Citation:

Zavala, J., J. Krug, S. Warren, Todd Krantz, C. King, S. Gavett, M. Lewandowski, Bill Lonneman, Tad Kleindienst, M. Meier, M. Higuchi, Ian Gilmour, AND D. DeMarini. Two Simulated-Smog Atmospheres with Different Chemical Compositions Produce Contrasting Mutagenicity in Salmonella. Society of Toxicology, New Orleans, LA, March 13 - 17, 2016.

Impact/Purpose:

This study was performed under the ACE 207 Smog research category and examines the potential differences in toxicity and mutagenicity between smog atmospheres composed of different starting materials. The final set of studies will provide insight to the Office of Air on the toxicology associated with smog atmospheres composed of different concentrations of selected priority pollutants.

Description:

Ozone (O3), particulate matter (PM), and nitrogen dioxide (NO2) are criteria pollutants used to evaluate air quality. Using a 14.3-m3 Teflon-lined smog chamber with 120 UV bulbs to simulate solar radiation, we generated 2 simulated-smog atmospheres (SSA-1 & SSA-2) with different concentrations of these criteria pollutants to explore their mutagenicity. For SSA-1 (high PM, low O3/NO2), we added 6 parts per million carbon (ppmC) α-pinene, 24 ppmC gasoline, and 0.5 ppm nitric oxide (NO) continuously into the chamber with nebulized ammonium sulfate (2 µg/m3) to provide a nucleation base for secondary reaction products. The photo-oxidized atmosphere produced 97 ppb O3, 244 ppb NO2, and 1.07 mg/m3 PM2.5. For SSA-2 (low PM, high O3/NO2), we added 6 ppmC isoprene, 9 ppmC gasoline, and 0.9 ppm NO, which produced an atmosphere with 440 ppb O3, 586 ppb NO2, and 55 µg/m3 PM2.5. We measured the concentrations of aromatics, peroxyacetyl nitrate (PAN), paraffins, olefins, and other volatile organics produced as a result of photochemical reactions. Plates of Salmonella TA100 ± S9 spread in a top agar were exposed for 0-14 h, incubated for 72 h, and colonies were counted. Both SSA-1 and -2 were mutagenic only with the lights on and did not require S9. Thus, all the mutagenicity was direct-acting and did not require metabolism. SSA-2 was ~3 times more mutagenic than SSA-1, and unlike SSA-1, SSA-2 was cytotoxic past 3 h of exposure. O3 at 440 ppb was not cytotoxic or mutagenic; therefore, the observed results with SSA-2 were due only to other secondary reaction products. Using next-gen DNA sequencing, the SSA-1-induced mutants were 50% G to T and 50% G to A. This study shows that secondary reaction products, which are typically not measured, play a key role in air-pollution mutagenicity. [Abstract does not necessarily reflect the views or policies of the U.S. EPA.]

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