Department of Earth Sciences, University of Toronto , Toronto, Ontario M5S 3B1, Canada.
Environ Sci Technol. 2014 May 6;48(9):4844-51. doi: 10.1021/es4054384. Epub 2014 Apr 23.
Chlorinated benzenes are ubiquitous organic contaminants found in groundwater and soils. Compound specific isotope analysis (CSIA) has been increasingly used to assess natural attenuation of chlorinated contaminants, in which anaerobic reductive dechlorination plays an essential role. In this work, carbon isotope fractionation of the three dichlorobenzene (DCB) isomers was investigated during anaerobic reductive dehalogenation in methanogenic laboratory microcosms. Large isotope fractionation of 1,3-DCB and 1,4-DCB was observed while only a small isotope effect occurred for 1,2-DCB. Bulk enrichment factors (εbulk) were determined from a Rayleigh model: -0.8 ± 0.1 ‰ for 1,2-DCB, -5.4 ± 0.4 ‰ for 1,3-DCB, and -6.3 ± 0.2 ‰ for 1,4-DCB. εbulk values were converted to apparent kinetic isotope effects for carbon (AKIE) in order to characterize the carbon isotope effect at the reactive positions for the DCB isomers. AKIE values are 1.005 ± 0.001, 1.034 ± 0.003, and 1.039 ± 0.001 for 1,2-DCB, 1,3-DCB, and 1,4-DCB, respectively. The large difference in AKIE values between 1,2-DCB and 1,3-DCB (or 1,4-DCB) suggests distinct reaction pathways may be involved for different DCB isomers during microbial reductive dechlorination by the methanogenic cultures.
氯苯是地下水中和土壤中普遍存在的有机污染物。化合物特定同位素分析（CSIA）已越来越多地用于评估氯化污染物的自然衰减，其中厌氧还原脱氯起着至关重要的作用。在这项工作中，研究了三种二氯苯（DCB）异构体在产甲烷实验室微环境中的厌氧还原脱卤过程中的碳同位素分馏。1,3-DCB 和 1,4-DCB 发生了较大的同位素分馏，而 1,2-DCB 仅发生了较小的同位素效应。从瑞利模型确定了总体富集因子（εbulk）：1,2-DCB 为-0.8 ± 0.1‰，1,3-DCB 为-5.4 ± 0.4‰，1,4-DCB 为-6.3 ± 0.2‰。εbulk 值被转换为 DCB 异构体碳反应位置的表观动力学同位素效应（AKIE），以表征碳同位素效应。AKIE 值分别为 1.005 ± 0.001、1.034 ± 0.003 和 1.039 ± 0.001，用于 1,2-DCB、1,3-DCB 和 1,4-DCB。1,2-DCB 和 1,3-DCB（或 1,4-DCB）之间 AKIE 值的巨大差异表明，在产甲烷培养物的微生物还原脱氯过程中，不同的 DCB 异构体可能涉及不同的反应途径。
