 31. Soil pesticide residues measured by NBP method for emulsifiable concentrate (top) and wettable powder (bottom). Data are uncorrected for extraction recoveries. Trian­gles are residue concentrations measured by liquid chromatography (SMITH and GUNTHER 1977).

here, is adequate for the intended field use but rather inaccurate. Battery­operated spectrophotometers are available which would greatly increase the accuracy of the color measurement step of the procedure. This substitution might be desirable in certain applications.

The average extraction efficiency of56± 10% is believed to be sufficiently good easily to indicate potentially hazardous residue concentrations in soil. The spread of the values for a series of soil samples, shown in Table XXII, is wider than desirable (38 to 77%) but demonstrates field sampling variability: this variation was not observed when replicate samples of soil were analyzed (values for five determinations ranged from 0.180 to 0.206).

The method described here does not differentiate between the parent compound and the oxon formed from it. The two compounds may be ex­pected to differ in toxicity due to a number of factors such as ease of absorp-

Citrus reentry problem 119

tion through the skin and the requirement that the parent compound be converted to the oxon before it attains its maximum toxicity, as discussed ear­lier. Thus, this method can give only an approximate indication of toxic hazard to workers, a case for public health professionals to resolve. At pres­ent, no reliable value exists for the dividing line which separates hazardous from nonhazardous levels of soil OP insecticide residues.

The NBP chromogenic reaction used as a basis for the rapid tests for foliar and soil residues gives roughly equivalent responses for both the parent pes­ticide and its oxon; the two compounds can be present in widely varying amounts, depending on a multitude of variables. For this method to be use­ful in the determination of potential worker hazard it is necessary to assume that there is probably a high concentration of oxon in all cases. An alternate approach to this method would be to use an additional test which would be sensitive only to oxons, perhaps based on ChE inhibition in vitro; tests of this type have been developed for the detection of the related nerve gases under field conditions.

c) Odorants as pesticide residue warning indicators

JOHNSON et al. (1976) studied the use of odorants as indicators of the quantities of insecticide, and thus reentry hazard, on a treated field. The odorant was applied to glass plates at the same time the pesticide was applied to the crop (cotton in their study). Methyl parathion, which disappears quite rapidly from cotton, could be matched reasonably well by skatole and

f3 -phenylethyl phenylacetate, but the other two insecticides studied, car­bofuran and azinphosmethyl, which are much less volatile, could not be sat­isfactorily matched.

d) Mathematical estimation methods

SERAT (1973) presented an equation for the calculation of a safe reentry time into an orchard which has been treated with an OP insecticide, the re­sidues of which produce a dose-dependent response in human beings. The equation relates the kinetics of the rate of loss of residues, which remain on the foliage of treated trees, and the kinetics of the rate of change in a mea­sureable physiological response (blood ChE activity), brought about by ex­posure of human beings to the decreasing residue levels, to the time of reen­try of workers into the orchard.

The procedure involves obtaining a persistence curve (Plot I) for the fo­liar dislodgable residues. The initial rapid residue dissipation (degradation curve) is ignored since it serves as a safety factor for subsequent calculations. The subsequent slower persistence curve, generally first-order, is used to obtain a residue decay rate constant. During the period of slower residue dissipation workers enter the field to harvest fruit for at least five consecutive days working eight hreach day. Plasma ChE levels are monitored. The re­sidue data taken on each working day reflect the cumulative exposure of workers. The residue is assumed not to vary significantly throughout the day and each day's residue value corrects for declining foliar residues. A semi-

120 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

logarithmic plot (Plot II) of ChE activity against cumulative insecticide expo­sure then gives a straight-line relationship which implies that the same frac­tion of the available residue was absorbed on each day of the exposure.

If a 30% decrease in ChE is acceptable, Plot II will give a value for the total amount of insecticide exposure that will cause this to occur. This value when related to Plot I will give the number of days that must have elapsed after spraying to give the desired residue level for safe reentry.

If the worker is to be in the field for five consecutive days, then use val­ues must be entered into a mathematical expression to give the minimum number of days that must elapse before workers can enter the treated field. Another physiological effect reflecting residue exposure, besides ChE de­pression, could be the urinary excretion of an insecticide chemical or its metabolites. The expression derived assumes decay of the applied insec­ticide and does not consider the formation and subsequent degradation of toxic alteration products.

The technique is an interesting approach for determining reentry inter­vals. It is one way of overcoming the ~ubjective setting of reentry intervals now used.

In the treatment of crops with pesticides, it is a fairly common practice to apply two or more materials during the growing season, sometimes simul­taneously. The question of assessing blame to one or more material arises when any worker suffers adverse effects from exposure to the residues. SERAT and BAILEY (1974) proposed a method for estimating the relative con­tribution each pesticide could have made assuming each produced the same physiological effect. The toxicologic potential, T, at any time was defined as the ratio between the pesticide residue level on foliage, P, and the dermal LD50 value. As equal amounts of residues of two compounds are not equally toxic, division "f the value by the respective dermal LDso values allows the direct comparison of the two compounds as to their relative potential toxic­ity. From the integrated expression for a first-order loss of pesticide residue

log P = log Po - kt

2.303

where P is the residue level level at time t after application, Po is the deposit level, and k is the specific rate constant for pesticide dissipation from foliage. Then,

log T = log __ P_o __

LD50

kt

2.303

Toxicologic potential, as defined, for each pesticide in a mixture of residues can thus be determined for any time after application as long as LD50 values and rate constants for pesticide disappearance are known. Where potentia­tion exists, dividing the LDso values for the respective pesticide by the potentiating factor allows a correction to be made. Only estimates can be

Citrus reentry problem 121

currently made until better and standardized methods are used to determine the levels of residues on crops, the dermal LD50 values, and the degree of potentiation pesticides show at varying levels of absorption as would be ex­pected from foliage at the times of reentry into treated fields.

