Long-term associations of sector-specific air pollution mixtures with mortality in Canada

Previous studies often focus on individual air pollutants rather than their mixtures or specific sources. To assess associations between mixtures of fine particulate matter (PM_2.5), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and ozone (O₃) from various industrial and residential sources and mortality from ischemic heart disease (IHD), cardiovascular disease (CVD), and non-accidental causes. The 2006 Canadian Census Health and Environment Cohort (CanCHEC) was linked to the Canadian Vital Statistics Database included 3,019,125 adults with 36,112,640 person-years of follow-up. Between 2006 and 2019, 56,190 IHD, 98,185 CVD, and 381,050 non-accidental deaths were identified. Annual concentrations of PM_2.5, SO₂, NO₂, and O₃ from upstream and downstream petroleum, non-ferrous smelting, the chemical industry, and residential fuel combustion were estimated by GEM-MACH model and assigned to participants' residential postal codes. Quantile g-computation estimated hazard ratios (HRs) per quartile increase in pollutant mixtures. We observed significant associations of IHD, CVD, and non-accidental mortality with the mixtures of air pollutants emitted from upstream petroleum [HR: 1.18 (95 % CI: 1.12-1.24), 1.12 (1.08-1.16), and 1.05 (1.04-1.05)], downstream petroleum [1.06 (1.05-1.08), 1.04 (1.03-1.05), and 1.03 (1.02-1.03)], chemical industry [1.10 (1.08-1.13), 1.07 (1.06-1.09), and 1.10 (1.08-1.13)], and residential fuel combustion [1.18 (1.12-1.23), 1.12 (1.08-1.16), and 1.07 (1.05-1.09)]. PM_2.5 and SO₂ contributed most to increased mortality risks, while non-ferrous smelting emissions showed no association with CVD and non-accidental causes. PM_2.5 and SO₂ from certain sectors, but not all, greatly contribute to the increased risk of non-accidental, IHD, and CVD deaths.