Association of Sulfur, Transition Metals, and the Oxidative Potential of Outdoor [PM.sub.2.5] with Acute Cardiovascular Events: A Case-Crossover Study of Canadian Adults

Background: We do not currently understand how spatiotemporal variations in the composition of fine particulate air pollution [fine particulate matter with aerodynamic diameter [less than or equal to] 2.5 [micro]m ([PM.sub.2.5])] affects population health risks. However, recent evidence suggests that joint concentrations of transition metals and sulfate may influence the oxidative potential (OP) of [PM.sub.2.5] and associated health impacts. Objectives: The purpose of the study was to evaluate how combinations of transition metals/OP and sulfur content in outdoor [PM.sub.2.5] influence associations with acute cardiovascular events. Methods: We conducted a national case-crossover study of outdoor [PM.sub.2.5] and acute cardiovascular events in Canada between 2016 and 2017 (93,344 adult cases). Monthly mean transition metal and sulfur (S) concentrations in [PM.sub.2.5] were determined prospectively along with estimates of OP using acellular assays for glutathione ([OP.sup.GSH]), ascorbate ([OP.sup.AA]), and dithiothreitol depletion ([OP.sup.DTT]). Conditional logistic regression models were used to estimate odds ratios (OR) [95% confidence intervals (CI)] for [PM.sub.2.5] across strata of transition metals/OP and sulfur. Results: Among men, the magnitudes of observed associations were strongest when both transition metal and sulfur content were elevated. For example, an OR of 1.078 (95% CI: 1.049, 1.108) (per 10 [micro]g/[m.sup.3]) was observed for cardiovascular events in men when both copper and S were above the median, whereas a weaker association was observed when both elements were below median values (OR= 1.019, 95% CI: 1.007, 1.031). A similar pattern was observed for OP metrics. [PM.sub.2.5] was not associated with acute cardiovascular events in women. Discussion: The combined transition metal and sulfur content of outdoor [PM.sub.2.5] influences the strength of association with acute cardiovascular events in men. Regions with elevated concentrations of both sulfur and transition metals in [PM.sub.2.5] should be examined as priority areas for regulatory interventions. https://doi.org/10.1289/EHP9449
Introduction Numerous epidemiological studies have documented the acute cardio-respiratory health impacts of outdoor fine particulate air pollution [fine particulate matter with aerodynamic diameter [less than or equal to] 2.5 [micro]m [...]