MTBE Pollution Widespread

by Mark Sampson

The researchers analyzed regular unleaded gasoline samples from more than 200 sites in Indiana, Illinois and Michigan. They found MTBE (methyl tertiary butyl ether) in more than 70 percent of the gasoline samples, even though the additive has seen limited use because ethanol is the main oxygenate for reducing air pollution in these states, says Purdue University's Reynaldo D. Barreto, the studyÕs lead investigator.

"MTBE is not supposed to be there," he says. The unexpectedly widespread presence of the chemical in gasoline samples suggests there is a "ticking time bomb" that could adversely affect drinking water, Barreto cautions.

MTBE has been used in increasing amounts since 1995, when amendments to the Clean Air Act mandated the use of reformulated gasoline in heavily polluted areas. By law, reformulated gasoline must contain oxygenates designed to reduce smog-causing emissions. The two most widely used oxygenates are MTBE, which is derived from natural gas, and ethanol, which is generally made from corn.

In Indiana, for which the most complete data are available, MTBE-contaminated gas samples were found in the northwestern part of the state where ethanol is used as the main oxygenate. Contaminated samples were also found in the central and eastern part of the state where reformulated gasoline is not used, according to the researcher.

Although data from Illinois and Michigan are not yet complete, gasoline samples surveyed in these areas so far indicate widespread MTBE contamination, according to Barreto. This was unexpected, given that ethanol is the predominant reformulating agent in Illinois and that reformulated gasoline is not used in Michigan, the researcher says.

The most likely source of the MTBE is tankers, storage tanks and pipelines that once carried reformulated gasoline and subsequently carried nonreformulated gasoline, says Barreto. He believes that a complete ban on the controversial additive is needed to prevent its spread.

MTBE came under intense scrutiny after numerous studies showed it can leak from underground storage tanks and other sources to contaminate the drinking water supply. Although its toxicity to humans is unclear, MTBE can make water undrinkable due to its foul smell and bad taste.

No one knows the exact extent of the contamination, but a growing number of studies have detected the chemical in drinking water samples throughout the country. The U.S. Environmental Protection Agency recently announced plans to reduce or eliminate use of MTBE. It could be replaced with ethanol, another oxygenate, or specially formulated gasoline with fewer smog-causing emissions.