The intellectual development of children may be lowered by prenatal exposure to common pollutants in wombs, a new study suggests.

The finding indicates that high prenatal exposure to these compounds such as automobile exhaust translates into lower IQ scores by the time a child reaches the age of five years, according to the study by researchers at the Mailman School of Public Health at Columbia University in New York City.

The study was published on Monday in the online issue of Pediatrics.

Specifically, 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.

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 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.

The study found that 140 of the children (a little more than 56 percent) 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.

"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.

"And here we're talking about extremely common urban pollutants, found all across the U.S. and the world," Perera added. "Traffic emissions from diesel and gasoline 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."

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.