enviromental pathways for radiocesium: atmosphere’lichenvreindeer Laplander (Linden and Gustaffson, 1967) and atmosphere +] ichenscar ibou Eskimo (Hanson, 1967). In these populations, seasonal fnfluences on dietary practices resulted in large fluctuations in }37Cs burdens. Many other environmental aspects of 137cs were summarized by Davis (1963) and were addressed by others in a symposium on radiation ecology (Aberg and Hungate, 1967). Metabolic pathways In the 1940s, fissfon-produced radfocesium was administered to rats (Hamilton, 1947). Absorption from the gut was 100 percent; its distribution was throughout soft tissues, with 45 percent deposited in muscle, and it was retained in the rat with a half-time of 15 days. Inhaled radiocesium was reajily absorbed fram the lungs. The metabolism of !37Cs was studied later in rats and several farm animals by Hood and Comar (1953), who found a similar wide and fairly uniform distribution throughout the body. They also found that 0.2 to 3.5% of administered 137Cs was transferred fran pregnant rats to fetuses in late gestation (at days 17 to 21, respectively) with a fairly constant tissue Beek Cs . wot . tees nee mp gale aR ree 4, me fone ee eerll,tm we : pe concentration of 0.06% dose per om regardless of fetal age. A dairy cow was show to secrete 13% of an injected dose of 1J7Cs into milk over a 30-day pertod. Fran an ora} dose of 137¢s, YOZ was secreted into milk in 30 days. The entrance of '3/Cs into animal tissues ts primarily through the ingestion of contaminated foods. Absorption of cestum fram the gut is close to 100% tn monogastric animals (Richmond, 1958), but ts generally only 50% to BOS in ruminants (McClellan et al., 1961; Wasserman et al., 196)). The redised absorption, along with the high fecal-to-urinary ratio of evcret oe