Radiation exposure was not responsible for the deaths of six workers helping to contain the crisis at the Fukushima No. 1 nuclear plant, a U.N. committee said in a preliminary assessment Wednesday.
Based on information available so far, their deaths are attributable to cardiovascular disease or other reasons, according to the report compiled by the U.N. Scientific Committee on the Effects of Atomic Radiation.
One of the six died of acute leukemia, but radiation exposure was ruled out as a cause because the time between possible exposure and death was so short, the committee said.
The committee is undertaking a study to assess the radiation doses and associated effects on health and the environment after the crisis started at the Tokyo Electric Power Co. plant, which was stricken by the March 11 earthquake and tsunami last year.
UNSCEAR Chairman Wolfgang Weiss said in a statement that the agency is aiming to evaluate irradiation levels for about 2 million people living in Fukushima Prefecture at the time the nuclear crisis started March 11.
He said the committee, which plans to report to the U.N. General Assembly next year, also has information about measurements made on the thyroids of over 1,000 children in the region.
On Wednesday, the World Health Organization said the maximum whole-body radiation dose individuals received from the nuclear accident at the Fukushima plant is estimated at 50 millisieverts over the first four months.
WHO disclosed dose estimates on Wednesday in the first international effort to assess global radiation doses from the accident caused by the disasters. The estimates took into account all major exposure pathways.
The total effective dose received by residents in two locations of relatively high exposure in the prefecture is within a band of 10 to 50 millisieverts, assuming they lived there for four months after the crisis started, the report said.
The two locations are parts of Namie and Iitate outside the no-go zone but within 20 km of the plant.
The effective annual doses are estimated at 1 to 10 millisieverts for other parts of Fukushima and 0.1 to 10 millisieverts for neighboring prefectures, including Miyagi.
Those estimates compare with 0.1 to 1 millisievert for the rest of Japan and less than 0.01 millisievert elsewhere on the globe.
A widely accepted annual limit for public exposure is 1 millisievert under normal conditions.
If annual doses exceed 100 millisieverts, the risk of developing cancer is believed to increase.
The WHO report also said estimated thyroid doses for 1-year-olds were highest in Namie, at 100 to 200 millisieverts, followed by 10 to 100 millisieverts in Iitate, Katsurao, Minamisoma and other Fukushima municipalities.
Elsewhere in Japan, thyroid doses are estimated between 1 and 10 millisieverts, the organization said, noting that doses in the rest of the world are less than 0.01 millisievert.
Among evacuees from areas affected by the 1986 Chernobyl disaster, thyroid doses averaged 490 millisieverts, according to a 2008 U.N. report.
The WHO compiled the latest report based on information publicly available up to mid-September last year. As conservative assumptions were used, some overestimation may have occurred, it said.
In reaction, Chief Cabinet Secretary Osamu Fujimura played down the WHO estimate.
It is “based on the assumption that no countermeasures, such as evacuations and restriction on eating contaminated food, were taken,” the government’s top spokesman told a news conference Thursday.