title: Stable carbon isotope analysis to distinguish biotic and abiotic degradation of 1,1,1-trichloroethane in groundwater sediments.
abstract: The fate and treatability of 1,1,1-TCA by natural and enhanced reductive dechlorination was studied in laboratory microcosms. The study shows that compound-specific isotope analysis (CSIA) identified an alternative 1,1,1-TCA degradation pathway that cannot be explained by assuming biotic reductive dechlorination. In all biotic microcosms 1,1,1-TCA was degraded with no apparent increase in the biotic degradation product 1,1-DCA. 1,1,1-TCA degradation was documented by a clear enrichment in (13)C in all biotic microcosms, but not in the abiotic control, which suggests biotic or biotically mediated degradation. Biotic degradation by reductive dechlorination of 1,1-DCA to CA only occurred in bioaugmented microcosms and in donor stimulated microcosms with low initial 1,1,1-TCA or after significant decrease in 1,1,1-TCA concentration (after∼day 200). Hence, the primary degradation pathway for 1,1,1-TCA does not appear to be reductive dechlorination via 1,1-DCA. In the biotic microcosms, the degradation of 1,1,1-TCA occurred under iron and sulfate reducing conditions. Biotic reduction of iron and sulfate likely resulted in formation of FeS, which can abiotically degrade 1,1,1-TCA. Hence, abiotic degradation of 1,1,1-TCA mediated by biotic FeS formation constitute an explanation for the observed 1,1,1-TCA degradation. This is supported by a high 1,1,1-TCA (13)C enrichment factor consistent with abiotic degradation in biotic microcosms. 1,1-DCA carbon isotope field data suggest that this abiotic degradation of 1,1,1-TCA is a relevant process also at the field site.
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark. Electronic address: mmbr@env.dtu.dk.
authors.forename: Mette M
authors.initials: MM
authors.lastname: Broholm
authors.affiliation: Centre for Hydrogeology, University of Neuchâtel, Neuchâtel, Switzerland. Electronic address: daniel.hunkeler@unine.ch.
authors.forename: Daniel
authors.initials: D
authors.lastname: Hunkeler
authors.affiliation: Orbicon, Roskilde, Denmark. Electronic address: ntux@orbicon.dk.
authors.forename: Nina
authors.initials: N
authors.lastname: Tuxen
authors.affiliation: Centre for Hydrogeology, University of Neuchâtel, Neuchâtel, Switzerland. Electronic address: simon.jeannottat@unine.ch.
authors.forename: Simon
authors.initials: S
authors.lastname: Jeannottat
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark. Electronic address: chas@env.dtu.dk.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Scheutz
mesh_terms: D001673:Biodegradation, Environmental; D002247:Carbon Isotopes / Q000032:analysis* / Q000737:chemistry; D004784:Environmental Monitoring / Q000379:methods*; D052918:Environmental Restoration and Remediation; D019015:Geologic Sediments / Q000737:chemistry*; D060587:Groundwater / Q000737:chemistry*; D054879:Halogenation; D013431:Sulfates / Q000378:metabolism; D014240:Trichloroethanes / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D013431:Sulfates; D014240:Trichloroethanes; D014874:Water Pollutants, Chemical; C024566:1,1,1-trichloroethane
keywords: Biodegradation; Chlorinated ethanes; Clayey till; Groundwater; Isotopic fractionation