US EPA

Oxygenates (e.g., methyl tertiary butyl ether [MTBE], ethanol) are required in gasoline in certain areas of the United Stated by the 1990 Clean Air Act Amendments and have also been used to increase gasoline octane since the 1970s. With the introduction of major new fuel programs requiring oxygenates in 1992 and 1995, complaints of health symptoms from inhalation exposure to oxygenated fuels and or their by- products were registered in some locales. More recently, concerns have arisen about contamination of water resources through oxygenated gasoline releases from leaking underground storage tanks and other sources. No nationwide characterization of oxygenate contamination of ground, surface, or drinking water exists, but the potential for multimedia exposure to oxygenates exists. Attention has intended to focus on MTBE in part because of its distinctive chemical properties. Sensory thresholds for MTBE have been measured at 24 - 135 ug/L for taste and 15 - 180 ug/L for odor. EPA has issued a Drinking Water Advisory of 20 - 40 ug/L MTBE based on taste and odor acceptability to consumers. However, no studies have described population distributions of these thresholds, and it cannot be presumed that exposure will necessarily be avoided because of the taste or odor of oxygenates. Health effects data are available on the toxicity of inhaled MTBE in laboratory animals and humans, but no data exist on ingested oxygenates (except ethanol) in humans. Because of the limited data on the toxicity of ingested MTBE, no EPA Health Advisory or oral reference dose (RfD) has been derived for MTBE. Among the issues that complicate the evaluation of the carcinogenic effects of MTBE are the role of alpha-2u-micro-globulin, the presence of concurrent toxicity , the relationship between mostly high dose effects in animals and low environmental exposure levels, and the relevance of oil-gavage and inhalation data to drinking water exposures. Evaluations of the toxicity of MTBE by various organizations have come to mixed conclusions. A pressing need exists to complete pharmacokinetic modeling and cancer mechanistic studies of MTBE, which would allow extrapolation from inhalation data to estimate oral toxicity risk. A sub-chronic study of MTBE in drinking water is also needed to evaluate oral toxicity and help validate the extrapolation from inhalation to ingestion. Filling these needs will enhance risk assessment and risk management efforts related to oxygenated fuels.

Davis, J. An Overview Of Health Issues For Fuel Oxygenates. Presented at ASTSWMO Symposium, September 1999.