Bioavailability indicators of inhaled cadmium compounds

In a thirty-day inhalation study male Wistar rats were continuously exposed to submicron aerosols of three different cadmium compounds. The cadmium chloride (CdCl2) and cadmium oxide (CdO) aerosol concentrations were 0.1 mg/m3 Cd. Because of its lower solubility the cadmium sulfide (CdS) level was 1 mg/m3 Cd. For CdCl2 and CdO, most of the cadmium was found in the lung cytosolic compartment, but for CdS only 30% of the cadmium was retrieved from the lung cytosols. This was observed both at the end of the inhalation and also after an additional 2-month period in fresh air. The cadmium contents of the lung homogenates, cytosols, and the lung cytosolic metallothionein were found to be twice as much for exposure to CdO than for exposure to CdCl2. For exposure to CdS at cadmium concentrations 10 times higher the same cadmium levels were found as for CdO. These results are confirmed by results from alveolar lavage analysis indicating that in the lung-inhaled CdO is even more available to lung tissue than the very soluble CdCl2, and CdO has an availability 10 times as much as CdS. This study proved that lung compartmental cadmium and metallothionein contents as well as lung lavage analysis can describe the bioavailability of inhaled cadmium.