Novel nitro-PAH formation from heterogeneous reactions of PAHs with NO ₂, NO₃/N₂O₅, and OH radicals: Prediction, laboratory studies, and mutagenicity

The heterogeneous reactions of benzo[a]pyrene-d₁₂ (BaP-d ₁₂), benzo[k]fluoranthene-d₁₂ (BkF-d₁₂), benzo[ghi]perylene-d₁₂ (BghiP-d₁₂), dibenzo[a,i]pyrene- d₁₄ (DaiP-d₁₄), and dibenzo[a,l]pyrene (DalP) with NO ₂, NO₃/N₂O₅, and OH radicals were investigated at room temperature and atmospheric pressure in an indoor Teflon chamber and novel mono-NO₂-DaiP and mono-NO₂-DalP products were identified. Quartz fiber filters (QFF) were used as a reaction surface and the filter extracts were analyzed by GC/MS for nitrated-PAHs (NPAHs) and tested in the Salmonella mutagenicity assay, using Salmonella typhimurium strain TA98 (with and without metabolic activation). In parallel to the laboratory experiments, a theoretical study was conducted to rationalize the formation of NPAH isomers based on the thermodynamic stability of OH-PAH intermediates, formed from OH-radical-initiated reactions. NO₂ and NO ₃/N₂O₅ were effective oxidizing agents in transforming PAHs to NPAHs, with BaP-d₁₂ being the most readily nitrated. Reaction of BaP-d₁₂, BkF-d₁₂, and BghiP-d ₁₂ with NO₂ and NO₃/N₂O₅ resulted in the formation of more than one mononitro isomer product, while the reaction of DaiP-d₁₄ and DalP resulted in the formation of only one mononitro isomer product. The direct-acting mutagenicity increased the most after NO₃/N₂O₅ exposure, particularly for BkF-d₁₂ in which di-NO₂-BkF-d₁₀ isomers were measured. The deuterium isotope effect study suggested that substitution of deuterium for hydrogen lowered both the direct and indirect acting mutagenicity of NPAHs and may result in an underestimation of the mutagencity of the novel NPAHs identified in this study.