Document DvXRnaB14n7EE4xdzQd7ny2g5

Reprinted from CHEMICAL ENGINEERING PROGRESS, September 1975 EMissidgf(Control Control Methods for Vinyl Chloride Some tips on how PPG handles sample collection and analyses of VCM, and on how it handles the tricky aspects of loading operations. Z. G. Bell, Jr., J. C. Lafleur, R. P. Lynch, and G. A. Work, PPG Industries, Inc., Pittsburgh, Pa. Vinyl chloride monomer (VCM) is hazardous not only because it is highly flammable, but also because of its toxicological effect on human beings. Consequently, the design and operating procedures of our vinyl chloride facilities at Lake Charles, La., and Caribe, P.R., provide that the release and exposure of VCM to personnel be minimal. This article describes two procedures that we have adopted, which have contributed to improved VCM confinement and employee exposure control. Sample collection and analyses The first of these techniques involves sample collec tion and analyses. In our process, quality control sample collection is achieved from different points in the system by attaching the sample cylinder or bomb to a small fit ting in a closed loop system, Figure 1. The sample bomb is installed vertically in the system with its stand leg fitting in the top position to prevent overfilling and bomb overpressurization. The bomb is equipped with a safety relief valve as further protection. To assure that the bomb is inserted properly, its fittings are of different sizes. The sample collection lines are small diameter stainless steel tubing. Valves are located as close as possible to the sample bomb connections to minimize the quantity of vinyl chloride in the tubing. Before the bomb is removed, the small amount of vinyl chloride trapped between the valves is released to a remote location, and the tubing between the valves is purged with nitrogen. The storage of sample bombs within the main or plant laboratories is prohibited, and although these sample bombs were capped between use, a storage rack or cabi net similar to a gun rack is provided, Figure 2. All vinyl chloride bombs must be stored in the cabinet while not in use, and all analyses of samples must be accomplished within a laboratory hood. A flexible line is installed on the gas chromatograph back into the laboratory hood. CHEMICAL ENGINEERING PROGRESS (Vol. 71, No. 9) September 1975 45 After the analysis, there is from 600 to 700 ml. of vinyl chloride remaining in the bomb. The sample bombs are capped and returned to the plant where the bomb and its residual contents are inserted during the next sample collection round, returning the unused vinyl chloride to the process. aW**' ----- tftJtt. . , 1/ . ' . ' V E. .-i- Figure 2. Storage rack for sample bombs. The bomb valve integrity is checked periodically using a Century organic vapor analyzer. All laboratory hoods where vinyl chloride is used or analyzed have been checked for adequate capture velocity. A baffle has been installed across the front lip of the hood to prevent any vinyl chloride vapors, which are heavier than air, from exiting the hood. The levels of vinyl chloride are routinely monitored. Loading operations The second procedure involves loading operations for tank cars, tank trucks, barges, and ships. The potential problem areas are sampling, vehicle emissions, vehicle gauging, and loading line clearing. The oxygen content of empty transportation vehicles is determined prior to loading, and the oxygen analyzer is vented remotely so that personnel exposure is avoided. There are equalizing lines so that vehicle vapor content may be displaced dur ing loading. See Figure 3 for tank car loading. The vapor space material is equalized with the storage tank from which the vehicle is being loaded. There are a number of ways to determine when a tank car or tank truck is full. The vinyl chloride may be scale loaded (for trucks and cars), or a flow meter may be used. A magnetic level indicator is used by some producers. Special procedures are required so that personnel expo sure may be avoided. Exposure may be prevented by us ing a flexible hose to connect the gauge rod to a bull's