Radiation dose estimation from foods due to the accident of TEPCO Fukushima Daiichi Nuclear Power Station

Explained are the purpose of dose assessment, its methods, actual radionuclide levels in food, amounts of food intake, dose estimated hitherto, dose in the future, dose estimated by total food studies, and problems of assessing the dose from food, all of which Tokyo Electric Power Company (TEPCO) Power Station Accident has raised. Dose derived from food can be estimated by the radioactivity measured in each food material and in its combined amounts or in actually cooked food. Amounts of radioactive materials ingested in the body can be measured externally or by bioassay. Japan MHLW published levels of radioactivity in vegetables', fruits, marine products and meats from Mar. 2011, of which time course pattern has been found different each other within and between month(s). Dose due to early exposure in the Accident can be estimated by the radioactivity levels above and data concerning the amounts of food intake summarized by National Institute of Health and Nutrition in 2010 and other institutions. For instance, the thyroid tissue equivalent dose by I-131 in a 1 year old child is estimated to be 1.1-5 mSv depending on the assumed data for calculation, in the first month after the Accident when ICRP tissue equivalent dose coefficient 3.7 x 10-6 Sv/Bq is used. In the future (later than Apr. 2012), new standard limits of radiocesium levels in milk/its products and foods for infant and in other general foods are to be defined 50 and 100 Bq/kg, respectively. The distribution of committed effective doses by radiocesium (mSv/y food intake) are presented as an instance, where it is estimated by 1 million stochastic simulations using 2 covariates of Cs-134, -137 levels (as representative nuclides under regulation) in food and of daily food intake. In dose prediction, conjecturing the behavior of environmental radionuclides and the time of resume of primary industries would be necessary. (T.T.)