World Health Organization weighs in on Fukushima
Today, the World Health Organization (WHO) released a preliminary estimate of the radiation dose received by the public as a result of last Marchs meltdowns at the Fukushima Daiichi nuclear plant in Japan. Nature has seen a draft of the final report, and it is mostly good news the doses are very low, and very few cancers would be expected as a result.
Most residents of Fukushima prefecture received between 110 millisieverts (mSv) in the first year after the accident, according to the estimate. Those in neighbouring prefectures received between 0.110 mSv, and the rest of Japan received between 0.11 mSv. These levels are well below the governments maximum recommended dose of 20 mSv and will cause a minimal increase in cancer risk.
The obvious question is how minimal. According to David Brenner, a radiation biophysicist at Columbia University in New York, a dose of 5 mSv would be estimated to lead to one excess cancer per 5,000 people exposed. Given that roughly 2,000 of those 5,000 people are going to develop cancer anyway, this is a tiny increase in risk, and Brenner emphasizes that the uncertainties in his calculations are high.
There were two areas that were above the 10-mSv range. In the town of Namie and the village of Itate, to the north-west of the plant, residents received 1050 mSv in the first year. This is because both towns were beneath a plume of fallout from the plant, but still outside the evacuation zone set up immediately after the accident. Residents in these areas remained until a few months later, when they voluntarily left at the governments request. As a consequence, they received a higher dose of radiation.
http://blogs.nature.com/news/2012/05/world-health-organization-weighs-in-on-fukushima.html