The concept of toxicologic potential developed by SERAT and BAILEY (1974) was later combined with the method for calculation of a safe reentry time described in the earlier paper by SEfuU (1973) to give a method for es­timating worker reentry intervals without the exposure of human subjects (SERAT et ai. 1975). Reasonably good agreement was obtained between val­ues calculated by this technique and values for reentry times based on ChE depressions of workers. This method thus allows a calculation of reentry times without tests involving human subjects. The authors caution that con­version of the parent pesticide to its oxon may need to be taken into account. In addition, areas having higher or lower humidities or temperatures, or very dusty foliage, may give residue persistences, and thus reentry times, which are much different from those calculated under other conditions.

GUTHRIE et al. (1974) explored the possibility of using laboratory mice to obtain preliminary information for initial approximation of reentry intervals without involving human subjects. Tobacco, cotton, or apple leaves collected after the desired interval after application were placed on the bottom of the animal cage. Mice were thus forced to walk on the treated leaves. They were subjected to ten hr of continuous exposure with leaves being changed every two hr. The correlation between amount of residue and ChE inhibition was in general agreement with dermal toxicity of the compound. Whereas re­sidue levels of 40 to 60 ppm had relatively little effect on ChE inhibition with malathion and methomyl treatments, residues of ten to 20 ppm gave decided enzyme inhibition for parathion, monocrotophos, and azinphosmethyl. The described test was proposed for use where human exposure studies would not likely be undertaken in the near future to obtain a measure of difference in exposure as affected by type of formulation, surface-subsurface residues, humid vs. arid conditions, hot vs. normal conditions, low-volume vs. dilute applications, different rates of application, etc. The method cannot simulate human activity but offers vastly greater control over the experimental test conditions. GUTHRIE et ai. (1976) also conducted tests involving 13 to 15 human volunteers working in a monocrotophos-treated tobacco field. Con­currently leaf samples were collected for tests with mice as described by GUTHRIE et al. (1974). Experiments with mice were in general agreement with human tests.

Recently NICC et al. (1977) described a mathematical modeling method for predicting the dislodgable residues remaining on citrus foliage. A compu­ter program based on this model has been written; the daily values of maximum and minimum temperature, humidity, and precipitation are used to calculate the percentage of pesticide remaining. The method has been used on data for parathion and carbophenothion (Trithion) from Florida orange groves and also on data from California groves furnished by R. Spear and coworkers; predicted residue values agree reasonably well with mea­sured residue values in the cases which have been studied.

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124 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

Acknowledgements

The UC Riverside reentry research program was made possible through financial assistance from the Department of Entomology and the University of California, Riverside, the Citrus Advisory Board, Regional Research Pro­ject W-45 (Residues of pesticides and related chemicals in the agricultural environment-Their nature, distribution, persistence, and toxicological im­plication), the Environmental Protection Agency (Contract 68-01-2479, Farm worker reentry data for organophosphorus pesticides in citrus growing areas of California), the California Department of Food and Agriculture (Ag­reement 4288, Worker reentry safety in citrus groves), Regional Research Project W-146 (Worker-safety reentry intervals for pesticide-treated crops), Ciba-Geigy, Ltd., Hercules, Inc., Uniroyal, Inc., and the Thompson­Hayward Chemical Co.

The encouragement and support of o. E. Paynter and G. Zweig of the Environmental Protection Agency and K. T. Maddy of the California De­partment of Food and Agriculture are especially appreciated.

The UC Riverside work was made possible through the supervision of W. E. Westlake and the technical assistance in the field and in the laboratory of ]. D. Adams, D. C. G. Aitken, ]. H. Barkley, T. M. Dinoff, M. E. Dusch, L. D. Elliott, C. Gericke, M. Ittig, N. Kawar, J. Kvalvag, J. R. O'Neal, ]. C. Ortega, D. E. Ott, J. L. Pappas, M. R. Resketo, L. P. Van Dyk, ]. Virzi, A. Westlake, D. L. White, and G. F. Wood.

The helpful discussions with J. B. Bailey and the secretarial assistance of S. A. Goldman and J. Shaw are also gratefully acknowledged.

Summary and conclusions

The reentry problem arises from agricultural workers becoming ill as a result of entering and working in a field, grove, or orchard some time after a pesticide application has been made to the crop plant. No fatal cases of poisonings due to worker exposure to treated crop plants have been verified; rather, the reentry problem is concerned with the debilitating effects on workers, with the added burden of loss of income. At present the problem is limited to cholinesterase (ChE) -inhibiting pesticides, which are being used more and more generally as biologically persistent compounds such as the organochlorine compounds become more restricted in use. The most com­monly implicated insecticide in cases of reentry poisoning is parathion.

When a pesticide is applied to a crop plant, some of it penetrates into the organic material; this portion is not available to workers. Another portion remains on the exterior of the fruit and foliage, or on the soil surface where it can redeposit on workers or on fruit or foliage; these two portions are respon­sible for reentry illnesses. With few exceptions, the organophosphorus (OP) insecticides may be converted in situ to their corresponding oxons, which are considered much more toxic than the parent compounds. While both the parent compounds and the oxons are subject to degradation, they may be greatly stabilized by some soil dusts, thus increasing the time the residues may be hazardous to workers.

