rates of iron in xemales than in males, with the result that females are more nearly at equilibrium with their environment. AS environmental levels of 556 decrease, females should, on the average, reflect this change by exhibiting lower 55 ie body burdens than those of males. Figure 1 shows that more female body burdens tended toward values £0.4 uci, while male body burdens were more normally distributed, about a mean of 0.43 pci. Regression analysis of age on body burdens showed a significant ' correlation (P<0.001); olderindividuals had h‘’ :ner SS ne body burdens. This observation is consistent with earlier data from ‘U.S. citizens (5). | Comparison of the 56 ‘body purdens of peoples of different countries (5) requires knowledge of the turnover rates of SF a6 in the environment and in humans. Jennings (12) has shown that the Sone specific activities of salmon taken from the northeast Pacific Ocean decreased eightfold between 1964-1967. Assuming that a first order reaction governed the removal of Sone from the mixed layer of the ocean (upper 100.m) he calculated the effective half-life for 5 ne loss as 11 moriths. Measurements in cattle and rain waters show decreases, but at lesser rates Yron-55 body burdens of adult males in Richland, Washington, decreased approximately fourfold between 1967 and 1970 (7), corresponding to an effective m6 half-life of 1.5 years. the 55 a6 turnover rates of Richland, Washington, If residents are (6).