Project at a Glance
Title: Measurement and chemical characterization of vapor-phase mutagens in diesel exhaust
Principal Investigator / Author(s): Hsieh, Dennis P. H.
Contractor: Department of Environmental Technology, UC Davis
Contract Number: A032-095
Research Program Area: Emissions Monitoring & Control
Topic Areas: Mobile Sources & Fuels, Toxic Air Contaminants
Vapor-phase mutagens (VM) are volatile and semi-volatile mutagenic compounds present in numerous emission sources and in ambient air. The VM are potentially a major class of toxic air contaminants that require special experimental approaches for sampling, recovering and mutagenicity testing due to their volatility. In this research effort, methods for the collection, extraction, fractionation, and concentration of vapor-phase compounds from the undiluted exhaust of a medium heavy-duty diesel truck were developed and integrated with chemical analysis and a sensitive mutagenicity bioassay. A sampling system composed of a Teflon filter, polyurethane foam (PUF) and XAD-4 (XAD) adsorbents, in series, was used to directly trap PM and VM in the diesel truck exhaust. The VM on the PUF and XAD adsorbents were extracted with supercritical carbon dioxide (s-CO2) into concentrated methanol fractions which were directly analyzed by a specially modified Ames Salmonella mutagenicity assay and a gas chromatograph interlaced to a quadrupole mass spectrometer (GC-MS). The PM-associated mutagens were extracted with organic solvents and assayed for mutagenicity. A significant finding was that the mutagenic activity of the VM collected from the undiluted diesel exhaust was comparabie in magnitude to that of the PM- associated mutagens and therefore constitutes a substantial portion of the total mutagenicity present in the sampled diesel exhaust. GC-MS analysis of the s-CO2 fractions from XAD indicated the presence of long chain alkanes, alkyl benzenes, alkyl naphthalenes, unsaturated naphthalenes, and other aromatics. The s-CO2 fractions from the PUF samples with high mutagenic activity were subfractionated using high performance liquid chromatography (HPLC) to facilitate identification of chemical components. The sub-fractions were concentrated by gentle nitrogen blowdown and were analyzed by GC-MS. Compounds found were naphthalene, alkyl naphthalenes, phenanthrene, alkyl phenanthrenes, alkyl substituted aromatics and long chain alkanes. The analytical procedures developed in this investigation could be optimized to achieve mutagenicity-directed chemical analysis for VM in air.
For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893
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