MTBE
(Methyl Tertiary Butyl Ether)

MTBE Summary of Facts

What is MTBE?

MTBE stands for Methyl Tertiary Butyl Ether. It is commonly used as a gasoline additive to reduce engine knocks. MTBE is being tested to see if it causes cancer or other health problems. The U. S. Environmental Protection Agency (EPA) is considering outlawing the use of MTBE as a result of the taste and odor problems in water and unreasonable risk to the environment.

What is the concern about MTBE?

It's showing up in groundwater all over the country, and it's tough to clean up.

Why is MTBE still in gasoline?

Gasoline may contain up to 15 percent by volume of MTBE. Higher percentages of MTBE are typically found only in premium grade gasoline. A law effectively banning MTBE in Missouri's gasoline supply was passed in 2002. Because of its wide use and the need for refiners to change their systems, MTBE cannot be eliminated immediately; however, a phase-out of MTBE that protects consumers without affecting gasoline supplies and costs is underway. The phase-out must be concluded by July 1, 2005.

MTBE and Missouri's water

How does MTBE get into drinking water?

MTBE may enter the water through gasoline spills, gasoline storage tank leaks, or discharges from two-cycle engines on motorboats and other watercraft. It also enters the atmosphere from airborne emissions from vehicles. MTBE travels through groundwater faster than the other components of gasoline. It does not readily break down.

How will I know if I have MTBE in my water?

If you get your water from a public water system, it is routinely tested for MTBE and if any were present your water system officials would notify you. MTBE has a very unpleasant taste and a strong turpentine-like odor. If you are on a private well you would be able to smell or taste MTBE contamination long before it would get to a harmful level. EPA has set an advisory level of 20 to 40 parts per billion (ppb) based on the ability of people with a sensitive sense of smell being able to detect it in this range.

Who watches over my drinking water?

The Missouri Departments of Health and Natural Resources are responsible for protecting the quality of drinking water in Missouri. The Department of Health assists private well owners by offering routine water analyses to all well owners and special analyses on an as-needed basis. The Department of Natural Resources is responsible for making sure that public water supplies are safe. The Department of Natural Resources also regulates well drillers to assure that wells are properly constructed and to protect groundwater quality.

What should I do if I have a private well and suspect that it is contaminated?

For routine water sampling, you should first contact your county health department. If you think that your well is contaminated with MTBE, please call the Missouri Department of Health and Senior Services - Section for Environmental Public Health at 1-866-628-9891.

What if I get water supplied to me?

The Missouri Department of Natural Resources routinely monitors about 2,000 community public drinking water wells for MTBE and over 100 other potentially harmful compounds at least once every three years. Testing for MTBE began in 1995, so there have been three complete rounds of testing on every public well. The 83 public drinking water systems that use surface water are tested annually for MTBE. Your public water supplier will inform you of any problems.

Click here to view a larger Public Water Map
Large version of the public water supplies statewide.

How big a problem is MTBE in our water?

MTBE has been detected in 15 public drinking water wells at 13 different sites in the time that DNR has been testing.

MTBE has also been found in 32 private drinking water wells, bringing the total number of wells in Missouri contaminated by MTBE to 38 at a total of 23 different sites as of June 2001.

Click Here to view larger map of contaminated well sites in Missouri
Large version of the contaminated well sites in Missouri.

The Table of Contaminated Wells lists all the contaminated sites, the date when MTBE was first detected, and the highest concentration of MTBE measured. Levels higher than about 20 parts per billion (ppb) can cause the water to have a bad taste and smell.

Click here to view a larger version of the MTBE timeline
Large version of the MTBE timeline.

Are these the only places that need to be concerned about MTBE?

No, groundwater moves much more slowly than water in streams, thus many pollution problems aren't found until years after the pollution entered the groundwater. This means that we may find additional sites contaminated with MTBE in the future and it is why DNR will continue to monitor public wells for MTBE.

How concerned should I be about MTBE contamination?

Most of Missouri's drinking water supplies come from treated surface water. Wells used for public drinking water supplies in Missouri are constructed to the state's highest standards. These wells are typically deeper than private wells and sealed more effectively to prevent near-surface contaminants from entering our drinking water. Private wells drilled since 1987 are also constructed to a higher standard than older wells. Consumers who are drinking water from older, shallow wells or springs located near gasoline storage or transportation systems are at greatest risk.

How many gasoline storage tanks are there in Missouri?

There are nearly 10,000 underground storage tanks in use in Missouri at just over 4,000 sites. Nearly 25,000 tanks have been permanently closed in the last two decades. Department of Natural Resources goal is to inspect each of the tanks in use approximately once every three years.

What is being done to check on underground tanks?

When a gasoline storage tank leaks, many harmful chemicals can flow into the groundwater. This has led Missouri to require new safety measures and to inspect all tanks. All underground tank operators must monitor their tanks and piping monthly. The records that they keep are reviewed by Department staff and staff of the Petroleum Storage Tank Insurance Fund. All tanks in use after Dec. 22, 1998 must meet strict design and operating requirements. More than 97 percent of the in-use underground storage tanks have been upgraded in the last 12 years and more than 95 percent of the tanks currently in use have leak detection devices installed.

