title: Pathway-dependent isotope fractionation during aerobic and anaerobic degradation of monochlorobenzene and 1,2,4-trichlorobenzene.
abstract: 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.
authors.affiliation: Department of Geology, University of Toronto , Toronto, Ontario M5S 3B1, Canada.
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Liang
authors.forename: Michael R
authors.initials: MR
authors.lastname: Howlett
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Nelson
authors.forename: Gavin
authors.initials: G
authors.lastname: Grant
authors.forename: Sandra
authors.initials: S
authors.lastname: Dworatzek
authors.forename: Georges
authors.initials: G
authors.lastname: Lacrampe-Couloume
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Zinder
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Edwards
authors.forename: Barbara
authors.initials: B
authors.lastname: Sherwood Lollar
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D002247:Carbon Isotopes; D005591:Chemical Fractionation / Q000379:methods*; D002722:Chlorobenzenes / Q000378:metabolism*; D054879:Halogenation; D007700:Kinetics; D053858:Metabolic Networks and Pathways
chemical_list: D002247:Carbon Isotopes; D002722:Chlorobenzenes; C009947:1,2,4-trichlorobenzene; C031294:chlorobenzene