Effect of Dose Level on Skeletal Retention of 239 Pu(IV) in the Beagle

Abstract

When 239Pu(IV) is injected i.v., its fractional retention in the skeleton of the beagle decreases and then approaches an approximately constant value. The initial fractional deposition of 239Pu is independent of dose level, but the long term fractional retention is less at the lower dose levels (0.0055-0.095 .mu.Ci/kg) than at the high dose levels (0.30-2.9 .mu.Ci/kg). These findings are in contrast with results on the retention of 239Pu(IV) in the liver of the beagle. The rate of decrease in hepatic retention of 239Pu diminishes with decreasing dose level. These opposing effects result from cellular necrosis which is an effect of the .alpha. irradiation from 239Pu. Skeletal retention equations are presented for each of the 3 higher dose levels of 239Pu and for the group of lower dose levels. These equations and those previously reported for the liver are used to calculate cumulative average radiation doses to the skeleton including marrow, and to the liver throughout the observed lives of the beagles, which were injected in young adulthood at 6 dose levels of 239Pu(IV) ranging from 0.016-2.9 .mu.Ci/kg. In the skeletal dose calculations an experimentally determined value of (7.5 .+-. 1.0)% for skeletal weight relative to body weight at injection is used. The concentration of Pu in plasma was measured from 1 min-12.5 yr following injection. A sum of 4 exponentials was fit to the data. Samples were obtained from dogs at 6 dose levels, and from well, ill and terminal dogs.