Pathway-Dependent Isotope Fractionation during Aerobic and Anaerobic Degradation of Monochlorobenzene and 1,2, 4-Trichlorobenzene

摘要

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 aperiments were carried out in both aerobic and anaerobic microcosms. Large isotope fractionation was observed in bom the anaerobic microcosm aperiments. Enrichment factors (ε) for anaerobic reductive dechlorination of MCB and 1,2,4-TCB were -5.0V ± 02%, and -3.0V ± 0.4V, respectively. In contrast, no significant isotope fractionation was found during aerobic microbial degradation of 1,2,4-TCB. The cleavage of a C-Cl a bond occurs during anaerobic reductive dechlorination of MCB and 1,2,4-TCB, while no a bond cleavage is involved during aerobic degradation via dioiygenase. 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.