title: Carbon and chlorine isotope fractionation during microbial degradation of tetra- and trichloroethene.
abstract: Two-dimensional compound-specific isotope analysis (2D-CSIA), combining stable carbon and chlorine isotopes, holds potential for monitoring of natural attenuation of chlorinated ethenes (CEs) in contaminated soil and groundwater. However, interpretation of 2D-CSIA data sets is challenged by a shortage of experimental Cl isotope enrichment factors. Here, isotope enrichments factors for C and Cl (i.e., εC and εCl) were determined for biodegradation of tetrachloroethene (PCE) and trichloroethene (TCE) using microbial enrichment cultures from a heavily CE-contaminated aquifer. The obtained values were εC = -5.6 ± 0.7‰ (95% CI) and εCl = -2.0 ± 0.5‰ for PCE degradation and εC = -8.8 ± 0.2‰ and εCl = -3.5 ± 0.5‰ for TCE degradation. Combining the values for both εC and εCl yielded mechanism-diagnostic εCl/εC ratios of 0.35 ± 0.11 and 0.37 ± 0.11 for the degradation of PCE and TCE, respectively. Application of the obtained εC and εCl values to a previously investigated field site gave similar estimates for the fraction of degraded contaminant as in the previous study, but with a reduced uncertainty in assessment of the natural attenuation. Furthermore, 16S rRNA gene clone library analyses were performed on three samples from the PCE degradation experiments. A species closely related to Desulfitobacterium aromaticivorans UKTL dominated the reductive dechlorination process. This study contributes to the development of 2D-CSIA as a tool for evaluating remediation strategies of CEs at contaminated sites.
authors.affiliation: Department of Applied Environmental Science, ITM, Stockholm University, 106 91 Stockholm, Sweden. charline.wiegert@itm.su.se
authors.forename: Charline
authors.initials: C
authors.lastname: Wiegert
authors.forename: Manolis
authors.initials: M
authors.lastname: Mandalakis
authors.forename: Tim
authors.initials: T
authors.lastname: Knowles
authors.forename: Paraskevi N
authors.initials: PN
authors.lastname: Polymenakou
authors.forename: Christoph
authors.initials: C
authors.lastname: Aeppli
authors.forename: Jiřina
authors.initials: J
authors.lastname: Macháčková
authors.forename: Henry
authors.initials: H
authors.lastname: Holmstrand
authors.forename: Richard P
authors.initials: RP
authors.lastname: Evershed
authors.forename: Richard D
authors.initials: RD
authors.lastname: Pancost
authors.forename: Orjan
authors.initials: O
authors.lastname: Gustafsson
mesh_terms: D000393:Air Pollutants / Q000737:chemistry*; D001673:Biodegradation, Environmental; D002247:Carbon Isotopes / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D004784:Environmental Monitoring / Q000379:methods*; D007554:Isotopes / Q000737:chemistry*; D014241:Trichloroethylene / Q000737:chemistry*
chemical_list: D000393:Air Pollutants; D002247:Carbon Isotopes; D007554:Isotopes; D014241:Trichloroethylene; D002713:Chlorine