Causality assessment of the acute health complaints reported in association with oxygenated fuels

In some areas where oxygenated fuel programs have been implemented, there have been widespread complaints of non-specific health effects attributed to the gasoline. There are a number of hypotheses that can account for this apparent association. This paper examines the hypothesis that the use of oxy-fuel (either oxygenated gasoline or reformulated gasoline) results in exposure of the general population to one or more chemicals at concentrations that cause toxicologic injury. Although several oxygenates can be used in oxy-fuels, this analysis focuses on MTBE because it is the most widely used oxygenate and because the database of relevant toxicologic data is greatest for this oxygenate. The causal assessment is based on an evaluation of the qualitative and quantitative plausibility that oxygenated fuel-related exposures have toxicological effects, and the epidemiologic studies that directly test the hypothesis that the use of oxygenated fuels causes adverse health effects. The plausibility that chemical exposures related to oxy-fuel use cause toxicological effects is very low. This determination is based on consideration of the exposure-response and time-action profiles for relevant toxicological effects of MTBE in animals, experimental MTBE exposure studies in humans, and the possibility that the addition of MTBE to gasoline results in toxicologically significant qualitative and/or quantitative changes in gasoline-related exposures. Similarly, the epidemiologic studies of oxy-fuel exposed cohorts do not support a causal relationship between oxy-fuel use and adverse health effects. Although the data are insufficient to rule the possibility of unique sensitivity in a small segment of the population, the strength of the evidence and the availability of other more plausible explanations for the health complaints reported in association with oxy-fuels support a high degree of confidence in the conclusion that MTBE-containing oxygenated fuels are not the cause of acute toxicity in the general population.