[M-AG44] Dynamics of radionuclides emitted from Fukushima Dai-ichi Nuclear Power Plant in the environment

[MAG44-08] Chemical implication of partition coefficient between suspended and dissolved Cs-137 in river water

*Katsumi Hirose¹, Yuichi Onda¹ (1.Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba)

Keywords:Cs-137, river water, partition coefficient

After the Fukushima Daiichi Nuclear Power Plant accident, terrestrial environment has been seriously contaminated by radiocesium. As a result, higher levels of radiocesium concentrations in river water have continued in Fukushima area, although they exhibit gradual decline trends. Partition coefficient between suspended and dissolved ¹³⁷Cs, Kd, has been introduced as a tool to have better understanding of dynamic behavior of ¹³⁷Cs in river system. However, the partition coefficient showed larger spatiotemporal variability. It is important to elucidate factors controlling the partition coefficient of ¹³⁷Cs in river system. We, here, introduce a chemical model to explain variability of the partition coefficient of ¹³⁷Cs in river system. The chemical model reveals that the partition coefficient of ¹³⁷Cs in river is inversely related to electro-conductivity and the suspended sediment (SS) concentration in river, respectively. Especially, to explain the effect of SS for Kd, presence of colloidal ¹³⁷Cs, passing through filter, is significant as dominant dissolved species of ¹³⁷Cs in river water. The result suggests that chemical speciation study of ¹³⁷Cs dissolved in river water is important to know chemical and ecological roles of dissolved ¹³⁷Cs in river water.