IARC MONOGRAPHS ON THE EVALUATION OF CARCINOGENIC ...

STYRENE 447
successive layers of chopped and/or woven fibre glass are deposited manually or with a
chopper gun at the same time as the resin is sprayed or brushed on, and then the surface
is rolled. During lamination and curing, about 10% of the styrene may evaporate into the
workplace air (National Institute for Occupational Safety and Health, 1983; Crandall &
Hartle, 1985). Exposure to styrene in this industry has been extensively documented and
summarized in several reports (National Institute for Occupational Safety and Health,
1983; WHO, 1983; Pfäffli & Säämänen, 1993). Table 4 lists levels of occupational exposure
to styrene (personal breathing zone samples) reported in various countries in the
larger studies.
Among the biological monitoring methods available (Section 1.1.5(b)), measurements
of mandelic acid and phenylglyoxylic acid (see Section 4.1.1(c)) in urine are the
most commonly used biological indices of exposure to styrene. Table 5 gives the concentrations
of the classical biological indicators of exposure from various studies. Symanski
et al. (2001) examined the variation in urinary levels of mandelic acid and phenylglyoxylic
acid among workers exposed to styrene in the reinforced plastics industry. Levels
of phenylglyoxylic acid varied less than those of mandelic acid, as did metabolite levels
expressed in terms of urinary creatinine concentration. Urinary metabolite levels were
highest for laminators and for samples collected at the end of the working week.
Several factors influence the level of styrene in air. The manufacture of objects with
large surface area, such as boats, truck parts, baths and showers, by the open-mould
process results in the highest exposure. Data from 28 plants producing reinforced plastics
products in the USA showed that the average exposure to styrene in open-mould
processes was two to three times higher than that in press-mould processes: 24–82 ppm
[102–350 mg/m 3 ] versus 11–26 ppm [47–111 mg/m 3 ] (Lemasters et al., 1985). In a
detailed survey of 12 plants making fibreglass in Washington State, USA, 40% of 8-h
samples contained more than 100 ppm [430 mg/m 3 ]. Chopper gun operators had the
highest exposure, followed by laminators and gel-coat applicators; boat-building
involved higher exposures than any other sector. For 11 plants, a relationship was seen
between level of exposure and the quantity of resin consumed per month per exposed
employee (Schumacher et al., 1981). Similar results were reported by Sullivan and
Sullivan (1986) in their survey of 10 plants in Ontario, Canada, who also noted that
although dilution ventilation and often auxiliary fans were used in almost all plants, there
was little use of local exhaust ventilation. This was also the case for boat construction in
the USA. Gel coaters have lower exposure because they generally work in ventilated
booths (Crandall & Hartle, 1985). The presence of flexible exhaust ventilation hoses was
reported to reduce styrene concentrations by a factor of two at a boat construction
company in Japan (Ikeda et al., 1982). So-called ‘low-styrene emission resins’ are in
theory promising for reducing exposure, but their potential to do so in the workplace has
not been sufficiently validated and they are not widely used (A.D. Little, Inc., 1981;
Sullivan & Sullivan, 1986; Säämänen et al., 1993).
An extensive data source on exposures to styrene in the styrene composites manufacturing
industry is the report of a study conducted in 1986 by Cal/OSHA (1986). This