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ACUTE BEHAVORIAL EFFECTS FROM EXPOSURE TO TWO-STROKE ENGINE EXHAUST
Benignus, V A. AND P J. Bushnell. ACUTE BEHAVORIAL EFFECTS FROM EXPOSURE TO TWO-STROKE ENGINE EXHAUST. Presented at Air Toxics Planning Meeting, Research Triangle Park, NC, June 11-12, 2002.
Benefits of changing from two-stroke to four-stroke engines (and other remedial requirements) can be evaluated (monetized) from the standpoint of acute behavioral effects of human exposure to exhaust from these engines. The monetization process depends upon estimates of the magnitude of the effects of such exposures in realistic situations. The present effort is to provide such estimates for two of the exhaust components, toluene and carbon monoxide (CO).
Quantitative estimates of acute effects of toluene dose-effect curves were made by meta analyses of the human experimental exposure literature. A physiologically-based pharmacokinetic (PBPK) model was used to estimate internal dose for each exposure scenario. Endpoints were transformed to a common scale. A logit curve was fitted to the data.
For CO the data from rats exposed to CO and from humans in hypoxia were adjusted for physiological conditions and extrapolated to humans exposed to CO. These data were pooled with human data from CO exposure. Adjustments were made and internal doses were estimated by a CO PBPK model. Endpoints were transformed and a curve was fitted as above.
Effects for CO were estimated to be behaviorally negligible. Toluene effects were then compared for potency by determining the dose-equivalence equation (DEE) between toluene and ethanol. The dose-effect curve for ethanol was determined by meta analysis as above. For purposes of determining a monetary value for effects all toluene effects were expressed as their ethanol equivalent via the DEE. Various exposure and activity scenarios were simulated with PBPK models by specifying the exposure and exercise levels as functions of time. Some typical results indicated that the exposure to toluene from two-stroke engine results was equivalent to approximately 0.06 g/dl of ethanol in blood.