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expressed as cumulative mg-days/m 3 . Varner (1983) reported the lung cancer PMR (proportional
mortality ratio) to be elevated. Sorahan and Waterhouse (1983), in two separate analyses, found an
elevated risk of respiratory cancer. The first analysis was based on the SMR and included all potentially
exposed workers. The second analysis used the regression method of life tables (RMLT) and assessed
exposure by cumulative years employed in a (1) high exposure job or (2) high or moderate exposure
job or (3) high or moderate exposure job excluding welding. Measures (2) and (3) resu1ted in a
significant effect of exposure on respiratory cancer, particularly for those with more than 30 years of
follow-up.
Table 1: Association Between Cadmium Exposure and Respiratory Cancer Mortality
Authors SMR Significant at p < 0.05
a
Sorahan and Waterhouse 1983 127 Y
Lemen et al., 1976 235 Y
Thun et al., 1985 229 Y
Armstrong and Kazantzis 1983 126 a Y
Inskip et al., 1982 101 b N
Andersson et al., 1984 120 N
For workers with >10 years exposure in the "always low" category (the number of workers with
"ever medium" and "ever high" exposures was small).
b vs. SMR-55 for the unexposed town.
Heavier smoking among cadmium workers as compared to the general population could account for the
small but statistically significant SMR for lung cancer (126) observed by Armstrong and Kazantzis
(1983) for those exposed >10 years at the "always low" category. No smoking histories were
available. Sorahan and Waterhouse (1983) also lacked data on smoking, but they argue that smoking
was unlikely to have been a confounder for two reasons. First, their analysis showed an increasing
association with duration of employment, while smoking habits are unlikely to be well-correlated with
duration of employment. Secondly, deaths from other diseases of the respiratory system were not
elevated, as they would have been if the cohort had included a disproportionate number of smokers.
However, the effect of nickel hydroxide could not be disentangled from that of cadmium oxide in this
cohort.
The strongest evidence for cadmium-induced carcinogenicity in humans is the study conducted by Thun
et al. (1985). The characteristics of this study which make it particularly convincing are the quality of
the exposure data and the analysis of potential confounding. Since the quantitative results of this study
constituted the basis for the DHS risk assessment of cadmium, a full description of this study is
presented below.
Thun et al. (1985) conducted a follow-up of the report by Lemen et al. (1976), who had found an
increase in mortality from respiratory and prostate cancer and from nonmalignant lung disease in a
cohort of cadmium smelter workers. Thun et al. (1985) expanded the cohort and extended the follow-
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