TOKYO—At a press briefing today Keiichi Nakagawa, a radiologist at University of Tokyo Hospital, predicted that the radiation emanating from the damaged Fukushima nuclear power plant will have a negligible effect on public health. But those working to contain the radiation leaks and quench the fires face an increased risk of cancer, particularly since the government raised the allowable exposure limit yesterday.
Nakagawa said that normally nuclear power plant workers in Japan are limited to accumulated radiation doses of 100 millisieverts. But as an emergency measure, the ministry of health on Tuesday raised that to an accumulated 250 millisieverts. Nakagawa says that at that higher level of exposure, the workers will likely face a 1% or more increased risk of cancer. "It's only a risk, but they are now carrying a heavier risk of cancer," he said.
Radiation levels of 400 millisieverts per hour were recorded within the site on Tuesday. But workers are wearing protective clothing, working in brief shifts and being occasionally pulled off the site to limit accumulated exposure.
Nakagawa explained that the situation in the local community is significantly different.
Residents have been evacuated from within 20 kilometers of the stricken power plant and those between 20 and 30 kilometers away have been warned to stay indoors. Radiation within the 20- to 30-kilometer belt has been 10 to 20 microsieverts per hour. But indoor levels are likely to be just one-tenth of outdoor levels. At 1 microsievert per hour, it would take 11 years of exposure to get an accumulated dose of 100 millisievert, a level that can cause an increased risk of cancer. "For the general public, definitely there will be no health impact," he said. And for those as far away as Tokyo, he said that he "wouldn't be worried" even in the case of a core meltdown.
In 1999, Nakagawa was involved in treating two employees of JCO, a nuclear fuel cycle company, whose mishandling of uranium resulted in massive doses of radiation. Both employees eventually died. Nakagawa said that an accumulated dose of 4 sievert kills 50% of those exposed within 60 days. A dose of 1 sievert produces nausea and vomiting. Accumulated exposure of more than 250 millisieverts can cause the loss of white blood cells, and exposure of 100 millisieverts produces an increase in the risk of cancer of about 0.5%.