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What It Is: (methyl tertiary-butyl ether) is produced in very large quantities (over 200,000 barrels per day in the U.S. in 1999) and is almost exclusively used as a fuel additive in motor gasoline. It is one of a group of chemicals commonly known as "oxygenates" because they raise the oxygen content of gasoline.

To date, independent expert review groups who have assessed MTBE inhalation health risks (e.g., "Interagency Assessment of Oxygenated Fuels") have not concluded that the use of MTBE-oxygenated gasoline poses an imminent threat to public health. However, researchers have limited data about what the health effects may be if a person swallows (ingests) MTBE. 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. Recent work by EPA and other researchers is expected to help determine more precisely the potential for health effects from MTBE in drinking water.

EPA reviewed available health effects information on MTBE in its 1997 Drinking Water Advisory guidance and decided that there was insufficient information available to allow EPA to establish quantitative estimates for health risks and as such would not set health advisory limits. The drinking water advisory document indicates that there is little likelihood that MTBE in drinking water will cause adverse health effects at concentrations between 20 and 40 ppb or below.

Contamination: Although often difficult and time consuming, MTBE contamination can be cleaned up in the soil and water using existing technologies such as air stripping, granular activated carbon (GAC), advanced oxidation, and soil vapor extraction (SVE). These technologies are discussed below. The latter three have been used successfully at individual homes with impacted drinking water wells. Some home treatment units can also remove MTBE in tap water.

When soil is contaminated with MTBE, treatment may be even easier than for other gasoline compounds since pure MTBE has a high vapor pressure and does not stick easily to organic carbon in soil. When MTBE is dissolved in water, its treatment may be the most difficult and time-consuming of all compounds.

The levels to which contaminated groundwater is cleaned up can vary as well as the methods used. If the ground water is used for drinking, it is often treated more rigorously to avoid unpleasant taste and odor and to protect against potential health effects, thereby restoring it to potable condition.

Although MTBE does not readily degrade in soil and water under most natural conditions but some lab and field studies have shown promising results using bacterial cultures to degrade it in these conditions.

How are the technologies used to remove MTBE from soil and/or water?
SVE technology pulls air through the soil to vaporize the contaminants. MTBE vapors that are extracted or vacuumed from the soil must be collected, properly treated, and disposed of to prevent further contamination.

GAC treatment technique pumps contaminated water through a bed of activated carbon to remove organic compounds. Since MTBE does not sorb ("stick") well to organics such as carbon, high volumes of the contaminated water must repeatedly pass through a GAC system before MTBE is effectively removed. Though less effective for MTBE, many individual homeowners use small carbon canisters to remove a variety of contaminants, including MTBE, from impacted private wells.

Air stripping is a process in which contaminated water is passed through a column filled with packing material while upward-flowing air removes chemicals from the water. In general, these vapors should not be released directly into the air and therefore, should be appropriately treated. MTBE doesn't readily separate from water into vapor, so it necessitates a high air to water ratio.

Oxidation technologies have been demonstrated to oxidize a wide range of organic chemicals, including MTBE, so they might be another option in transforming the chemicals.

Is it expensive to clean up MTBE?
MTBE can complicate remedial activities because of its greater water solubility and resistance to natural biodegradation. Thus, the costs can be higher than those associated with the treatment/remediation for benzene or other gasoline components.

The contact for MTBE in the New York region:
Department of Health
Bureau of Public Water Supply Protection
Phone: 518-458-6731