Toxicity of inhaled 239PuO2 in Beagle dogs. A. Monodisperse 0.75 μm AD particles. B. Monodisperse 1.5 μm AD particles. C. Monodisperse 3.0 μm AD particles. III

Studies on the metabolism, dosimetry and biological effects of inhaled particles of 239PuO2 in Beagle dogs are in progress. To obtain information on the relative importance of homogeneity versus nonhomogeneity of radiation doses to the lung, dogs have been exposed to monodisperse aerosols of 239PuO2 of 0.75, 1.5 or 3.0 μm aerodynamic diameter (AD). By using monodisperse aerosols of three different suitable particle sizes, the average dose to lung can be held constant for a given initial lung burden while the local dose around the different sized particles can differ by a factor of approx. = 140. The exposures have resulted in graded initial lung burdens ranging from 0.0002 to 2.6 μCi/kg body weight. Other dogs were exposed to the aerosol diluent to serve as controls. Fifteen dogs have died at 152 to 728 days after exposure in the 1.5 μm AD study and 16 dogs have died at 105 to 876 days after exposure in the 3.0 μm AD study. These dogs had radiation pneumonitis and pulmonary fibrosis at death. All of the dogs exposed to 0.75 μm AD 239PuO2 are alive. Levels of exposure to 0.75 μm AD were all lower than those which caused early deaths from exposures to the other aerosols. The remaining dogs have survived up to 999 days after exposure and are being observed for the remainder of their life span