Children who attend school in heavy traffic areas may show slower cognitive development and lower memory test scores, Spanish researchers have found.

About 21,000 premature deaths are attributed to air pollution in Canada each year, according to the Canadian Medical Association. The detrimental effects of air pollution on cardiovascular health and on the lungs are well documented and now researchers are looking at its effects on the brain.

Cold weather in Sudbury

Car exhaust contains pollutants such as nitrogen dioxide. Authorities are recommending that schools be kept a safer distance from traffic emissions. (Yvon Theriault/CBC)

To that end, Dr. Jordi Sunyer and his colleagues from the Centre for Research in Environmental Epidemiology in Barcelona measured three aspects of memory and attentiveness in more than 2,700 primary school children every three months over 12 months.

"What was surprising for us is among our children, we see very robust, consistent effects," Sunyer said Tuesday from Rome.

The associations between slower cognitive development and higher levels of air pollutants remained after the researchers took factors such as parents’ education, commuting time, smoking in the home and green spaces at school into account.

The researchers measured air pollutants from traffic twice, in the school courtyard and inside the classroom for schools with high and low traffic-related air pollution. Pollutants from burning fossil fuels, carbon, nitrogen dioxide and ultrafine particles were measured.

For example, working memory improved 7.4 per cent among children in highly polluted schools compared with 11.5 per cent among those in less polluted schools.

Sunyer called on politicians to understand and act on how air pollution can be harmful to the developing brains of children, given that one of the cognitive measures studied is a good predictor of learning achievement.

The study builds on experiments in animal models and smaller human studies, Sunyer said. But the only way to prove a link between air pollution and poorer cognition would be to remove the cause and see if the effect improves.

Stop idling

The findings have important implications for Canadian children, said environmental health Prof. Ryan Allen of Simon Fraser University in Burnaby, B.C. His research team has found more than one-third of public elementary schools in Canadian cities are located within 200 metres of a highway or major road, a distance where he said traffic-related air pollutants are significantly elevated.

"The best long-term strategy is to reduce the amount of pollution that is produced in the first place," Allen said in an email. "We should also take environmental pollution into account when selecting sites for new schools. For example, legislation in California prevents the construction of new schools within 150 metres of a freeway." 

For existing schools, Allen suggested locating playgrounds as far from traffic as possible, moving air intakes for ventilation systems away from traffic and using enhanced air filtration.

University of Toronto chemistry Prof. Greg Evans studies sources of air pollution, how people get exposed and health outcomes. For Evans, it's too early for parents to worry about how close schools are to roads.

"What we can do, which really doesn't need more evidence, is try to reduce the traffic emissions and that is done most simply by removing some of the highest emitting vehicles on the roadway," Evans said. "Secondly, for parents who are worried about this, I'd encourage them to stop idling in front of schools."

While Canadian cities generally have good air quality, a 2013 commentary published in the Canadian Medical Association Journal estimated 54 per cent of the population live in areas with high exposure. 

Evans said the levels of traffic air pollutants measured in Spain are quite comparable to those in most Canadian cities. 

Sunyer would like to see more children walk to school, adults walk to work and more rides on public transit to mitigate the traffic problem. 

The study was funded by the European Research Council. 

With files from CBC's Christine Birak