IARC MONOGRAPHS ON THE EVALUATION OF CARCINOGENIC ...

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IARC MONOGRAPHS VOLUME 82
In a plant in the USA where acrylic ester–styrene copolymers [wrongly called polystyrene
by the authors] were produced, concentrations in the breathing zone in 50
samples ranged from none detected (less than 1 ppb [4.3 μg/m 3 ]) to 19.8 ppm
[84 mg/m 3 ], with an average of about 0.6 ppm [2.5 mg/m 3 ]; the highest concentrations
occurred during styrene unloading operations (Samimi & Falbo, 1982).
The numerous other substances to which workers may be exposed in these processes
include 1,3-butadiene, acrylonitrile, acrylates, acrylic acid, α-methylstyrene (meta-vinyltoluene),
4-vinylcyclohexene, toluene, benzene, ammonia, formaldehyde, colourants and
a variety of solvents (Ott et al., 1980; Samimi & Falbo, 1982; National Institute for
Occupational Safety and Health, 1983). Accelerators are chemical compounds that
increase the rate of cure and improve the physical properties of natural and synthetic
rubbers, including SBR. Thiuram sulfides and salts of dialkyldithiocarbamic acids, including
dimethyldithiocarbamate, are used as vulcanization accelerators. Sodium and
potassium dimethyldithiocarbamates are used as modifiers in emulsion polymerization
(Schubart, 1987; Lattime, 1997).
(c) Processing of styrene-based polymers
Styrene was measured as a thermal degradation product in the air of a Finnish factory
during the processing of polystyrene, impact polystyrene and acrylonitrile−butadiene−
styrene (ABS) resins. The mean concentrations (6 h) were 0.4, 0.1 and 0.06 mg/m 3 ,
respectively (Pfäffli, 1982). Personal 8-h samples taken in 1978, 1979 and 1980 in
companies in the USA where polystyrene and ABS moulding was performed contained
[17–285 mg/m 3 ] (Burroughs, 1979); 1.4–3.2 mg/m 3 (Belanger & Elesh, 1980) and
< 0.01 mg/m 3 (below the limit of detection) (Ruhe & Jannerfeldt, 1980).
Styrene is one of the volatile organic compounds released during extrusion and
vulcanization of SBR. Rappaport and Fraser (1977) reported styrene concentrations of
61–146 ppb [0.3–0.6 mg/m 3 ] in the curing area of the press room of a company manufacturing
passenger-car tyres. Area samples taken in the vulcanization and extrusion
areas of shoe-sole, tyre retreading and electrical cable insulation plants contained styrene
at concentrations of 2–500 μg/m 3 (vulcanization) and 0–20 μg/m 3 (extrusion) (Cocheo
et al., 1983). A more complete description of the work environment encountered in the
rubber products manufacturing industry may be found in a previous monograph (IARC,
1982).
(d ) Manufacture of glass fibre-reinforced polyester products
Occupational exposure to styrene is most extensive, with respect to number of
workers and levels of exposure, in the fabrication of objects from glass fibre-reinforced
polyester composite plastics, such as boats, tanks, wall panels, bath and shower units and
automotive parts (National Institute for Occupational Safety and Health, 1983). Styrene
serves as a solvent and a reactant for the unsaturated polyester resin, in which it constitutes
about 40% by weight. In the open mould process, a releasing agent is usually
applied to the mould, a first coat containing pigments (gel coat) is applied, then