Application of diffusive gradients in thin films (DGT) for the dynamic speciation of radioactive cesium in Fukushima Prefecture, Japan

田中 琢朗*; 福岡 将史*; 戸田 賀奈子*; 中西 貴宏   ; 寺島 元基  ; 藤原 健壮 ; 庭野 佑真*; 加藤 弘亮*; 小林 奈通子*; 田野井 慶太朗*; 斉藤 拓巳*

Tanaka, Takuro*; Fukuoka, Masafumi*; Toda, Kanako*; Nakanishi, Takahiro; Terashima, Motoki; Fujiwara, Kenso; Niwano, Yuma*; Kato, Hiroaki*; Kobayashi, Natsuko*; Tanoi, Keitaro*; Saito, Takumi*

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 in river water exists as suspended forms, being strongly fixed by micaceous clay minerals. If this fraction can change its form into dissolved forms, this results in additional input of bioavailable Cs. In this study, in-situ sampling of Cs at multiple rivers in Fukushima Prefecture was conducted using the DGT (diffusive gradient in thin film) devices to investigate the dynamics of radioactive cesium in river environments. At almost all sampling points, the DGT Cs concentrations exceeded dissolved Cs concentrations, revealing the existence of a flux from the suspended to the dissolved forms. This additional input was found to have higher Cs/ Cs ratios, compared those of Cs in the dissolved form. This study demonstrates that the bioavailability of Cs can be underestimated by assessing only the dissolved form due to Cs flux from the suspended particles likely caused by their dissolution.