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MTBE

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What is MTBE?

MTBE (methyl-tertiary-butyl-ether) is an oxygenate that is added to gasoline throughout the United States to make it burn cleaner. It reduces carbon monoxide and ozone levels caused by auto emissions. However, MTBE can contaminate water supplies during gasoline spills. More subtly, it can escape from boat emissions and leaky underground storage tanks and gasoline transport pipes.

MTBE has been added to gasoline since the 1970s. However, the Clean Air Act of 1990 required the use of reformulated gasoline (RFG) containing oxygenates, like MTBE, in nine areas of United States with the most severe ozone pollution. Other areas voluntarily joined the RFG program, and by the late 1990s, nearly 30 percent of all gasoline sold in the United States contained MTBE, according to the U.S. Department of Energy.

MTBE was favored over other potential oxygenates because of its low cost, ease of production, and favorable blending characteristics with conventional gasoline.

MTBE in drinking water is not regulated by the U.S. Environmental Protection Agency. However, the agency has set an advisory level of 20-40 parts per billion because even at these very small concentrations, MTBE causes foul taste and odor. Furthermore, at high levels, MTBE is a suspected carcinogen.

The U.S. Geological Survey completed a study in 2002 revealing that 36 states had water supplies contaminated by MTBE. Most concentrations were below the EPA advisory level of 20-40 ppb, however researchers did find concentrations as high as 17,800 ppb. Overall, the study found MTBE in 14 percent of surface waters tested and 5.4 percent of groundwater supplies. MTBE contamination is most common in urban areas with high motor vehicle use and high population density.

Due to the threat of MTBE in water supplies, the EPA Blue Ribbon Panel on Oxygenates in Gasoline issued a recommendation that MTBE be substantially reduced, while some members even suggested it be completely removed. While no federal regulations prevent the use of MTBE, as of 2007, 25 states had issued partial or complete bans on MTBE.

MTBE dissolves easily in water, and because it is a very small molecule, it moves quickly through soil and groundwater. Unfortunately, it is also difficult to remove during water treatment.

In 1996, the City of Santa Monica, California, learned that much of its drinking water supply was contaminated with MTBE levels as high as 610 parts per billion. In response, the city shut down two of its well fields, which represented 50 percent of the city's drinking water supply, and was then forced to purchase replacement water.

To remove MTBE from contaminated water supplies, public water systems may need to use additional treatment technologies, which can make drinking water more costly. According to the EPA, there are three treatment technologies that are effective in removing MTBE:

Air stripping is a process by which air is forced through contaminated water until MTBE becomes a gas and separates from the water.

Filtration with granular activated carbon causes MTBE to stick to carbon particles, separating MTBE from the water.

Advanced oxidation causes MTBE to react with oxygen, changing it to a form that is less harmful or easier to remove.

If you are concerned about MTBE contamination, call your local utility to find out if they test for MTBE. In 2001, the EPA required that all large public water systems and a sample of medium and small utilities monitor for MTBE. If your utility does test for MTBE, find out whether it has been detected in your drinking water system and if so, at what levels.

If you own a private well or your local utility does not test for MTBE, you can have your water tested at a state certified lab. The EPA provides a list of state certification officers whom you can contact for additional information. Also, feel free to contact the EPA.

If you are concerned about MTBE in your drinking water, you may consider purchasing a home treatment device. However, in order to make a well-informed and cost-effective decision, consider:

  • Checking with your water system or consumer confidence report to learn about the amount of total MTBE in your water.
  • Identifying a device that has been independently certified to remove MTBE.
NSF International, the Water Quality Association, Underwriters Laboratories and CSA International all certify home treatment products for removal of contaminants. The relevant MTBE removal standard is NSF/ANSI Standard 53. If you choose to use a home treatment device, it is very important to follow the manufacturer's operation and maintenance instructions carefully in order to make sure the device works properly.

  • MTBE is used in gasoline to make it burn cleaner.
  • In a number of places where MTBE is used, it has also been detected in water.
  • MTBE has a turpentine-like taste and odor, so even small amounts of MTBE in water can make it unacceptable for drinking.
  • At high levels, MTBE may pose a public health threat.
  • As of 2007, 25 states had issued partial or complete bans on MTBE.