Young adult female Dutch Belted rabbits were given a single intravenous injection of polymeric 23gPu-nitrate ( 15% ultrafilterable) or of monomeric 239Pu-citrate (90% ultrafilterable) and killed at 3 days. The plutonium content of the intact femur (bone plus marrow) was higher after the polymeric form. Physical removal of marrow from bone in the tibia showed the plutonium content of the bone to be slightly lower and of the marrow to be 17-fold higher after polymeric than after monomeric plutonium. Polymeric plutonium was also more concentrated in spleen, ovaries, intestines (with contents), skeletal muscle and urine but less concentrated in liver. About the same levels of the two forms of plutonium were found in blood, bile and lung. For the first 30 min after injection, the polymeric plutonium was cleared from the circulation more rapidly than the monomeric. After about 60 min, the two forms were cleared at generally comparable, decreasing rates. Polymeric plutonium was as much as 10-30 times more concentrated in predominantly red (erythropoietic) marrow than in fatty marrow. Monomeric plutonium was 1.3-2.8 times more concentrated in the red marrow.Mice injected with the same plutonium solutions as the rabbits showed, in comparison, a higher per cent of the injected monomeric plutonium in the femurs and a lower per cent in the liver; they showed a higher uptake of polymeric plutonium in the marrow, and a higher uptake of both forms in the spleen and lungs than did the rabbits.
Iron-59 has been used in mice as a tracer for bone marrow to extrapolate from the plutonium measured in a standard sample of tibial marrow to the plutonium in total marrow 5-6 days after intravenous injection of different physical-chemical forms of plutonium. A factor of 44 was obtained for conversion of the radioactivity measured in the tibial sample to total body marrow. Using this factor, and calculating the total skeletal plutonium burden as the amount measured in two femurs times 13, one can calculate the proportion of skeletal plutonium located in the marrow. For monomeric, mid-range polymeric and highly polymeric plutonium, values of 2, 7-15 and 62 %, respectively, were obtained. Similarly, for monomeric americium and a highly polymeric americium, 1 and 20% of the total skeletal burden was calculated to be in the marrow.In two experiments, in which monomeric plutonium had been found to be about twice as carcinogenic in bone as the mid-range polymeric plutonium, the amount ofplutonium in all the bones and spinal segments was measured at 15 days. Using these data and the 59Fe measurements, we have calculated and tabulated the marrow content of these two forms of plutonium throughout the skeleton. The total marrow burdens, calculated from the tibial samples, were 0.796 % of the injected monomeric vs 3.66 % of the mid-range polymeric plutonium. These amounts were 2.35 vs 14.3% of the amount of plutonium measured in the total skeleton, respectively.
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