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Two Simulated-Smog Atmospheres with Different Chemical Compositions Produce Contrasting Mutagenicity in Salmonella**
Citation:
Zavala, J., J. Krug, S. Warren, Todd Krantz, C. King, S. Gavett, M. Lewandowski, W. 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 Meeting, New Orleans, LA, March 13 - 17, 2016.
Impact/Purpose:
Abstract will be presented at the Society of Toxicology Annual Meeting, March 13-17, 2016, New Orleans, LA
Description:
Ozone (O3), particulate matter (PM), and nitrogen dioxide (NO2) are criteria pollutants used to evaluate air quality. Using EPA’s Mobile Reaction Chamber (MRC), we generated 2 simulated-smog atmospheres (SSA-1 & SSA-2) with different concentrations of these criteria pollutants to explore their mutagenicity. The MRC consists of a 24-foot trailer containing a 14.3-m3 Teflon-lined photochemical chamber operated in dynamic mode. Photochemical reaction chambers are sophisticated systems that can be used to generate realistic, reproducible, and controlled urban-like atmospheres. Along with characterizing the chemical composition of such atmospheres, the MRC can be coupled with in vitro and in vivo systems, permitting evaluation of the atmospheres for potential health effects. Photochemistry in the MRC is catalyzed by 120 fluorescent bulbs mixed evenly with black light bulbs and UV bulbs (300-400 nm) to simulate the presence of solar radiation in urban atmospheres. For SSA-1, a mixture of 6 parts per million carbon (ppmC) α-pinene, 24 ppmC gasoline, and 500 ppb nitric oxide (NO) was injected continuously into the MRC along with nebulized ammonium sulfate (2 µg/m3) to provide a nucleation base for photochemical reaction products. The photo-oxidized atmosphere contained 97 ppb O3, 244 NO2, and 1.07 mg/m3 PM2.5. For SSA-2, a mixture of 6 ppmC isoprene, 9 ppmC gasoline, and 900 ppb nitric oxide (NO) were injected continuously into the MRC, resulting in an atmosphere containing 440 ppb O3, 586 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. The photo-oxidized contents of the MRC were drawn into a Billups-Rothenberg Modular Incubator Chamber (MIC) via a vacuum pump. Each MIC contained 4 standard 100-mm glass Petri dishes of Salmonella TA100 ± S9, which detects base-substitution mutations, spread in a top agar at the air-agar interface. Exposure duration ranged from 0-14 h. After exposure, the cultures were incubated for 72 h, the mutants (revertants) were counted, and linear regressions were calculated to assess the mutagenic potencies (revertants/h) of the smog atmospheres. The unreacted components injected into the MRC were not mutagenic. However, once photochemical reactions were initiated to produce secondary reaction products by turning on the lights, the resulting atmospheres were mutagenic and toxic. The mutagenicity of SSA-1 and -2 was from direct-acting mutagens requiring no metabolism to be mutagenic. SSA-2 was approximately 3 times more mutagenic than SSA-1; however, SSA-2 was cytotoxic past 3 h of exposure. O3 at 440 ppb was not cytotoxic or mutagenic; therefore, the mutagenicity and cytotoxicity of SSA-2 were due only to other secondary reaction products. Neither atmosphere was mutagenic in strain TA98, which detects frameshift mutations. Next-gen DNA sequencing of the SSA-1-induced mutants showed that 50% of the mutants were G to T and 50% were G to A base substitutions. 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.]