2023 Volume 105 Issue 6 Pages 209-215
Due to radioactive contamination following the Fukushima Daiichi Nuclear Power Plant accident in 2011, shipping restrictions have been imposed on wild mushrooms in a wide area of eastern Japan. In order to contribute to more efficient restriction and its lifting, I focused on the variation of radiocesium (137Cs) concentration for each species obtained within the same municipality, and 7,920 sample data collected in prefectures in eastern Japan from 2014 to 2019 were analyzed. The 137Cs concentrations of mushroom species collected in municipalities could be regarded as a lognormal distribution. The geometric standard deviation (GSD) for each species and municipality, which is an indicator of the variability of the lognormal distribution, tended to converge as the number of samples increased, while the values were considered to vary to 2-3 by species. The ratio of the geometric mean (GM) of 137Cs concentrations for each species was constant regardless of the sampling municipality, suggesting that the trend in species concentrations is common regardless of the region. The concentration distribution considering the variation of species showed that there were cases where the concentration distributions overlapped even when the geometric mean concentrations differed by a factor of 10. On the other hand, there were cases in which the concentration distributions were very similar even though the species differed (e.g., nameko and mukitake, or bunaharitake and hiratake). Such information is important when considering shipping restriction or its lifting.
