EFFECTS OF IONIZING RADIATION present in the G, J. tract at one day post detona- tion in the members of Group IT was estimated us approximately 3me. This activity was contributed chiefly by isotopes of short radiological and biolowical half-life and limited solubility. Thus the levels of activity in the tissues of the hody were relatively low. The concentration of radioisotapes at G months posi detonation was barely detectulie in the urine of most exposed individuals. Todine, which is quite solable. ts probably the mast lazardous internal endioemitéer in the early period following exposure (10). The dose to the thyroid was appreciable, but low compiayed to the partially or totally ablatine doses of 11" used in therapy of hyperthyroidism or carcinoni. At one day post detonation Sr was calculated to be near the maxiuviun pernossille level (4) for this nuclide. At later times following exposure, this longer-lived fission product presents the zreatest potential in- ~ ternuad drazard. The present study confirms the observation natde in animal experiments that most of the racioucltive elements fosmed in fission as well ts the fissile material itself, are uot readily ale sorbed from the hiungs and the G. 7. tract. Only I, Sv, Ba anda few of the rare earth elements were absorbed to any significant degree, + F"3002718 An attempt to measure bone-fixed radioactive emitters by means of sensitive filny badges taped below the knee, over the epiphysis of the tibia on a number of persons, yielded no positive results. . No correlation could be obtained between the degree of internal contamination and the clinical and hematological findings. . In view of the short half-life of the most abundant fission products cleposited internally in this situation, the possibility that chronic irradiation effects will occur is quite small. Thus, an evaluation of the data on the internal contamination, in- malin On the basis of an assumed uptake of 20 per- cent per 24 hours, the integrated dose to the thyroid from I and other shorter-lived iodine isotopes was calculated by the USNRDLto be about 100 rep. The LASL has estimated that this dose was about 150 rep for Rongelap group and 50 rep for the Americans. The differing appronches used by the ESNRDL and the LASL for estimating the body burden gave results which, except for Balt, are very close. The mean body burdens of the individual nuclides presented in Table 5.6 were calculated for the Rongelap group. Values for the Ailinginne group were approximately half those of the Rongelap group, and values for “Americans, about one-fourth those of the Rongelap group. The total amount of radioactive material cluding that of Sr*, leads to the conclusion that the internal hazard to the contaminated inhahitants of the Marshall Islands is minimal both from the acute and the long range point of view. 5.33 Source of Iocernal Contamination The fallout material consisted Jargely of calcium oxide and calcium carhonate. The fission products were adsorbed mainlyon fairly large particles. The material was 10 percent soluble in water, and completely soluble in acid. Internal deposition of fission products resulted from inhalation and ingestion of the fallout maiterial. Ingestion appears to be the more important of the twa routes of entry into the ody. ‘Fhe activity in the air settles ont fairly rapidly, but contaminated food. water and utensils retain their activity for long periods of time. The amount of fission products reaching the hioodstream Chrough the respiratory tract isa function of particle size and solubility of the airborne contaminants. The particles with which the activity was assoctated were considerably Jarger than the optimum size for deposition in the alveolar tissue of the lung. Thus, the probabilityof the retention of inhaled airborne confamination was not appreciable during the exposure period. The lipothesis that Ingestion was the chief source of imternal contamination is supported by the finding that the gastro-intestinal tract, its contents, and the liver of autopsied chickens and pigs sacrificed at early jutervials following a, Bae wee * * a, vere | * a 8 ee ee ee ee ee 74 ——