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CAS Number: 1634-04-4
Synonyms: methyl tertiary-butyl ether, methyl-t-butyl ether
Contaminant Type: Chemical

Methyl tertiary-butyl ether (MTBE) is a chemical compound that is manufactured by the chemical reaction of methanol and isobutylene [1578]. MTBE has been added to gasoline as an octane enhancing replacement for lead and as an oxygenate to lower the ozone and carbon monoxide emission levels [1557]. MTBE is highly volatile in room temperature because of its high vapor pressure (245-276 mm Hg @ 25 C) but it is difficult to volatilize once it dissolves in water because of its low Henry's law constant (0.023 to 0.12).

The main sources of MTBE contamination of groundwater supplies are leaking underground storage tanks and pipelines, spills and contaminated sites and releases from manufacturing and storage sites. The primary sources of MTBE contamination in urban surface water supplies are releases from gasoline-powered recreation watercrafts and atmospheric deposition through precipitation of industrial or vehicular emissions [1557][1577].

A growing number of studies have detected MTBE in ground water throughout the country; in some instances, these contaminated waters are sources of drinking water [1578].  Because of its small molecular size and because of its high solubility, it moves rapidly in ground water.  MTBE by itself is not likely to cause environmental harm at levels normally found in the environment but can contribute to the formation of photochemical smog when it reacts with other volatile organic carbon substances in air [1577].

The majority of the human health-related research conducted to date on MTBE has focused on effects associated with the inhalation of the chemical. EPA's Office of Water has concluded that available data are not adequate to estimate potential health risks of MTBE at low exposure levels in drinking water but that the data support the conclusion that MTBE is a potential human carcinogen at high doses [1578].

MTBE is not regulated by USEPA in drinking water, but it has been assessed as a part of the Unregulated Contaminants Monitoring Rule.  It is on USEPA's Contaminant Candidate List 3. The drinking water advisory recommended keeping the concentrations in the range of 20 and 40 ppb or below to likely avert unpleasant taste and odor effects.  The Agency advises that below the 20 to 40 ppb range, the public will be protected against potential health effects [1577]. 

The Agency has noted air strippping, granular activated carbon adsorption, and advanced oxidation processes as technologies that can control MTBE in drinking water. 

MTBE can be biodegraded under aerobic conditions.  A product is tertiary butyl alcohol (TBA).  In spill situations near a source, MTBE can also be found with benzene, toluene, ethyl benzene and xylenes (BTEX), thus, treatment may involve targets beyond MTBE itself [1555, 1557].

Date of Literature Search: July 2009

1555 Raynal, M. and Pruden, A.; 2008; Aerobic MTBE biodegradation in the presence of BTEX by two consortia under batch and semi-batch conditions; Biodegradation; 19:2:269
1557 Kavanaugh, M., Chowdhury, Z., Kommineni, S., Liang, S., Min, J., Croue, JP, Corin, N., Amy, G., Simon, E., Cooper, W., Tornatore, P., and Nickelsen, M.; 2004; Removal of MTBE With Advanced Oxidation Processes; Removal of MTBE With Advanced Oxidation Processes; Report No. 90933F. pp 33-193. American Water Works Association Research Foundation, Denver, CO.
1577 US EPA; 1997; MTBE Factsheet; http://www.epa.gov/waterscience/criteria/drinking/mtbefact.pdf; As posted on September 11, 2009. USEPA Office of Ground Water and Drinking Water, Washington, DC.
1578 US EPA; 2009; Methyl Tertiary Butyl Ether (MTBE); http://www.epa.gov/MTBE/faq.htm; As posted on September 11, 2009. USEPA Office of Ground Water and Drinking Water, Washington, DC.
1579 US EPA; 2005; Drinking Water Contaminant Candidate List and Regulatory Determinations; http://www.epa.gov/ogwdw/ccl/ccl2.html; As posted on September, 2009. USEPA Office of Ground Water and Drinking Water, Washington, DC.