6
POTENTIAL HEALTH EFFECTS OF OTHER POLLUTANTS

The HEI Oxygenates Evaluation Committee report identified three main areas of concern from MTBE exposure—including acute symptoms associated with short-term exposure, potential neurotoxicity, and potential carcinogenicity—but because of limited data little emphasis was given to other pollutants that may result from use of oxygenated fuels. Although the goal of the winter oxygenated-fuel program is to reduce ambient carbon monoxide (CO) pollution to protect public health, particularly patients with cardiovascular disease, who are most susceptible to the adverse effects of CO, at least two factors may limit the overall effectiveness of the program, including insufficient lowering of ambient CO with these fuels and an increase in other pollutants because of fuel oxygenates. The main conclusions in the HEI report regarding these two factors are as follows: "the health benefit of reducing CO is uncertain because of severe limitations in the information about the number of sensitive individuals with



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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels 6 POTENTIAL HEALTH EFFECTS OF OTHER POLLUTANTS The HEI Oxygenates Evaluation Committee report identified three main areas of concern from MTBE exposure—including acute symptoms associated with short-term exposure, potential neurotoxicity, and potential carcinogenicity—but because of limited data little emphasis was given to other pollutants that may result from use of oxygenated fuels. Although the goal of the winter oxygenated-fuel program is to reduce ambient carbon monoxide (CO) pollution to protect public health, particularly patients with cardiovascular disease, who are most susceptible to the adverse effects of CO, at least two factors may limit the overall effectiveness of the program, including insufficient lowering of ambient CO with these fuels and an increase in other pollutants because of fuel oxygenates. The main conclusions in the HEI report regarding these two factors are as follows: "the health benefit of reducing CO is uncertain because of severe limitations in the information about the number of sensitive individuals with

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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels coronary artery disease, their personal exposures to CO, and their activity patterns" (page 101); "the short-term symptoms reported with using MTBE are not unlike those sometimes reported after exposure to gasoline vapors or motor vehicle emissions from conventional gasoline" (page 101); and "our current understanding of the human effects from various carcinogens in motor vehicle emissions (including MTBE and those air toxics that have increased or decreased levels when oxygenates are used) is not sufficient to make confident predictions about whether using MTBE will cause any overall increase or decrease in the total carcinogenicity of emissions compared with using conventional gasoline. However, a substantial increase in carcinogenic risk from using gasoline containing MTBE or ethanol is not expected" (page 101). COMMITTEE CRITIQUE The literature review and conclusions of the HEI report concerning oxygenated fuels and their effect on other pollutants—including CO, benzene, 1,3-butadiene, formaldehyde, and acetaldehyde—provide a qualitative assessment of the limited information that is available. However, several statements require further detail and/or clarification. Because several data sources are available, the phrase "severe limitations in the information about the number of sensitive individuals with coronary artery disease" seems to overstate the problem. More emphasis needs to be placed on the emerging human data on air toxics and cancer (HEI report, page 94) in order to determine which animal models are relevant for human cancer risk assessment. A more comprehensive evaluation of the overall effects of oxygenated fuels on air quality is a major objective of a review being conducted by OSTP (HEI report, page 91). In addition, while the HEI report identified large gaps in our knowledge about the relationship between oxygenated fuels and

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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels their potential effects on ambient air pollution and health effects, specific research recommendations were not provided. The OSTP report Interagency Assessment of Potential Health Risks Associated with Oxygenated Gasoline did not address changes in air quality or potential health effects associated with other pollutants that may result from oxygenated fuels. These factors will be considered in the second phase of the review that is anticipated to be completed in mid-1996 (page iii). Thus, the committee agrees with the conclusion stated in the OSTP report (page 64) that the "continued use of oxygenated gasoline will require a continuing evaluation of potential health effects (short and long term) of the oxygenates, their metabolites, and any emission or atmospheric degradation products … such as t-butyl formate." In addition, the committee agrees with statements endorsed in the executive summary of the HEI report (page 4) concerning gaps in our knowledge about the health effects of MTBE and other pollutants from the use of oxygenated fuels. "In addition to its conclusions about possible health effects, the Oxygenates Evaluation Committee noted a general lesson to be learned from introducing oxygenates to the general public. Although it is not possible to have complete information about a substance before it is used, the diverse experiences after introducing oxygenated fuels argue strongly that any future new use of a substance should (1) be preceded by a sufficiently comprehensive research and testing program (including mechanistic and human studies), and (2) be accompanied by rigorous exposure assessment and epidemiologic studies." CONCLUSIONS Although the goal of the winter oxygenated-fuels program is to reduce ambient CO levels to protect public health, particularly

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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels among patients with cardiovascular disease, data are not available to evaluate the effectiveness of the program in protecting human health. RESEARCH NEEDS Because the goal of the winter oxygenated-fuel program is to lower ambient CO with the specific aim of reducing carboxyhemoglobin and risk for exacerbation of cardiovascular disease, a fundamental question that has to be addressed is how effective the program is in accomplishing these outcomes. While this question will be considered in a subsequent OSTP report (OSTP report, page iii), research recommendations and priorities about other pollutants are fundamental for a comprehensive evaluation of the oxygenated-fuel program. Specific research recommendations are presented below. CARBON MONOXIDE Epidemiologic studies to determine the effect of oxygenated fuels on population distributions of personal exposures to CO and/or of carboxyhemoglobin levels among patients with cardiovascular diseases. Epidemiologic studies of carboxyhemoglobin levels and risk for cardiovascular morbidity and mortality among patients with cardiovascular diseases. AIR TOXICS AND SHORT-TERM HEALTH EFFECTS Epidemiologic studies to determine exposures to air toxics that

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Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fuels   may produce short-term health effects from combustion of oxygenated fuels and conventional gasoline. Experimental studies to examine the potential irritant effects of aldehydes and other toxics at levels likely to be found from the combustion of oxygenated fuels and conventional gasoline under real-life conditions (e.g., low temperature). OTHERS Cost-effectiveness study of the winter oxygenated-fuel program using data from studies described in the recommendations above. Risk assessment using data from the recommendations described above.

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