INTERNAL IRRADIATION Radiochemical analyses of numerous urine samples of the exposed population showed internal absorption of radioactive materials, probably brought aboutlargely through eating and drinking contaminated food and water and to lesser extent through inhalation. During the first few days when the bodylevels were at their highest, the maximum permissible concentrations were ap- proached orslightly exceeded only in the case of strontium-89 and the isotopes of iodine. The con- centrations were believed to be too lowto result in any serious effects. Body levels fell rapidly, so that by 2 and 3 years post exposure, they were far below the accepted maximum permissible level; by 6 months activity in the urine was barely detectable. In 1957 analyses of bone samples on one of the men whodied showed 3.7 strontium-90 units/g den for 1959 was 0.57 uC. The mean body burden of Zn®estimated from whole-body counting data was, in 1958, after the return to Rongelap, 0.36 uC, 8 times as high as in 1957, and 0.44 pC in 1959. Thus, whereas the Cs'*” levels appear to have reached a maximum andactually to have dropped in 1959, the Zn® levels have shown a continued increase which is probably related to the long biological half-life of the latter. The Sr® level in 1958 estimated from excretion data was 2 muC, about 20 times as high as in 1957 before the return to Rongelap. The estimated body burdenin 1959 increased to 6.0 mpC, about 20% of the estimated ultimate equilibrium value. Little of the body burden of the exposed groupis apparently dueto their initial exposure, since at presentthereis little difference between the levels of the exposed and unexposed populations living on RongelapIsland. Whenthese three isotopes have reachedtheiresti- calcium. Beginning in 1957, gammaspectroscopy by use of a low-level counting chamber was added to the techniques of radiochemical analysis. The mated equilibrium values, the body burdenswill still be of small significance in terms of radiation (which after careful survey was consideredsafe for habitation, despite a persisting low level of radio- OTHER STUDIES hazard. “ ” . ' ne ere eeeemerniae! Semen? emma oo “ = ~ return of the Rongelapese to their home island | | | active contamination) wasreflected in a rise in their body burdens and increased urinary excre- tion of certain radionuclides. During the years since the original contaminating event, additional weaponstests held in the area have contributed to the fission products in the environment. Since _the diet includes a variety of imported foods, the people are not living in a “closed” environment, and therefore may not be rapidly approaching equilibrium with the environmental fission products, as might be expected underother circumstances. Body burdens of gamma-emitting fission products (such as Cs'*’ and Zn *) were measuredin a whole-body counter and checked by radiochemical analysis of urine specimens. Body burdensof Sr°° were estimated from urinary excretion as determined byradiochemical analyses. Both the external dose measurements on Rongelap Island and the levels of radioactive isotopes in the food on the island indicated that someincrease in Cs'*’, Zn*°, and Sr*" body burdens was to be expected whenthe people returned there in 1957. The Cs'*" body burden in 1958 was about 0.68 1C, about 60 times as great as in 1957, and the urinary Cs'** level rose by a factor of 140; the mean body bur- Studies ofgenetically inherited characteristics. Blood grouping studies in the Marshallese showed a relatively high B gene frequency, a high N genefrequency, an extremely high R" gene frequency, and total absence of Kell and Diego factors. These characteristics differ from those of Polynesians and suggest relationship with Southeast Asians and Indonesians. Haptoglobin studies showed the frequency of the Hp’ gene to be higher than in European populations thus far tested and consistent with populationsliving near the equator. Thedistribution of haptoglobin types showed the population to be relatively homogeneous. Transferrins in all sera were type CC, the common European type. 8-Amino-iso-butyric acid urinary levels showed the Marshallese to be the highest excretors of this acid of any population thus far reported. Levels in the exposed group were about the sameas in the unexposed group, and nocorrelation was found with body burden level of radionuclides; this indicates that there is probably no correlation with radiation exposure. Hemoglobin types were considered normal. Sickling tests showed no sickling tendency in any ofthe people. Giucose-6phosphate dehydrogenase of the red celis appeared to be deficient in the Marshallese. Considerable cau-