Uranium (U) presents a unique challenge for ecological risk assessments around installations related to the nuclear fuel cycle because of both chemical and radiological toxicity. Their relative importance depends on the chemical speciation and isotopic composition of the radionuclide, the latter being strongly correlated to its natural or anthropogenic origin (enriched or depleted U) [1]. In this framework, the Diffusive Gradient in Thin-films (DGT) technique is an appealing tool for monitoring the water quality around uranium processing plants, nuclear facilities or mining areas. Indeed, the DGT sampling allows to preconcentrate in situ the labile U(VI) species, allowing to simultaneously characterize the labile UO22+ fraction in aqueous phase (i.e., this provides qualitative information on the "available stock of UO22+ for the aquatic organisms") and the isotopic composition at trace levels [2]. Among the eleven DGT methods developed for UO22+ [3], the ones containing Chelex-100® (an ion-exchange resin with iminodiacetic acid functional groups) or Metsorb® (a TiO2-based adsorbent) are the most employed due to their commercial availability. Nevertheless, their performances can be significantly degraded by high concentration levels of competing ions like Ca2+ in the deployment solution, which results in the underestimation of the overall concentration of labile U(VI) species in environmental waters [3, 4]. To improve the reliability of measurements, further analytical developments are therefore required. One important research direction includes the design of more selective UO22+ sorbent materials.In this study, we propose new DGT samplers for labile UO22+ species that incorporate novel complexing materials obtained by the covalent grafting of siderophore-like chelators on a hydrophilic organic resin. Siderophores are well-known to exhibit a high affinity for strong Lewis acids, such as iron(III) and actinide cations [5-7]. Rigorous laboratory validation of the new DGT devices was conducted, confirming the suitability of the samplers to quantitatively measure all UO22+ species in simple matrices in which UO22+-CO32– complexes dominate the speciation of U. In addition, cross-tests were performed with commercial Chelex-100® and Metsorb® based-DGT devices on several types of moderately basic waters (pH ≈ 8), either in the laboratory (i.e., soft and hard mineral waters and seawater) or during field tests. DGT probes were deployed in the alkaline surface water of the Œuf River, a tributary to the Seine River (France), in which Ca2+-UO22+-CO32– complexes are the dominant U species according to speciation modelling calculations. These experiments highlighted the superiority of the new DGT devices over those incorporating either Chelex-100® or Metsorb® sorbents. Finally, thermodynamic speciation calculations were performed as a first approach to better understand the functioning and potential limitations of our new and Chelex-100®-based DGT samplers in different deployment conditions.Acknowledgements:This work has been supported by IRSN, CNRS, and the French grant agency Agence Nationale de la Recherche (project PLUTON, grant n° ANR-17-CE08-0053). Osian FONQUERNIE and Tony FERNANDES are grateful to the Conseil Régional de Bourgogne Franche-Comté and the European Regional Development Fund (FEDER) for granting them a PhD fellowship. The authors thank Graver Technologies (www.gravertech.com) for the provision of the Metsorb® HMRP 50 products used in this study. All DGT experiments were performed at LUTECE (the SEDRE's experimental platform), and isotopic measurements at PATERSON (the IRSN's mass spectrometry platform). This work benefited from the knowledge acquired on the spatial and temporal distribution of U concentration in the Œuf-Essonne River through the research project UTOPIA conducted by Dr Mathilde ZEBRACKI (IRSN) and funded by the French program NEEDS.References:[1] T. Mathews, K. Beaugelin-Seiller, J. Garnier-Laplace, R. Gilbin, C. Adam, C. Della-Vedova, Environ. Sci. Technol. 2009, 43, 6684-6690[2] G. S. C. Turner, G. A. Mills, M. J. Bowes, J. L. Burnett, S. Amos, G. R. Fones, Environ. Sci.: Processes Impacts 2014, 16, 393-403.[3] V. Smolíková, P. Pelcová, A. Ridošková, M. Leermakers, Talanta 2022, 240, 123168.[4] G. S. C. Turner, G. A. Mills, P. R. Teasdale, J. L. Burnett, S. Amos, G. R. Fones, Anal. Chim. Acta 2012, 739, 37-46.[5] M. P. Neu, J. H. Matonic, C. E. Ruggiero, B. L. Scott, Angew. Chem. Int. Ed. 2000, 39, 1442-1444.[6] H. Boukhalfa, G. A. Icopini, S. D. Reilly, M. P. Neu, Appl. Environ. Microbiol. 2007, 73, 5897-5903.[7] L. Février, F. Coppin, S. Pierrisnard, M. Bourdillon, L. V. Nguyen, N. Zaiter, S. Brandès, V. Sladkov, J.-C. Chambron, M. Meyer, J. Environ. Radioact. 2021, 235-236, 106645.