Abstract
Radionuclide contamination in foods has been a great concern after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. To estimate time trends of daily intake and annual committed effective dose of radionuclides after the accident, radioactive cesium (r-Cs; 134Cs and 137Cs) and potassium-40 (40K) in market basket (MB) samples prepared at 6-month intervals in periods from September 2013 to March 2019 in 15 regions of Japan were analyzed using γ-ray spectrometry. The annual committed effective dose of r-Cs, calculated at non-detected radionuclide levels assumed to be half the limit of detection (LOD), appeared to decrease gradually in 11 regions close to the FDNPP that were more likely to be affected by the accident. Differences in doses among the 15 regions were large just after the accident, but gradually decreased. In particular, 134Cs has not been detected in any MB sample in any region since September 2018, and annual committed effective dose from 134Cs in all regions was mostly constant at around 0.3 μSv/year (given the respective LODs). The maximum annual committed effective dose of r-Cs in this study was decreased from 2.7 μSv/year in September 2013 to 1.0 μSv/year in March 2019. In contrast, the range of annual committed effective dose of 40K varied from approximately 150 to 200 μSv/year during that time frame and did not change much throughout the period of this study. Although annual committed effective doses of r-Cs in regions close to the FDNPP appeared to be higher than in regions far from the FDNPP, doses in all regions are remaining at a much lower levels than the intervention exemption level, 1 mSv/year, in foods in Japan.
Highlights
The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident happened on March 2011 due to the tsunami triggered by the Tohoku earthquake
We reported on daily intake and annual committed effective dose of r-Cs using a market basket (MB) study design17,18)
Daily intake and annual committed effective dose of 137Cs in regions relatively close to the FDNPP such as Fukushima, Iwate, and Tochigi are still slightly higher than those in the far-FDNPP region. These results suggest that differences in daily intake and annual committed effective dose among regions were mainly attributed to 137Cs, which tended to decrease in the near-FDNPP region
Summary
The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident happened on March 2011 due to the tsunami triggered by the Tohoku earthquake. In April 2012, new standard limits were established for foods (10, 50, and 100 Bq/kg for drinking water, milk and infant foods, and general foods, respectively, as the concentration of radioactive cesium [r-Cs; the sum of 134Cs and 137Cs]) by the Ministry of Health, Labour and Welfare (MHLW) based on risk assessments by the Food Safety Commission in Japan[4]) These standard limits were set to avoid exceeding the intervention exemption level of the Codex Alimentarius Commission (CODEX), 1 mSv/year, a level considered as safe for the public. Continuous surveys of dietary intake of r-Cs are necessary to evaluate the effects of food regulations resulting from standard limits on r-Cs. In this study, to evaluate the time trends of dietary intake of r-Cs, concerned radionuclides after the FDNPP accident, we estimated daily intake and annual committed effective dose of r-Cs by analyzing MB samples derived from 15 regions in Japan during the periods from September 2013 to March 2019. Our findings were compared to the results of surveys reported before the FDNPP accident
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