Pulmonary deposition, clearance and effects of inhaled soluble and insoluble cadmium compounds

The factors affecting the deposition of inhaled cadmium particles in different regions of the respiratory tract are discussed. The retention kinetics of inhaled cadmium compounds is determined by the various clearance processes. It is necessary to differentiate clearly between in vitro (water) solubility and in vivo (lung) solubility. Thus both cadmium oxide and cadmium sulfide particles are rather insoluble in water but the former are readily solubilized in the lung while the latter are cleared mainly by mechanical transport via alveolar macrophages. The pulmonary retention half-times of inhaled cadmium compounds are longer by approximately a factor of ten in primates than in rats. Acute pulmonary inflammatory effects of inhaled cadmium compounds are related to their in vivo solubility, and an approximately 10-fold higher dose of cadmium sulfide as compared with the chloride or oxide must be administered to the lung to elicit the same inflammatory response. Differences in biological effects may also exist with respect to the chronic effects of inhaled cadmium compounds, e.g., the pulmonary carcinogenic potency of inhaled cadmium sulfide may be less than that of other cadmium compounds.