Appendix VI A SUMMARY OF THE FINDINGS OVER THE 25-YEAR PERIOD ON THE JAPANESE FISHERMEN EXPOSED TO FALLOUT IN 1954 Toshiyuki Kumatori, M.D. Director General, National Institute of Radiological Sciences 0-1, Anagawa 4-chome, Chiba-shi, Chiba 260 Japan On March 1, 1954, 23 Japanese fishermen aged from 18 to 39 were exposed to radioactive fallout produced by a thermonuclear test explosion performed by U.S. authorities at Bikini Atoll. They were the crew of a tuna fishing boat, The 5th Lucky Dragon. The location of the boat was 166°58' E and 11°53' N. (Japanese standard time) while fishing for tune, At about 3:50 a.m. they saw a huge red light in the west, and they heard detonationlike sounds 7 to 8 minutes later. At about 7 a.m. white ashes began to fall on the boat and continued to fall for about 4.5 hours. After 14 days' navigation, the fishermen returned to their harbor, Yaizu, on March 14, 1954. After landing, all were found to have been injured by the radioactive materials. Seven of them were hospitalized in the Tokyo University Hospital and the other 16 were sent to the First National Hospital of Tokyo by March 28. They were discharged from both hospitals in May 1955, except for one fatal case who died on September 23, 1954. After being dis- charged, most of them have been examined so far as possible on an annual basis. A. Mode of Irradiation and Estimated Radiation Dose During the most intensive fallout the fishermen could not keep their mouths and eyes open. Fallout deposited on the deck was thick enough to show footprints. Irradiation was received in the following three ways: * From the radioactive materials adhering to the skin. * Externally from the radioactive materials in the cabins, om the deck, * Internally from the radioactive materials entering various organs. etc. Estimation of radiation dose to skin as well as the dose by internal exposure was difficult. On the other hand, the estimated external radiation dose was +170 to 600 rad for 14 days, about half or more being received on the first day. The dose to each person differed depending on his behavior on the boat and the position of his cabin. The integrated dose to thyroid glands from 1311 was calculated to be about 20 to 120 rad by external counting. Besides 1311, other iodine isotopes, mainly 1337 and 135y, contributed to the irradiation of thyroid glands. Assuming that the fishermen inhaled radioiodine isotopes for 5 hours after the detonation, the total thyroid dose from incorporated iodine isotopes was esti- mated to have been about 80 to 450 rad. Urine samples collected at 4 weeks after the explosion revealed significant amounts of radioactivity. However, the radioactivity decreased rapidly; at about 6 months post detonation it was barely detectable. In the analysis after 8.5 years and 10 years the levels of 137cs and 90Sr in urine were the - 136 -