Methyl Tertiary Butyl Ether (MTBE)

The majority of the human health-related research conducted to date on MTBE has focused on adverse effects that might result through inhalation of the chemical. At high doses by the inhalation route, MTBE has caused non-cancer health effects as well as tumors in two strains of rat and one strain of mouse in a variety of organs; however, studies have been lacking for human or animal health effects resulting from the ingestion of MTBE in drinking water.

EPA classified MTBE as a "possible" human carcinogen under its 1986 cancer risk assessment guidelines on the basis of results of inhalation cancer tests and has suggested that it be regarded as posing a potential carcinogenic hazard and risk to humans, though no quantitative estimate of the cancer potency of MTBE has been established by EPA because of limitations in the available data. While MTBE has been characterized as an animal carcinogen, both the International Agency for Research on Cancer and the U.S. Department of Health and Human Services (DHHS) have indicated that there are not enough data to classify MTBE with regard to human carcinogenicity under their classification schemes. In 2011, DHHS again noted the lack of sufficient data to evaluate MTBE in the 12th edition of its Report on Carcinogens. It should be noted that conclusions in the Office of Science and Technology Policy's 1997 Interagency Assessment of Oxygenated Fuels [cited under Environmental Occurrence] and in a 1996 report by the Health Effects Institute generally support EPA's view on potential carcinogenic hazard. The Interagency Assessment stated, in regard to inhalation risks, that "it is not known whether the cancer risk of oxygenated gasoline containing MTBE is significantly different from the cancer risk of conventional gasoline." The estimated upper bound cancer units risks of MTBE are similar to or slightly lower than those of fully vaporized conventional gasoline, which has been listed by EPA as a probable human carcinogen based on animal carcinogenicity data; however, because of lack of health data on the nonoxygenated gasoline vapors to which humans are actually exposed, it is not possible to have a reasonably good estimate of population cancer risk to conventional gasoline.

EPA reviewed available health effects information on MTBE in its 1997 drinking water advisory guidance and determined that there was insufficient information available on MTBE health effects and exposure to allow EPA to establish a national primary drinking water regulation. The drinking water advisory document indicated there is little likelihood that MTBE concentrations between 20 and 40 µg/L would cause adverse health effects. Nevertheless, California, New Hampshire, New York, and other states have proposed or adopted conservative health-based primary drinking water standards of their own for MTBE.

Human Health

Acute Exposure Guideline Levels (AEGLs) for Methyl tertiary-Butyl Ether [Interim]
National Advisory Committee for AEGLs, 49 pp, 2009

Changes to Interim values and Technical Support Documents may occur prior to publication of final AEGL values. Refer to the AEGL Chemicals database to check for updated information.

Drinking Water Advisory: Consumer Acceptability Advice and Health Effects Analysis on Methyl Tertiary-Butyl Ether (MtBE)
U.S. EPA, Office of Water, EPA 822-F-97-009, 48 pp, 1997.

Human Exposure to Methyl tert-Butyl Ether (MTBE) While Bathing with Contaminated Water
S.M. Gordon.
EPA 600-R-05-094, 59 pp, 2003

Describes the results of a study to estimate the relative contribution of the inhalation and dermal pathways during normal baths in water containing MTBE.

Human-Health Effects of MTBE: A Literature Summary
Patty Toccalino, Oregon Health & Science University.
U.S. Geological Survey, National Water-Quality Assessment (NAWQA) Program [2003].
Contact: Patty Toccalino, toccalino@ese.ogi.edu

Interagency Assessment of Potential Health Risks Associated with Oxygenated Gasoline
National Science and Technology Council, Committee on Environment and Natural Resources. 1996.

Methyl tert-butyl ether (MTBE) (CASRN 1634-04-4)
U.S. EPA, Integrated Risk Information System (IRIS).

Methyl tert-Butyl Ether: Summary of Data Reported and Evaluation
IARC Monographs Programme on the Evaluation of Carcinogenic Risks to Humans, Vol 73, p 339, 1999.

• See also the full text of IARC Monograph 73-18

Methyl tertiary-Butyl Ether (MTBE) in Drinking-Water: Background Document for Development of WHO Guidelines for Drinking-water Quality
World Health Organization, WHO/SDE/WSH/05.08/122, 26 pp, 2005

MTBE: Recent Carcinogenicity Studies
Burns, K.M. and R.L. Melnick.
International Journal of Occupational and Environmental Health 18(1):66-69(2012)

This paper briefly summarizes new findings and puts into perspective the totality of carcinogenic effects and environmental health risks on MTBE.

MTBE in Gasoline: Clean Air and Drinking Water Issues
McCarthy, J.E. and M. Tiemann.
Congressional Research Service Reports: Paper 26, 29 pp, 2006

Proceedings of the Conference on MTBE and Other Oxygenates: a Research Update
U.S. EPA, National Center for Environmental Assessment.
EPA 600-R-95-134, 274 pp, 1995.

Public Health Goal for Methyl Tertiary Butyl Ether (MTBE) in Drinking Water
Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, 136 pp, 1999.

Tert-Butyl Methyl Ether, CAS No: 1634-04-4, EINECS No: 216-653-1, Risk Assessment
European Union, Finnish Environment Institute, 292 pp, 2002

Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels
National Research Council, National Academies Press, 176 pp, 1996.

Toxicological Profile for Methyl tert-Butyl Ether (MTBE)
Agency for Toxic Substances and Disease Registry, 2022.

Toxicological Summary for Methyl tert-butyl Ether (MTBE)
Minnesota Dept. of Health, Health Risk Assessment Unit, Environmental Health Division, 6 pp, 2013

Wanderlust: MTBE Taste and Odor Thresholds ... The Myth of Protectiveness
White, H.
LUSTLine Bulletin 39:6-7(2001)

This article explores the complications of dispersion and desensitization on MTBE taste and odor thresholds.

Ecological Impacts

Determination of the Ecological Risk Associated with a Groundwater Plume of MTBE at Port Hueneme, CA
Bates, M., K. Kuvakas, P. Leonard, and S. McKagan.
University of California, Santa Barbara, 139 pp, 2000

Several years after a gasoline release occurred at the Port Hueneme Naval Facilities Engineering Service Center, a literature review conducted on the effects of MTBE on soil microbial communities indicated that little research had been undertaken on the effects of MTBE on microbes. To fill gaps in the data, Team MTBE2000 designed and performed a field experiment aimed at elucidating the relationships between MTBE and BTEX concentrations and toxicity to microbial organisms.

Methyl Tertiary-Butyl Ether (MTBE): Canadian Water Quality Guidelines for the Protection of Aquatic Life
Canadian Council of Ministers of the Environment, 5 pp, 2003.

MTBE (t-butyl methyl ether, Methyl tertiary butyl ether, Methyl-Tert-Butyl-Ether, CAS number 1634-04-4)
Environmental Contaminants Encyclopedia, R.J. Irwin, M. VanMouwerik, L. Stevens, M.D. Seese, and W. Basham (compilers).
National Park Service, Water Resources Division, Fort Collins, CO. 36 pp, 1997.