eye. Liquid can be observed in the bull's eye when the car is filled. The bull's eye must be vented remotely to an in cinerator or tall stack, as shown in Figure 3. The final problem of loading operations is the clearing of the loading hose so that the hose may be disconnected without allowing exposure. The liquid in the loading hose &QU1L/Z/SJG LtK/ 46 September 1975 Figure 3. Piping diagram for tank car loading. J. CHEMICAL ENGINEERING PROGRESS (Vol. 71, No. 9) SL 041537 A v TO Figure 4. VCM storage vent recovery. must be pushed (with nitrogen) into the transportation vehicle. The loading line is then nitrogen-purged to an in cinerator or tall stack so that vinyl chloride vapors are removed before the hose is disconnected. The displacement of inerts to the storage tank' from transportation vehicles during loading operations will cause the storage tank pressure to be excessive as the tank is refilled unless a recovery system is provided. If a refrigerated vent recovery system is used, some vinyl chloride must be vented to the atmosphere or to an in cinerator. A viable alternative is to compress this stream and feed it to the plant process where the VCM is recov ered and the inerts, normally nitrogen, accompany the byproduct HC1 stream, Figure 4. Clearing a filter There are other procedures that may be followed so that equipment can be cleared for maintenance work, or made ready foT service without exposing personnel to VCM. In order to do this, some high pressure nitrogen must be used and a sufficient amount of nitrogen must be available for purging. The procedure for clearing a filter for element replacement will provide an example of how most process equipment and piping may be cleared. Fig ure 5. The first step is to push the Alter liquid into the pro cess piping with high pressure nitrogen. The Alter is then blocked and the Alter depressurized through a hose to a vent system. The Anal step is to continue a small nitrogen purge through the Alter until VCM is removed. After the elements are removed and replaced, the Alter is nitrogen purged to remove air and a leak check is made. The Alter is then depressurized and Ailed with vinyl chloride. When the Alter is completely Ailed, a nitrogen purge is used to clear all hoses to the vent system prior to disconnecting. # Bell CHEMICAL ENGINEERING PROGRESS (Vol. 71, No. 9) SL 041538 Lafleur Lynch Work September 1975 47 Toxicology Letters, 6 (1980) 33--3(1 j Elsevier/North-Holland Biomedical Press 33 PHARMACOKINETICS OF VINYL CHLORIDE IN THE RHESUS MONKEY A. BUCHTER*, J.G. FILSER, H. PETER and H.M. BOLT Institute of Occupational and Social Medicine, University of Cologne, and Section on Toxicology, Institute of Pharmacology, University of Maine (F.R.G.j (Received February 14th, 1980) (Accepted February 18th, 1980) SUMMARY The metabolic elimination of vinyl chloride in Rhesus monkeys is a dosedependent, saturable process, as in rats. Below 200--300 ppm of vinyl chloride (VC) in atmosphere, elimination obeys a first-order law; the clearance rate is much closer to that found in man than the values for rats, mice and gerbils. The maximal velocity of metabolic elimination of VC at high concentrations in Rhesus monkeys is only about half that of rats when related to kg body weight. It is suggested that Rhesus monkeys mimic the quantitative aspects of VC metabolism better than rats or mice. INTRODUCTION From experimental research on the mechanism of action of VC it has been inferred that this compound is transformed by the liver to reactive meta bolite^) capable of binding irreversibly to nucleic acids and thereby initiating malignancy [1 3]. It has been postulated that any resolution of dose-re sponse toxicity data for VC must be based on the amounts of VC actually metabolized rather than on exposure concentrations [4]. Attempts to cal culate the risk of angiosarcoma in man after exposure to VC must consider possible species differences in the rate of VC metabolism [5]. Some knowledge of the rates of VC metabolism in man is required and in a previous report [6] data for low exposure concentrations were presented. However, it is well known from animal experiments that saturation of metabolic pathways of VC occurs at higher exposure concentrations [4, 5, 7]. Send correspondence and reprint requests to: Priv.