Foetal exposure to high levels of a common airborne pollutant compound seems to threaten the intellectual development of children, a new study suggests.
The finding is based on the experience of black and Dominican-American families living in the New York City area. Specifically, it indicates that high prenatal exposure to these compounds -- automobile exhaust is one example -- translates into lower IQ scores by the time a child reaches the age of five years.
This linkage builds on prior research, which has suggested that exposure to these pollutants, known as polycyclic aromatic hydrocarbons (PAHs), while still in the womb can provoke developmental changes that damage lung health and boost the risk for developing childhood asthma.
"As a reference, most people know that lead exposure is harmful to children, and the effects we saw in terms of the association between PAH exposure and decreased IQ scores are comparable with low-level lead exposure, which is of concern because IQ level is a known predictor of a child's future academic performance," explained study author Frederica P. Perera, a professor in the department of environmental health sciences with the Mailman School of Public Health at Columbia University in New York City.
"And here we're talking about extremely common urban pollutants, found all across the world," Perera added. "Traffic emissions from diesel and petrol vehicles -- like buses, trucks and cars -- are a major source of these pollutants, as is fuel-burning coal. So, certainly the exposure is widespread and not confined to any one population or area, and we have no reason to think that the effects that we see in our study will be any different for other ethnicities or locations."
How the study was done
Perera -- who also serves as director of the Columbia Centre for Children's Environmental Health -- reports the findings in Paediatrics.To assess the impact of PAH exposure in the womb, the authors conducted air monitoring between 1998 and 2003, during the pregnancy of 249 black and Dominican-American mothers in the Washington Heights and Harlem areas of New York City.
The researchers pointed out that none of the children were born to parents who smoked, removing that type of pollutant exposure from the equation.
All of the women were between the ages of 18 and 35, and none had diabetes, HIV, high blood pressure or a history of illegal drug use.
Perera and her colleagues found that 140 of the children (a little more than 56%) had been exposed to high levels of PAH in the womb.
After adjusting for a range of potentially influential factors -- such as maternal IQ levels and varying types of home caretaking environments -- the authors found that by age 5, those children exposed to high PAH exposure in the womb scored more than four points lower on full-scale IQ tests, and nearly five points lower on verbal IQ tests.
Clean environment, healthy diet best
Although such evidence suggests that early intellectual development is indeed negatively affected by high levels of pollutant exposure, research is ongoing and the child participants will continue to be monitored through age 11, the researchers noted.
Meanwhile, Perera says that "aside from making sure that there are no other pollutant sources in the house such as tobacco smoke, families can proactively protect themselves by maintaining a clean home environment and good ventilation of cooking fumes, and by making sure that pregnant women and children consume healthy diets."
But, she noted, "as far as outdoor air exposure, that's a question for policymakers. I'm not a policy expert, but I would say fortunately that there are means at hand to address this problem. They include plans to reduce vehicle emissions, and to develop the technologies that would do so, along with policies that focus on energy efficiency and energy alternatives."
Michael Jerrett, an associate professor of environmental health sciences with the School of Public Health at University of California, Berkeley, expressed little surprise at the findings, and suggested that an association between inutero PAH exposure and a lower IQ is "certainly plausible."
"Children exposed to prenatal or inutero air pollution from traffic oftentimes have lower birth weights, somewhat smaller head circumferences, and a number of adverse outcomes," he noted. "There's certainly enough there to suggest an effect. And I think any one of those outcomes -- if they happen early enough in life -- can affect development through childhood and exert an impact on intelligence," Jerrett said.
"Of course you can't rule out other factors -- the school environment, the home environment, even the neighbourhood environment -- that might affect IQ," Jerrett cautioned. "But certainly it is important for us to investigate this, and see what further study reveals." – (HEalthDay News, July 2009)