53 ppC/] indicates a body burden in the exposed Rongelap group of 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 Cesivm-137. The body burdensof Cs'%’ of the various groupsstudied during the 1959 survey are presented in Table 34. The variationsin levels within each group are quite large. If Cs?37 body burden is expressed in units per unit body weight, no significant difference is found between persons older and younger than 15 years. The mean Cs'*’ level tends to be slightly lower for females than for males, but again the differenceis not significant. It is to be noted that no significant difference was found between the Rongelap exposed, the Ronge- lap unexposed, and the Ailingnae groups. How- ever, the mean Cs'*’ body burden of the Utirik group (4.3 muC/kg) is (as in the case of Sr®) 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 pC (12.0 myuC/kg) compared to 0.68 nC in 1958. The level 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 cs'37 EXCRETION (upC/ LITER) 1000 T T T T T inal island in 1957: the body burden in 1958 was about 0.68 uC, about 60 times as great as in 1957, and the urinary level rose by a factor of 140, be- cause ofthe ingestion of Cs'** in food on Rongelap during the 9 monthssince their return. The average Cs'** content of 250 Americans studied in 1958 was 6.6 muC or ‘oo of the mean Rongelap body burden. The average daily intake of Cs'*’ for an inhabitant of Rongelap in 1958 (average of 13 daily rations) was estimated to be 3.9 muC.*" Thisis about 1.3% of the nonindustrial maximum per- missible daily intake, which is the productof the maximum permissible concentration*’ and the daily intake of water: (2 10°* wC/ml) x (1.5 « 10° ml/day) =300 mpC/day . Zine-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 burdensof Zn** in 1957, measured directly, averaged 44 muC in five Rongelap inhabitants (Figure 57) and 350 muC in two Utirik inhabitants. Miller, in 1957, determined aneffective half-life of 110 days for the elimination of Zn**, which givesa biologi- T 800 + 4 600 + 4 400 4 ty ~70 DAYS 200 F level. The slight increase in environmental level of Cs'3’ during the 1956 and 1958 periods of weapontesting was reflected in an increased body burden in the Marshallese. As pointed out,a very marked increase in Cs'*” was also observed in the Rongelap people after they returnedto their orig- 4 cal 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 #C in 1958 after the return of the Rongelap people to their 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® 100 F 80 ° 4 1 30 1 60 L 30 1 120 1 150 1 180 TIME IN DAYS - AFTER MARCH |, 1954 Figure 56. Urinary excretion of Cs’ in exposed Marshallese. levels reportedforfish. In 1956,fish from Rongelap Lagoon were foundto contain 0.6 muC Zn* per |b muscle, or 7.5 muC per tb whole fish.5¢ The 1959 body burdens of Zn*are presented in Table 35. As with Cs'*’, the variation within any group is large, and nosignificant difference is found in Zn*®per unit body weight correlated