Generation of hydroxyl radicals by urban suspended particulate air matter. The role of iron ions

Recent epidemiologic studies showed statistical associations between particulate air pollution in urban areas and increased morbidity and mortality, even at levels well within current national air quality standards. Inhalable particulate matter (PM10) can penetrate into the lower airways where they can cause acute and chronic lung injury by generating toxic oxygen free radicals. We tested inhalable total suspended particulates (TSP) from the Athens area, diesel and gasoline exhaust particles (DEP and GED), and urban street dusts, by Electron Paramagnetic Resonance (EPR). All particulates can generate hydroxyl radicals (HO*), in aqueous buffered solutions, in the presence of hydrogen peroxide. Results showed that oxidant generating activity is related with soluble iron ions. Leaching studies showed that urban particulate matter can release large amounts of Fe3+ and lesser amounts of Fe2+, as it was shown from other studies. Direct evidence of HO* was confirmed by spin trapping with DMPO and measurement of DMPO-OH adduct by EPR. Evidence was supported with the use of chelator (EDTA), which increases the EPR signal, and the inhibition of the radical generating activity by desferrioxamine or/and antioxidants (D-mannitol, sodium benzoate). (C) 2000 Elsevier Science Ltd. All rights reserved.