title: Dual carbon-chlorine stable isotope investigation of sources and fate of chlorinated ethenes in contaminated groundwater.
abstract: Chlorinated ethenes (CEs) are ubiquitous groundwater contaminants, yet there remains a need for a method to efficiently monitor their in situ degradation. We report here the first field application of combined stable carbon and chlorine isotope analysis of tetrachloroethene (PCE) and trichloroethene (TCE) to investigate their biodegradation in a heavily contaminated aquifer. The two-dimensional Compound Specific Isotope Analysis (2D-CSIA) approach was facilitated by a recently developed gas chromatography-quadrupole mass spectrometry (GCqMS) method for δ(37)Cl determination. Both C and Cl isotopes showed evidence of ongoing PCE transformation. Applying published C isotope enrichment factors (ε(C)) enabled evaluation of the extent of in situ PCE degradation (11-78%). We interpreted C and Cl isotopes using a numerical reactive transport model along a 60-m flow path. It revealed that combined PCE and TCE mass load was dechlorinated by less than 10%, and that cis-dichloroethene was not further dechlorinated. Furthermore, the 2D-CSIA approach allowed estimation of Cl isotope enrichment factors ε(Cl) (-7.8 to -0.8‰) and characteristic ε(Cl)/ε(C) values (0.42-1.12) for reductive PCE dechlorination at this field site. This investigation demonstrates the benefit of 2D-CSIA to assess in situ degradation of CEs and the applicability of Cl isotope fractionation to evaluate PCE and TCE dechlorination.
authors.affiliation: Department of Applied Environmental Science (ITM), Stockholm University, Svante Arrhenius väg 8c, SE-106 91 Stockholm, Sweden.
authors.forename: Charline
authors.initials: C
authors.lastname: Wiegert
authors.forename: Christoph
authors.initials: C
authors.lastname: Aeppli
authors.forename: Tim
authors.initials: T
authors.lastname: Knowles
authors.forename: Henry
authors.initials: H
authors.lastname: Holmstrand
authors.forename: Richard
authors.initials: R
authors.lastname: Evershed
authors.forename: Richard D
authors.initials: RD
authors.lastname: Pancost
authors.forename: Jiřina
authors.initials: J
authors.lastname: Macháčková
authors.forename: Örjan
authors.initials: Ö
authors.lastname: Gustafsson
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis; D002713:Chlorine / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods*; D060587:Groundwater / Q000737:chemistry*; D054879:Halogenation; D013750:Tetrachloroethylene / Q000032:analysis*; D014241:Trichloroethylene / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification
chemical_list: D002247:Carbon Isotopes; D014874:Water Pollutants, Chemical; D014241:Trichloroethylene; D002713:Chlorine; D013750:Tetrachloroethylene