Methyl Tert-Butyl Ether (MTBE)
Also known as: Methyl t-butyl ether, MTBE, Tert-butyl methyl ether,
Chemical reference number (CAS): 1634-04-4
What is MTBE?
MTBE is a gasoline additive with a very strong odor. By adding chemicals like MTBE,
engines produce less carbon monoxide and other carbon-containing air pollutants by burning
this "reformulated" gasoline. In cities where air quality is a problem,
reformulated gasoline may contain up to 15% MTBE.
MTBE dissolves easily in water and also evaporates quickly. If its spilled, MTBE
will evaporate quickly. However, if MTBE is spilled on soil, some of it can seep into
groundwater where it can remain unchanged for many years.
When underground storage tanks leak, MTBE may be one of the first chemicals to show up
in area drinking water wells. Most people can smell MTBE in contaminated water at levels
as low as 100 parts per billion (ppb).
How are people exposed to MTBE?
Breathing: Exposure to MTBE can occur when people fill gas cans or
automobiles with gasoline. You should avoid breathing gasoline vapors while refueling. We
suggest you store gasoline in a tightly sealed container, and place the container away
from your home in a locked storage shed so vapors cannot enter your home.
People can also be exposed to MTBE when they breathe engine exhaust. When drinking
water is contaminated, people can inhale MTBE as they bathe or do laundry.
Drinking/Eating: Low level exposure can happen when contaminated water
is used for drinking and/or for food preparation.
Touching: MTBE can be absorbed through skin when people handle
gasoline, contaminated soil, or water. Skin contact is most likely to happen as people
fill their tanks with gasoline. As you refuel engines, avoid spilling gasoline on your
clothing or skin.
Do standards exist for regulating MTBE?
Air: No standards exist for regulating the amount of MTBE
allowed in the air of homes. However, the Wisconsin Department of Natural
Resources (DNR) has set a residential indoor air action level for MTBE at 26
parts per billion by volume (ppbv). The action level is considered to be
protective of public health. Breathing MTBE for a lifetime at 26 ppbv is
very unlikely to be harmful to people. If MTBE concentrations in air are
above the action level, we recommend taking an action to halt exposure.
The Wisconsin Department of Natural Resources regulates the amount of MTBE
that can be released into outdoor ambient air by industries.
Water: The Wisconsin groundwater standard for MTBE is 60 parts per
billion (ppb). We suggest you stop drinking water containing more than 60 ppb of MTBE. If
levels of MTBE are very high in your water, you may need to avoid washing, bathing or
using the water for other purposes. Contact your local public health agency for more
information specific to your situation.
Will exposure to MTBE result in harmful health effects?
Although the following symptoms are associated with MTBE, gasoline contains other
ingredients that may cause similar health effects.
Immediately or shortly after exposure to MTBE (at levels similar to when you fill your
car with gasoline) people may experience irritation of the eyes, nose and throat, and
headache or dizziness. Some of these symptoms may result from the bad odor of the
chemical. At even higher levels (in industrial settings) people can feel drunk, have
trouble breathing and lose coordination.
Currently, the effects on humans of long-term exposure to low levels of MTBE are
unknown. The following are results of studies using laboratory animals:
Organ Systems: When fed high doses of MTBE, some laboratory animals
lost weight and developed liver and kidney problems.
Cancer: When exposed to high levels of MTBE over a long period of
time, some laboratory animals developed kidney tumors, testicular tumors, lymphoma and
Reproductive Effects: Its not known whether MTBE exposure can
affect fertility or pregnancy.
In general, chemicals affect the same organ systems in all people who are exposed.
However, the seriousness of the effects may vary from person to person. A person's
reaction depends on several things, including individual health, heredity, previous
exposure to chemicals including medicines, and personal habits such as smoking or
It is also important to consider the length of exposure to the chemical; the amount of
chemical exposure; and whether the chemical was inhaled, touched, or eaten.
Ca a medical test determine exposure to MTBE?
Because it leaves the body quickly, MTBE and its breakdown product, "butyl
alcohol," can only be measured in exhaled breath, urine, and blood for 1-2 days after
exposure. Doctors can use function tests of the nervous system, kidneys, or liver to track
the long-term health of people regularly exposed to MTBE at work.
Seek medical advice if you have any symptoms that you think may be related to chemical
(P-44737 Revised 05/2012)
This fact sheet summarizes information about this chemical and is not a complete
listing of all possible effects. It does not refer to work exposure or emergency
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