Oxidative potential (OP) is under active study as a metric that may be better than PM2.5 mass at predicting health outcomes. Here, we investigate how OP depends on chemical components, and how exposures to different levels of OP vary among socioeconomic groups in the Greater Los Angeles California area. We measured OH formation (OPOH) and dithiothreitol loss (OPDTT) for PM2.5 samples collected for two weeks each at 55 sites during September 2019 and February 2020. Our results show both volume-normalized and mass-normalized OPOH and OPDTT were highly correlated, and their association with PM2.5 was fairly strong. Because OPOH and OPDTT significantly correlate with PM2.5, their volume-normalized single-variate correlations with (total) metals are difficult to interpret. Mass-normalized OPOH and OPDTT were less correlated with the metals, with the highest correlations observed in Zr, Ba, Cu for OPOH and Pb, Ba, Zr for OPDTT. Of these, Zr has low solubility. We measured OPOH and OPDTT of the most active metals individually and in some cases, pairs. Our laboratory measurements confirmed the high activity for Cu(II) in both assays, and Fe(II) and to a lesser degree Fe(III) in the OH assay, and uncovered an antagonistic effect for Pb. Ba showed no activity in both assays. Additionally, we linked the OP data with CalEnviroScreen, a census block-level compilation of several socioeconomic, pollutant exposure and health outcomes metrics. The most socioeconomic disadvantaged quartile was exposed to about 27, 37 and 62% higher levels of PM2.5, OPDTT, and OPOH than the lowest quartile, respectively. The significant correlations observed between OPOH and all three health outcomes (adverse birth outcomes, cardiovascular events and asthma) in CalEnviroScreen, and between OPDTT and birth outcomes may suggest a role for the oxidative potential assays, particularly the OH assay, in predicting adverse health outcomes.

Associations between aerosol oxidative potential measured with the dithiothreitol and hydroxyl radical assays and metals, and socioeconomic status in the greater Los Angeles area

ACS Spring 2022

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