Memory Research News in Children's Learning

Air pollution exposure walking to school linked to slower growth of working memory

  • A large study has found higher levels of traffic-related air pollution, still within the EU safe limits, are associated with slower growth in working memory capacity in primary/elementary school children.

A Spanish study investigating the effects of traffic-related air pollution on children walking to school has found higher levels of particulate matter and black carbon were associated with decreased growth in working memory capacity. Working memory capacity grows during childhood (and tends to fall in old age).

The study involved 1,234 children aged 7-10, from 39 schools across the city of Barcelona. The children were tested four times over a year to establish their developmental trajectories in working memory and inattentiveness. Average particulate matter, black carbon, and nitrogen dioxide, were estimated for the children’s walking routes using standard measures.

None of the pollutants were associated with inattentiveness. The effect of NO2 on working memory was inconclusive. However, increased concentrations of particulate matter and black carbon were associated with a reduction in the annual growth of working memory of 4.6% and 3.9%, respectively. Boys were more affected than girls.

The study followed an earlier study showing that exposure to traffic-related pollutants in schools was associated with slower cognitive development. Research has previously shown that 20% of a child's daily dose of black carbon (which is directly related to traffic) is inhaled during urban commutes.

The finding emphasizes that even “short exposures to very high concentrations of pollutants can have a disproportionately high impact on health”, and this may be especially true for children, with their smaller lung capacity and higher breathing rate.

The researchers emphasize that the solution for parents is not to stop children walking to school, since those who commute by car or public transport are also exposed to the pollution. Rather, the aim should be to try and find (or make) less polluted, low-traffic paths to school.


[4326] Alvarez-Pedrerol M, Rivas I, López-Vicente M, Suades-González E, Donaire-Gonzalez D, Cirach M, de Castro M, Esnaola M, Basagaña X, Dadvand P, et al. Impact of commuting exposure to traffic-related air pollution on cognitive development in children walking to school. Environmental Pollution [Internet]. 2017 ;231:837 - 844. Available from:

Air pollution during pregnancy linked to cognitive impairment in children

  • A largish study involving school-age children not at any particular risk has found that higher levels of air pollution experienced by the mother during pregnancy are linked to less gray matter in some brain regions.

Research using data from a population-based birth cohort from Rotterdam, in The Netherlands, has found that children exposed to higher levels of air pollution when they were in womb had significantly thinner cortex in several brain regions. Some of this appeared to be related to impaired inhibitory control.

The study involved 783 children aged 6 to 10, who were given brain imaging and cognitive tests. Levels of air pollution in the mother’s environment during pregnancy were estimated using a standardized procedure. Mean fine particle levels were 20.2 μg/m3, and nitrogen dioxide levels were 39.3μg/m3. Note that the EU limit for mean fine particles is actually above that (25μg/m3), while the NO2 level is at the EU limit (40μg/m3), with 45% of the Dutch population experiencing higher levels. The World Health Organization sets a much lower level for fine particles: 10 μg/m3.

Children whose mothers were smokers were excluded from the study, as were children from areas where pollution measures weren’t available. Children included tended to be from a higher socio-economic position compared to those not included. Moreover, children with ADHD, or developmental or behavioral problems, were also excluded.

Global brain volume was not affected by fetal exposure. However, several brain regions showed significantly thinner cortex — in particular, the precuneus and rostral middle frontal regions, which partially accounted for the observed association between fetal exposure to fine particles and impaired inhibitory control (the ability to control your own behavior, especially impulsive behavior). This sort of cognitive impairment at early ages could have significant long-term consequences in academic achievement, later career success, and even in risk of mental disorders.

The findings are consistent with other studies linking acceptable air pollution levels with problems including cognitive impairment and child development.


[4325] Guxens M, Lubczyńska MJ, Muetzel RL, Dalmau-Bueno A, Jaddoe VWV, Hoek G, van der Lugt A, Verhulst FC, White T, Brunekreef B, et al. Air Pollution Exposure During Fetal Life, Brain Morphology, and Cognitive Function in School-Age Children. Biological Psychiatry [Internet]. 2018 . Available from: