Genotoxicity of urban air pollutants in the Czech Republic Part II. DNA adduct formation in mammalian cells by extractable organic matter

The study was aimed at determining the genotoxic potential of extractable o rganic matter (EOM) from ambient air particles PM10 (< 10 mu m) using mamma lian cells in culture as test system. Air samples were collected in the cou rse of summer and winter periods in two regions of the Czech Republic repre senting low and high levels of air pollution, the districts of industrial T eplice and rural Prachatice, respectively. EOM was fractionated by acid-bas e partitioning and silica gel column chromatography. Aliquots of fractions were incubated with cultured hepatocytes derived from male rats or Chinese hamster lung V79NH cells expressing nitroreductase activity but virtually n o cytochrome P450 activity. DNA adduct levels were analyzed by P-32-postlab eling using butanol extraction for adduct enrichment. In hepatocytes, crude extracts caused the formation of substantial amounts of DNA reactive mater ial bring detectable in a broad diagonal radioactive zone (DRZ) in the chro matograms. Highest DNA adduct levels were found in the aromatic fractions a nd slightly polar fractions which contain most of the polycyclic aromatic h ydrocarbons (PAH) and nitro-substituted PAH (nitro-PAH), respectively, comp rising 75-90% of total adducts. This partitioning was independent of the sa mpling period and locality. In agreement with the higher average ambient ai r concentrations of PAH in the winter than the summer, 3-4-fold higher DNA adduct levels were detected in extracts sampled in the winter. Calculated o n the basis of EOM/m(3), DNA adduct levels of samples collected in winter p eriod were 10-fold higher than those collected in the summer period and 2-f old higher in Teplice than in Prachatice. Pretreatment of hepatocytes with 2,3,7,8-tetrachlorodibenzo-p-dioxin decreased DNA binding by 50-75%. In con trast to the findings in hepatocytes, in V79NH cells about 80% of the DNA a dducts were caused by material in the slightly polar fractions appearing as distinct spots in the radiochromatograms. Seasonal variation of DNA adduct s in V79NH cells was greater than variation between localities. Our results suggest that PAI-I as well as nitro-PAH are the main contributors to the g enotoxicity of EOM derived from both industrial and rural areas. The result s, furthermore, indicate that analysis nf DNA adducts in mammalian cells in culture offers a suitable method for monitoring the genotoxicity of comple x of environmental chemicals. (C) 2000 Elsevier Science B.V. All rights res erved.