Pesticides in Food

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INTRODUCTION

Since the last part of the 20th Century, the issue of pesticides in foods has generated considerable public concern and debate.

Pesticides are chemicals designed specifically for their toxicological effects on target pests, such as insects, weeds, and plant diseases. Public awareness that such chemicals are commonly detected in the food .supply as residues contributes .greatly to the debate.

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Several widely-publicized events and reports have emerged in the past two decades to focus consumer, media, and regulatory attention upon pesticide residues in food.

The illegal use of the insecticide aldicarb on watermelons in California in 1985 resulted in more than 1000 cases of probable or possible human pesticide poisoning.This event was followed by the release of a landmark report by the U.S.

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This event was followed by the release of a landmark report by the U.S. National Research Council (NRC) that presented exaggerated estimates of potential human cancer risks from pesticides in the diet resulting from the use of worst-case human exposur eassumptions .

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In 1989, an environmental advocacy group issued a report alleging ‘‘intolerable’’ risks to children from exposure to residues cancer-causing pesticides in food.

Such changes were widely adopted after the unanimous passage of the Food Quality Protection Act (FQPA) of 1996 by the U.S. Congress.

The FQPA requires pesticide regulators to ensure that pesticides comply with a‘‘reasonable certainty of no harm’’ statute before .they can be allowed for use on food crops.

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In the determination of a ‘‘reasonable certainty of no harm,’’ regulators are required to consider the potential increased susceptibility of infants and children, and the exposure to pesticides through food, water, and residential sources (aggregate exposure).

The implementation of the FQPA dominated the pesticide landscape for several years as the scientific community struggled to develop the risk assessment methodologies required by the U.S. Congress and the regulatory community faced the challenges of interpreting the new law.

Several controversial pesticide regulatory decisions were made in the early years of FQPA implementation but most decisions were completed by 2002 when procedures for conducting aggregate and cumulative risk assessments were finalized.

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Consumer demand for foods certified as ‘‘organic’’ rose greatly over the past two decades and much of the increased demand may be related to consumer concern over pesticide residues in foods.

The organic foods industry benefited from the development of a U.S. .national standard for organic foods, which was published in 2000.

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According to the U.S. organic standards, organic-food producers are typically not allowed to use synthetic chemicals, although they may use certain natural pesticides derived from mineral, botanical, and microbial sources.

In a few cases, synthetic chemicals, such as sulfur, oil sprays, insecticidal soaps, and insect pheromones, are allowed.

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PESTICIDES: TYPES, TOXICITY, AND USETYPES OF PESTICIDES

According to the U.S. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), a pesticide is defined as ‘‘any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest, any substance or mixture of substances intended for use as a plant regulator, defoliant, or desiccant, and any nitrogen stabilizer. . .’’

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A variety of classifications for pesticides have been developed that are specific for the type of pest controlled Insecticides, for example, are pesticides that control insects, while herbicides control weeds and fungicides control plant diseases (molds). In addition to these major classifications of pesticides classifications.

These include nematicides (for nematode control), acaracides (mite control), rodenticides (rodent control), molluscicide (snail and slug control), algacides (algal control), bacteriocides (bacterial control), and defoliants (leaf control).

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PESTICIDE TOXICITY

Insecticides

The toxicity of insecticides to insects typically results from a variety of mechanisms, such as nerve damage, muscle .poisoning .sterilization, and desiccation.

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The first major synthetic group of insecticides, developed in the1930s and 1940s, is the chlorinated hydrocarbon family. This family includes DDT, aldrin, dieldrin, methoxychlor, and chlordane.

Dramatic improvements in insect control were noted when the chlorinated hydrocarbons began to be used frequently due to their .high insect toxicity.The chlorinated hydrocarbons are also noted for their high environmental persistence, which resulted in longterm insect control but also contributed to environmental buildup and biological magnification, leading to significant ecological and environmental impact.

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Recent reports have indicated that some chlorinated hydrocarbon insecticides are associated with possible adverse effects on fertility and reproduction in non-target organisms, which may result from the enzyme inducing or estrogenic properties of the chemicals.

Because of the potential adverse impacts of chlorinated hydrocarbons on the environment and on nontarget organisms, very few chlorinated hydrocarbon insecticides are currently allowed for use in the U.S.

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In the 1960s and 1970s, the organophosphate and carbamate compounds replaced the chlorinated hydrocarbons as the most prominently used insecticides.

These two families of insecticides share a common toxicological mechanism, the inhibition of cholinesterase enzymes in the both insects and mammals nervous systems of They are typically far less persistent in the environment than are the chlorinated hydrocarbons but are much more acutely toxic.

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A newer class of insecticides is the pyrethroids. These are synthetic derivatives of pyrethrins, which are natural extracts from chrysanthemums.

