Research conducted in New York City found that children exposed to urban air pollution before birth were more likely to have a lower IQ than less exposed children. The researchers said the levels of IQ reductions they found would be enough to affect children’s academic performance.
The study was the work of Dr Frederica P Perera of the Mailman School of Public Health at Columbia University, New York, New York, and colleagues, and was published online on 20 July in the journal Pediatrics.
Helped by funds from the National Institute of Environmental Health Sciences (NIEHS), a component of the National Institutes of Health, the US Environmental Protection Agency and some private foundations, Perera and colleagues measured New York City children’s prenatal exposure to polycyclic aromatic hydrocarbons (PAHs) and then linked it to IQ scores measured when they reached 5 years of age.
PAHs are chemicals that get into the air as a result of burning coal, diesel, oil and gas, plus other organic substances such as tobacco. Motor vehicles are thought to be the main contributor in urban areas.
The researchers found that children with above the median level of exposure to PAH had overall and verbal IQ scores that were 4.31 and 4.67 points lower respectively than those children whose exposure was below the median (median PAH exposure was defined to be 2.26 nanograms per cubic meter, or ng/m3).
Perera and colleagues concluded that:
“These results provide evidence that environmental PAHs at levels encountered in New York City air can affect children’s IQ adversely.”
Perera, who is professor of Environmental Health Sciences and director of the Columbia Center for Children’s Environmental Health at Columbia University Mailman School of Public Health, said we should be concerned about these findings because such reductions in IQ score are enough to make a difference to children’s performance at school.
“The decrease in full-scale IQ score among the more exposed children is similar to that seen with low-level lead exposure,” she added.
“Fortunately, airborne PAH concentrations can be reduced through currently available controls, alternative energy sources and policy interventions,” said Perera, adding that:
“The good news is that we have seen a decline in air pollution exposure in our cohort since 1998, testifying to the importance of policies to reduce traffic congestion and other sources of fossil fuel combustion byproducts.”
The children in the study, who were followed from before birth up to 5 years of age, were born to nonsmoking black or Dominican-American women aged between 18 to 35 living in Washington Heights, Harlem or the South Bronx in New York.
The researchers asked the expectant mothers to wear personal air monitors to measure PAH exposure during pregnancy, during which time they also filled in questionnaires.
When the children reached 5 years of age, 249 of them took an IQ test known as the Wechsler Preschool and Primary Scale of Intelligence-Revised. This test gives verbal, performance and full-scale IQ scores.
Using statistical tools called multivariate linear regression models, the researchers then looked for links between the children’s IQ scores at age 5 and their pre-birth exposure to PAH pollutants.
These models allow them to take out the effect of factors that might interfere with the results (potential confounders), such as second-hand smoke exposure, lead exposure, mother’s education and the quality of the home caretaking environment (this data came from the mothers’ questionnaire responses).
“Prenatal Airborne Polycyclic Aromatic Hydrocarbon Exposure and Child IQ at Age 5 Years.”
Frederica P. Perera, Zhigang Li, Robin Whyatt, Lori Hoepner, Shuang Wang, David Camann, and Virginia Rauh.
Pediatrics, published online July 20, 2009.
Written by: Catharine Paddock, PhD