33 IRS > uuC/l indicates a body burden in the exposed Rongelap group e£280 muC (=49%) with an equilibrated body burden of 330 muC.*? The Zn*° level was therefore 85% of the estimated equilibrium level in 1958 (see Table 32). Whole-Body Counting With the Gamma Spectrometer ine ee ee te and the urinarylevel rose by a factor of 140, be- cause of the ingestion of Cs'* in food on Rongelap no significant difference is found between persons older and younger than 15 vears. The mean Cs'*’ level tends to be slightly lower for females than for males, but again the difference is not significant. It is to be noted that no significant difference was found between the Rongelap exposed, the Rongelap unexposed, and the Ailingnae groups. However, the mean Cs‘*? body burden of the Utirik body burden.” about one-third that of the Rongelap exposed group (12.0 muC/kg). The mean Cs'*" body burden of the exposed Rongelap group in 1959 was 0.57 wC (12.0 has fluctuated over the years since the original contaminating event. (See Figure 57, which shows values obtained by whole-body gammaspectrometry and by extrapolation from urinalysis data.) Unlike Sr®°, which is firmly fixed in the skeletal tissue, Cs?’ has a relatively short biological halflife, and thus readily reflects the environmental » about 0.58 uC, about 60 times as great as in 1957, various groups studied during the 1959 survey are presented in Table 34. The variations in levels within each group are quite large. [f Cs'*” bodv group (4.3 muC/kg) is (as in the case of Sr°°) 1g00 T T T T 800 - cs'8? EXCRETION (upC/ LITER) Rongelap people after they returned to their orig- T . 4 600 - during the 9 monthssince their return. The aver- age Cs''’ content of 250 Americans studied in 1958 was 6.6 muC or Yioo of the mean Rongelap The average daily intake of Cs'*’ for an inhabit- ant of Rongelap in 1958 (average of 13 daily rations) was estimated to be 3.9 muC.*’ This is about 1.3% of the nonindustriai maximum permissible daily intake, which is the product of the maximum permissible concentration®’ and the daily intake of water: (2% 107+ uC/ml) x (1.5107 mi/day) * = 300 muC/day. Zinc-65. Zn** was first detected by Miller®** in 1957 in the seven Marshallese examined at Argonne National Laboratory by whole-body spectrometry, although it had been observed in high concentrations in fish as early as one year following the 1954 detonation.*® Body burdens of Z£n** in 1957, measured directly, averaged 44 myC in five Rongelap inhabitants (Figure 57) and 350 mpwC intwo Uurik inhabitants. Miller, in 1957, determined an effective half-life of 110 days for the elimination of Zn®, which gives a biological half-life of 200 days. However, a value of 89 days was obtained for the biological half-life in two patients over a 2-monthperiod.*® The mean body burden of Zn*estimated from whole-body counting data was 0.36 uC in 1958 after the return of the Rongelap people to their 400 f AY th ~? 0 DAYS 200 + 4 island, or 8 times the 1957 value (Figure 57). The estimated Zn® intake in food (2 to 4 muC/ day) can be largely accounted for by the Zn*° levels reported for fish. In 1956, fish from Ronge- lap Lagoon were found to contain 0.6 myC Zn** 100 B80 0 l 30 TIME I 60 1 30 L a 1 120 150 180 (IN DAYS - AFTER MARCH |, 1954 Figure 56. Urinary excretion of Cs'*" in exposed Marshallese. | per |b muscle, or 7.5 muC per Ib whole fish.** The 1959 body burdens of Zn*® are presented in Table 35. As with Cs'*’, the variation within any group is large, and no significant difference is found in Zn*° per unit body weight correlated wh= - The body burdens of Cs! of the muC/kg) compared to 0.68 uC in 1958. Thelevel a aee ee ee marked increase in Cs'*" was also observed in the inal island in 1957: the body burden in 1958 was burden is expressed in units per unit body weight, cae geeA WR enern cere orm weapon testing wasreflected in an increased body burden in the Marshallese. As pointed out, a very ineeran a Cesium-137. level. The slight increase in environmental level of Cs'** during the 1956 and 1958 periods of