The formation of reactive oxygen species catalyzed by neutral, aqueous extracts of NIST ambient particulate matter and diesel engine particles

It is important to characterize the chemical properties of particulate matt er in order to understand how low doses, inhaled by a susceptible populatio n, might cause human health effects. The formation of reactive oxygen speci es catalyzed by neutral, aqueous extracts of two ambient particulate sample s, National Institute of Standards & Technology (NIST) Standard Reference M aterials (SRM) 1648 and 1649, and two diesel particulate samples, NIST SRM 1650 and SRM 2975, were measured. The formation of reactive oxygen species was estimated by measuring the formation of malondialdehyde from 2-deoxyrib ose in the presence of ascorbic acid; H2O2 was not added to this assay. SRM 1649, ambient particulate matter collected from Washington, DC, generated the most malondialdehyde, while SRM 2975, diesel particulate matter collect ed from a forklift, yielded the least amount. Desferrioxamine inhibited the formation of malondialdehyde from the particulate samples providing additi onal data to support the observation that transition metals were involved i n the generation of reactive oxygen species. Six transition metal sulfates (iron sulfate, copper sulfate, vanadyl sulfate, cobalt sulfate, nickel sulf ate, and zinc sulfate) were assayed for their ability to generate reactive oxygen species under the same conditions used for the particulate samples i n order to facilitate comparisons between particles and these transition me tals. The concentration of transition metals was measured in aqueous extrac ts of these particulate samples using ion-coupled plasma mass spectrometry (ICP-MS) analysis. There was qualitative agreement between the concentratio ns of Fe, Cu, and V and the amount of malondialdehyde produced from extract s of these particulate samples. These data suggest that transition metals c an be dissolved from particles in neutral, aqueous solutions and that these metals are capable of catalyzing the formation of reactive oxygen species.