Involvement of nitro-compounds in the mutagenicity of urban Pm2.5 and Pm10 in Turin

Abstract

Fine particles can be active carriers of toxic compounds into the alveoli of the lungs. Among these compounds are numerous mutagens and carcinogens. The direct mutagenicity per unit mass of fine particulate matter (PM) is significantly higher than that of coarse particles, especially in urban areas. In this study, the mutagenic properties of urban PM2.5 and PM10 were evaluated, and the role of nitro-compounds was estimated. PM2.5 and PM10 samplings, and measurements of NOx and some PAHs were performed daily in 2007 in Turin, following a consolidated in vitro test – the Salmonella mutagenicity assay – conducted with organic extracts of PM2.5 and PM10. The mutagenic properties were assessed for each month of sampling with Salmonella typhimurium strain TA98 and TA98-derived strains: a nitroreductase-deficient mutant strain (TA98NR) and an additional nitroreductase-producing plasmid strain (YG1021). The annual measured mean levels of PM2.5 and PM10 were 34 ± 20 and 48 ± 18 μg/m 3. The PM2.5/PM10 ratio ranged from 0.36 to 0.89. The Salmonella assay showed higher mutagenicity in autumn/winter (20 ± 15 TA98NR; 54 ± 39 TA98; 173 ± 161 YG1021 net revertants/m 3) compared with spring/summer (2 ± 2 TA98NR; 7 ± 8 TA98; 24 ± 27 YG1021 net revertants/m 3) ( p < 0.01). There are also statistically significant seasonal differences in the gravimetric analysis data. The number of TA98 net revertants per μg of PM2.5 is 6.5 times greater than per μg PM10. Moreover, the bioassay results showed an amplified response in the YG1021 strain and a reduced response in the TA98NR strain. The net revertant ratio TA98NR/YG1021 is 11 ± 4 for organic extracts of PM2.5 and 13 ± 6 for extracts of PM10 ( p < 0.01). There is a significant correlation between the NOx and PAH concentrations. These findings illustrate the relevant role of nitro compounds, and they underline the priority in improving preventive measures to reduce air pollution by nitrated molecules.