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Methyl Tert-Butyl Ether (MTBE)

Also known as: Methyl t-butyl ether, MTBE, Tert-butyl methyl ether, 2-methoxy-2-methylpropane
Chemical reference number (CAS): 1634-04-4

MTBE is a gasoline additive with a very strong odor. When chemicals like MTBE are added to gasoline, engines produce less carbon monoxide and other carbon-containing air pollutants by burning this "reformulated" gasoline. In cities where air quality is a problem, reformulated gasoline may contain up to 15% MTBE.

MTBE dissolves easily in water and also evaporates quickly. If it's spilled, MTBE will evaporate quickly. However, if MTBE is spilled on soil, some of it can seep into groundwater where it can remain unchanged for many years.

When underground storage tanks leak, MTBE may be one of the first chemicals to show up in area drinking water wells. Most people can smell MTBE in contaminated water at levels as low as 100 parts per billion (ppb).

You should avoid breathing gasoline vapors while refueling as you can be exposed to MTBE when filling gas cans or automobiles with gasoline. We suggest you store gasoline in a tightly sealed container, and place the container away from your home in a locked storage shed so vapors cannot enter your home. People can also be exposed to MTBE when they breathe engine exhaust.

When drinking water is contaminated, people can inhale MTBE as they bathe or do laundry. Low-level exposure can happen when contaminated water is used for drinking and food preparation. MTBE can be absorbed through skin when people handle gasoline, contaminated soil, or contaminated water. Skin contact is most likely to happen as people fill their tanks with gasoline.

No standards exist for regulating the amount of MTBE allowed in the air of homes. However, the Wisconsin Department of Natural Resources (DNR) has set a residential indoor air action level for MTBE at 26 parts per billion by volume (ppbv). The action level is considered to be protective of public health. Breathing MTBE for a lifetime at 26 ppbv is very unlikely to be harmful to people. If MTBE concentrations in air are above the action level, we recommend taking action to halt exposure.

The Wisconsin Department of Natural Resources regulates the amount of MTBE that can be released into outdoor ambient air by industries.

The Wisconsin groundwater standard for MTBE is 60 parts per billion (ppb). We suggest you stop drinking water containing more than 60 ppb of MTBE. If levels of MTBE are very high in your water, you may need to avoid washing, bathing or using the water for other purposes as well.

Everyone's Reaction is Different

A person's reaction to chemicals depends on several things, including individual health, heredity, previous exposure to chemicals including medicines, and personal habits such as smoking or drinking. It’s also important to consider the length of exposure to the chemical, the amount of chemical exposure, and whether the chemical was inhaled, touched, or eaten.

Although the following symptoms are associated with MTBE, gasoline contains other ingredients that may cause similar health effects.

Immediately or shortly after exposure to MTBE (at levels similar to when you fill your car with gasoline) people may experience irritation of the eyes, nose and throat, and headache or dizziness. Some of these symptoms may result from the bad odor of the chemical. At even higher levels (in industrial settings), people can feel drunk, have trouble breathing, and lose coordination.

Currently, the effects on humans of long-term exposure to low levels of MTBE are unknown. The following are results of studies using laboratory animals:

  • When exposed to high levels of MTBE over a long period of time, some laboratory animals developed kidney tumors, testicular tumors, lymphoma and leukemia.
  • When fed high doses of MTBE, some laboratory animals lost weight and developed liver and kidney problems.

Because it leaves the body quickly, MTBE and its breakdown product, "butyl alcohol," can only be measured in exhaled breath, urine, and blood for 1-2 days after exposure. Doctors can use function tests of the nervous system, kidneys, or liver to track the long-term health of people regularly exposed to MTBE at work.

Seek medical advice if you have any symptoms that you think may be related to chemical exposure.

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Last revised June 15, 2022