Citrus reentry problem 125

To lower or eliminate the hazard to workers due to persisting pesticide residues, exclusion times, also known as reentry intervals, have been insti­tuted by the federal and by the California state governments, which specifY the length of time which must be allowed to elapse after pesticide application before workers can be allowed to come into extensive contact with fruit or foliage. These exclusion times, to be effective, must be long enough to allow for the wide variation in the disappearance rates of dislodgable residues, which are affected by formulation and method of application, humidity, rain, temperature, amounts and types of foliar and soil dusts, and other factors. The effects of these variables are covered in this review.

Means of lowering residue levels, such as washing of trees, wetting of orchard soil, and application of chemicals to accelerate degradation rates, have been studied on citrus, under certain conditions washing with water may be a useful procedure. Other approaches to lowering agricultural work­er hazard have been studied: among the most promising is the analysis of foliar and soil residues by rapid portable analytical methods prior to worker reentry in order to determine that safe levels of residues actually exist in the work environment.

It looks as though chemical and physical reentry research on citrus as the substrate has progressed to the point of diminishing returns from further nonphysiological data gathering except, perhaps, to evaluate further the role of soil types (especially clay contents) in prolonging the lives and modifYing the natures of surface OP residues in grove environments. Thus, in capsule form, we now know:

(1) Physiologically active residues are transferred to agricultural work­ers via dislodgable foliar residues and soil surface "dust" residues. At least with parathion, the major reentry-incident miscreant, inhalation residues are not a very important part of the total physiological dosage normally ac­quirable by grove workers. Dislodgable fruit residues are also a minor part of worker exposure with this chemical.

(2) These residues consist of variable amounts (proportions) of parent compound (P=S) and of oxon (P=O). Both types on foliage are readily re­duced by moderately heavy rainfall or by water washing; soil surface residues of these compounds are short-lived in moist soil.

(3) In commercial citriculture, long-lived dislodgable residues of P=S and p=o compounds are the exception rather than the rule. Longevity of parent (P=S) compound, and extent of formation of and persistence of the oxon (P=O), are markedly affected by the presence of certain clays in the foliar dust and also by clay adjuvants in the formulation. Sunlight, tempera­ture, and moisture are important in these respects; ozone may well be in­volved in the P=S to P=O conversion under field conditions. None of these highly variable parameters is controllable under field conditions.

(4) Persisting residues on foliage and in soil dust may be as high as sev­eral hundred ppm for parent compound and/or oxon. Dislodgable foliage re­sidues normally decrease by slough-off, volatilization, hydrolysis, and oxida­tion. Soil surface residues may be very stable in dry soils.

(5) Different varieties of citrus trees exhibit essentially similar dislodg­able residue behavior.

126 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

(6) The role of soil and other clays in increasing the field longevity of available foliar and soil surface residues is so striking that perhaps eventually some groves can be characterized as potentially reentry hazardous simply because of the soil type.

(7) Under dusty field conditions there is no reentry consideration dif­ference between wettable powder and emulsifiable concentrate formula­tions.

(8) Low-volume (concentrate) applications represent more of a reentry hazard than high-volume (dilute) applications, but largely in connection with dislodgable foliar residues rather than also with soil surface residues.

(9) There are available fast and simple field methods for assaying mag­nitudes of both foliar surface and soil surface residues with satisfactory detectability and reliability considering the "reentry problem" in all its as­pects and implications.

(10) In the United States, reentry hazard in citrus groves is clearly ::l

California (not a Florida) problem because of the characteristic lack of rainfall in California from March through late November. Other citrus-growing areas of the world with similar climates and dusty conditions should antici­pate reentry incidents.

(11) Enough information and techniques are now at hand to permit pub­lic health professionals to proceed with the next step in establishing safe reenfry intervals for parathion and some other insecticides in citrus groves, namely, the assignment of dislodgable foliar and soil surfaces concentration values for the P=S and p=o compounds permissible for safe worker reen­try, as contrasted with unsafe levels. Means are at hand for easily and rapidly monitoring any grove to assure compliance with the safe values. If safe values are exceeded, and other grower-market considerations warrant it, the grove can easily be water-washed to produce safe levels; otherwise, a monitored waiting period will be necessary to assure time-delay decrease of the trans­ferrable residues present to safe reentry levels.

Clearly, more work along the present lines needs to be done with the other crops where there have been some reentry illnesses, such as grapes, peaches, and tobacco.

The followtng generalized design of a useful protocol for acquiring the necessary chemical, biological, and physical data for significant reentry evaluation by public health professionals (in terms of safe or not-safe agricul­tural worker environment) is hereby proposed for the OP compounds on cit­rus:

(1) Acute, chronic, and dermal toxicological information must be availa­ble for both the parent OP compound and its ChE-inhibiting alteration pro­ducts, such as its oxon (other types of pesticidal parent compounds cannot yet be considered in the present context). Other requisite information would include rates of dermal penetration and temperature-vapor tension curves of the P=S and p=o compounds (since inhalation toxicities could be impor­tant).

