Plutonium in Mammals

Current concepts of Pu metabolism are reviewed. (1) Both the amounts and rates of Pu absorption from the gastrointestinal tract, wound sites, or the lung decrease in the order: soluble complexes > hydrolyzable salts > insoluble compounds. (2) Absorption of Pu from the gastrointestinal tract is greater in very young animals than in adults. Deposition of Pu in bone is greater in growing animals than in young adults. (3) When introduced as a metabolizable complex or simple salt, Pu is transported in plasma chiefly by the iron-transport protein, transferrin. Circulating as the Pu-transferrin complex, Pu is deposited as single atoms in liver parenchymal cells and at the cell-mineral interface of those bone surfaces in closest proximity to erythropoietic marrow. (4) Liver deposition is favored when Pu is introduced directly into the body by parenteral injection. Skeletal deposition is favored when Pu has been transported across cell barriers as in the case of ingestion or inhalation. (5) In the dog, Pu in hepatic cells is initially associated with soluble ferritin, and later with subcellular structures. Upon the death of hepatic cells, Pu-laden debris accumulates in liver reticuloendothelial (RE) cells. Some of the phagocytized Pu is eventually released from the liver. (6) Concentrations of Pu on bone surfaces are not uniform and decrease in the order: endosteal > periosteal > Haversian. Plutonium concentrations on endosteal surfaces decrease in the order: resorbing > resting > growing. Sone surfaces labeled with Pu may remain unchanged; they may be buried by Formation of new bone; or, in the course of growth or maintenance remodeling, they may be resorbed by osteoclasts. Some of the resorbed Pu is dissolved and recirculated, and may be redeposited in the skeleton. Apparently some of the Pu in resorbed bone cannot be dissolved, and it accumulates in osteoclasts in the marrow. Following death of the osteoclasts, the Pu is taken up by marrow RE cells, which slowly disappear from the marrow. (7) Insoluble Pu compounds initially deposited in lung or beneath the skin may gradually enter the body without having been dissolved, and pass by way of RE cells into the lymph and local lymph nodes, and ultimately into RE cells in liver, spleen, and bone marrow.