Pyrethroids have been developed to be more stable (and thus more effective as insecticides) than the pyrethrins, which are particularly instable in light. Pyrethroids are frequently used as broad-spectrum insecticides.

They have high insect toxicity, but lower mammalian toxicity than their organophosphate or carbamate counterparts. Pyrethroids are still limited in effectiveness due to their environmental lability, their high cost, and their .potential for resistance development.17

Herbicides

Herbicides are used widely throughout the world to control weeds and exist in a wide variety of different types. Examples of classes of herbicide include the triazine, sulfonylurea, phenoxy, and quaternary Herbicides exert their toxic action on weeds through a number of different mechanisms.

Preplant herbicides are applied before a crop is planted, preemergent herbicides are applied after planting but prior to the development of weeds, and postemergent herbicides are used after weeds have appeared ammonium herbicides.

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Some herbicides, such as glyphosate, exert broad-spectrum weed killing effects making them toxic to virtually all forms of plant material, including the crop.

Recently, many crops, such as soy, corn, and cotton, have been engineered through genetic modification to be resistant to damage by glyphosate or other In contrast to the broad-spectrum herbicides, others are more selective.

The phenoxy herbicides, which include chemicals such as 2,4-D, 2,4,5-T, and MCPA, are toxic to broad-leaf plants but do not affect narrow-leaf plants .such as grasses.

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Fungicides

Molds and other plant diseases are controlled by fungicides, which act to affect the growth or metabolism of fungal pests. Many different fungicides exist, including sulfur, aryl- and alkyl-mercurial .compounds, bis-dithiocarbamates, and chlorinated phenols.

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Potentially Carcinogenic Pesticides Public and regulatory concern over the potential cancer risks posed by pesticide residues in the diet has been significant over the past two decades.

While the consumption of foods containing residues of pesticides has not been correlated with the development of human cancers, pesticide exposure has been linked to some cancers in agricultural workers.Such studies are conducted using doses typically several orders of magnitude greater than humans would be expected to receive and are frequently performed in animal species .developing specific types of cancer.

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PESTICIDE USE

Pesticides are frequently applied in agriculture but are also extensively employed for industrial, commercial, and government uses, as well as in the home and garden sector.

It has been estimated that in 1999 the agricultural use of pesticides represented an expenditure of $7.6 billion dollars in the U.S.

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The most commonly used class of pesticides was herbicides (36%), followed by ‘other pesticides’ (which includes nematicides,fumigants, rodenticides, molluscicides, aquatic and fish or bird pesticides, other miscellaneous conventional pesticides, plus other chemicals used as pesticides, such as sulfur and petroleum)(29%), insecticides (25%), and fungicides .(10%)There are a number of reasons that explain the differences; these include the use of different data sets, different methods to regulate pesticide metabolites, and different agricultural production and pest control practices.

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REGULATING PESTICIDES IN FOOD

The use of pesticides in agriculture does not inevitably mean that food residues will result.

In many cases, pesticides are applied to non-food agricultural crops, while in other instances pesticides may be applied around, but not directly on food crops, such as the case in which a broad-spectrum herbicide is used.

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In some cases, pesticides may be applied prior to the development of edible portions of the crop, while in others the rapid environmental degradation of the pesticide between the time of application and the time of harvest may also avoid food residues.

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U.S. REGULATION

When the normal use of a pesticide on a food crop may pose the potential to leave a food residue, the EPA establishes a tolerance. The tolerance represents the maximum level of a pesticide residue allowed on the food crop.

Tolerances are pesticide and crop specific; different crops may have different tolerance levels for a particular pesticide, while a particular crop may have different tolerance levels for the different pesticides that may be used on it.

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Pesticide tolerances are not based solely on safety, but rather are set to represent the maximum expected residue levels of a pesticide on a commodity as a result of the legal application of the pesticide.

The maximum expected levels are derived from the results of controlled field studies conducted by the pesticide manufacturer, in which application conditions are chosen to provide the highest level of residue. Conditions include applying the pesticide at the maximum allowable rate, making the maximum number of applications per growing season, and harvesting the food after the minimum anticipatedinterval between application and harvest.27

Pesticide residues will be considered illegal when pesticides are detected at levels that exceed the tolerance level, or when residues of a pesticide are detected, at any level, on a commodity for which a tolerance has not been established.

Illegal residues should not be confused with ‘unsafe’ residues,however, since pesticide tolerances are most appropriately viewed .as The practices used by EPA to assess the risks of pesticides to consumers became much more complicated following the passage of the FQPA in 1996.

Prior to the passage of the FQPA, the EPA allowed tolerances to be established on a chemical-by-chemical basis and only considered exposure from food enforcement tools rather than as safety standard.28

Provisions of the FQPA require that the EPA now considers the aggregate exposure from pesticides in food, drinking water, and in residential settings.

