Risk assessment of soil contaminated with radionuclides was performed by considering the intake of radionuclides in foods based on measured concentrations. Due to the disaster at the Fukushima nuclear power plant in 2011, radionuclides were spread out over an area of 13,000 km2. Radionuclides were found in the food, and the Japanese people are concerned about eating foods from Fukushima and the surrounding area. Radionuclides such as 134Cs and 137Cs were found on soil, buildings, plants, and so on. The exposure routes were determined to be (1) food intake, (2) ingestion and inhalation of soil particles, and (3) external radiation from the ground. Then, the total doses of all exposure routes for one year and over a lifetime were calculated, and the committed effective doses for the lifetime were evaluated. To estimate the intake of food, the concentrations can be obtained from the database of the Ministry of Health and Welfare. The foods are divided into 16 types to estimate the daily intake. The geometrical means of the intake were calculated using monthly data for each group of food. Then, the intake from food for one year was calculated for each generation. The committed effective doses were calculated using the intake of each radionuclides times the dose coefficient. For the air dose, three cases were set as exposure scenarios. Case 1 was used for people who stay in a house for 24 hours, such as infants, pregnant females, and bedridden people. Case 2 was used for house wives and office workers, who stay outside for 4 hours and inside for 20 hours. Case 3 was used for children, farmers, and construction workers, who stay outside for 8 hours and inside for 16 hours. As a result, exposure through the ingestion and inhalation of soil particles were negligible, and exposures by food intake and external exposure from the ground were comparatively large. This study shows that the air dose by this disaster should be less than 0.2 μSv/hour to control the radiation dose with the consumption of food being less than 1 mSv/year. However, to maintain the lifetime dose under 100 mSv, several mSv/y is sufficient, considering radioactive decay and dilution by advection and diffusion. The risk assessment based on land use can provide information about the priority of countermeasures against the contamination and provides reasonable decontamination methods or risk management strategies.
Letter to the editor regarding “spatiotemporal association of low birth weight with Cs-137 deposition at the prefecture level in Japan after the Fukushima nuclear power plant accidents”
