Background: An elevated risk of lung cancer among workers in chromate production facilities has previously been reported. This excess risk is believed to be the result of exposure to hexavalent chromium. There have been mixed reports about whether trivalent chromium exposure is also associated with an excess lung cancer risk. Previous studies of measured hexavalent chromium exposure and lung cancer risk have not examined cigarette smoking as a risk factor.
Methods: A cohort of 2,357 workers first employed between 1950 and 1974 at a chromate production plant was identified. Vital status of the workers was followed until December 31, 1992. Work histories of cohort members were compiled from the beginning of employment through 1985, the year the plant closed. Annual average exposure estimates, based on historical exposure measurements, were made for each job title in the plant for the years 1950-1985. These exposure estimates were used to calculate the cumulative hexavalent chromium exposure of each member of the study population. Following closure of the plant, settled dust samples were collected and analyzed for hexavalent and trivalent chromium. The trivalent/hexavalent concentration ratios in each plant area were combined with historic air-sampling data to estimate cumulative trivalent chromium exposure for each individual in the study cohort. Smoking status (yes/no) as of the beginning of employment and clinical signs of potential chromium irritation were identified from company records.
Results: Cumulative hexavalent chromium exposure showed a strong dose-response relationship for lung cancer. Clinical signs of irritation, cumulative trivalent chromium exposure, and duration of work were not found to be associated with a risk of lung cancer when included in a proportional hazards model with cumulative hexavalent chromium exposure and smoking. Age-specific data on cumulative hexavalent chromium exposure, observed and expected numbers of lung cancer cases, and person-years of observation are provided.
Conclusions: Cumulative hexavalent chromium exposure was associated with an increased lung cancer risk; cumulative trivalent chromium exposure was not. The excess risk of lung cancer associated with cumulative hexavalent chromium exposure was not confounded by smoking status. The current study offers the best quantitative evidence to date of the relationship between hexavalent chromium exposure and lung cancer. Am. J. Ind. Med. 38:115-126, 2000. Published 2000 Wiley-Liss, Inc.