Department of Geology, University of Toronto , Toronto, Ontario M5S 3B1, Canada.
Environ Sci Technol. 2011 Oct 1;45(19):8321-7. doi: 10.1021/es201224x. Epub 2011 Sep 9.
Stable carbon isotope fractionation is a valuable tool for monitoring natural attenuation and to establish the fate of groundwater contaminants. In this study, we measured carbon isotope fractionation during aerobic and anaerobic degradation of two chlorinated benzenes: monochlorobenzene (MCB) and 1,2,4-trichlorobenzene (1,2,4-TCB). MCB isotope fractionation was measured in anaerobic methanogenic microcosms, while 1,2,4-TCB isotope experiments were carried out in both aerobic and anaerobic microcosms. Large isotope fractionation was observed in both the anaerobic microcosm experiments. Enrichment factors (ε) for anaerobic reductive dechlorination of MCB and 1,2,4-TCB were -5.0‰ ± 0.2‰ and -3.0‰ ± 0.4‰, respectively. In contrast, no significant isotope fractionation was found during aerobic microbial degradation of 1,2,4-TCB. The cleavage of a C-Cl σ bond occurs during anaerobic reductive dechlorination of MCB and 1,2,4-TCB, while no σ bond cleavage is involved during aerobic degradation via dioxygenase. The difference in isotope fractionation for aerobic versus anaerobic biodegradation of MCB and 1,2,4-TCB can be explained by the difference in the initial step of aerobic versus anaerobic biodegradation pathways.
稳定碳同位素分馏是监测自然衰减和确定地下水污染物归宿的一种有效工具。在本研究中，我们测量了两种氯苯（单氯苯和 1,2,4-三氯苯）在好氧和厌氧降解过程中的碳同位素分馏。在厌氧产甲烷微宇宙中测量了单氯苯的同位素分馏，而 1,2,4-三氯苯的同位素实验则在好氧和厌氧微宇宙中进行。在两个厌氧微宇宙实验中都观察到了较大的同位素分馏。单氯苯和 1,2,4-三氯苯的厌氧还原脱氯的富集因子（ε）分别为-5.0‰±0.2‰和-3.0‰±0.4‰。相比之下，在好氧微生物降解 1,2,4-三氯苯的过程中没有发现明显的同位素分馏。在单氯苯和 1,2,4-三氯苯的厌氧还原脱氯过程中会发生 C-Cl σ键的断裂，而在好氧降解途径通过双加氧酶时则不会涉及 σ 键的断裂。好氧生物降解和厌氧生物降解的单氯苯和 1,2,4-三氯苯之间的同位素分馏差异可以通过好氧和厌氧生物降解途径的初始步骤的差异来解释。
