Pulmonary carcinogenicity of cadmium by inhalation in animals

Although, the tumorigenic effect of cadmium after subcutaneous and intramuscular injection has been known since 1961, lung tumours after inhalation exposure were reported only more than 20 years later by Takenaka et al. (1983), using cadmium chloride aerosols. Based on these results, aerosols of cadmium sulfate, cadmium oxide and cadmium sulfide pigment were investigated for carcinogenic effects after inhalation exposure in rats, hamsters and mice. All the cadmium compounds tested appeared to have a very similar carcinogenic potency in the rat lung, whereas no exposure-related tumours occurred in hamsters and in mice only cadmium oxide seemed to increase the lung tumour rate. Subsequent analytical investigations of the aqueous suspension of cadmium sulfide used to generate the aerosol showed that it was soluble in water to some extent as a result of photo-oxidation. The exposure atmosphere therefore actually consisted of a mixture of sulfide and sulfate, and the observed lung tumour rate must be attributed to a combined action of the two compounds. For this reason, a clear-cut carcinogenic effect of cadmium sulfide could not be proved by this inhalation study, but because of the high carcinogenic potency of cadmium ions in the rat lung and because cadmium sulfide retained in the lung is bioavailable to a certain extent, aerosols of this compound should be regarded as a probable human carcinogen.