21 Internal Radiation Long-term effects of internally 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 gonadalirradiation. As with radium, Sr®° irradiation of the bone mayresult in osteoporosis, sarcoma, and possibly leukemia if depos- ited in sufficient amounts. The Sr*"activity of the Thepresence of detectable Zn** peaks on gamma spectroscopyis of interest, since this isotope is not fission product. The isotope may haveoriginated from metallic structures involved in the nuclear detonations. Zinc has been foundto be concentrated in marinelife.** The large consumption by these people offish containing Zn** would therefore accountfor the zinc peaks. Co*° has been foundto be concentrated in clamsin the Marshall Islands. Presumably since these are not eaten to any great extent, Co*° peaks were not detected. Rongelap urine samples at two years post-exposure was Calculated 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 thatthe individual with the highest level of Cs'*’ probably received an additional amountof radiation equalto about one-fifth that ordinarily received as cosmic radia- tion. 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 with little or no effort to avoid internal deposition. The original body burdens have dwindied rapidly over the three-year period. Indeed, at this time such low levels are present that evalu- ation of the componentdueto the original fallout becomes difficult to differentiate from the added components due to subsequent world-widefallout. Thefact that the Cs’*? level in the Marshallese man not exposed to 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 theoriginal exposure. Therelatively much higherlevels observed in the Utirik people are due eitherto the fact that these people have been living continuously on their slightly con- taminatedisland since four monthsafter the acci- dent, or that further fallout has occurredsince the original event. Probably both factors are involved. REPATRIATION OF THE RONGELAP PEOPLE The decision to move the Rongelap people back to their home island was madeafter careful consideration of the hazardsassociated with theslight residual contamination ofthe island to which the people would be subjected ona lifetime basis. The evaluation of the hazardresolveditself primarily into a consideration of the gamma dose 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 gammareadingsontheisland at two years post-contamination showed levels (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 beless than 30 mr/week, and at the endof the first year the accumulated dose would probably not exceed 0.5 rem with lower doses in succeeding years. Radiochemical analyses of food sourcesofthe island revealed that in spite of some degree of uncertainty, the estimated future body burdensof the Rongelap people would beless than 100 pyc Sr°° provided that land crabs (which selectively 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 addedradiation burden imposed byliv-