Impact of sediment mineralogical composition on bioavailability? An integrated approach laboratory-field campaign-bioindicator-speciation calculation

The European Water Framework Directive introduced in 2000 has allowed to establish numerous quality environment standards for the last 18 years for compounds stemming from anthropic activity. However, the natural presence of uranium in the environment as well as its reactivity complicates the construction of standards. The transfer of uranium between sediment, water and the biological compartment is complex. Indeed, the passage of uranium through the cellular membrane can depend on the mineralogical composition as well as on the physico-chemical parameters. The objective of this study is to bring scientific foundations around these various parameters and hence to determine their impact on the accumulation. This way, the future definition of these new standards (NQE) takes into account the notion of bioavailability of contaminants. The strong impact of mineralogical phases such as ferrihydrite is both demonstrated in a post-mining context as well as within experiments in laboratory, as opposed to the quartz whose sorption capacity is low. A correlation is noted between the accumulation obtained by bioindicator 'Chironomus riparius' and the one measured by a system of integrative passive sensors called DGT. This correlation is linked to the presence of potentially bioavailable species such as UO₂OH₂(aq), whose abundance is obtained by speciation calculations. These first conclusions give scientific foundations to feed the debate around the construction of the environment quality standards. (author)