Contribution of Cesium-Bearing Microparticles to Cesium in Soil and River Water of the Takase River Watershed and Their Effect on the Distribution Coefficient

Abstract

AbstractRadioactive cesium-bearing microparticles (CsMPs) are glassy particles containing large amounts of radioactive cesium (Cs, i.e., 134Cs and 137Cs). Because Cs in CsMPs is covered with insoluble glass, CsMPs may not release Cs into the liquid phase of river water. Previous studies have shown that CsMPs may drive overestimation of Cs transfer between the solid and liquid phases in rivers. In this study, we investigated the contribution of CsMPs to Cs concentrations in forest soil and river water in the Takase River watershed to explore the migration of CsMPs from a forest catchment and their effect on the distribution coefficient in the river water. The Cs concentration derived from CsMPs as a proportion of that in the bulk soil and particulate Cs in the river water was not large; therefore, CsMPs did not have a significant effect on the distribution coefficient. In forest soil, variation in the distribution of CsMPs in soil was greater than that in the distribution of Cs adsorbed onto soil particle. This variation might cause the Cs concentration derived from CsMPs flowing into rivers to vary more than the particulate Cs concentration. To elucidate CsMPs migration and its effects on the Cs concentration in the river, further research such as soil sampling to assess the spatial distribution of CsMPs in the watershed is needed.