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首页> 外文期刊>Environmental Science & Technology >Potential for Identifying Abiotic Chloroalkane Degradation Mechanisms using Carbon Isotopic Fractionation
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Potential for Identifying Abiotic Chloroalkane Degradation Mechanisms using Carbon Isotopic Fractionation

机译：使用碳同位素分馏确定非生物氯烷降解机理的潜力

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Degradation of 1,1- and 1,2-dichloroethane (1,1-DCA, 1,2-DCA) and carbon tetrachloride (CCl4) on Zn~0 was investigated using compound specific isotope analysis (CSIA) to measure isotopic fractionation factors for chloroalkane degradation by hydrogenolysis, by a-elimination, and byβ-elimination. Significant differences in enrichment factors (ε ) and associated apparent kinetic isotope effects (AKIE) were measured for these different reaction pathways, suggesting that carbon isotope fractionation by β -elimination is substantially larger than fractionation by hydrogenolysis or by α-elimination. Specifically, for 1,1-DCA, the isotopic composition of the reductive a-elimination product (ethane) and the hydrogenolysis product (chloroethane) were the same, indicating that cleavage of a single C-CI bond was the rate-limiting step in both cases. In contrast, for 1,2-DCA, ε = ε_(reactive position) = -29.7 ± 1.5%, and the calculated AKIE (1.03) indicated that β-elimination was likely concerted, possibly involving two C-CI bonds simultaneously. Compared to 1,1-DCA hydrogenolysis, the AKIE of 1.01 for hydrogenolysis of CCl_4 was much lower, indicating that, for this highly reactive organohalide, mass transfer to the surface was likely partially rate-limiting. These findings are a first step toward delineating the relative contribution of these competing pathways in other abiotic systems such as the degradation of chlorinated ethenes on zerovalent iron (ZVI), iron sulfide, pyrite, or magnetite, and, potentially, toward distinguishing between degradation of chlorinated ethenes by abiotic versus biotic processes.
机译：使用化合物特异性同位素分析法（CSIA）测定同位素分馏因子，研究了Zn〜0上1,1-二氯乙烷（1,1-DCA，1,2-DCA）和四氯化碳（CCl4）的降解通过氢解，α-消除和β-消除来降解氯烷。对于这些不同的反应途径，测定了富集因子（ε）和相关的表观动力学同位素效应（AKIE）的显着差异，表明通过β-消除作用进行碳同位素分馏比通过氢解或α-消除作用进行的碳同位素分馏要大得多。具体地，对于1，1-DCA，还原性α-消除产物（乙烷）和氢解产物（氯乙烷）的同位素组成相同，表明单个C-CI键的裂解是其中的限速步骤。两种情况。相反，对于1,2-DCA，ε=ε_（反应位置）= -29.7±1.5％，计算得出的AKIE（1.03）表明β消除可能是协调一致的，可能同时涉及两个C-CI键。与1,1-DCA氢解相比，CCl_4氢解的AKIE为1.01更低，这表明，对于这种高反应性的有机卤化物，向表面的传质可能是部分限速的。这些发现是描述这些竞争途径在其他非生物系统中相对贡献的第一步，例如在零价铁（ZVI），硫化铁，黄铁矿或磁铁矿上氯化乙烯的降解，以及可能在区分氧化铁的降解方面非生物与生物过程中的氯化乙烯。

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