Within-City Variation in Reactive Oxygen Species from Fine Particle Air Pollution and COVID-19

RATIONALE Evidence linking outdoor air pollution with COVID-19 incidence and mortality is largely based on ecological comparisons between regions that may differ in factors such as access to testing and control measures that may not be independent of air pollution concentrations. Moreover, studies have yet to focus on key mechanisms of air pollution toxicity such as oxidative stress. OBJECTIVES To conduct a within-city analysis of spatial variations in COVID-19 incidence and the estimated generation of reactive oxygen species (ROS) in lung lining fluid attributable to fine particulate matter (PM2.5). METHODS Sporadic and outbreak-related COVID-19 case counts, testing data, population and sociodemographic data for 140 neighbourhoods were obtained from the City of Toronto. ROS estimates were based on a mathematical model of ROS generation in lung lining fluid in response to iron and copper in PM2.5. Spatial variations in long-term average ROS were predicted using a land use regression model derived from measurements of iron and copper in PM2.5. Data were analyzed using negative binomial regression models adjusting for covariates identified using a directed acyclic graph and accounting for spatial autocorrelation. MEASUREMENTS AND MAIN RESULTS A significant positive association was observed between neighbourhood level ROS and COVID-19 incidence (incidence rate ratio = 1.07, 95% confidence interval 1.01-1.15 per interquartile range ROS). Effect modification by neighbourhood-level measures of racialized group membership and socioeconomic status was also identified. CONCLUSIONS Examination of neighbourhood characteristics associated with COVID-19 incidence can identify inequalities and generate hypotheses for future studies. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/).