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Global Perspective on the Oxidative Potential of Airborne Particulate Matter: A Synthesis of Research Findings Arian Saffari, Nancy Daher, Martin M. Shafer, James J. Schauer, and Constantinos Sioutas Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es500937x • Publication Date (Web): 29 May 2014 Downloaded from http://pubs.acs.org on June 2, 2014
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Environmental Science & Technology
Global Perspective on the Oxidative Potential of Airborne Particulate Matter: A Synthesis of Research Findings
Arian Saffari1, Nancy Daher1, Martin M. Shafer2, James J. Schauer2, Constantinos Sioutas1*
1
University of Southern California, Department of Civil and Environmental Engineering, Los Angeles, CA, USA
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University of Wisconsin-Madison, Department of Civil and Environmental Engineering, Madison, WI, USA
*Corresponding Author Email address:
[email protected] Tel: +1 213 740 6134; Fax: +1 213 744 1426
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Abstract Art
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Abstract 1
An emerging hypothesis in the field of air pollution is that oxidative stress is one of the
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important pathways leading to adverse health effects of airborne particulate matter (PM). To
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advance our understanding of sources and chemical elements contributing to aerosol oxidative
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potential and provide global comparative data, we report here on the biological oxidative
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potential associated with size-segregated airborne PM in different urban areas of the world,
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measured by a biological (cell-based) reactive oxygen species (ROS) assay. Our synthesis
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indicates a generally greater intrinsic PM oxidative potential as well as higher levels of exposure
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to redox-active PM in developing areas of the world. Moreover, based on our observations,
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smaller size fractions are generally associated with higher intrinsic ROS activity compared to
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larger PM size fractions. Another important outcome of our study is the identification of major
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species and sources that are associated with ROS activity. Water-soluble transition metals (e.g.
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Fe, Ni, Cu, Cr, Mn, Zn and V) and water-soluble organic carbon (WSOC) showed consistent
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correlations with the oxidative potential of airborne PM across different urban areas and size
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ranges. The major PM sources associated with these chemical species include residual/fuel oil
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combustion, traffic emissions and secondary organic aerosol formation, indicating that these
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sources are major drivers of PM-induced oxidative potential. Moreover, comparison of ROS
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activity levels across different seasons indicated that photochemical aging increases the intrinsic
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oxidative potential of airborne PM.
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Keywords: Oxidative potential, Particulate matter (PM), Chemical composition, Sources,
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Reactive oxygen species (ROS)
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In recent years, there has been increasing attention paid to air pollution associated with airborne
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particulate matter (PM) due to the complicated composition and source profile of PM compared
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to other air pollutants as well as their capability to carry significant quantities of toxic
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chemicals.1,2 Numerous studies have linked PM exposure to a wide range of adverse health
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endpoints, including, but not limited to, cardiovascular diseases,3 respiratory problems4 and
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adverse neuro-developmental effects5. Many of the toxic effects of PM are thought to be
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mediated by inflammatory responses, originating from PM-induced oxidative activity leading to
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the generation of reactive oxygen species (ROS) upon the interaction of PM with epithelial cells
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and macrophages.6–9 Several studies have attempted to develop assays to quantify PM oxidative
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potential, using mostly abiotic, non-cellular methods.10–13 Although these methods can, in theory,
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be used to measure PM oxidative stress, they have limited physiological relevance to real-world
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PM exposure, since they do not directly simulate the actual PM-cell interaction and its biological
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inflammatory responses. In a recent cohort epidemiological study conducted in the Los Angeles
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area, it was shown that the cell-based macrophage assay, used in our present analysis,
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demonstrates a robust association with airway as well as systematic inflammation biomarkers
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that lead to adverse health effects.14 This assay employs a fluorescent probe (2´,7´-
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dichlorodihydrofluorescein diacetate, DCFH-DA) to quantify PM oxidative potential, induced by
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the generation of ROS upon interaction of redox-active particle components with macrophage rat
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alveolar cells.15 Here we integrate the results of several studies that we conducted over the last
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decade at different locations across the world, in order to highlight and synthesize the
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overarching conclusions and observations regarding the relation of PM-induced oxidative
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potential with particle chemical composition and sources.
Introduction
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In Table 1 we summarize relevant information about previous studies that are considered in our
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synthesis. The analytical measurements conducted in each study are also listed in Table 1. In
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brief, comprehensive elemental characterization of PM collected on Teflon filters was performed
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using microwave-assisted mixed-acid digestion and high-resolution sector field inductively
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coupled plasma mass spectrometry (ICP-MS) of the digestate, as described in Herner et al.16
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Water-soluble organic carbon (WSOC) was measured by a Sievers 900 Total Organic Carbon
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Analyzer, following water-extraction and filtration (0.22 µm) of the samples.17 Organic carbon
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(OC) and elemental carbon (EC) concentrations were quantified from PM collected on quartz
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filters by NIOSH thermal optical transmission method.18 Gas chromatography mass spectrometry
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(GC-MS) (as described in Stone et al.19) as well as Ion chromatography (IC)20 were further
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employed in some of the studies to speciate, in detail, organic compounds and inorganic ions,
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respectively. It should be noted that in this study, we focused on reporting chemical species that
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exhibited strong (i.e. R>0.7 and p
