Methyl Tert butyl Ether (MTBE) is a volatile organic compound that is added to gasoline to decrease carbon monoxide and ozone levels in auto emissions (1). In California, the addition of MTBE improved air quality by cutting auto emissions by 14% statewide (2). Unfortunately, MTBE is showing up in water supplies.

Originally it was thought that MTBE would only cause minor problems to water supplies via leaking underground storage tanks. However in Santa Monica, CA, this was not the case. This city had leaking tanks that were situated next to municipal wells. Resulting contamination caused closure of 3 of the 5 wells (3). Treatment or dilution of the tainted water proved too expensive, so now water has to be purchased from another water district at a substantial cost to consumers (2).

In addition, MTBE is getting into lakes and rivers from motor boats and jet skis. The amount of MTBE pollution peaks during summer months and then declines as temperatures drop. Reservoir monitoring for MTBE has been increasing, and routine monitoring will soon take effect (2).

It is not absolutely clear whether MTBE is a health hazard. Most information from MTBE comes from animal studies. However, it is known that at low concentrations, inhalation of MTBE causes nose and throat irritation. Ingestion of low amounts of MTBE has the potential to cause diarrhea and irritation to the gastrointestinal tract . More serious effects may occur at high doses, but such levels are not likely to occur in drinking water. Fortunately, the body can break down the MTBE readily, and excrete it in breath, blood, and urine. Tests to see if you have been exposed to MTBE are not yet available; symptoms are common, so it may be difficult to rule out other causes (4).

MTBE has a turpentine odor, and can be detected by smell at concentrations of 15-45 ppb. Even though there is a smell to the water, it is not necessarily harmful. The EPA has proposed a health advisory for levels not to exceed 20 - 40 ppb which should be easily detectable by smell (4). The latest EPA advisory on MTBE and drinking water can be downloaded at

While MTBE may be present in water due to leaking wells or boats, it most likely will not cause harmful effects, unless it is in high concentrations. However, if you notice a turpentine taste in the water, or if you are concerned about the quality of your water, contact your water department, or have your well checked for MTBE.

If you want more information about MTBE, and how it enters the environment, as well as some case studies, look at the U.S. Geological Survey's website for their analysis of MTBE.

If you are interested in a general overview of MTBE and how it is regulated, the EPA has a fact sheet that may help you out. If you would like in depth information about MTBE, the EPA also provides a chemical summary that is quite useful. If you are having difficulty linking to either of these sites, you can also go to the EPA chemical fact site, and scroll down to MTBE.

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  1. U.S. Geological Survey. Occurrence of the Gasoline Additive MTBE in the Shallow Ground Water in Urban and Agricultural Areas. October 1996. Fact Sheet #: FS-114-95.URL:
  2. The Sacramento Bee. Chris Bowman. Ugly byproduct of smog-busting gas: Lake pollution. January 14, 1997.
  3. U.S. Water News Online. Santa Monica water supply threatened by MTBE. July, 1996.
  4. Toxicological Profile for Methyl Tert Butyl Ether. U.S. Agency for Toxic Substances and Disease Registry. Atlanta, GA: 1996.

URL Reference Sites

  1. U.S. EPA General Chemical Fact Sheet. Chemicals in the Environment: OPPT Chemical Fact Sheet. URL:,,

This page was prepared by S.L. Keyser, June 1997, UCD EXTOXNET FAQ Team.
Revised by B.T. Johnson, October 1997