Research A Cohort Study of Traffic-Related Air Pollution and Mortality in Toronto, Ontario, Canada Michael Jerrett,1 Murray M. Finkelstein,2 Jeffrey R. Brook,3 M. Altaf Arain,4 Palvos Kanaroglou,4 Dave M. Stieb,5 Nicolas L. Gilbert,5 Dave Verma,6 Norm Finkelstein,4 Kenneth R. Chapman,7 and Malcolm R. Sears8 1Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, Berkeley, California, USA; 2Department of Family and Community Medicine, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada; 3Meteorological Services, Environment Canada, Toronto, Ontario, Canada; 4School of Geography and Earth Science, McMaster University, Hamilton, Ontario, Canada; 5Healthy Environments and Consumer Safety Branch, Health Canada, Ottawa, Ontario, Canada; 6Program in Occupational Health & Environmental Medicine, McMaster University, Hamilton, Ontario, Canada; 7Division of Respirology, Department of Medicine, University of Toronto, Toronto, Ontario, Canada; 8Division of Respirology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada o Bjectivs Ontario, Canada. Bdnuorgkca : Chronic exposure to traffic-related air pollution (TRAP) may contribute to premature mortality, but few studies to date have addressed this topic. : In this study we assessed the association between TRAP and mortality in Toronto, 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 regres- sions to predict NO2 exposure on a fine scale within Toronto. We used interpolations to predict levels of particulate matter with aerodynamic diameter ≤ 2.5 µm (PM2.5) 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 pul- monologists. We tracked mortality between 1992 and 2002. We used standard and multilevel Cox proportional hazard models to test associations between air pollution and mortality. r esult : After controlling for age, sex, lung function, obesity, smoking, and neighborhood depriva- tion, we observed a 17% increase in all-cause mortality and a 40% increase in circulatory mortality from an exposure contrast across the interquartile range of 4 ppb NO2. We observed no significant associations with other pollutants. c isulcno : 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 the findings to populations with a substantial proportion of susceptible individuals. k ey words : air pollution, GIS, mortality, nitrogen dioxide, traffic air pollution, Toronto. Environ Health Perspect 117:772–777 (2009). doi:10.1289/ehp.11533 available via http://dx.doi.org/ [Online 5 January 2009] 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 2.5 years and a significant increase in all-cause mortal- ity 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 mat- ter (PM) ≤ 2.5 µm in aerodynamic diam- eter (PM2.5) in California have shown that 772 intraurban exposure gradients are associated with preclinical markers of atherosclerosis (Künzli 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; Künzli et al. 2005) used geo- statistical interpolation models that capture regional patterns of pollution well, but may not fully account for near-source impacts from local traffic because of the limited vari- ation in PM2.5 within cities and potential oversmoothing from the interpolation model used to assess exposure (Moore et al. 2007). The aforementioned European and Canadian studies used distance proxies for exposure to traffic, sparse government monitoring net- works to interpolate background exposure, or dispersion models with limited cross- validation against measured data. To date, no study has used extensive field measurements with well-validated models to assess the asso- ciation between TRAP and mortality. In this study, we applied 143 field measurements of nitrogen dioxide, an inorganic gas marker of TRAP, to a well-characterized cohort of patients from a respiratory clinic in Toronto, Ontario, Canada. Our objective was to assess the association between TRAP and mortality. Materials and Methods Study site description. We undertook our study in the City of Toronto, situated on the north- ern shore of Lake Ontario, Canada. Toronto is Canada’s largest city, with a metropolitan pop- ulation of nearly 4.7 million in 2001 (Statistics Canada 2001). Several busy expressways and numerous urban arterial roads traverse the city, leading to a wide range of variation in traffic exposures and related pollutants. The study cohort. Subjects for this study were drawn from a respiratory disease clinic in the Toronto Western Hospital, University Health Network, for the purpose of studying the health effects of air pollution. Patients seen at the clinic were referred to a pul- monologist for investigation or manage- ment of a respiratory complaint. The study was approved by the research ethics boards of the Mt. Sinai Hospital, Toronto, and the St. Joseph’s Health Center, Hamilton. All residents of Ontario are covered under the Ontario Health Insurance Plan (OHIP), a government-operated universal health insurance program. In 1992, unique Address correspondence to M. Jerrett, University of California, Berkeley, School of Public Health, Division of Environmental Health Sciences, 50 University Hall, Berkeley, CA 94720-7360 USA. Telephone: (510) 725-9991. Fax: (510) 642-5815. E-mail: jerrett@berkeley.edu Supplemental Material is available online at http:// www.ehponline.org/members/2009/11533/suppl.pdf This work was funded by Canadian Institutes of Health Research grant MOP-64463. The authors declare they have no competing financial interests. Received 2 April 2008; accepted 5 January 2009. ovlume 117 | number 5 | May 2009 • Environmental Health Perspectives