Zl Internal Radiation Long-term effects ofinternally deposited isotopes from the fallout would result largely from the bone-seeking isotopes, of which Sr®° with a halflife of 28 years is by far the most important. Bone deposition does not impose a genetic hazard,since radiation is almost entirely confined to bones, with little or no gonadal irradiation. As with radium, Sr°° irradiation of the bone mayresult in osteoporosis, sarcoma, and possibly leukemia if deposited in sufficient amounts. The Sr°° activity of the Rongelapurine samples at two years post-exposure wascalculated to be 0.6 d/m/24 hr, and of bone samples on the deceased to be 1.60.06 d/m/g ash. Both values indicate the body burden of Sr*° to be well below the accepted tolerance levels and within the limits of American samples. Cs'*" is distributed generally in the soft tissues and so might cause some gonadal radiation and present a genetic hazard. However, the levels in the Marshallese, though several times higher than those found in Americans, are far below the toler- ance level. It was estimated that the individual with the highest level of Cs'*” probably received an additional amountof radiation equal to about one-fifth that ordinarily received as cosmic radiation. It is quite reassuring that such low levels of body burden of radionuclides were reached so quickly, when one considers the extreme degree of contamination that these people lived with for two days withlittle or no effort to avoid internal deposition. The original body burdens have dwindled rapidly over the three-year period. Indeed, at this time such low levels are present that evaluation of the componentdueto the original fallout becomes difficult to differentiate from the added components due to subsequent world-widefallout. The fact that the Cs’*” level in the Marshallese man not exposedto the original fallout was nearly as high as that in the exposed Rongelap people makes it seem plausible that additional sources of fallout are now contributing more to the body burdenthan the original exposure. Therelatively muchhigherlevels observed in the Utirik people are dueeither to the fact that these people have been living continuously on their slightly contaminatedisland since four monthsafter the accident, or that further fallout has occurred since the original event. Probably both factors are involved. The presence of detectable Zn** peaks on gammaspectroscopyis of interest, since this isotope is not a fission product. The isotope may haveoriginated from metallic structures involved in the nuclear detonations. Zinc has been found to be concentrated in marinelife.** The large consumption by these people of fish containing Zn® would therefore accountfor the zinc peaks. Co®° has been foundto be concentratedin clamsin the Marshall Islands. Presumably since these are not eaten to any great extent, Co®* peaks were not detected. REPATRIATION OF THE RONGELAP PEOPLE Thedecision to move the Rongelap people back to their home island was madeafter careful consideration of the hazards associated with theslight residual contamination of the island to which the people would be subjected on a lifetime basis. The evaluation of the hazardresolveditself primarily into a consideration of the gammadose and Sr*° levels. Extensive radiological surveys of Rongelap Atoll with radiochemical analysis of samples have been carried out by several agencies sponsored by the Atomic Energy Commission.**** The results of the surveys have been summarized by Dunning.*° External gammareadingson theisland at two years post-contamination showedlevels (at 3 ft above the ground) varying from 0.2 to 0.5 mr/hr with an average of 0.4 mr/hr. However,since part of this dose was dueto relatively recentfallout of slight degree (at that time), it was expected that the dose rate at the time of repatriation (July 1957) would be less than 30 mr/week, and at the endofthe first year the accumulated dose would probably not exceed 0.5 rem with lower doses in succeedingyears. Radiochemical analyses of food sources of the island revealed that in spite of some degree of uncertainty, the estimated future body burdensof the Rongelap people would beless than 100 pwc Sr®° provided that land crabs (whichselectively concentrate Sr®° ) were eliminated from thediet. This is the value (100 sunshine units) that has been considered allowable by the U.S. National Academyof Sciences report. In view of the present low levels of body burden of radionuclides, and since the added radiation burden imposedbyliv-