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Water: MTBE

Aquatic Life Criteria for MTBE - Methyl Tertiary-Butyl Ether

Fact Sheet; March 2006; EPA-822-F-06-002

On October 29, 1999, the U.S. Environmental Protection Agency (EPA) announced its intent to revise aquatic life criteria for copper, silver, lead, cadmium, iron and selenium and its intent to develop aquatic life criteria for atrazine, diazinon, nonylphenol, methyl tertiary-butyl ether (MTBE) and dissolved oxygen in saltwater (64 FR 58409).

In follow-up to this announcement, EPA is now providing an update on aquatic life ambient water quality criteria development for methyl tertiary-butyl ether (MTBE). Since 1999, EPA conducted a careful review of 33 toxicity studies and a national survey of MTBE occurrence in surface waters. EPA has determined that MTBE typically is found in the aquatic environment at levels far below those that are toxic to aquatic life. Consequently, EPA does not intend at this time to publish new ambient water quality criteria for MTBE under Section 304(a) of the Clean Water Act.


What is MTBE?

MTBE is an organic chemical that has been used as a gasoline additive throughout the U.S. to improve the combustability of gasoline and reduce air pollutants. MTBE is highly volatile, very soluble in water, and resistant to natural degradation in groundwater. Because of its chemical properties and widespread use as a fuel additive, concerns were raised over the potential risks to aquatic life from exposure to MTBE in surface water.

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How did EPA reach this determination?

To investigate the risks of MTBE to aquatic life, EPA reviewed toxicity data to determine what levels of MTBE would be toxic to freshwater and saltwater aquatic life. EPA calculated MTBE concentrations below which no harmful effects to aquatic life are expected. EPA then compared these concentrations to the levels of MTBE which were found in surface waters of the U.S.

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Findings

MTBE would have to occur in freshwater over the short-term (acute toxicity) at or above concentrations of 151 mg/L to be harmful. Over the long-term (chronic toxicity), MTBE would have to occur in freshwater at or above 51 mg/L to be harmful. For saltwater environments, MTBE would have to be above concentrations of 53 mg/L short-term, and 18 mg/L long-term.

When EPA examined the occurrence of MTBE in surface waters, EPA found that ambient concentrations of MTBE are 10,000 times lower than the calculated harmful levels.

These determinations, and the methods used, were published in 2002 in the scientific journal Environmental Science and Technology (2002, Volume 36, pages 125-129) in an article entitled: "MTBE Ambient Water Quality Criteria Development: A Public/Private Partnership".

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How do I Obtain More Information on MTBE?

For more information on MTBE, contact Dr. Frank Gostomski (gostomski.frank@epa.gov) of the US EPA at (202) 566-1105. You can also send conventional mail to Dr. Gostomski at US EPA, Office of Science and Technology, Health and Ecological Criteria Division, Mail Code 4304T, 1200 Pennsylvania Avenue NW, Washington, DC 20460.


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