London - Children exposed to even "safe" levels of air pollution in the womb have brain abnormalities and are less able to focus.
A study has found school-age children’s brains may be changed by fumes which come from traffic on city roads.
Aged six to ten, children exposed to air pollution as unborn babies find it harder to concentrate and avoid distraction.
MRI scans show the outer layer of their brains are thinner in areas related to self-control. The changes were seen in children whose mothers experienced air pollution within safe EU limits.
Lead author Dr Monica Guxens, from the Barcelona Institute for Global Health, said: "This finding adds to previous studies that have linked acceptable air pollution levels with other complications including cognitive decline and foetal growth development. Therefore, we cannot warrant the safety of the current levels of air pollution in our cities."
Dr John Krystal, editor of the journal Biological Psychiatry in which the study is published, said: "Air pollution is so obviously bad for lungs, heart, and other organs that most of us have never considered its effects on the developing brain.
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"But perhaps we should have learned from studies of maternal smoking that inhaling toxins may have lasting effects on cognitive development."
The results are taken from scans of 783 children in the Netherlands, whose mothers’ exposure to air pollution was taken by monitoring campaigns.
Measurements were taken of nitrogen dioxide, which comes mainly from traffic, especially diesel vehicles, and coarse and fine pollution particles.
A link was found between children exposed to fine particles in the womb and a thinner outer layer of the brain, called the cortex, in several regions.
The study suggests these brain abnormalities contribute to differences in self-control over temptations and impulsive behaviour which were seen in the children.
The average residential levels of fine particles in the study were well below the current acceptable limit set by the EU – only 0.5 percent of the pregnant