WHO okays Fukushima radiation

Increased radiation levels caused by the Fukushima nuclear accident last year were below levels thought to be cancer-causing in almost all of Japan, the World Health Organization (WHO) study concluded.

The massive earthquake and subsequent tsunami on March 11 last year prompted a nuclear accident at the Fukushima Daiichi power plant - with the WHO saying its study represented "the first international effort to assess global radiation doses from the … accident considering all major exposure pathways."

The report, which used conservative assumptions, found that only people in two locations within the Fukushima prefecture - the town of Namie and Itate village - had been subjected to a dose of 10-50 millisieverts (mSv).

"In these most affected locations, external exposure is the major contributor to the effective dose. In the rest of Fukushima prefecture the effective dose was estimated to be within a dose band of 1 to 10 mSv," the WHO wrote in the executive summary for the report.

It put the effective doses in the rest of Japan between 0.1 and 1 mSv, while in the rest of the world, radiation levels were close to normal background levels, "below 0.01 mSv and usually far below this level."

Evacuees and emergency workers not included

The report also said that most extra radiation dosage outside the Fukushima prefecture would have been due to internal exposure - usually consuming contaminated food or liquid - adding that its estimates on these levels might prove to be too high.

A radiation dose of 10 mSv is roughly equal to a computed tomography (CT) scan often used for medical imaging. A 50-mSv dose is the single-year limit for people working with radioactive material, while the five-year limit is 100 mSv. Exceeding these boundaries is thought to notably increase the risk of cancer, especially of the thyroid, while a dose of 1 Sv (1000mSv) is the threshold for acute radiation syndrome.

"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 those available to the panel," the report said.

A separate WHO report will be compiled looking into the exposure of emergency response workers who helped with the cleanup operation, and calculating any short- and long-term health risks they face.

The WHO panel of experts based their reports on data available up to September last year concerning radioactivity levels in air, soil, water and food.

msh/tj (AFP, dpa, Reuters)