(2) Persistence curves for both P=S and p=o compounds as foliar sur­face residues and total foliar or foliar-penetrated residues should be estab-

Citrus reentry problem 127

lished for each type of formulation in use and for two dosages of the most commonly used formulations, including the highest dosage level to be re­commended. These curves should include samplings at pretreatment and at approximately 3-, 6-, 10-, 17-, 24-, 38-, and 52-day post-treatment intervals. Applications should be by commercial-type, conventional techniques. This procedure should be repeated at least three times to span the entire normal fruit harvesting period to take into account seasonal effects upon residue per­sistence curves.

(3) As above for mature or nearly-mature fruits present at the time of ap­plication.

(4) Tests involving the treatment parameters herein outlined should be conducted in a minimum of two geographically remote locations within a major citrus-producing area and each treatment should be replicated three times at each test location at each interval (see item 2).

(5) Because of prevailing trends, both concentrate (low-volume) and di­lute (full-coverage) applications should be compared through items 1-4 above.

(6) Soil surface (soil dust) residues from just within the skirts of the trees should be measured for both the parent compound and its ChE-inhibiting alteration products at the approximate intervals specified in item 2 above.

(7) From each field replicate plot, duplicate field samples should be taken or duplicate subsamples taken from a single field sample. Field sam­ples and/or extractives mixtures should be stored (frozen or otherwise) only if fortified controls are included to permit evaluation of possible storage de­terioration of sought compounds.

(8) Pilot studies of air-borne (vapor-phase or on particulate matter) con­centrations in the mechanically disturbed grove environment should be sufficiently extensive to allow relegation of air transfer of studied compound to important or unimportant status; if important, detailed studies as discus­sed in the present review are indicated.

Details for all these items are presented in the body of the present re­view.

References

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--Worker Environment Research. V. Effect of soil dusts on dissipation of paraoxon dislodga­ble residues on citrus foliage. Bull. Environ. Contam. Toxico!. In press (1977).

ANDERSEN, A. A.: A sampler for respiratory health hazard assessment. Amer. Ind. Hyg. J. 27, 160 (1966).

BAILEY, J. B.: The effects of pesticide residues on farm laborers. Agrichem. Age 15,6 (1972). BROWN, J. H., K. M. COOK, F. G. NEY, and T. HATCH: Influence of particle size upon the

retention of particulate matter in the human lung. Amer. J. Pub. Health 40, 450 (1950). B UR.."IS, J. E., and R. D. PARKER: An investigation of the safety of cotton reentry after or­

ganophosphate application. Arch. Environ. Contam. Toxico!. 3,344 (1975). CAHILL, W. P., B. ESTESEN, and G. W. WARE: Foliage residues of insecticides on cotton. Bull.

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128 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

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volume sprays on citrus in California. Bull. Environ. Contam. Toxicol. 8, 38 (1972). --, F. A. GUNTHER, R. C. BLINN, and R. D. GARMUS: The physical fate of parathion applied

to citrus. J. Econ. Entomol. 45, 767 (1952). ----, W. E. WESTLAKE, and Y. IWATA: Reduction of foliar dislodgable pesticide residues

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Chemagro Division Research Staff: Guthion® (azinphosmethyl): Organophosphorus insecticide. Residue Reviews 51, 123 (1974).

CULVER, B. D.: Worker reentry safety. VI. Occupational health aspects of exposure to pesticide residues. Residue Reviews 62, 41 (1976).

DAUGHTON, C. G., D. G. CROSBY, R. L. GARNAS, and D. P. H. HSIEH: Analysis of phosphorus-containing hydrolytic products of organophosphorus insecticides in water. J. Agr. Food Chern. 24, 236 (1976).

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Citrus reentry problem 129

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130 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

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Citrus reentry problem 131

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132 F. A. GUNTHER, Y. IWATA, G. E. CARMAN, AND C. A. SMITH

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Manuscript received December 23, 1976; accepted December 23, 1976.

Subject Index

Acre-inch of rain ,52 Adjuvants 67 Aerosols, composition 103 Airborne particulate residues 104 ff, --- residues 103 ff. --- residues by tree shaking 105-107 Air sampling devices, collection limits 103 --- sampling, efficiency 103 --- tpnlpf"ratnre<.; in citru<.; groves.37 -39.

48 Ah'eolar penetration, particle size 7. 104 Apples, dislodgable residues, effect of for-

mulation 88 --- leaf vs. li'uit contact 79 --' reentrY intervals ,53 --- reentry problem 2, 19, 67 Application method and dislodgahle resi-

dues 62 ff. Area ratios. leaf:fruit 79 Artichokes, reentry problem 3 Azinphosmethyl and airhorne particulate mat-

ter 106 --- application periods, citrus 26-28 --- decay on cotton foliage 25 --- dermal toxicity 21,22,48 --- dislodgable residues, dissipation

curves 40, 49-51 --- dislodgable residues, effect of rain­

fall .50, 80 --- foliar residues and ChE in-

hibition 121 --- half-life in soil 102 --- leaf disc storage stability 31 32 --- on fruit, removal bv rai~fall '50 80 --- oral toxicity 21,25' , --- penetrated foliar residues 62, 64-66 --- reentry intervals 26-28 --- reentry problem 2, 4, .5 --- residues and odorant warning indica-

tor 119 --- residues, reduction by tree wash-

ing 76,78 --- soil residues and moisture 91 102 --- soil residues vs. climate 91,99-101 --- use on California citrus 24 Azinphosmethyl oxon dislodgable residues,

dissipation cun'es 49-51, 54 --- oxon, GLC 33 --- oxon soil residues vs, climate 91,

