Risk of Nonaccidental and Cardiovascular Mortality in Relation to Long-term Exposure to Low Concentrations of Fine Particulate Matter: A Canadian National-Level Cohort Study

TLDR

Few cohort studies have evaluated the risk of mortality associated with long‑term exposure to fine particulate matter (PM₂.₅). The study investigates the association between long‑term ambient PM₂.₅ exposure and cardiovascular mortality in 2.1 million nonimmigrant Canadian adults using satellite‑derived exposure estimates. Deaths from 1991‑2001 were identified via record linkage, and hazard ratios were estimated with standard Cox and spatial random‑effects survival models adjusted for individual and contextual covariates. Long‑term exposure to PM₂.₅ was associated with increased cardiovascular mortality, with hazard ratios of 1.15 for nonaccidental deaths and 1.31 for ischemic heart disease per 10 µg/m³ increase (Cox models), and 1.10 and 1.30 respectively (spatial models), even at mean concentrations of 8.7 µg/m³.

Abstract

Few cohort studies have evaluated the risk of mortality associated with long-term exposure to fine particulate matter [≤ 2.5 μm in aerodynamic diameter (PM(2.5))]. This is the first national-level cohort study to investigate these risks in Canada.We investigated the association between long-term exposure to ambient PM(2.5) and cardiovascular mortality in nonimmigrant Canadian adults.We assigned estimates of exposure to ambient PM(2.5) derived from satellite observations to a cohort of 2.1 million Canadian adults who in 1991 were among the 20% of the population mandated to provide detailed census data. We identified deaths occurring between 1991 and 2001 through record linkage. We calculated hazard ratios (HRs) and 95% confidence intervals (CIs) adjusted for available individual-level and contextual covariates using both standard Cox proportional survival models and nested, spatial random-effects survival models.Using standard Cox models, we calculated HRs of 1.15 (95% CI: 1.13, 1.16) from nonaccidental causes and 1.31 (95% CI: 1.27, 1.35) from ischemic heart disease for each 10-μg/m(3) increase in concentrations of PM(2.5). Using spatial random-effects models controlling for the same variables, we calculated HRs of 1.10 (95% CI: 1.05, 1.15) and 1.30 (95% CI: 1.18, 1.43), respectively. We found similar associations between nonaccidental mortality and PM2.5 based on satellite-derived estimates and ground-based measurements in a subanalysis of subjects in 11 cities.In this large national cohort of nonimmigrant Canadians, mortality was associated with long-term exposure to PM(2.5). Associations were observed with exposures to PM(2.5) at concentrations that were predominantly lower (mean, 8.7 μg/m(3); interquartile range, 6.2 μg/m(3)) than those reported previously.