A Cohort Study of Traffic-Related Air Pollution and Mortality in Toronto, Ontario, Canada

By Jerrett, Michael; Finkelstein, Murray M. et al. | Environmental Health Perspectives, May 2009 | Go to article overview

A Cohort Study of Traffic-Related Air Pollution and Mortality in Toronto, Ontario, Canada


Jerrett, Michael, Finkelstein, Murray M., Brook, Jeffrey R., Arain, M. Altaf, Kanarogiou, Palvos, Stieb, Dave M., Gilbert, Nicolas L., Verma, Dave, Finkeistein, Norm, Chapman, Kenneth R., Sears, Malcolm R., Environmental Health Perspectives


BACKGROUND: Chronic exposure to traffic-related air pollution (TRAP) may contribute to premature mortality, but few studies to date have addressed this topic.

OBJECTIVES: In this study we assessed the association between TRAP and mortality in Toronto, Ontario, Canada.

METHODS: We collected nitrogen dioxide samples over two seasons using duplicate two-sided Ogawa passive diffusion samplers at 143 locations across Toronto. We calibrated land use regressions to predict [NO.sub.2] exposure on a fine scale within Toronto. We used interpolations to predict levels of particulate matter with aerodynamic diameter [less than or equal to]2.5 um ([PM.sub.2.5]) and ozone levels. We assigned predicted pollution exposures to 2,360 subjects from a respiratory clinic, and abstracted health data on these subjects from medical billings, lung function tests, and diagnoses by pulmonologists. We tracked mortality between 1992 and 2002. We used standard and multilevel Cox proportional hazard models to test associations between air pollution and mortality.

Results: After controlling for age, sex, lung function, obesity, smoking, and neighborhood deprivation, we observed a 17% increase in ail-cause mortality and a 40% increase in circulatory mortality from an exposure contrast across the interquartile range of 4 ppb [NO.sub.2]. We observed no significant associations with other pollutants.

CONCLUSIONS: Exposure to TRAP was significantly associated with increased all-cause and circulatory mortality in this cohort. A high prevalence of cardiopulmonary disease in the cohort probably limits inference of die findings to populations with a substantial proportion of susceptible individuals.

KEY WORDS: air pollution, GIS, mortality, nitrogen dioxide, traffic air pollution, Toronto. Environ Health Perspect 117:772-777 (2009). doi:10. 1289/ehp.l 1533 available via http://dx.doi.org/ [Online 5 January 2009]

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Recent evidence suggests that chronic exposure to traffic-related air pollution (TRAP) may be associated with premature mortality. Dutch researchers demonstrated a near doubling of cardiopulmonary mortality for subjects living near major roads (Hoek et al. 2002) although a more recent follow-up with a larger sample produced generally smaller but still elevated risk estimates (Beelen et al. 2007). A study from Norway reported an increase of 18% in male all-cause mortality based on a comparison of the lowest to the highest quartile of" exposure in nitrogen oxides estimated from a dispersion model (Nafstad et al. 2004). Canadian studies showed that subjects living close to major roads had mortality rate advancements of 2,3 years and a significant increase in all-cause mortality of 18% (Finkelstein et al. 2004). These large health effects might be attributable to higher intake fractions and subsequent doses for residents living near roadways (Marshall et al. 2005) or to the higher toxicity of traffic pollutants compared with other sources (Nel 2005; Schlesinger et al. 2006).

Studies of ambient particulate matter (PM) [less than or equal to]2.5 pm in aerodynamic diameter ([PM.sub.2.5]) in California have shown that intraurban exposure gradients are associated with preclinical markers of atherosclerosis (Kiinzli et al. 2005) and risks of premature mortality (Jerrett et al. 2005). Using a sub-cohort of about 23,000 from the American Cancer Society cohort in Los Angeles, Jerrett et al. (2005) observed relative risks (RRs) three times greater than those reported in the national study (Pope et al. 2002), with the major difference being the within- rather than between-city exposure assignment. This increase in the risk may have been attributable to more accurate exposure assignment or the relatively higher contribution of traffic sources in Los Angeles compared with other cities in the United States.

These recent Los Angeles studies (Jerrett et al. 2005; Kunzli et al. …

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