Babies exposed to pesticides before birth may have significantly lower intelligence scores by age 7 than children who were not exposed, three separate studies published on Thursday said.
Results from the studies -- two in New York and one in an agricultural community in California -- suggest prenatal exposure to pesticides can have a lasting effect on intelligence.
In one study, a team at the University of California Berkeley found that every tenfold increase in prenatal exposure to organophosphate pesticides corresponded with a 5.5 point drop in overall IQ scores in children by age 7.
"That difference could mean, on average, more kids being shifted into the lower end of the spectrum of learning, and more kids needing special services in school," Berkeley's Brenda Eskenazi, who led one of the three studies published online in Environmental Health Perspectives, said in a statement.
The two other studies -- one at Mount Sinai Medical Center and the other at Columbia University -- also examined prenatal exposure to pesticides and IQ in children at age 7.
The teams at Berkeley and Mount Sinai sampled pesticide residues in maternal urine, while the team at Columbia tested umbilical cord blood levels of chlorpyrifos, part of a class of pesticides known as organophosphates that are known to be toxic to brain cells.
Until it was banned for indoor residential use by the U.S. Environmental Protection Agency in 2001, chlorpyrifos was one of the most widely used insecticides for residential pest control.
In the Columbia study, researchers sampled 265 New York City minority children born before the ban. The higher levels of chlorpyrifos in the babies' umbilical cord blood were linked with lower performance on two different IQ tests.
Children who were in the highest 25 percent of exposure levels scored 2.7 points lower on IQ tests than children whose exposures were in the lowest quarter of the study.
The UC Berkeley study involved 329 children whose mothers enrolled when they were pregnant.
Urine samples were taken twice during pregnancy from the mothers and after birth from the children at regular intervals between ages 6 months and 5 years.
The team said while prenatal exposure to pesticides were significantly linked with childhood IQ, pesticide exposure after birth was not, suggesting exposure during fetal brain development was a more critical period than childhood exposure.
Children in the UC Berkeley study were exposed to pesticides in 1999 through 2000. Since the 2001 ban, use of organophosphates in the United States has fallen by more than 50 percent, but agricultural use of chlorpyrifos is still permitted.
"It is vitally important that we continue to monitor the levels of exposure in potentially vulnerable populations, especially in pregnant women in agricultural communities, as their infants may continue to be at risk," Dr. Robin Whyatt of Columbia said in a statement.