Abstract
Abstract. A variety of methods are used to measure the capability of particulate matter (PM) to catalytically generate reactive oxygen species (ROS) in vivo, also defined as the aerosol oxidative potential. A widely used measure of aerosol oxidative potential is the dithiothreitol (DTT) assay, which monitors the depletion of DTT (a surrogate for cellular antioxidants) as catalyzed by the redox-active species in PM. However, a major constraint in the routine use of the DTT assay for integrating it with large-scale health studies is its labor-intensive and time-consuming protocol. To specifically address this concern, we have developed a semi-automated system for quantifying the oxidative potential of aerosol liquid extracts using the DTT assay. The system, capable of unattended analysis at one sample per hour, has a high analytical precision (coefficient of variation of 15% for positive control, 4% for ambient samples) and reasonably low limit of detection (0.31 nmol min−1). Comparison of the automated approach with the manual method conducted on ambient samples yielded good agreement (slope = 1.08 ± 0.12, r2 = 0.92, N = 9). The system was utilized for the Southeastern Center for Air Pollution & Epidemiology (SCAPE) to generate an extensive data set on DTT activity of ambient particles collected from contrasting environments (urban, roadside, and rural) in the southeastern US. We find that water-soluble PM2.5 DTT activity on a per-air-volume basis was spatially uniform and often well correlated with PM2.5 mass (r = 0.49 to 0.88), suggesting regional sources contributing to the PM oxidative potential in the southeastern US. The correlation may also suggest a mechanistic explanation (oxidative stress) for observed PM2.5 mass-health associations. The heterogeneity in the intrinsic DTT activity (per-PM-mass basis) across seasons indicates variability in the DTT activity associated with aerosols from sources that vary with season. Although developed for the DTT assay, the instrument can also be used to determine oxidative potential with other acellular assays.
Highlights
Performance of the automated system was assessed by conducting tests to determine instrument response, limit of detection (LOD), precision, and accuracy using both positive controls and ambient particles
The system response was assessed by PQN, which was used as a positive control when running a series of ambient samples
The data show that water-soluble PM2.5 DTT activity on a per-volume-of-air basis was spatially uniform and generally correlated with PM2.5 mass (r = 0.49 to 0.88), indicating DTT activity in the southeast is likely, to a significant extent, related to regional sources and not dominated by a single source or a limited number of species
Summary
Epidemiological studies have associated increases in particulate matter (PM) levels with exacerbation of cardiovascular diseases (Zanobetti et al, 2014; Sun et al, 2010; Pope et al, 2004; Samet et al, 2000) and elevated incidence of respiratory disorders such as airway inflammation, bronchial muscle contraction, and asthma (Harkema et al, 2004; Schaumann et al, 2004; Aust et al, 2002; Norris et al, 1999) The mechanisms underlying these associations are not entirely clear, but reactive oxygen species (ROS) have been identified as a class of molecules that induce oxidative stress, causing cell damage (Nel, 2005; Gurgueira et al, 2002). Fang et al.: A semi-automated system for quantifying oxidative potential chemical components, when attempting to link aerosols and health end points
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