Analysis of Temporal Changes in Terrestrial Cesium-137 Using Publicly Available Monitoring Data in Japan

摘要

Since the Fukushima Daiichi Nuclear Power Plant accident, vast amounts of radionuclide monitoring data obtained from various governmental and institutional surveys have been released to the public. In this study, we analyzed these large amounts of data to evaluate the long-term, large-scale fate of Cesium-137 in eastern Japan. Analysis of in situ measurements showed that temporal changes in the virtual amount of Cs-137 deposited, which were estimated from measured air dose rate data, varied greatly among measurement points, depending on air dose level and land use. The decrease in virtual amounts deposited was comparable to the decay rate of radioactive cesium, but was large in areas where the air dose rate had been relatively high and human activities had occurred. An analysis of Cs-137 concentrations in river and lake sediments showed Cs-137 levels to decrease at a fast rate, one order of magnitude faster than the radioactive decay rate. The present study highlights the importance of the effects of vertical and/or horizontal migrations of Cs-137 within the terrestrial area (including decontamination activities), direct deposition of Cs-137 into surface water, behavior of Cs-137 in built-up areas, and Cs-137 behavior in stagnant water bodies (e.g., ponds and lakes). The present study has demonstrated the utility analyzing large amounts of publicly available data for evaluating the environmental behavior of Cs-137.