Toxicity of inhaled 238PuO2 in beagle dogs. A. Monodisperse 1.5 μm AD 238PuO2 particles B. Monodisperse 3.0 μm AD particles. IV

To obtain essential information on the relative importance of homogeneity of radiation dose to lung from inhaled alpha-emitting radionuclides, Beagle dogs have received inhalation exposure to two sizes of monodisperse aerosols (sigma/sub g/ less than 1.2) of 238PuO2 to achieve graded levels of initial lung burdens. In each subgroup, 72 Beagle dogs received inhalation exposure to either a 1.5 or 3.0 μm aerodynamic diameter (AD) monodisperse aerosol. For a given level of initial lung burden, the average dose to lung remains constant whereas the local dose to tissue varies by a factor of approximately 10; six levels of initial lung burden ranging from 0.005 to 2.2 μCi 238Pu/kg body weight result in average initial dose rates to lung ranging from 0.12 to 56 rads per day. Twenty-four dogs were exposed to the diluent aerosol and served as controls. All animals will be studied over their life span. A total of 15 dogs have died to date due to radiation-related injury; the initial lung burdens in these 15 animals ranged from 0.27 to 2.2 μCi 238Pu/kg body weight. Of the 15 radiation injury deaths, six animals died with radiation pneumonitis and pulmonary fibrosis, two died with lung tumors and seven animals died with bone tumors. Assessment of the distribution of 238Pu in organs and tissues and histopathological examination is complete for eight animals that have died. Two control animals have died in the study. One hundred and twenty-nine exposed and 22 control animals are surviving at 540 to 1389 days after inhalation exposure