-Doz. Dr. A. Buchter, Institut und Poliklinik fur Arbeits- und Sozialmedizin der Universitat Koln, Josef-Stelzmann-Str. 9, D-5000 Koln 41 (F.R.G.). Abbreviation: VC, vinyl chloride. SL 4l539 34 As ethical considerations do not allow human experimentation with VC at higher concentrations, the present report evaluates the usefulness of Rhesus monkeys. MATERIALS AND METHODS The pharmacokinetics of VC were assessed by methods previously describ ed [7]. The animals were placed in a closed exposure system [8] into which VC was injected and air samples taken for gas-chromatographic analysis. From the decline of VC in the gas phase of the system the processes both of equilibration of the organism with the atmospheric VC and of metabolic elimination were determined [7]. Rhesu= monkeys were exposed in a similar system; for a 4 kg animal a sys tem of 2u0 1 was used. This relatively large volume was necessary to introduce the animal's transport cage easily into the closed exposure system and facili tated handling of the animals. In some experiments, metabolism of VC was inhibited by disulfiram; a 4 kg animal received a 0.1 g Antabus tablet 1 h prior to exposure. VC was purchased from Linde, Munich, not < 99% pure as checked by gas chromatography. The gas-chromatographic method of determination of VC in air samples taken from the exposure cage and the basic pharmacokinetic anal ysis of results have already been described [7]. RESULTS When Rhesus monkeys were exposed to VC at concentrations up to 200 ppm in the closed exposure system, VC disappeared from the atmosphere according to a first-order law. The clearance was 3.551 /h/kg body weight, but could be decreased by 90% after administration of a metabolic inhibitor, TABLE I FIRST ORDER METABOLIC CLEARANCE RATES FOR VINYL CHLORIDE IN RHESUS MONKEY AS COMPARED WITH OTHER SPECIES Clearance (1 /h/kg body wt.) Ref. Rhesus monkey Rhesus monkey, pretreated with disulfiram 3.55 0.35 Rat (Wistar) Mouse Gerbii Rabbit Man 11.0 25.6 12.5 2.74 2.02 7 6 6 6 6 SL 0415^0 35 Fig. 1, Metabolic elimination of vinyl chloride in the Rhesus monkey at different con centrations of atmospheric exposure. Different symbols represent different sets of ex periments with different animals. disulfiram (Table I). A comparison of the metabolic clearance of VC in the Rhesus monkey with appropriate values for other species is given in Table I. In further experiments determinations of the rates of metabolic elimination of VC have been carried out at multiple ranges of atmospheric concentration of VC. In Fig. 1 the absolute rates of metabolism are plotted against the ex posure concentrations. First-order kinetics apply in the lower concentration range, up to 200--300 ppm (solid line). At higher concentrations (broken line) the curve is non-linear and shows saturation characteristics, in agreement with findings in other species [4, 5, 7]. DISCUSSION Available data on rates of (first-order) metabolism of VC in different spe cies (Table I) have demonstrated that rats, mice and gerbils metabolize VC 5--12 times faster than humans. From this point of view these laboratory animals represent models of only limited validity for man. Rhesus monkeys are closer to man, as indicated by (first-order) metabolic rates of VC. Gehring et al. [5], on the basis of rat experiments, calculated a risk of angiosarcoma in man after a 35-year exposure to 1 ppm VC (8 h/day; 5 days/ week) of 1.5-1CT8. This calculation did not take into account the differences in metabolism of VC between rat and man. Such calculations may overemphasize the risk of low levels of VC in human population. 