I
INTRODUCTION

The Clean Air Act Amendments of 1990 mandated the use of fuels with higher oxygen content (at least 2.7% by weight) in several areas of the country that are in nonattainment with the National Ambient Air Quality Standards (NAAQS) for carbon monoxide (CO). The use of such oxygenated fuels is intended to reduce CO emissions from motor vehicles during the winter months, when lower temperatures tend to cause vehicles to emit more CO. Increased ambient concentrations of CO are a particular concern for people with cardiovascular disease. In this report, ''oxygenated fuels" is intended to refer only to the fuels used within the winter oxygenated-fuels program.

Methyl tertiary-butyl ether (MTBE) has become the most widely used motor vehicle fuel oxygenate in the United States. Typically, MTBE-oxygenated gasoline contains approximately 15% MTBE by volume. Other compounds used as oxygenates in gasoline include ethanol (which is the dominant oxygenate in some areas), tertiary-butyl alcohol, ethyl-tertiary-butyl ether, and tertiary-amyl-methyl ether.

Since the 1970s, MTBE has been added to motor-vehicle fuels as



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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels I INTRODUCTION The Clean Air Act Amendments of 1990 mandated the use of fuels with higher oxygen content (at least 2.7% by weight) in several areas of the country that are in nonattainment with the National Ambient Air Quality Standards (NAAQS) for carbon monoxide (CO). The use of such oxygenated fuels is intended to reduce CO emissions from motor vehicles during the winter months, when lower temperatures tend to cause vehicles to emit more CO. Increased ambient concentrations of CO are a particular concern for people with cardiovascular disease. In this report, ''oxygenated fuels" is intended to refer only to the fuels used within the winter oxygenated-fuels program. Methyl tertiary-butyl ether (MTBE) has become the most widely used motor vehicle fuel oxygenate in the United States. Typically, MTBE-oxygenated gasoline contains approximately 15% MTBE by volume. Other compounds used as oxygenates in gasoline include ethanol (which is the dominant oxygenate in some areas), tertiary-butyl alcohol, ethyl-tertiary-butyl ether, and tertiary-amyl-methyl ether. Since the 1970s, MTBE has been added to motor-vehicle fuels as

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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels an octane booster, in concentrations of less than 1% by volume in regular gasoline and 2% to 9% by volume in premium gasoline (USEPA, 1993). The dilution of gasoline with MTBE reduces certain other organic compounds (e.g., benzene) in gasoline. The intended result for motor vehicle emissions is decreased amounts of CO and of some toxic air pollutants. However, increased amounts of MTBE and byproducts, such as formaldehyde, are also emitted. Concurrently with the start of the federal oxygenated-gasoline program in 1992, MTBE has been implicated in complaints of headaches, coughs, and nausea, principally in Alaska, but also in Montana, New Jersey, and Wisconsin. There have also been anecdotal reports of reduced fuel economy in some locations and questions about engine performance. Additional concerns have been raised about the detection of low levels of MTBE in some samples of groundwater. Also, use of oxygenated fuel has increased costs of gasoline at the pump by several cents per gallon. Due to the heightened public concern over the potential health effects of MTBE-oxygenated fuels, scientific studies costing more than $2 million have been conducted by EPA and others, in order to investigate the reported symptoms. These studies included both experimental human studies with pure MTBE and epidemiologic studies of MTBE mixed with gasoline. As of this date, the reported symptoms have not been explained or reproduced experimentally. However, due to the widespread pattern of exposure, the possibility of susceptible subpopulations, and reports of other noncancer effects, EPA has also concluded that more research and testing are required to better understand the comparative risks of different fuels. In its continuing efforts to evaluate the toxicological effects and benefits of oxygenated gasoline, EPA asked the National Research Council to conduct a brief study to review a draft interagency report from the federal government, prepared under the direction

