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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.

Forty-eight beagle dogs were exposed to plutonium dioxide aerosols of three particle size distributions. The aerosol concentrations ranged from lo-' to lOP3pc per cm? air and the total amount of plutonium deposited in the dogs varied from 0.01 to 100 pc during exposure periods that ranged from 10 to 30 min. Total deposition in dogs exposed to aerosols with Count Median Diameters of 0.086, 0.43, and 0.60 p averaged 4, 30, and 60 per cent, respectively, of the total amount of plutonium inhaled. For all particle sizes the percentage of plutonium apparently deposited in the alveoli of the lung increased with decreasing microcuries of deposited plutonium. For a given amount of plutonium deposited, the percentage deposited in the alveoli was greatest for the aerosol with particles of the largest median diameter. The rates of pulmonary clearance, translocation and excretion in both urine and feces were greatest for the aerosol with particles of the smallest median diameters. In comparing the three aerosols it was concluded that all processes favored pulmonary deposition and retention of P U~~~O , inhaled as an aerosol with the largest Count Median Diameter, 0.60 p.

Beagle dogs were given single exposures to one of seven P U~~~O , aerosols that differed in particle size from 0.2 to 7.6 , u mass median diameter (MMD). Translocation of plutonium to other tissues and excretion in both urine and feces up to a month after exposure were greatest for dogs exposed to aerosols with the smallest median diameter. Dogs exposed to an aerosol with a MMD of 4.3 ,u were studied for about 10 months. The half-time for retention of Pu239 in lungs was about 300 days; however, during this period there was continuous accumulation of Pu289 in bronchial lymph nodes, which resulted in about a 1500-1800 day half-time for total body retention of plutonium. Inhaled and intravenously injected plutonium nitrate (0.2 N HNO,) were compared in still other dogs. After inhalation, 70per centofthe body burden was in the lungs, 10 per cent in the liver and 15 per cent in bone. After intravenous injection, more than 80 per cent of the body burden was in liver and about 6 per cent each in the spleen and.bone. The rate of excretion in urine was about five times greaterafter inhalation than after intravenous injection. Corresponding differences were observed in the levels of plutonium in blood. The results of these studies emphasize the importance of the chemical form and the particle size of inhaled plutonium aerosols on retention, translocation and excretion, and point out the problems to be encountered in estimating the body burden from excretion analysis.