Congested cities are fast becoming test tubes for scientists studying the impact of traffic fumes on the brain.
As roadways choke on traffic, researchers suspect that the tailpipe exhaust from cars and trucks—especially tiny carbon particles already implicated in heart disease, cancer and respiratory ailments—may also injure brain cells and synapses key to learning and memory.
New public-health studies and laboratory experiments suggest that, at every stage of life, traffic fumes exact a measurable toll on mental capacity, intelligence and emotional stability. "There are more and more scientists trying to find whether and why exposure to traffic exhaust can damage the human brain," says medical epidemiologist Jiu-Chiuan Chen at the University of Southern California who is analyzing the effects of traffic pollution on the brain health of 7,500 women in 22 states. "The human data are very new."
So far, the evidence is largely circumstantial but worrisome, researchers say. And no one is certain yet of the consequences for brain biology or behavior. "There is real cause for concern," says neurochemist Annette Kirshner at the National Institute of Environmental Health Sciences at Research Triangle Park in North Carolina. "But we ought to proceed with caution."
To be sure, cars and trucks today generate one-tenth the pollution of a vehicle in 1970. Still, more people are on the road and they are stuck in traffic more often. Drivers traveling the 10-worst U.S. traffic corridors annually spend an average of 140 hours, or about the time spent in the office in a month, idling in traffic, a new analysis reported.
No one knows whether regular commuters breathing heavy traffic fumes suffer any lasting brain effect. Researchers have only studied the potential impact based on where people live and where air-pollution levels are highest. Even if there were any chronic cognitive effect on drivers, it could easily be too small to measure reliably or might be swamped by other health factors such as stress, diet or exercise that affect the brain, experts say.
Recent studies show that breathing street-level fumes for just 30 minutes can intensify electrical activity in brain regions responsible for behavior, personality and decision-making, changes that are suggestive of stress, scientists in the Netherlands recently discovered. Breathing normal city air with high levels of traffic exhaust for 90 days can change the way that genes turn on or off among the elderly; it can also leave a molecular mark on the genome of a newborn for life, separate research teams at Columbia University and Harvard University reported this year.
Children in areas affected by high levels of emissions, on average, scored more poorly on intelligence tests and were more prone to depression, anxiety and attention problems than children growing up in cleaner air, separate research teams in New York, Boston, Beijing, and Krakow, Poland, found. And older men and women long exposed to higher levels of traffic-related particles and ozone had memory and reasoning problems that effectively added five years to their mental age, other university researchers in Boston reported this year. The emissions may also heighten the risk of Alzheimer's disease and speed the effects of Parkinson's disease.
"The evidence is growing that air pollution can affect the brain," says medical epidemiologist Heather Volk at USC's Keck School of Medicine. "We may be starting to realize the effects are broader than we realized."