title: Compound specific stable isotope analysis (CSIA) to characterize transformation mechanisms of α-hexachlorocyclohexane.
abstract: A systematic investigation of environmentally relevant transformation processes of alpha-hexachlorocyclohexane (α-HCH) was performed in order to explore the potential of compound specific stable isotope analysis (CSIA) to characterize reaction mechanisms. The carbon isotope enrichment factors (ɛC) for the chemical transformations of α-HCH via direct photolysis, indirect photolysis (UV/H2O2), hydrolysis, electro-reduction or reduction by Fe(0) were quantified and compared to those previously published for biodegradation. Hydrogen abstraction by hydroxyl radicals generated by UV/H2O2 led to ɛC of -1.9 ± 0.2 ‰ with an apparent kinetic carbon isotope effect (AKIEC) of 1.012 ± 0.001. Dehydrochlorination by alkaline hydrolysis yielded ɛC of -7.6 ± 0.4 ‰ with AKIEC of 1.048 ± 0.003. Dechlorination either by homolytic bond cleavage in direct photolysis (ɛC=-2.8 ± 0.2 ‰) or single-electron transfer in electro-reduction (ɛC=-3.8 ± 0.4 ‰) corresponded to AKIEC of 1.017 ± 0.001 and 1.023 ± 0.003, respectively. Dichloroelimination catalyzed by Fe(0) via two-electron transfers resulted in ɛC of -4.9 ± 0.1 ‰. AKIEC values assuming either a concerted or a stepwise mechanism were 1.030 ± 0.0006 and 1.015 ± 0.0003, respectively. Contrary to biodegradation, no enantioselectivity of α-HCH was observed in chemical reactions, which might be used to discriminate chemical and biological in situ transformations.
authors.affiliation: Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.affiliation: Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Safdar
authors.initials: S
authors.lastname: Bashir
authors.affiliation: Department of Environmental Microbiology, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Jinyi
authors.initials: J
authors.lastname: Qin
authors.affiliation: Department of Chemistry, Leibniz Institute for Tropospheric Research (TROPOS), Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Janine
authors.initials: J
authors.lastname: Schindelka
authors.affiliation: Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany; Isodetect-Company for Isotope Monitoring, Deutscher Platz 5b, 04103 Leipzig, Germany.
authors.forename: Anko
authors.initials: A
authors.lastname: Fischer
authors.affiliation: Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Ivonne
authors.initials: I
authors.lastname: Nijenhuis
authors.affiliation: Department of Chemistry, Leibniz Institute for Tropospheric Research (TROPOS), Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Herrmann
authors.affiliation: Department of Environmental Microbiology, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Lukas Y
authors.initials: LY
authors.lastname: Wick
authors.affiliation: Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany. Electronic address: hans.richnow@ufz.de.
authors.forename: Hans H
authors.initials: HH
authors.lastname: Richnow
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis; D004785:Environmental Pollutants / Q000737:chemistry*; D001556:Hexachlorocyclohexane / Q000737:chemistry*; D006868:Hydrolysis; D007501:Iron; D053758:Nanoparticles; D010084:Oxidation-Reduction; D010782:Photolysis
chemical_list: D002247:Carbon Isotopes; D004785:Environmental Pollutants; C040534:alpha-hexachlorocyclohexane; D001556:Hexachlorocyclohexane; D007501:Iron
keywords: AKIE; Alpha-hexachlorocyclohexane (α-HCH); Compound specific stable isotope analysis (CSIA); Enantiomer specific stable isotope analysis (ESIA)