The metabolism of americium in the rat.

The announcement of the discovery of element 95 was made in 1946 by Seaborg and his associates (1). Like neptunium (element 93), plutonium (element 94), and curium (element 96) this new element, americium, is radioactive and has not been observed in nature in appreciable amounts. During the war an extensive study was made of the metabolic properties of plutonium (2) and several other heavy elements, notably thorium, protoactinium (3), uranium,l* 2 and neptunium (3). Similar studies were also made with a large number of the radioactive elements which arise from fission (4). This work was done at the laboratories of the Manhattan Project, located in different parts of the country. Particular attention was directed towards a very detailed investigation of the metabolism of plutonium in rats and other laboratory animals. These studies, initiated at 0 e University of California at Berkeley, were also carried out at the University of C,hicago, Oak Ridge, and Los Alamos. The outstanding characteristic of the metabolism of plutohium is the high degree of localization and prolonged retention of this element. in the skeleton following parenteral administration. Unlike calcium, strontium, barium, and radium, which are deposited primarily in the mineral structure of the skeleton, plutonium may be laid down in the uncalcified osteo’d matrix of the bone (5). At the present time, it cannot be definitely stated whether or not all of the plutonium so accumulated is in the organic components of the osteoid rr.atrix. A significant fraction of plutonium may be laid down on the adjacent surfaces of the mineral structure of the bone. If this is so, the amount of penetration in the normal adult, rat, has been demonstrated by the radioautographic techniques to be less than 25 p. The accumulation of plutonium in the other tissues of the body following parenteral administration is quite small compared to the deposition in the