Iron and copper in fine particulate matter, reactive oxygen species concentration in lung epithelial fluid and respiratory health: A population-based cohort study

Abstract

Background: Metal components in fine particulate matter (PM2.5) originating from non-tailpipe emissions may play important roles in underlying its adverse effects on respiratory health due to the potential in generating reactive oxygen species (ROS). However, relevant epidemiological evidence is scarce. Methods: We investigated the associations of long-term exposure to iron (Fe) and copper (Cu) in PM2.5 (two metal components mainly originating from non-tailpipe emissions), and their combined impact on the concentration of reactive oxygen species (ROS) with respiratory health in a population-based cohort of ~0.8 million adults in Toronto, Canada. Incidence of asthma, chronic obstructive pulmonary disease (COPD) and respiratory mortality was ascertained using health administrative databases. Exposures to Fe and Cu in PM2.5 and their combined impact on ROS were estimated using land use regression models. We used mixed-effects Cox regression models to examine the associations between the exposures and health outcomes. Results: We found positive associations between long-term exposure to Fe, Cu and ROS, and the risks of all three respiratory outcomes. The associations were more robust for COPD and respiratory disease death than for asthma. In terms of exposures, we observed stronger associations for ROS than for Fe or Cu individually. For example, the hazard ratios (95% confidence interval) for respiratory death associated with an interquartile-range increment in Fe, Cu and ROS were 1.046 (1.034, 1.058), 1.020 (1.008, 1.033) and 1.076 (1.058, 1.094), respectively. In two-pollutant models, adjustment for NO2 attenuated the associations while PM2.5 had little influence. Conclusions: Long-term exposure to Fe and Cu in PM2.5 and estimated ROS concentration in lung fluid was associated with increased incidence of respiratory outcomes, particularly COPD and respiratory mortality, suggesting adverse respiratory effects of non-tailpipe emitted air pollution.