PRODUCTION OF POLYCHLORINATED DIBENZO-p-DIOXINS (PCDD) ANI) DIBENZO NS (pCDF)

FROM RESOURCE RECOVERY FACILITIES PART 1. SOURCES, EMISSIONS AND AIR

QUALITY STANDARDS

STEPHEN J. GRAHAM, DANA C. PEDERSEN, DONALD M. POMPELlA, and EDWARD P. KUNCE

Camp Dresser & McKee Inc. Boston, Massachusetts

ABSTRACT

An overview of measured PCDD/PCDF emissions and of sources and proposed mechanisms for the appearance of PCDD/PCDF in U.S. and European recovery facilities is provided. Observed health effects, and existing standards or guidelines for ambient acceptable levels, of PC DO/PC OF are presented. Furture research needs are identified.

INTRODUCTION

Recent media coverage of dioxin contamination in road dust suppressant oil in Times Beach and other towns in Missouri, and jn soil and buildings adjacent to chloro­phenol factories (e.g., Dow Chemical in Midland, MI) has made "dioxin" practically a household word in the United States.

The term "dioxins" has been used to refer to a class of organic compounds that are considered among the most toxic known to man. "Dioxins" are actually polychlori­nated dibenzo-p-dioxins (PCDD), tricyclic aromatic com­pounds with a central 1,4-dioxane ring. Chlorine atoms can theoretically attach to dibenzo-p-dioxin at any one of the sites enumerated in Fig. 1. The addition of from one to eight chlorine atoms can form eight homologues with up to 75 different isomers; only 22 have been identified or synthesized to date [1, 2] . Closely related to PCDD are polychlorinated dibenzofurans (PCDF), which have gener­ally been neglected by the press, but since certain PCDF isomers approach PCDD in potential toxicity and originate Similarly it is appropriate to discuss them here also. Furans are similar in structure to dioxins but have a five-sided ring core containing only one oxygen (Fig. 1). The loci and nomenclature for chlorine addition to dibenzofuran

345

parallels that for PCDD (Table 1). Because of irregular configuration 135 PCDF isomers are possible, but only 38 are known to exist [3, 13] .

THE PROBLEM

Some municipal resource recovery facilities and in­cinerators in Europe [2-8], Japan [9], the United States [10-13] , and Canada [9, 14] have been reported to emit PCDD and/or PCDF. Concentrations in flue gas, particu­lates, and fly ash have generally ranged from <0.1-100 ugf kg, varying with sampling apparatus and methodology, waste composition, and operating conditions. Facilities in Europe, particularly the Netherlands, have shown emis­sions an order of magnitude higher than those found in North America [6, 15, 16].

A November 1981 EPA study [11] of five United States plants, including RDF, co-combustion with coal, and mass-burn units, concluded that these facilities' emi­sions for 2,3,7,8-TCDD, the most toxic PCDD isomer, did not present a public health hazard for residents living in the immediate vicinity [11, 12]. Certain in -stack and ground-level concentrations of total TCDD were calculated. New York State in November 1982 adopted the total TCDD ground-level concentration from that report as an acceptable ambient level of TCDD [83]. Canada and the Netherlands have recently established guidelines for ac­ceptable concentrations of 2,3,7 ,8-TCDD for both total PC DO and PCDF based on ambient levels and potential daily intake, respectively [82, 84] . Given the increasirig concern over the occurrence of PCDD and PCDF, it is imperative that government and the public have accurate and adequate information upon which to base regulatory

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FIG. 1 PCDD AND PCDF CHEMICAL STRUCTURE

EQUATION 1 OH 0 -HC I 0 CI CI ...... CI or CI -

a.) 0 -Hel ) 0 0 -NaG I ) 0 0 CI CI CI CI OH CI CI 0 (ONa)

CI 0 CI

b.) 0 NaOH) -NaCI CI Cl CI

CI CI CI

Formation of 2, 3, 7, 8 TCDD from chlorophenols by

a.} Chlorination of phenols

b.} Alkaline hydrolysis of chlorobenzenes

EQUATION 2 �� o- CI�:::;;" Clx

CI 0-t;:, )

Two chlorophenol ate molecules A PCDD

CI

CI

action and assess environmental impact. Towards that ob­jetive this paper reviews current information on PCDD/ PCDF origin and emissions in resource recovery facilities, and observed health effects and current guidelines for ambient concentrations with regard to protection of public health. The discussion contained herein (part I) provides background for engineering evaluation of the potential for incinerators and resource recovery facilities to gen­erate PCDD/PCDF (part II).

SOURCES OF PCDD/PCDF

Chlorinated dioxin and furan emissions from resource recovery facilities appear to: (1) result from volatilization of PCDD/PCDF present as artifacts in chemicals in the combusted refuse, hence originate from non-combustion sources; and (2) form under combustion conditions via reactions involving chlorinated and perhaps also non­chlorinated organic compounds [5] .