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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels of 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). INTERAGENCY REPORT The Interagency Oxygenated Fuels Assessment draft report was prepared by a working group comprising technical and scientific experts from several federal agencies, as well as representatives from state government, industry, and environmental groups (Interagency Report, 1996). The draft interagency report was provided to the committee on March 15, 1996. (The preface and executive summary of the interagency report are presented in Appendix A.) The interagency report discusses MTBE to a much greater degree than other oxygenates. The scientific literature reviewed by the authors included published, peer-reviewed literature; unpublished reports from a number of sources, including industry, government agencies, and scientists; and personal communications. The potential health effects of oxygenated gasoline were evaluated in three separate documents, which made up the health effects section of the interagency report. The three documents are the following: A report from the Health Effects Institute (HEI) Oxygenates Evaluation Committee, The Potential Health Effects of Oxygenates Added to Gasoline: A Review of the Current Literature (February 1996), referred to as the HEI report;  A report from CENR and the Interagency Oxygenated Fuels Assessment Steering Committee, Interagency Assessment of Potential Health Risks Associated with Oxygenated Gasoline (February 1996), referred to as the OSTP report; and

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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels A memorandum from the Centers for Disease Control and Prevention (CDC) signed by Richard J. Jackson and directed to the Interagency Oxygenated Fuels Assessment Steering Committee, dated March 12, 1996 (referred to as the CDC white paper), which compared and contrasted the other two reports. The interagency report also included documents addressing air quality (Howard et al., 1996), water quality (Zogorski et al., 1996), and fuel economy and engine performance. Each of the chapters in the interagency report underwent extensive external peer review prior to the submission of the entire report for review by the National Research Council. The draft interagency report will be revised in response to the findings and recommendations of the National Research Council (Robert Watson, OSTP, April 1, 1996, personal communication). CHARGE TO THE NATIONAL RESEARCH COUNCIL COMMITTEE In response to EPA's request, the National Research Council convened a multidisciplinary committee—the Committee on Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels. The committee was charged with the following tasks: (1) review the draft interagency report on the potential toxicological effects of MTBE and other oxygenates and compare such effects and multimedia exposures with those of conventional gasoline; (2) review the draft interagency report on the impacts of MTBE and other oxygenates on vehicle emissions, air pollution, fuel economy, and engine performance and compare such impacts with those of conventional gasoline; and (3) identify priorities for research to fill data gaps. The committee was asked to focus on the interagency report,

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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels which dealt exclusively with the winter oxygenated-fuels program. The interagency report did not specifically examine the reformulated gasoline program, which is intended to reduce motor-vehicle emissions that lead to increased ozone concentrations in the lower atmosphere. Thus, the committee did not address the reformulated-fuels program. Also, the committee was not charged to assess the costs and benefits of the oxygenated-fuels program. COMMITTEE APPROACH The committee members were provided with the six draft documents described previously prior to their only meeting. A full and complete critique of scientific credibility, comprehensiveness, and internal consistency of the data was not possible within the short time-frame of this study. In general, the committee responded to its charge by first summarizing critical aspects of the interagency report upon which its critique was based. The committee's critique was followed by recommendations for future research. STRUCTURE OF THE REPORT The results of the committee's deliberations are found in the chapters of this report. Chapter 2 is a critique of sections of the interagency report related to air quality, fuel economy, and engine performance. Chapter 3 and Chapter 4 critique water-quality and exposure-assessment discussions of the interagency report, respectively. In Chapter 5, the report evaluates the federal government's assessment of the potential health effects of exposure to oxygenates, as presented in three reports (the HEI report, OSTP report, and the CDC white paper) contained in the interagency

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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels report. Chapter 6 evaluates the potential health effects of other pollutants resulting from the combustion of oxygenated fuels and conventional gasoline. Chapter 7, the final chapter, provides the committee critique of the approaches to the assessment of human health risk adopted in the HEI and OSTP reports. It should be noted that each chapter provides recommendations for research efforts.