Inhalation Exposures of Beagle Dogs to Cerium Aerosols

A biomathematical model for describing tissue distribution and whole-body retention of inhaled 144Ce was developed from studies with beagle dogs. Lung clearance of 144Ce after inhalation exposure to 144CeCl3 in CsCl or CeCl3 aerosol particles was measured and compared with elution rates for 144Ce from aerosol samples in an in vitro, static solvent dissolution system. Various solvents including NaCl or sodium citrate in Tris buffered solutions at pH 6.5, 7.0 or 7.5 and simulated serum solutions were used. Increased elution rates were obtained by including sodium citrate, a chelating agent, and by decreasing pH. Elution rates for 144Ce from aerosol samples in sodium citrate at pH 7.0 and 7.5 were the most similar to estimated absorption rates for 144Ce from lungs of dogs after inhalation exposure. In contrast to previous studies in which barium was eluted from various aerosols in simulated serum solutions at similar rates to lung clearance in dogs, no elution of 144Ce from filter samples was observed in this study. Lung clearance and in vitro elution of 144Ce were more rapid from CsCl aerosol particles than from CeCl3 particles. Further dissolution studies with 144Ce oxide and 144Ce entrapped in fused clay aerosols yielded predicted lung clearance half times of several hundred days.