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Removal of EDB and 1,2-DCA by Abiotic Reaction with Iron(II) Sulfide
Citation:
WILSON, J. T., Y. He, AND T. Kuder. Removal of EDB and 1,2-DCA by Abiotic Reaction with Iron(II) Sulfide. Presented at The 10th International In-Situ and On-site Bioremediation Symposium, Baltimore, MD, May 05 - 08, 2009.
Impact/Purpose:
To evaluate the risk associated with exposure to EDB and 1,2-DCA in ground water from old spills of leaded gasoline.
Description:
Ethylene Dibromide (EDB) and 1,2-Dichloroethane (1,2-DCA) were used as lead scavengers in leaded motor gasoline in the USA until the late 1980s. Leaded gasoline in contact with ground water should produce concentrations of EDB near 1900 µg/L, and concentrations of 1,2-DCA near 3700 µg/L. The maximum contaminant level (MCL) for EDB and 1,2-DCA are 0.05 µg/L and 5 µg/L respectively. Old spills of leaded gasoline still have a significant capacity to contaminate ground water used as a drinking water supply. To properly evaluate the risk associated with exposure to EDB and 1,2-DCA in ground water from old spills of leaded gasoline, it is necessary to understand the mechanisms that may attenuate concentrations of these compounds in ground water. TCE reacts rapidly with iron (II) sulfide in subsurface material. Based on their chemical similarity to TCE, it is possible that EDB and 1,2-DCA will also react with iron(II) sulfide. Iron-reducing and sulfate-reducing conditions pertain at most old gasoline spill sites; as a result, iron(II) sulfide can be expected to accumulate. This study evaluates the rate of abiotic degradation of EDB and 1,2-DCA during reaction with biogenic iron(II) sulfide. In earlier work, a laboratory column study was conducted to model a mulch-based passive reactive barrier to treat TCE in ground water. Biological sulfate reduction supported by the plant mulch caused accumulations of iron(II) sulfide in the columns. The first order rate constant for reaction of TCE with the iron(II) sulfide in the column varied from 0.19 to 0.84 per year per millimole of iron(II) sulfide in contact with each liter of pore water (yr-1mM-1). The contents of the column were frozen solid, the glass cylinder that contained the column was discarded, and the contents of the column were sectioned while still frozen with a hand saw. One section was allowed to thaw in an anaerobic glove bag. The plant mulch was separated from the sand and iron(II) sulfide with a sieve, and the sediment was used to construct batch microcosms. The content of iron(II) sulfide in the sediment was estimated as acid volatile sulfide. The rate of removal of EDB in the microcosms varied from 0.16 to 0.40 yr-1mM-1, a rate that is equivalent to the rate of removal of TCE by iron(II) sulfide. The rate of removal of 1,2-DCA was slower, 0.035 and 0.048 yr-1mM-1. EDB was strongly fractionated during degradation by iron(II) sulfide. The isotopic enrichment factor (ε) reported for anaerobic biodegradation of EDB is -5.7 ± 1‰. The isotopic enrichment factor for abiotic reaction with iron(II) sulfide is was -20.2 ± 2.23‰ at 95% confidence. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.
