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Biological and Abiotic Transformations of Ethylene Dibromide and 1,2-Dichloroethane in Ground Water at Leaded Gasoline Spill Sites
Citation:
WILSON, JOHN T. Biological and Abiotic Transformations of Ethylene Dibromide and 1,2-Dichloroethane in Ground Water at Leaded Gasoline Spill Sites. Presented at RemTec Summit, Chicago, IL, May 16 - 19, 2011.
Impact/Purpose:
Presentation for the RemTec Summit - (May 16-19, 2011, Chicago, IL)
Description:
Tetra-ethyl lead was widely used in leaded automobile gasoline from 1923 until 1987. To prevent lead deposits from fouling the engine, 1,2-dibromoethane (EDB) and 1,2-dichloroethane (1,2-DCA) were added to the gasoline to act as lead scavengers. The Maximum Contaminant Levels (MCLs) for EDB and benzene are 0.05 μg/L and 5.0 μg/L respectively. The concentrations of EDB and benzene that would be expected in ground water in contact with unweathered leaded automobile gasoline are 1.9 and 38 mg/L respectively. Benzene can occur at concentrations that are 7,400 times greater than the MCL, while EDB can occur at concentrations that are 38,000 times greater. The hazard associated with EDB in leaded gasoline is greater than the hazard associated with benzene Lead was effectively banned in gasoline in the USA before the underground storage tank program was fully implemented. As a result, only a portion of the state agencies that implement the federal UST program routinely monitor for EDB and 1,2-DCA at leaded gasoline spill sites. In response to the hazard associated with lead scavengers at legacy spills of leaded gasoline, in May 2010, the EPA Office of Underground Storage Tanks issued a recommendation that states, tribes and EPA regions monitor for lead scavengers in ground water, and remediate lead scavengers when they threaten a source of drinking water. If states act on the recommendation of the EPA Office of Underground Storage Tanks, there will be increased interest in risk management of lead scavengers, and in remediation of lead scavengers. Strains of anaerobic bacteria such as Dehalobacter and Dehalococcoides use EDB or 1,2-DCA as electron acceptors. The haloalkanes can be transformed to ethylene, to the corresponding haloalkane, or to the corresponding 2-haloethanol. Iron(II) sulfides produced by biological sulfate reduction can also transform EDB or 1,2-DCA. In addition, EDB can also react with HS- to produce a variety of sulfur containing compounds. The rates of natural biotransformation of EDB and 1,2-DCA in anaerobic aquifer sediment are roughly equivalent to the rate of transformation of benzene. The rates of abiotic transformation of EDB on FeS were roughly equivalent to rates of transformation of TCE on FeS; however, the rates of transformation of 1,2-DCA on FeS is approximately an order of magnitude slower. At sites where monitored natural attenuation of benzene is plausible, MNA of EDB and 1,2-DCA may also be a plausible risk management approach. Enhanced anaerobic biodegradation may also be effective to treat EDB and 1,2-DCA contamination in ground water. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.
