CHANGES IN SOFT-TISSUE CONCENTRATIONS OF PLUTONIUM AND AMERICIUM WITHTIME AFTER HUMAN OCCUPATIONAL EXPOSURE

Concentrations of Pu-239+240 and Am-241 in human soft tissues (testes, thyroid gland, kidneys, spleen, heart, skeletal muscle, brain, and pa ncreas) were compared to those in livers of the same subjects. The sub jects were volunteer donors with occupational exposures to plutonium a nd americium autopsied as part of the United States Transuranium and U ranium Registries program. The temporal distributions of tissue-to-liv er ratios were compared to liver uptake fractions assumed on the basis of current models to estimate the initial uptake fractions for each t issue studied. Regressions of the ratios were used to compare tissue r etention half-times to those of the liver. Effective half-times for pl utonium and americium in the tissues studied were similar to those for the liver with three exceptions: (1) the clearance half-time for plut onium in kidneys is shorter than that of liver; (2) the retention half -time for plutonium in testes is longer than that of liver; and (3) th e retention half-time for americium in skeletal muscle was longer than in the liver. Next to liver, the greatest initial uptake of systemic actinides was in skeletal muscle and the greatest initial concentratio ns were in the spleen. The uptake fraction of plutonium in the testes proposed by the ICRP was verified.