Long-term trends in 137Cs concentrations in rivers across Europe originating from Chornobyl

Large-scale nuclear accidents may contaminate large areas of land with long-lived radionuclides such as ¹³⁷Cs. Rivers are important pathways for transporting these radionuclides from upstream to downstream. The ¹³⁷Cs concentration released during the Chornobyl nuclear accident has been shown to decrease over time. Previous studies also have shown that the concentration of ¹³⁷Cs in rivers is influenced by competing ions, hydrological processes, the amount of adsorption sites on suspended particles, and the land cover of the catchment. However, comparative studies between rivers are limited, and the factors that determine the variation in ¹³⁷Cs concentrations in rivers remain unclear. In this study, we collected time-series measurements of ¹³⁷Cs from nine major rivers across Europe, each from different regions and countries affected by varying environmental conditions. We also characterized the properties of each river’s catchment, including land cover, water chemistry, and hydrological characteristics. By linking the ¹³⁷Cs concentration data with these catchment attributes, we aimed to identify the most significant factors influencing ¹³⁷Cs transport. Our findings reveal a quantitative relationship between the transport of ¹³⁷Cs and the catchment characteristics, highlighting key factors that control radionuclide behavior in rivers. These results can be used for long-term predictions of radionuclide transport in rivers, which is crucial for risk assessment and management in regions affected by nuclear accidents.