0415A1 36 The present data (Fig. 1) show that the inference from rat experiments [4, 5, 7] that metabolism of VC is a dose-dependent and saturable process, is valid also for the Rhesus monkey. The relative similarity of the pharma cokinetic behavior of VC in the lower concentration range between the Rhesus monkey and man (Table I) might indicate that a similar saturation phenomenon might occur in humans at higher exposures to VC. Compared with the maximal velocity of VC metabolism in the rat [7] of 110 pmol/h/ kg body weight, the maximal velocity is about 50 pmol/h/kg body weight in the Rhesus monkey (Fig. 1). ACKNOWLEDGEMENTS The authors thank the government of the state of Nordrhein-Westfalen for financial support. Thanks are especially due to Prof. Dr. G. Dotzauer (Direktor des Instituts fur Rechtsmedizin der Universitat zu Koln) for generous support and allowing access to his Rhesus monkey colony; thanks are also due to Dr. Sticht and Dr. Kaferstein. REFERENCES 1 S. Osterman-Golkar, D. Hultmark, D. Segerback, C.J. Calleman, R. Gothe, L. Ehrenberg and C.A. Wachtmeister, Alkylation of DNA and proteins in mice exposed to vinyl chloride, Biochem. Biophys. Res. Commun., 76 (1977) 259--266. 2 T. Green and D.E. Hathway, Interactions of vinyl chloride with rat liver DNA in vivo, Chem.-Biol. Interact. 22 (1978) 211--224. 3 R.J. Laib, and H.M. Bolt, Formation of 3,N4-ethenocytidine moieties in RNA by vinyl chloride metabolites in vitro and in vivo, Arch, Toxicol., 39 (1978) 235--240. 4 P.J. Gehring, P.G. Watanabe and C.N. Park, Resolution of dose-response toxicity data for chemical requiring metabolic activation: Example--vinyl chloride, Toxicol. Appl. Pharmacol., 44 (1978) 581-591. 5 P.J. Gehring, P.G. Watanabe and C.N. Park, Risk of angiosarcoma in workers exposed to vinyl chloride as predicted from studies in rats, Toxicol. App. Pharmacol., 49, (1979) 15-21. 6 A. Buchter, H.M, Bolt, J.G. Filser, H.W. Goergens, R.J. Laib and W. Bolt, Pharmakokinetik und Karzinogenese von Vinylchlorid. Arbeitsmedizinische Risikobeurteilung. Verhandlungen der Deutschen Gesellschaft fur Arbeitsmedizin, Vol. 18, Gentner Verlag, Stuttgart, 1978, pp. 111-124. 7 J.G, Filser, and H.M. Bolt, Pharmacokinetics of halogenated ethylenes in rats. Arch. Toxicol., 42 (1979) 123-136. 8 H.M., Bolt, H, Kappus, A. Buchter, and W. Bolt, Disposition of l,2-14C-vinyl chloride in the rat, Arch. Toxicol., 35 (1976) 153--162. SL 041542 Journal of Toxicology and Environmental Health 6(1980):5-6 CHEMICAL HAZARDS IN THE PLASTICS INDUSTRY H. Vainio, P. Pfaffli, A. Zitting Department of Industrial Hygiene and Toxicology, Institute of Occupational Health, Helsinki, Finland Since continuing technical development of new processes and products in the plastics industry must be expected in the years to come, it is increasingly essential to work toward the toxicity testing of new chemicals. The many untested and suspected chemicals used in the field of plastics and synthetic elastomers demonstrate the importance of control of both the occupational environment and the distribution of such chemicals from occupational sources, in the plastics processing industry it is necessary to evaluate possible health hazards of the fumes from plastics at high temperatures. INTRODUCTION The annual production of monomers and polymers in the plastics and elastomers industry over the past 30 yr has greatly increased (Fig. 1), In 1977, three countries-the United States, West Germany, and Japan--accounted for more than 60% of the total plastics production worldwide (Table 1). As far as the per capita use of plastics in different countries is concerned, Finland is first, using 92 kg per person in 1977 (Table 2). Plastic materials have an extremely wide range of uses, and thus humans are very likely to be exposed to them both occupationally and through air, water, and food. Furthermore, there is close physical contact with manufactured products used in packaging, consumer products, construction materials, transport applications, textile fibers for clothing and furnishings, rubber goods, adhesives, insulation, electronic and electrical products, paints, etc. (Fishbein, 1979). Polymeric materials were originally thought to be biologically inert. It must be borne in mind, however, that the biological effects of the plastic may include those of the monomer, of low-molecular-weight oligomers, or of additives such as plasticizers, stabilizers, curing agents, and catalysts. Thermal degradation