Mice exposed to Pu23900, aerosols deposited about 20 per cent of the amount inhaled in lungs. From 40 to 60 per cent was distributed between the nasal and oral passages and the gastrointestinal tract. Although the major portion of the body burden was associated with the lung during a 70-week period there was gradual translocation to the skeleton, muscle, liver and spleen. The skeleton accumulated the largest quantity of translocated Pu239, about 0.3 per cent of the total dose. This was equal to the amount remaining in lung. The half-life for clearance of about 4 per cent of the Pu239 initially deposited in lung was 460 days. The remainder was cleared with half-lives of 20 days or less. Assuming uniform distribution after deposition of 0.02 pc Pu239 in lung, the total cr-dose to mouse lung tissue during the 70-week period was 550 rad.

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The intratracheal administration to BAF1 or CAF, mice of plutonium and ruthenium particles suspended in Tween-80 or Pluronics caused an increased incidence of pulmonary adenomas compared with controls at levels of0"l/zc *3*PuO 2 and 3.0/zc Joe RuOv Decreased incidence of adenomas was obtained at 0"16/~c *~*PuO2 and 24-'0/zc I°eRuO*. Intravenous administration of similar particles caused an increased incidence at a level of 0-16 ~c 239Pu(OH)4 and a decrease at 0-37/zc *39PuO,. Certain inconsistencies in the incidence values were noted.Histological lesions resulting from deposition of plutonium particles included fibrosis with bronchiolar proliferation and squamous metaplasia. Ruthenium particles caused the presence of numerous bizarre cells in fibrotic lesions. Plutonium particles were considered responsible for the development of two squamous-cell carcinomas and a bronchiolar carcinoma. Two bronchiolar carcinomas occurred in ruthenium-treated animals.

Approximately 800 mice, divided into four age groups varying from 122 to 369 days, were given single exposures to P U~~~O , aerosols. Each age group was separated into a control and five subgroups, containing different amounts (0.038-0.72 nc) of Pu239 in the lung. The mean age at time of death wits established for each subgroup. Comparison of P~~3~-exposed mice with controls indicated no significant shortening of life span. No malignant tumors were seen.