BACKGROUND Immigrants make up 20% of the Canadian population; however, little is known about the mortality impacts of fine particulate matter (PM) air pollution on immigrants compared with non-immigrants, or about how impacts may change with duration in Canada . DATA AND
METHODS This study used the 2001 Canadian Census Health and Environment Cohort, a longitudinal cohort of 3.5 million individuals, of which 764,000 were classified as immigrants (foreign-born). Postal codes from annual income tax files were used to account for mobility among respondents and to assign annual PM concentrations from 1998 to 2016 . Exposures were estimated as a three-year moving average prior to the follow-up year . Cox survival models were used to determine hazard ratios (HRs) for cause-specific mortality, comparing the Canadian and foreign-born populations, with further stratification by year of immigration grouped into 10-year cohorts .
RESULTS Differences in urban-rural settlement patterns resulted in greater exposure to PM for immigrants compared with non-immigrants (mean = 9.3 vs. 7.5 μg/m), with higher exposures among more recent immigrants . In fully adjusted models, immigrants had higher HRs per 10 μg/m increase in PM concentration compared with Canadian-born individuals for cardiovascular mortality (HR [95% confidence interval] = 1.22 [1.12 to 1.34] vs. 1.12 [1.07 to 1.18] ) and cerebrovascular mortality (HR = 1.25 [1.03 to 1.52] vs. 1.03 [0.93 to 1.15] ), respectively . However, tests for differences between the two groups were not significant when Cochran's Q test was used . No significant associations were found for respiratory outcomes, except for lung cancer in non-immigrants (HR = 1.10 [1.02 to 1.18] ). When stratified by year of immigration, differences in HRs across varied by cause of death .
DISCUSSION In Canada, PM is an equal-opportunity risk factor, with immigrants experiencing similar if not higher mortality risks compared with non-immigrants for cardiovascular-related causes of death . Some notable differences also existed with cerebrovascular and lung cancer deaths . Continued reductions in air pollution, particularly in urban areas, will improve the health of the Canadian population as a whole.