In a sweltering summer in New York City back in 1999, Yolanda Baldwin was eight months pregnant with her first child. She lived near a gas station and across the street from an intersection choked with exhaust-spewing cars and buses. Sometimes the air was so thick with pollution that she could see it, breathe it, smell it, even taste it. And she often wondered what it might be doing to her unborn child.
Now Baldwin and several hundred other mothers whose sons and daughters have been monitored for a decade have an answer: Before children even take their first breath, common air pollutants breathed by their mothers during pregnancy may reduce their intelligence.
A pair of studies involving more than 400 women in two cities has found that 5-year-olds exposed in the womb to above-average levels of polycyclic aromatic hydrocarbons, or PAHs, score lower on IQ tests. The compounds, created by the burning of fossil fuels, are ubiquitous in urban environments.
In African American and Dominican communities of New York City, 249 children are being monitored for the effects of environmental contaminants until the age of 11. And across the Atlantic, in Krakow, Poland, another 214 children are participating in a parallel study.
The findings in Poland, reported this spring, are strikingly similar to New York City’s: The children whose mothers had above-average exposure to PAHs scored about four points lower on IQ tests than children whose mothers had below-average exposure.
The difference in IQs is modest, but experts say it is enough to hamper school performance and perhaps lifelong learning. It is about the same deficit linked to low-level exposure to lead, a well-documented cause of reduced IQs in children.
“We think that this is a finding of concern because child intelligence is one of the predictors of how well a child will do in the academic setting later on,” said Frederica Perera, the senior author of the studies and director of Columbia Center for Children’s Environmental Health in New York City.
The pair of studies “adds to a growing literature implicating exposures to environmental toxicants with stunting of children's intellectual abilities and increased risk for attention deficit hyperactivity disorder and conduct disorders,” said Bruce Lanphear, professor of children’s environmental health at British Columbia’s Simon Fraser University. He was not involved in the research.
The link between prenatal exposure to pollutants and cognitive development is a growing area of concern “that's been getting a lot more attention,” said David Bellinger, an environmental epidemiologist and professor of neurology at Harvard Medical School.
One strength of the Columbia University research is that the scientists know precisely how much pollution the mothers were exposed to during a brief period of their pregnancy.
Recruited for the study between 1998 and 2006, Baldwin and the other 462 pregnant women in New York City and Krakow carried backpacks for 48 hours that contained equipment for measuring PAHs. Then their children were divided into high and low exposure groups – those above the median and below –and when they reached the age of five, they underwent standardized tests to measure their cognitive skills.
“It’s scary and alarming that we can live in a society where these things are happening and they go unnoticed,” said Baldwin, now the mother of five children. “I know now that what we do can affect us in the future. The things we eat or breathe in, our environment, it does affect the children.