eon T. M. BEASLEY, E. E. HELD and R. M. CONARD sa frequency 3 of males and , were included of those indiernal radiation blood samples cit count rate 33% (20) conere weighed in approximately 1/100th of the maximum permissible body burden which has been established for non-occupationally exposed individuals considering the total body as thecritical organ.93) Previous measurementsof 55Fe body burdens during a period of increasing 55Fe fallout generally showed that **Fe body burdens of females were higher than those of males.(4-5) food volumes. Presumably this is due to higher turnover rates of iron in females than in males, with the result ‘+t therefore the their environment. As environmental levels of 55Fe decrease, females should, on the average, reflect this change by exhibiting lower 55Fe . previous years : years applied > weight generdividual esti-c likely to be in the males i body burdens maximum ob- was 1.0 #Ci, of Rongelapese 55Fe (uCi) * 0.43 + 0.17 0.40 + 0.27 247 from the northeast Pacific Ocean decreased eightfold between 164-1667. Assuming that a first order reaction governed the removal of °*Fe from the mixed layer of the ocean (upper 100 m) he calculated the effective half-life for 55Fe loss as 11 months. Measurementsin cattle and rain waters show decreases, but at lesser rates."©) Tron-55 body burdens of adult males in Richland, Washington, decreased approxi- that females are more nearly at equilibrium with mately 4 fold between 1667 and 1970, corresponding to an effective 55Fe half-life of LS yr. If the 55Fe turnover rates of Richland, body burdens than those of males. Figure 1] shows that more female body burdens tended insular populations, we conclude that people from maritime cultures would exhibit similar and perhaps faster turnover rates of 55Fe because of the short ‘“‘ecological half-life’@5) of toward values <0.4 wCi, while male body burdens were more normally distributed, about a mean of 0.43 wCi. Regression analysis of age on body burdens showed a significant correlation (P <0.001); older individuals had higher 55Fe body burdens. Table 2 shows a tabulation of the average 55Fe body of males and females by age groups. The number of samples per age group is admittedly small yet the general increase of 55Fe body burden with age appears qualitatively consistent with earlier data obtained by analyzing blood from Seattle, Washington, residents are similar to those of this radionuclide in the marine environment. The highest “Fe body burdens previously measured were in female natives at Bethel, Alaska, during 1966.) The average body burden of 18 females was 1.1 wCi. During the same year, the average *5Fe body burden of females and males at Tokai-mura, Japan was 0.92 wCi and 0.63 wCi respectively.’ We determined the ®*5Fe body burdens of 32 females and 37 males from Tokai-mura from blood collected in October 1970; the average Washington males in 1966. ‘values were 0.12 and 0.17 respectively. Thus, Comparison of the 55Fe body burdens of not only do the Rongelapese have significantly peoples of different countries") requires knowl- higher *5Fe body burdens than those of the edge of the turnoverrates of 55Fe in the environ- Tokai-mura residents, but the decrease in the ment and in humans. Jenninos"4) has shown 55Fe body burdens of this latter group from that the ®5Fe specific activities of salmon taken 1966 to 1970 appears comparable to that for Table 2. Average body burden of Fe in Rongelapese restdents of different ages Age Males Females 16-20 21-31 32-42 4353 54-64 >64 16-20 21~31 32-42 43-53 54-64 >64 Number of samples Body burden (uCi) 8 0.31 _4 5 2 6 3 6 12 5 7 2 2 0.33 0.52 0.58 0.53 0.48 0.23 0.34 0.33 0.66 0.57 0.66 Richland, Washington, males. As previously stated, all of the donors of the Rongelap study were subjected to external radiation during the accidental contamination of Rongelap Atoll in 1954. Because of the high levels of radioactivity at the Atoll, the Rongelap natives were moved to Majuro Atoll where they resided for 3.5 yr. Following exposure in 1954, whole body counting and urinalysis disclosed measurable quantities of internally deposited fallout radionuclides. By 1957, however, the only radionuclides present in the Rongelapese in significantly measurable quantities were °5Zn, WCs and *Sr.29 No 55Fe analyses were per- formed at that time so body burdens of this radionuclide are not known. However, based