Human Lymphoblast Mutagens in Urban Airborne Particles

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Abstract

While it is known that urban airborne particles typically contain trace levels of bacterial mutagens and rodent carcinogens, little work has been done to identify chemicals in such particles that can genetically alter human cells. In this paper, we describe the analysis of an organic extract of a Washington, DC, airborne particle sample (SRM 1649) for human cell mutagens. Due to the chemical complexity of the extract, a bioassay-directed fractionation method was used to separate mutagenic constituents into chemically simplified fractions. Mutagenicity testing was done using the h1A1v2 cell line, a line of human B-lymphoblastoid cells that have been engineered to overexpress the human cytochrome P4501A1. Chemical analysis of mutagenic fractions was accomplished using GC−MS and HPLC−UV techniques. Our results indicate that ∼20% of the total mutagenicity the extract was accounted for in two fourth-order fractions that contained ∼3% of the total extract mass. These fractions were composed largely of polycyclic aromatic hydrocarbons (PAH). A total of 13 PAH were identified that accounted for ∼15% of the mutagenicity of the extract. Of these, the most important mutagens were cyclopenta[cd]pyrene, benzo[a]pyrene, and benzo[b]fluoranthene, accounting for ∼7, ∼4, and ∼2%, respectively, of the extract mutagenicity. Naphtho[2,1-a]pyrene (N[2,1-a]P) and naphtho[2,3-a]pyrene (N[2,3-a]P), two previously unknown potent human lymphoblast mutagens, were also identified in the sample. N[2,1-a]P accounted for ∼3% of the extract mutagenicity; N[2,3-a]P, which was present at relatively low levels, accounted for <1% of the extract mutagenicity. The remainder of the mutagenicity was found in fractions that contained more polar compounds. One of these polar fractions contained many different classes of oxygenated polycyclic aromatic compounds (oxy-PAH) including ketones, quinones, coumarins, and carboxylic acid anhydrides; however, of the mutagenic oxy-PAH identified, only the ketone 6H-benzo[cd]pyren-6-one (∼0.5%) was found to account for a significant portion of the total mutagenicity of the extract. Nitro-PAH, many of which are potent bacterial mutagens, did not contribute significantly to the mutagenicity of this sample because they were present at low concentrations and because they are not particularly mutagenic in h1A1v2 cells.

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