C and Cl Isotope Fractionation of 1,2-Dichloroethane Displays Unique 未13C/未37Cl Patterns for Pathway Identification and Reveals Surprising C鈥揅l Bond Involvement in Microbial Oxid

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• 作者：Jordi Palau ; Stefan Cretnik ; Orfan Shouakar-Stash ; Martina H枚che ; Martin Elsner ; Daniel Hunkeler
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：August 19, 2014
• 年：2014
• 卷：48
• 期：16
• 页码：9430-9437
• 全文大小：354K
• ISSN：1520-5851

文摘

This study investigates dual element isotope fractionation during aerobic biodegradation of 1,2-dichloroethane (1,2-DCA) via oxidative cleavage of a C鈥揌 bond (Pseudomonas sp. strain DCA1) versus C鈥揅l bond cleavage by S_N2 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 (蔚_bulk^Cl) was determined by measurements of the same samples in three different laboratories using two gas chromatography鈥搃sotope ratio mass spectrometry systems and one gas chromatography鈥搎uadrupole mass spectrometry system. Strongly pathway-dependent slopes (螖未¹³C/螖未³⁷Cl), 0.78 卤 0.03 (oxidation) and 7.7 卤 0.2 (S_N2), delineate the potential of the dual isotope approach to identify 1,2-DCA degradation pathways in the field. In contrast to different 蔚_bulk^C values [鈭?.5 卤 0.1鈥?(oxidation) and 鈭?1.9 卤 0.7 and 鈭?2.0 卤 0.9鈥?(S_N2)], the obtained 蔚_bulk^Cl values were surprisingly similar for the two pathways: 鈭?.8 卤 0.2鈥?(oxidation) and 鈭?.2 卤 0.1 and 鈭?.4 卤 0.2鈥?(S_N2). Apparent kinetic isotope effects (AKIEs) of 1.0070 卤 0.0002 (¹³C-AKIE, oxidation), 1.068 卤 0.001 (¹³C-AKIE, S_N2), and 1.0087 卤 0.0002 (³⁷Cl-AKIE, S_N2) fell within expected ranges. In contrast, an unexpectedly large secondary ³⁷Cl-AKIE of 1.0038 卤 0.0002 reveals a hitherto unrecognized involvement of C鈥揅l bonds in microbial C鈥揌 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.