MTBE Contamination: A Microbial Approach for Ground Water
Max Häggblom's Rutgers laboratory has taken an important step on the path to using microbes to rid the environment of methyl tertiary-butyl ether (MTBE), a toxic gasoline additive now classified as a potential human carcinogen.
In a recent paper in Applied and Environmental Microbiology, the researchers bring to light a tool that will help them find the key bacteria capable of breaking down MTBE. The additive has contaminated a great deal of ground water in the United States through fuel spills and leaking underground gasoline storage tanks.
“While gasoline hydrocarbons are much more toxic than MTBE, they are just candy to microbes and don't become as persistent a problem,” says Häggblom, a professor in the department of biochemistry and microbiology at Rutgers, The State University of New Jersey, and the Biotechnology Center for Agriculture and the Environment on Rutgers' Cook College campus.
Since MTBE contamination is underground, anaerobic bacteria - those that operate in the absence of oxygen - are the most likely candidates for the cleanup job. The recent journal article establishes a way to facilitate their use by employing carbon isotope fractionation: the changes in the isotopic ratios of carbon (its different molecular versions, carbon-12 and carbon-13) brought about from the selective degradation of the carbon-12 form in the case of MTBE. “So when the ratio of carbon-12 to carbon-13 decreases, it indicates the presence of the kind of bacteria we are looking for,” Häggblom explains. “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.”
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 still is 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 ground water.
Producers have been to adding MTBE to gasoline since 1979 as an octane-boosting replacement for tetraethyl lead, a major contributor to toxic levels of lead in the environment. MTBE also is blended into winter fuel formulations for colder regions to make the fuel burn more cleanly. Twenty-five states have passed legislation to ban its future use, with seven more considering its prohibition.
“MTBE is slowly being banned, but it's going to stay in our ground water for centuries,” says Häggblom, also known for his work in biodegradation and bioremediation of other environmental pollutants, such as PCBs and dioxins.
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. This snail-like pace is a serious obstacle, but once again, Häggblom and company may have a solution.
“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,” Hägglom says. The researchers are in the midst of applying for a patent on the technique.