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Title: Formation of mutagens from the atmospheric photooxidants of polycyclic aromatic hydrocarbons and their occurrence in ambient air

Principal Investigator / Author(s): Arey, Janet

Contractor: UC Riverside

Contract Number: a132-075

Research Program Area: Health & Exposure, Atmospheric Processes

Topic Areas: Chemistry & Reactivity, Toxic Air Contaminants


Ambient air analyses demonstrated that the polar mutagenic reaction product of the simulated atmospheric photooxidation of phenanthrene, 2-nitrodibenzopyranone, is a wide-spread contaminant in the environment. 2-Nitrodibenzopyranone was observed in all of the approximately two dozen southern California ambient air filter and polyurethane foam (PUF) plug samples analyzed, and 4-nitrodibenzopyranone (also an atmospheric reaction product of phenanthrene) was observed in the majority of these samples. Both isomers were observed in the Standard Reference Material (SRM) 1649 urban dust.

The results obtained from our laboratory experimental studies (which continued the work of our previous ARB Contract No. A732-154) showed that simulated atmospheric photooxidations of the gas-phase 2- to 4-ring polycyclic aromatic hydrocarbons (PAH) lead to mutagenic products. The specific PAR studied were: 1-methylnaphthalene, 2-methylnaphthalene, acenaphthene, acenaphthylene, biphenyl. dibenzothiophene, anthracene, retene (l-methyl- 7-isopropylphenanthrene) , fluoranthene, pyrene, benz[a]anthracene and chrysene. The total mutagenic activities of the product mixtures from the simulated atmospheric reactions of the PAH varied widely depending on the particular PAH, and also the mutagenicity profile varied from PAH to PAH, at least in terms of the polarity of the mutagenic products. In general. the PAH studied lead to either mutagenic nitro-PAH which elute. with the HPLC fractionation program used here, in fraction #3 or 4, or to more polar products including the nitro-PAR lactones. Our data, when compared with ambient air mutagenicity testing using the same sample collection. extraction, fractionation and bioassay testing procedures, allow ~50% of ambient air direct-acting mutagenicity (gas plus particle phase), Salmonella typhimurium strain TA98 (-S9, Kado microsuspension modification of Ames assay), to be ascribed to PAH atmospheric transformation products formed in the atmosphere during transport from source to receptor. Our data also allow ranking of the PAH studied to be made with respect to the number of revertants per unit PAH concentration ("mutagenicity formation potential"), with a range of over three orders of magnitude from biphenyl and benz[a]anthracene (the lowest) to fluoranthene (the highest). It is possible that this ranking can be used in assessments of emission changres brought about through emission control measures or the use of alternate fuels.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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