of a polymer may take place when the material is placed or handled at high temperatures, producing additional risks of worker exposure to these chemicals. PRODUCTION HAZARDS OF PLASTICS The number of plastic materials is large and the list is growing. The large number of processes by which plastics can be produced is a further complication. However, nearly all plastics can be classified into two groups: thermosetting materials and thermoplastic materials. Thermosetting plastics are cured, set, or hardened into a permanent shape. This curing is an irreversible reaction and usually occurs under heat and pressure. Thermoplastics are not cured or set under heat; when heated, they soften to a fluid state. On cooling in a mold, thermoplastics harden and take the shape of the mold. Supported by a grant from the Swedish Work-Environment fund (241 A-C/77). 1179(259] Copyright 1980 by Hemisphere Publishing Corporation SL 041543 1180[260] PLASTICS PRODUCTION (10 tons) SO 40 30 H, VAINIO ET AL 10 - 1900 1920 1^40 1960 FIGURE 1. Plastics production worldwide. 1980 In the three main chemical processes yielding polymers-polymerization, addition, and condensation-many additives and intermediates are physiologically active as irritants and sensitizers of the skin and the respiratory system (Table 3). Moreover, neurotoxic monomers such as methyl methacrylate and acrylamide have been identified. Neurotoxic organic phosphates are widely used as plasticizing additives. Ever since vinyl chloride was recognized as a human carcinogen (Creech and Johnson, 1974), there has been increased concern about a number of the monomers used in the manufacture of synthetic polymers in the plastics and rubber industries. The common structural feature of these monomers involves either olefinic or aromatic double bonds, which can be metabolically oxidized to yield oxiranes or arene oxides. Because these an potentially reactive mutagenic or carcinogenic intermediates, long-term toxicity of th? monomers from which they derive is suspected. Many of the monomers studied have proved TABLE 1. Plastics Production in the World in 1977 Country Percentage of total production United States West Germany Japan U.S.S.R. France Italy United Kingdom Spain Other 34.5 14.6 13.6 7.2 6.2 5.8 5.6 2.3 10.1 99.9 Q From NOWEA Presse-lnformationen (1979). SL 041544 CHEMICAL HAZARDS IN THE PLASTICS INDUSTRY TABLE 2. Use of Plastics in 1977 Country Amount per capita (kg) Finland West Germany Sweden Austria United States Switzerland France United Kingdom Japan 92 89 79 71 64 60 48 44 41 "From NOWEA Presse-lnformationcn (1979). 1181[261] TABLE 3. Main Classes of Plastics, Basic Components, and Occupational Occurrence'7 Polymer Component Occupational occurrence of active components Polyvinyls6 Polyurethane" Polyethylene6 and propylene Polyacrylics6 Polyamides (nylon 66) Polytetrafluoroethylene Polystyrene6 Polyesters (saturated6) Polyesters (unsaturated") Phenoplasts" and aminoplasts" Acrylonitrile-butadiene' styrene6 Epoxy resins" Vinyl chloride Diisocyanates and polyhydroxy compounds Ethylene and propylene Acrylic acid, methyl meth acrylates, acrylonitrile, and acrylamide Adipic acid and hexamethylenediamine or caprolactam (nylon 6) - Tetrafluoroethylene Styrene (vinyl benzene) Alkyls, MAArf, and polyalcohols (glycerol) MAA6 or PAA" and ethylene glycol in styrene Polycondensates of phenols and aldehydes, urea and aldehydes Mutagenic, carcinogenic Diisocyanatcs powerful respiratory irritants and sensitizers Moderately narcotic, toxicity? Methyl methacrylate and acrylamide neurotoxic, acrylo nitrile mutagenic and carcinogenic Diphenyls used in heat transfer can be neurotoxic and carcinogenic "Polymer fume fever" Mutagenic MAA produced by oxidizing toxic solvent benzene Fiber production--dimethylterephthalate and a diol (ethylene glycol) dissolved in styrene Formaldehyde mutagenic, carcinogenic? All mutagenic Cpichlorhydrin and polyhydroxy compounds, bisphenol A Mutagenic, carcinogenic? "Modified from Kay (1977). ^Thermoplastic, "Thermosetting. "Maleic acid anhydride. Phthaiic acid anhydride. SL 041545 1182(262) H. VAINIO ET AL, to