NON-COMBUSTION SOURCES OF PCDD/PCDF

Commercial manufacture and processing of chloro­benzenes, polychlorinated biphenyls (PCBs), and chlori­nated phenols and their derivatives - phenoxy acid herbicides and pesticides, and diphenyl ethers - have not uncommonly generated PCDD and/or PCDF as trace impurities (Table 2). Agricultural residues, household dis­cards (e.g., cleaners, insecticides), and certain industrial waste fractions (e.g. treated wood, PCB containers) may contribute quantities of these commercial artifacts to the refuse processed by resource recovery facilities [1, 5] . PCDD/PCDF introduced into municipal solid waste (MSW) in this manner could volatilize or adhere to particles upon combustion to some unknown degree and exit a facility to the surrounding environment [1, 10] .

Dimerization (ring formation) of chlorophenols to form PCDD

Researchers disagree as to how much PCDD/PCDF ends up in MSW prior to combustion. Some researchers citing their work on Italian MSW stated that these sub­stances are most likely only minor constituents of domestic refuse [22]. However, others [5, 20] have noted the lack of systematic studies to confirm or deny this. It is well­known that the MSW of many U.S. and northern Europe cities contains a significant industrial fraction, in contrast to Italian MSW with its higher agricultural waste content [23] . A major problem encountered in comparing MSW is their extreme variation due to differences in climate, culture, socioeconomics and method of sampling and waste processing [24] .

EQUATION 3

CI. OH ) PCDD

Thermal cyclization Of polychlorinated phenoxyphenols

to form PCDD

346

The presence of PCDDjPCDF in commercial chemicals is described below.

Manufacture of PCBs

Commerical polychlorinated biphenyl solutions can contain over 100 PCB isomers with varying numbers of chlorine atoms [17]. PCBs have been found to contain PCDFs as trace impurities [8, 18] . PCB manufacture was prohibited in the United States after 1976 and its current limited use and disposal is strictly regulated [2S] .

Manufacture of Chlorophenols

Chlorophenols, typically produced by: (a) chlorination of phenols; or (b) alkaline hydrolysis of chlorobenzenes, can contain PCDD as a result of either reaction, as shown in Equation 1 [29] .

Generally the PCDD formed will contain one chlorine atom more than the initial substrate possessed; i.e., tri­chlorophenol manufacture forms TCDD, tetrachlorophenol production forms mostly PnCDD or HxCDD (at levels from <1-100 ppm by weight of initial tetrachlorophenol), and pentachlorophenol manufacture produces HxCDD or higher chlorinated phenols. Chi oro phenols and their salts, the chlorophenolates, are used as fungicides, herbicides, slimacides, bactericides, and in the manufacture of chlori­nated phenoxy acid herbicides such as 2,4,S-T and 2,4-D and the bactericide hexachlorophene. Chi oro phenols can contain polychlorinated phenoxyphenols, diphenylesters, PCDD, and PCDF as artifacts. Tetra-, penta-, and hexa-

CDD have been found in trio, tetra-, and pentachlorophenol and their salts in concentrations ranging up to 100 ppm [18, 26-33].

PCDD content in commerical chlorophenols and deriva­tives varies according to manufacturing process and condi­tions [32]. U.S. production of chlorophenol and its derivatives continued as of 1982 in over 20 states at near­ly 100 locations. Manufacturer awareness has generally decreased PCDD content to <0.1 ug/g in 2,4,S-T [32]. Chlorophenol use is banned in Sweden [34] .

Manufacture of Polychlorinated Benzenes

Hexachlorobenzene, a wheat fungicide, and various chlorinated benzenes, common industrial solvents and chemical manufacture feedstocks, have been noted to contain trace PCDD [1, 3 S] .

Manufacture of Chlorophenoxy Acids and

Hexachlorophene

Manufacture of the chlorophenol derivatives chloro­phenoxy acid pesticides and herbicides, such as 2,4,S-T, and hexachlorophene, a bactericide, also have produced PCDD as contaminants [1]. TCDD, including the 2,3,7,8-isomer, and HxCDD are formed; Agent Orange, derived from 2,4-S-T and the defoliant used by the U.S. Army in

TABLE 1 NOMENCLATURE AND TOTAL NUMBER OF THEORETICAL PCDD AND PCDF ISOMERS [1,121

•

Monochlorinated

Dichlorinated

Trichlorinated

Tetrachlorinated

Pentachlorinated

Hexachlorinated

Heptachlorinated

Octachlorinated

.

Dibenzo-p-dioxin Possible No.

Homologue Isomers

2

-DCDD 10

-TrCDD 14

-TCDD 22

-PnCDD 14

-HxCDD 10

-HpCDD 2

-OCDD 1

•

347

Di benzofuran Possible No.

