CLU-IN.ORG | Contaminant Focus: METHYL TERTIARY BUTYL ETHER (MTBE), Chemistry and Behavior

For more information on MTBE Treatment, please contact:

Linda Fiedler
Technology Assessment Branch
(703) 603-7194
fiedler.linda@epa.gov

Methyl tertiary butyl ether (MTBE, CAS No. 1634-04-4) is an ether compound made by combining methanol and isobutylene. The methanol typically is derived from natural gas; isobutylene can be derived as a byproduct of the petroleum refinery process.

MTBE is a liquid, colorless, volatile organic compound with a terpene-like odor, a vapor pressure of 249 mm Hg at 25º C, a water solubility of 51,000 mg/L, and a specific gravity of 0.74. When released to the air, it has a 5 to 6 day half life and degrades primarily by reacting with photochemically produced hydroxyl radicals to form tertiary butyl formate. The exposure to atmospheric UV light alone will not be sufficient to decompose this compound. The low log K_ow (1.24) suggests that MTBE will be very mobile in soils. MTBE has a Henry's Constant of 0.022 and hence is not likely to form a vapor plume in the vadose zone above a dissolved phase plume.

In comparison to other components of concern in gasoline, including benzene, toluene, ethylbenzene, and xylenes (BTEX), MTBE may pose additional problems when it escapes into the environment through gasoline releases. MTBE is capable of traveling through soil rapidly, is very soluble in water (much more so than BTEX), and is highly resistant to biodegradation (much more so than BTEX). MTBE that enters ground water moves at nearly the same velocity as the ground water itself. As a result, it often travels farther than other gasoline constituents, making it more likely to affect public and private drinking water wells. Due to its affinity for water and its tendency to form large contamination plumes in ground water, and because MTBE is highly resistant to biodegradation and remediation, gasoline releases with MTBE can be substantially more difficult and costly to remediate than gasoline releases that do not contain MTBE. This is a substantial concern in the United States, where approximately 40 to 46% of the population uses ground water as a source of drinking water. Unless frozen, MTBE in surface water will volatilize and find its way into the atmosphere. This accounts for the less frequent and generally lower concentrations of MTBE found in surface water.

MTBE has a very unpleasant turpentine-like taste and odor that at low levels of contamination can render drinking water unacceptable for consumption. Studies conducted on the concentrations of MTBE in drinking water at which individuals can detect the taste and odor of the chemical have shown that human sensitivity to the taste and odor of MTBE varies widely.

Adapted from:

Handbook of Environmental Fate and Exposure Data for Organic Chemicals, Volume II Solvents
P. Howard. Lewis Publishers, 1991.

Toxicological Profile Methyl tert-Butyl Ether
Agency for Toxic Substances and Disease Registry, 1996.

Environmental Behavior and Fate of Methyl tert-Butyl Ether (MTBE)
U.S. Geological Survey, FS-203-96, 1998.

Methyl Tertiary Butyl Ether (MTBE): Advance Notice of Intent to Initiate Rulemaking Under the Toxic Substances Control Act to Eliminate or Limit the Use of MTBE as a Fuel Additive in Gasoline; Advance Notice of Proposed Rulemaking
Federal Register, Vol 65 No 58, p 16093-16109, 20 Mar 2000.

Chemical and Physical Information
Toxicological Profile Methyl t-Butyl Ether (MTBE), Chapter 3.
Agency for Toxic Substances and Disease Registry, 4 pp, 1996.

Disclaimer
http://cluin.org/sec/Methyl_Tertiary_Butyl_Ether_(MTBE)/cat/Chemistry_and_Behavior/
Last updated on Thursday, July 24, 2008