Toxin: Methyl Tertiary Butyl Ether

TOXIN: Methyl Tertiary Butyl Ether (MTBE)

- What is MTBE?
- Why is it used?
- What are the oxygenate requirements of the Clean Air Act?
- With these air quality benefits, why is there concern with the use of MTBE?
- Is MTBE harmful to humans?
- Has EPA set a drinking water health standard for MTBE?
- How do I know if I have MTBE in my water?
- How does MTBE get in drinking water sources?
- How widespread and at what levels is MTBE contamination in water supplies?
- What happens when MTBE gets into the environment?

What is MTBE?
MTBE (Methyl Tertiary Butyl Ether) is a chemical compound that is manufacutred by the chemical reaction of methanol and isobutylene. MTBE is produced in very large quantities (over 200,000 barrels per day in the U.S. in 1999) and is almost eculsively used as a fuel additive in motor gasoline. MTBE is a volatile, flammable and colorless liquid that dissolves rather easily in water.

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Why is it used?
MTBE has been used in U.S. gasoline at low levels since 1979 to replace lead as an octane enhancer (helps prevent the engine from "knocking"). Most refiners have chosen to use MTBE over other oxygenates primarily for its blending characteristics and for economic reasons.

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What are the oxygenate requirements of the Clean Air Act?
The Clean Air Act Amendments of 1990 (CAA) require the use of oxygenated gasoline in areas with unhealthy levels of air pollution. The CAA does not specifically require MTBE. Refiners may choose to use other oxygenates, such as ethanol.

Refiners have chosen MTBE as the main oxygenate in RFG in cities outside of the Midwest primarily for economic reasons and its blending characteristics. Unlike ethanol, MTBE can be shipped through existing pipelines, and its volatility is lower, making it easier to meet the emission standards.

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With these air quality benefits, why is there concern with the use of MTBE?
A growing number of studies have detected MTBE in ground water throughout the country; in some instances these contaminated waters are sources of drinking water. Low levels of MTBE can make drinking water supplies undrinkable due to its offensive taste and odor.

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Is MTBE harmful to humans?
The majority of the human health-related research conducted to date on MTBE has focused on effects associated with the inhalation of the chemical. When research animals inhaled high concentrations of MTBE, some developed cancers or experienced other non-cancerous health effects. Recent work by EPA and other researchers is expected to help determine more precisely the potential for health effects from MTBE in drinking water.

EPA reviewed available health effects information on MTBE in its 1997 Drinking Water Advisory guidance and decided that there was insufficient information available to allow EPA to establish quantitative estimates for health risks and as such would not set health advisory limits. The drinking water advisory document indicates that there is little likelihood that MTBE in drinking water will cause adverse health effects at concentrations between 20 and 40 ppb or below.

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Has EPA set a drinking water health standard for MTBE?
EPA has not set a national standard for MTBE, although some states have set their own limits. EPA also reviewed the available information on health effects in the 1997 advisory and stated that there is little likelihood that MTBE concentrations between 20 and 40 ppb in drinking water would cause negative health effects.

EPA is continuing to study both the potential health effects and the occurrence of MTBE, and it is on a list of contaminants (Contaminant Candidate List) for which EPA is considering setting health standards. As a means of gathering occurrence information, beginning in 2001, EPA will require all large drinking water systems and a representative sample of small systems to monitor and report the presence of MTBE (Unregulated Contaminant Monitoring Regulation).

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How do I know if I have MTBE in my water?
It is possible your water would taste and/or smell like turpentine if MTBE is present at levels around or above 20-40 ppb (some people may detect it at even lower levels). Though you cannot currently purchase a home testing kit, you can determine if your water contains MTBE the following ways. If your drinking water is supplied by a public water system, you can contact the system directly and ask whether they monitor for MTBE and what levels, if any, have been detected. In 2001, most public water systems will be required to monitor for MTBE. If you have a private well, you may want to have your well water tested. Your local health department may be able to tell you if MTBE has been found in water in your area. If you want to get your water tested, call the Safe Drinking Water Hotline (800-426-4791) or go to http://www.epa.gov/safewater/faq/sco.html to get the phone number for the office in your state that certifies drinking water laboratories.

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How does MTBE get in drinking water sources?
There are opportunities for MTBE to leak into the environment (and potentially get in drinking water sources) wherever gasoline is stored, and there are opportunities for it to be spilled whenever fuel is transported or transferred. While federal and state programs minimize the potential for leaks and spills, no system is foolproof.

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How widespread and at what levels is MTBE contamination in water supplies?
Although there are no nation-wide data sets from which to fully characterize MTBE contamination of water, a growing number of studies to-date have detected MTBE in drinking water supplies throughout the country. Current data on MTBE levels in ground and surface waters indicate widespread and numerous detections at low levels of MTBE.

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What happens when MTBE gets into the environment?
Because MTBE dissolves easily in water and does not "cling" to soil very well, it migrates faster and farther in the ground than other gasoline components, thus making it more likely to contaminate public water systems and private drinking water wells. MTBE does not degrade (breakdown) easily and is difficult and costly to remove from ground water.

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