Homologue Isomers

4

-DCDF 16

-TrCDF 28

-TCDF 38

-PnCDF 28

-HxCDF 16

-HpCDF 4

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Hexachlorophene is produced from the same starting material as 2,4,5-T but due to additional purification 2,3,7,8-TCDD in this product is <0.03 ug/g [29]. 2,4-D has been reported to be contaminated with PCDD but only as a result of using 2,4,5-T contaminated processing equipment [37] .

Manufacture of Diphenyl Ether Herbicides

TCDD, PnCDD and HxCDD have been reported as contaminants in diphenyl ether herbicides; concentrations of the latter two species were found up to 150 and 30 ppm, respectively [19]. No 2,3,7 ,8-TCDD was detected.

COMBUSTION SOURCES OF PCDD/PCDF

Chlorinated dioxin and furan emissions from resource recovery facilities that result from combustion system conditions appear to occur either from reactions of chlorinated aromatic "precursors" alone or in combustion with other precursors; and have also been suggested to form from "de novo"* synthesis of reaction contributors, chlorinated aliphatic and non chlorinated aromatic com­pounds which combine to form PCDD/PCDF [5, 20]. Reaction contributors have also been suggested to donate compounds to precursor reactions. Based on comparative thermokinetics, PCDD/pcDF formation appears more readily accomplished from precursor reactions rather than de novo synthesis [20] .

Precursors

Precursor compounds identified thus far are chlorinated aromatic compounds usually containing various hydroxyl groups or ether linkages (Table 2). Postulated and syn­thetically created reactions identified to date for PCDD/ PCDF formation from precursors are discussed below.

PCBS

Ambient quantities of polychlorinated biphenyls in the U.S. have decreased dramatically in the past decade due to regulatory action, but discarded PCB-containing conden­sors (e.g., fluorescent lighting ballast), capacitors (in air

''''de novo" synthesis is the formation of PCDD and/or PCDF "as

a consequence of a complex array of pyrolytic processes of chemically unrelated organics" such as PVC; other nonchlori­nated plastic polymers; coal; wood (lignin); non-benzene chloro­carbons; and inorganic chlorine compounds such as HCI, Nacl, or CI. [20].

349

conditioners, some refrigerators, television sets, and stereos), and miscellaneous electrical equipment mostly manufactured prior to 1972 still end up in MSW [36, 38]. Discarded PCB has been suggested as a potential major source of PCDF either through volatilization of artifacts or direct formation [8]. Support for this theory was claimed from the similarity of GC/MS analyses of PCB pyrolysate from sealed quartz ampoules to incinerator and utility boiler fly ash in Switzerland, verified to contain PCDF. Various tri-through heptachlorobiphenyls were found to form mono- through hexa-PCDF by rearrange­ment and/or dechlorination and oxyenation, in concentra­tions up to 2 percent. 2,3,7 ,8-TCDF was reported as a major isomer [8]. Incineration of PCB between 1247-1832°F (675-1000°C) showed that hexachlorobenzenes (HCB) production increases with increasing temperature, from 2 up to 35 mg HCB/kg PCB [34] . EPA-sponsored high temperature PCB destruction tests aboard the M/T Vulcanus found a conversion of up to 0.0025 percent to tetra-CDD and tetra-CDF at >1200-2200°F (>650-1204°C) and >1 sec residence time [39]. Laboratory analyses showed destruction efficiencies of 99.995 percent at 1472°F (800°C) and a 2 sec residence time [39] and PCB destruction appears to be complete at incineration temperatures above 2192-2552°F (1200-1400°C) [40]. Tests conducted at EPA-licensed PCB incinerators in Deer Park, Texas and El Dorado, Arkansas revealed the presence of "very low levels of PCD!) and PCDF" in samples [38] . Tests at each facility in 1979 and 1980 found PCDF only in 1980, at levels of 0.281 and 0.060 ng/dscf. PCDD was sampled for in 1980 at each facility and found at levels of 0.018 and 0.005 ng/dscf. Average incinerator temperatures at both facilities during all tests exceeded 2147°F (1175°C) [38]. Cement kilns in the U.S. [38] and Sweden [44] operating at high temperatures, >2192°F (>1200°C), were not observed to produce PCDD/PCDF or other high molecular weight chlorinated organics from PCB feed­stocks.

