G360 Institute for Groundwater Research, College of Engineering and Physical Sciences , University of Guelph , 50 Stone Road East , Guelph , Ontario , Canada N1G 2W1.
Department of Civil Engineering , University of Toronto , 35 Saint George Street , Toronto , Ontario , Canada , M5S 1A4.
Environ Sci Technol. 2018 Jul 3;52(13):7296-7306. doi: 10.1021/acs.est.8b01173. Epub 2018 Jun 19.
This study aims to investigate whether compound-specific carbon isotope analysis (CSIA) can be used to differentiate the degradation pathways of chlorohydrocarbons in saturated low-permeability sediments. For that purpose, a site was selected, where a complex mixture of chlorohydrocarbons contaminated an aquifer-aquitard system. Almost 50 years after contaminant releases, high-resolution concentration, CSIA, and microbial profiles were determined. The CSIA profiles showed that in the aquitard cis-dichloroethene (cDCE), first considered as a degradation product of trichloroethene (TCE), is produced by the dichloroelimination of 1,1,2,2-tetrachloroethane (TeCA). In contrast, TeCA degrades to TCE via dehydrohalogenation in the aquifer, indicating that the aquifer-aquitard interface separates two different degradation pathways for TeCA. Moreover, the CSIA profiles showed that chloroform (CF) is degraded to dichloromethane (DCM) via hydrogenolysis in the aquitard and, to a minor degree, produced by the degradation of carbon tetrachloride (CT). Several microorganisms capable of degrading chlorohydrocarbons were detected in the aquitard, suggesting that aquitard degradation is microbially mediated. Furthermore, numerical simulations reproduced the aquitard concentration and CSIA profiles well, which allowed the determination of degradation rates for each transformation pathway. This improves the prediction of contaminant fate in the aquitard and potential magnitude of impacts on the adjacent aquifer due to back-diffusion.
本研究旨在探讨化合物特异性碳同位素分析（CSIA）是否可用于区分饱和低渗透沉积物中氯代烃的降解途径。为此，选择了一个地点，其中氯代烃的复杂混合物污染了含水层-隔水层系统。在污染物释放近 50 年后，确定了高分辨率浓度、CSIA 和微生物分布。CSIA 分布表明，在隔水层中，顺式-二氯乙烯（cDCE）最初被认为是三氯乙烯（TCE）的降解产物，是由 1,1,2,2-四氯乙烷（TeCA）的双氯消除产生的。相比之下，TeCA 在含水层中通过脱卤化氢降解为 TCE，这表明含水层-隔水层界面将 TeCA 的两种不同降解途径分开。此外，CSIA 分布表明，三氯甲烷（CF）在隔水层中通过氢解作用降解为二氯甲烷（DCM），在较小程度上由四氯化碳（CT）的降解产生。在隔水层中检测到几种能够降解氯代烃的微生物，这表明隔水层的降解是微生物介导的。此外，数值模拟很好地再现了隔水层的浓度和 CSIA 分布，这允许确定每个转化途径的降解速率。这提高了对隔水层中污染物命运的预测以及由于反向扩散对相邻含水层的潜在影响的预测。