99-101 Azodrin, see \Ionocrotophos

Bidrin, see Dicrotophos Bonamite and dermatitis 5 --- reentry problem .5 Broccoli, reentrv problem 3

Brussels sprouts, reentry problem 3

Cabbage, reentry problem 3 Carbaryl penetration, body parts 9 Carbofuran residues and odorant warning in-

dicator 119 Carbophenotbion foliar residues, mathemati-

cal modeling 121 --- reentn' intervals 13 .. 53 --- oral a;d dermal toxicitips 2.'5 --- reentry problem .5 -, -- use on California citrus 24 Carcinogenicity testing 7 Cauliflower. reentrY problem 3 Celerv, reentry problem .3 Chemical degradation of dislodgable resi-

dues 76 ff. Cholinesterase, action 3 ff --- analyses, variability 10 --- as measure of exposure 1.5 ff. --- inhibition and reentrv 2 fr. --- levels, variability 16' --- no-effect leve I 1'.5 --- safe levels 1.5, 18 Citrus fruit harvest periods. California 28 --- fruit residues. reduction bv wash-

ing 82,83 . --- leaf:fruit area ratio 8 --- reentry intervals 13, .53 ---- reentry problem 1 ff. --- variety and dislodgable residues 69 ff. Climatic factors and dislodgable residues 37 ff. --- factors and soil dust residues 91 Conjunctivitis and reentry 2 Copper ions, effect on OP compound hvdrol-

ysis 79 ' Corn, reentry problem 2, 3, 10 Cotton reentry intervals and rainfall 52 --- reentry problems 2, 8, 19 --- scouts, accumulation of parathion 8 --- scouts, ChE and nitrophenol val-

ues 16 --- scouts, green clothing stains 2.5,.54 --- scouts, reentry exposure 3 --- scouts, rupture of cotton foliage 2.5,54 Cygon, see Dimethoate

Degradation curve, definition and exam-ples 86

Delnav, see Dioxathion Demeton, application periods, citrus 27 --- oral and dermal toxicities 25 --- reentry intervals 13, 27, 53 --- use on California citrus 24 Dermal exposure 7 Dermatitis and reentrY 2 Dialifor reentry interv'als 13

134 Subject Index

--- reentry problem 5 --- residues and method of appli-

cation 63 --- residues on fruit, reduction by wash-

ing 83 Diazinon oral and dermal toxicities 25 --- reentry intervals 13, 53 --- use on California citrus 24 Dibrom, see Naled Dichlorvos, carcinogenesis and mutagen-

esis 7 Dicrotophos, mutagenesis 7 Dimecron, see Phosphamidon Dimethoate, application periods, citrus 27, 28 --- carcinogenesis and mutagenesis 7 --- dislodgable residues and rainfall 67 --- oral and dermal toxicities 25 --- reentrv inten'als 13, 27, 28, .53 --- reentry problem 5 --- use on California citrus 24 Dimethoate oxon dislodgable residues and

rainfall 67 Dioxathion and airborne particulate mat-

ter 105, 106 --- application periods, citrus 26, 28 --- content offoliar dust 33 --- degradation and persistence

curves 86 --- dislodgable residue half-life 23 --- half-life in soil 102 --- oral and dermal toxicities 25 --- reentry problem 4 --- reentry studies on citrus 23

studies on citrus 23 --- residue reduction by tree wash-

ing 73, 81, 82 --- residues, effect of lime 76 ff. --- soil residues and mosture 91, 102 --- use on California citrus 24 Dislodgable particulate matter on leaf sur-

faces 33 --- residue sampler, field 110-112 --- residues, analysis 33 --- residues, analytical procedure 31 --- residues and climatic mctors 37 ff. --- residues and citrus variety 69 ff. --- residues and formulation' 67 ff. --- residues and method of application

62 ff. --- residues and soil dust type 33 ff. --- residues, chemical degradation 76 ff. --- residues, collection 25 ff., 33, 34 --- residues, extraction 25 ff., 34 --- residues, foliar 20 ff. --- residues, low-volume vs. dilute appli-

cations 11 --- residues, measurement 2.5 ff. --- residues, prediction by mathematical

modeling 121, 122

--- residues, reduction by rainfall 10, 52,54

--- residues, reduction by tree wash-ing 73 ff.

--- residues, significant figures 33 --- residues, vacuuming techique 33,34 Disulfoton reentry intervals 53 Di-Syston, see Disulfoton Drift 83 ff. Dust, see Foliar dust, Soil dust Dylox, see Trichlorfon

EC formualtions 67 Encapsulated dislodgable residues, analytical

procedure 31 --- formulations 67 EPN hydrolysis, effect of copper ion 79 --- reentry intervals 13, 53 Ethion, application periods, citrus 26 --- dislodgable residues, dissipation on

grape foliage 48 --- half-life in soil 102 --- leaf disc storage stability 31, 32 --- oral and dermal toxicities 25 --- reentry intervals 13, 26, 53 --- reentry problem 4,5 --- soil residues and mosture 91, 102 --- use on California citrus 24 Ethion oxons, GLC 33 --- oxons in grape vineyards 22 Exposures, pesticide, measurement 15 ff. --- to residues, routes 7 ff. Extraction, leaf discs 32-34 Eye irritation and sulfur 2

Farm workers in California, numbers 11 --- workers in U.S., numbers 11 Fatalities in agriculture 1 Field methods for OP residues 110 ff. --- soil extraction procedure 115 ff. Foliage washing (see also Tree washing, spe-

cific compounds) 76 Foliar dust accumulation, hands and arms 79 --- dust build-up with time 34, 35 --- dust vs. soil type and solid carrier 34 --- residue estimation, minimum detect-

ability 110 --- residues, organic solvent removal,

hazards 32-34 Formulations 67 ff. --- effects on dislodgable residues 67 ff. Fruit harvest periods, citrus, California 28 --- rind residues, dislodgable 79 ff.

