United States
Environmental Protection
Agency
Office Of Solid Waste And
Emergency Response
(5401G)
EPA 510-F-97-014
January 1998
www.epa.gov/OUST/
xvEPA
Office Of Underground Storage Tanks
MTBE
Fact Sheet #1
Overview
What Is MTBE?
Methyl tertiary-butyl ether (MTBE) is
a fuel additive made by combining
methanol and isobutylene. The meth-
anol is typically derived from natural gas;
isobutylene can be derived as a byproduct
of the petroleum refinery process. Since
1979, MTBE has been used in the United
States as an octane-enhancing
replacement for lead, pri-marily in mid-
and high-grade gasoline at concentrations
as high as 8 percent (by volume). Since
the middle of the 1980s, it has been
widely used through-out the country for
this purpose. It is also used as a fuel
oxygenate at higher concentrations (11 to
15 percent by volume) as part of the U.S.
EPA's programs to reduce ozone and
carbon monoxide levels in the most
polluted areas of the country.
MTBE And EPA's Clean
Air Program
The Oxygenated Fuel (Oxyfuel) and
Reformulated Gasoline (RFG) Programs
were initiated by the U.S. EPA in 1992
and 1995, respectively,
to meet requirements of the 1990
Clean Air Act Amendments (CAAA).
The Oxyfuel Program
The Oxyfuel Program requires 2.7-
percent oxygen (by weight) in gasoline
during fall and winter months to reduce
carbon monoxide emissions. In order to
meet this requirement, gasoline pro-
ducers must use oxygen containing
compounds termed "fuel oxygenates"
(e.g., ethanol, MTBE). When MTBE is
used to meet the Oxyfuel requirements, it
is added at a concentration of approx-
imately 15 percent (by volume) to
gasoline.
Although the total number of areas par-
ticipating in the Oxyfuel Program may
change from year to year, as of Novem-
ber 1997, the CAAA required 28 areas to
participate. Some of these areas also use
RFG in the non-winter months. The
Minneapolis-St. Paul area is the only area
to use Oxyfuel year round. The areas of
the country that use Oxy-fuel are
presented in Exhibit 1.
The RFG Program
The RFG Program requires 2-percent
oxygen (by weight) year round in the
most polluted metropolitan areas to re-
duce ozone and smog. When MTBE is
used to meet the RFG requirements, its
concentration in gasoline is 11 percent
(by volume).
January 1998
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Ten metropolitan areas are required by
the CAAA to use RFG (Baltimore,
Chicago, Hartford, Houston, Los
Angeles, Milwaukee, New York,
Philadelphia, Sacramento, San Diego).
Another 22 areas in 13 states and the
District of Columbia voluntarily par-
ticipate in the RFG Program (Arizona,
Connecticut, Delaware, Kentucky, Maine,
Maryland, Massachusetts, New
Hampshire, New Jersey, New York,
Rhode Island, Texas, and Virginia).
California has a separate statewide
program with more stringent standards
than the federal RFG program. As with
the Oxyfuel Program, the total number of
areas participating in the RFG Program
may change from year
to year. The areas of the country that use
RFG are shown in Exhibit 2.
Although more data need to be collected
to determine the specific benefits that
these programs have had on air quality,
the initial research has shown significant
reductions in carbon monoxide, ozone,
benzene, and other toxic air pollutants as
a result of the use of oxygenated fuels.
Why Is There Concern
About MTBE?
CERCLA ("Superfund") lists MTBE as
a hazardous substance. Although it is
known to be less toxic than many other
gasoline constituents, people have raised
concerns about the potential for acute
effects from inhaling it at service stations
and longer term effects from drinking
water contaminated with it. MTBE is
also considered a potential human
carcinogen.
In comparison to petroleum products,
MTBE poses additional problems when it
escapes into the environment through
gasoline releases; typically from under-
ground storage tank systems, above-
ground storage facilities, or pipelines.
MTBE is capable of traveling through
soil rapidly, is much more soluble in
water than most other petroleum consti-
tuents, and is more resistant to bio-
degradation. As a result, it often travels
farther than other gasoline constituents,
making it more likely to impact public
and private drinking water wells. Be-
cause of its affinity for water and, con-
sequently, its tendency to form large
plumes, petroleum releases with MTBE
can be more difficult and costly to
remediate than petroleum releases that do
not contain MTBE.
U.S. EPA Health Advisory
In December 1997, the U.S. EPA Office
of Water released Drinking Water
Advisory: Consumer Accepta-bility
Advice and Health Effects Analysis on
Methyl tertiary-Butyl Ether (MTBE)
EPA 822-F-97-008. The document is a
summary and interpre-tation of the latest
data on MTBE health effects and
organoleptic properties. It does not
impose any regulatory require-ments on
the providers of public drinking water;
instead, it recommends contaminant level
concentrations that would be acceptable
to most consumers of public drinking
water supplies.
The recommendations are based
primarily on taste and odor thresholds.
The Advisory states that drinking water
containing ". . . concentrations in the
range of 20 to 40 //g/L [ppb] would
likely avoid unpleasant taste and odor
effects .. ." for a large majority of
people. The document also notes that
there is a large variation in the
concentrations people are able to detect.
The various factors influencing detection
limits include individual sensitivities,
MTBE Fact Sheet #1: Overview
January 1998
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water quality, and water temperature. As
a result, some people may detect MTBE
below 20 ppb while others may not
notice it until levels exceed 100 ppb or
more.
The document also concludes that there is
little likelihood that MTBE concen-
trations between 20 and 40 ppb would
cause adverse health effects because the
concentration is 4 to 5 orders of magni-
tude lower than the lowest concentra-tion
that caused observable health effects in
animals. Specifically, con-centrations in
this range are about 20,000 to 100,000 or
more times lower than the range of
exposure levels in which cancer or
noncancer effects were observed in
rodent tests. This margin of exposure is
in the range of margins of exposure
typically provided for cancer effects in
drinking water standards and is greater
than such stan-dards typically provided
for noncancer effects.
After a thorough evaluation of all avail-
able health effect studies, the U.S. EPA
has determined that a lifetime exposure
health effects-based recommendation for
MTBE cannot be extrapolated from the
data at this time. Once additional studies
are completed that permit a justifiable
extrapolation for human exposure, the
current document will be replaced by a
final health advisory.
State Standards
Twenty-three states have established
regulatory guidelines or standards for
MTBE contamination in groundwater or
drinking water. These states are:
Arizona, Arkansas, California, Con-
necticut, Florida, Illinois, Indiana,
Kansas, Maine, Maryland, Massachu-
setts, Michigan, New Hampshire, New
Jersey, New Mexico, New York, North
Carolina, Pennsylvania, Rhode Island,
South Carolina, Vermont, Wisconsin, and
Wyoming. Cleanup levels range from 12
ppb in Wisconsin to 240 ppb in
Michigan; three states (Arkansas,
Indiana, and Maryland) have site-specific
guidelines.
January 1998
MTBE Fact Sheet #1: Overview
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MTBE Fact Sheet #1: Overview
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January 1998
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