Growing Up Near Polluted Highways Can Impact the Brain, Even Before Birth

"The study took place in an area with low to moderate air pollution level, and we still observed some adverse effects."

The turbid air of city life already takes its toll on happiness and has been linked to psychological illnesses. But the pollution that lingers in the city isn’t stagnant in urban areas: It snakes out into the suburbs along car-studded highways. There, write scientists in an Environmental Research study released Tuesday, its impacts on kids begin even before birth.

This study deals with a type of air pollution known as PM2.5, which are particles 2.5 microns across (a human hair is about 40 microns across) as well as ozone. In previous research, PM2.5 and ozone have already been linked to decreased lung function and aggressive asthma. The new research links it to delays in cognitive development — specifically in kids who live within spitting distance of New York State’s highways.

Lead author and University of California, Merced epidemiologist Sandie Ha, Ph.D., reports that children raised within 50 and 500 meters of major highways where both pollutants were present were twice as likely to fail at cognitive communication tasks than those who lived 1,000 meters away or more, even after adjusting for socioeconomic factors. Some of those effects of air pollution on kids may even begin before they’re born.

“We thought: These findings are curious,” Ha tells Inverse. “The study took place in an area with low to moderate air pollution level, and we still observed some adverse effects. Thus, studies in area with higher levels of air pollution may be warranted.”

Kids who grew up closer to major highways were more likely to fail cognitive development tests 

Failing Marks Around Highways

Ha found this effect by examining questionnaire responses from the Ages and Stages Survey, which asks parents to answer specific questions about their child’s behavior that indicates whether they’ve reached certain age-appropriate levels of communication, motor skills, and problem solving, and from this data it produces a score. Results that are two standard deviations below the average for children in their age group are considered failing marks.

Ha and her colleagues looked at the survey scores from 4,809 kids between 8 and 36 months old in each area, then estimated the PM2.5 and ozone exposure near each child’s home, based on local environmental data They also estimated how much air pollution their mothers were exposed to while they were pregnant. That comparison showed that higher exposure to both ozone and PM2.5 is linked to different effects on cognitive development.

During pregnancy, every every 10-microgram increase in PM2.5 during trimesters one and three increased a child’s risk of failing to achieve age-appropriate scores in any domain between 1.6 and 2.7 percent. After birth, continued exposure was only strongly associated with failing the communications exams, but the kids who lived closer to highways were twice as likely to do so compared to those further away.

Ozone also had pre-birth effects, but the most dramatic effects of ozone exposure seemed to occur after birth. At only 8 months old, kids were 3.3 percent more likely to fail any developmental test for every 10 parts per billion (ppb) increase in ozone exposure. By 24 months, the effects were more dramatic: They were 17.7 percent more likely to fail for each small increase in ozone.

How Pollution May Wreak Havoc

Ha cautions that her results can’t show cause and effect, and the study doesn’t explain why pre-birth effects from air pollution exist. But her results hint at the idea that air pollution exposure wreaks havoc during certain windows of development that can have lasting consequences as kids get older. However, it’s still unclear why.

Ha says earlier studies provide a clue. Air pollution has been linked to inflammation, which can impact brain function during childhood.

“Our study didn’t focus on mechanisms linking air pollution to child development, but the findings are consistent with other studies,” adds Ha. “Research has shown that air pollution exposure can induce oxidative stress and inflammatory mechanisms that can eventually have adverse effects on the brain as well as other organs.”

It remains unclear whether the biggest risk factor is actually the air pollution itself, or another side effect from life near a highway: incessant noise, which has been proposed by other scientists studying air pollution’s effects on cognition. And as Ha suggests, the levels of air pollution that these children were exposed to were actually pretty low — they grew up in upstate New York, far from LA or New York City, where levels of air pollution are even higher. There may be a far more complicated reason why life along the highway seems to take such a high toll.


Background: Residential proximity to major roadways, and prenatal exposures to particulate matter <2.5 μm (PM2.5) and ozone (O3) are linked to poor fetal outcomes but their relationship with childhood development is unclear.

Objectives: We investigated whether proximity to major roadways, or prenatal and early-life exposures to PM2.5 and O3 increase the risk of early developmental delays.

Study design: Prospective cohort.

Settings: New York State excluding New York City.

Participants: 4089 singletons and 1016 twins born between 2008 and 2010.

Exposures: Proximity to major roadway was calculated using road network data from the NY Department of Transportation. Concentrations of PM2.5 and O3 estimated by the Environmental Protection Agency Downscaler models were spatiotemporally linked to each child’s prenatal and early-life addresses incorporating residential history, and locations of maternal work and day-care.

Outcomes: Parents reported their children’s development at ages 8, 12, 18, 24, 30 and 36 months in five domains using the Ages and Stages Questionnaire. Generalized mixed models estimated the relative risk (RR) and 95% CI for failing any developmental domain per 10 units increase in PM2.5 and O3, and for those living <1000 m away from a major roadway compared to those living further. Models adjusted for potential confounders.

Results: Compared to those >1000 m away from a major roadway, those resided 50–100 m [RR: 2.12 (1.00–4.52)] and 100–500 m [RR: 2.07 (1.02–4.22)] away had twice the risk of failing the communication domain. Prenatal exposures to both PM2.5 and ozone during various pregnancy windows had weak but significant associations with failing any developmental domain with effects ranging from 1.6% to 2.7% for a 10 μg/m3 increase in PM2.5 and 0.7%–1.7% for a 10 ppb increase in ozone. Average daily postnatal ozone exposure was positively associated with failing the overall screening by 8 months [3.3% (1.1%–5.5%)], 12 months [17.7% (10.4%–25.5%)], and 30 months [7.6%, (1.3%–14.3%)]. Findings were mixed for postnatal PM2.5 exposures.

Conclusions: In this prospective cohort study, proximity to major roadway and prenatal/early-life exposures to PM2.5 and O3 were associated with developmental delays. While awaiting larger studies with personal air pollution assessment, efforts to minimize air pollution exposures during critical developmental windows may be warranted.

Media via Pixabay , NASA, Pxhere