Lung cancer, heart disease, nausea, headaches, allergic reactions and chronic respiratory disease are just some of the adverse effects of air pollution. Now you can add less intelligent kids to the list. Two separate scientific studies, one conducted in New York City and the other in Poland, found that 5-year-olds exposed to above-average levels of polycyclic aromatic hydrocarbons (PAHs) in the womb score lower on IQ tests. The difference is about the same as the well-documented IQ drop caused by low-level lead exposure.


In New York City, 249 children are currently being monitored, while 214 are being monitored in the parallel Krakow, Poland study. Pregnant, mothers wore backpacks that detected the levels of PAHs for 48 hours to divide the women into high and low pollution exposure groups. Then at age five they gave standardized IQ tests. In both studies, the children of mothers who had above-average exposure to air pollution, or PAHs, while pregnant,  scored roughly 4 points lower than the kids whose moms had below-average exposure. Though the exposure levels to PAHs were eight times higher in Krakow than in NYC!

PAHs are common in urban environments. In New York City the top source is exhaust coming from buses, cars and trucks. In Poland, factories and home heating cause the most pollution of this kind.

Sure 4 points doesn’t sound like a lot, and it’s typically not something parents or teachers would notice. Average IQ scores fall somewhere between 90 and 109, so a 4-point swing could keep kids in the same average range pretty easily. However, the drop is enough to make a difference in both school performance and possibly, in lifelong learning.

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Research examining similar IQ deficits due to lead exposure found that for every dollar invested in reducing lead exposure, there would be a $17 to $220 benefit largely because less exposure to toxins would raise kid’s intelligence, allowing them to earn more over their lifetimes.

When viewed together, these two studies of the affect of PAHs on IQ are “a striking finding” because they each found “a measurable and statistically significant decrease in IQ,” according to Jennifer Adibi, an epidemiologist who studies how environmental exposures affect fetal development at University of California San Francisco.

Some experts aren’t surprised by the drop in IQ since multiple studies have already linked air pollution to asthma, low birth weight, lung cancer and diminished lung function. A growing pile of research has already begun to suggest that environmental toxins can lead to problems with cognitive development, conduct disorders and attention deficit hyperactivity disorder.

These pollutants are highest in urban areas, but you can help reduce your children’s air pollution exposure no matter where you live. Check out our article on combatting automotive air pollution for tips from pushing your baby in a stroller that’s higher off the ground to checking air quality before you go for a walk.

Frederica Perera, the lead author on both air pollution studies, is the director of Columbia Center for Children’s Environmental Health in New York City. The good news she says, is that during the New York City study from 1998 to 2006, data from the women’s air pollution-detecting backpacks showed that airborne levels of PAHs decreased by more than 50 percent. Here’s hoping for continued reductions in air pollution and smart kids!

Images: Ed Yourdon, anissat