IARC MONOGRAPHS ON THE EVALUATION OF CARCINOGENIC ...

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IARC MONOGRAPHS VOLUME 82
workers with less than five years of employment and was significantly increased among
workers after 15 years of follow-up (SMR, 1.6; 95% CI, 1.0–2.4).
Hodgson and Jones (1985) reported on 622 men who had worked for at least one year
in the production, polymerization and processing of styrene at a plant in the United
Kingdom between 1945 and 1974 who were followed until 1978. Of these, 131 men were
potentially exposed to styrene in laboratories and 491 in production of styrene monomer,
polymerization of styrene or manufacture of finished products. No measurements of
exposure were provided, but many other chemicals were present in the working
environment. Expected numbers of deaths were calculated on the basis of national rates.
There were 34 deaths (43.1 expected) among the 622 exposed workers. A significant
excess of deaths from lymphoma (SMR, 5.4; [95% CI, 1.1–16]; 3 deaths) was observed.
An analysis of cancer registrations for this population revealed an additional case of lymphatic
leukaemia, giving a total of four incident cases of lymphatic and haematopoietic
cancer, whereas 1.6 would have been expected from local cancer registration rates
[standardized incidence ratio (SIR), 2.5; 95% CI, 0.67–6.4]. In addition, three incident
cases of laryngeal cancer were found (0.5 expected; [SIR, 6.0; 95% CI, 1.2–18]).
2.2.2 Use of styrene in reinforced plastics
Okun et al. (1985) studied 5021 workers who had been employed in two reinforcedplastic
boat-building facilities in the USA for at least one day between 1959 and 1978.
On the basis of industrial hygiene surveys, 2060 individuals were classified as having
had high exposure to styrene, with means in the two facilities of 42.5 and 71.7 ppm [181
and 305 mg/m 3 ]. Of these, 25% had worked for less than one month, 49% had worked
for one month to one year and only 7% had worked for more than five years. There were
47 deaths in the high-exposure group (41.5 expected); no cases of lymphatic or haematopoietic
cancer were observed in the high-exposure group (approximately one expected)
or in the full cohort (4.2 expected).
Wong (1990) and Wong et al. (1994) reported on a cohort of 15 826 male and female
employees who had worked at one of 30 reinforced-plastics plants in the USA for at least
six months between 1948 and 1977. Workers were followed until 1989; vital status was
determined using Social Security Administration files, the National Death Index and the
records of credit agencies. A total of 307 932 person–years at risk were accumulated.
Expected numbers of deaths were based on national age-, gender-, cause- and yearspecific
death rates for whites, as no information was available on race. Exposure to
styrene was calculated using a job–exposure matrix that included work history and
current and past time-weighted average exposures. A total of 1628 (10.3%) members of
the cohort were found to have died, and death certificates were obtained for 97.4% of
them. The overall SMR was 1.08 (95% CI, 1.03–1.13) and the SMR from all cancers was
1.16 (95% CI, 1.05–1.27). Mortality from cancers at a number of sites was increased
significantly; the SMRs for these sites were: oesophagus, 1.9 (95% CI, 1.1–3.2; 14
deaths); bronchus, trachea and lung, 1.4 (95% CI, 1.2–1.6; 162 deaths); cervix uteri, 2.8