Gloves, protection for parathion penetra-tion 79

Grapes, foliage washing to reduce residues 76 --- reentry intervals 53 --- reentry problems 2, 4, 5, 12, 13 Guthion, see Azinphosmethyl

Subject Index 135

Hand labor operations in agriculture 3 Heater, portable, test-tube 114, 115 Hops, reentry problems 2

Imidian, see Phosmet Inhalation health hazard and particle size

7, 104

Kahn guide for reentry experiments 17 If.

Laboratory soil extraction procedure 116 If. Leaf disc sample size, citrus, grapes,

peaches 29 --- disc sampling, portion of leaf 29,30 --- disc sampling procedure 29 --- disc storage stability 31, 32 --- disc washing technique, efficiency

32-34 Leaf:fruit area ratios 79 Leaf punche s 29, 30 --- wax, reentrv hazard 54 Legislative approaches to reentry 12 If. Lettuce, reentry problem 3, 5 Lime as degradant for OP residues 76 If. Low-volume spraying, definition and advan-

tages 62, 63 --- vs. high-volume sprays and resulting

residues 63 Lung penetration by particulates 7, 104 --- ventilation in man 104

Malathion, application periods, citrus 26, 27 --- foliar residues and ChE inhibition

121 --- oral and dermal toxicities 25 --- penetration, body parts 9 --- reentry intervals 13,26,27,53 --- reentry problem 4, 5 --- use on California citrus 24 Mathematical estimation methods to evaluate

reentrv hazard 119 If. Meta-Systa"x, see Oxydemeton-methyl .'vlethamidophos, reentry problem 5 Methidathion, application periods, citrus 26

--- oral and dermal toxicities 25 --- reentry intervals 13, 26 --- use on California citrus 24 .'vlethomyl foliar residues and ChE in-

hibition 121 --- reentry problem .5 .'vlethyl parathion, decay on cotton foliage 25 --- parathion in blood and urine 1,5, 16 --- parathion reentry intervals 13,,53 --- parathion reentry problems 2 --- pamthion residues and odorant warn-

ing indicator 119 --- parathion residues, elfect of grape

foliage washing 76 .'v!evinphos, application periods, citrus 27, 28

--- oral and dermal toxicities 25 --- reentry intervals 13, 27, 28, 53 --- use on California citrus 24 Mini-samplers, air and particulate matter 106 Monocrotophos, decay on cotton foliage 25 --- dislodgable residues on tobacco .52 --- foliar residue levels and ChE in-

hibition 121 --- oral and dem1al toxicities 25 --- reentry intervals 53 --- use on California citrus 24

Naled, application periods, citrus 28 --- oral and dermal toxicities 25 --- reentry intervals 13, 28, 53 --- reentry problem 4 --- use on California citrus 24 1\ectarines," reentry problem 12, 13 J\'itrophenol excretion, temperature elfect 48 :\ itrophenols in urine 16

Odorants as hazard (warning) indicators 119 Olives, reentry problem 5 Oral exposure 7 Orange tree, surface area 90 Organophosphorus compounds, alkylating ef-

fects 7 --- compounds, fate in blood 3 If. --- compounds, GLC 33 --- compounds, intoxication, symp-

toms 6 --- compound, phosphorylating effects 6 --- compounds, physiological effects 3 If. --- compounds, poisoning, recovery 6 --- compounds, residues in soil dust, field

method III ff. --- compounds, residues on foliage, field

method 110 --- compounds, stabilization by soil dusts

(see also specific compounds) 124 --- compounds, storage stability 31 Oxydemeton-methyl, mutagenesis 7 --- oral and dermal toxicities 25 --- reentry intervals 53 --- use on California citrus 24 Oxons ofOP compounds, GLC 33

Paraoxon and airborne particulate mat-ter 108, 109

--- and reentrY illnesses 2 --- ChE assay' 33 --- ChE inhibition 23 --- dermal penetration rate 9 --- dermal toxicitv 9 --- dislodgable re'sidues and rainfall 54 --- dislodgable residues, dissipation

curves 40-47 --- dissipation, elfect of soil dust type

34-36

136 Subject Index

--- effect of formulation 68 ff. --GLC 33 --- half-life in soil 102 --- half-life on foliage 37, 69 ff. --- hydrolysis, effect of copper ion 79 --- in citrus groves 22 --- in cotton fields 22 --- in peach orchards 22 --- in soil and rainfall 10,91, 103 --- in soil dust 84 ff. --- intravenous toxicity 9 --- liquid chromatography 33 --- on apple foliage 68 --- on citrus foliage 1 ff. --- on cotton foliage 25 --- on peach foliage 68 --- persistence on drv vs. wet soil 84 ff. --- rapid soil proced~re, efficiency 117 --- residues and method of appli-

cation 63 --- residues, effect ofvarietv 69 ff. --- residues, reduction bv t~ee wash-

ing 76 . --- soil residues and rainfall 10, 91,

103 --- sloughed residues 87 --- vapor concentrations in grove air 104,

105 --- water solubilitv 9 Parathion and airborn~ particulate matter

106-109 --- and reentry problems 2 --- application periods, citrus 26-28 --- dermal penetration rate 9 --- dermal toxicity 3, 21, 22, 25, 48 --- dislodgable residues and ChE in-