Chlorophenols and Chlorophenolates

Chlorophenols and chlorophenolates evidently can convert to PCDD and/or PCDF or precursors under sufficient heat. A total of 385 ug/g of tri- and 856 ug/g of tetrachlorophenol mixed with wood chips was introduced into a pilot-scale incinerator at 932-1112°F (500-600°C) in Europe. PCDD production decreased with increasing' temperature 1112°F (>600°C), copper salts addition, increased residence time, and increased combustion oxygen. Temperature appeared to exert greater influence on PCDD production than oxygen presence and <35 ug/g of all isomers was found at 1544°F (840°C) and similar combustion conditions for tri- and tetrachlorophenol

[34] . Pentachlorophenol reacted under similar conditions in the same incinerator to generate "small PCDD emis­sions" except where oxygen was deficient . No TCDD was formed at IS62°F (8S0°C) from pentachlorophenol [34] .

Chlorophenolate-coated wood and leaves when open­burned have yielded various PCDD. Combustion of trichlorophenolate produced mostly TCDD, while penta­chlorophenolate produced mostly OCDD [29]. Dimeriza­tion of chlorophenols or their salts (Eq. 2) and dechlorina­tion of higher chlorinated PCDD to form less chlorinated isomers have been advanced as PCDD formation mechan­isms from this [29] and other work [S, 33] . The pyrolysis of polychlorinated phenoxy phenols and their salts, which are commercial trichlorophenol impurities, was observed to generate TrCDD and PnCDD by thermal cyclization (ring closure), seen in Eq. (3). PCDD formation in increased from 0.4 percent to 9.06 percent yield by weigh t as temperatures increased from 677°F to 1796°F (3S8°C to 980°C) [21] . 2,3,7 ,8-tetra-CDD has been suggested as forming only from dechlorination or cyclization [29] .

Chlorinated Phenoxy Acids

PCDD has been reported to be formed at a yield of O.OOOS percent from open-burning 2,4,S-T and related phenoxy acids [43]. A similar study on a 2,4,S-T ester (2-butoxyethyl) observed only TCDD to be produced from temperatures of 212 - 1247°F (100 - 67SOC) at a 0.0001 percent yield [44]. From these experiments, 1382°F (7S0°C) was suggested as the optimal tempera­ture for PCDD production from 2,4,S-T and related com­pounds; lower temperatures formed less PCDD and higher temperatures, 1472°C (>800°C), destroyed PCDD [10].

Chlorobenzenes

Pyrolysis of trio, tetra- and pehtachlorobenzenes in sealed quartz ampoules at 1 148°F (620°C) in air gen­erated PCDD and PCDF via thermal oxidation in yields of O.OOOS percent and 0.0001 percent by weight, respec­tively [4S]. 2,3,7 ,8-TCDD and other especially toxic isomers were present in minor concentrations, as were chlorophenols and PCBs. The yields are expected to be much less if lower concentrations of starting material were used [20]. No correlation to municipal incinerator opera­tion of PCDD/PCDF formation from chlorobenzene­contaminated MSW has been suggested from these results [S] , but the source separation of industrial chlorobenzenes from MSW has nonetheless been recommended [4S]. Other researchers found no increase in either PCDD or PCDF from the addition of a 400 g slug of hexachloro­benzene to 2 m3 of MSW in a municipal incinerator [46]. A review [20] of several independent pyrolysis reactions

3S0

involving chlorobenzene has shown that significant HCI and some chlorinated biphenyls and naphthalene form at < 1472°F (>800°C), but at >1472°F (>800°C) vinyl chloride is the main product and at the least biphenyls concentration is reduced .

Polychlorinated Diphenyl Ethers

Polychlorinated hydroxy diphenyl ethers (PCDPE) as contaminants in chlorophenols were suggested to generate PCDD via cyclization [29]. It is has been reported that 2,3,7,8-TCDD may be formed from pyrolysis of these PCDPE. 2S percent of these compounds decomposed at 932°F (SOO°C), 99 percent at 1292°F (700°C); PCDD formed only upon dechlorination of ortho-chlorinated compounds [4S] .

Synthetic Precursor Combination

PCDD has been produced synthetically in the laboratory from various precursors in attempts to elucidate TCDD formation [1]. The relevance of these reactions to field conditions is unknown. Catechol salts have been reacted with o-dichlorobenzenes in dimethyl sulfoxide to yield 19 percent PCDD [1] . Dibenzo-p-dioxin has been reacted with Cl2 and FeCl3 to produce a mixture of tri- through penta-CDD, although 2,3,7 ,8-TCDD was in low yield. Much higher yields of 2,3,7 ,8-TCDD were reported (>40 percent) from reaction of Cl2 alone or with FeCl3 and 12 but no Ch [1].

Photo production

Ul traviolet irradiation of OCDD has produced small amounts of mixed trio, penta-, hexa-, and hepta-CDD [1] . The role of photolysis in PCDD/PCDF decomposition, and the resulting dechlorination of higher chlorinated homologues (e.g., OCDD) to lesser chlorinated, more toxic isomers has been the focus of considerable research [46] .

