Table 3. Estimated whole-body (gamma) and thyroid doses (rad). Thyroid dose (incl. gamma), at exposure ages Population Rongelap Ailingnae Utirik No. 65 18 158 Whole-body dose 175 69 14 <10 810-1800 275-450 60~-95 10-18 >18 335-810 190 30-60 335 135 30 estimated average dose of 1000 rads to the thyroids of young children appears to be low; certainly for two boys who developed thyroid atrophy and myxedema. The calculated doses are obviously rough estimates. The incompatibility of these observed effects with the calculated doses based on !3l] must be related partly to the short-lived iodine isotopes (see refs. 188-192). However, the option must be kept open that the actual doses were higher than those esti- mated and that possibly other radionuclides may have been absorbed by the bones and contributed to the dose. B. Residual Radiation (Accumulated Exposure From Habitation on Rongelap or Utirik Atoll) 1. Early Calculations The subject will be only briefly reviewed here. for earlier estimates can be found in the refs. 1, 13, More detailed treatment 18, and 22. When the Rongelap and Utirik people returned to live on their home islands, these atolls, although considered radiologically safe for habitation, still had low levels of residual radiation. Before the Utirik people returned in July 1954 and the Rongelap people in July 1957, they had largely excreted the radionuclides initially absorbed at the time of the fallout. By six months, radiochemical analyses of urines of the Rongelap population revealed barely detectable radioactivity (see Table 2). A number of radiological surveys on Rongelap and Utirik following the accident showed low levels of residual gamma radiation and small amounts of radionuclides in the soil, water, and plant, animal and marine life. The principal isotopes were 137¢5, 90s, 6 Zn, and Fe, though very low levels of several other isotopes were found. When the people returned, personnel monitoring procedures showed low body burdens of these isotopes absorbed from the environment. (The short-lived isotopes of iodine had long since died out.) The major contributing food plants were pandanus and coconut. The coconut crab, a food delicacy, had to be banned from the diet for >15 years because of unacceptable levels of radioactivity. Measurable levels of 25Fe were found in the blood of Rongelap people (1,236), but since they were <1/100 of the maximum permissible body burden, this was not considered a significant hazard. - 114 -