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Evidence of radiation exposure found in teeth and blood of fishermen who experienced U.S. hydrogen bomb test at Bikini Atoll

by Yota Baba, Staff Writer

A group of researchers led by Masaharu Hoshi, a professor emeritus at Hiroshima University and an expert in radiation biology and physics, has found scientific evidence, for the first time, which shows that not only crew members of the Daigo Fukuryu Maru (The Lucky Dragon No. 5) but also those in other Japanese fishing boats were exposed to radiation released by the U.S. hydrogen bomb test conducted in 1954 at the Bikini Atoll. This finding was reported at a meeting held at Hiroshima University on August 7.

With the cooperation of former crew members of tuna fishing boats and a cargo ship, from Kochi Prefecture, Miyagi Prefecture, and other prefectures, which were sailing from March to May 1954 around the hydrogen bomb test site in the Pacific Ocean, Dr. Hoshi analyzed the traces of radiation in their blood and lost teeth.

The teeth were provided by two fishermen on two boats. From one tooth, Dr. Hoshi found that the person’s estimated exposure dose was 414 milligrays. Even if medical exposure to radiation in subsequent years is excluded, this is equivalent to the exposure suffered in the atomic bombing of Hiroshima at 1.6 kilometers from the hypocenter. Dr. Hoshi also collected blood from 19 former crew members of eight fishing boats and a cargo ship and checked if there are chromosome abnormalities in their lymphocytes. Dr. Hoshi estimated that these crew members were exposed to a higher level of radiation by 90 millisieverts on average, compared with nine men in the control group, who are in their 70s and 80s, about the same age as the crew members.

The International Commission on Radiological Protection (ICRP) recommends that the annual exposure to radiation for the general public be limited to one millisievert. Dr. Hoshi said, “The radiation levels we detected are abnormally high. Although the samples are limited, both of these analyses show higher levels of estimated radiation exposure. Therefore, we can conclude that these individuals were exposed to significantly high levels of radiation.”

It was assumed that the hydrogen bomb test conducted at the Bikini Atoll contaminated fish caught by many Japanese fishing boats and caused harm to the health of crew members due to exposure to the radioactive fallout, but the actual radiation exposure of crew members had not been elucidated. Dr. Hoshi’s group studied the official report on the contaminated fishing boats, which was made by the Ministry of Foreign Affairs but was kept classified. From this document, the researchers found that the former Ministry of Health and Welfare had conducted health examinations on fishermen who were on other boats besides the Daigo Fukuryu Maru, and that there were many cases in which leukopenia (a fall in the number of white blood cells), due to radiation exposure, was suspected.

Masatoshi Yamashita, executive director of the Kochi Prefecture Pacific Ocean Nuclear Test Suffering Support Center (Sukumo City, Kochi Prefecture), is a member of this group and has studied the circumstances surrounding these boats for many years. “As many as 10,000 fishermen may have been exposed to radiation,” he said. “The Japanese government must create a mechanism to address this issue and investigate the actual situation and offer health examinations.”

(Originally published on August 8, 2014)

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