Understanding mechanisms of radionuclide (RN) migration in wetlands and continental aquatic environments is a major challenge in light of numerous environmental, societal, and health issues raised by TENORM contamination (Technologically Enhanced Naturally Occurring Radioactive Materials). To address these questions, a contaminated wetland near a former uranium (U) mining and waste storage site (Rophin, France) has been instrumented within ZATU program. Previous studies have highlighted: (i) the presence of a whitish subsurface clay horizon enriched in U (up to 1855 mgU·kg-1) inherited from mining activities and (ii) high amounts of organic colloids (primary transport vector for U) and inorganic colloids (secondary transport vector for U) in the wetland waters.
The present researches aim to understand colloids role in U migration in aquatic environments, with a first step focusing on their characterization. For this purpose, the liquid chromatography - organic carbon detector - organic nitrogen detector - ultraviolet detector (LC-OCD-OND-UVD) system, coupled with an inductively coupled plasma mass spectrometer (ICP-MS) is used. This setup allows the separation of different components present in an aqueous sample according to their size and chemical functions via LC, and then measurement of dissolved organic carbon, dissolved organic nitrogen, as well as the specific absorbance index at a selected wavelength and molecular weight for each identified fraction. However, ICP-MS coupling is a novelty that allows for semi-quantitative detection of target analytes in each colloidal fraction. Results were consistent with previous observations by Meyer-Georg (2021), where U appears to be preferentially associated with humic substances (i.e., organic colloids) compared to inorganic colloids. To complement the LC-OCD-OND-UVD-ICP-MS analyses, another size-based fractionation technique was employed, i.e., the Asymmetric Flow-Field Flow Fractionation (AsFlFFF) also coupled to an ICP-MS. Later on, the aim is to compare the results of this field study on colloidal U migration, with data acquired from model colloids and their reactivity towards U.
