The World Health Organization (WHO) today released a report saying that the Fukushima nuclear disaster will cause no observable increases in cancer rates among residents of other countries and a very minimal increased risk of cancer among residents in the vicinity of the power plant. Workers who battled problems at the plant do face higher risks of some cancers.

The environmental group Greenpeace immediately condemned the report as being "a political statement to protect the nuclear industry." But at least one radiation health specialist believes the report overstates some of the risks.

WHO's assessment of the potential health effects is based on a May 2012 report that estimates the radiation exposure in different locations around the Fukushima Daiichi Nuclear Power Plant, which released significant amounts of radioactive material after suffering multiple meltdowns and explosions in the aftermath of the 11 March 2011 earthquake and tsunami.

The WHO team of 13 experts estimated the increased lifetime risk of leukemia, thyroid cancer, and female breast cancer for people living in geographical locations ranging from the most affected areas adjacent to the power plant to distant parts of the rest of the world. Beyond areas near the plant, radiation doses were below the levels known to produce health effects, the report states. "Outside of the geographical areas most affected by radiation, even in locations within Fukushima prefecture, the predicted risks remain low and no observable increases in cancer above natural variation in baseline rates are anticipated," reads the executive summary. The report notes that in the two most affected areas of Fukushima, estimated doses in the first year ranged from 12 to 25 millisieverts (mSv).

"For leukaemia [sic], the lifetime risks are predicted to increase by up to around 7% over baseline cancer rates in males exposed as infants; for breast cancer, the estimated lifetime risks increase by up to around 6% over baseline rates in females exposed as infants," the report concludes. "[F]or all solid cancers, the estimated lifetime risks increase by up to around 4% over baseline rates in females exposed as infants; and for thyroid cancer, the estimated lifetime risk increases by up to around 70% over baseline rates in females exposed as infants."

The report explains that these are relative increases over baseline rates and not absolute risks. So, because the baseline lifetime risk of thyroid cancer for females is just 0.75%, the additional risk due to exposure in the most affected location is 0.5%. Risks in the second most affected location are one-half of those in the most affected region.

Kazuo Sakai, a radiation biologist at Japan's National Institute of Radiological Sciences, believes that the risks "are overestimated." He explains that the dose estimates used were based on preliminary data; actual measurements have shown actual dose levels to be lower. He also says that the risk is based on a calculation that assumes 4 months of exposure to radiation in the different zones. But because of timely evacuation, there are probably no infant females, for instance, who actually received the doses estimated for the most affected location, he says.

Greenpeace, however, believes the doses are greatly underestimated. "The WHO report shamelessly downplays the impact of early radioactive releases from the Fukushima disaster on people inside the 20 km evacuation zone who were not able to leave the area quickly," a statement quotes Rianne Teule, Greenpeace International nuclear radiation expert, as saying. The statement says modeling by German nuclear expert Oda Becker concluded that people inside the 20-kilometer evacuation zone were possibly exposed to hundreds of mSv.

The WHO report does say that power plant emergency workers do face an increase in lifetime risks for leukemia, thyroid cancer, and all solid cancers.