Concentrations of 134, 137Cs and 90Sr in agricultural products collected in Fukushima prefecture

Abstract

On April 1, 2012, new Standard Limits for radionuclide concentrations in food were promulgated, superseding the Provisional Regulation Values in Japan set in 2011. The new Standard Limits are calculated based on 1 mSv y−1 of annual internal radiation dose through food ingestion of 134Cs, 137Cs, 90Sr, Pu and 106Ru, which were detected or possibly released into the environment from the accident at the TEPCO Fukushima Daiichi Nuclear Power Stations (FDNPS). The concentrations of the radionuclides were based on the values of radiocesium (134, 137Cs) and of the other radionuclides (90Sr, Pu and 106Ru); the ratio observed in the determination or predicted concentrations in the soils from the FDNPS accident was used for estimating the concentration of the other radionuclides by means of the ratio against 137Cs. The new Standard Limit of radiocesium in general foods was defined to be 100 Bq kg−1 fresh weight by the Ministry of Health, Labour and Welfare. In the present study the concentration of radiocesium was measured in agricultural products collected mostly in Fukushima-shi and Date-shi, Fukushima Prefecture, in 2012 and 2013. The average concentration of radiocesium in agricultural plants in 2012 was 7.6 (<0.2–40) Bq kg−1 fresh weight, decreasing to 2.0 (<0.1–14) Bq kg−1 fresh weight in 2013, which was approximately one-fourth of the concentration in 2012. The concentration of 90Sr in agricultural products collected in Fukushima Prefecture in 2013 was 0.0047–0.31 Bq kg−1 fresh weight, which was a similar range to those collected throughout Japan. The concentration ratio of 90Sr/137Cs in the agricultural plants collected from the area 5 km west from the Nuclear Power Stations (difficult-to-return zone) was lower than the predicted 90Sr/137Cs ratio, which was calculated using the ratio in the soils and soil-to-plant transfer factors.