Clean air, dirty water
A gasoline additive turns out to be dangerous

By Laura Tangley

It's a classic case of good intentions gone awry. When Congress amended the Clean Air Act a decade ago, the lawmakers' goal was to banish lung-destroying smog from the nation's cities. But now it turns out that the chemical known as MTBE, which was subsequently added to gasoline to make the fuel burn cleaner, has actually contaminated wells that supply drinking water to tens of millions of Americans from coast to coast.

MTBE, or methyl tertiary-butyl ether, reduces toxic auto emissions by boosting the amount of oxygen in gasoline. Now present in about a third of the nation's gas, the additive has been very effective in helping formerly smoggy cities clean up their act. But a new study, scheduled for publication next month in Environmental Science & Technology, has found that as many as 9,000 community wells in 31 states are threatened by MTBE contamination, primarily because they are located near leaking underground tanks that store gasoline. John Zogorski of the U.S. Geological Survey, one of the study's authors, calls his team's results "generally representative of the entire nation."

Long-lived problem. A handful of states, including California, Maine, and New Jersey, already have plans to stop or at least reduce the use of MTBE, which has been found to cause cancer in laboratory animals. Last week, the U.S. Environmental Protection Agency made a commitment to begin phasing out the additive nationwide. Specifically, EPA administrator Carol Browner has asked Congress to further amend the Clean Air Act to discourage the use of MTBE in gasoline. In addition, the agency will try to restrict the chemical under authority provided by the Toxic Substances Control Act. But both of these strategies could take years to make a dent in the MTBE content of gas. Meanwhile, scientists worry that the additive's most likely alternative, ethanol derived from corn, has not been adequately tested for safety.

Even if MTBE were banned tomorrow, it would very likely remain a concern for many years. Because the compound degrades slowly and moves easily over long distances, Zogorski believes that past MTBE leaks and spills will threaten water-supply wells until at least the year 2010.

Other scientists have taken the offensive. At this week's meeting of the American Chemical Society in San Francisco, dozens of researchers will present papers at a four-day symposium devoted entirely to MTBE–including novel strategies for getting the poison out of drinking water. One study suggests that simply adding oxygen to contaminated groundwater encourages native bacteria to degrade the pollutant.