Scientists in the US have found evidence to suggest that exposure to sooty traffic fumes are costing children up to 3 IQ points of intelligence.
Writing in the American Journal of Epidemiology Harvard researcher Shakira Franco Suglia studied 200 children living in Boston, US, and found that those with the highest exposure to traffic pollution performed less well on intelligence tests than their cleaner-breathing counterparts, even after taking factors such as social class into account. This puts traffic pollution on par with lead in terms of its potential to stunt a child's brain development, although the researchers aren't yet sure exactly which components of exhaust fumes are responsible.
But previous studies on animals suggests that particulates (tiny invisible particles smaller than the body's own cells) are likely to be the culprits. These can enter the bloodstream through the lungs but there is also evidence that they can penetrate into the central nervous system via the nose, travelling along the olfactory nerves that carry the sense of smell into the brain. Once there they can directly damage cells and also trigger inflammation that further injures the brain. So the possibility is not as unlikely as it sounds. Indeed studies on dogs living on the smoggy streets of Mexico City have been shown that animals exposed to the most pollution develop brain damage similar to the changes seen in humans with Alzheimer's Disease.
Now researchers need to track down what components of traffic pollution are responsible and determine how to remove them from the exhaust pipes of the millions of cars and trucks pounding the tarmac of big cities in every part of the world...so don't hold your breath. Or on second thoughts, do hold your breath!