Characterization of the nature of the suspended particles transported during the low water levels of the Rhône River (France) - CANADER project

Studies conducted on the Rhone River (France) highlights that, in the current context of climate change, the frequency of lowflow situations are likely to increase throughout its basin. For these extreme periods, it is expected that the proportion of organic matter (OM) contained in suspended particles will increase. However, the fixation of several contaminants is strongly linked to OM, where its form favors their complexation/adsorption. This is confirmed by the results of the CANADER project conducted on the Rhone River and its main tributaries (Saone, Ardeche and Durance Rivers) where the concentrations in suspended solids of several contaminants (anthropogenic metals, mercury and radionuclides) tend to increase during low water periods. For several anthropogenic metals (Cr, Ni, Zn), concentrations sometimes exceed the probable effect concentration (PEC). The decrease on natural metals (from the earth's crust) coupled with the increase in methyl-mercury (suggesting bioaccumulation of concentrations in phytoplankton) shows that a significant proportion of the OM that transits at low flow is autochthonous. The first results of sterol analysis suggest that OM origins differ depending the Rhone River and its tributaries, and further work must be done to characterize the sources of these particles.