Five Beagle dogs were exposed by inhalation to an aerosol farmed by passing liquid droplets containing 241Am through a heating column at 600°C. The resulting particles, presumed to be relatively insoluble, formed a distribution with an activity median aerodynamic diameter of about 0.9 μm and a geometric standard deviation of about 1.5. One dog was frozen shortly post-inhalation and used as a counting standard; the remaining four were held for urine and feces collections for up to 138 days; these four were sacrificed at 127, 256, 512 and 1022 days post-exposure. Initial body burdens ranged from 4.4 to 4.9 μCi/kg. Tissue analyses indicated the greatest long-term doses to be received by the tracheobronchial lymph nodes, liver, lung, bone and thyroid in descending order. Respiratory measurements showed increased frequency and decreased tidal volumes in the two early sacrifice dogs only. Hematologic findings included reduced total white cells, platelets, lymphocytes and neutrophils, but little change in hematocrit. Pathologic findings centered around fibrotic changes in lung and lymph nodes, fatty deposits and cellular degeneration in liver, bone marrow depletion, glomerulosclerosis and severely damaged thyroid.
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