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Assisting Microbial Clean-up of MTBE Contamination

A team of researchers has developed a tool to help identify bacteria capable of breaking down methyl tertiary-butyl ether (MTBE), a toxic gasoline additive that is now classified as a potential human carcinogen.

MTBE, which is used as an oxygenate in gasoline, is now prohibited in 25 states (with seven more considering the same action) due to concerns over the contamination of groundwater caused by fuel spills and leaking from underground storage tanks. MTBE use began in 1979 as an octane-boosting replacement for tetraethyl lead, a major contributor to toxic levels of lead in the environment.

Since MTBE contamination is underground, anaerobic bacteria are the most likely candidates for the cleanup job. The researchers employ carbon isotope fractionation—the changes in the isotopic rations of carbon brought about from the selective degradation of carbon-12 in MTBE—to identify the best candidates for the cleanup process. The results appear in a February 2006 paper in Applied and Environmental Microbiology.

When the ratio of carbon-12 to carbon-13 decreases, it indicates the presence of the kind of bacteria we are looking for. This approach also will help us eventually home in on precisely which bacterium is doing the eating—possibly the best choice for large-scale underground applications.

—Max Häggblom, Rutgers professor of biochemistry and microbiology and lead researcher

Häggblom and his coworkers are characterizing the community of bacteria feeding on MTBE in their cultures and, based on initial analyses, there appears to be a dozen or so players. It is still unclear if just one bacterium or several are doing the job; perhaps one or more of them may just be feeding on the waste products of the main degrader or degraders. But Rutgers researchers are getting closer to answering these questions, and thereby making the anaerobes a practical solution to remediation of MTBE contaminated groundwater.

While the methodology is a step in the right direction, Häggblom remains concerned about the slow pace at which the anaerobes seem to operate as they break down MTBE, a feature of the microbes he observed in his laboratory. Only after the first three years of their 10-year study could Häggblom and his group discern that a microbe was feeding on the MTBE in his cultures.

We are trying some tricks to actually speed it up, one of which is adding a relatively innocuous natural substance that appears to stimulate the process.

—Max Häggblom



Rafael Seidl

It's amazing that bioremediation works at all, but clearly it's a slow process. Perhaps one day refinery sites will follow where individual filling stations are leading today. Concern about soil pollution is the primary reason why no new refineries have been built in the US for 30 years.

Btw, fuel leaks are avoidable with double-hulled storage tanks at filling stations and regular inspections (cp. double-hulled oil tankers). This was mandated in Europe several decades ago and, MTBE remains a legal octane improver here. As for the carcinogenic risk, none of the stuff in gasoline is exactly healthful.

In those US states (especially, California) that prohibit the use of MTBE, refineries are adding ethanol instead. Currently, the only available supply is the expensive corn-based variety. This is driving up prices at the pump. On the other hand, it is generating the market pull required for innovations such as cellulose ethanol to reach industrial scale.

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