EXPERIMENTAL ATMOSPHERE MONITORING IN GASOLINE VAPOR INHALATION STUDIES

Conditions affecting the composition and stability of test atmospheres of gasoline were investigated. Vapor was generated at 60 degrees C fr om 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- m(3) inhalation chambers. Three nominal concentrations (equivalent to 5150, 515, 51.5 ppm methanol) were produced under dynamic flow conditi ons. Analyses of vapor were carried out by gas chromatography with mas s 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 degrees C) compon ents (e.g., 2,2,4-trimethyl pentane) were observed over a daily 6-h ex posure period. However, increase in high boilers such as 1,3,5-trimeth yl 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. Physi ologically based pharmacokinetic modeling predicted a sensitivity of i nternal doses of benzene, toluene, and xylene in rats to the batch-to- batch variability in composition of gasoline due to kinetic interactio ns. The data illustrate some complexities of the assessment of chemica l mixtures of environmental relevance. Adequate analytical and dose mo deling methods should be applied to the characterization of experiment al conditions in view of the heterogeneous nature of gasoline.