Tin-113 and Selenium-75 radiotracer adsorption and desorption kinetics in contrasting estuarine salinity and turbidity conditions

摘要

Batch experiments were performed to study adsorption and desorption of Se-75 and Sn-113 radiotracers at environmentally representative concentrations of similar to 0.3 ng L-1 and similar to 3 ng L-1, respectively. The radiotracers were incubated with wet bulk sediments from the Gironde Estuary and the Rhone River, combining freshwater and coastal seawater salinity (S = 0, S = 32) and three different Suspended Particulate Matter (SPM) concentrations (10 mg L-1, 100 mg L-1, 1000 mg L-1) to simulate six hydrologically contrasting situations for each particle type. Results showed no measurable adsorption for Se-75 under the experimental conditions, whereas >90% of Sn-113 rapidly adsorbed onto the particles during the first hours of exposure. Adsorption efficiency increased with increasing SPM concentration and seemed to be slightly greater for the Rhone River sediments, potentially related to the intrinsic mineral composition. Desorption of spiked sediments exposed to filtered, unspiked freshwater and seawater only occurred for Sn-113 (<15% of the previously adsorbed Sn-113) in the Garonne River sediments. This study provides insights to the potential environmental behaviour of hypothetical radionuclide releases of Se and Sn into highly dynamic and contrasting aquatic systems. Multiple accidental scenarios for the case of the Gironde Estuary and the Rhone River are discussed. These scenarios suggest that the environmental fate of soluble radionuclides like Se will be associated to water hydrodynamics and potentially more bioavailable whereas highly particle-active radionuclides like Sn will follow natural river/estuarine sedimentary regimes. Information on reactivity of radionuclides is important for improving the precision of current approaches aiming at modelling environmental radionuclide dispersion in continent-ocean transition systems.