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Approche moléculaire pour quantifier la biodégradation des micropolluants en aval des stations d’épuration. Evaluation des outils de fractionnements isotopique et énantiomérique

Abstract : The widespread occurrence of pharmaceutical and personal care products (PPCP) in surface waters, due to their incomplete removal in wastewater treatment plants (WWTP), is of concern since these compounds may be harmful to living organisms. Environmental risks associated with the presence of PPCP in aquatic environment have to be evaluated in order to help the main actors involved in the water cycle such as public authorities and environmental companies, including Veolia, to manage them properly. Quantitative and qualitative assessment of in situ biodegradation of PPCP is a major need in the context of risk assessment. Quantitative information remains scarcely available due the lack of appropriate methods. The objective of this work was then to develop tools able to quantify specifically in situ biodegradation of PPCP at trace levels. Two different tools have been selected to be evaluated, namely enantiomeric fractionation dedicated to chiral compounds and isotopic fractionation limited to chlorine-isotope analysis dedicated to chlorinated PPCP. To evaluate these tools, environmental occurrence studies and in vitro mechanistic and kinetic studies were together performed using five probe compounds : two chiral PPCP (a beta-blocker, the metoprolol and an antidepressant, the venlafaxine) and three chlorinated PPCP (two biocides, the triclocarban and the triclosan, and a nonsteroidal anti-inflammatory drug, the diclofenac). These experiments demonstrated that chlorine isotope fractionation can hardly provide quantitative information on in situ biodegradation of chlorinated PPCP. Multi-dimensional isotopic fractionation might be better adapted to quantify biodegradation. Furthermore, through the experiments, new insights on biodegradation pathways and mechanisms of the studied compounds have also been gained. Dechlorination of triclosan within sediment has been evidenced for the first time. Concerning triclocarban, dechlorination of this compound in environment had already been reported in previous studies but aerobic and anaerobic dechlorination mechanisms have been elucidated in the present study. Results obtained on enantiomeric fractionation demonstrated that this tool is very promising. Experiments using metoprolol as probe compound showed existence of a linear relationship between enantiomeric enrichment and the extent of biodegradation both under controlled conditions and within WWTP. Enantiomeric enrichment might then constitute a good indicator of in situ biodegradation of metoprolol. Supplementary studies are needed to extrapolate these results to other micropollutants. In addition, stereoselective degradation of metoprolol in acid metoprolol within WWTP and under controlled conditions has been observed similarly to other studies and one degradation mechanism has been proposed to explain the reaction stereochemistry. In situ kinetics associated with degradation pathways of the studied PPSPs have to be measured to assess the ability of the environment to eliminate these compounds, hence the importance of making operational the quantitative indicators studied in this thesis. Crossed with ecotoxicity data, quantitative information on biodegradation can help public authorities to target PPCPs that need to be regulated first. They can also help private operators to direct their source reduction strategies and their water treatment process optimization so that they eliminate in priority the most risked micropollutants.
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Marine Souchier. Approche moléculaire pour quantifier la biodégradation des micropolluants en aval des stations d’épuration. Evaluation des outils de fractionnements isotopique et énantiomérique. Ingénierie de l'environnement. Université Montpellier, 2015. Français. ⟨NNT : 2015MONTS128⟩. ⟨tel-01985534⟩

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