[M-AG34] Radioisotope migration: Development from Environmental Dynamics Research on the F1NPS Accident

[MAG34-01] New Insights into the Dissolution Mechanism of Dissolved Cs-137 in Headwater Catchments

★Invited Papers

*Yuichi Onda¹, Kosuke Tomura¹, Yasunori Igarashi¹, Yutaro Nagata¹, Naoyuki Wada¹, Junko Takahashi¹, Aya Sakaguchi¹, SHAOYAN FAN² (1.Center for Research in Radiation, Isotopes and Earth System Sciences, University of Tsukuba, 2.Fukushima Prefectural Center for Environmental Creation)

Keywords:Cs-137, Cs-133, Forested headwater catchment, Water Chemistry

This study investigated changes in radiocesium (Cs-137) dissolution mechanisms from forested headwater catchments to downstream rivers. While previous studies identified (1) ion exchange and (2) microbial decomposition, this study introduced (3) isotopic exchange with stable Cs-133, which had not been explored in forested areas. Research in Fukushima’s Yamakiya district and the Kuchibuto River watershed analyzed water for potassium (K+), ammonium (NH4+), dissolved organic carbon (DOC), and Cs-133. Long-term monitoring of Cs-137 in suspended, dissolved, and coarse organic matter was conducted. Cs-137 concentrations stabilized after 2021. Dissolved Cs-137 and K+ increased downstream, suggesting K+ inputs enhanced ion exchange. Cs-133, though present at one-millionth K+’s concentration, showed similar trends. Regression analysis found Cs-133 to be 50,000 times more effective than K+ in Cs-137 dissolution. This study highlights isotopic exchange as a key process, requiring further research on seasonal influences.