be mutagens and/or carcinogens, but considerably more research is needed to evaluate the final health significance of these data (Table 4). A In the production of plastics, closed processes are usually employed, since many of th" components are gases or volatile liquids. The main occupational exposure to reactants and products probably occurs when reaction equipment is cleaned out. Since reactions of plastic components do not generally go to completion, residual components arc present, either occluded or dissolved, in the final products. Hence production workers bagging the finished plastic are probably exposed not only to plastic dust but also to gaseous monomers. Table 3 lists the main classes of plastics and examples of occupational occurrence of reactive components. The data in Table 5 indicate that there are toxicologically active components even among the auxiliary substances used in the manufacture of plastics. PROCESSING HAZARDS Plastics arc processed at temperatures high enough to produce a viscous product that permits the blending in of various auxiliary substances and allows for shaping, such as calendering to produce thin film and sheets. Thus there is a potential for exposure to gaseous and volatilized unreacted raw materials, auxiliary substances added before molding, and decomposition products. Plastics partially degrade under the influence of agents such as ultraviolet light, oxygen, ozone, sulfur dioxide, nitrogen oxides, etc. They can also be broken down rapidly by high temperatures. The processes, temperatures, machinery, and raw materials vary greatly in the plastics processing industry and the nature and amounts of different thermal decomposition products depend on all these parameters. The mechanisms of thermal degradation are often very complicated, leading to a wide variety of products that can be emitted to the workroom air. Some examples of thermal degradation products that can arise from plastics at temperatures of 150-500C are given in Table 6. Among these are a number of known mutagens and/or carcinogens (e.g., benzene and styrene). Reports on exposure levels of thermal degradation products in the processing industry arc, however, lacking, so that no definitive conclusions TABLE 4. Mutagenicity and Carcinogenicity of Some Monomers and Plastics Chemicals0'* Mutagenicity Chromosomal aberrations Carcinogenicity Chemical compound Salmonella Animals Humans typhimurium Drosophila (bone marrow) (lymphocytes) Animals Humans Acrylonitrile Aromatic epoxy resins Chloroprcne Epichlorohydrin Styrene Vinyl bromide Vinylidene chloride Vinyl chloride + + + + + + + + NDC ND + + + ND ND + ND ND + ND + ND ND ND - +7 ND 7 ND + 77 + +7 + 77 ND + ND ND + ND + ++ "From Hemminkiet al. (1979), Bartsch et al. (1979), IARC (1979), Lee et al. (1978), NCI (1979). "Sufficient evidence for mutagenicity or carcinogenicity in animals is indicated by a plus sign; limited evi dence Is indicated by a question mark. cNo data. sc CHEMICAL HAZARDS IN THE PLASTICS INDUSTRY 118 3{ 263] TABLE 5. Auxiliary Substances Used in Plastics Manufacture and Prucessing0 Type Example Occupational occurrence of active substances Fillers and reinforcements Plasticizers Fibers of asbestos, carbon black, and glass Dialkyl phthalates, alkyl or aryl' phosphates Colorants--dyes and pigments Solvents Stabilizers Transparent organic dyes, opaque pigments-chrome yellow, titanium dioxide Toluene, benzene, ethyl and amyl acetates, chlorinated hydrocarbons Dialkyl tin esters; lead soaps and salts; Ba, Cd, Zn soaps Antioxidant stabilizers Butylated hydroxytoluene, dilauryldithiopropionate hydrazides, triazoles Ultraviolet-absorbing Benzophenones, triazoles, stabilizers organonickel compounds Biological preservatives Copper quinolinolate, organomercurials, tributyltin oxide Foaming agents Lubricants and flow control agents Azoisobutyronitrile, chlorinated hydrocarbons, hydrogen peroxide Ca, Zn, and Pb stearates and petroleum wax Flame retardants Catalysts and accelerators Antistats Organophosphates, organohalogens with antimony oxide synergist Organic peroxides, alkylaluminum compounds, cobalt naphthenate