Air Pollution's Long Reach

November 6, 2014

Take a deep breath. If you’re in the United States or anywhere with decent air quality regulations, occasional smog alert aside, the air you breathe is free and clear of dangerous levels of pollution. Or is it? 

Over the last ten years, researchers at the Columbia Center for Children’s Environmental Health have shown that exposure to air pollution, even at levels undetectable without scientific instruments, can have lasting consequences, and not always in obvious ways.

In their latest study published in the journal PLOS ONE, Frederica Perera and colleagues found that children born to mothers exposed to high levels of a component of air pollution during pregnancy had five times the odds of having an increased number and degree of symptoms that characterize ADHD than children born to mothers exposed at lower levels.

The symptoms they observed make up the first two letters of the acronym ADHD. This inattentive-type ADHD is a common subtype of the disorder. Calling the finding concerning, Perera notes, “attention problems are known to impact school performance, social relationships, and occupational performance.”

The researchers from the Columbia University Mailman School of Public Health set their sights on a family of chemicals called polycyclic aromatic hydrocarbons, or PAH for short. Despite their name, these chemicals do not smell sweet; in fact, they have no scent at all. The byproducts of burning organic material, PAH is created in large volume by cars, trucks and buses, oil and coal-burning residential boilers and power plants; other sources include tobacco smoke and grilled food.

Breathing PAH is particularly risky during pregnancy. Imagine a ballet with pirouettes and graceful leaps executed with precision timing. Perera says this “exquisite choreography” is a metaphor often applied to the brief, vulnerable prenatal period when genes are programmed and the fetal brain is rapidly developing. Like other toxic chemicals, PAH has the potential to disrupt this developmental dance with possible consequences throughout the child’s life. 

In a series of studies based on a cohort of New York City mothers and children, the researchers have linked PAH exposure during pregnancy to developmental delay at age 3, reduced IQ at age 5, and symptoms of anxiety/depression and attention problems at ages 6 and 7.

These developmental problems aren’t explained by PAH alone; Perera and others believe a mix of factors is at work, including genes, stress and a range of environmental exposures. The same holds true for ADHD, which is known to have a hereditary component. But genes aren’t the whole story. “Genetic factors are thought to play an important role,” she says, “but by themselves do not appear to account for many of the cases of behavior problems we’re seeing in children.” The new findings suggest that PAH may contribute to ADHD. If replicated, the data open new avenues for prevention.

Unlike the genes we’re born with, environmental pollutants are within human control.

So what’s a pregnant mom to do?

Moving to the country is not a feasible option for most people and anyway PAH is everywhere. Despite the Clean Air Act, there are no pristine areas. At home she can avoid tobacco smoke and candle and burning incense; and use proper ventilation when cooking, especially when grilling. But the bulk of PAH exposure is involuntary; we all need to breathe. Change will only come through stricter emissions standards.

“Mainly this is an issue of public policy,” says Perera. “But people can get informed and become involved in campaigns for cleaner air.”