hunichi Yamashita, vice president at Fukushima Medical University and a longtime researcher on the impact of radiation on human health.
Toshiso Kosako, a Tokyo University expert on radiation protection, estimated that, over the long run, Fukushima Daiichi will increase the incidence of thyroid problems, including cancer, for 300 to 500 people. Chernobyl, by contrast, resulted in 5,000 to 6,000 cases of thyroid illness, mostly among children, he said. A global group created to study the health effects of Chernobyl expects a total of 4,000 fatal cancers among those most highly exposed.
Mr. Kosako drew international attention in April when he tearfully resigned as an adviser to then-Prime Minister Naoto Kan, blaming the government for failing to protect communities. Though he still has complaints, he also credits the low toll to the government's relatively quick effort to control food and water supplies after the meltdowns. In Chernobyl, contaminated milk was a major cause of illness among children.
One government survey of 10,468 people from three towns at high risk—Namie, Iitate and Kawamata—was released in late February. Among them, 58% are estimated to have received less than one millisievert of exposure, and 95% less than five millisieverts. Just 23 people, including 13 nuclear workers, were assumed to have been subjected to more than 15 millisieverts.
By comparison, the U.S. Environmental Protection Agency estimates that Americans are exposed, on average, to three millisieverts of radiation per year from natural and man-made sources. Japanese safety rules allow a nuclear worker up to 100 millisieverts a year—a level that was temporarily raised to 250 millisieverts as workers tried to contain the stricken plant.
The exposure figures were based on surveys of where residents were at certain times and the radiation levels in those areas. Separately, Fukushima prefecture offers testing by whole-body scanners to directly measure internal radiation exposure. By the end of January, 15,408 people had been tested, but none showed levels that would lead to "health effects," the prefecture said. Among those tested, only 25 people showed exposure levels of one millisievert or higher, with the highest number, three millisieverts, found in two people.
The prefecture has also conducted thyroid tests on children, including 3,765 children tested in October and November. Medical advisers concluded that none in that group had problems related to radiation exposure.
Foreign correspondents were taken on a tour of the blasted Fukushima Daiichi nuclear reactors. The WSJ's Phred Dvorak tells Yumiko Ono what she saw at Fukushima.
One year after Japan's March 11 disaster, WSJ's Yumiko Ono talks to reporter Yuka Hayashi about the fate of Fukushima evacuees from the town of Namie who are still living in temporary housing.
Recovery workers at Japan's crippled Fukushima nuclear plant still fear for the future, one year after the country's worst ever nuclear accident. (Video: Reuters/Photo: AP)
Still, reports on population exposure are as much guesswork as science. Experts from Hirosaki University did their own thyroid tests on evacuees and found exposure levels higher than the government figures. Shinji Tokonami, a professor who helped to run the study, said that his group used different assumptions than the government about whether evacuees faced high exposure immediately or whether it was spread out over two weeks.
And it's hard to know just how much exposure people really had. Minoru Kamata, a physician at Suwa Chuo Hospital in Nagano, said that officials belatedly discovered that contaminated pebbles had been used to make the foundation of apartment buildings that housed evacuees—a fact revealed only because a teenager in the housing came from one of the few communities requiring children to wear dosimeters.
Workers at the plant have received considerably higher levels of exposure, according to data from Tokyo Electric Power Co., the operator of Fukushima Daiichi. Of the 20,115 people who have worked there since last March, 167 were exposed to 