Can lung cancer risk among nickel refinery workers be explained by occupational exposures other than nickel?

Exposures in nickel refineries represent complex chemical mixtures, but only the effect of nickel has been evaluated quantitatively in epidemiologic studies of nickel workers.

For a Norwegian refinery, time- and department-specific exposure estimates were developed for arsenic, sulfuric acid mists, and cobalt in air on the basis of personal measurements and chemical data on raw materials and process intermediates. Exposure to asbestos, as well as employment in high-risk occupations outside the refinery, were assessed. We conducted a case-control study nested in a cohort of refinery workers, with 213 cases (diagnosed 1952-1995) and 525 age-matched controls. We analyzed lung cancer risk, adjusted for smoking, by cumulative exposure and duration of work.

There was a substantial association between cumulative exposure to water-soluble nickel and lung cancer risk. Weaker effects were suggested for exposure to arsenic at the refinery and for occupational exposures outside the refinery for 15 years or more. No detectable excess risk was found for refinery exposure to asbestos or sulfuric acid mists, and no dose-related increase in risk was seen from cobalt.

Exposure to water-soluble nickel remained the most likely explanation for the excess lung cancer risk in the cohort. Other occupational exposures did not confound the strong dose-related effect of nickel to any appreciable degree.