Quaternary ammonium com pounds, organic phosphates, stannous chloride As dust at addition; may run 10*15% in finished product; asbestos carcinogenic Low-volatility heavy solvents to increase moldability of plastics; content to 60%; some skin irritation, enzyme inhibitors, and ncurotoxins Organic dyes added in volatile solvents that are narcotic and skin-defatting; pigment dust may occur on addition or mechanical stress Provide milieu for some polymerizations; volatile; fat-soluble; hepatotoxic or leukemogenic (benzene) To prevent heat degradation of polyvinyl chloride; stabilizer content up to 10%; hazard undetermined To counteract atmospheric oxidation of unsaturated double bonds (e.g., in polyesters); occupational hazard undetermined To protect against oxidation; hazard undeter mined but organonickel exposure potentially dangerous No evidence that these preservatives constitute an occupational hazard in plastics, but they have demonstrated toxic potential Release vapor during setting of plastics; in atmosphere during foaming; released from bubbles by mechanical stress; toxic Interpose between linear macromolecules; can be used only in small quantities; occupational hazard undetermined Compounds of low volatility but high toxicity; hazard undetermined Ail low-volatility compounds; peroxides present eye hazard (splashing); Al compounds explosive Low-volatility compounds; occupational hazard undetermined Modified from Kay (1977). about health hazards can be given. These evaluations are needed because of the increasing number of workers in the expanding processing industry. Below we will discuss in more detail the mechanisms of thermal degradation and the evolution of possible degradation products. Monomers The appearance of monomers among thermal degradation products of plastics depends on the degradation mechanism of the plastic. Thermal degradation of polymers can be SL 041547 TABLE 6. Thermal Degradation Products of Some Polymers In Air at 150-500 Polymer Monomer Aliph atic hydrocarbons, C, -Cfr ... C/j (alkanes, alkenes, alkadienes) Aromatic hydrocarbons, c.-c,... Cl0 Oxidized aliphatic compounds, c.-c. Oxidized aromatic compounds, c.-c, Aliphatic nitriles Aromatic Haiogenated nitriles hydrocarbons Polyolefins (+)C 444 '(+) 44 - -- - Polyethylene Polypropylene Polystyrene ++++ + 44 4 +4 -- Copolymers ABS, SANrf +++ + 4 44 + 4- + 4 4 - SBe Polyacrylonitrile ++++ 4+ 44 + 44 + -- - ++ {*) Polyvinyl chloride Polyurethanes <+) 4 4 44 + 4 (benzene) 44 4 ++ H - - (*) (+> Gases +++ (CO) Aerosols +++ () (CO) (+) (CO) +(HCN) + (CO) + (CO) +(HCN) +** (co) ++++ (HCI) +++(CO) ++(HCN) + (NHJ 44 + 4 +4+ +4+ +4 +4 "From Boettner et al. (1973) and Hoff (1977). ^The proportional concentration among the decomposition products is indicated, with + denoting the iowest and ++++ the highest. c(+) denotes probable occurrence of trace amounts. ^ABS, copolymer of styrene with acrylonitrile and butadiene; SAN, copolymer of styrene with acrylonitrile. eSB, copolymer of styrene with butadiene (high-impact polystyrene). SL 041548 > CHEMICAL HAZARDS IN THE PLASTICS INDUSTRY 1185[265] divided into two general categories: random chain scission and depolymerization (Conley, 1970). The scission occurs at random points along the chain, leaving fragments of different molecular weights. It can be assumed that practically no or only small amounts of the monomer are liberated in this type of thermal degradation. This is the case with, for example, polyolefins and polyvinyl chloride. The second type of degradation is depolymerization, where monomer units are released (e.g., polystyrene, polymethyl methacrylate). Depending on the composition of the polymer, both of these mechanisms may also occur simultaneously. Aliphatic and Aromatic Hydrocarbons Aliphatic and aromatic hydrocarbons are released from plastics by the random scission mechanism. The aliphatic hydrocarbons appearing in the gaseous phase are relatively low-molecular-weight compounds, having 0-2 double bonds. The aromatic hydrocarbons are alkyl benzenes. The alkyl group can also contain double bonds. Even benzene (C6H4) is reported to develop (e.g., from polyvinyl chloride) in significant amounts (Boettner et al., 1973; Hoff, 1977). Oxidized Aliphatic and Aromatic Compounds The action of oxygen during thermal degradation causes the most important group of secondary reaction products. The reaction is oxidation of free hydrocarbon radicals, with peroxy radicals, hydroperoxides, and peroxides acting as intermediates (Conley, 1970), The end products of oxidation are acids, ketones, and aldehydes. After oxidation of lowmolecular-weight aliphatic hydrocarbons, formic acid, acetic acid, propionic acid, acetone, methyl ethyl ketone, formaldehyde, acetaldehyde, and acrolein are generated. Aromatic hydrocarbons produce similar compounds, including benzoic acid, cinnamic acid, aceto phenone, benzaldehyde, and cinnamaldehyde. Other oxygen-containing compounds (e.g., alcohols) can appear among thermal degradation products if the plastic exposed to heat is based on polyols or polyethers. Nitriles Both aliphatic and aromatic nitriles come from plastics that contain nitrogen, and especially nitrile groups. Halogenated Hydrocarbons Halogenated hydrocarbons are generated from halogen-containing plastics, such as polyvinyl chloride and polytetrafluoroethane (Teflon). Gases Carbon monoxide and carbon dioxide are common oxidation products. The amounts seem to be highest when plenty of low-molecular-weight hydrocarbons are produced. Hydrogen chloride is released from polyvinyl chloride at moderately low temperatures before the beginning of hydrocarbon chain scission. Nitrogen-containing plastics produce hydrogen cyanide and, at high temperatures, nitrogen oxides. Aerosols The aerosol phase contains dimers, trimers, and other oligomers, as well as other fragments of polymer chains having the same elementary composition as the plastic itself. New double bonds and oxidized functional groups joined to molecules may also appear. 0A15A9 SL 1186(266] H. VAINIO ET AL. Free Radicals When oxidation reactions go through radical formation, the thermal degradation products may contain free radicals, hydroperoxides, and peroxides. Free alkoxy radicals, which exist long enough to reach the breathing zone of workers, have been detected among the thermal degradation products of polyethylene and polystyrene (P. Pfaffli et al., in preparation). REFERENCES Bartsch, H., Malaveille, C., Barbin, A., and Planche, G. 1979. Mutagenic and alkylating metabolites of haloethylenes, chlorobutadienes and dichlorobutanes produced by rodent or human liver tissues. Evidence for oxirane formation by P450-linked microsomal monooxygenases. Arch. Toxicol. 41:249-279. Boettner, E. A., Ball, G. L., and Weiss, B. 1973. Combustion Products from the incineration of Plastics. Springfield, Va.: National Technical Information Service. Conley, R. T. 1970. Thermal Stability of Polymers, vol. 1. New York: Dekker. Creech, ). L'. and Johnson, M. N. 1974, Angiosarcoma of the liver in the manufacture of polyvinyl chloride. /. Occup. Med. 16:150-151. Fishbein, L. 1979. Potential Industrial Carcinogens and Mutagens. Amsterdam: Elsevier. Hcmminki, K,, Sorsa, M., and Vainio, H. 1979. Genetic risks caused by occupational chemicals. Scand. I. Work Environ. Health 5:307-327, Hoff, A. 1977. Termiska sonderfallsprodukter frJn plaster (Litteraturstudie). Inst, for Polymeriteknologi, Kungl. Tekniska Hogskolan, Stockholm. IARC. 1979. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans: Some Monomers, Plastics and Synthetic Elastomers, and Acrolein, vol. 19. Lyon: International Agency for Research on Cancer. Kay, K. 1977. In Handbook of Physiology, Sect. 9: Reactions to Environmental Agents, ed, D. H. K. Lee, pp. 181-191. Bethesda, Md,: American Physiological Society. Lee, C. C., Bhandri, ]. C., Winston, ). M., House, W. B., Dixon, R. L., and Woods, J. S. 1978. Carcinogenicity of vinyl chloride and vinylidene chloride. /. Toxicol. Environ. Health 4:15-30. NCI. 1979. Bioassay of Styrene for Possible Carcinogenicity. DHEW Publ. (NIH) 79-/74/. Bethesda, Md.: National Cancer Institute. NOWEA Presse-lnformationen. 1979. International Trade Fair Plastics + Rubber, Dusseldorf, Ocl 10-17. 041550 SL