Editorial:MTBE in Maryland

Dec. 6, 2004
Fear has a way of brushing aside potentially comforting facts. Fear over methyl tertiary butyl ether has gripped Maryland. The gasoline oxygenate has shown up in the state's water supplies, as it has elsewhere in the US. The phenomenon became a major news event in June with reports of well contamination around the small towns of Upper Crossroads and Fallston, in Harford County northeast of Baltimore.

Fear has a way of brushing aside potentially comforting facts. Fear over methyl tertiary butyl ether has gripped Maryland. The gasoline oxygenate has shown up in the state's water supplies, as it has elsewhere in the US. The phenomenon became a major news event in June with reports of well contamination around the small towns of Upper Crossroads and Fallston, in Harford County northeast of Baltimore.

In most of the wells, MTBE concentrations fell below the state's health-response threshold of 20 ppb. At one home close to a service station, however, the concentration was 300 ppb—a finding that made state officials intensify testing, which led to detection of MTBE in more wells. A woman whose water tested 36.3 ppb MTBE was quoted in the Baltimore Sun as declaring, "It's pretty scary."

Service station

Suspicion initially focused on a service station owned by ExxonMobil Corp. According to a state investigator, a groundwater sample taken beneath the station's fuel tanks registered MTBE at 26,000 ppb.

The station has experienced no spills or leaks from its tanks. One theory is that MTBE vaporized in the tanks, escaped from valves and fittings, and condensed and migrated in the subsurface. Without acknowledging liability, ExxonMobil has bought bottled water and filtration systems for affected households and conducted extensive tests of area water supplies. It also installed a treatment system at the service station. Tests of water below the tanks recently measured MTBE at 1.2 ppb.

Lawsuits began within a month of the first news reports about presence of a suspected carcinogen in drinking water. Lawyers, some of whom have conducted MTBE litigation in other states, bought newspaper advertisements to recruit plaintiffs for class-action filings.

As testing spread, so did the apparent contamination. When the number of Fallston-area properties with wells tainted by MTBE reached 84 and a trace of the substance turned up in a sample from the Harford County public water system, the county government began to consider a moratorium on service-station construction and eventually passed one effective for 6 months.

State legislators demanded more and more tests and proposed an MTBE ban. Regulators proposed replacement of underground pipes at service stations. Other service stations came to be considered possible MTBE sources.

By last month, according to presentations to state lawmakers, MTBE had been detected in 600 wells in Maryland, in almost all cases at concentrations below the state threshold. Calls persist for an MTBE ban, which would require that fuel sold in Maryland contain ethanol if the oxygenate mandate remains in place for reformulated gasoline.

The furor is understandable. People have learned that the water they drink contains a substance that in large doses correlates with the occurrence of tumors in laboratory animals. They have learned that no one knows the effects on humans of low-dose exposure. The uncertainty raises fear, and the fearful have good reason to want to err on the side of caution.

The missing information in all this concerns the caution already built into MTBE guidance. In 1997, the US Environmental Protection Agency studied MTBE and concluded that it couldn't, based on available data, specify health limits for the substance. Instead, it issued an advisory stating that the likelihood was small that MTBE in drinking water would cause health effects at concentrations of 20-40 ppb or below, the range within which taste and odor can become troublesome. Maryland cautiously picked the bottom of this range as its trigger for remedial action.

Safety margin

EPA's 1997 advisory went on to point out that MTBE concentrations of 20-40 ppb are "20,000 to 100,000 (or more) times lower than the range of exposure levels in which cancer or noncancer effects were observed in rodent tests." The large safety margin made EPA confident enough to assert that "protection of the water source from unpleasant taste and odor as recommended will also protect consumers from potential health effects." The agency nevertheless began to phase out MTBE in 2000, citing the spreading occurrence of the substance in water supplies.

EPA did not rescind the essential message of its 1997 advisory, which is that drinkable water is very unlikely to pose a health threat from whatever MTBE it may contain. Has anyone asked Marylanders if their water tastes or smells bad?