IARC MONOGRAPHS ON THE EVALUATION OF CARCINOGENIC ...

STYRENE 501
The frequency of spontaneous abortions among women with definite or assumed
occupational exposure to styrene has been investigated. An early study suggested an
association between exposure to styrene and spontaneous abortions (Hemminki et al.,
1980), but several later investigations, by the same group and others, of greater
population size failed to confirm the association (see, e.g., Lindbohm et al., 1985). It is
possible to conclude that styrene is not associated with a major increase in the occurrence
of spontaneous abortions, but because of the relatively small study population sizes in all
of the investigations, the possibility of a small increase in risk cannot be excluded
(Brown et al., 2000).
There are only few studies on potential effects of exposure to styrene on birth weight.
One study suggested that exposure to multiple solvents, including exposure to styrene
levels above 80 ppm [340 mg/m 3 ], may be associated with around 4% reduced birth
weight; however, the difference was not statistically significant (Lemasters et al., 1989;
Brown et al., 2000).
Data regarding the effects of styrene on the menstrual cycle are conflicting.
Abnormalities in pituitary secretion in women exposed to styrene have been suggested
and may be connected with putative effects on the menstrual cycle (Brown et al., 2000).
In a recent study, exposure to aromatic solvents including styrene was associated with a
trend towards increased frequency of oligomenorrhoea (average menstrual cycle length,
> 35 days). Individually, exposure to styrene showed the greatest increase in odds ratio
among the solvents (1.7; 95% CI, 1.1–2.6) and this increase was statistically significant
(Cho et al., 2001).
One study (Jelnes, 1988) suggested an increase in sperm abnormalities in workers
exposed to high levels of styrene in the reinforced-plastics industry, but the data are weak
and no firm conclusions can be drawn (Brown et al., 2000). In a later study, semen
samples were collected from 23 workers during the first week of employment in the
reinforced-plastics industry and after six months of exposure to styrene and from 21 nonexposed
farmers. A significant decline in sperm density was seen during exposure to
styrene, whereas no decline was seen in the non-exposed men. No indication of an exposure–response
relationship was seen when individual changes in semen quality within
the group of reinforced-plastics workers were related to post-shift urinary mandelic acid
concentrations, controlled for change in potential time-dependent confounders.
However, the exposure gradient in the group was modest. The earlier finding of an
increase in sperm abnormalities was not corroborated by this study (Kolstad et al., 1999).
Among 1560 male workers in the reinforced-plastics industry in Denmark, Italy and
The Netherlands, 220 styrene-exposed workers and 382 unexposed referents who had
fathered a child were identified. The relationship between occupational exposure to
styrene of these men and time-to-pregnancy of their partners was investigated. No
consistent pattern of reduced male fecundity was found when the time to pregnancy was
related to work tasks that involved higher levels of exposure to styrene or for which
semiquantitative or quantitative measures of exposure to styrene were available. The
workers with high exposure levels showed a fecundity ratio of 1.1 (95% CI, 0.69–1.7).