Methyl tert-butyl ether (MTBE) is a synthetic chemical which is colorless, flammable liquid and has a distinctive, disagreeable odor. It was first introduced as an additive for unleaded gasolines in the 1980s to achieve more efficient burning. Most MTBE is mixed with gasoline, so most people would come in contact with it while exposed to automobile fuel vapors or exhausts. MTBE is used in medicine to dissolve gallstones.

Routes of exposure:

• Breathing exhaust fumes while driving a car and breathing air near highways or in cities.
• Direct skin contact or breathing contaminated air while pumping gasoline. 
• Drinking, swimming, or showering in MTBE contaminated water.
• Receiving MTBE treatment for gallstones.

Health effects

MTBE has a very unpleasant odor that most people can smell before any harmful effects would occur.  Breathing small amounts of MTBE for short periods may cause nose and throat irritation.  Some people exposed to MTBE while pumping gasoline, driving cars, or working in gas stations have reported having headaches, nausea, dizziness, and mental confusion.  However, actual levels of exposure in these cases are unknown.  At present there is no data on the effects in people of drinking MTBE. Animal studies suggest that drinking MTBE may cause gastrointestinal irritation, liver and kidney damage, and nervous system effects.
 
Does MTBE cause cancer?

At present, there is no evidence that MTBE causes cancer in humans.  Only animal studies indicate exposure to high levels of MTBE for long periods may cause kidney and liver cancers.  The Department of Health and Human Services (DHHS) and the International Agency for Research on Cancer (IARC) has not classified MTBE as a carcinogen.
 
Regulation and guidelines:

• The American Conference of Governmental Industrial Hygienists (ACGIH) has recommended an exposure limit of 40,000 parts per billion (ppb) for an 8-hour workday, 40-hour workweek. 
• US Environmental Protection Agency (EPA) has not established drinking water standards for MTBE.  In 1997, EPA issued a Drinking Water Advisory of 20 to 40 micrograms per liter, primarily for taste and odor considerations.
• EPA has established an inhalation Reference Concentration (RfC) of 830 ppb or 3 milligrams per cubic meter (3 mg/m3) for chronic exposure.
• The EPA has issued guidelines recommending that, to protect children, drinking water levels of MTBE should not exceed 4 milligrams per liter of water (4 mg/L) for an exposure of 1 – 10 days, and 3 mg/L for longer-term exposures.

Reference:
Agency for Toxic Substances and Disease Registry (ATSDR). 2007. ToxFAQs™ for MTBE. Atlanta, GA: U.S. Department of Health and Human Services.