SAN FRANCISCO--The gasoline additive MTBE, intended to cleanse vehicle emissions of smog-producing crud, is fouling U.S. drinking water more seriously than researchers expected. New studies show that MTBE taints more than one of every eight water wells in urban areas. Further, the chemical persists underground, forming long-lasting plumes that may harm wells long after states enforce plans to stop blending MTBE into their gas.
MTBE (methyl tertiary-butyl ether) increases the oxygen content of gasoline. It makes a car's engine burn gas more completely, so that fewer byproducts of combustion--such as ozone and carbon monoxide--escape through the tailpipe into the air. Gas in many metropolitan areas--and in all of California--has contained MTBE since the mid-1990s to help reduce air pollution. Although the strategy has worked, MTBE has invaded groundwater via leaking underground storage tanks, as well as reservoirs when boaters and jet skiers spill gas into the water. MTBE causes cancer in rats, but the U.S. Environmental Protection Agency (EPA) doesn't yet regulate the additive because its effects on human health are poorly known. Even at low levels, however, it renders water undrinkable because of its unpleasant taste and smell.
Alaska and Maine have already banned MTBE, and California will phase it out within 3 years. Several studies presented here today at a meeting of the American Geophysical Union may hasten the pace at which other states take action. A team of water quality scientists led by Paul Squillace of the U.S. Geological Survey (USGS) in Rapid City, South Dakota, measured detectable levels of MTBE in 13% of 482 water wells in and near cities throughout the country. Similarly, Stephen Grady of the USGS in East Hartford, Connecticut, reviewed records of 16,717 water samples from community water districts in 10 northeastern and mid-Atlantic states, finding MTBE in 9% of them. In both studies, 2% of the MTBE levels exceeded the EPA's advisory guideline of 20 parts per billion. Well below that level, says Grady, "people are adamant about getting MTBE out of their water" because of the foul taste.
More troubling, two groups of California researchers have found that natural processes in the soil and in aquifers barely seem to degrade MTBE. Teams led by environmental scientist Anne Happel of Lawrence Livermore National Laboratory in California and hydrologist Graham Fogg of the University of California, Davis, showed that MTBE-contaminated plumes of underground water can wander hundreds of meters for a decade without significantly breaking down--much longer than hazardous hydrocarbons such as benzene, Fogg says: "The longer this water migrates and spreads out, the more it can move into deep regions that we can't access easily with remediation techniques."