. rates of iron in xemales than in males, with the result that females are more nearly at equilibriun with their environment. “AS environmental levels of er 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 pci, while male body ‘burdens were more normallydistributed, about a mean of 0.43 pci. Regression analysis of age on body burdens showed a significant - correlation (P<0.001); older individuals had hi -:her 556 body burdens. — This observation is consistent with earlier data from ‘U.S. citizens (5). | Comparison of the 355 ‘body burdens of peoples of different countries (5) requires knowledge of the turnover rates of 55 ie in the environment and in humans. the Jennings (12) has shown that >Pe 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 35 ne from the mixed layer of the ocean (upper 100.m) he calculated the effective half-life for S56 loss as ll moriths. Measurements in cattle and rain waters show decreases, but at lesser rates Iron-55 body burdens of adult males in Richland, Washington, decreased approximately fourfold between 1967 and 1970 (7), corresponding to an effective mer half-life of 1.5 years. If the S56 turnover rates of Richland, Washington, residents are (6).