hibition 121 --- dislodgable residues, dissipation

curves 40-47 --- dislodgable residues, effect of

rainfall 52 --- dislodgable residues, mathematical

modeling 121 --- dislodgable residues on fruit 79 ff. --- dissipation, effect of soil dust

type 34-36 --- dissipation, effect of temperature 40 --- half-life in soil 102 --- half-life on foliage 37,69,73 --- half-life on fruit 80 --- half-lives offoliar penetrated resi-

dues 62,63 --- hydrolysis, effect of copper ion 79 --- hydrolysis products, ChE inhibi-

tion 23 --- in air, first report 7 --- inhalation residues 125 --- in soil dust 84 ff. --- in soil dust, effect of rainfall 103

--- in soil dust, effect ofform ulation 117, 118

--- isomers as reentry hazard 22 --- leaf disc storage stability 31, 32 --- liquid chromatography 33 --- losses from unit foliage and unit

tree 90 --- maximum permissible concentration

in air 104 --- on foliage at time of application after

drying 90, 91 --- on foliage, removal by tree wash-

ing 81 --- on fruit, removal by rainfall 80 --- on fruit, removal by tree washing 81 --- oral toxicity 21,25 Parathion-paraoxon ratio and dust particle

size 104 Parathion, penetrated foliar residues 55-62 --- penetration, body parts 9 --- penetration rates 90 --- percent absorption by skin 8, 9 --- persistence and foliar dust buildup 52 --- persistence on dry vs. wet soil 84 ff. --- rapid soil procedure, efficiency 117 --- reentry intervals 13, 26-28, 53 --- residue reduction by tree shaking 81,

105-107 --- residues, effect of formulation 67 Jr. --- residues, effect of lime 76 ff. --- residues, effect of method of appli-

cation 63 --- residues, effect of tree washing 75 ff. --- residues, eJrect of variety 69 Jr. --- respiratory exposure in grove air 7, 8,

104, 105 --- sloughed residues, various for-

mulations 86 Jr. --- soil residues and moisture 91 ff. --- soil residues and rainfall 91 --- soil residues vs. climate 91 Jr. --- solubility in leaf wax 54 Parathion-to-paraoxon conversion by ozone

37, 85 --- conversion, effect of soil dust

type 34-36 --- conversion on soil 84 Parathion, use on California citrus 24 --- vapor concentrations in grove air 7, 8,

104, 105 --- volatilization rates from foliage 40,

90,91 --- water solubility 9, 52 Particle penetration into respiratory tract 7,

104 --- sampling 103 ff. --- size and parathion-paraoxon ratio 104 Particulate matter in grape, peach, and

orange grove air 104

Subject Index 137

--- matter sampling 103 If. Peaches, dislodgable residues, elfect offormu-

lation 88 --- leaf:fruit area ratio 8 --- reentry intervals 53 --- reentry problem 2, 4, 8, 10, 12, 13,

19,68 Peach harvester's clothing 8 Pears, reentry problems 2, 4 Persistence curve. definition and examples 86 Pesticide exposure, ChE levels 15 If. --- exposure, measurement 15 If. --- exposure, serum pesticide levels 15 If. --- exposure, urinary metabolite lev-

els 1.5 If. --- losses during application 83 If. --- losses from plant surfaces, mech-

anism 86 --- volatilization 103 Pesticides in air, sampling 103 If. Phenthoate and airborne particulate mat-

ter 106, 107 --- half-life in soil 102 --- half-life of dislodgable residues 24 --- reentrv studies on citrus 23 --- residu~s, reduction by tree wash-

ing 73,82 --- soil residues and moisture 91, 102 --- vapor in grove air 107 Phosalone dislodgable residues, dissipation on

grape foliage 48 --- oral and dermal toxicities 25 --- reentry intervals 13, 53 --- reentry problem 5 --- use on California citrus 24 Phosalone oxons, GLC 33 --- oxons in vineyards 22 Phosdrin, see ~levinphos Phosmet reentry intervals 13, 53 --- reentry problem 5 Phosphamidon, application periods, cit-

rus 27, 28 --- dislodgable residue half-life 23 --- oral and dermal toxicities 25 --- reentrv intervals 13, 27, 28, 53 --- reentr;' studies on citrus 23 --- residues on fruit, reduction by

washing 83 --- use on California citrus 24 Pike's Peak clay, elfect on parathion/paraoxon

34-36, 125, 126 Potentiation 120 Prolate, see Imidan Propargite application periods, citrus 26 --- leaf disc storage stability 31, 32 --- reentry intervals 26 --- residu~s on fruit, reduction by

washing 83 Protective clothing, reentry safety 8

Protocol for reentry evaluation 17 If., 126, 127

Rainfall, elfect on residues 10, 50, 52, 54, 67, 80,91, 103

Reentry and ChE inhibition 2 If. --- and OP pOisoning 2 If. --- apples 2, 19, 67 --- artichokes 3 --- azinphosmethyl 2, 4, 5 --- Bonamite 5 --- broccoli 3 --- Brussels sprouts 3 --- cabbage 3 --- carbophenothion 5 --- cauliflower 3 --- celery 3 --- citrus 1 If. --- cOrn 2, 3, 10 --- cotton 2,8, 19 --- dialifor 5 --- dimethoate 5 --- dioxathion 4 --- ethion 4, 5 --- evaluation, protocol 17 If., 126, 127 --- experiments, Kahn guide 17 If. --- fatalities 11, 124 --- grapes 2, 4, 5, 12, 13 --- hazard, citrus fruit 79 --- hazard evaluation, foliar residue es-

