Metabolism of monomeric and polymeric plutonium in the rabbit

Young adult female Dutch Belted rabbits were given a single intravenous injection of polymeric 239Pu-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 he 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.