Department of Mineralogy, Petrology and Applied Geology, Faculty of Earth Sciences, University of Barcelona (UB), Water Research Institute (IdRA-UB), Serra Húnter Tenure-elegible Lecturer, C/ Martí i Franquès, s/n, E-08028 Barcelona, Spain.
Department of Mineralogy, Petrology and Applied Geology, Faculty of Earth Sciences, University of Barcelona (UB), Water Research Institute (IdRA-UB). C/ Martí i Franquès, s/n, E-08028 Barcelona, Spain.
Sci Total Environ. 2022 Apr 10;816:151532. doi: 10.1016/j.scitotenv.2021.151532. Epub 2021 Nov 6.
Chlorinated solvents occur as dense nonaqueous phase liquid (DNAPL) or as solutes when dissolved in water. They are present in many pollution sites in urban and industrial areas. They are toxic, carcinogenic, and highly recalcitrant in aquifers and aquitards. In the latter case, they migrate by molecular diffusion into the matrix. When aquitards are fractured, chlorinated solvents also penetrate as a free phase through the fractures. The main objective of this study was to analyze the biogeochemical processes occurring inside the matrix surrounding fractures and in the joint-points zones. The broader implications of this objective derive from the fact that, incomplete natural degradation of contaminants in aquitards generates accumulation of daughter products. This causes steep concentration gradients and back-diffusion fluxes between aquitards and high hydraulic conductivity layers. This offers opportunities to develop remediation strategies based, for example, on the coupling of biotic and reactive abiotic processes. The main results showed: 1) Degradation occurred especially in the matrix adjacent to the orthogonal network of fractures and textural heterogeneities, where texture contrasts favored microbial development because these zones constituted ecotones. 2) A dechlorinating bacterium not belonging to the Dehalococcoides genus, namely Propionibacterium acnes, survived under the high concentrations of dissolved perchloroethene (PCE) in contact with the PCE-DNAPL and was able to degrade it to trichloroethene (TCE). Dehalococcoides genus was able to conduct PCE reductive dechlorination at least up to cis-1,2-dichloroethene (cDCE), which shows again the potential of the medium to degrade chloroethenes in aquitards. 3) Degradation of PCE in the matrix resulted from the coupling of reactive abiotic and biotic processes-in the first case, promoted by Fe sorbed to iron oxides, and in the latter case, related to dechlorinating microorganisms. The dechlorination resulting from these coupling processes is slow and limited by the need for an adequate supply of electron donors.
氯代溶剂以致密非水相液体（DNAPL）的形式存在，或溶解在水中时以溶质的形式存在。它们存在于城市和工业区的许多污染地点。它们在含水层和隔水层中是有毒的、致癌的和高度难降解的。在后一种情况下，它们通过分子扩散迁移到基质中。当隔水层有裂缝时，氯代溶剂也会作为自由相通过裂缝渗透。本研究的主要目的是分析围绕裂缝和节理点带的基质内发生的生物地球化学过程。这一目标的更广泛意义源于以下事实，即不完全的天然污染物在隔水层中的降解会导致子产物的积累。这会导致隔水层和高水力传导率层之间陡峭的浓度梯度和反向扩散通量。这为开发修复策略提供了机会，例如，基于生物和反应性非生物过程的耦合。主要结果表明：1）降解主要发生在与正交裂缝网络和结构异质性相邻的基质中，其中结构对比有利于微生物的发展，因为这些区域构成了生态过渡带。2）一种不属于 Dehalococcoides 属的脱氯细菌，即痤疮丙酸杆菌，在与 PCE-DNAPL 接触的高浓度溶解六氯乙烷（PCE）中存活下来，并且能够将其降解为三氯乙烯（TCE）。Dehalococcoides 属至少能够将 PCE 进行还原脱氯，直至顺-1,2-二氯乙烯（cDCE），这再次表明该介质具有在隔水层中降解氯代烯烃的潜力。3）基质中 PCE 的降解是由反应性非生物和生物过程的耦合引起的，在第一种情况下，由铁氧化物吸附的铁促进，在后一种情况下，与脱氯微生物有关。这些耦合过程导致的脱氯作用缓慢，受到电子供体供应的限制。
