U.N. panel: Thyroid radiation doses in Fukushima infants within safe limits

February 27, 2013

By YURI OIWA/ Staff Writer

FUKUSHIMA--Thyroid gland doses of internal radiation in year-old infants living within 30 kilometers of the Fukushima No. 1 nuclear power plant are well within safety limits, according to a United Nations committee.

At a Feb. 26 international conference in Fukushima, a representative of the U.N. Scientific Committee on the Effects of Atomic Radiation said the infants averaged less than 50 millisieverts, about half the estimate presented by the World Health Organization in May.

International Atomic Energy Agency guidelines recommend the ingestion of iodine tablets to block thyroid irradiation for people with a dose of 50 millisieverts. It is believed the risk of cancer increases in levels that exceed 100 millisieverts.

The U.N. estimate used data that was not compiled in time for the WHO evaluations, and also considered typical evacuation behaviors on an area-by-area basis.

During the conference, several Japanese researchers said the U.N. evaluations were more realistic than the WHO estimates.

The WHO estimated that thyroid gland doses were between 100 and 200 millisieverts for 1-year-olds in the town of Namie, and 10 to 100 millisieverts for 1-year-olds in the rest of Fukushima Prefecture.

The WHO assumed that residents in the 20- to 30-km zone surrounding the nuclear plant evacuated their homes around four months after the crisis began to unfurl on March 11, 2011, and considered both the inhalation of airborne radioactivity and the ingestion of contaminated foodstuffs and water.

The U.N. estimate, by contrast, only considered harmful effects through inhalation.

The U.N. committee also evaluated whole-body doses of adults within a 30-km radius of the nuclear plant. Such doses were estimated at less than 5 millisieverts on average for those who evacuated on March 12, 2011, and at less than 10 millisieverts on average for those who evacuated later.

The WHO's Zhanat Carr, who attended the Feb. 26 session, said it was common for the WHO, whose mission is to protect people's health, to present cautious estimates so as not to underestimate doses.

The U.N. committee will present a report, being drawn up by about 80 experts from countries, including Japan, to a session of the U.N. General Assembly in September.

By YURI OIWA/ Staff Writer
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A National Institute of Radiological Sciences employee shows reporters how to test for thyroid gland doses of internal radiation in 2011. (Asahi Shimbun file photo)

A National Institute of Radiological Sciences employee shows reporters how to test for thyroid gland doses of internal radiation in 2011. (Asahi Shimbun file photo)

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  • A National Institute of Radiological Sciences employee shows reporters how to test for thyroid gland doses of internal radiation in 2011. (Asahi Shimbun file photo)

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