Young children who live near a major highway are twice as likely to score lower on tests of communications skills, compared to kids who live farther away from a major roadway, according to a new study published in the journal Environmental Research.
The findings also show that kids born to women exposed during pregnancy to higher-than-normal levels of traffic-related pollutants — ultra-fine airborne particles and ozone — had a small but significantly higher likelihood of developmental delays during infancy and early childhood.
“Our results suggest that it may be prudent to minimize exposure to air pollution during pregnancy, infancy, and early childhood — all key periods for brain development,” said senior author Pauline Mendola, Ph.D., from the the Division of Intramural Population Health Research at NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).
Prior research has associated fetal exposure to common air pollutants with low birthweight, preterm birth and stillbirth. A few studies have also shown a greater risk of autism and of lower cognitive functioning in children living near highways. But overall findings of how prenatal and early childhood exposure to air pollution might affect development have been inconsistent.
Since a large proportion of the U.S. population lives close to major roadways, major sources of air pollution, the study sought to determine if living near heavily traveled roads was linked to lower scores on developmental screens; questionnaires or checklists that indicate whether a child is developing normally or needs to be referred to a specialist for further testing.
The team analyzed data from the Upstate KIDS Study. They matched the addresses of 5,825 study participants to a roadway data set, calculating the distance of each address to the nearest major roadway.
They also matched each participant’s home address, mother’s work address during pregnancy, and address of the child’s day care location to an Environmental Protection Agency (EPA) data set for estimating air pollution levels.
From 8 months to 36 months of age, the children were screened every 4 to 6 months with the Ages and Stages Questionnaire, a validated screening measure evaluating five domains of child development: fine motor skills, large motor skills, communication, personal social functioning and problem-solving ability.
The findings reveal that, compared to children living more than half a mile from a major roadway, kids living from roughly 164 feet to .3 miles from a major roadway were twice as likely to have failed at least one screen of the communications domain.
The team also estimated participants’ exposure to ozone and fine inhalable particles (PM2.5), two pollutants produced by car traffic. Fine inhalable particles are 30 times smaller than the width of a human hair, can pass through the lungs’ defenses, and are absorbed directly into the bloodstream.
They discovered that prenatal exposure to elevated PM2.5 led to a 1.6 to 2.7 percent greater risk of failing any developmental domain, while heightened ozone exposure led to a .7 to 1.7 percent higher risk of failing a developmental domain. In contrast, higher postnatal exposure to ozone was associated with a 3.3 percent higher risk of failing most domains of the developmental screen at 8 months; a 17.7 percent higher risk of overall screening failure at 24 months; and a 7.6 percent greater risk of overall screening failure at 30 months.
The findings led the researchers to conclude that early childhood exposure to air pollutants may be tied to a greater risk for developmental delays, compared to similar exposures in the womb. The study is associational and so cannot prove cause and effect. The authors noted that larger studies are necessary to confirm the findings.
“It is not clear why exposure to pollutants after birth is linked to a higher risk of developmental delay,” said Sandie Ha, Ph.D., of the Department of Public Health at the University of California, Merced, and lead author of the study. “However, unlike exposure during pregnancy, exposure during childhood is more direct and does not go through a pregnant woman’s defenses.”