The Effect of Chemical Form on the Clearance of 239-Plutonium from the Respiratory System of the Rat

This study has investigated the effect of chemical form on the tissue distribution and excretion of plutonium following its deposition in the respiratory system of the rat. Solutions of various chemical forms of plutonium (nitrate, citrate, oxalate, dioxide, DTPA complex) have been administered to rats by intubation into the nasopharyngeal, tracheobronchial or pulmonary regions of the respiratory tract. The injection volume was less than 3 μl and the activity administered (2–3 nCi kg−1) was comparable to a few maximum permissible body burdens of plutonium in man. The absorption of both plutonium nitrate and citrate from the pulmonary region was approximately four times greater than the absorption from either the tracheobronchial or nasopharyngeal regions. However, of the plutonium deposited in any of the three regions, the relative proportion that is translocated to other tissues is greater following administration as citrate than nitrate (approximately in the ratio of 1.6:1). The absorption of various chemical forms of plutonium from the pulmonary region was in general agreement with the conclusions of the ICRP Task Group on Lung Dynamics. About 13% of activity entering the blood during the first week after administration of plutonium nitrate or citrate was retained in the liver at 7 days implying that plutonium was circulating in the blood in a “monomeric” form. The cumulative excretion of plutonium in the urine in the same period was equivalent to about 4 of the total activity deposited in tissues from the blood. The experimental results suggest that this value could be used for calculating the total tissue deposit from urinary excretion measurements.