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首页> 外文期刊>Journal of Contaminant Hydrology >Complementing approaches to demonstrate chlorinated solvent biodegradation in a complex pollution plume: Mass balance, PCR and compound-specific stable isotope analysis
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Complementing approaches to demonstrate chlorinated solvent biodegradation in a complex pollution plume: Mass balance, PCR and compound-specific stable isotope analysis

机译：证明复杂污染羽流中氯化溶剂生物降解的补充方法：质量平衡，PCR和化合物特异性稳定同位素分析

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This work describes the use of different complementing methods (mass balance, polymerase chain reaction assays and compound-specific stable isotope analysis) to demonstrate the existence and effectiveness of biodegradation of chlorinated solvents in an alluvial aquifer. The solvent-contaminated site is an old chemical factory located in an alluvial plain in France. As most of the chlorinated contaminants currently found in the groundwater at this site were produced by local industries at various times in the past, it is not enough to analyze chlorinated solvent concentrations along a flow path to convincingly demonstrate biodegradation. Moreover, only a few data were initially available to characterize the geochemical conditions at this site, which were apparently complex at the source zone due to (i) the presence of a steady oxygen supply to the groundwater by irrigation canal losses and river infiltration and (ii) an alkaline pH higher than 10 due to former underground lime disposal. A demonstration of the existence of biodegradation processes was however required by the regulatory authority within a timeframe that did not allow a full geochemical characterization of such a complex site. Thus a combination of different fast methods was used to obtain a proof of the biodegradation occurrence. First, a mass balance analysis was performed which revealed the existence of a strong natural attenuation process (biodegradation, volatilization or dilution), despite the huge uncertainty on these calculations. Second, a good agreement was found between carbon isotopic measurements and PCR assays (based on 16S RNA gene sequences and functional genes), which clearly indicated reductive dechlorination of different hydrocarbons (Tetrachloroethene-PCE-, Trichloroethene-TCE-, l,2-cisDichloroethene-cis-l,2-DCE-, 1.2-rransDichloroethene-rrans-l,2-DCE-, 1,1-Dichloroethene-1,1-DCE-, and Vinyl Chloride-VC) to ethene. According to these carbon isotope measurements, although TCE biodegradation seems to occur only in the upgradient part of the studied zone, DCE and VC dechlorination (originating from the initial TCE dechlorination) occurs along the entire flowpath. TCE reductase was not detected among the Dehalococcoides bacteria identified by quantitative PCR (qPCR), while DCE and VC reductases were present in the majority of the population. Reverse transcriptase PCR assays (rt-PCR) also indicated that bacteria and their DCE and VC reductases were active. Mass balance calculations showed moreover that 1,1-DCE was the predominant DCE isomer produced by TCE dechlorination in the upgradient part of the site. Consequently, coupling rt-PCR assays with isotope measurements removes the uncertainties inherent in a simple mass balance approach, so that when the three methods are used jointly, they allow the identification and quantification of natural biodegradation, even under apparently complex geochemical and hydraulic conditions.
机译：这项工作描述了使用不同的补充方法（质量平衡，聚合酶链反应分析和化合物特异性稳定同位素分析）来证明冲积含水层中氯化溶剂的生物降解的存在和有效性。受溶剂污染的地点是位于法国冲积平原上的一家老化学工厂。由于目前在该地点的地下水中发现的大多数氯化污染物都是过去当地政府在不同时期生产的，因此不足以分析流动路径中的氯化溶剂浓度以令人信服地证明其生物降解。此外，最初只有少量数据可以表征该地点的地球化学条件，由于（i）由于灌溉渠的损失和河流的渗透以及（ ii）由于以前的地下石灰处理，碱性pH值高于10。然而，监管机构要求在一个时间框架内证明生物降解过程的存在，而该时间框架无法对如此复杂的地点进行全面的地球化学表征。因此，使用不同快速方法的组合来获得生物降解发生的证据。首先，进行了质量平衡分析，结果表明存在强大的自然衰减过程（生物降解，挥发或稀释），尽管这些计算存在很大不确定性。其次，在碳同位素测量和PCR分析（基于16S RNA基因序列和功能基因）之间发现了很好的协议，这清楚地表明了不同碳氢化合物（四氯乙烯-PCE-，三氯乙烯-TCE-，1,2-顺二氯乙烯）的还原脱氯作用。 -顺式-1，2-DCE-，1.2-二甲基乙烷-二氯乙烯-1，2-DCE-，1，1-二氯乙烯-1，1-DCE-和氯乙烯-VC）成乙烯。根据这些碳同位素测量值，尽管TCE生物降解似乎仅发生在研究区域的上升部分，但DCE和VC脱氯（起源于最初的TCE脱氯）沿整个流路发生。在定量PCR（qPCR）鉴定的Dehalococcoides细菌中未检测到TCE还原酶，而大多数人群中都存在DCE和VC还原酶。逆转录酶PCR分析（rt-PCR）也表明细菌及其DCE和VC还原酶具有活性。质量平衡计算还表明，在现场的升级部分中，TCE脱氯是1,1-DCE的主要DCE异构体。因此，将rt-PCR分析与同位素测量相结合消除了简单的质量平衡方法固有的不确定性，因此，当将这三种方法结合使用时，即使在明显复杂的地球化学和水力条件下，它们也可以鉴定和定量自然生物降解。

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