Greater exposure to ambient ultrafine particles (UFPs, <0.1 µm) produced by fuel burning could increase people’s chances of getting brain cancer according to a new study by a team of researchers in Canada in the journal Epidemiology. This is the first study to suggest a relationship with the incidence of brain tumors, although previous work has shown that nanoparticles can get into the brain and that they can carry carcinogenic chemicals.

An open-access paper on the work is published in the journal Epidemiology.

The researchers 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).

The researchers assigned UFP exposures (3-year moving averages) to residential locations using land use regression models with exposures updated to account for residential mobility within and between cities.

They followed cohort members for malignant brain tumors 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 (PM_2.5), nitrogen dioxide (NO₂), and various sociodemographic factors.

In total, they identified 1,400 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 PM_2.5, 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). PM_2.5 and NO₂ were not associated with an increased incidence of brain tumors.

… we conducted to our knowledge the first cohort study of outdoor UFP concentrations and incident brain tumors and noted a consistent positive association. This relationship was robust to adjustment for various sociodemographic factors as well as indirect adjustment for smoking and body mass index. Future studies should aim to replicate our findings as UFPs are known to reach the human brain and exposure prevalence is high in urban areas around the world.

—Weichenthal et al.

Resources

• Weichenthal, Scott; Olaniyan, Toyib; Christidis, Tanya; Lavigne, Eric; Hatzopoulou, Marianne; Van Ryswyk, Keith; Tjepkema, Michael; Burnett, Rick (2019) “Within-City Spatial Variations in Ambient Ultrafine Particle Concentrations and Incident Brain Tumors in Adults” Epidemiology doi: 10.1097/EDE.0000000000001137