Objective: to assess the association between daily variations in traffic-related air pollution and attention in primary school children.
Design: cohort study between January 2012 and March 2013.
Setting: classrooms in 39 schools in Barcelona (Catalonia, Spain).
Study population: primary school students (aged 7-10 years) without special education needs. The authors invited 5019 schoolchildren to participate, and obtained consent from the families of 2897 (59%).
Risk factor assessment: air quality levels were assessed through the levels of nitrogen dioxide (NO2) and elemental carbon (EC) in particle filters < 2.5 μm (PM 2.5). Measurements were made daily at a city monitoring station and twice in schools, 6 months apart, for four full days, Monday through Thursday. Schools were categorised by pollution level into high and low, by type into public or private, and by the socioeconomic vulnerability index of the neighbourhood (based on educational attainment, unemployment and occupation). The following were also measured: mean daily temperature and relative humidity, long-term exposure to NO2 and EC in the home based on the geographical location of the home address, and indoor noise level in each classroom.
Outcome measurement: cognitive development was assessed through change in attention and working memory functions. The authors assessed four domains of children’s attention processes every 3 months over four visits lasting 40 minutes each. They used the child attention network test (ANT) and the n-back task to assess working memory. Children with more than 30% of errors in any visit were excluded from the analysis (1.4%). Children performed the tasks on laptop computers with a specific psychology software (E-Prime, version 2.0). Teachers reported the presence or absence of symptoms of attention-deficit hyperactivity disorder (ADHD). Parents completed a strengths and difficulties questionnaire (SDQ) on child behavioural problems. The authors fit linear mixed effects models to test for associations between daily levels of pollutants and the quantitative outcomes at each visit, and negative binomial mixed regression models to assess associations with semiquantitative outcomes. Child and school variables were included as random effects in the models. The authors performed sensitivity analysis and assessed effect modification. Temporal trends were adjusted by semiparametric methods.
Main results: complete data were obtained for 2687 children. Daily ambient levels of both NO2 and EC were negatively correlated to every attention process. Children in the bottom quartile of daily exposure to ambient NO2 levels had a 14.8 ms (95% confidence interval [95 CI]: 11.2 to 18.4) faster time response than children in the top quartile, which was equivalent to a 1.1-month delay (95 CI: 0.84 to 1.37) in the natural developmental improvement in response speed with age. The results did not change significantly using alternative statistical models, or adjusting for indoor pollution in classrooms, sex, maternal educational attainment, ADHD symptoms, season or noise.
Attention parameters were moderately correlated with working memory, but the authors did not observe short-term associations between pollution and working memory.
Conclusion: The short-term association of traffic-related air pollutants with fluctuations in attention adds to the evidence that air pollution may have harmful effects on neurodevelopment.
Conflicts of interest: the authors declared that they had no conflicts of interest.
Funding source: funded by the European Research Council (ERC Grant agreement number 268479-the BREATHE project).