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C and Cl Isotope Fractionation of 1,2-Dichloroethane Displays Unique δ<sup>13</sup>C/δ<sup>37</sup>Cl Patterns for Pathway Identification and Reveals Surprising C–Cl Bond Involvement in Microbial Oxidation
Auteur(s)
Palau, J
Cretnik, S
Shouakar-Stash, O
Höche, M
Elsner, M
Date de parution
2014
In
Environmental Science & Technology, American Chemical Society, 2014/48/16/9430-9437
Résumé
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 (<i>Pseudomonas</i> sp. strain DCA1) versus C−Cl bond cleavage by S<sub>N</sub>2 reaction (<i>Xanthobacter autotrophicus</i> GJ10 and <i>Ancylobacter aquaticus</i> AD20). Compound-specific chlorine isotope analysis of 1,2-DCA was performed for the first time, and isotope fractionation (ε<sup>Cl</sup><sub>bulk</sub>) 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 (Δδ<sup>13</sup>C/Δ δ<sup>37</sup>Cl), 0.78 ± 0.03 (oxidation) and 7.7 ± 0.2 (S<sub>N</sub>2), delineate the potential of the dual isotope approach to identify 1,2-DCA degradation pathways in the field. In contrast to different ε<sup>C</sup><sub>bulk</sub> values [−3.5 ± 0.1‰ (oxidation) and −31.9 ± 0.7 and −32.0 ± 0.9‰ (S<sub>N</sub>2)], the obtained ε<sup>Cl</sup><sub>bulk</sub> values were surprisingly similar for the two pathways: −3.8 ± 0.2‰ (oxidation) and −4.2 ± 0.1 and −4.4 ± 0.2‰ (S<sub>N</sub>2). Apparent kinetic isotope effects (AKIEs) of 1.0070 ± 0.0002 (<sup>13</sup>C-AKIE, oxidation), 1.068 ± 0.001 (<sup>13</sup>C-AKIE, S<sub>N</sub>2), and 1.0087 ± 0.0002 (<sup>37</sup>Cl-AKIE, S<sub>N</sub>2) fell within expected ranges. In contrast, an unexpectedly large secondary <sup>37</sup>Cl-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.
Identifiants
Type de publication
journal article
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