Integrative spectroscopic, geochemical, and microbiological approaches for assessing uranium (U) speciation and...

Naturally occurring radionuclides (NOR), such as uranium (U), can have adverse effects on both human and non-human biota. Identifying the abiotic and biotic parameters that control NOR transfer and redistribution in the environment is therefore crucial to better predict their behaviour. To this end, a multidisciplinary approach was used to characterize the soil-microbiota-plant root system in a U mine-impacted wetland. Geochemical analyses revealed higher concentrations of U (722 µg g^-1 on average) and Pb (1743 µg g^-1 on average) in soils layers collected from the mine-impacted area compared to those from a nearby control area (24 and 200 µg g^-1 on average for U and Pb, respectively). A comparative analysis of the two areas showed no evidence of physiological stress or significant differences in root-associated prokaryotic communities for either of the two native plant species. In contrast, root-associated fungal communities and microbial assemblages in surrounding surface soils differed significantly between the sites. In the inherited U-rich soil layer below the surface a distinct microbial community was identified, characterized by lower diversity than that of the surface layer. This community included the ascomycetous genera Pseudorotium and Lulwoana, as well as bacteria involved in the sulphur (S) cycle (e.g., Desulfosporosinus, Desulfobacca), and the iron (Fe) cycle (e.g., Geobacteraceae, Geothrix, Clostridium, Gallionella, Thiobacillus), all potentially modulating U speciation and mobility. Finally, the detection of a U(VI) phosphate species in both the soil and the soil water, together with bacteria potentially able to form U-phosphate biominerals (e.g., Pseudomonas, Sphingomonas, Chryseobacterium), suggests a key role of microorganisms in U immobilization in this ecosystem.