Although epidemiological studies have established a correlation between pm10 levels and acute cardiovascular and respiratory complications, hardly any data is available on possible chronic effects such as cancer. The purpose of this study was to investigate the production of free radicals by ambient particulate matter (tsp) and to link these data to oxidative dna damage in lung epithelial cells. In line with previous findings on pm10, supercoiled plasmid dna was depleted by tsp as well as tsp supernatant (p <.001), and this effect was reduced in the presence of mannitol (5 mm). Using electron spin resonance (esr) and the spin trap dimethyl-1-pyrroline n-oxide (dmpo) we were able to show that hydroxyl radicals (oh) are formed from both tsp and tsp supernatant. The dmpo-oh signal was completely abrogated when tsp was preincubated with deferoxamine (5 mm), showing the importance of iron and other soluble metals in this process. Atomic absorption spectroscopy (aas) analysis of the tsp supernatant showed the presence of soluble fe, v,and ni (respectively 253.0, 14.7, and 76.0 mug/g insoluble tsp). To investigate the biological significance of oh formation by tsp,8-hydroxydeoxyguanosine (8-oxodg) was measured in a rat type ii cell line by immunocytochemistry. The formation of this hydroxyl-radical-specific dna adduct was increased twofold (p <.01) after incubation with tsp supernatants, and this effect was inhibited by deferoxamine (p <.01). In summary, our results provide direct evidence that ambient particulate matter generates hydroxyl radicals in acellular systems. Furthermore, we showed that these particulates induce the hydroxyl-radical-specific dna lesion 8-oxodg in lung target cells via an iron-mediated mechanism.