Most Fukushima radiation doses within norms: WHO

Last Updated: 2012-05-23 9:15:23 -0400 (Reuters Health)

GENEVA (Reuters) - Spikes in radiation caused by the Fukushima nuclear accident were below cancer-causing levels in almost all of Japan and neighboring countries had levels similar to normal background radiation, the World Health Organization said on Wednesday.

In a preliminary report using conservative assumptions, independent experts said that people in only two locations in Fukushima prefecture may have received a dose of 10-50 millisieverts (mSv) in the year after the accident at the power station operated by TEPCO.

Populations exposed to radiation typically stand a greater chance of contracting cancer after receiving doses above 100 mSv, according to the United Nations health agency. The threshold for acute radiation syndrome is about 1 Sv (1000 mSv).

"A worldwide average annual dose from natural background radiation is about 2.4 mSv, with a typical range of 1-10 mSv in various regions of the world," the report said.

In the rest of Fukushima prefecture, the effective dose was estimated to be within a dose band of 1-10 mSv, while effective doses in most of Japan were put at just 0.1-1 mSv. In the rest of the world, doses were below 0.01 mSv or less.

The massive earthquake and tsunami on March 11, 2011 wrecked the Fukushima Daiichi nuclear plant, triggering meltdowns that caused contamination and forced mass evacuations.

"Doses have not been estimated for the zone within 20 kilometers from the Fukushima Daiichi site because most people in the area were evacuated rapidly and an accurate estimation of dose to these individuals would require more precise data than were available," the report said.

"Some exposure may have occurred prior to evacuation but the assessment of this requires more precise data than those available to the panel," it added.

The experts did not examine the short- and long-term health risks for the emergency response workers who worked on the site. That will be part of a wider WHO report due from a separate group of experts in July.

That report will also assess the prospect for long-term increases in cancer cases, including cancers of the thyroid, the most exposed organ in the body as radioactive iodine concentrates there.

The experts based their assessment on data available up to last September on the amount of radioactivity in air, soil, water and food supplies after the disaster.

SOURCE: http://bit.ly/JCcBhA World Health Organization, May 2012.