Note: EPA no longer updates this information, but it may be useful as a reference or resource. At the same time, Congress also instituted a renewable fuel standard. In response, refiners made a wholesale switch removing MTBE and blending fuel with ethanol. A similar decrease in MTBE use has also been observed in conventional gasoline areas. MTBE methyl tertiary-butyl ether is a chemical compound that is manufactured by the chemical reaction of methanol and isobutylene.
MTBE is produced in very large quantities over , barrels per day in the U. It is one of a group of chemicals commonly known as "oxygenates" because they raise the oxygen content of gasoline. For example, it is much harder and more expensive to remove MTBE from drinking water than it is to remove other organic components of gasoline. Interstate Technology Regulatory Council Fuel Oxygenates D.
Barcelo ed. Springer, New York. Contains papers on the characterization, chemistry, and behavior in the subsurface of fuel oxygenates, primarily MTBE, as well as information on the occurrence of MTBE and other fuel oxygenates in source water and drinking water of the United States.
New molecular tools are reported for assessing the biodegradability of oxygenates by microflora from MTBE-contaminated sites, as is compound-specific isotope analysis to characterize degradation pathways and to quantify in situ degradation of fuel oxygenates and other fuel-derived contaminants. Skip directly to site content Skip directly to page options Skip directly to A-Z link. National Biomonitoring Program.
Section Navigation. Facebook Twitter LinkedIn Syndicate. Minus Related Pages. These "opt-in" areas may opt out of the program by substituting other control measures achieving the necessary reductions in emissions. Also, MTBE has been used since the late s in gasoline as an octane enhancer. MTBE use grew rapidly in the s, as it replaced lead in gasoline and was used in premium fuels.
State and local environmental agencies and EPA attribute marked improvements in air quality to the use of fuels containing MTBE and other oxygenates, but the exact role of oxygenates in achieving these improvements is subject to debate. Whether the oxygenates themselves should be given credit for these improvements has been the subject of debate, with the answer depending to some extent on what one assumes would replace the oxygenates if they were removed.
Asked to look at the ozone-forming potential of different oxygenates used in reformulated gasoline, a National Academy of Sciences panel concluded that "the addition of commonly available oxygenates to RFG is likely to have little air-quality impact in terms of ozone reduction.
Less controversy exists regarding oxygenates' role in reducing carbon monoxide emissions. EPA also "believes that the reductions estimated in air quality studies are significant and that these reductions help to protect the public from the adverse health effects associated with high levels of CO in the air. The improvements in measured air quality have not come without questions. Some complaints centered around the use of MTBE in cold weather; two of the principal areas noting complaints were Alaska and Milwaukee, Wisconsin.
The Interagency Task Force examined these complaints and concluded:. Additional health effects research is being conducted by EPA, universities, and others.
Under the authority of Section of the Clean Air Act, EPA has requested refiners to conduct health effects studies on conventional, reformulated, and oxygenated particularly MTBE-oxygenated gasoline. These studies examine health effects associated with the inhalation of evaporative emissions, and several are near completion. Very little research has been done to assess the potential health risks associated with exposure to MTBE in drinking water ingestion.
Much discussion has centered on whether MTBE has the potential to cause cancer. Also, one metabolite of MTBE formaldehyde is considered a probable human carcinogen, and another metabolite tertiary butyl alcohol TBA induces male rat kidney tumors.
Based on animal studies, EPA has concluded that MTBE poses a potential for carcinogenicity to humans at high doses; however, because of uncertainties and limitations in the data, EPA has been unable to make a confident estimation of risk at low exposure levels.
The IARC noted that MTBE was "not classifiable as to its carcinogenicity in humans," based on inadequate evidence in humans and limited evidence in experimental animals. Regarding noncancer effects, a California advisory committee determined that there was not clear scientific evidence to support listing MTBE as a toxic substance affecting human development or reproduction.
In reviewing the research on cancer and noncancer effects, these groups generally noted that research gaps exist, and that the data were particularly limited on health effects associated with MTBE ingestion.