What about aboveground tanks?

Aboveground tank owners are required to meet safety and fire requirements. This includes having leak and spill prevention equipment. The Missouri Department of Agriculture inspects aboveground fuel storage and dispensing systems. Some of the aboveground tanks are also insured by the Petroleum Storage Tank Insurance Fund, which also makes sure that the owner has a current spill prevention plan.

How is MTBE related to Reformulated Gasoline (RFG)?

MTBE was first used in the United States in the late 1970s to enhance octane as the use of lead in gasoline was discontinued. It helps gasoline burn cleaner and reduces engine "knock" and carbon monoxide and air toxics emissions. This is why it is used in reformulated gasoline. MTBE has been used in the St. Louis area as part of the federal reformulated gasoline program since June 1999. Gasoline with ethanol makes up approximately 97percent of the reformulated gasoline in the St. Louis area, with gasoline containing MTBE comprising the other three percent.

MTBE and Human Health

How much MTBE is bad for me?

EPA sets health-based, legally enforceable drinking water standards called Maximum Contaminant Levels (MCLs) for potential drinking water contaminants. MTBE does not currently have an MCL, but it is on EPA's list of Unregulated Contaminants and is being considered for regulation in the future. In lieu of an MCL, Missouri's Department of Health has recommended three action levels for MTBE based on the latest risk assessment information. The first action level is a long-term, or lifetime number, which would be equivalent to an MCL and it is 20 ppb. A second action level, which would be protective of shorter-term exposures, is 400 ppb. This action level is designed to set a limit on the amount of exposure that a community public water supply could receive from MTBE while obtaining an alternate water supply. The third action level is an acute one where the water would not be considered safe to drink, even for a short period of time. The acute action level is 1,000 ppb.

It is important to know that MTBE has a strong taste and odor that make it unlikely that you would drink enough MTBE to make yourself seriously ill. EPA's Human Health and Criteria Division has recommended keeping contamination below the 20 to 40 ppb range to ensure that your water does not have a bad taste and odor. Levels much higher than this advisory range quickly become unacceptable to the public. EPA estimates that concentrations from 20,000 to 100,000 times higher than this are associated with illness or disease in rodent studies.

How much do we know about MTBE’s health effects?

Rats and mice have been given MTBE internally and forced to breathe air rich in MTBE. Some of these animals have gotten sick or developed cancers, apparently as a result of their exposure to high concentrations of MTBE. Few tests have been conducted on humans, and none of these studied the effects of drinking MTBE. Because MTBE is mixed with other harmful chemicals, it has been difficult to study its effects on humans. MTBE is thought to cause cancer based on the animal studies, but only at concentrations far above those likely to be found in humans because of MTBE's offensive taste and smell.

How much of a risk is gasoline?

A federal government study concluded that other components of gasoline pose much more serious cancer risks than MTBE. Benzene, a component of all gasoline, is known to cause cancer at levels much lower than the likely exposure of anyone to MTBE. In addition, gasoline contains other compounds known to pose health risks at high concentrations.

If MTBE is bad for humans, why is it still in use?

Much of the information on the health effects of MTBE has only come to light recently. Eliminating MTBE immediately would cause gasoline shortages, higher costs and more air pollution from automobiles. The EPA is considering phasing out MTBE use over the next few years to prevent these possibilities.

What can I do?

Handle all petroleum products carefully and never pour them on the ground. Make sure that your well is properly constructed and never dump anything on the ground near your well. If you are on a public water system, read the annual Consumer Confidence Report that is made available each year describing the quality of your water. If your water smells or tastes of turpentine or has some other unusual smell or taste, contact your local water supplier. For private well owners, please call the Missouri Department of Health and Senior Services at 1-866-628-9891.

Where can I get more information?

For more information on MTBE call or write

Missouri Department of Natural Resources
P.O. Box 176, Jefferson City, MO 65102-0176
800-361-4827

What programs deal with drinking water quality in Missouri?

Public Drinking Water Program - Helps ensure the safety of public drinking water by monitoring for as many as 90 chemicals and bacteria that can cause illness.

Environmental Services Program - Conducts field sampling and laboratory tests on Missouri’s water and air. Responds to emergencies involving hazardous chemicals.

Hazardous Waste Program - Underground Tanks Section - Helps prevent contamination caused by corrosion, leaks, overfilling and spills from underground storage tanks.

Wellhead Protection Section - Protects the groundwater from contamination by ensuring that all private wells are built to state standards.

E-mail Icon.   Missouri Department of Health and Senior Services - Section for Environmental Public Health

Missouri Department of Agriculture Petroleum Quality and Inspection Program - Assures that all motor fuels and other fuels meet minimum quality specifications.

Petroleum Storage Tank Insurance Fund - Provides pollution liability insurance to owners and operators of underground and aboveground tanks and pays to clean up old tank sites.

Links to other sites about MTBE

MTBE Publications

PUB2080--MTBE Summary of Facts - to download the entire explanation in printable form with maps and tables. (02/04) PDF