US EPA

Despite the ubiquity of gasoline for several decades and more recent modifications in fuel formulations to achieve “cleaner” gasoline, a quantitative comparative assessment of the health risks related to these fuels remains to be performed. Under authority of Clean Air Act section 211(b), EPA has required manufacturers of certain oxygenates, including methyl tertiary butyl ether (MTBE) and other ethers and alcohols, to conduct toxicity studies on mixtures of individual oxygenates in gasoline, as well as baseline gasoline alone. Because more extensive testing (e.g., 2-year inhalation bioassays) was required for baseline gasoline and MTBE-gasoline than for the other oxyfuels, a direct quantitative comparison of the health effects of these fuels should be possible. In addition, studies comparing personal exposure levels to fuels and fuel by-products in cities using either non-oxygenated or oxygenated gasoline were required under CAA 211(b). Based on these and other data, a comparative risk characterization is planned for these fuels because of their national and international significance.

Although questions have long been raised about potential health effects associated with MTBE in gasoline, data have not been available to directly compare MTBE-gasoline with non-oxygenated gasoline. As information on the health effects and exposure levels related to these fuels becomes available from CAA 211(b) testing and other sources, it should be feasible to perform direct, quantitative, comparative health risk characterizations of baseline gasoline and MTBE-gasoline. This comparative assessment is expected to be used by OAR and possibly other program offices in evaluating and developing policies related to fuels and fuel additives. In addition, data on other oxygenate-gasoline mixtures, including ethanol-gasoline, will be evaluated to determine whether more extensive testing may be warranted for any of these oxyfuels.