Reaction Contributors

A variety of chlorinated aliphatic and non-<:hlorinated aromatic compounds have been proposed to combine via de novo [1] synthesis to produce PCDD/PCDF or form certain precursors, notably chlorobenzene and chloro­phenols. Inorganic chlorine compounds have also been suggested to contribute chlorine to non-chlorinated aromatic compounds at sufficient temperature to generate PCDD/PCDF [S, 20] .

Chlorinated Aliphatics

Polyvinyl chloride (PVC) plastics are known to produce various aromatic and aliphatic compounds upon PVC thermal degradation, in addition to gaseous HCl, CO, and CO2 [48]. Chlorinated benzenes (precursors) are produced and reactive chlorine (HCI) released which under high temperatures could substitute to precursors [5, 20]. Al­though original work on PVC combustion emissions in the late 1960s revealed no PCDD or PCDF [47], analytical methodology at that time could rarely measure chemical concentrations <0.1 ppm. Pyrolysis of PVC has been ob­served to generate various benzenes and HCI as the major organic and inorganic products, respectively [20]. Various chlorobenzenes have been reported from PVC pyrolysis [20] but apparently concentrations resulting have been <1 ppm where oxygen is present [5] . Other pyrolysis experi­ments occurring from 1022-2012°F (550-1100°C) meas­ured vinyl chloride and di- through hexachlorobenzene (HCE) production. Total organic bound chlorine increased with temperature up to 50 ug/g, over half of which was HCB [34]. Quantitative conversion of >90 percent PVC chlorine to HCl has been observed during direct combus­tion 1300-1600°F (704-871°C) of MSW 24 percent PVC by weight [48]; during pyrolysis it has been estimated that quantitative conversion occurs above 572°F (300°C) [49, 50] . PVC is typically 45 percent chlorine by weight. Chlorine gas (Ch) or phosgene (COCh) have not been detected from PVC combustion [48] .

PVC plastic has been theorized as a chlorine donor (HCl) to phenols and polyphenols to account for the production of PCDD and PCDF from incineration of raw MSW in Italy [22] . Incineration of agricultural waste or "recycled" or compost residue fractions of the MSW produced no PCDF and fewer PCDD isomers, in concentra­tions ranging from 140 ppb, an order of magnitude lower. This difference was said to occur because in the non-MSW fractions either phenol-generating tannin or chlorine­donating plastics were absent [22]. Acceptance of this argument should be withheld pending further character­ization of the four waste streams. The large quantity of raw cellulose (containing lignin) probably common in each of those wastes could readily replace tannin as a phenol donor. Also it would be most unusual if the "chlorine-donating plastics" (and paper, rubber, textiles, leather, etc., potentially containing chlorine, PCDD/PCDF artifacts, or precursors) found in raw MSW were not also present in both recycled and compost wastes, according to waste analyses from other Italian provinces and northern Europe [23, 51]. Further discussion of this point is provided elsewhere [52] .

The role of PVC plastics, and other MSW components, as potential HCI donors to precursors and nonchlorinated

351

aromatics should be further investigated given the current attention. PVC is widely employed, comprising 15.2 per­cent of total U.S. plastics consumption in 1981 [53] and predominating in use by type of plastic in the Netherlands in 1975 [54]. However, because PVC is found predomi­nantly in durable goods, such as piping, construction products, and automobile upholstery, it generally does not end up in MSW, although an occasional bleach bottle or vinyl record, toys, etc., will. PVC markets in the U.S. have reached maturity, increasing in sales by <4 percent for each of the last 5 years but decreasing in total per­centage of all plastics since 1977 [53]. Other common refuse products can contain chlorine which could also convert to HC!. Paper (e.g., newsprint) can contain from 0.04-0.16 percent chlorine, almost all of which is sup­posedly completely expelled upon burning [55]. In Detroit, textiles, paper, food, wood, and yard waste and sweepings were found in limited sampling to contain 86 percent of total organic chlorine in the refuse, with plastics accounting for 14 percent. Total organic chlorine in this MSW amounted to 0.17 percent by weight [56]. Others have also estimated PVC contribution to organic chlorine content in U.S. MSW to be <0.2 percent [57].

Other chlorinated aliphatics form hexachlorobenzene (HCB) under certain conditions, which could produce the precursor chlorobenzene. Carbon tetrachloride (CCI4) and hydrogen gas (H2) have been combined in a hot tube at 600-650°C to yield 60 percent HCB [20]. Over long periods at 405°C various perchlorocarbons (C2CI4, C3Cl6 and C9C16) evidently can also form HCB [20].

Non-Chlorinated Aliphatics

Polyethylene, polystyrene, and related non-chlorinated polymers have been suggested to serve as intermediates or to form organic radicals upon thermal degradation [20], but mechanisms for these reactions have not been advanced.

