Retention patterns in beagle dogs repeatedly exposed to aerosols of 137Cs-labeled fused clay particles. II

To provide an experimental evaluation of the adequacy of extrapolating single inhalation exposure kinetics to the repeated exposure situation, 12 Beagle dogs were given 10, 20, or 40 weekly, 10-min inhalation exposures to 137Cs in fused clay particles. Whole-body counting immediately before and after each exposure and at other intervals has been used to assess the kinetics of buildup and retention of the deposited material. Current analyses indicate that neither the deposition percentage nor the rate of buildup of 137Cs in the lung was affected by the number of exposures. Two dogs each were sacrificed at 7 days after 10, 20, or 40 inhalation exposures. Tissue analyses indicated that 96 percent of the body burden was in the lung, 0.3 to 1 percent in the tracheobronchial lymph nodes, and the remainder mainly in other soft tissues. Preliminary analysis of the whole-body retention data obtained after the last inhalation exposure for the six remaining living dogs indicates that the 137Cs is being retained somewhat more tenaciously than was observed in dogs that received a single inhalation exposure to a similar aerosol. Observations are continuing on these six dogs. (U.S.)