FREE-RADICAL ACTIVITY OF PM10 - IRON-MEDIATED GENERATION OF HYDROXYL RADICALS

The purpose of this study was to test the hypothesis that particulate matter less than or equal to 10 mu m in aerodynamic diameter (PM10) pa rticles have the ability to generate free radical activity at their su rface. We collected PM10 filters from the Edinburgh, United Kingdom, E nhanced Urban Network sampling site, removed particles from the filter : and tested their ability to cause free radical damage to supercoiled plasmid DNA. We found that the PM10 particles did cause damage to the DNA that was mediated by hydroxyl radicals, as shown by inhibition of the injury with mannitol, The PM10-associated hydroxyl radical activi ty was confirmed using a high-performance liquid chromatography-based assay to measure the hydroxyi radical adduct of salicylic acid. Desfer rioxamine abolished the hydroxyl radical-mediated injury, which sugges ts that iron was involved. Analysis of PM10 filters confirmed the pres ence of large amounts of iron and leaching studies confirmed that the PM10 samples could release substantial amounts of Fe(III) and lesser a mounts of Fe(II). To investigate the size of the particles involved in the hydroxyl radical injury, we centrifuged the suspension of PM10 to clarity, tested the clear supernatant, and found that it had all of t he suspension activity. We conclude, therefore, that the free radical activity is derived either from a fraction that is not centrifugeable on a bench centrifuge, or that the radical generating system is releas ed into solution.