home edit2 whole TSD November 2002 PDF format - OEHHA

In view of the data indicating a deficit of smokers in this cohort compared to the general population, the
baseline SMR for lung cancer would have been reduced 30%.
It is unknown, however, whether the smoking histories of the 49% sample were representative of the
cohort as a whole, and whether the histories themselves were biased, since they were collected
retrospectively. While smoking may have confounded the relationship between cadmium and lung
cancer, it is unlikely that smoking was responsible for all of the excess. Furthermore, if the smoking
habits in this cohort were correctly reported, i.e., if the observed deficit of smokers was real, then the
excess of lung cancer deaths is larger than originally calculated. In other words, confounding due to
smoking did not create the appearance of a nonexistent carcinogenic effect from cadmium; rather, the
confounding reduced the apparent magnitude of cadmium's carcinogenicity.
Table 4: Technique Used to Adjust for Cigarette Smoking (Thun et al., 1986)
Percent of Population, 1965
Nonsmokers 3
(1X)
Population
Moderate 1
Smokers
(10X)
Heavy 2
Smokers
(20X)
Rate Ratio of
Overall Population
Relative to
Nonsmokers
Rate Ratio Relative
to U.S.
Exposed 48.4% 40.8% 10.8% 6.724 0.70
U.S. 27.1% 53% 20% 9.571 1.0
1. 1-24 cigarettes/day
2. 25+ cigarettes/day
3. The numbers in parentheses refer to the relative risk for lung cancer associated with each
level of smoking.
4. Usable information available on 250 persons hired after 1926.
(b) Arsenic
The plant employing the workers in this cohort refined cadmium metals and compounds from 1926
onwards. Between 1918 and 1925 it had functioned as an arsenic smelter. Therefore, the analysis by
Thun et al. excluded workers employed prior to January 1, 1926. (For those employed prior to 1926
the lung cancer SMR was 714). Nevertheless, it is possible that residues of arsenic contributed to the
lung cancer excess for those first employed in 1926 or later.
To estimate the possible contribution of arsenic to lung cancer in this cohort, Thun et al.:
(1) identified the departments and job categories which were likely to have involved continued
exposure to arsenic;
(2) calculated the proportion of person-years spent in areas with probable arsenic exposure based
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