BACKGROUND: A few studies have reported associations between traffic-related air pollution exposure at schools and cognitive development. The role of PM components or sources other than traffic on cognitive development has been little explored. OBJECTIVES: We aimed to explore the role of PM sources in school air on cognitive development. METHODS: A cohort of 2,618 schoolchildren (average age, 8.5 years) belonging to 39 schools in Barcelona (Spain) was followed up for a year. Children completed computerized tests assessing working memory, superior working memory, and inattentiveness during four visits. Particulate matter ≤ 2.5 μm (PM2.5) was measured during two 1-week campaigns in each school, both outdoors and in the classroom. Source apportionment resulted in nine sources: mineral, organic/textile/chalk, traffic, secondary sulfate and organics, secondary nitrate, road dust, metallurgy, sea spray, and heavy oil combustion. Differences in cognitive growth trajectories were assessed with mixed models with age-by-source interaction terms. RESULTS: An interquartile range increase in indoor traffic-related PM2.5 was associated with reductions in cognitive growth equivalent to 22% (95% CI: 2%, 42%) of the annual change in working memory, 30% (95% CI: 6%, 54%) of the annual change in superior working memory, and 11% (95% CI: 0%, 22%) of the annual change in the inattentiveness scale. None of the other PM2.5 sources was associated with adverse effects on cognitive development. CONCLUSIONS: Traffic was the only source of fine particles associated with a reduction in cognitive development. Reducing air pollution from traffic at primary schools may result in beneficial effects on cognition.

This work was supported by the European Research Council under the ERC [grant number 268479] – the BREATHE project. Fulvio Amato is beneficiary of the Juan de la Cierva postdoctoral Grant (JCI-2012-13473) from the Spanish Ministry of Economy and Competitiveness. We are acknowledged with all the families participating into the study for their altruism and particularly to the schools Antoni Brusi, Baloo, Betània – Patmos, Centre d’estudis Montseny, Col.legi Shalom, Costa i Llobera, El sagrer, Els Llorers, Escola Pia de Sarrià, Escola Pia Balmes, Escola concertada Ramon Llull, Escola Lourdes, Escola Tècnica Professional del Clot, Ferran i Clua, Francesc Macià, Frederic Mistral, Infant Jesús, Joan Maragall, Jovellanos, La Llacuna del Poblenou, Lloret, Menéndez Pidal, Nuestra Señora del Rosario, Miralletes, Ramon Llull, Rius i Taulet, Pau Vila, Pere Vila, Pi d'en Xandri, Projecte, Prosperitat, Sant Ramon Nonat - Sagrat Cor, Santa Anna, Sant Gregori, Sagrat Cor Diputació, Tres Pins, Tomàs Moro, Torrent d'en Melis, Virolai. We also acknowledge the ESCAPE project for the design and supervision modelling of air pollution. Furthermore, Xavier Mayoral did the technical development of the n-back test; Cecilia Persavento, Judit Gonzalez, Laura Bouso and Pere Figueras contributed to the field work.