Mobilization of radionuclides from sediments. Potential sources to Arctic waters

Contaminated soils and sediments can act as secondary sources of radionuclides to Arctic waters. In cases where the original source of contamination has ceased or been greatly reduced (e.g., weapons' testing, waste discharges from Mayak and Sellafield) remobilization of radionuclides from preciously contaminated sediments increases in importance. With respect to Arctic waters, potential secondary sources include sediments contaminated by weapons' testing, by discharges from nuclear installations to seawater, e.g., the Irish Sea, or by leakages from dumped waste containers. The major land-based source is run-off from soils and transport from sediments in the catchment areas of the Ob and Yenisey rivers, including those contaminated by Mayak discharges. Remobilization of radionuclides is often described as a secondary source of contamination. Whereas primary sources of man-made radionuclides tend to be point sources, secondary sources are usually more diffuse. Experiments were carried out on marine (Kara Sea, Irish Sea, Stepovogo and Abrosimov Fjords), estuarine (Ob-Yenisey) and dirty ice sediments. Total 137Cs and 90Sr concentrations were determined using standard radiochemical techniques. Tracer studies using 134Cs and 85Sr were used to investigate the kinetics of radionuclide adsorption and desorption. It is concluded that 90Sr is much less strongly bound to marine sediments than 137Cs, and can be chemically mobilized through ion exchange with elements is seawater. Radiocaesium is strongly and rapidly fixed to sediments. Discharges of 137Cs to surface sediments (i.e., from dumped containers) would be expected to be retained in sediments to a greater extent than discharges to sea-waters. Physical mobilization of sediments, for example resuspension, may be of more importance for transport of 137Cs than for 90Sr. 7 refs., 4 figs