In response to the need for research to evaluate the potential health risks from exposure to MTBE and other oxygenates in drinking water, EPA in published a document that identified the most critical and immediate research needs. The document was intended to serve as a guide to planning future research; however, EPA has not pursued research to address the needs identified in this document.
For practical purposes, the interpretation of any health risks associated with the addition of MTBE to gasoline could benefit from a comparison to the health risks associated with conventional gasoline. The Interagency Task Force, EPA, and some environmental groups have all argued that current knowledge suggests that MTBE is a less serious pollutant than the gasoline components it replaced. According to the OSTP report, the cancer risk from exposure to MTBE is "substantially less than that for benzene, a minor constituent of gasoline that is classified as a known human carcinogen; and more than times less than that for 1,3-butadiene, a carcinogenic emission product of incomplete fuel combustion.
A major issue regarding the use of MTBE concerns its detection in ground water at thousands of locations nationwide, and, usually at low levels, in various municipal drinking water supplies, private wells, and reservoirs. Although MTBE has provided air quality benefits, the inclusion of MTBE in gasoline has been a growing concern as an environmental risk since the s, for several reasons.
Specifically, compared to other gasoline components, MTBE 1 is much more soluble in water, 2 has a lower taste and odor threshold, 3 has a higher transport rate, and 4 often requires more time to be remediated and must be treated by more complicated and expensive treatment technologies.
Once in ground water, it is slow to biodegrade and is more persistent than other gasoline-related compounds. In surface water, it dissipates more rapidly.
Studies show that most of it evaporates from the upper levels of surface water in a few weeks, while it persists longer at greater depths. Other significant sources include leaking above-ground storage tanks, fuel pipelines, refueling facilities, and accidental spills.
The most significant source of MTBE in lakes and reservoirs appears to be exhaust from motorized watercraft, while smaller sources include gasoline spills, runoff, and ground water flow. Available information on the occurrence of MTBE in public drinking water supplies has increased substantially in recent years, but has been somewhat limited geographically.
Although a number of serious contamination incidents have been reported, particularly in California, the available data generally do not indicate a broad presence of MTBE in drinking water supplies at levels of public health concern. However, as monitoring has increased among the states, so has the number of public water systems and private wells showing low-level detections of MTBE.
Through April , some 2, systems had tested 9, sources of drinking water. MTBE was detected in 85 0. Overall, 53 1. As of October , monitoring results had been reported for 13, sources. Nearly all of these results were nondetections, while sources had two or more MTBE detections. Nationwide, the data on the presence of MTBE in drinking water have been more limited.
Most MTBE concentrations ranged from 0. This survey monitored sources of drinking water for randomly selected community water systems including samples from groundwater-supplied systems and samples from surface-water-supplied systems. MTBE was found in 8. The researchers found MTBE in Looking at ground water generally not only drinking water wells , the data indicate that low levels of MTBE are found often.
In all, MTBE was detected in ground water in 22 of the 42 states. The California Environmental Protection Agency has estimated that, based on monitoring information available for these sites, MTBE can be expected to be found in shallow, unused ground water at thousands of UST sites in the state, and often at high concentrations in the parts per million range.
Safe Drinking Water Act Initiatives. In December , the agency issued a drinking water advisory for MTBE based on consumer acceptability for taste and smell. EPA issues drinking water advisories to provide information on contaminants in drinking water that have not been regulated under SDWA.
Specifically, the advisory states that. Compounds on the contaminant candidate list are categorized as regulatory determination priorities, research priorities, or occurrence priorities. Thus, while EPA has not selected MTBE for regulation to date, the agency is pursuing research to fill the existing data gaps so that a regulatory determination may be made.
The Safe Drinking Water Act also directed EPA to publish a rule by August requiring public water systems to conduct monitoring for a list of unregulated contaminants that may require regulation. The occurrence data generated under the Unregulated Contaminant Monitoring Rule, combined with the results of ongoing health effects studies, are intended to provide information needed by EPA to make a regulatory determination for MTBE.
Under SDWA, the next round of regulatory determinations will be made in EPA typically requires roughly three and one-half years to promulgate a drinking water regulation; thus, the earliest EPA would be expected to issue a drinking water regulation for MTBE is Underground Storage Tank Regulation.
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