timation 11 0 --- hazard evaluation, mathematical es­

timation methods 119 If. --- hazard evaluation, odorants 119 --- hazard evaluation, soil residue es-

timation III If. --- hazard, first discussion 12 --- hazard, foliage vs. fruit 8 --- hazard, leaf wax 54 --- hazard, orchard soil dust 84 If. --- hops 2 --- illnesses, lack of fatalities 6 --- illnesses, reporting systems 10 If. --- interval research, fundamental ele-

ments 17 --- intervals (see also specific compounds

and crops) 12 If. --- intervals, calculation 119 If. --- intervals, criteria for safety 15 --- intervals, definition 12, 12.5 --- intervals, effectiveness 13 --- intervals, establishment with mice on

apple, cotton, and tohacco leaves 121 --- intervals, next step by puhlic health

professionals 126 --- intervals, protocol 17 If., 126, 127 --- intervals, summary of knowledge

125, 126 --- lettuce 3, .5

138 Subject Index

--- malathion 4, .5 --- methamidophos .5 --- methomvl .5 --- methyl parathion 2' --- naled 4 --- nectarines 12. 13 --- olives .5 --- parathion 2 If. --- peaches 2, 4, 8, 10, 12, 13, 19, 68 --- pears 2, 4 --- period (interval), definition 12 --- phosalone .5 --- phosmet 3 --- problem causes and elfects 1 If. --- problem, definition 2, 124 --- problem, dimensions 10 If. --- problem, history 2 If. --- problem, legislative approaches 12 ff. --- problem, minimization 1 If. --- problem, nature 6 --- problem, sources of exposure 21 --- problem, various crops 1 If. --- protocol 17 If., 126, 127 --- reported illnesses 2, 4, 3, 12 --- research, citrus in California 19 If. --- studies and human subjects 19 --- tobacco 2, 19, 32, .53 Residue intoxication, factors affecting 21 Residues, airborne, see Airborne residues,

Drift --- dislodgable, see Dislodgable residues --- dissipation from fruit 79 If. --- exposures to 7 If. --- routes of exposure to 7 If. --- sloughable, see Sloughable residues --- soil dust, see Soil dust residues --- vapor-phase (see also specific com-

pounds) 103 Respiratory exposure 7, 12, 104 --- exposure, problems in estimating 103 --- range, particle size 7, 104 Runolf 83 If. --- magnitude 84 --- pattern under trees 84 If.

Safe conditions, measurement 110 If., 124 If. Sample size, leaf discs 29 -. -- size, soil dust 11.5 Sampling, air and particulate matter 106 --- portion ofleaf 29, 30 --- procedure, leaf disc 29 --- procedure, soil dust 83, 111 If. Sebum 8 Shock wave tree shaker 81, 10.5 Skin area, adult 8 Sloughable residues 86 If. --- residues, definition 86 Soil dust 83 If.

--- dust analytical procedure, calibration curves 11.5, 116

--- dust analytical procedure, extraction efficiency 116, 117

--- dust analytical procedure, variability 118

--- dust, collection 83, III If. --- dust residues and climatic factors 91 --- dust residues and soil moisture

91 If. --- dust residues from spray drift and

runolf 83 If. --- dust residues, measurement il3 --- dust residues, reduction by rain-

fall 10, 91, 103 --- dust sampling and analytical pro­

cedure 11.5 --- dust scraper 112, 113 --- dust type and dislodgable residues

33 If. --- moisture and soil dust residues 91 If. Sources of exposure, reentry illnesses 21 Spoon, soil sample measuring 114, 11.5 Sulfur, application periods, citrus 28 --- eye irritation 2 --- reentry intervals 13, 28 Supracide, see Methidathion Surface area, orange tree 90 Systox, see Demeton

Task Group on Occupational Exposure to Pes-ticides 13 If.

Temperatures, citrus groves 48, 69 TEPP, oral and dermal toxicities 2.5 --- reentry intervals 13, 33 --- use on California citrus 24 Tobacco, reentry intervals .53 --- reentry intervals and rainfall .52 --- reentry problems 2, 19 Torak, see Dialifor Toxaphene, decay on cotton foliage 2.5 Toxicologic potential 120, 121 Tree shaking 81, 10.5-107 --- shaking to reduce residues and pro

duce airborne residues 81, 10.5-107 --- washing and reduction of dislodgable

residues 73 If., 81 --- washing efficiency, elfect of type of

application 76 --- washing variables, elfects on ef-

ficiency 7.5 ff. Trichlorfon, carcinogenesis and mutagenesis 7 --- oral and dermal toxicities 2.5 --- reentry intervals .53 --- use on California citrus 24 Trithion, see Carbophenothion

Urinary alkyl phosphate values 16

--- nitrophenol values 16 Urine vs. blood samples 16

Subject Index

Vapor-phase' residues (see also specific com­pounds) ]03

Vapor sampling 103 II'. Volatilization of pesticides (see also specific

compounds) 7, 103

Washing of fmit to reduce residues, see specific compounds

--- of skin to reduce exposure k --- of trees, see Tree washing Worker reentry period, definition 12, 12.5

Zolone, see Phosalone

139