Diurnal change of direct-acting mutagenicity of soluble organic fraction of airborne particles collected at Southern Osaka: correlation between the mutagenicity, particles-associated nitroarenes, and gaseous emission

The direct-acting mutagenicity of soluble organic fraction (SOF) of airborne particles, and the concentration of five gaseous air pollutants and two nitroarenes, 1-nitropyrene (1-NP) and 2-nitrofluoranthene (2-NF) were determined to clarify their diurnal variation pattern by collecting airborne particles every 3 or 4 h in a slightly polluted residential area at southern Osaka, Japan. The direct-acting mutagenicity of SOF toward Salmonella typhimurium YG1024 strain, i.e. mutagenicity in the absence of microsomal activation, was high early in the morning and late in the evening, while it was low both in the daytime and in the nighttime. The diurnal variation pattern of the mutagenicity was similar to those of the concentration of NO, CO, and 1-NP, which were primarily emitted from combustion processes such as diesel-powered vehicles. On the other hand, a significant correlation was observed between diurnal variations of the concentration of 2-NF and hydroxyl radical in October. The concentration of 2-NF in airborne particles collected in July was comparable to that in October. Based on the specific mutagenic activity of 1-NP and 2-NF, their contribution to the total direct-acting mutagenicity of SOF toward YG1024 strain were estimated to be small as 0.03–0.06% and 0.2–1.1%, respectively. However, some of atmospherically formed nitroarenes would contribute to the direct-acting mutagenicity of the air in the daytime, when atmospheric formation of nitroarenes initiated by the reactions with radical species is expected to occur even since the mutagenicity originated from primarily emitted mutagens should be suppressed by photo-decomposition of the mutagens.