M iscellanous Organ ics

Coal, wood, and other lignin-containing substances have been proposed to generate reaction contributors which may combine with chlorine to form precursors or even PCDD/PCDF. Lignin, the second most abundant natural compound, acts as a cementing agent to bind cel­lulose fibers together to make wood rigid [58, 59] . Lignin is comprised of polymeric hydroxy and methoxy subs­stituted phenylpropanes [59]. Lignin has been shown to yield a variety of cresols, catechols, phenols, and other hydroxy-substituted benzene compounds when heated [20] .

Coal

109 different organic compounds including various non-· chlorinated furans and numerous polycyclic aromatic hydrocarbons (PAH) , have been detected from the emis­sions of several coal-fired utilities in recent years [60]. Sampling of fly ash from a coal-fired facility discovered chlorobenzenes but no PCDD at the ppb level [40 ]. Some researchers have reported a variety of chlorinated dioxins in the fly ash from a coal-and-oil co-fired power plant [61 ] , but these results have not yet been fully accepted

by EPA and others [14,62].

Wood

The combustion of wood generates a variety of organ­ics, including phenols and P AH. Chlorobenzenes also result probably because treated wood (containing chloro­phenol-based preservatives) has often been used in experi­ments to date. A "modern open fire" was found to gen­erate 40 ug of chlorobenzenes/kg of aged wood and 50-1600 ug of tetra- and 4200 ug of pentachlorophenols/ kg of green wood [34]. A pre-kiln burner generated 2 ug chlorobenzene and 500 ug chlorophenol/kg of wood [34] . In other work, a pilot-scale incinerator produced chloro­benzenes from the combustion of concentrated bleach pulping (lignin-rich) residue said to contain only inorganic chlorides [34] .

Combustion of new pentachlorophenol-treated wood in a fluidized bed oven produced no increased of PCDD/ PCDF compared to similarly heated 60 year-old treated wood [63].

It has been speculated that PCDD and/or PCDF might be produced from the burning of wood alone. PCDD/PCDF has been proposed to be formed during forest fires [20 ] , and up to 0.4 ppb TCDD, 3 ppb HxCDD, 16 ppb HpCDD, and 25 ppb OCDD have been reported from home fire place soot [61]. These latter results have been criticized, however [62]. Based on results from the burning of lignosulfonate pulp waste in the presence of HCI or PVC at temperatures >590°C, the combination of lignin or a lignin-like structure and some chlorine donor (e.g., HCl) under sufficient heat has been proposed to contribute largely towards PCDD/PCDF formation [63].

Inorganic Sources of Chlorine

Gaseous chlorine (CI2), hydrochloric acid (HCI), and sodium chloride (NaCl) have been suggested to substitute to precursors to form PCDD. When each of these inorganic chlorine compounds were combusted with bituminous coal under air, C1 2 was found most able of the three species to provide chlorine towards PCDD precursor re­actions [20]. HCl appeared to donate chlorine half as well as C1 2 towards PCDD/PCDF formation, while NaCI ap-

peared not to contributed any chlorine, as observed elsewhere [56].

Chlorine gas has been observed to combine with other additives to degrade monochlorobenzene to various chlori­nated biphenyls [20] .

EMISSIONS OF PCDD AND PCDF

Date characterizing emissions of PCDD and PCDF have been compiled from various sampling programs conducted at American and European municipal solid waste combus­tion facilities. Reported test results were screened to develop an emissions data base from which a comparative analysis could be made. The studies referenced were selected primarily for the following reasons:

(a) recently published (within past three years) with sampling program focus on PCDD and PCDF.

(b) multiple isomers of PCDD and PCDF were sampled in each study.

(c) from the literature reviewed, all facilities sampled appeared to have similar control devices; i.e., electro­static precipitators.

(d) facilities utilized similar combustion technologies, i.e., mass-b urn .

In general, U.S. EPA investigations focused on evaluat­ing TCDD emissions with particular emphasis on the 2,3,7,8 isomer. European investigators, on the other hand, have evaluated emissions for all PCDD and PCDF com­pounds.

Emissions data from European and American testing programs have been condensed and provided in Table 3 in ug of PCDD/PCDF isomer per metric ton of refuse burned. These units are typical of emission factors and enable a comparison of data obtained from different facilities. A listing of these data for each detected isomer and for total PCDD/PCDF compounds is shown.

Data from domestic and European studies show a wide variation in the amounts and types of PCDD and PCDF compounds emitted. From the data presented, test results from the American studies appear to be consistently lower than the European data, as much as an order of magnitude lower for TCDD and total PCDD, although U.S. TCDF ievels are only two thirds that of the calculated European mean emission rate, and U.S. PCDF levels are half of Europe's [6,12,13,16].

