A landmark study by Columbia University's Center for Children's Environmental Health (CCCEH) has found that children exposed in the womb to urban air pollutants score significantly lower on intelligence tests than children of mothers who breathed cleaner air during their pregnancies.
The study, published July 20 in the online edition of the journal Pediatrics, reported that five-year-olds scored more than four points lower than peers on IQ tests if their mothers had been exposed to as little as 2.26 nanograms per cubic meter -- two and a quarter billionths of a gram of pollutants in a space roughly the size of restaurant refrigerator -- of polycyclic aromatic hydrocarbons (PAHs). Unlike smog and soot, PAH pollution -- vapors and fine particles generated by vehicle emissions, coal-burning and second-hand smoke -- is too fine and sparse to be seen, smelled or felt.
Yet, as the Columbia researchers showed, PAHs can affect neurodevelopment, even in miniscule doses.
"The study underscores the importance of protecting that window of vulnerability in the in utero period," said lead author Frederica Perera, Dr.P.H, director of the center and professor of Environmental Health Sciences at Columbia's Mailman School of Public Health. "It provides evidence that air pollutants at the levels commonly found in urban settings are harmful in terms of children's intellectual development."
The IQ loss, Perera told Environmental Working Group, is similar to that observed in children exposed to low levels of lead, a potent neurotoxin sometimes found in old water pipes and chipping paint.
The scientists conducted the study by monitoring 249 children born to non-smoking black and Dominican-American women living in New York City's Washington Heights, Harlem and the South Bronx, urban neighborhoods near the Columbia campus. The women wore personal air monitors during the last trimester of their pregnancies to determine their PAH exposures.
As well, the researchers collected and analyzed umbilical cord blood for pollutants that had crossed the placenta.
Researchers followed the children to age five, at which point they administered standardized intelligence tests. Mathematical calculations adjusted for extraneous factors such as maternal intelligence, quality of home environment and smoking in the home and came up with associations between general air pollution and test performance. The scientists intend to continue studying the children to age 11 and perhaps longer.
The study does not predict the eventual success or failure of specific children. In many cases, a strong educational environment may help them compensate for any learning deficits caused by exposure to PAH pollution.
Nor does the study determine the physical mechanisms by which PAH exposure undermines normal neurodevelopment. One possibility, the study suggests, is that the chemicals may disrupt the endocrine system and reduce fetal access to oxygen and nutrients. Another possibility is that they may damage DNA, altering development in other ways. Much more research is needed to establish the answers.
There's a bright note: Perera says that policymakers in New York have already used Columbia's extensive research on children and air quality to reduce air pollution, for instance, by attempting to limit traffic generally, reduce idling time for diesel trucks and buses and make sure the city's buses have effective emission controls.
As a result, Perera says, between 1998 and 2003, the researchers observed "a modest but steady and significant decline in PAH levels."
Other reforms, such as new strictures on coal-burning power plants and cleaner energy alternatives, could further reduce urban air pollution.
The Columbia study bolsters the case for making environmental health a major national priority. It shows that:
• The placenta is not a protective barrier that shields the fetus from the outside world. The tiniest and most insidious pollutants, like PAHs. easily transgress it and pollute the unborn child.
• Prenatal exposure to pollution is extraoridinarily, perhaps uniquely, perilous. "Humans pass more biological milestones before birth than at any other time in their lives, " the Columbia scientists wrote, "and the prenatal period is highly sensitive to neurotoxic effects of environmental chemicals."
"This research clearly shows that environmental PAHs at levels encountered in an urban setting can adversely affect a child's IQ," said Linda Birnbaum, Ph.D., director of the National Institute for Environmental Health Sciences, which funded the Columbia study.
"This is the first study to report an association between PAH exposure and IQ, and it should serve as a warning bell to us all," Birnbaum said, referring to her announced intent to pour more grant money into research into pre-and peri-natal exposures to toxic environmental chemicals. "We need to do more to prevent environmental exposures from harming our children."
You can join the debate about environmental health, air pollution and pollution in people at Environmental Working Group's online news and discussion site, Kid-Safe Chemicals.