Application of Diffusive Gradients in Thin Films (DGT) for the Dynamic Speciation of Radioactive Cesium in Fukushima Prefecture, Japan

Radioactive cesium released by the Fukushima Daiichi Nuclear Power Plant accident in March 2011 remains in the forest environment and is being transported to the ocean via residential areas by runoff into river systems. Most of the Cs-137 in river water exists as suspended forms, being strongly fixed by micaceous clay minerals. If this fraction can change its form to dissolved forms, this results in additional input of bioavailable Cs-137. In this study, in situ sampling of Cs-137 at multiple rivers in Fukushima Prefecture was conducted using diffusive gradient in thin film (DGT) devices to investigate the dynamics of radioactive cesium in river environments. At almost all sampling points, the DGT Cs-137 concentrations exceeded the dissolved Cs-137 concentrations, revealing the existence of a flux from the suspended to the dissolved forms. This additional input was found to have higher Cs-137/Cs-133 ratios than those of Cs in the dissolved form. This study demonstrates that the bioavailability of Cs-137 can be underestimated by assessing only the dissolved form due to the flux of Cs-137 from the suspended particles likely caused by their dissolution.