352

Apparent discrepancies between domestic and European data on PCDD and PCDF compounds are not surprising because of differences in operational procedures and equipment, feed-stock composition, sampling techniques and analytical protocols, and standards for quantification. Sampling techniques used by U.S. investigators were identical, while European investigators have used a variety of sampling techniques which are poorly documented.

Recent work performed by major European investigators included the collection and analysis of flue gas and asso­ciated particulates.

Emissions data for PCDD and PCDF are typically reported by U.S. researchers in terms of nanograms per dry standard cubic meter (at 20°C) corrected to 12 percent CO2 , while European data is usually reported in terms of nanograms per normal cubic meter (at O°C). The two data sets can be better compared by standardization of tem­perature, excess air, and moisture. Temperature differ­ences are easily overcome by a simple conversion factor, but to present data at 12 percent CO2 (standardized ex­cess air) on a dry basis requires knowledge of actual CO2 and moisture content, information not generally reported by European researchers. The lack of such source data from abroad hinders its comparison with U.s. data for PCDD/PCDF emissions.

.

HEALTH EFFECTS

As mentioned previously, 2,3,7,8-TCDD has been found to be the most toxic of the PCDD and PCDF isomers. Toxicity of the other 209 isomers has been linked to the position and the number of chlorine atom substituted on the dibenzo-p-dioxin or dibenzofuran structure·. The most toxic isomers are those containing chlorine atoms in at least three of the four lateral posi­tions (2.3,7,8) and which have at least one additional posi­tion unsubstituted; thus, OCDD is comparatively inactive [67, 68] .

TOXICITY OF PCDD AND PCDF IN ANIMALS

The toxicity of PCDD and PCDF varies widely with isomer tested and the animal species exposed. The most

TABLE 3 PCDD AND PCDF EMISSIONS INCINERATORS IN EUROPE AND THE U.S. (ug/t MSW)

Compound

TrCDD

TCDD

PnCDD

HxCDD

HpCDD

OCDD

PCDD

TrCDF

TCDF

PnCDF

HxCDF

HpCDF

OCDF

PCDF

[66J

NR

610

2418

3263

3366

1899

11556

NR

1562

2704

4786

2614

581

12247

•

[65J -

-

-

-

-

-

2563

-

-

-

-

-

-

4159

E urope 6

NR

250

467

642

581

704

2644

NR

700

743

804

880

590

3717

353

10

NR

175

451

766

766

175

2333

NR

260

541

906

640

80

2427

L64

NR

26

72

164

158

323

743

NR

146

179

123

82

54

584

Mean

-

266

853

1209

1218

776

4322

-

667

1042

1655

1054

326

4744

u.s. [13J

65

32 -

82

37

13 229

1529

446 -

306

37

3

2321

common measure of acute toxicity in animal species is the LDso, the dosage lethal to 50 percent of a laboratory population. The lower the LDso, the more toxic the com­pound to that particular species. For 2,3,7 ,8-TCDD alone, values range over 5,000-fold from an LDso of 0.6 ug/kg body weight in guinea pigs [69] to 1,157 to 5,051 ug/kg body weight in hamsters [70, 71] . Comparing the toxicity of different PCDD isomers within the most sensitive animal species, guinea pigs, it is found that LDso s are 300,000 ug/kg for 2,8-DCDD, 72.5 ug/kg for 1,2,3,4,7,8-HxCDD, and 600-7,180 ug/kg for 1,2,3,4,6,7,8-HpCDD [69] .

Other factors which may affect toxicity include mode of exposure i.e., inhalation, ingestion or application to the skin and whether the compound is dissolved in a solvent or adsorbed to a solid particle. In rats, attachment of TCDD to soil particles was found to reduce its absorp­tion after oral administration by half and, when attached to activated carbon, absorption was almost completely prevented [72]. Other researchers have found matrix effects in rabbits [73, 74] and in rats [75] .

The most well-known effect of PCDD/PCDF exposure is the development of chloracne, a skin ailment similar to acne vulgariS. This effect has been observed in humans, rhesus monkeys [69], rabbits, and hairless mice [77] , but not in guinea pigs, hamsters, rats or other mice. Pathological effects to the immune system, liver, urinary tract and gastric mucosa have also been noted in various test animals. TCDD has also been demonstrated to be fetotoxic, em­bryotoxic and teratogenic; and in rats and mice to be carcinogenic [78-81 ] .

TOXICITY OF PCDD AND PCDFS IN HUMANS

In addition to chloracne, liver dysfunction, and dis­orders of fat and carbohydrate metabolism and of the cardiovascular, urinary, respiratory and pancreatic systems have been reported. Neuropsychiatric disorders may also develop.

