Radionuclides in waters and suspended sediments in the Rhone River (France) - Current contents, anthropic pressures and trajectories

The Rhone River is one of the most nuclearized river in the world. Radionuclide concentrations in water and 6 suspended sediments transferred to the marine environment were intensively monitored in this river over the last 7 decades (2002–2018). While more than 60% of plutonium, americium, cesium, cobalt, silver, beryllium and 8 actinium radioisotopes are carried by sedimentary particles, sodium, tritium, antimony and strontium are mainly 9 exported as dissolved species (>90%) due to their low affinity with particles. Most natural radionuclides contents 10 show low seasonal variation. No significant trends are observed over the last two decades for these elements, 11 even for 40K widely used in fertilizers after the middle of the last century, indicating that the basin has currently 12 converged towards geochemical equilibrium for all of them. In contrast, the concentrations of numerous 13 anthropogenic radionuclides originating from nuclear industries significantly declined since the beginning of the 14 2000s. Assuming no change of the current anthropic and climatic pressures over the next decades, apparent 15 periods, i.e. the time required for a reduction by half the concentrations in the downstream part of the Rhône 16 River, would be close to 6 years for most artificial radionuclides, except for tritium and other artificial radionuclides 17 conveyed to the river by soil leaching and erosion (90Sr, 241Am, plutonium isotopes) which would be far longer. 18 Referring to regional referential backgrounds, only few anthropogenic radionuclides specifically produced by 19 nuclear industries are still detectable at the downstream part of the Rhone River and excess contents of tritium, 20 238Pu and 241Am are observed in filtered waters.Dispositif de recherche interdisciplinaire sur les Interactions Hommes-Milieu