Carbon isotope fractionation in reactions of 1,2-dibromoethane with FeS and hydrogen sulfide.
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 Na(2)S (<0.7 mM) and mackinawite (FeS) (180 mM). Degradation rates in vials containing FeS exceeded those in Na(2)S-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 S(N)2 substitution with S(II) nucleophiles were detected (1,2-dithioethane, DTA). Relatively high yields of DTA suggested that the S(N)2 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 S(N)2 substitution by nucleophiles combined with two-electron transfer reductive debromination.
School of Geology and Geophysics, University of Oklahoma, 100 E. Boyd Street, SEC 710, Norman, Oklahoma 73019, United States. tkuder@ou.edu
Tomasz
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Kuder
John T
JT
Wilson
Paul
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Philp
Y Thomas
YT
He
D002247:Carbon Isotopes; D005591:Chemical Fractionation; D052918:Environmental Restoration and Remediation; D015946:Ethylene Dibromide / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D006862:Hydrogen Sulfide / Q000737:chemistry*; D007700:Kinetics; D012995:Solubility
D002247:Carbon Isotopes; D005296:Ferrous Compounds; D015946:Ethylene Dibromide; C022597:ferrous sulfide; D006862:Hydrogen Sulfide