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
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