IARC MONOGRAPHS ON THE EVALUATION OF CARCINOGENIC ...

model indicated that absorbed styrene 7,8-oxide contributed 3640 times more of this
compound to the blood than an equivalent amount of inhaled and metabolized styrene.
4.2 Toxic effects
4.2.1 Humans
STYRENE 493
Exposure to styrene has been reported to cause irritation of the eyes, throat and respiratory
tract (Lorimer et al., 1976, 1978). Subjective health complaints were not reported
in the glass fibre-reinforced plastics industry with concentrations of styrene below
105 mg/m 3 (Geuskens et al., 1992).
There are a number of reports of central and peripheral nervous system effects in
exposed workers. Some studies have reported decreased nerve conduction velocities in
workers exposed to styrene (Lilis et al., 1978; Rosén et al., 1978; Cherry & Gautrin,
1990; Murata et al., 1991; Štetkárová et al., 1993), whereas others have shown no
changes at styrene concentrations below 100 ppm [430 mg/m 3 ] (Edling & Ekberg 1985;
Triebig et al., 1985). Electroencephalographic (Seppäläinen & Härkönen, 1976;
Matikainen et al., 1993), dopaminergic (Mutti et al., 1984a; Arfini et al., 1987;
Checkoway et al., 1992, 1994; Bergamaschi et al., 1996, 1997), functional (Lindström
et al., 1976; Cherry et al., 1980) and psychiatric anomalies (Flodin et al., 1989; Edling
et al., 1993) were observed in styrene-exposed workers compared with controls. Most of
these effects were observed at concentrations of styrene of about 100 ppm [430 mg/m 3 ],
although memory and neurobehavioural disturbances were noted at styrene concentrations
ranging from 10 to 30 ppm [43–130 mg/m 3 ] and above (Flodin et al., 1989; Letz
et al., 1990; Edling et al., 1993; Jégaden et al., 1993; Tsai & Chen, 1996; Viaene et al.,
2001).
Thresholds for hearing were unchanged in workers exposed to styrene concentrations
less than 150 mg/m 3 . However, a comparison within the group of styreneexposed
workers (least exposed versus most exposed) showed a significant difference in
hearing thresholds at high frequencies (Muijser et al., 1988). In a group of 18 workers
exposed for 6–15 years to styrene at levels below 110 mg/m 3 , seven workers showed
disturbances in the central auditory pathways (Möller et al., 1990). Morioka et al. (1999)
found a reduction in the upper limit of hearing in workers occupationally exposed to
organic solvents. This effect was dose-dependent and correlated with the concentration
of styrene in the breathing zone of the workers and with the amount of mandelic acid in
urine. In a group of 299 workers in the glass fibre-reinforced plastics industry, there was
no evidence for an effect of exposure to styrene on hearing acuity when both noise and
lifetime exposures to styrene were accounted for (Sass-Kortsak et al., 1995).
Colour vision was found to be impaired in styrene-exposed workers in a number of
studies (Gobba et al., 1991; Fallas et al., 1992; Chia et al., 1994; Campagna et al., 1995;
Eguchi et al., 1995; Campagna et al., 1996; Gobba, 2000). Solvent-induced loss of
colour vision is indicative of changes in neural functioning along optic pathways. A