Issues in the risk assessment of chromium.

Although hexavalent chromium is well established as a human carcinogen by the inhalation route, there are significant uncertainties in the quantitative estimation of cancer risk. One of the important uncertainties is the assumption that the carcinogenic potency, determined under conditions of occupational exposure where most workers were cigarette smokers, applies to the nonsmoking individual in the general population. There is substantial evidence that carcinogenicity is a function of the rate of cell turnover in the target tissue. The chromate worker would be expected to have a relatively high rate of cell proliferation in the bronchial mucosa due to airborne irritants and smoking. The potency of chromium might therefore be relatively high under conditions of occupational exposure. This problem in quantitative risk assessment applies equally well to another important indoor pollutant, radon.