An hour sniffing exhaust fumes may not just give you a headache - it could even alter the way the brain functions, Dutch researchers have suggested.
The study replicated what city traffic wardens might expect to inhale
Scientists have known nanoparticles reach the brain when inhaled, but this is the first time they have been shown to affect how we process information.
Researchers sought to replicate the environment experienced by those who work in a garage or by the roadside.
Their findings were published in the journal Particle and Fibre Toxicology.
A team at Zuyd University in the Netherlands persuaded 10 volunteers to spend an hour in a room filled either with clean air or exhaust from a diesel engine.
They were wired up to an electroencephalograph (EEG), a device that records the electrical signals of the brain. They were monitored during the period of exposure and for an hour after they left the room.
After about 30 minutes, the brains of those in the exhaust rooms displayed a stress response on the EEG, which is indicative of a change in the way information is being processed in the brain cortex.
This effect continued after they were no longer in the room.
"We can only speculate what these effects may mean for the chronic exposure to air pollution encountered in busy cities where the levels of such soot particles can be very high," said lead researcher Paul Borm.
"It is conceivable that the long-term effects of exposure to traffic nanoparticles may interfere with normal brain function and information processing. Further studies are necessary to explore this effect."
The fact that the brain responds when confronted with a new smell is not entirely surprising, says Ken Donaldson, professor of respiratory toxicology at the University of Edinburgh.
"And it may not necessarily be negative, but such physiological changes do warrant investigation because there could indeed be a long-term effect. It's a very interesting, and potentially important, study."
Controlled studies examining the impact of pollution on the brain are ethically problematic, while longer-term studies of the population in polluted areas can be practically difficult as brain diseases are not necessarily noted on the death certificate as the cause of death.
Alzheimer's patients for instance often die of infection.
But a study of dogs in Mexico found those who lived in highly-polluted Mexico City had brain lesions similar to those seen in Alzheimer's patients, while those who lived in much less-polluted rural areas showed a much lower rate of damage to the brain.