et yt ne eae. A,myfas Bias, Sdoo 37 The OR denoted the individual tissues, excretions, or physiological processes involved in the preferential utilization of calcium over strontium, and when less than 1, expresses such a preference. rats on a canmercial diet was 0.27. causing the discrimination. For example, the Qbpone-diet for The OR did not imply action by the tissue Instead, to denote the phystological process of discriminat fon in a given tissue, the authors utflized the term “StrontiumCalcium Discrimination Factor" (OF). The product of the DFs equalled the OR. That strontium was preferentially discriminated against by the placenta | I was found in beagle dogs (AEC Project No. 6, 1958). ' The ORfetal bone-diet was 0,3], based upon data from two pups, a value somewhat Jower than the ORadult bone-diet of 0.4-0.5 of mature beagles (Della Rosa et al., 1972). The metabolic studies of radiostrontium intensified when its potential toxicity as a conponent of radioactive fallout was recognized and studies on its effects began. The radiobiologfcal significance of strontium metabolism was discussed in reviews (Thompson, 1960; Loutit, 1962; ICRP, 1972) and symposia (Lenihan et a}., 1967; Goldman and Bustad, 1972). Radiobjological Effects The tumorigenic ability of radiostrontium was recognized jn the 1940s. Strontium-89 was descrihed as a “producer par excellence of bone tumors” by Brues et al. (1947), who reported that tumor development tn over 3000 mice was approximately proportional to dose and to time, with a latent period that itself was related inversely to dose. Such a scheme was shown to fit data that were available for human radtun dtfal painters. Besides bone turors, aplastic anenia and myeloid metaplasia were canmon at necropsy (Brues et al., 1949),