title: Compound specific isotope analysis of hexachlorocyclohexane isomers: a method for source fingerprinting and field investigation of in situ biodegradation.
abstract: BACKGROUND
  The manufacturing and uses of hexachlorocyclohexane (HCH) have resulted in a serious environmental challenge and legacy. This study highlights the ability of compound specific isotope analysis (CSIA) to distinguish among various HCH sources and to support the evaluation of the potential for in situ biodegradation in contaminated groundwater.
  
  
  METHODS
  Tests were conducted to verify the absence of significant isotope fractionation during HCH sample pre-concentration including dichloromethane extraction, solvent exchange into iso-octane, and H2SO4 clean-up, and analysis by gas chromatography/combustion-isotope ratio mass spectrometry (GC/C-IRMS). The method was then applied to four Technical Grade (TG) HCH mixtures procured from different sources and to groundwater samples from a contaminated site.
  
  
  RESULTS
  The pre-concentration method enabled determination of carbon isotope ratios (δ(13)C values) of HCH isomers with no significant isotopic fractionation. The TG-HCH mixtures had significantly different δ(13)C values. Moreover, for any given TG-HCH, all isomers had δ(13)C values within 1.1‰ of each other - a distinctly uniform fingerprint. At the HCH-contaminated field site, compared with source wells, downgradient wells showed significant (up to 5.1‰) enrichment in (13)C and the δ(13)C values of the HCH isomers were significantly different from each other.
  
  
  CONCLUSIONS
  A method was successfully developed for the CSIA of HCH isomers that showed potential for HCH source differentiation and identification of HCH in situ biodegradation. At the HCH-contaminated site, the observed preferential isotopic enrichment of certain isomers relative to others for a given source allows differentiation between biodegraded and non-biodegraded HCH.
authors.affiliation: Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, ON, M5S 3B1, Canada.
authors.forename: Michelle
authors.initials: M
authors.lastname: Chartrand
authors.affiliation: Department of Civil Engineering, University of Toronto, 35 Russell Street, Toronto, ON, M5S 1A4, Canada.|Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON, M5S 3E5, Canada.
authors.forename: Elodie
authors.initials: E
authors.lastname: Passeport
authors.affiliation: Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, ON, M5S 3B1, Canada.
authors.forename: Carla
authors.initials: C
authors.lastname: Rose
authors.affiliation: Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, ON, M5S 3B1, Canada.
authors.forename: Georges
authors.initials: G
authors.lastname: Lacrampe-Couloume
authors.affiliation: Dept. of Chemistry, Umeå University, Linnaeus väg 6, SE-901 87, Umeå, Sweden.
authors.forename: Terry F
authors.initials: TF
authors.lastname: Bidleman
authors.affiliation: Air Quality Processes Research Section, Environment Canada, 6248 Eighth Line, Egbert, ON, L0L1N0, Canada.
authors.forename: Liisa M
authors.initials: LM
authors.lastname: Jantunen
authors.affiliation: Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, ON, M5S 3B1, Canada.
authors.forename: Barbara
authors.initials: B
authors.lastname: Sherwood Lollar
mesh_terms: D001673:Biodegradation, Environmental; D002247:Carbon Isotopes / Q000032:analysis; D004784:Environmental Monitoring; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D060587:Groundwater / Q000737:chemistry; D001556:Hexachlorocyclohexane / Q000737:chemistry*; D007536:Isomerism; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D014874:Water Pollutants, Chemical; D001556:Hexachlorocyclohexane