Lung cancer mortality in a cohort of workers employed at a cadmium recovery plant in the United States: an analysis with detailed job histories.

OBJECTIVES: To identify and measure any relations between occupational exposure to cadmium compounds (oxide, sulphide, and sulphate) and the risk of mortality from lung cancer.
METHODS: The mortality experience of 571 male production workers from a cadmium recovery facility in the United States was investigated for the period 1940-82. All study subjects were first employed in the period 1926-69; they had all been employed for at least six months between 1 January 1940 and 31 December 1969. Newly abstracted detailed job histories for the period 1926-76 were combined with assessments of exposures to cadmium over time to develop individual estimates of cumulative exposure to cadmium (total exposure and exposures received both in the presence and absence of "high" exposures to arsenic trioxide). Poisson regression was used to investigate risks of mortality from lung cancer in relation to four concentrations of cumulative exposure to cadmium (< 400, 400-999, 1000-1999, > 2000 mg.m-3.days).
RESULTS: After adjustment for age attained, year of hire, and Hispanic ethnicity, there was a significant positive trend (P < 0.05) between cumulative exposure to cadmium and risks of mortality from lung cancer. Relative to a risk of unity for the lowest exposure category (first level), risks were 2.30 (95% confidence interval (95% CI) 0.72 to 7.36), 2.83 (95% CI 0.75 to 10.72), and 3.88 (95% CI 1.04 to 14.46) for the second, third, and fourth categories, respectively. Similar findings were obtained after adjustment for age only. Trends were more pronounced when employment histories were lagged first by 10 years and then by 20 years. A separate analysis examined the independent effects of exposure to cadmium received in the presence of high exposures to arsenic trioxide (mainly cadmium oxide) and exposures to cadmium received without such exposure to arsenic (mainly cadmium sulphide and cadmium sulphate). A significant trend for a risk of lung cancer was found only for exposures to cadmium received in the presence of arsenic trioxide.
CONCLUSIONS: Hypotheses which are consistent with the study findings include: (a) cadmium oxide in the presence of arsenic trioxide is a human lung carcinogen, (b) cadmium oxide and arsenic trioxide are human lung carcinogens and cadmium sulphate and cadmium sulphide are not (or they are less potent carcinogens), or (c) arsenic trioxide is a human lung carcinogen and cadmium oxide, cadmium sulphate, and cadmium sulphide are not. There were only 21 deaths from lung cancer available for this analysis and it is impossible to gauge which, if any, of these hypotheses are correct.