More than a year after a devastating tsunami inundated the Fukushima Daiichi nuclear power plant, a report from the World Health Organization says people in most parts of Japan got "low" added radiation, but estimates much higher doses in some areas that were not immediately evacuated.
The health risks are still unclear, said the group, which is waiting for a second report this summer.
"We don’t want people jumping to conclusions," said Gregory Hartl, a spokesman for the World Health Organization. "This is the first step in something that will go on for years."
A team of experts gathered by WHO used information from the Japanese government to estimate how much radiation had found its way into people in Japan and abroad through external exposure, inhalation and food, erring on the high side to avoid underestimating the problem.
In most of Japan, the added doses of radiation after the accident were estimated to be one millisievert or less, within guidelines from the International Commission on Radiological Protection, which recommends limiting added exposure to one millisievert. People who work in jobs involving radiation are supposed to average no more than 20 millisieverts annually and avoid going over 50 in a single year.
Across the Fukushima region, radiation doses were estimated to fall between 1 and 10 millisieverts. But the added doses of radiation were believed to be much higher in the towns of Namie and Itate, where doses were estimated to run as high as 50 millisieverts in the year after the accident.
In some areas of Namie, infants were estimated to have gotten a dose of as much as 200 millisieverts in the thyroid, where radiation can build up in the body. Babies are especially vulnerable because smaller amounts of radiation have a larger effect on their bodies.
Some experts say the new Fukushima findings back up their concern about the way governments across the world have planned to protect people during nuclear disasters.The two areas are outside the roughly 12-mile radius that was first evacuated after the accident; people there were later relocated.
"There are these built-in assumptions about who’s going to be safe and who’s not. That needs to change," said Edwin Lyman, a senior scientist at the Union of Concerned Scientists.
Lyman argues that the minimum evacuation radius should be expanded and governments should check weather patterns to assess where else to clear beyond that bigger radius, he said.
Widening the evacuation zones around nuclear plants has been hotly debated in the United States, where bigger evacuation zones could mean emptying big cities if accidents occur.
The new report does not include any radiation immediately received by people within the evacuation zone before they left, which the experts said would require more precise data to assess.
The estimates also leave out workers at the plant after the accident, who will be covered by the next study, it said. A separate U.N. investigation said Wednesday that six worker deaths after the accident were not tied to radiation and that although several workers suffered irradiation, there were no evident effects.
After the WHO report was released, the operator of the stricken Fukushima plant said its own study found that more radiation had been emitted than the Japanese government had estimated. Experts cautioned against overreacting to the news; Lyman said it wouldn’t affect the WHO findings.
"Estimates can differ substantially if conditions change, even just a little," Kinki University Professor Hideo Yamazaki told Yomiuri Shimbun, adding that "the figure is within the assumed margin of error."
-- Emily Alpert in Los Angeles
Photo: A young evacuee is screened at a shelter for radiation from the damaged Fukushima nuclear plant March 24, 2011, in Fukushima. Credit: Wally Santana / Associated Press