A year after the Fukushima nuclear accident, the emerging consensus among scientists is that its effects on physical health and the environment have so far been minimal. There have been no reported radiation-related deaths or illnesses from the accident, even among workers who faced very high exposure. That's a stark contrast with the world's last major nuclear accident, in Chernobyl in 1986, when 28 workers died of acute radiation syndrome within the first year.
"From a radiological perspective, we expect the impact to be really, really minor," said Kathryn Higley, a specialist in tracking radiation in the environment at Oregon State University.
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While several advanced countries prepare to curb or eliminate their nuclear power programs, heavy construction of reactors is planned in developing countries, particularly in Asia.
Those studying the accident warn, however, that the early, reassuring conclusions may understate the extent of exposure for certain people. They add that scientists still know very little about the effect on the human body of extended exposure to low-level radiation. There also have been some disturbing developments—a reduction in the bird population near the plant, high levels of radiation in local fish—that biologists say they will continue to watch.
"The most important thing is to monitor everyone's health carefully over the longer term," said Shunichi 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 n