April 21, 2019Public Health
Previous studies have linked exposure to common air pollutants in pregnancy to low birthweight, preterm birth and stillbirth. A few studies have found a higher risk of autism and of lower cognitive functioning in children living near freeways, but results of studies about how prenatal and early childhood exposure to air pollution might affect development have been inconsistent. Given that a large proportion of the U.S. population lives close to major roadways, which are major sources of air pollution, a study published in Environmental Research (9 April 2019), 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.
Results showed that young children who live close to a major roadway are twice as likely to score lower on tests of communications skills, compared to those who live farther away from a major roadway. Moreover, children 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.
For the study, the authors analyzed data from the Upstate KIDS Study where 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. For each participant, they matched home address, mother's work address during pregnancy, and address of the child's day care location to an Environmental Protection Agency data set for estimating air pollution levels. From 8 months to 36 months of age, the children were screened every four to six 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. Results showed that compared to children living more than half a mile from a major roadway, children living from roughly 164 feet to 0.3 miles from a major roadway were twice as likely to have failed at least one screen of the communications domain.
The authors also estimated exposures 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. A prenatal exposure to elevated PM2.5 led to a 1.6 to 2.7% higher risk of failing any developmental domain, while higher ozone exposure led to a .7 to 1.7% higher risk of failing a developmental domain. In contrast, higher postnatal exposure to ozone was linked to a 3.3% higher risk of failing most domains of the developmental screen at 8 months, a 17.7% higher risk of overall screening failure at 24 months, and a 7.6% higher risk of overall screening failure at 30 months. According to the authors, early childhood exposure to air pollutants may convey a higher risk for developmental delays, compared to similar exposures in the womb, and that larger studies are needed.