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Carbon Isotope Fractionation in Reactions of 1,2-Dibromoethane with FeS and Hydrogen Sulfide
Citation:
Kuder, T., J. Wilson, P. Philip, AND Y. He. Carbon Isotope Fractionation in Reactions of 1,2-Dibromoethane with FeS and Hydrogen Sulfide. ENVIRONMENTAL SCIENCE AND TECHNOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 46(14):7495-7502, (2012).
Impact/Purpose:
Article for the peer reviewed journal Environmental Science and Technology
Description:
EDB (1,2-dibromoethane) is frequently detected at sites impacted by leaded gasoline. In reducing environments, EDB is highly susceptible to abiotic degradation. A study was conducted to evaluate the potential of compound-specific isotope analysis (CSIA) in assessing abiotic degradation of EDB in sulfate-reducing environments. Water containing EDB was incubated in sealed vials with various combinations of Na2S (<0.7 mM) and mackinawite (FeS) (180 mM). Degradation rates in vials containing FeS exceeded those in Na2S-only controls. In the presence of FeS, first-order constants ranged from 0.034 ± 0.002 d−1 at pH 6 to 0.081 ± 0.005 d−1 at pH 8.5. In the presence of FeS, products from reductive debromination (ethylene) and from SN2 substitution with S(II) nucleophiles were detected (1,2-dithioethane, DTA). Relatively high yields of DTA suggested that the SN2 reactions were not mediated by HS− only but likely also included reactions mediated by FeS surface. Significant carbon isotope effects were observed for nucleophilic substitution by HS− (ε = −31.6 ± 3.7‰) and for a combination of reductive and substitution pathways in the presence of FeS (−30.9 ± 0.7‰), indicating good site assessment potential of CSIA. The isotope effects (KIEs) observed in the presence of FeS corroborated the predominance of SN2 substitution by nucleophiles combined with two-electron transfer reductive debromination.
