The Debate and Fate of MTBE

Do the risks outweigh the benefits? That’s the debate swirling around the gasoline additive methyl tertiary-butyl ether, better known by its acronym: MTBE. The proven benefit of the addition of MTBE to gasoline is the substantially improved tailpipe emission quality from automobiles. The risks are the presumed environmental problems caused by the presence of MTBE in ground- and surface waters that arise from fugitive releases of gasoline near retail gasoline filling stations, at bulk fuel storage facilities, or even from discharge of uncombusted gasoline by engine-powered watercraft. How, exactly, did this debate begin?

As the Environmental Protection Agency (EPA) mandated the lowering and eventual removal of lead from automotive gasolines, new classes of octane-boosting additives, with less presumed negative impacts than organic lead, were being developed and used in increasing frequency to improve gasoline performance. The additives included a variety of alcohols and ethers. In the 1980s when the need to reduce automobile tailpipe emissions became more obvious, alcohols and ethers proved even more beneficial. These additives introduced additional oxygen into the gasoline that increased combustion efficiency which, in turn, reduced carbon monoxide (CO) emissions from automobiles. As a result, the use of these oxygen-containing compounds in gasoline formulations increased markedly throughout the 1980s and 1990s.

In the early to mid ’90s, increasing reports of low-levels of MTBE in groundwater (arising primarily from leaking underground storage tanks) raised concerns about the chemical’s long-term aesthetic, ecological, and human health impacts. The unique physical and chemical properties of the compound, coupled with its significant environmental recalcitrance, suggested that MTBE would partition from gasoline-hydrocarbons and have the potential to move relatively quickly in groundwater and surface waters. In 1997, EPA issued a Drinking Water Advisory indicating that concentrations of MTBE in the range of 20 to 40 ppb or below in water would not cause unpleasant taste and odor for most people. In this same advisory, EPA also reviewed information on health effects of MTBE, and stated there was little likelihood that MTBE between 20 and 40 ppb in drinking water would cause negative health effects to consumers of water. Even in the face of these findings, a number of states and the federal government have or are considering banning future use of MTBE.

In the United States, tremendous research efforts in the areas of fate and transport, remediation, and human health effects of MTBE in groundwater and surface water have been undertaken in the last few years. Battelle scientists have been deeply involved in many aspects of applied MTBE research and site investigation, including:

• developing improved analytical methods for the measurement of MTBE and related gasoline compounds in environmental media;
• investigating and demonstrating natural and enhanced in situ bioremediation of MTBE in the environment;
• conducting risk assessments of exposure to MTBE, in particular an EPA-sponsored study to determine dermal and inhalation exposure to the fuel additive;
• conducting multi-media fate and transport modeling of MTBE; and
• carrying out detailed investigations into the occurrence and fate of MTBE at complex sites.

For more information, please contact Dr. Paul Boehm, (781) 895-4862, boehmp@battelle.org.