Ten-Year Transition of Radiocesium Contamination in Wild Mushrooms in the University of Tokyo Forests After the Fukushima Accident

Abstract

AbstractWe investigated the changes in the dynamics of radiocesium in wild forest mushrooms, mainly mycorrhizal fungi, in the University of Tokyo Forests in relation to soils during the 10 years following the Fukushima accident. Overall, there was a clear tendency for the 137Cs activity concentration to decrease over time in the O horizon. It seems that part of the 137Cs in the O horizon was transferred to the A or C/O horizon, but there was no clear continuous increase or decrease in the A or C/O horizon. A large difference in the temporal change of 137Cs concentration in mushrooms was observed, but in general, 137Cs was stably retained from the beginning, or partially decreased and then shifted to patterns of retention. Further analyses such as the ratio of 137Cs/134Cs corrected for decay, and the ratio of remaining pre-Fukushima 137Cs calculated from the ratio with 134Cs, 137Cs from the global fallout before the Fukushima accident due to the nuclear weapons test and Chernobyl accident is held in mushrooms and soil. In addition, while the 137Cs derived from the Fukushima accident is initially fluid and migrates relatively easily from the mushrooms and O horizon, the 137Cs from the global fallout tends to be firmly retained in the ecosystem.