TOXICITY OF INHALED PLUTONIUM DIOXIDE IN BEAGLE DOGS

This study was conducted to determine the biological effects of inhale d (PuO2)-Pu-238 over the life spans of 144 beagle dogs. The dogs inhal ed one of two sizes of monodisperse aerosols of (PuO2)-Pu-238 to achie ve graded levels of initial lung burden (ILB). The aerosols also conta ined Yb-169 to provide a gamma-ray-emitting label for the Pu-238 inhal ed by each dog. Excreta were collected periodically over each dog's li fe span to estimate plutonium excretion; at death, the tissues were an alyzed radiochemically for plutonium activity. The tissue content and the amount of plutonium excreted were used to estimate the ILB. These data for each dog were used in a dosimetry model to estimate tissue do ses. The lung, skeleton and liver received the highest alpha-particle doses, ranging from 0.16-68 Gy for the lung, 0.08-8.7 Gy for the skele ton and 0.18-19 Gy for the liver. At death, all dogs were necropsied, and all organs and lesions were sampled and examined by histopathology . Findings of non-neoplastic changes included neutropenia and lymphope nia that developed in a dose-related fashion soon after inhalation exp osure. These effects persisted for up to 5 years in some animals, but no other health effects could be related to the blood changes observed . Radiation pneumonitis was observed among the dogs with the highest I LBs. Deaths from radiation pneumonitis occurred from 1.5 to 5.4 years after exposure. Tumors of the lung, skeleton and liver occurred beginn ing at about 3 years after exposure. Bone tumors found in 93 dogs were the most common cause of death. Lung tumors found in 46 dogs were the second most common cause of death. Liver tumors, which were found in 20 dogs but were the cause of death in only 2 dogs, occurred later tha n tumors in bone and lung. Tumors in these three organs often occurred in the same animal and were competing causes of death. These findings in dogs suggest that similar dose-related biological effects could be expected in humans accidentally exposed to (PuO2)-Pu-238. (C) 1996 by Radiation Research Society