Association of Sulfur, Transition Metals, and the Oxidative Potential of Outdoor PM2.5 with Acute Cardiovascular Events: A Case-Crossover Study of Canadian Adults

Abstract

Background: We do not currently understand how spatiotemporal variations in the composition of fine particulate air pollution [fine particulate matter with aerodynamic diameter $\le 2.5\mu m$ (${\mathrm{PM}}_{2.5}$)] affects population health risks. However, recent evidence suggests that joint concentrations of transition metals and sulfate may influence the oxidative potential (OP) of ${\mathrm{PM}}_{2.5}$ and associated health impacts.

Objectives: The purpose of the study was to evaluate how combinations of transition metals/OP and sulfur content in outdoor ${\mathrm{PM}}_{2.5}$ influence associations with acute cardiovascular events.

Methods: We conducted a national case-crossover study of outdoor ${\mathrm{PM}}_{2.5}$ and acute cardiovascular events in Canada between 2016 and 2017 (93,344 adult cases). Monthly mean transition metal and sulfur (S) concentrations in ${\mathrm{PM}}_{2.5}$ were determined prospectively along with estimates of OP using acellular assays for glutathione (${\text{OP}}^{\text{GSH}}$), ascorbate (${\text{OP}}^{\text{AA}}$), and dithiothreitol depletion (${\text{OP}}^{\text{DTT}}$). Conditional logistic regression models were used to estimate odds ratios (OR) [95% confidence intervals (CI)] for ${\mathrm{PM}}_{2.5}$ 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 ${10\mu g/m}^3$) 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 ($\text{OR}=1.019$, 95% CI: 1.007, 1.031). A similar pattern was observed for OP metrics. ${\mathrm{PM}}_{2.5}$ was not associated with acute cardiovascular events in women.

Discussion: The combined transition metal and sulfur content of outdoor ${\mathrm{PM}}_{2.5}$ influences the strength of association with acute cardiovascular events in men. Regions with elevated concentrations of both sulfur and transition metals in ${\mathrm{PM}}_{2.5}$ should be examined as priority areas for regulatory interventions. https://doi.org/10.1289/EHP9449.