Airborne cadmium and carcinogenesis of the respiratory tract.

Exposure to airborne cadmium occurs mainly at the workplace. Significant exposure also occurs through smoking. Results of a recent epidemiologic study suggest that occupational inhalation of cadmium is connected with an increased lung cancer risk. This finding corroborates the high lung cancer incidence found among rats after chronic low-level exposure to cadmium chloride aerosols. Differences in the tumor sites, exposure conditions, and the pulmonary metabolism of cadmium between rodents and man make it difficult to extrapolate quantitatively from rats to humans. In contrast to the workplace, concentrations of cadmium in ambient air are very low, and the risk of lung cancer is probably very low, even for people living close to cadmium-emitting industries. The chemical form of inhaled cadmium appears to be important. While cadmium oxide and cadmium chloride seem to be equally toxic, cadmium sulfide exhibits a lower acute pulmonary toxicity. However, whether this is also true for carcinogenic effects is not known. Additional long-term inhalation studies with animals and further evaluation of epidemiologic studies are necessary to answer questions about the carcinogenic potency of cadmium compounds of different chemical form. As long as such results are not available, it is prudent to regard all cadmium compounds as having a carcinogenic potential.