Citation:

Zavala, J., T. Riedel, M. Lewandowski, J. Krug, S. Warren, Todd Krantz, C. King, S. Gavett, Bill Lonneman, Tad Kleindienst, M. Meier, M. Higuchi, AND Ian Gilmour. The Concentrations but Not the Components of Particulate Material and Secondary Transformation Products May Account for Much of the Variation in Air Mutagenicity. Brazilian Environmental Mutagenesis and Genomics Society, Ribeirao Preto, Sao Paulo, BRAZIL, June 01 - 03, 2017.

Impact/Purpose:

The U.S. EPA regulates a variety of primary air pollutants, such as benzene, toluene, naphthalene, etc. The action of sunlight on these primary pollutants form secondary atmospheric transformation products, and these are generally the basis for smog and air pollution associated with the gas phase of ambient air. This study created a set of 12 smog atmospheres using these individual primary pollutants (such as benzene, toluene, etc.) in an experimental smog chamber with ultraviolet (UV) light to simulate solar radiation and evaluated the gas phase of these atmospheres for mutagenicity in the Salmonella mutagenicity assay. The results showed that 8 out of 12 atmospheres were mutagenic, all were direct-acting and did not require metabolism to be mutagenic, and none of the primary chemical pollutants used to initiate the reactions were mutagenic (i.e., none of the atmospheres was mutagenic with the UV lights off). Thus, this study shows that most of the mutagenicity of the gas phase of ambient air is largely to due to the secondary reaction products formed by the action of sunlight on the primary reactants. The study also showed that reducing the concentration of the primary reactants, which are regulated by the U.S. EPA, reduced the mutagenicity of the atmospheres, which were due to secondary reaction products, which are largely not monitored or regulated by the U.S. EPA. Thus, this study shows that regulating the primary reactants also regulates the formation of the secondary reactants, which are the actual cause of the mutagenicity of the gas phase of ambient air.

Description:

The mutagenic potency of ambient air PM in the Salmonella mutagenicity assay (rev/mg PM) varies only ~1 order of magnitude worldwide; however, the mutagenic potency of the air itself (rev/m3 of air) varies ~5 orders of magnitude (IARC Monograph Vol 109, 2016). Thus, the components and mutagenic potency of PM are somewhat similar worldwide, but the concentration of PM is highly variable. A similar situation may apply to the gas phase of ambient air—i.e., its components may be similar, but the concentrations of the components may vary among air sheds. To explore this, we generated 12 atmospheres in chambers containing UV lights simulating solar radiation and assessed their mutagenicity by exposing plates of Salmonella TA100 minus S9 at the air-agar interface. We produced individual atmospheres with 10 separate US EPA-regulated air pollutants: benzene, ethylbenzene; 1,3,5- and 1,2,4-trimethylbenzene; toluene; o-, m-, and p-xylene; m-cresol; and naphthalene. We generated 2 atmospheres using complex mixtures: gasoline + α-pinene and gasoline + isoprene. Ten atmospheres were direct-acting mutagens and required UV irradiation; m-cresol and naphthalene atmospheres were not mutagenic. The mutagenic potencies [rev/h/(mgC/m3)] varied less than one order of magnitude (5.8 fold, 1.97-11.43) and correlated (R2 > 0.7) with the concentrations of a selected few of 104 oxidized reaction products identified. The mutation spectrum of the gasoline atmospheres was 54% C → T and 46% C → A; ambient PM induces 26% C → T and 72% C → A. Reduced concentrations of ethylbenzene, a regulated pollutant, reduced the mutagenicity of the resulting atmosphere, which was due to secondary reaction products not typically measured or regulated. Thus, as with PM, the mutagenicity of the gas phase of ambient air may be composed of a similar mix of organics whose concentrations vary among air sheds. [Abstract does not reflect policies of the EPA.]

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