First study reports very low internal radioactivity after Fukushima disaster via Washington Post

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.

“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.

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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.

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Ref. (referred article): Internal Radiation Exposure After the Fukushima Nuclear Power Plant Disaster via Journal of the American Medical Association (subscription is required)