ABSTRACT

In the United States a debate is raging over the environmental consequences of the increased use of methyl tertiary-butyl ether (MTBE). Originally used as an antiknock agent for gasoline, this chemical is being used at concentrations of up to 10% (by weight) in the United States, and it is an oxygen source to improve gasoline combustion and hence reduce pollution from car exhausts. The controversy started with a report submitted in November 1998 by the University of California (UC Davis), on Health and Environmental Assessment of MTBE to the State of California. This study was authorized by the California Senate to assess a variety of issues and public concerns associated with the use of MTBE in gasoline. According to this report, MTBE and other oxygenates were found to have no significant effect on exhaust emissions from advancedtechnology vehicles. There is no significant difference in the emissions reduction of benzene between oxygenated and nonoxygenated fuels. Thus, there is no significant additional air quality benefit to the use of oxygenates such as MTBE in reformulated gasoline (RFG), relative to alternative nonoxygenated formulations. There are significant risks and costs associated with water contamination due to the use of MTBE. MTBE is highly soluble in water and will transfer readily to groundwater from gasoline leaking from underground storage tanks, pipelines, and other components of the gasoline distribution system. In addition, the use of gasoline containing MTBE in motor boats results in the contamination of surface water reservoirs. It was stated in the report that the limited water resources in United States are at risk by using MTBE. If MTBE continues to be used at current levels and more sources become contaminated, the potential for regional degradation of water resources, especially groundwater basins, will increase. Severity of water shortages during drought years will be exacerbated. The UC Davis report recommended the phasing out of MTBE over an interval of several years, and that the refiners should be given flexibility to achieve air quality objectives by modifying the specifications to allow wide-scale production of nonoxygenated reformulated gasoline.