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Within-City Spatial Variations in Ambient Ultrafine Particle Concentrations and Incident Brain Tumors in Adults

Weichenthal, Scott*,1,2; Olaniyan, Toyib3; Christidis, Tanya3; Lavigne, Eric2; Hatzopoulou, Marianne4; Van Ryswyk, Keith2; Tjepkema, Michael3; Burnett, Rick5

doi: 10.1097/EDE.0000000000001137
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Background: Ambient ultrafine particles (UFPs, <0.1 µm) can reach the human brain but to our knowledge epidemiologic studies have yet to evaluate the relationship between UFPs and incident brain tumors.

Methods: We conducted a cohort study of within-city spatial variations in ambient UFPs across Montreal and Toronto, Canada among 1.9 million adults included in multiple cycles of the Canadian Census Health and Environment Cohorts (1991, 1996, 2001, and 2006). UFP exposures (3-year moving averages) were assigned to residential locations using land use regression models with exposures updated to account for residential mobility within and between cities. We followed cohort members for malignant brain tumors (ICD-10 codes C71.0-C71.9) between 2001 and 2016; Cox proportional hazards models (stratified by age, sex, immigration status, and census cycle) were used to estimate hazard ratios (HRs) adjusting for fine particle mass concentrations (PM2.5), nitrogen dioxide (NO2), and various sociodemographic factors.

Results: In total, we identified 1400 incident brain tumors during the follow-up period. Each 10,000/cm3 increase in UFPs was positively associated with brain tumor incidence (HR=1.112, 95% CI: 1.042, 1.188) after adjusting for PM2.5, NO2, and sociodemographic factors. Applying an indirect adjustment for cigarette smoking and body mass index strengthened this relationship (HR=1.133, 95% CI: 1.032, 1.245). PM2.5 and NO2 were not associated with an increased incidence of brain tumors.

Conclusions: Ambient UFPs may represent a previously unrecognized risk factor for incident brain tumors in adults. Future studies should aim to replicate these results given the high prevalence of UFP exposures in urban areas.

1 Department of Epidemiology, Biostatistics, and Occupational Health, McGill University, Montreal, Canada

2 Air Health Science Division, Health Canada, Ottawa, Canada

3 Statistics Canada, Ottawa, Canada

4 University of Toronto, Department of Civil Engineering, Toronto, Ontario, Canada

5 Population Studies Division, Health Canada, Ottawa, Canada

Conflict of interest: None declared.

Financial Support: This study was funded by Health Canada. Dr. Weichenthal also received support from a GRePEC salary award funded by the Cancer Research Society, the Quebec Ministry of Economy, Science and Innovation, and FRQS (Fonds de Recherche du Québec- Santé).

Data Availability: All exposure data used in this manuscript are freely available. The CanCHEC cohort is not publicly available but can be accessed through Statistics Canada Research Data Centers conditional on the necessary approval/review procedures.

*Corresponding Author:Dr. Scott Weichenthal , Department of Epidemiology, Biostatistics, and Occupational Health McGill University, 1020 avenue des Pins Ouest, Montreal, QC, Canada, H3A 1A2 Email: scott.weichenthal@mcgill.ca Tel: (514) 398-1584,

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