MTBE and the Potential Production of TBA

Methyl tertiary-butyl ether (MTBE) is not the only highly soluble, potentially toxic fuel oxygenate found at gasoline release sites. Tertiary butyl alcohol (TBA) can also be found at many sites around the country. Although often used itself as an octane enhancer an may be a co-contaminant with MTBE, there is some evidence from laboratory studies in the literature that it can be produced from the biological de-methylation of MTBE under aerobic conditions. We examined these potential sources of TBA to ground-water systems using two approaches.

At the Laurel Bay research site, TBA was detected in ground-water monitoring wells that contained MTBE, but TBA was also measured in the unsaturated zone in the source area. This suggests that TBA may have been present in the original fuel spilled and not necessarily reflect biodegradation of MTBE. This lack of TBA production was confirmed by laboratory column studies using aquifer sediments from the site performed at the Oregon Graduate Institute. James Pankow and Paul Tratnyek are researchers at Oregon Graduate Institute. However, other aquifer sediments analyzed by their lab did indicate some TBA production and simultaneous MTBE disappearance.

TBA was found to degrade to CO₂, in addition to MTBE, under oxic conditions in sediments collected from the bottom of a stream that received MTBE-contaminated ground-water discharge. (link to 1.1Mb pdf file) These observations provide evidence that natural sinks for MTBE (and TBA) exist, and suggests that MTBE and TBA may not accumulate in the hydrosphere even after its use is lowered.

Related Headlines

• Challenging a Paradigm: MTBE Shown to Degrade to TBA Without Microorganisms

Publications

• Bradley, P.M., Chapelle, F.H., and Landmeyer, J.E., 2006 (in press), Effect of H2 and redox condition on biotic and abiotic MTBE transformation: Ground Water Monitoring and Remediation, v. 26, no. 4
• Bradley, P.M., Landmeyer, J.E., and Chapelle, F.H., 2002, TBA biodegradation in surface-water sediments under aerobic and anaerobic conditions: Environmental Science and Technology, v. 36, no. 19, p. 4087-4090.
• Bradley, P.M., Landmeyer, J.E., and Chapelle, F.H., 1999, Aerobic mineralization of MTBE and tert-butyl alcohol by stream-bed sediment microorganisms: Environmental Science and Technology, v. 33, no. 11, p. 1877-1879.
• Church, C.D., Isabelle, L.M., Pankow, J.F., Tratnyek, P.G., and Rose, D.L., 1997, Assessing the in situ degradation of methyl tert-butyl ether (MTBE) byproduct identification at the sub-ppb level using direct aqueous injection GC/MS, in 213th American Chemical Society National Meeting, Proceedings, San Francisco, Calif., April 13-17, 1997: American Chemical Society, p. 411-413.
• Church, C.D., Tratnyek, P.G., Pankow, J.F., Landmeyer, J.E., Baehr, A.L., Thomas, M.A., and Schirmer, M., 1999, Effects of environmental conditions on MTBE degradation in model column aquifers, in Morganwalp, D.W., and Buxton, H.T., eds., U.S. Geological Survey Toxic Substances Hydrology Program—Proceedings of the Technical Meeting, Charleston, South Carolina, March 8-12, 1999—Volume 3 of 3—Subsurface Contamination from Point Sources: U.S. Geological Survey Water-Resources Investigations Report 99-4018C, p. 93-101.

Back to Laurel Bay Page