— ne eel ticeale RR at menEON Bin wee poeee ee ee 62 cially the smaller ones. Prior to 1962, the concentration of °°Sr in the urine was used asa basis for estimating °°Sr body burdens. Subsequently, the ratio of ®°Sr to Ca in the urine has been used. On this 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 '*’Cs 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 decay, 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 unknownoverestimation error in 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 maintaining the specific activity at the previous levels. This hypothesis is supported by data obtained from E. Held, University of Washington,* to the effect that soil and plant surveys indicate that the '*’Cslevels in plants haveremained about the same since 1961. There is no ready explanation of the mechanismfor this. These findings are to be contrasted with those cited below for an Eskimo population. Table 28 shows the relationship between '*'Cs body burden andits excretion rate for those resi- 5008346 Table 28 Comparison of Body Burdens and Excretion Rates MCs Subject No. body’ burden, nCi "Cs, nCi/ liter Urine volurne, } '7Cs, nCi/ day Fraction/ day 8 15 51 53 508.9 405.6 484.8 971.2 5.0 6.2 23.0 4.4 0.730 0.730 0.289 0.650 3.65 4.526 6.647 2.86 0.00717 0.01115 0.01343 0.00294 58 575.0 3.4 0.710 0.645 0.774 2.414 0.00419 LI 525.5 2.1 0.940 1.974 0.00375 59 20 27 40 41 20 73 835 843 928 932 942 822 833 840 853 855 732.7 - 773.9 1326.0 1047.0 1209.0 7289 1861.0 644.8 419.8 491.4 549.6 1058.0 694.6 636.9 1455.0 814.9 606.2 1.2 6.0 3.1 4.7 2.2 0.6 19:0 3.2 1.5 6.5 9.7 18.0 4.5 3.1 6.0 2.0 3.6 0.500 1.320 0.560 0.890 1.800 0.650 0.350 1.340 1.040 0.350 0.540 0.835 1.000 0.800 1.750 0.500 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 3.30 1.80 Mean 0.00105 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 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 turnover half-times of 120 days, 660 days. and 50 days, respectively. Except for some of the very slow turnover rates, 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 collec- tions. Thusit if 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 bythe whole-body counting method. (Theoretically it might be possible to estimate °"Sr ae of Table 26 shows that the body burdensof **’Cs and *°Co are notsignificantly different among the various subdivisions by age and sex of the Rongelap resident population. The values given for the children may be overestimates, because thecalibrations werein terms of an adult-size phantom only and the counting geometry is such that a higher efficiency obtains for the children, espe-