DISPOSITION OF INHALED CADMIUM-OXIDE AEROSOL IN THE RAT

Male F344/N rats were exposed to target air concentrations of 0.0, 0.1 0, 0.25, or 1.0 mg CdO/m(3) for approximately 6 h/day, 5 days/wk, for 13 wk. The lung burdens of Cd, the concentration of Cd in whole blood, and the concentration oi Cd in the kidneys from exposure groups were determined at study days 3, 9, 30, and 93. Accumulated lung burdens we re not directly proportional to the exposure concentration, but became progressively less than expected when exposure concentrations were in creased. This was attributed to differences in exposure material depos ition at different exposure concentrations, although the basis for the se differences was not determined. Based on lung burden measurements m ade during the study, the lung clearance rate of Cd in F344 rats agree d well with values reported in the literature for Long-Evans and Wista r rats. Lung clearance half-lives did not change significantly with ex posure concentration. Estimation of the deposition rate and the cleara nce rate constant allowed calculation of the equilibrium lung burdens expected in each of the exposure groups after long-term exposure. The concentration of Cd in blood was found to be very low in all exposure groups studied. Evidence suggests that the low blood concentration is most likely a result of rapid clearance from the blood to the kidney, and possibly the liver. The amount of Cd observed in the kidneys of ex posed animals represented a significant fraction of the accumulated lu ng burden, and the concentration of Cd in the kidney was linearly prop ortional to the accumulated lung burden. Based on a linear model, proj ected accumulation of Cd in the kidneys of rats indicated that kidney Cd concentrations should be well below the toxic threshold when lung b urdens reach steady state. However, this extrapolation will most likel y underestimate accumulation of Cd in the kidney after steady-state lu ng burdens are achieved.