Abstract
Abstract. We assessed the oxidative potential (OP) of both water-soluble and methanol-soluble fractions of ambient fine particulate matter (PM2.5) in the Midwestern United States. A large set of PM2.5 samples (N=241) was collected from five sites set up in different environments, i.e., urban, rural, and roadside, in Illinois, Indiana, and Missouri during May 2018–May 2019. Five acellular OP endpoints, including the consumption rate of ascorbic acid and glutathione in a surrogate lung fluid (SLF) (OPAA and OPGSH, respectively), dithiothreitol (DTT) depletion rate (OPDTT), and ⚫OH generation rate in SLF and DTT (OPOH−SLF and OPOH−DTT, respectively), were measured for all PM2.5 samples. PM2.5 mass concentrations in the Midwestern US as obtained from these samples were spatially homogeneously distributed, while most OP endpoints showed significant spatiotemporal heterogeneity. Seasonally, higher activities occurred in summer for most OP endpoints for both water- and methanol-soluble extracts. Spatially, the roadside site showed the highest activities for most OP endpoints in the water-soluble extracts, while only occasional peaks were observed at urban sites in the methanol-soluble OP. Most OP endpoints showed similar spatiotemporal trends between mass- and volume-normalized activities across different sites and seasons. Comparisons between two solvents (i.e., water and methanol) showed that methanol-soluble OP generally had higher activity levels than corresponding water-soluble OP. Site-to-site comparisons of OP showed stronger correlations for methanol-soluble OP compared to water-soluble OP, indicating a better extraction of water-insoluble redox-active compounds from various emission sources into methanol. We found a weak correlation and inconsistent slope values between PM2.5 mass and most OP endpoints. Moreover, the poor to moderate intercorrelations among different OP endpoints indicate different mechanisms of OP represented by these endpoints and thus demonstrate the rationale for analyzing multiple acellular endpoints for a better and more comprehensive assessment of OP.
Highlights
IntroductionOxidative stress induced by ambient fine particulate matter (PM2.5; particulate matter with size less than 2.5 μm) has been widely recognized as a biological pathway for fine particles to exert adverse health effects in humans (Sørensen et al, 2003; Risom et al, 2005; Garçon et al, 2006; Wessels et al, 2010; Cachon et al, 2014; Haberzettl et al, 2016; Feng et al, 2016; Rao et al, 2018; Mudway et al, 2020)
We have previously developed an automated oxidative potential (OP) analysis instrument named SAMERA – the Semi-Automated Multi-Endpoint reactive oxygen species (ROS)-activity Analyzer – that can measure the five most commonly used OP endpoints for a particulate matter (PM) extract in less than 3 h (Yu et al, 2020)
We suggest that a collection of a diverse range of OP endpoints, measured separately as done in our study, could better capture the role of different PM components and their interactions via different pathways for driving the oxidative levels of the PM in a region
Summary
Oxidative stress induced by ambient fine particulate matter (PM2.5; particulate matter with size less than 2.5 μm) has been widely recognized as a biological pathway for fine particles to exert adverse health effects in humans (Sørensen et al, 2003; Risom et al, 2005; Garçon et al, 2006; Wessels et al, 2010; Cachon et al, 2014; Haberzettl et al, 2016; Feng et al, 2016; Rao et al, 2018; Mudway et al, 2020). A variety of chemical species in ambient particles, such as transition metals and aromatic organic species, possess redox cycling capability and can catalyze electron transfer from cellular reductants (e.g., NADPH) to molecular oxygen (O2), which subsequently forms highly reactive radicals (e.g., the superoxide radical – qO−2 – and the hydroxyl radical – qOH) and non-radical oxidants (e.g., hydrogen peroxide – H2O2) (Kampfrath et al, 2011; Qin et al, 2018; Kumagai et al, 2002; Lee et al, 2016) These oxygen-containing species with high redox activity and short lifetimes are collectively defined as reactive oxygen species (ROS). The capability of particulate matter (PM) to catalyze the generation of ROS and/or the depletion of antioxidants is defined as the oxidative potential (OP) of PM (Bates et al, 2019)
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