Methyl Tertiary Butyl Ether (MTBE) Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Methyl tertiary butyl ether (MTBE) is a volatile, oxygen-containing hydrocarbon primarily used worldwide as an oxygenated fuel additive. Oxygenates are added to motor vehicle fuels to make them burn more cleanly, thereby reducing toxic tailpipe pollution, particularly carbon monoxide and volatile organic ozone precursors. Oxygenates are favored not only for their role in reducing combustion engine vehicle emissions, but also as octane boosters and volume extenders. The primary oxygenates are alcohols and ethers, including: fuel ethanol, MTBE, ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME).

Following the U.S. Environmental Protection Agency’s (EPA’s) approval of MTBE as a fuel additive in 1981, it became the oil refiner’s oxygenate of choice because its blending attributes include a high octane rating and gasoline miscibility, and it dilutes undesirable gasoline components such as benzene, a known human carcinogen, and sulfur. In 1988 the EPA extended the blending limit of MTBE in gasoline to 15 percent by volume (from 11 percent in 1981).

Worldwide MTBE usage grew in the early 1980s in response to octane demand resulting initially from the phaseout of lead from gasoline, and later from rising demand for premium gasoline. In the United States, the Federal Reformulated Gasoline (RFG) Program, established in the Clean Air Act Amendments of 1990 and implemented in 1995, required the use of RFG in cities with high levels of ground level ozone.

About 30 percent of gasoline sold in the United States is RFG, and it is currently used in 17 states and the District of Columbia. The RFG program stimulated a threefold increase in MTBE production from 83,000 barrels a day in 1990 to 269,000 barrels a day by 1997.

Worldwide, the United States is easily the largest consumer of MTBE at 12 million tons per year (Mtpy); followed by Europe and the former Soviet Union at 4 Mtpy; Asia Pacific at 3 Mtpy; South America at 1 Mtpy; and Africa and the Middle East at under 0.5 Mtpy.

Although MTBE has provided important health benefits in terms of reduced hazardous air pollutants, the increasing detection of MTBE in ground waters and reservoirs due to leaking underground storage tanks and pipelines, spills, and recreational water craft is cause for concern. MTBE is highly soluble in water and does not biodegrade easily. There is no human data on the health effects of drinking MTBE, although data have been collected to provide the risk assessment process with pharmacokinetic information relevant to the most common human exposures-through air and drinking water.

Studies with rats and mice suggest that drinking MTBE may cause gastrointestinal irritation, liver and kidney damage, and nervous system effects. There is no evidence that MTBE causes cancer in humans.

Two studies with rats found that breathing high levels of MTBE for long periods may cause kidney and liver cancer. The U.S. Department of Health and Human Services, the International Agency for Research on Cancer, and the EPA have not yet classified MTBE as to its carcinogenicity.

Because of the widespread presence of MTBE in water supplies, the EPA formed the Blue Ribbon Panel on Oxygenates in Gasoline. In 1999 the Panel recommended the following: (1) Reduce the use of MTBE substantially, (2) have Congress clarify federal and state authority to regulate and/or eliminate the use of gasoline additives that threaten drinking water supplies, and (3) eliminate the current Clean Air Act requirement of 2 percent oxygen, by weight, in RFG.

Several U.S. states have enacted bans on using MTBE in gasoline, including California, New York, Illinois, and Ohio; many others have limited the content of MTBE in gasoline to less than 1.0 percent by volume. Ethanol is projected as the likely oxygenate alternative, although its higher volatility makes it more difficult for refiners to meet emissions standards. However, the same volume of ethanol contains almost twice as much oxygen as MTBE, so only about half as much is needed to meet the RFG requirements.

Bibliography:

Environmental Protection Agency, The Blue Ribbon Panel on Oxygenates in Gasoline, Executive Summary and Recommendations, July 27, 1999;
J. Prah et , “Dermal, Oral, and Inhalation Pharmacokinetics of Methyl Tertiary Butyl Ether (MTBE) in Human Volunteers,” Toxicological Sciences (v. 77/2, 2004).