Additionally, the EPA must also consider the cumulative exposure from pesticide families possessing a common mechanism of toxicological action,such as the organophosphate and carbamate insecticides.

The EPA may consider the acceptable level(expressed on the basis of the amount of pesticide consumed relative to body weight per day) to be as much as ten times lower than a comparable acceptable exposure level for adults.

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INTERNATIONAL REGULATION

While all nations of the world possess the sovereign right to establish their own acceptable levels for pesticide residues in foods, many lack the resources to develop their own regulatory programs and instead rely upon a set of international standards developed by the Codex Alimentarius Commission, frequently referred to as Codex.

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PESTICIDE MONITORING

Two regulatory agencies are responsible for the majority of pesticide residue monitoring in the U.S. The U.S. Food and Drug Administration (FDA) is the agency primarily responsible for enforcement of tolerances in domestic and imported foods .shipped in interstate commerce.

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The U.S. Department of Agriculture (USDA) administers the Pesticide Data Program, which is designed to most-accurately capture actual resides of foods that reflect levels near the time of consumption of the food items.

The USDA also administers the National Residue Program, which samples meat, poultry, and raw egg products for pesticide residues, .animal drugs, and environmental contaminants.

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FDA MONITORING

The FDA’s monitoring activities rely on food sampling procedures in which the types of commodities to be sampled, and the origins of the samples, are chosen specifically to enhance the FDA’s abilities to identify violative residues..not a random process.

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The maximum expected levels are derived from the results of controlled field studies conducted by the pesticide manufacturer, in which application conditions are chosen to provide the highest level of residue.

Conditions include applying the pesticide at the maximum allowable rate, making the maximum number of applications per growing season, and harvesting the food after the minimum anticipatedinterval between application and harvest.

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Results from imported foods were somewhat similar, although violation rates were higher and the rates of residue detection were lower.

Of the 4374 imported samples analyzed for pesticide residues, 72.0% had no detectable residues, 23.2% had detectable residues within legal limits, and 4.8% had violative residues.

Violations were observed in the ‘other’ category (8.1%), vegetables (6.4%), fruits (2.8%), and ‘fish, shellfish, other aquatic products’(0.3%).

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Pesticide residues are deemed violative if the residues encountered exceed the established tolerances or when residues for which no tolerance has been established are detected on the sampled commodity.

In the case of imported food sample, the FDA noted that 92.9% of the violations occurred when pesticides were detected on commodities for which no tolerance was established, with the remaining 7.1% of violations occurring when residues exceeded tolerances.

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Violative residues from domestic food samples presented a different pattern, with 50% of the violations stemming from levels exceeding tolerance and the other 50% resulting from pesticides being detected on commodities for which no tolerance was established.

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USDA PESTICIDE DATA PROGRAM

The USDA’s Pesticide Data Program (PDP) each year collects several thousand food samples, which are analyzed for pesticide residues.

In contrast with the FDA’s residue monitoring, the PDP is not an enforcement program. Instead, it has developed sampling procedures that are designed to use measurements of actual residue levels to determine residue levels near the time the food items are consumed.

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PDP data are also employed to examine pesticide residue issues that may impact agricultural practices and U.S. trade, and may be used to identify crops where alternative pest management practices are needed and in promoting export of U.S. commodities .in a competitive global market.

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Fruits and vegetable samples were taken most commonly (9903 samples), followed by beef (911 samples), enriched milled rice (689 samples), poultry (464samples), and drinking water (297 samples).

Domestic samples comprised 82% of the total and sampling was based on a statistical design to ensure that the data are reliable for use in exposure assessments.In 2001, 44% of all samples contained no detectable residues, while 24% showed one residue and 32% showed more than one residue. In 0.1% of the samples, residues were detected that exceeded tolerances, while residues were found on commodities for which no tolerance was established on 1.8% of the samples.41

RESIDUES IN ORGANIC FOODS

Much of the rapid growth in the consumption of foods labeled as ‘organic’ may result from the perception among consumers that organic foods may be healthier than conventional foods.

While some pesticides are allowed for use on organic foods, it is logical to assume that the pesticide residue profiles for organic and conventional foods .should differ, qualitatively and quantitatively.

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These results indicate that pesticide residues are less common in organic samples than in conventional samples, although residues are frequently detected in organic produce.

Potential explanations for the greater-than expected presence of pesticides in organic foods include mislabeling of products, misidentification of the samples during data entry, postharvest fungicide contamination, and inadvertent contamination from environmentally- persistent pesticides or from drift from pesticide applications made to adjacent crops.

