4O 2886 I #50 38% HT 6 3) " EF ORRAUER ORBAN, HICMARFHER m I mM 2 BUNSAIBABEATENBREF ACTA HAEM. JAP. 38: 635~645, 1975 Clinical, especially Hematological Observations over the 20-Year Period on the Japanese Fisherman Exposed to Fallout in 1954 Division of Radiation Health, National Institute of Radiological Sciences, Chiba On March 1 in 1954, 23 Japanese fishermen aged from 18 to 39 were exposed to radioactive fallout produced by the thermonuclear test explosion at Bikini Lagoon. After 14 days navigation they returned to their harbor where they were found to have been injured by radioactive materials. They were hospitalized for 13 months, After being discharged most of them have been examined so far as possible on an anual basis. The fishermen were irradiated in the following three ways: (1) From the radioactive materials adhered to the skin. (2) Externally from the radioactive materials in the cabins, on the deck etc.. (3) Internally from the redioactive materials entered various organs. While the estimate of radiation dose to skin as well as the dose by internal radiation were difficult, the estimated external radiation dose was approximately 170-500 rad for 14 days, about, half or more of which was irradiated on the first day. The dose to each person differed depending on his behavior on the boat and the position of his cabin, and had the intimate relationship with his minimum value of leukocytes and neutrophils. Soon after exposure most of the fishermen experienced anorexia, fatigue, and conjunctivitis. and in some of them nausea and vomiting occurred. Shortly after the exposure, they suffered from erythema which was followed by edema, vesicle, erosion, ulceration or necrosis. Epilations were observed in 20 cases. Though the skin injuries recovered gradually, some persons continued to show residual changes. However, neither chronic radiation dermatitis nor malignant changes was obserbed. Leukocytes count decreased gradually, showing minimum count at 4th-7th week. 5 cases revealed a count of less than 2,000/mae, 13 less than 3,990 and 5 less than 4.000. penia was noticed and then neutropenia became marked. At frst lympho- At the recovering stage, eosinophillia and the appearance of immature neutrophis were observed in many cases. In severe cases slight anemia was observed, accompanied by the depression of reticulocytes. Platelets count showed minimum value at the 4th-7th week. Slight hemorrhagic tendencies were observed in severe cases. Bone marrow of severe cases was highly hypoplastic at the critical stage, which changed to slightly hypoplastic and turned into almost normal marrow. The coexistence of hypoplastic area and hyperplastic area was observed in histological] sections at the recovery stage and even in the examinations of 10-15 years after the exposure. Morphological abnormalities of blood cells were noticed in both peripheral blood and bone marrow. The cumulative distribution curve of leukocytes counts dispiaced slightly to the left of normal one even 6 years after the exposure. Follow-up of chromosome observations in blood cells has been performed since 1964. Even 20 years after exposure, cells with chromosome abnormalities (both Cu and Cs cells) exist in the peripheral lymphocytes with much higher frequencies than in general population. While the frequency of Cu cells (dicentrics and rings) was decreasing Cs cells remained fairy constant. 635 The frequencies of