Longitudinal Verification of Post-Nuclear Accident Food Regulations in Japan Focusing on Wild Vegetables

Abstract

Focusing on the importance of wild vegetables for local residents, this study aims to validate the effects of food regulations under the current criteria (e.g., 100 Bq/kg for general foods) established approximately a year after the Fukushima Dai-ichi Nuclear Power Plant accident. Over 2,500,000 monitoring tests were performed under the criteria until fiscal year (FY) 2020. We estimated changes in internal exposure dose using test results. The effective dose was estimated using the radioactive concentration randomly sampled from the results, food intake, and dose conversion factor. As a new attempt, dose estimation reflecting the intake of wild vegetables that may have irreplaceable value for local residents was conducted. The median, 95th, and 99th percentile of the estimated dose without reflecting the wild vegetables’ intake were 0.0485, 0.183, and 10.6 mSv/year, respectively, in the estimation with all test results (no regulation) and 0.0431, 0.0786, and 0.236 mSv/year, respectively, in the estimation with results within the standard limits (regulated) in FY2012. These doses decreased with time. Although estimated doses with or without the reflection of wild vegetables’ intake were similar, estimation that is more plausible is possible, particularly for a high percentile, by reflecting the wild vegetables’ intake. Radiation doses (regulated) were significantly less than 1 mSv/year in different FYs. In Japan, food regulation measures benefit food safety.

Long-Term Analysis of Internal Exposure Dose-Reduction Effects by Food Regulation and Food Item Contribution to Dose after the Fukushima Daiichi Nuclear Power Plant Accident

“…The basic methodology is in accordance with our previous studies [ 16 , 17 ]. On this basis, the target year was expanded, the radiation dose estimation method was further refined, and the food categories contributing to the radiation dose were analyzed.…”

“…This survey shows the average food intake (g/day) classified into 98 small categories of foodstuffs ( Table 2 ) [ 19 ]. The average food intake value is typically used in radiation dose estimation studies of internal exposure due to food ingestion [ 20 ], including in our previous reports [ 16 , 17 ]. However, radiation dose estimation based on average food intake might underestimate internal doses for people with high intake.…”

“…Therefore, we selected foods that would be classified as wild vegetables from the results of a detailed food intake survey irregularly conducted in 2010 [ 27 ] and totaled their intakes. As in our previous study [ 17 ], the summed value of 7.67 g/day was used as the wild vegetable intake. Because the value is the sum of the average individual wild vegetable intake, no SD (i.e., variation in intake among individuals) information is available.…”

“…As in our previous study [ 16 , 17 ], the foodstuff item names (6670 items in 10 years) in the monitoring test results were corresponded to the 100 categories in the food intake data. Our previous study described the methodology in detail [ 16 ].…”

“…More than 2,700,000 samples from the postaccident period to FY2021 were included in the monitoring tests. We have been effectively using these accumulated monitoring test results and verifying the effectiveness of the food regulations after the FDNPP accident in Japan [ 16 , 17 ]. However, the types of foods that contribute to radiation exposure dose have not been specified.…”