Oxidative potential (OP) has been widely recognized as a potential mechanism for explaining the health effect of PM2.5. However, different OP endpoints are linked with different biological pathways of PM2.5 in expressing oxidative stress. Here, we developed a semi-automated multi-endpoint reactive oxygen species (ROS)-activity analyzer (SAMERA) which integrated five commonly used acellular OP endpoints, including the consumption rate of ascorbic acid and glutathione in 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) for automatic OP measurement. High analytical precision and high accuracy obtained from the comparison between SAMERA and manual operation ensured the quality assurance of OP data generated by SAMERA, while the reduced time (less than 3 h for a single sample) and labor guaranteed a high throughput for its application into epidemiological studies. SAMERA was employed in analyzing a large set of PM2.5 samples (N = 241) collected from five sites, encompassing urban, rural and roadside environments, in Midwest US and extracted in water and methanol separately. A higher heterogeneity in spatiotemporal profile was observed for most OP endpoints than PM2.5 mass. Seasonally, higher activities occurred in summer for SLF-based OP (i.e. OPAA, OPGSH and OPOH-SLF) and OPOH-DTT for both water- and methanol-soluble extracts. Spatially, roadside site showed highest SLF-based OP activities among all sites for water-soluble extracts, while only occasional peaks were observed at urban sites for those endpoints in methanol-soluble extracts. OPDTT was spatiotemporally uniformly distributed for both water- and methanol-soluble extracts. The poor-to-moderate intercorrelations among different OP endpoints infer different mechanisms of OP represented by these endpoints, and thus demonstrate the rationale for analyzing multiple acellular endpoints for a better and comprehensive assessment of OP.

Development of a semi-automated multi-endpoint ROS activity analyzer (SAMERA) and its application in assessing spatiotemporal variability of PM2.5 oxidative potential in Midwest USA

ACS Fall 2021

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