Genotoxicity of environmental air pollution in three European cities: Prague, Košice and Sofia

Abstract

The genotoxic potential of extractable organic matter (EOM) associated with the respirable particulate matter (PM <10 μm) of atmospheric pollution has been determined in three European cities—Prague (Czech Republic, two monitoring sites, Libuš and Smı́chov), Košice (Slovak Republic) and Sofia (Bulgaria) using the alkaline single-cell gel electrophoresis (the comet assay). The EOM samples were extracted by dichloromethane from ambient airborne particles collected daily (24 h intervals) during 3-month sampling periods in winter and summer seasons. The human metabolically competent cell line Hep G2 was used as a test system and benzo[a]pyrene (BaP), a known carcinogen, was applied as a positive control (internal standard) in each electrophoretic run. Two-hour exposure of Hep G2 cells to equivalent EOM concentrations ranging from 5 to 150 μg EOM/ml resulted in a linear dose-dependent increase of DNA migration ( r > 0.9, P < 0.01). A less significant dose-response ( r = 0.61) was only induced by the EOM sample from the locality Prague-Libuš (PRG-LB) in the winter. Generally, a 1.5 to four-fold increase of DNA strand breaks over the background control level was determined in EOM-exposed cells. In order to compare the genotoxic potential of individual EOMs, a mathematical model was used to correct the ‘real’ data. No substantial location- or season-related differences were found in EOM genotoxicity (EOM μg/ml), except for the EOM sample from Sofia, collected in the summer. This EOM sample induced a nearly two-fold lower level of DNA damage in comparison with other EOMs. On the other hand, clear statistically significant location- and season-related differences ( P < 0.001) in ambient air genotoxicity were determined when the EOM quantity per cubic meter of air (μg/m 3) was taken into account. In that case, the genotoxicity of winter air pollution was six- to 10-fold higher in comparison with summer air. The air pollution genotoxicity in individual localities rose during the winter season in the order: PRG-LB < Košice < Prague-Smı́chov (PRG-SM) < Sofia, while during the summer season the highest ambient air genotoxicity was revealed in the locality Prague-Smı́chov and approximately equal air pollution genotoxicity was determined among localities Prague-Libuš, Košice and Sofia (PRG-LB ∼ Košice ∼ Sofia < PRG-SM). The greatest overall air pollution genotoxicity was determined in the locality Sofia during the winter season. In a time course study to evaluate the kinetics of DNA strand break rejoining it was shown that the level of DNA strand breaks in EOM-exposed cells has returned to near the background level within 24 h after the treatment.