First study reports very low internal radioactivity after Fukushima disaster

Japanese researchers have found very low amounts of radioactivity in the bodies of about 10,000 people who lived near the Fukushima Daiichi power plant when it melted down.

The first published study that measured the radiation within a large number of residents reassured health experts because the numbers reported imply only negligible health risks. The threat appeared to be considerably lower than in the aftermath of the Chernobyl accident, the experts agreed.

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Japan’s no-go zone: Beyond the crippled Fukushima Daiichi nuclear plant, for at least 12 miles in any direction, the Japanese government maintains a no-entry zone, with teams of policemen sealing off all roads going in.

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Japan’s disaster: On March 11, Japan marks one year since a deadly earthquake and tsunami struck its northeastern coast, killing at least 15,000 people and leading to the country’s worst-ever nuclear accident.

“Exposure levels were much lower than those reported in studies even several years after the Chernobyl incident,” said Masaharu Tsubokura of the University of Toyko, lead author of a short paper published in the Thursday issue of the Journal of the American Medical Association.

The study measured radiation in 8,066 adults and 1,432 children in the town of Minamisoma, about 14 miles north of the Fukushima Daiichi power plant. Researchers found an average radiation dose of well under 1 millisievert, which is considered a safe amount.

The residents stood in a full-body radiation counter for two minutes, which allowed the scientists to measure the presence of radioactive cesium isotopes. Those isotopes, which can be taken in from the air or through eating contaminated food, are generally considered to be among the ones posing the greatest health risk from the Fukushima accident. The measurements were taken between September 2011 and March.

Roy Shore, chief of research at the Radiation Effects Research Foundation in Hiroshima, Japan, said in an interview that the measured doses constitute a very low health risk.

“Out of 10,000 people with a dose of 1 millisievert, the radiation would cause two to get cancer during their lifetimes, but about 3,500 would get cancer also without any radiation,” he said. “The jury is still out, but I expect the public health impact from radiation to turn out to be considerably lower than that of Chernobyl.”

But he said radiation is not the only health risk after the Fukushima accident. “The psychological impact has been very great and has caused a lot of anxiety,” he said.

Although the study results appear to be reassuring, they are considered preliminary and come with a number of caveats.

The measurements of radiation were not initiated as a scientific study, for instance, but meant as health checkups for volunteers from the local population. Therefore, there may be a selection bias in the results, although it is not known whether it would lead to an overestimation or underestimation of the measured doses.

“We would expect that people most concerned and therefore with a higher chance of exposure would seek out the screening, yet we cannot know for sure,” said Stuart Gilmour, co-author of the study at the University of Tokyo.

Kiyohiko Mabuchi, head of the Chernobyl Research Unit at the National Cancer Institute, said that only internal radiation from one source — cesium — was measured. Therefore, the study does not address external radiation from contaminated areas, which can be harmful, too.