Get Informed | What is MTBE / Methyl tert-butyl ether?

Methyl tert-butyl ether (MTBE) is made from methanol and is a by-product of the oil refining process. It was added to gasoline in an attempt to make gas burn cleaner, but studies show it has had little effect on curbing air pollution. At room temperature, MTBE is a volatile, flammable, and colorless liquid that is highly soluble in gasoline and slightly so in water. MTBE is 28 times more soluble than benzene in water and MTBE will diffuse 8.6 times faster than benzene in water although, it must be admitted, benzene is almost insoluble in water at 1.79 g/L. This allows MTBE to spread laterally faster than the other hydrocarbons, creating a wider and longer contaminant plume and facilitating the movement of the volatile organic compounds that were not as soluble in water.

MTBE is 2.6 times more likely to vaporize than benzene and is 9.2 times more likely to stay in water or to enter water from the atmosphere than benzene. MTBE's low Henry's Law Constant (0.024) indicates that it greatly prefers water to air and any MTBE vapor that contacts water will preferably move into the water at a ratio of 1:42. The decision to put MTBE in gasoline to reduce air pollution resulted in an increase in groundwater contamination associated with leaky underground petrochemical storage tanks. Unfortunately, the experts that were attempting to save the planet by making gasoline burn cleaner instead created jobs for environmental professionals, chemists, geologists, and laboratories, because their short-sighted decision resulted in widespread groundwater and drinking water contamination with yet another chemical, MTBE.

MTBE is manufactured by the chemical reaction of methanol, generally made from natural gas, and isobutylene. It promotes the more complete combustion of gasoline, reducing emissions of carbon monoxide (CO) and organic compounds. It does so by adding oxygen to the gasoline which increases the temperature at which it burns in the engine, reducing the amount of harmful byproducts in the vehicle's exhaust. Because it mixes readily with gasoline, is easily transported, has a low production cost and high octane-rating, MTBE has become the oxygenate of choice for most gasoline producers who face state and federal mandates to produce less-polluting gasoline. In the late 1970s, gasoline companies started adding MTBE in relatively low concentrations to gasoline to replace tetraethyl lead and to boost octane, a measure of a gasoline's ability to resist engine knock . In about 1996, the MTBE concentration in gasoline was increased to 10 to 12 percent to enhance complete combustion and reduce tailpipe emissions, especially in states like California that have widespread air quality problems. In 1990, in response to concerns over air pollution and aggressive industry lobbying, the U.S. Congress amended the Clean Air Act to require the use of fuels which add oxygen to gasoline. MTBE is the best known oxygenate, and the one embraced by most oil companies although other oxygenates are used in some areas. Approximately 31% of all U.S. gasoline contained MTBE and MTBE makes up about 85% of the oxygenates used nationally. Other oxygenates include: ethanol and ethanol-based ethers.

In a major setback to the oil and chemical industries, on July 27, 1999 an EPA panel recommended that MTBE be reduced in use as a gasoline additive because of the toxic hazards that MTBE poses to drinking water supplies throughout the country. MTBE is a known animal carcinogen and possible human carcinogen. The reported U.S. production of MTBE in 1992 exceeded nine billion pounds - virtually all of it is added to gasoline. Oil companies reportedly make approximately $3 billion per year from MTBE production. It was not until 2005 that, the Federal Policy Act removed the requirement to mix MTBE in gasoline (Source). California banned MTBE as an additive in 2002 and New York banned it as a fuel additive in 2004.

How Does MTBE / Methyl tert-butyl ether become a problem?

MTBE is highly volatile and would typically be expected to volatilize rapidly from soil surfaces or water, but MTBE is somewhat soluble in water and is highly mobile in soils; it adsorbs only weakly to soil and aquifer material. The solubility of MTBE in water at 25°C is approximately 5000 mg/L but its solubility in gasoline is much, much greater; gasoline can be as much as 10% MTBE. In comparison, the solubility of non-oxygenated gasoline is only about 120 mg/L. In the atmosphere, MTBE is rapidly transformed into formaldehyde which is an air pollutant. Bioremediation of MTBE in soil, both natural and human-assisted, has not been very effective. If found in groundwater at concentrations greater than 30 ppb, it is likely that the source is a leaking underground storage tank (UST), a point source. Lower concentrations probably represent a combination of point and nonpoint sources, which may include atmospheric washout and stormwater runoff from parking lots, roads, and other paved surfaces.

What are the Health Risks for MTBE / Methyl tert-butyl ether?

The U.S. Environmental Protection Agency (EPA) had proposed a "health advisory" level for MTBE in drinking water of 0.070 mg/L, but they ultimately set it as an aesthetic-based advisory standard in 1997/1998. Inhalation exposure of MTBE, while pumping gas, has been associated with "headaches, nausea, dizziness, irritation of the nose or throat, and feelings of spaciness or confusion" and as an irritant to the throat and/or nose. "If MTBE leaks from the gallbladder into other areas of the body, the patient can have minor liver damage, a lowering of the amount of white blood cells, nausea, vomiting, sleepiness, dizziness, and confusion." "Some animals that were given MTBE by mouth had diarrhea and irritation in their stomachs and intestines. Some animals also had very slight liver damage." "MTBE irritated the skin and eyes of animals when exposed" (Source).

What are the Standards for MTBE / Methyl tert-butyl ether?

Because of taste and odor concerns, the EPA, in 1997/1998, suggested that the MTBE concentration should be no more than 0.02 (Odor threshold) to 0.04 mg/L (Taste threshold). In Pennsylvania, the Department of Environmental Protection established a health advisory level of 0.02 mg/L and Massachusetts set a secondary standard of 0.02 to 0.04 mg/L (Source). New Hampsphire and California set an MTBE primary drinking water standard of 0.013 mg/L because of concerns related to the gastrointestinal system and to minimize a risk of cancer to 1 in 1 million.

Get Tested | MTBE

You should get your drinking water tested for MTBE when you suspect your drinking water has been impacted by a leak or spill associated with a petrochemical operation, if you are adjacent to a landfill, a manufacturer that uses MTBE, old fuel stations, or is located near an activity with high MTBE emissions. In addition, MTBE can add a turpentine-like, sweet, solvent-like, alcohol taste or odor to the water, but this occurs at a level that is at least 10 times higher than the smell/taste thresholds for other volatile organic compounds in water. If your water has a film with a metallic sheen that, after being disrupted comes back together, then this would suggest the sheen is related to a petrochemical problem.