XI. SUMMARY AND COMMENTS Until 1954, the Japanese at Hiroshima and Nagasaki were the only human populations exposed to significant radiation from nuclear detonations. As a result of the Bravo accident in 1954, following the detonation of a megaton nuclear device in the Pacific, 250 Marshallese, 28 American servicemen, and 23 Japanese fishermen were exposed to a relatively unknown hazard, radioactive fallout. The medical observations of the exposed Marshallese over the past 27 years have resulted in significant findings reported in numerous publications. Health care and treatment of the expose: people during the course of the sur-— veys and examinations also represent an important contribution. The medical findings provide the only knowledge about the effects of radioactive fallout on human beings from detonation of nuclear devices. The exposure of the Marshallese to fallout radiation differs in several important respects from the exposure of the Japanese at Hiroshima and Nagasaki. In Japan, there were many casualties from blast and heat effects, and psychological trauma was extreme. The Marshallese, being far removed from the site of detonation, had no effects from blast or burns, and the psychological effects of their experience appeared to be minimal. Radiation effects in the Japanese were due to whole-body exposure to gamma and neutron radiation from the detonating bomb with insignificant fallout. Their exposure resulted in acute effects with high early mortality, and in late effects involving principally the development of malignancies, with leukemia appearing first and solid tumors later. Radiation effects in the Marshallese were related only to fallout exposure: whole-body gauma irradiation (no neutron expcesure); skin irradiation from deposition of fallout on the body; and internal exposure due to absorption of radionuclides (principally radioiodines) from ingestion of radioactively contaminated food and water and inhalation of fallcut particles. As emphasized in this report, many uncertainties were involved in calculating the early radiation dose received by the Marshallese prior to their evacuation. This was particularly true for the internal dose calculations (thyroid dosimetry). Estimates of early exposures for whole-body gamma radi- ation were 175 rads on Rongelap, 69 rads on Ailingnae, and 14 rads on Ucirik. Clinical findings (principally hematologic) generally supported these estimates. For Rongelap, thyroid dose estimates varied from 335 rads in adults to 700-1400 to perhaps >2000 rads in young children. For Ailingnae and Utirik Atolls, thyroid dose estimates were roughly parallel to gamma dose estimates. People living on Rongelap, Utirik, and Bikini since the 1954 accident have been exposed to low doses of radiation, delivered at a slow dose rate, from residual contamination (see Appendix II). No detectable effects of this low exposure have been noted, and it is unlikely that any will be. Periodic personnel and environmental radiological monitoring is carried out on these atolls and on inhabitants who. have moved to other atolls. It now appears that the early thyroid dose calculations may have resulted in underestimation, and all the dosimetry calculations are being reevaluated at this Laboratory on the basis of more recent data that have become available. ~ The ‘findings in the exposed Marshallese populations are briefly summarized as follows. - 85 -