Some Questions and Answers Regarding MTBE

Q. What is MTBE and why is it in gasoline?

A. MTBE (methyl tertiary-butyl ether) is a volatile organic compound. MTBE has been added to gasoline as an octane booster since the phase out of lead in the late 1970s. Conventional gas has MTBE in amounts of usually less than 3% by volume, though some premium blends can have MTBE in amounts up to 9%. Reformulated gasoline (RFG), which was developed for use in localities which do not meet National air quality standards, contains 11% MTBE.

RFG is the cornerstone of Maine’s Clean Air Plan. Its use accounts for 40% of emissions reductions required for compliance with the federal Clean Air Act. These federal requirements are in place to protect public health and the environment from the harmful effects of exposure to elevated concentrations of ground-level ozone.

RFG contains less of the ingredients that contribute to harmful air pollution (air toxics as well as ozone), and Maine has monitored clean air benefits since its introduction. 1995 data shows that, during the first year of RFG use, benzene levels in Maine air dropped 22.5%: other gasoline constituents (toluene, ethylbenzene, xylene) also significantly decreased.

Q. How does MTBE get into drinking water?

A. Contamination of drinking water with MTBE is most likely to be the result of a gasoline spill. Spills may be large, such as a leaking underground or above ground gasoline storage tank. Spills may be small, such as those that can occur while refueling, discarding old gasoline improperly, or leaking from vehicles. The larger the spill the greater the potential for widespread contamination of ground water, though small spills can sometimes have significant localized impacts depending on the vulnerability of nearby wells. Because of its solubility in water and resistance to decomposition, MTBE moves rapidly in groundwater, indeed faster than do other gasoline components such as the chemicals benzene, ethylbenzene, toluene and xylene. MTBE is also more difficult to remove from water than other gasoline components.

Q. Is MTBE showing up in drinking water a new problem?

A. No. Maine, one of the first states to document groundwater contamination with MTBE as a consequence of leaking underground fuel tanks, has been finding MTBE in drinking water since 1984. Between 1992 and 1996, Maine Department of Environmental Protection staff documented more than 200 private wells contaminated with gasoline, mostly due to leaks or spills from underground or above ground storage tanks. About half the time only MTBE was found present, and for the rest, other toxic components of gasoline such as benzene and ethylbenzene were also present.

Q. Is MTBE in drinking water harmful?

A.The potential for effects of MTBE on human health depend on how much MTBE is present in water and the length and frequency of exposure. Exposure can occur from direct consumption of water as well as by inhaling MTBE vapors released from water while bathing or cooking. However, it is unlikely that adverse health effects would occur from exposure to water containing MTBE. At water levels that would make it likely for adverse health effects to occur, people would generally find the water undesirable to drink. MTBE has an unpleasant odor and taste, and indeed some individuals can detect the presence of MTBE in water (and air) at very low levels.

MTBE has been shown capable of causing cancer, kidney, reproductive, developmental, and nervous system toxicity in laboratory animals exposed to large amounts. Maine's current drinking water standard for MTBE of 35 parts per billion (ppb) has been set to provide large margins of safety from these toxic effects. For example, daily consumption of 2-liters of water containing 35 ppb of MTBE over a lifetime is estimated to increase a person’s chance of getting cancer by no more than 3-in-a-million. This same level of intake is also about 100,000 times smaller than intake levels found to cause noncancer effects in animal studies.

Q. What do we know about how much contamination has already occured?

A.The Maine Bureau of Health has been monitoring MTBE in public drinking water supplies - which includes community systems, schools, nursing homes, and larger businesses - for more than a year. MTBE has been detected in 7 % of the more than 600 drinking water systems tested thus far, and a number of systems initially testing positive have subsequently been found to have levels below detection in follow-up testing. Two systems were found to have levels exceeding the state drinking water standard, and both were associated with gasoline spills. As most public systems obtain their drinking water from groundwater, these test results also have some relevance to private residential wells.

Q. Can I test for MTBE in my drinking water and should I?

Levels of MTBE in water can be determined by a test that costs from $80 to $100. Test kits can be obtained from the Maine State Health and Environmental Testing Laboratory (287-2727), and may also be available from private laboratories found in the yellow pages of your phone directory. If your water comes from a public water supply, you do not need to test. Public water systems are required to routinely test for MTBE. If you have a private well, you may want to consider testing your well if you have experienced a change in taste or odor or if you suspect a gasoline spill in close proximity to your well.

Prepared by Bureau of Health, Department of Human Services
And
Department of Environmental Protection,

5/21/98