Dépollution | EPFL Graph Search

vignette|Des bénévoles nettoient les côtes après la catastrophe du Prestige. La dépollution désigne l'élimination des pollutions et des contaminations des milieux ambiants tels les sols, les nappes phréatiques, les sédiments ou les eaux de surface. Les enjeux de la dépollution sont souvent financiers mais aussi d'intérêt général : protection de la santé publique et de l'environnement, ou par exemple dans le cas d'un site industriel ou commercial désaffecté, la réutilisation. La dépollution doit généralement remplir un ensemble de normes législatives et peut aussi être basée sur des évaluations des risques sanitaires ou écologiques lorsqu'aucune norme législative n'existe, ou lorsque celles-ci sont à titre consultatif. Évaluation de site vignette|Dépollution d'un bâtiment administratif Quand un site est suspecté de contamination, une première étape est l'évaluation quantitative et qualitative de la contamination. L'utilisation passée du site (quand elle est connue) et les

Insights into the microbial reduction of pentavalent and hexavalent uranium species by Shewanella oneidensis MR-1

Margaux Camille Andréa Molinas

Decades of uranium-related activities such as ore mining, nuclear power generation, weapon manufacture, storage of nuclear wastes, have contributed to the release of U in the environment. U occurrence is concerning, since in surface environments, U is typically found in the U(VI) oxidation state, as uranyl, complexed with various ligands, and is highly soluble. Therefore, this toxic metal is likely to leech into soils and contaminate surface waters and groundwaters. In addition, owing to the long half-lives of the predominant isotopes 238U and 235U, U is considered as a persistent contaminant over geological timescales. For several decades, efforts have focused on the development of in situ remediation solutions to tackle U pollution in the subsurface, and limit its mobility.With this aim, interest in the metabolic potential for U(VI)-respiration by dissimilatory metal-reducing bacteria (DMRB), such as Shewanella oneidensis MR-1, has seen a significant increase. This metabolically-versatile bacterium has been reported to reduce mobile U(VI) to typically insoluble crystalline and amorphous U(IV). The reduction of U(VI) in S. oneidensis MR-1 is coupled to the oxidation of an electron donor, which feeds electrons into an electron transport chain, extending from the cytoplasm to the outer-membrane of the cells. The microbially mediated reduction of U(VI) to U(IV) is the result of a two-step process. It is assumed that one electron is first transferred to U(VI) to form a pentavalent U(V) intermediate, followed by the abiotic disproportionation of two U(V) atoms into U(IV) and U(VI). However, evidence for this mechanism is limited to experimental systems rich in carbonate, which permits the rapid disproportionation of U(V). Thus, it remains unclear whether a second, biologically-mediated, electron transfer to U(V) is possible under conditions in which disproportionation is limited. To explore this, a novel U(V)-dpaea complex, that is stable in water at pH 7, was utilized to investigate the second step of the reduction mechanism. Here, we observed that U(V) can be biologically reduced by an additional one-electron transfer, resulting in the accumulation of U(IV) without the need for disproportionation. To improve our understanding of the molecular mechanism of U-dpaea reduction, we incubated mutant strains of S. oneidensis MR-1, lacking (i) only outer-membrane c-type cytochromes or (ii) all c-type cytochromes, with solid phase U(VI)-dpaea and aqueous U(V)-dpaea. We determined that U(VI)-dpaea reduction proceeds via the initial dissolution of the solid phase and that U(V)-dpaea reduction is mediated by outer-membrane c-type cytochromes. In particular, in vitro reactions between the purified outer-membrane c-type cytochrome MtrC and U(V)-dpaea demonstrated that MtrC can directly transfer electrons to U(V)-dpaea.Finally, we sought to determine the factors that influence electron transfer kinetics between DMRB and U. To this end, we reacted U(VI) coordinated by various aminocarboxylate ligands with purified MtrC. Here, U speciation significantly impacted reduction rates and appeared to be related to the binding strength of the U-MtrC interaction, i.e., hydrogen bonding versus electrostatic.All together, these findings provide further insights in the reduction mechanism of U by DMRB, and underline the importance of U speciation in controlling the pathway and rate of electron transfer.

EPFL2021

LCA and contaminated sites

Francesca Gambazzi

Life cycle assessment (LCA) is a tool for assessing the environmental impact of services or products. This project wants to explore the potential contribution of LCA for contaminated site management, via the comparison of several remediation strategies (excavation, phytoremediation and “do nothing” options) for soils contaminated by heavy metals. The study aims at identifying the main methodological gaps in modelling impacts at midpoint and endpoint levels and providing insights for filling in these gaps. In particular, emphasis is put on the impact of the site itself on the surrounding environment compared to remediation options. Excavation resulted to have the greater impact on the human health, while it is the smallest for the water ecosystem. Temporal and spatial dimension play a role in the evaluation of the damage. The results given by global and regional IMPACT2002 model are compared, and their allocation in short-term and long-term periods is shown with the introduction of the Stored Additional Impact (SAI), which goal is to help the comprehension of the outcome. The most important missing information in the method is the evaluation of the pollution impact on the contaminated site itself and its ecological and economical value after the management. To do this the combination of Ecological Risk Assessment (ERA) and LCA is suggested. The conclusion is that LCA can bring additional information that contribute to the decision making process of site management. In particular, the “do nothing” scenario serves as a reference impact and helps deducing the real efficiency and utility of the other remediation processes.

2008

Effects of different soil amendments on phytoremediation from a cadmium and DDTs co-contaminated soil by Sedum alfredii (Cd hyperaccumulator) co-cropped with Ricinus communis (DDT accumulator)

Pauline Grandjean

Soil pollution is a major environmental problem actually in China and in the world. It increases environmental risks and can affect humans through the food chain. Like solutions to clean-up the soils are generally expensive and can have side effects on environment, phytoremediation, an environmental friendly technology is a good alternative to traditional remediation. Nevertheless, some improvements must be done to increase its efficiency and make it economically viable. The goal of this work is to study two strategies respectful of the environment to improve the efficiency of phytoremediation: the co-cropping and the addition of amendments. Two Chinese species, Sedum alfredii (hyperaccumulator of cadmium) and Ricinus communis (accumulator of DDT) were co-cropped in pots with a soil contaminated by cadmium and DDT, in which different amendments (rapeseed waste, pig manure, a bio-surfactant: tea saponin, one of its by-product, and sulfur) were added to observe if they increase the efficiency of the phytoremediation. Bacteria were also used to improve DDT degradation. If the ricinus grew fast and easily, sedum biomass was very low and seems not suitable for co-cropping in these conditions. The rapeseed waste inhibit the growth of plants, suggesting that the dose was probably to high. Other amendments allowed a relatively similar growth with sensitively the best for tea saponin and microbes do not affect significantly the biomass. After determined in laboratory that tea saponin enhance the desorption of DDT and Cd in soil, an other pot experiment was started with Ricinus communis in soil amended with different concentrations of saponin to see if it also improve the phytoremediation. In the future, if the addition of amendments can enhance the phytoremediation as expected, analysis of parameters such as the quantity of nutrients or pollutants bioavailable or the structure of dissolve organic matter (DOM) might be done to see if they can explain this phenomenon. Further analysis in field conditions and with optimal concentrations of amendments are needed to determine if and in which conditions these strategies can be applicable at large scale.

2011