Experimental Atmosphere Monitoring in Gasoline Vapor Inhalation Studies

Abstract

Conditions affecting the composition and stability of test atmospheres of gasoline were investigated. Vapor was generated at 60°C from a methanol-gasoline blend (85:15, v:v) in a carrier air flow (25 L/min) and mixed with dilution air (580 L/min) for distribution to 2.5-m³ inhalation chambers. Three nominal concentrations (equivalent to 5150, 515, 51.5 ppm methanol) were produced under dynamic flow conditions. Analyses of vapor were carried out by gas chromatography with mass spectrometer and flame ionization detectors. Analyte concentrations determined for the high, medium, and low exposure levels were within ±1%, ±4%, and ±7% of the nominal values, respectively. Within-day variation and day-to-day variation in the analyte concentrations were <5%. Virtually constant levels of low boiling (<115°C) components (e.g., 2,2,4-trimethyl pentane) were observed over a daily 6-h exposure period. However, increase in high boilers such as 1,3,5-trimethyl benzene in the vapor with time was associated with the accumulation of residue in the vapor generation system. Variations in composition between three distinct batches of gasoline were also documented. Physiologically based pharmacokinetic modeling predicted a sensitivity of internal doses of benzene, toluene, and xylene in rats to the batch-to-batch variability in composition of gasoline due to kinetic interactions. The data illustrate some complexities of the assessment of chemical mixtures of environmental relevance. Adequate analytical and dose modeling methods should be applied to the characterization of experimental conditions in view of the heterogeneous nature of gasoline.

Key Words: :

• alternative fuel
• chemical mixtures
• gasoline
• inhalation toxicology
• M-85
• physiologically based pharmacokinetics