Citation:

Zavala, J., T. Riedel, M. Lewandowski, J. Krug, S. Warren, Todd Krantz, C. King, S. Gavett, Bill Lonneman, Tad Kleindienst, M. Higuchi, Ian Gilmour, AND D. DeMarini. Gas-Phase Mutagenicity in Salmonella of 12 Distinct Simulated Smog Atmospheres Generated Using Environmental Irradiation Chambers. SOT, Baltimore, MD, March 12 - 16, 2017.

Impact/Purpose:

As part of the ACE program, this research effort identifies some of the chemicals that are secondary reaction products in the gas phase of polluted atmospheres as mutagens. This will provide guidance to OAQPS and other arms of the Agency concerned with regulating air pollution.

Description:

Urban smog is a complex mixture resulting from interactions of anthropogenic and biogenic emissions in the presence of sunlight. To study this complex interaction in a controlled laboratory environment, we used indoor environmental irradiation chambers containing UV lights (300-400 nm) that simulated solar radiation. We generated 12 distinct smog atmospheres and characterized their chemical composition and mutagenicity. We exposed plates of Salmonella TA100 minus S9 at the air-agar interface to the atmospheres for up to 16 h, followed by 72 h of incubation to permit mutant colonies (revertants, rev) to grow. We generated the atmospheres by continuously injecting nitric oxide, ammonium sulfate as a seed aerosol, and selected hydrocarbon(s) with UV to create a photo-oxidized smog mixture. The mutagenic potencies (rev/h ± SE) of 10 atmospheres generated with a single aromatic compound were: toluene (12.0 ± 0.7), o-xylene (11.0 ± 0.8), ethylbenzene (10.7 ± 0.8), 1,3,5-trimethylbenzene (10.7 ± 1.2), m-xylene (7.4 ± 0.8), 1,2,4-trimethylbenzene (7.1 ± 1.0), benzene (5.0 ± 0.6), p-xylene (3.1 ± 0.6), naphthalene (0; cytotoxic), and m-creosol (0; cytotoxic). Gas-phase analysis of the atmospheres showed that the mutagenicity correlated (R2 > 0.7) with the concentrations of many secondary reaction products. The mutagenic potency of the atmosphere produced by gasoline + the aromatic α-pinene was 19.36 ± 2.2 rev/h, and that by gasoline + the olefin isoprene was 29.89 ± 5.1 rev/h; the potencies were not significantly different (P = 0.44). Because the gasoline mixtures were the most mutagenic, we analyzed the mutants by Next-Gen DNA sequencing and found that the gasoline + α-pinene mutants were 48% G to A and 52% G to T, and that the gasoline + isoprene mutants were 57% G to A and 43% G to T; the mutation spectra were not significantly different (P = 0.16). In all cases the mutagenicity of the atmospheres was direct-acting and occurred only with UV irradiation; atmospheres of the primary reactants (no UV) were not mutagenic. The results showed that the secondary reaction products formed in the ambient atmosphere account for the mutagenicity of the gas phase of polluted air. [Abstract does not reflect views/policies of the U.S. EPA.]

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