The evidence for TCDD carinogenicity in humans is still equivocal, although support seems to be increasing for the correlation of TCDD exposure and the develop­ment of soft tissue sarcomas [82] . Uncertainty exists be­cause exposure has generally been to chemicals (e.g., chloro­phenols and their derivatives) contaminated with TCDD as impurities. This mixed exposure makes it difficult to definitively show that TCDD alone is a human carcinogen. The potential carcinogenicity of PC OF has not been studied to date.

EXISTING EXPOSURE STANDARDS

A variety of government agencies, in Canada, the Netherlands and in the U.S. have established exposure

standards for PCDD and PCDF, although primarily for 2,3,7,8-TCDD. These exposure limits appear to range widely in concentration, although all were developed from a similar data base.

Most relevant to this discussion is the U.S. Environ­mental Protection Agencies' 1981 "Interim Evaluation of Health Risks Associated with Emissions of TCDD from Resource Recovery Facilities" [11]. Based on emission data from five domestic refuse combusting facilities, this document concluded that up to 3.8 X 10-8 ug/m3 of 2,3,7,8-TCDD and up to 9.2 X 10-8 ug/m3 of total TCDD would not represent a health hazard. This conclusion was based upon quantitative carcinogenic risk assessments using a series of mathematical models.

The New York State Department of Environmental Conservation subsequently adopted the EPA's level for total TCDD as an acceptable ambient level from a point source in their Air Guide No. 1 document [83] .

•

The Ontario Ministry of Labour, Ontario, Canada [84] and the government of The Netherlands [82] have both established guidelines for acceptable air levels of 2,3,7 -8-TCDD. Both of these guidelines are based on levels that were found to have no adverse effects in animal testing with a safety factor added in to account for animal-human differences. The Netherlands' standard is based upon an acceptable daily intake of 1 nanogram (ng)/kg/day of 2,3,7,8-TCDD (the no adverse-effect level reported by Kociba, et al. [80] ; Murray, et al. [85]); which reduces to 4 picogram (pg)/kg/day when a 250-fold safety factor is applied. Assuming a 60 kg person breathing 20m3 per day, an acceptable ambient level of 1.2 X 10-5 ug/m3 can be calculated based on the Netherlands Standard.

The Ontario Ministry of Labour also used the 1 ng/kg/ day no-effect-Ievel, but included a lower safety factor of 100. Assuming the same 60 kg person breathing 20 m3 per day, they arrived at a recommended air standard of 3.0 X 10-5 ug/m3.

CONCLUSIONS

Based on the information presented herein, the follow­ing conclusions are made.

1. Much research has been conducted or is underway on sources of PCDD/PCDF in the environment, but many unknowns exist, especially as concerns large-scale solid waste combustion units. Precursor content of MSW needs to be further investigated because of the relative ease with which precursors can convert to or volatilize PCDD/PCDF at temperatures typical of resource recovery facilities. More research into mechanisms for de novo synthesis of PCDD/PCDF from chlorinated aliphatic and nonchlori­nated aromatic compounds would also be helpful, but it is

354

very difficult to correlate laboratory reaction analyses to PCDD/PCDF formation in incinerators of heterogeneous refuse. More useful information will be obtained from a determination of chlorine content in MSW components from which reactive chlorine is formed. Since synthetic and natural aromatic compounds are abundant in MSW, chlorine presence becomes the rate limiting factor for PCDD/PCDF formation via the de novo theory. The most significant contributors of reactive chlorine have not yet been defined.

2. It has been suggested that the removal of PVC, an obvious organic chlorine-containing component in waste, could limit HCl formation. Other sources of organic chlorine in MSW (e.g., paper, textiles) exist, so implement­ing PVC source separation or other removal programs would be premature until the nature of other possible chlorine donors for HCl formation in MSW is investigated further. In addition, the role of inorganic chlorine conver­sion to HCl remains to be determined; indications to date. are that it plays a very minor role.

3. Investigation of the role of lignin decomposition to provide essentially nonchlorinated precursors in important because of its ubiquitous presence in newsprint, cardboard, rough wood, and food and yard waste in MSW.

4 . An analysis of representative emission data indicates that PCDF and PCDD emissions from European resource recovery facilities are 2 and 10 times, respectively, those of U.S. facilities. However, until source data for European facilities becomes available, strict comparison with U.S. plants is not advisable.

5. A comparison of existing air quality standards shows a wide range of concentrations that are considered adequate to protect the public health. It is interesting to note that these range of levels are all based on a similar toxicological data based. The extensive research under­way in PCDD/PCDF health effects should be correlated to ambient predictions and risk assessments developed for all PCDD and PCDF isomers, not just 2,3,7 ,8-TCDD, as is presently the case in the U.S.

ACKNOWLEDGMENT

The work presented in this paper was supported in part by the Port Authority of New York and New Jersey. Special thanks are extended to Paul Giordano and Frances Topping of CDM for staff support.

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.

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