world-wide meteorology (Machta et al., 1956). In addition, measurements of | 90Sr concentrations in foods and human tissues were made, and the potential hazard to people was considered (Libby, 1956; Efsenbud, 1957, Kulp et al., 1957; Langham, 1958), Work in°the early 1940s (Erf and Pecher, 1940) had reported the secretion of strontium into cows’ milk. Some other aspects of environmenta) behavior of _ radfostrontium, nanely, the uptake of the radionuclide by plant roots, had also been investigated in the 1940s (Jacobsen and Overstreet, 1947). Studies on the transfer of 99Sr and other fission products into milk were begun in the mid-1950s (Comar and Wassegnan, 1956; Lengemann and Comar, 1956). Ingestion was considered to be the most signiffcant route of human assiaflation of 90Sr (Langham, 1960), and daify products were considered the primary source of 99Sr in the diet (Russel!, 1960). The transfer of 90sr from the atmosphere to diet to man was reviewed by a number of authors (e.9.. Wasserman et al., 1965; Bennett, 1972). Metabolic Pathways Even though some investigations into the metabolism of strontium were done earlier (for instance, McCance and Widdowson, 1939), ft was not until the availability of radioactive strontium (895r) that its metabolism became wel! understood. Much of the experimental use of radiostrontium was as a substitute for calcium. Early studies demonstrated the similarity of strontium and calcium in their matabolic pathways. Pecher (1941a,194lb) described the distribut ian art tissue upteke of injected 39sr ani §5ca, showing skeletal uptake by the two radionuclides. After 24 hours, 58 percent of the administered 3509 was