Long-term behavior of 239Pu, 241Am and 233U in different bones of one-year-old rats: macrodistribution and macrodosimetry.

Female and male rats of the Sprague-Dawley strain, aged about 13 months, were injected intravenously with monomeric 239Pu-(30.7 kBq/kg), 241Am-(54.8 kBq/kg) or 233U-citrate (56.6 kBq/kg) and killed between 7 and 540 days after injection. In both sexes the wet skeletal weight was proportional to body weight; however, the skeletal weight of female rats remained constant, whereas the skeletal weight, and body weight, of male rats increased as a function of age. The initial skeletal deposition decreased in the order 239Pu greater than 241Am greater than 233U and for americium and uranium was greater in male rats. The 'half-time' of retention of plutonium and americium was considerably greater than 1 year but the corresponding values for uranium were 140 (females) and 80 (males) days. The relative concentration of the radionuclides in the skeleton varied between 0.2 and 2.0, the variation was greatest for plutonium and lowest for americium and decreased with increasing time after injection. For calculation of the nuclide content of the whole skeleton the most suitable reference bone was found to be the humerus in the case of uranium, and the femur and humerus for plutonium and americium. The cumulative mean skeletal absorbed radiation dose 1 year after injection decreased in the order 239Pu greater than 241 Am greater than 233U; for plutonium it was equal for both sexes, whereas for americium and uranium it was 1.5 times higher in male than in females rats. In the individual bones the cumulative dose was greatest in the vertebral column, except the tail, and lowest in the paws.