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Also, a trend was observed correlating increased cancer risk with increased severity of exposure.
Workers in the moderate exposure group with a probable latent period of at least 15 years exhibited 13
cases of cancer of all types vs. 5.5 expected, and 5 cases of lung cancer vs. 1.4 expected (p < 0.05).
One potential confounding factor in this study is the lack of controls for tobacco smoking. US EPA
(1983) investigated the possible impact of smoking on lung cancer incidence in the O’Berg (1980)
study. DuPont provided additional data on 32 of 36 cancer cases reported on in the plant under study
(some cases were not in the study cohort) and on smoking data for a matched group of non-cancer
cases. Of the 32 cancer cases for which smoking data was available, 22 were cancer types other than
lung, and 16 of the non-lung cancer cases (73%) were smokers. Of the matched noncancer controls,
25 (69%) were smokers. US EPA estimated that 70% of the plant population were smokers and 30%
nonsmokers, and of the smoker population, 50% were “moderate” smokers and 20% were “heavy”
smokers. Based on the assumption that the relative risk of lung cancer for nonsmokers, moderate, and
heavy smokers is 1, 10 and 20, respectively, US EPA adjusted the number of expected lung cancer
cases in the study cohort to reflect the smoking prevalence data. The number of expected lung cancer
cases after adjustment for smoking is 1.61 cases. This is about 15% higher than the 1.4 cases expected
without considering smoking differences; however, this adjustment did not substantially alter the
significance of the increased prevalence of lung cancer in the workers exposed to acrylonitrile. US EPA
(1983) concluded that the observations by O’Berg (1980) of a statistically significant excess of lung
cancer in acrylonitrile-exposed workers constitutes significant evidence that acrylonitrile is likely to be a
human carcinogen.
A followup to the O’Berg (1980) study was conducted by O’Berg et al. (1985). Observations of
cancer incidence and mortality for the study cohort of 1345 DuPont workers exposed to acrylonitrile
was extended through 1981 for mortality and through 1983 for cancer incidence. Exposed workers
demonstrated 43 cases of all types of cancer, with 37.1 expected. Of these cases, 10 were lung cancer
versus 4.4 expected. These rates were in excess but were not statistically significant. Additionally,
prostate cancer rates were significantly elevated, with 6 cases observed compared to 1.8 cases
expected (p < 0.05).
Theiss et al. (1980) (reviewed by US EPA, 1983) conducted a cohort mortality study of 1469 workers
from 12 factories owned by the BASF company in the Federal Republic of Germany (FRG). BASF
purchased acrylonitrile during the study period in order to produce styrene-acrylonitrile and
acrylonitrile-butadiene-styrene polymers in addition to organic intermediate products. Processing
methods differed between factories, and worker exposure data was not available. The study population
was defined as all workers employed for over 6 months in acrylonitrile processing from the time of first
use of acrylonitrile (approximately 1956) to the study cut-off date of May 15, 1978. The cohort
included 1081 German workers and 338 workers of other nationalities. Followup was 98% complete
on the German workers, but only 56% complete on the foreign workers. Expected deaths were
calculated from mortality rates for the city of Ludwigshafen, the state of Rheinhessen-Pfalz, and the
FRG as a whole. An elevated risk of cancer (all types) mortality was noted in the study cohort (27
observed, 20.5 expected based on FRG mortality rates). The study cohort also demonstrated a
significantly elevated risk of lung cancer (11 observed, 5.65 expected based on FRG rates, p < 0.05;
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