Increased Rates of Neurocognitive Issues Linked to High Traffic Areas

Excess levels of tailpipe exhaust from high traffic areas are already connected to heart disease, cancer, and respiratory ailments, but numerous recent studies indicate that exhaust fumes may also affect mental capacity, intelligence, emotional stability, and overall cognitive function—including increased rates of autism—at every stage of life.

The studies and laboratory experiments have been conducted in multiple areas globally—from New York City to the Netherlands—and the results are uncannily similar. So far, the data is circumstantial—but as more and more studies are published, the evidence accumulates and paints a worrisome picture.

"There are more and more scientists trying to find whether and why exposure to traffic exhaust can damage the human brain," reported medical epidemiologist Jiu-Chiuan Chen from the University of Southern California. Chen is currently assessing 7,500 women across 22 states concerning the possible effect traffic pollution can have on brain health. "The human data are very new,” he continued.

Earlier this year, two separate studies from Columbia University and Harvard University found that continued exposure to polluted air can leave a lifelong molecular mark on the genome of a newborn.

An unrelated study performed by scientists in the Netherlands discovered that an individual breathing street-level fumes for just 30 minutes will experience more intense electrical activity in brain regions accountable for behavior, personality, and decision-making—a change that is normally an indication of stress, they stated. Further, they found that an elderly individual breathing normal city air with high levels of traffic exhaust for 90 days could suffer alterations to how his/her genes turn on or off.

Researchers in Boston reported that older men and women who are exposed to higher levels of traffic-related particles and ozone for long periods of time suffered from memory and reasoning difficulties. In total, these cognitive issues added five years to their mental age. With these alterations in mind, it is theorized that the emissions may also increase the risk of Alzheimer's disease and accelerate the effects of Parkinson's disease.

In an interesting display of how exhaust seems to have the same effects on human beings globally, separate research teams in New York, Boston, Beijing, Karkow, and Poland all reached the same conclusion when studying the intelligence and emotional stability of children residing in areas affected by high levels of emissions. On average, such children scored worse on IQ tests and were more prone to depression, anxiety, and attention issues than children who lived in areas with cleaner air.

"The evidence is growing that air pollution can affect the brain," said medical epidemiologist Heather Volk at USC's Keck School of Medicine. "We may be starting to realize the effects are broader than we realized."

The most unsettlingly find of all, however, may be what Volk and her colleagues discovered when reviewing birth records. They calculated that children born to mothers who resided within 1,000 feet of a major road or freeway in Los Angeles, San Francisco, or Sacramento were twice as likely to be autistic. This correlation was found to be isolated to many autism-related factors, such as gender, ethnicity, and education level, maternal age, and cigarette smoke exposure. The results were published earlier this year in the journal Environmental Health Perspectives.

"Based on our data, it looks like air pollution might be a risk factor for autism," Dr. Volk said. There were too many other potential genetic and environmental influences involved in the study, however, that she deemed it "too soon for alarm.”

In 1998, Frederica Perera at Columbia University's Center for Children's Environmental Health began a study on the potential effect exhaust could have on expectant mothers and their babies. She gave hundreds of women personal air monitors to gauge the chemistry of the air they breathed.

When their babies were born, Perera and her colleagues examined all of the infants who had been exposed to high levels of exhaust fumes while in the womb and discovered a distinctive biochemical mark in the DNA of about half of them. They determined that this marker was left by the high levels of polycyclic aromatic hydrocarbons in exhaust they were exposed to before birth.

By the time the children were three years old, the ones who were exposed to elevated exhaust levels in the womb were developing mentally only slightly slower than children who were not exposed prenatally to high levels of exhaust. By the age of five, however, their IQ scores averaged roughly four points lower on standard intelligence tests.

The researchers updated the study this year, saying that by the age of seven, the children bearing the biomarker were more likely than the other children to display symptoms of anxiety, depression, and attention problems.

"The mother's exposure—what she breathed into her lungs—could affect her child's later behavior," Dr. Perera said. "The placenta is not the perfect barrier we once thought."

The situation is not entirely hopeless, however, as there are many small changes that can be made in order to cut down on exhaust fume exposure. According to reports published in scientific journals this year and in 2009, premature births—a well-known risk factor for cognitive impairment—in regions of New Jersey near highway toll plazas decreased by 10.8% after the implementation of E-ZPass, which decreased traffic congestion and reduced exhaust fumes. Further, air-pollution levels in Times Square fell by 63% are New York traffic managers redirected streets in the area to lessen congestion.

As there is no real conclusive evidence as of yet, "there is real cause for concern," as neurochemist Annette Kirshner from the National Institute of Environmental Health Sciences at Research Triangle Park in North Carolina said. "But we ought to proceed with caution."