Implementation of dihydroxamate-based binding gels in DGT devices for uranium(VI) sampling in freshwater. An intercomparison study
Résumé
Mining activities, production and use of nuclear fuel (65 kt/year), processing of spent fuel and storage of nuclear wastes may lead to the release of uranium into the environment, its transfer between the different compartments of the biosphere, and the ultimate contamination of trophic chains [1].
Nowadays, the monitoring of contaminated sites requires new breakthroughs in analytical techniques in order to assess in detail the impact and bioavailability of actinides discharged into aquatic environments. In that respect, Diffusive Gradient in Thin-films (DGT) devices are particularly attractive tools for the passive sampling of various contaminants in aquatic environments.
Unfortunately, the most frequently used and commercially available binding gels for uranium, namely the Chelex-100 ion-exchange resin or the TiO2-based Metsorb adsorbing material, behave poorly in carbonate-rich, hard freshwater and seawaters [2-3]. To overcome these limitations, we relied on a biomimetic approach for designing efficient pincer-like UO22+ chelators, bearing two terminal hydroxamate bidentate groups, which are able to coordinate the uranyl cation in its equatorial plane [4]. Equilibrium constants for complex formation with UO22+, Ca2+ and Mg2+ were determined by
potentiometry. High affinity for the former and selectivity with respect to the two latter interfering species prompt us to graft covalently one of these binders on a hydrophilic organic resin, which was then incorporated in an agarose binding gel. Performances of the DGT samplers made thereof to
accumulate uranium(VI) in natural freshwaters will be presented and compared to the experimental results obtained for a series of other binding resins, including Chelex-100 and Metsorb. These validation tests were performed both in the laboratory, using mineral water spiked with uranium, and in field by deploying the DGT samplers directly in a river.