In this study a sensitive macrophage-based in vitro reactive oxygen species (ROS) assay was coupled with chemical fractionation tools and a year-long sampling program to further our understanding of the role of water-soluble metals in aerosol toxicity. The location is the polluted urban environment of Lahore, Pakistan, where we collected 24 h PM10 and PM2.5 samples every 6^th day from January 2007 through January 2008. The intrinsic (i.e. particulate matter (PM) mass-normalized) toxicity of the Lahore aerosol, representative of highly polluted developing nations, is compared with toxicity of aerosols from several urban environments in the USA. The monthly patterns of PM2.5 and PM10 water-soluble aerosol ROS-activity were similar with maxima in fall and mid-late winter, and minima over the period April through August and in early winter. Coarse PM ROS-activity was a consistent and significant component (42 ± 13%) of total activity. The intrinsic activity of the PM2.5 and coarse PM was remarkably similar in a given month. Chelex treatment of the Lahore PM extracts removed a very large and consistent fraction of the water-soluble ROS-activity (96.5 ± 2.8% for the PM10). Desferrioxamine (DFO) treatment of these extracts also removed a large and relatively consistent fraction of the water-soluble ROS-activity (87.8 ± 5.3%). Taken together, the DFO and Chelex data imply that transition metals, particularly iron, are major factors mediating ROS-activity of water extracts of the Lahore PM. Statistical modeling (step-wise linear regression and cluster analysis) identified a small subset of metals (Mn, Co, Fe, Ni) as the potential ROS-active species. Several water-soluble “trace” metals present at very high concentrations in the PM extracts (Zn, Pb, Cd), that were effectively removed on Chelex, but are not redox-active, exhibited relatively poor correlations with ROS. The median intrinsic water-soluble ROS-activity measured in the Lahore PM was more than an order-of-magnitude greater than that measured in aerosols from the Long Beach/Los Angeles region and approximately 4-fold greater than the activity of Denver area PM.

Short-term exposure to ambient air pollution has been associated with acute increases in cardiovascular hospitalization and mortality. However, causative chemical components and underlying pathophysiological mechanisms remain to be clarified. We hypothesized that endothelial dysfunction would be associated with mobile-source (traffic) air pollution and that pollutant components with higher oxidative potential to generate reactive oxygen species (ROS) would have stronger associations. We carried out a cohort panel study in 93 elderly non-smoking adults living in the Los Angeles metropolitan area, during July 2012-February 2014. Microvascular function, represented by reactive hyperemia index (RHI), was measured weekly for up to 12 weeks (N = 845). Air pollutant data included daily data from regional air-monitoring stations, five-day average PM chemical components and oxidative potential in three PM size-fractions, and weekly personal nitrogen oxides (NOx). Linear mixed-effect models estimated adjusted changes in microvascular function with exposure. RHI was inversely associated with traffic-related pollutants such as ambient PM2.5 black carbon (BC), NOx, and carbon monoxide (CO). An interquartile range change increase (1.06 μg/m3) in 5-day average BC was associated with decreased RHI, −0.093 (95 % CI: −0.151, −0.035). RHI was inversely associated with other mobile-source components/tracers (polycyclic aromatic hydrocarbons, elemental carbon, and hopanes), and PM oxidative potential as quantified in two independent assays (dithiothreitol and in vitro macrophage ROS) in accumulation and ultrafine PM, and transition metals. Our findings suggest that short-term exposures to traffic-related air pollutants with high oxidative potential are major components contributing to microvascular dysfunction.