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USE OF COMPOUND-SPECIFIC STABLE CARBON ISOTOPE ANALYSES TO DEMONSTRATE NATURAL BIODEGRADATION OF MTBE IN GROUND WATER AT A GASOLINE RELEASE SITE
Citation:
Kolhatkar, R., T. Kuder, P. Philp, J. Allen, AND J T. Wilson*. USE OF COMPOUND-SPECIFIC STABLE CARBON ISOTOPE ANALYSES TO DEMONSTRATE NATURAL BIODEGRADATION OF MTBE IN GROUND WATER AT A GASOLINE RELEASE SITE. ENVIRONMENTAL SCIENCE & TECHNOLOGY 36(23):5139-5146, (2002).
Description:
Methyl tertiary butyl ether (MTBE) has been used as an additive in gasoline to enhance
octane rating and to improve combustion efficiency. It is also a commonly detected contaminant in both surface water and ground water systems. This study presents concentration and stable carbon isotope ratio (13C/12C expressed as 13C) data for MTBE in ground water to demonstrate natural biodegradation of MTBE at a retail gasoline site. At this site, ground water MTBE concentrations have reduced by a factor of forty over eighteen meters of flowpath away from the presumed source. Over the same flowpath, 13C of MTBE increased by 30 0/00 (from -250/00 to+5 0/00) indicating that this was a result of natural biodegradation of MTBE.
Laboratory microcosms set up using sediments and ground water from this site have been
indicated 10- to 100-fold reductions in MTBE concentrations compared to autoclaved controls.
Analyses of 13C of MTBE in sub-samples from these microcosm demonstrate 13C enrichment
of residual MTBE in live microcosms, while no such enrichment was observed for autoclaved
controls. The isotopic enrichment factor estimated from the ground water data = -7.68 was
similar to the enrichment factor estimated from live microcosms ( = -9.16). These results
demonstrate that natural biodegradation was the dominant natural mechanism for MTBE at this
site. The data also strongly suggest that 13C of MTBE could be used as an "indicator" of
MTBE biodegradation.