Centre for Hydrogeology and Geothermics, University of Neuchâtel , 2000 Neuchâtel, Switzerland.
Environ Sci Technol. 2014 Aug 19;48(16):9430-7. doi: 10.1021/es5031917. Epub 2014 Jul 24.
This study investigates dual element isotope fractionation during aerobic biodegradation of 1,2-dichloroethane (1,2-DCA) via oxidative cleavage of a C-H bond (Pseudomonas sp. strain DCA1) versus C-Cl bond cleavage by S(N)2 reaction (Xanthobacter autotrophicus GJ10 and Ancylobacter aquaticus AD20). Compound-specific chlorine isotope analysis of 1,2-DCA was performed for the first time, and isotope fractionation (ε(bulk)(Cl)) was determined by measurements of the same samples in three different laboratories using two gas chromatography-isotope ratio mass spectrometry systems and one gas chromatography-quadrupole mass spectrometry system. Strongly pathway-dependent slopes (Δδ13C/Δδ37Cl), 0.78 ± 0.03 (oxidation) and 7.7 ± 0.2 (S(N)2), delineate the potential of the dual isotope approach to identify 1,2-DCA degradation pathways in the field. In contrast to different ε(bulk)(C) values [-3.5 ± 0.1‰ (oxidation) and -31.9 ± 0.7 and -32.0 ± 0.9‰ (S(N)2)], the obtained ε(bulk)(Cl) values were surprisingly similar for the two pathways: -3.8 ± 0.2‰ (oxidation) and -4.2 ± 0.1 and -4.4 ± 0.2‰ (S(N)2). Apparent kinetic isotope effects (AKIEs) of 1.0070 ± 0.0002 (13C-AKIE, oxidation), 1.068 ± 0.001 (13C-AKIE, S(N)2), and 1.0087 ± 0.0002 (37Cl-AKIE, S(N)2) fell within expected ranges. In contrast, an unexpectedly large secondary 37Cl-AKIE of 1.0038 ± 0.0002 reveals a hitherto unrecognized involvement of C-Cl bonds in microbial C-H bond oxidation. Our two-dimensional isotope fractionation patterns allow for the first time reliable 1,2-DCA degradation pathway identification in the field, which unlocks the full potential of isotope applications for this important groundwater contaminant.
本研究通过有氧生物降解 1,2-二氯乙烷（1,2-DCA）时的 C-H 键氧化断裂（假单胞菌 DCA1 菌株）与 S(N)2 反应的 C-Cl 键断裂，考察了双元素同位素分馏。首次对 1,2-DCA 进行了特定氯同位素分析，并通过在三个不同实验室中使用两种气相色谱-同位素比质谱系统和一种气相色谱-四极质谱系统测量相同样品，确定了同位素分馏（ε(bulk)(Cl))。强烈的途径依赖性斜率（Δδ13C/Δδ37Cl），0.78 ± 0.03（氧化）和 7.7 ± 0.2（S(N)2），描绘了双同位素方法在现场识别 1,2-DCA 降解途径的潜力。与不同的 ε(bulk)(C)值[-3.5 ± 0.1‰（氧化）和-31.9 ± 0.7 和-32.0 ± 0.9‰（S(N)2）]相比，两种途径的获得的 ε(bulk)(Cl)值令人惊讶地相似：-3.8 ± 0.2‰（氧化）和-4.2 ± 0.1 和-4.4 ± 0.2‰（S(N)2）。1.0070 ± 0.0002（13C-AKIE，氧化）、1.068 ± 0.001（13C-AKIE，S(N)2）和 1.0087 ± 0.0002（37Cl-AKIE，S(N)2）的表观动力学同位素效应（AKIEs）在预期范围内。相比之下，出乎意料的大二次 37Cl-AKIE 为 1.0038 ± 0.0002，表明微生物 C-H 键氧化中 C-Cl 键的参与程度前所未有的。我们的二维同位素分馏模式首次能够在现场可靠地识别 1,2-DCA 降解途径，这为该重要地下水污染物的同位素应用开辟了全部潜力。
