Reactive oxygen species activity and chemical speciation of size-fractionated atmospheric particulate matter from Lahore, Pakistan: an important role for transition metals

Abstract

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.

Ambient Fine Particulate Matter Induces Apoptosis of Endothelial Progenitor Cells Through Reactive Oxygen Species Formation

“…Particles especially PM widely exist in the environment and may carry ROS within gas phase [13] or water phase (aerosol) [34] into the lower respiratory tract to create an increased risk on health. There is growing evidence for oxidative stress in response to air pollution in different organs [35].…”

Evidence and quantitation of aromatic organosulfates in ambient aerosols in Lahore, Pakistan

“…These correlation analyses draw upon prior measurements reported elsewhere Shafer et al, 2010) and new measurements made in this study. Statistical analyses were limited to 13 monthly-average benzyl sulfate measurements, and other data with higher time resolution were averaged accordingly.…”

A new technique for online measurement of total and water-soluble copper (Cu) in coarse particulate matter (PM)

“…Recent studies suggest that the role of coarse PM on asthma and other diseases has been significantly underestimated (Becker et al, 2005;Becker and Soukup, 2003). Some other studies also demonstrated that Cu in coarse PM was strongly associated with the redox activity of these particles Shafer et al, 2010). This manuscript describes the development of a technique for online measurement of Cu in ambient coarse PM.…”