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DIETARY PESTICIDE RISK ASSESSMENTBACKGROUND

The dietary risks from pesticides are frequently, although inappropriately,discussed in relation to the relative breakdown .between legal and violative It is critical to realize that pesticide tolerances themselves are not safety standards but rather enforcement tools for indicating whether pesticides have been applied according to directions.

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Violative residues result when residue levels exceed the tolerance due to the misapplication of a pesticide, or when residues at any level are found on a commodity for which a tolerance was not established (which could result from product misuse).

While a few isolated cases of violative residues have resulted in human harm, the vast majority of violative residues are of little or no toxicological consequence.

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Contemporary risk assessment practices for pesticides in foods require far more data than simply the residue levels evaluated in government monitoring programs.

Exposure to pesticides is determined by multiplying the residue levels on food by the amount of the food item consumed; once determined, exposure is compared with standard toxicological criteria derived from animal toxicology studies to determine the .acceptability of the exposure.

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TOXICOLOGICAL CRITERIA FOR SAFETY

The basic principle of toxicology, as first noted by the Swiss physician Paracelsus, is that ‘‘the dose makes the poison.’’ While this principle is easy to understand, the processes used to understand the relationships between dose and biological response, and ultimately to determine what dose of a chemical poses ‘a reasonable certainty of no harm’, are much more complicated.

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Models for determining the dose-response relationship vary based upon the type of toxicological hazard. In the dose-response for chemical carcinogens, it is frequently assumed that no threshold level of exposure (an exposure below which no effects would occur) exists, and, therefore, any level of exposure leads to some .

does apply at low levels of exposure, implying that exposure below the threshold is not likely to be significant. The toxicity threshold dose for noncarcinogenic effects is largely theoretical, it is practical only in relation to the effects that occur at dose levels slightly above .and slightly below the threshold.48

An estimate for the lowest level of toxicological concern for human\ exposure to a chemical is developed by dividing the appropriate NOAEL by the uncertainty factor.

Historically, this estimate has been termed the ‘acceptable daily intake’ (or ADI) although it has been replaced by what EPA calls the ‘reference dose’ (or RfD).

Both ADIs and RfDs are expressed in terms of the amount of chemical exposure per amount of body weight per day.

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For carcinogen risk assessments, multiplying the proposed daily exposure by the unit cancer potency factor (derived from animal cancer studies) yields the cancer risk; cancer risks greater than 1 106 may trigger regulatory concern while those below 1 106 are frequently considered to be negligible. For non-carcinogenic risks, a comparison between the estimated exposure level and the RfD determines the significance of the risk.

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EXPOSURE ASSESSMENT

The determination of the estimated levels of exposure is obviously a critical component of the risk assessment process. Both pesticide residue levels and food consumption estimates must be considered. Methods for determining exposure are frequently classified as deterministic and probabilistic methods.

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Deterministic Methods Measurement of dietary exposure to pesticides has historically relied upon deterministic methods that assign finite values to both the pesticide residue level and the food consumption estimates to yield a ‘point’ estimate of exposure.

The calculations are relatively simple, but consideration needs to be given to the accuracy of the assumptions concerning residue level and food consumption.

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The FDA, in addition to conducting its pesticide regulatory monitoring program, also conducts its annual Total Diet Study to estimate dietary exposure to pesticides and other contaminants.

In the Total Diet Study, FDA inspectors purchase market baskets of more than 200 food items and have the items prepared for consumption prior to analysis for pesticide residues.

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Probabilistic Methods While deterministic methods are still quite useful in determining long-term, chronic exposures to pesticides, they are being replaced with probabilistic methods for the analysis of acute (short-term) exposures. These probabilistic methods take advantage of improvements in computational capabilities.

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SUMMARY AND CONCLUSIONS

It has been demonstrated that pesticides are frequently encountered in foods,although typically at levels not considered to cause concern from the regulatory community. When placed into perspective with other food safety risks, the dietary risks from exposure to pesticides are risks from microbiological contamination, nutritional imbalance, environmental contaminants, and even naturally-occurring.

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The techniques used to establish the risks posed by pesticides are dynamic and evolving. The passage of the FQPA in 1996 paved the way for the development of sophisticated computational models for assessing pesticide exposure, and future refinement of such models is anticipated.

Such advancements in pesticide risk assessment techniques should be applicable to the risk assessment of other chemicals in foods and in the environment.

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Toxin in food :Zdzisl⁄aw E. Sikorski Ph.D., D.Sc Professor Department of Food Chemistry, Technology and Biotechnology Faculty of Chemistry Gdan´sk University of Technology, PolandZdzisl⁄aw E. Sikorski Ph.D., D.Sc Professor Department of Food Chemistry, Technology and Biotechnology Faculty of Chemistry Gdan´sk University of Technology, Poland.

REFERENCES

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