Chemical implication of the partition coefficient of 137 Cs between the suspended and dissolved phases in natural water

• Published in: Journal of environmental radioactivity Vol. 278; p. 107486
• Main Authors: Hirose, Katsumi, Onda, Yuichi, Tsukada, Hirofumi, Hiroyama, Yuko, Okada, Yukiko, Kikawada, Yoshikazu
• Format: Journal Article
• Language: English
• Published: England 01-09-2024
• Subjects: Cesium Radioisotopes - analysis; Fukushima Nuclear Accident; Geologic Sediments - chemistry; Japan; Models, Chemical; Radiation Monitoring; Rivers - chemistry; Water Pollutants, Radioactive - analysis; Water Pollutants, Radioactive - chemistry; Japan; Cs; Chemical model electric conductivity; Suspended sediment; Partition coefficient; Stable Cs; River water
• ISSN: 1879-1700
• DOI: 10.1016/j.jenvrad.2024.107486

After the Fukushima Daiichi nuclear power plant accident, the terrestrial environment became severely contaminated with radiocesium. Consequently, the river and lake water in the Fukushima area exhibited high radiocesium levels, which declined subsequently. The partition coefficient of
Cs between the suspended sediment (SS) and dissolved phases, K
, was introduced to better understand the dynamic behavior of
Cs in different systems. However, the K
values in river water, ranging from 2 × 10
to 7 × 10
 L kg
, showed large spatiotemporal variability. Therefore, the factors controlling the
Cs partition coefficient in natural water systems should be identified. Herein, we introduce a chemical model to explain the variability in
Cs K
in natural water systems. The chemical model includes the complexation of Cs
with mineral and organic binding sites in SS, metal exchange reactions, and the presence of colloidal species. The application of the chemical model to natural water systems revealed that Cs
is strongly associated with binding sites in SS, and a major chemical interaction between
Cs and the binding sites in SS is the isotope exchange reaction between stable Cs and
Cs, rather than metal exchange reactions with other metal ions such as potassium ions. To explain the effect of the SS concentration on K
, the presence of colloidal
Cs passing through a filter is significant as the dominant dissolved species of
Cs in river water. These results suggest that a better understanding of stable Cs dissolved in natural water is important for discerning the geochemical and ecological behaviors of
Cs in natural water.