Environ. Sci. Technol. lQ92,26, 320-329
Generation of Mutagenic Transformation Products during the Irradiation of Simulated Urban Atmospheres Tadeusz E. Kleindienst,” David F. Smith, and Edward E. Hudgens ManTech Environmental Technology, 1nc.-Environmental
Sciences,+ Research Triangle Park, North Carolina 27709
Larry D. Claxton Health Effects Research Laboratory, US. Environmental Protection Agency, Research Triangle Park, North Carolina 277 11
Joseph J. Bufallni and Larry T. Cupltt Atmospheric Research and Exposure Assessment Laboratory, US. Environmental Protection Agency, Research Triangle Park, North Carolina 2771 1 ~
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Mixtures of air pollutants simulating urban atmospheres were irradiated in a smog chamber, and the resultant products were monitored for the production of mutagenic and other hazardous compounds. The production of biologically active compounds was detected through use of the Ames mutagenicity assay with Salmonella typhimurium, strain TA100. Irradiations of the pollutant mixture were conducted at HC/NO, ratios of 20 and 11. Overall, the mutagenicity of the products and the formation of oxygenated primary and secondary reaction products were greater for the simulations with the higher initial HC/NO, value. The origin of the mutagenicity from the reactant mixture was examined by conducting experiments with individual paraffinic, olefinic, and aromatic hydrocarbons. The chemicals examined during this aspect of the study were the paraffin n-butane, the olefin propylene, and the aromatic toluene. For the conditions studied, the activity of the toluene products was generally greater than that of propylene or n-butane, and the propylene products showed greater activity than did the n-butane products. The production of n-butane products was generally limited by its low rate of reaction with hydroxyl radicals. Photooxidation products from secondary reactions were most important in the toluene and propylene systems. Introduction In the presence of sunlight, volatile organic compounds (VOCs) and oxides of nitrogen (NO,) react to form ozone and other photochemical products. The rate at which these products are generated from individual VOCs depends on a number of factors including the NO, concentration, the intensity of sunlight, and the lifetime of the VOC. These factors greatly impact the atmospheric reactivity of a compound (that is, in terms of its ozone formation potential, NO, removal, VOC conversion, etc.). Moreover, these factors can also influence the extent to which the photooxidation of VOCs leads to the formation of biologically active compounds ( I ) . Determinations of the health risks associated with pollutants in urban atmospheres are often solely concerned with the risk from primary emissions, that is, directly emitted by the source. For example, a recent report on the human cancer risks from automobile emissions (2) focused mainly on the risk from components directly emitted into the atmosphere from the exhaust and evaporative emissions. VOCs which appeared to contribute most to the aggregate cancer incidence included 1,3-butadiene, formaldehyde, and benzene. When the contribution of the t Formerly NSI Technology Services Corporation-Environmental Sciences.
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specific urban pollutants and sources to the aggregate cancer risk was estimated, the photochemical formation or removal of these compounds, while recognized as an important factor, was not included. Such an omission ignores critically important contributions to the exposure and risk assessment, especially for compounds that are removed quickly from the atmosphere or that produce hazardous products. However, the need to consider the effects of transformation processes is widely acknowledged. The 1990 Amendments to the Clean Air Act (Public Law 101-549) mandates EPA to “conduct a program of research with respect to sources of hazardous air pollutants in urban areas and shall include ... consideration of atmospheric transformation and other factors which can elevate public health risks from such pollutants”. The role of photochemical products in evaluations of risks has not been included for several reasons. Concentrations of individual photooxidation products except ozone are generally low under urban conditions (
