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Environmental Assessment


MTBE and fuel oxygenates have been the subject of health risk assessments and research strategies prepared by the National Center for Environmental Assessment (NCEA)

Oxygenates, including MTBE, have been under consideration by NCEA since the late 1980s, beginning with the Alternative Fuels Research Strategy (1992), which was intended to lay a foundation for developing the scientific information needed to compare the benefits and risks of various fuels and fuel additives, including MTBE and ETBE, to those of conventional gasoline and diesel fuels.

As symptom reports of acute illness (e.g., headache, nausea, eye irritation) began to occur in late 1992 with the introduction of oxygenated fuels in certain areas of the United States that were not meeting the national ambient air quality standard (NAAQS) for carbon monoxide, efforts were mounted to investigate further the possible toxic effects of MTBE vapors when inhaled. Several studies were initiated to investigate these effects. These and other studies were reported at a conference organized by NCEA: Proceedings of the "Conference on MTBE and Other Oxygenates: A Research Update", Falls Church, Virginia, July 26-28, 1993.

The interpretation and integration of research results in a risk assessment was accomplished by NCEA in the Assessment of Potential Health Risks of Gasoline Oxygenated with MTBE (1993), which was updated and presented for a broader audience in Health Risk Perspectives on Fuel Oxygenates (1994). Part of this assessment effort included the derivation of an inhalation reference concentration (RfC) for MTBE, which is defined as an estimate (with uncertainty spanning about an order of magnitude) of a continuous inhalation exposure level for the human population (including sensitive subpopulations) that is likely to be without appreciable risk of deleterious noncancer effects during a lifetime. More information on the RfC for MTBE may be found in the Agency's IRIS database.

As the issues surrounding oxygenated and reformulated fuels (oxyfuels), particularly the possible inhalation toxicity of MTBE, continued to raise concerns, NCEA coordinated the development of Oxyfuels Information Needs (1996) to identify areas of needed research and data generation to support quantitative risk assessment efforts related to oxygenates.

To address public concerns and to take full advantage of the expertise within and outside the Federal Government, the Office of Science and Technology Policy (OSTP), through the Committee on Environment and Natural Resources (CENR) of the President's National Science and Technology Council (NSTC), was asked by EPA to coordinate preparation of the Interagency Assessment of Oxygenated Fuels (1997), a comprehensive assessment of the issues surrounding the use of oxygenated gasoline. The interagency working group that focused on "Potential Health Effects of Oxygenated Gasoline" (Chapter Four) included representatives from NCEA.

EPA's Office of Water developed non-regulatory guidance on levels of MTBE contamination that would affect the taste and odor of drinking water and hence its acceptability to consumers. This guidance is called Drinking Water Advisory: Consumer Acceptability Advice and Health Effects Analysis on Methyl Tertiary-Butyl Ether (MtBE). The document includes an evaluation of potential health effects related to MTBE.

Key issues related to assessing and managing the potential health and environmental risks of oxygenate contamination of water are identified in Oxygenates in Water: Critical Information and Research Needs (1998). This document focuses on the most critical and immediate needs to be addressed in support of risk assessment and risk management efforts related to oxygenates in water.

To EPA's Main MTBE page

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