Natural Attenuation of MTBE at Laurel Bay, South Carolina
The occurrence of methyl tert-butyl
ether (MTBE) in ground water at gasoline spill sites challenges the
paradigm of natural attenuation remediation and our understanding of the
impact of gasoline spills on the environment.
- The U.S. Geological Survey (USGS) has identified two important pathways
that contribute to the natural attenuation of MTBE. The first is volatilization
of MTBE from the spill source into the unsaturated
zone, and the second is volatilization of MTBE from the water table
down gradient from the source through the unsaturated zone. In both
cases, MTBE volatilized to the unsaturated zone is subject to more efficient
aerobic (with oxygen) biodegradation than MTBE in the anaerobic (without
oxygen) saturated zone. These pathways are important, given MTBE's low
degradation rates relative to BTEX
(benzene, toluene, ethylbenzene, and zylene) compounds in the saturated
zone. The USGS has developed methods to determine the magnitude of these
natural attenuation pathways for MTBE.
- The USGS has shown that microorganisms indigenous to surface-water
sediments are capable of rapidly degrading MTBE to carbon dioxide. This
is the first significant microbial process that has been shown to degrade
MTBE in natural environments. Previous studies (including our own) had
suggested that MTBE was highly recalcitrant to biodegradation in ground-water
systems. Based on these past studies, it was thought that MTBE-contaminated
ground water might seep into surface water and accumulate, providing
a source of exposure to humans and wildlife. However, this new result
shows that MTBE is rapidly degraded in streambed sediments, and suggests
that accumulation to environmentally harmful levels is unlikely.
Landmeyer, J.E., Chapelle,
F.H., Bradley, P.M., Pankow, J.F., Church, C.D., and Tratnyek, P.G., 1998,
Fate of MTBE relative to benzene in a gasoline-contaminated aquifer (1993-98):
Ground Water Monitoring and Remediation, v. 18, no. 4, p. 93-102.
Bradley, P.M., J.E. Landmeyer,
and F.H. Chapelle, 1999, Aerobic mineralization of MTBE and tert-butyl
alcohol by stream-bed sediment microorganisms: Environmental Science and
Technology, vol. 33, p. 1877-1879.
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