62 of Table 26 showsthat the body burdensof '*’Cs Table 28 and ©°Co are not significantly different among the various subdivisions by age and sex of the Ronge- lap resident population. The values given for the children may be overestimates, because the calibrations were in terms of an adult-size phantom only and the counting geometry is such that a higher efficiency obtains for the children, especially the smaller ones. Prior to 1962, the concentration of *°Sr in the urine was used as a basis for estimating °°Sr body - burdens. Subsequently, the ratio of *°Sr to Ca in the urine has been used. Onthis basis the 1965 mean concentrations of 10.1 pCi *°Sr/liter and 0.093 g Ca/liter correspond to a body burden of 11.4 nCi. Data were not obtained on children in 1965. In previous years the urinary °°Sr to Ca ratios in children have been about twice thatfor adults. Urines for *°Sr analysis were not collected in 1966. Comparison of the 1965 survey data with the results from previous surveys (Figure 70) shows that the mean levels of '*"Cs and °°Sr have remained nearly constant since 1961, and that '°7Cs is at about the 1958 level. Further comparison with the 1954 and 1957 results indicates that the activities now being seen are almost entirely due to intake subsequentto the return of the Rongelap population to their homeatoll in 1958. If the ecological cycle were in equilibrium, it would be expected that, by virtue of physical de- cay, the specific activities of ‘*’Cs and *°Sr in the food and the corresponding body burdensof these radionuclides would have decreased about 9% during the interim 1961 to 1965. Actually there may have been a small decrease that is masked by the unknown overestimation errorin the children. Even with a correction for this, the sustained levels suggest that increasing amountsofthe originally contaminated materials are getting into the food chain and thus maintainingthe specific activity at the previouslevels. This hypothesis is supported by data obtained from E. Held, University of Washington,”to the effect that soil and plant surveys ind.vate that the ’*’Cs levels in plants have remained about the samesince 1961. There is no ready explanation of the mechanism for this. These findings are to be contrasted with those cited be- low for an Eskimo population. Table 28 shows the relationship between '*’Cs body burden andits excretion rate for those resi- Comparison of Body Burdens and Excretion Rates NICs Subject No. 8 15 51 53 58 59 11 20 27 40 41 50 73 835 843 928 932 942 822 833 840 853 855 body 7Cs, burden, nCi/ nCi 508.9 405.6 484.8 971.2 575.0 732.7 525.5 773.9 1326.0 1047.0 1209.0 728.9 1861.0 644.8 419.8 491.4 549.6 1058.0 694.6 636.9 1455.0 814.9 606.2 liter 5.0 6.2 23.0 4.4 3.4 1.2 2.1 6.0 5.1 4.7 2.2 0.6 19.0 3.2 1.5 6.5 97° 18.0 4.5 3.1 6.0 2.0 3.6 NICs, Urine nCi/_ -Fraction/ 0.730 0.730 0.289 0.650 0.710 0.645 0.940 0.500 1.320 0.560 0.890 1.800 0.650 0.550 1.340 * 040 .350 0.540 0.835 1.000 0.800 1.750 0.500 3.65 4.526 6.647 2.86 2.414 0.774 1.974 3.000 6.732 2.63 1.958 1.08 12.35 2.86 2.01 6.76 3.395 9.72 3.758 5.10 4.80 3.50 1.80 0.00717 0.01115 0.01343 0.00294 0.00419 0.00105 0.00375 0.00387 0.00507 0.00251 0.00161 0.00148 0.00663 0.00443 0.00478 0.01375 0.00617 0,00918 0.00540 0.00800 0.00329 0.00429 0.00296 volume, | day Mean day 0.00553 dents of Rongelap for whom individual urine specimens were analyzed. An average of 0.553% of the body burdenis excreted per day, the range being 0.105% to 1.375%. These values correspond to turnoverhalf-times of 120 days, 660 days, and 50 days, respectively. Except for some of the very slow turnoverrates, these values fall within the ranges cited or reported for other populations, in which the means were 75, 74, 87, 115, and 135 days."? Some of the lowest turnover rates in the Rongelap population may be ascribed to uncertainties in the completeness of the urine collections. Thusit is to be expected that the '°'Cs value would fall to near-zero levels in a yearof living in a noncontaminated environment. That this fall does occur is shown bythe results with the Ebeye population, who have been absent from Rongelap for various times from | to 18 months. Becauseit is not a gamma-ray emitter, “’Sr is not detected by the whole-body counting method. (Theoretically it might be possible to estimate "’Sr