Influence of Uranium on Bacterial Communities: A Comparison of Natural Uranium-Rich Soils with Controls

This study investigated the influence of uranium on the indigenous bacterial community structure in natural soils with high uranium content. Radioactive soil samples exhibiting 0.26% - 25.5% U in mass were analyzed and compared with nearby control soils containing trace uranium. EXAFS and XRD analyses of soils revealed the presence of U(VI) and uranium-phosphate mineral phases, identified as sabugalite and meta-autunite. A comparative analysis of bacterial community fingerprints using denaturing gradient gel electrophoresis (DGGE) revealed the presence of a complex population in both control and uranium-rich samples. However, bacterial communities inhabiting uraniferous soils exhibited specific fingerprints that were remarkably stable over time, in contrast to populations from nearby control samples. Representatives of Acidobacteria, Proteobacteria, and seven others phyla were detected in DGGE bands specific to uraniferous samples. In particular, sequences related to iron-reducing bacteria such as Geobacter and Geothrix were identified concomitantly with iron-oxidizing species such as Gallionella and Sideroxydans. All together, our results demonstrate that uranium exerts a permanent high pressure on soil bacterial communities and suggest the existence of a uranium redox cycle mediated by bacteria in the soil

Investigation of a biosurfactant-enhanced electrokinetic method and its effect on the potentially toxic trace elements in waterways sediments

International audienc

Over-sulfated soils and sediments treatment: A brief discussion on performance disparities of biological and non-biological methods throughout the literature

High sulfate concentrations in industrial effluents as well as solid materials (excavated soils, dredged sediments, etc.) are a major hindrance for circular economy outlooks. SO 4 2- acceptability standards are indeed increasingly restrictive, given the potential outcomes for public health and ecosystems. This literature review deals with the treatment pathways relying on precipitation, adsorption and microbial redox principles. Although satisfactory removal performances can be achieved with each of them, significant yield differences are displayed throughout the bibliography. The challenge here was to identify the parameters leading to this variability and to assess their impact. The precipitation pathway is based on the formation of two main minerals (ettringite and barite). It can lead to total sulfate removal but can also be limited by aqueous wastes chemistry. Stabilizer kinetics of formation and equilibrium are highly constrained by background properties such as pH, Eh, SO 4 2- saturation state and inhibiting metal occurrences. Regarding the adsorption route, sorbents’ intrinsic features such as the q max parameter govern removal yields. Concerning the microbial pathway, the chemical oxygen demand/SO 4 2- ratio and the hydraulic retention time, which are classically evoked as yield variation factors, appear here to be weakly influential. The effect of these parameters seems to be overridden by the influence of electron donors, which constitute a first order factor of variability. A second order variability can be read according to the nature of these electron donors. Approaches using simple monomers (ethanol lactates, etc.) perform better than those using predominantly ligneous organic matter

Traitement de sédiments portuaires méditerranéens contaminés en arsenic et en métaux (géochimie et écotoxicologie)

Ce travail de thèse étudie la faisabilité d un traitement des sédiments marins multi-contaminés par stabilisation géochimique à l aide d additifs minéraux. L efficacité du traitement a été évaluée en déterminant la qualité chimique et écotoxicologique des extraits aqueux de sédiments. Dans le cas de la stabilisation de l arsenic, des expériences préliminaires de sorption sur des additifs à base de fer ont révélé que l hématite adsorbe efficacement l arsenic sur une large gamme de pH et de concentration. Les tests de stabilisation en batch et en colonne montrent que les concentrations en arsenic diminuent de 30 à 40 % en présence de 5 % d hématite. L application du procédé de stabilisation à plus grande échelle en milieu extérieur confirme l efficacité du traitement pour la rétention de l arsenic mais aussi des métaux en présence d hématite et de fer métallique. Les bio-essais ont permis (i) de déterminer la toxicité potentielle de sédiments portuaires et (ii) d évaluer l effet des additifs minéraux en terme de toxicité. Les résultats montrent que le gradient de toxicité peut varier en fonction du test de toxicité utilisé. Après traitement par additifs minéraux, l hématite s est révélée être l additif le plus efficace pour améliorer la qualité écotoxicologique des élutriats les plus contaminés. Dans le cas de la mise en dépôt de sédiments contaminés, ce type de traitement permettrait d améliorer la qualité chimique et écotoxicologique des eaux de lixiviationThis thesis work studies the feasibility of treatment by geochemical stabilization mixing mineral additives with contaminated marine sediments. Treatment efficiency was evaluated by determining chemical and toxicity parameters on elutriates from sediment samples. In the case of arsenic stabilization, preliminary sorption experiments on iron based minerals revealed that hematite efficiently adsorbs arsenic on a large range of pH and concentrations. Stabilization tests in batch and column experiments showed that, in sediments mixed with 5% of hematite, arsenic concentrations decreased by 30 to 40 %. The use of this stabilization process in a small scale experiment performed outdoors confirmed the treatment is efficient not only for arsenic but also for metals especially when hematite and zero valent iron were used. Bioassays allowed (i) to determine potential toxicity of port sediments and (ii) to assess the effect of mineral additives on toxicity. Results show that the toxicity gradient can vary as a function of the toxicity test. After treatment by mineral additives, hematite was the most efficient additive to improve the ecotoxicological quality of the most contaminated elutriates. For storage of contaminated sediments, this type of treatment would allow to improve the chemical and toxicological quality of leachatesNICE-BU Sciences (060882101) / SudocSudocFranceF