Temporal variation of hydroxyl radical generation and 8-hydroxy-2′-deoxyguanosine formation by coarse and fine particulate matter

Aims: To determine the induction of 8-hydroxy-2'-deoxyguanosine (8-OHdG) by fine (<2.5 mu m) and coarse (10-2.5 mu m) particulate matter (PM) sampled over time at one sampling location, and to relate the observed effects to the hydroxyl radical (center dot OH) generating activities and transition metal content of these samples, and to meteorological parameters. Methods: Weekly samples of coarse and fine PM were analysed for H2O2 dependent center dot OH formation using electron spin resonance (ESR) and formation of 8-OHdG in calf thymus DNA using an immunodotblot assay. Immunocytochemistry was used to determine 8-OHdG formation in A549 human epithelial lung cells. To determine temporal effects, samples from six weeks in summer and six weeks in autumn/winter were compared using ESR and the dotblot assay. Concentrations of leachable V, Cr, Fe, Ni, and Cu were determined by inductively coupled plasma mass spectrometry. Results: Both PM fractions elicited center dot OH generation as well as 8-OHdG formation in calf thymus DNA and in A549 cells. 8-OHdG formation in the naked DNA was significantly related to center dot OH generation, but not to metal concentrations except for copper. A significantly higher center dot OH generation was observed for coarse PM, but not fine PM collected during the autumn/winter season; this was not due to differences in sampled mass or metal content. Specific weather conditions under which increased center dot OH formation in the coarse mode was observed suggest that other, as yet unknown, anthropogenic components might affect the radical generating capacity of PM. Conclusions: Both coarse and fine PM are able to generate center dot OH, and induce formation of 8-OHdG. When considered at equal mass, center dot OH formation shows considerable variability with regard to the fraction of PM, as well as the sampling season. The toxicological implications of this heterogeneity in center dot OH formation by PM, as can be easily determined by ESR, need further investigation.