A combined DGT - DET approach for an in situ investigation of uranium resupply from large soil profiles in a wetland impacted by former mining activities

An in situ methodology combining DET and DGT probes was applied in a wetland soil, downstream of a former uranium mine (Rophin), to evaluate metal resupply by calculating the R ratio (R = [U]DGT/[U]pore water) from a high resolution and large (75 cm) soil profile. Our study confirms its applicability in soil layers affected by uranium mining activities. The investigation revealed that the metal resupply is significant, with a calculated R value of 0.87 indicating a noteworthy resupply of uranium from the mine deposit layer. Furthermore, results demonstrate that a considerable amount of up to 1,750 mg kg-1 of uranium is retained in wetland topsoil due to organic complexation processes. Additionally, changes in redox-sensitive elements were observed below the soil-water interface, emphasizing the complex geochemical interactions present in such impacted environments. Our findings contribute valuable insights into the behavior of uranium in wetland ecosystems affected by mining, highlighting the importance of integrating advanced measurement techniques for assessing metal mobility and speciation.