Toxic Substances Hydrology Program
Challenging a Paradigm: MTBE Shown to Degrade to TBA Without Microorganisms
The remediation and degradation of contaminants in recent years has focused on biological processes, and rightly so because many contaminants either do not degrade at all or degrade extremely slowly without microorganisms aiding the process. With this focus on microbiology at contaminated sites, it's easy to discount or forget the important role abiotic (without biology) processes can have in the degradation of contaminants. For example, the degradation of the fuel oxygenate methyl tertiary-butyl ether (MTBE) to tertiary butyl alcohol (TBA) previously was considered to be solely a biological process. However, U.S. Geological Survey (USGS) scientists have shown that the degradation of MTBE to TBA can occur at contamination sites without the help of microorganisms, given the right conditions. Their laboratory studies of MTBE-contaminated aquifer sediments from the Laurel Bay, South Carolina, Site showed that large concentrations of dissolved hydrogen in ground water promoted the degradation of MTBE to TBA without biological activity. Scientists have used the concentration of dissolved hydrogen in ground water to indicate the type of biodegradation reactions taking place in the subsurface at sites contaminated with chlorinated solvents. The results of this study indicate that measurements of dissolved hydrogen concentrations are useful for identifying the type of reactions occurring in the subsurface at fuel-oxygenate sites. Previous studies have shown that combining hydrological, chemical, and microbiological field methods are needed to accurately assess the processes responsible for the natural attenuation of contaminants. In addition to a greater understanding of the range of degradation pathways for MTBE, the results of this study add an addition field method, the determination of hydrogen concentration, that can be combined with others to assess the natural attenuation of fuel oxygenates.
Bradley, P.M., Chapelle, F.H., and Landmeyer, J.E., 2006, Effect of H2 and redox condition on biotic and abiotic MTBE transformation: Ground Water Monitoring and Remediation, v. 26, no. 4, 74-81. doi: 10.1111/j.1745-6592.2006.00119.x
Methods and Approaches for Assessing Natural Attenuation