Residents of areas near the stricken Fukushima No. 1 nuclear power plant have been exposed to radiation levels of up to 0.16 millisievert per year from radioactive cesium in food and airborne dust, according to scientists at Kyoto University and other research institutions.
Residents of areas near the stricken Fukushima No. 1 nuclear power plant have been exposed to radiation levels of up to 0.16 millisievert per year from radioactive cesium in food and airborne dust, according to scientists at Kyoto University and other research institutions.
These levels are lower than the publicly permissible dose of 1 millisievert per year, the authors said Nov. 14.
The research team, led by Hirohiko Ishikawa, a professor of environmental disaster at Kyoto University's Disaster Prevention Research Institute, measured cesium-134 and cesium-137 levels in samples of food, water and air in the region between July 2 and 8.
The scientists purchased food and drinking water at supermarkets located between a 20- to 70-kilometer radius from the nuclear plant, and estimated the levels of internal exposure through ingestion on the basis of their radioactive cesium content.
The median estimated dose level was 0.003 millisievert per year, whereas the maximum estimate, which assumes that the subject consumes highly contaminated food on a daily basis, was 0.083 millisievert per year.
The group also collected samples of airborne dust at a height of 1.5 meters above ground and evaluated exposure levels on the basis of their cesium content. The dose levels by inhalation were estimated to be less than 0.003 millisievert per year at most locations, and peaked at 0.077 millisievert per year in Namie. Combined with the maximum dose level by ingestion, this gives a total of 0.16 millisievert per year.
These estimated annual internal exposure dose levels are the same as external radiation doses that can be exceeded in a matter of hours depending on locations, so the measures against external exposure are more important, the scientists said.