Barbara Maher of Lancaster University (UK) and her team looked at the brains of 37 people who had lived in Manchester in the UK or Mexico City. All contained millions of iron oxide nanoparticles per gram of brain tissue, suggesting that tiny specks of metal in car exhaust gases seem to fly up our noses and travel into our brains, where they may contribute to Alzheimer’s disease.

A closer look at six brains found that round particles outnumbered angular crystals 100 to one. Crystal forms of iron oxide are more likely to have a natural source, whereas round particles normally come from melting iron at high temperatures. Maher says the particles’ round shape is compelling evidence that they come from pollution. These nanoparticles are less than 200 nanometres in diameter, so may be moving from the air into the nerve endings in our noses, and from there to the brain, says Maher’s team.

Previous work on cells grown in the lab has suggested that iron oxide is present in the protein plaques thought to have a role in Alzheimer’s disease, and that it generates reactive compounds called free radicals, which can kill nerve cells. Population studies have found that people who live nearer busy roads have a higher risk of mental impairment in old age.(Clare Wilson, New Scientist)

The good news is that studies have also found that our risk of getting Alzheimer’s by a particular age is falling, so if pollution is contributing to the disease, it doesn’t seem to be making it more common. Even so, reducing air pollution might cut our risk of Alzheimer’s. There is a serious possibility now that electric cars are really going to catch on, that their cost will come down, and the re-charging issue will be solved. If this finally materialises then the health of all those living in cities or near busy roads should improve.