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f, I ft * Jcurnal 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 6096 of the total plasticsproduction 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 101662 1180(260] PLASTICS PRODUCTION ,i 4 i H. VAINIO ET AL. 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 are potentially reactive mutagenic or carcinogenic intermediates, long-term toxicity of the 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 From NOWEA Presse-lnformationen (1979). SL 101663 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-informationcn (1979). 1181[261] TABLE 3. Main Classes of Plastics, Basic Components, and Occupational Occurrence0 Polymer Component Occupational occurrence of active components Polyvinyls* Polyurethanec Polyethylene* and propylene Polyacrylics* Polyamides* (nylon 66) Polytetrafluoroethylene* Polystyrene^ Polyesters (saturated*) Polyesters (unsaturatedc) Phenoplasts1' and aminoplasts1* Acrylonitrile-butadienestyrene* Epoxy resinsc Vinyl chloride Diisocyanates and polyhydroxy compounds Ethylene and propylene Acrylic acid, methyl meth acrylates, acrylonitrile, and acrylamide Adipic acid and hexamethylene* diamine or caprolactam (nylon 6) Tetrafluoroethylene Styrene (vinyl benzene) Alkyls, MAA^, and polyalcohols (glycerol) MAA* or PAAf and ethylene glycol in styrene Polycondensates of phenols and aldehydes, urea and aldehydes Mutagenic, carcinogenic Diisocyanates 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 Epichlorhydrm and polyhydroxy compounds, bisphenol A Mutagenic, carcinogenic? 0Modified from Kay (1977). "Thermoplastic. ^Thermosetting, Maleic acid anhydride. ePhthalic acid anhydride. SL l0l664 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). In the production of plastics, closed processes are usually employed, since many of the 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 are 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 volatilised 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 Chemicals'^ Mutagenicity Chromosomal aberrations Carcinogenicity Chemical compound Salmonella Animals Humans typhimurium Drosophila (bone marrow) (lymphocytes) Animals Humans Acrylonitrile + NDC ND Aromatic epoxy resins 4- ND ND Chloroprcne ++ + Epichlorohydrin + ND Styrene -I- + + Vinyl bromide + ND ND Vinylidene chloride ND ND Vinyl chloride + ND _ +7 ND 7 ND f 7 ? + +7 + 7? NO + ND ND ND + ++ `'From Hemminki et al. (1979), Bartsch et al. (1979), I ARC (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. Si 101665 CHEMICAL HAZARDS IN THE PLASTICS INDUSTRY 1183(263] TABLE 5. Auxiliary Substances Used in Plastics Manufacture and Processing17 Type Example Occupational occurrence of active substances Fillers and reinforcements Plasticizers Colorants--dyes and pigments Solvents Stabilizers Antioxidant stabilizers Ultraviolet-absorbing stabilizers Biological preservatives Foaming agents Lubricants and flow control agents Flame retardants Catalysts and accelerators Antistats Fibers of asbestos, carbon black, and glass Dialkyi phthalates, alkyl or aryl phosphates 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 Butylated hydroxytoluene, dilauryldithiopropionate hydrazides, triazoles Benzophenones, triazoles, organonickel compounds Copper quinolinolate, organomercurials, tributyltin oxide Azoisobutyronitrile, chlorinated hydrocarbons, hydrogen peroxide Ca, Zn, and Pb stearates and petroleum wax 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-soiuble; 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 All low-volatility compounds; peroxides present eye hazard (splashing); Al compounds explosive Low-volatility compounds; occupational hazard undetermined 0 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 10ZSSS 1184(264] Polymer Polyolefins Polyethylene Polypropylene Polystyrene Copolymers ABS, SANd SBe Polyacrylonitrile Polyvinyl chloride Polyurethanes Monomer ++++ ++ w Aliphatic hydrocarbons, C, -Cfr ... C/7 (alkanes, alkenes, alkadienes) Aromatic hydrocarbons. C''* -Cl"re * * C'-jg +++ (benaene) Oxidised aliphatic compounds, Cj-C^ Oxidized aromatic compounds, C6-Ce Aliphatic ++ W Aromatic Halogenated nitriles nitrileshydrocarbons +++ (CO) (+) (CO) (+) (CO) + (HCN) + (CO) (+) t(CO) t (HCN) (+> +++ (CO) ++++ (HCI) M +++(CO) ++ (HCN) + (NH j} "From Boettner el al. (1973) and Hoff (1977). ^The proportional concentration among the decomposition products is indicated, with + denoting the lowest and ' t + * 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). CO tr< 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 (C6H6) 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 polycthers. 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. SL 101668 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.p Malavedle, 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: Oekker. 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. Hemminki, K,, Sorsa, M., and Vainio, H, 1979. Genetic risks caused by occupational chemicals. Soand. /. Worh Environ. Health 5:307-327. Hoff, A. 1977. Termiska sonderfallsprodukter frln plaster (Litteraturstudie). Inst, far 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, J, M., House, W. B., Dixon, R. L., and Woods, |. 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) 79-1741. Bethesda, Md.: National Cancer Institute. NOWEA Presse-lnformationen. 1979. International Trade Fair Plastics + Rubber, D'usseldorf, Oct. 10-17. SL lOX^69