Pesticide Exposure in Womb Linked to Lower IQ

April 21, 2011 -- Children exposed to pesticides in the womb are more likely to have measurable problems with intelligence, memory, and attention, three new studies show.

The pesticides in question, a class of chemicals called organophosphates, have long concerned both scientists and regulators because they work by irreversibly blocking an enzyme that’s critical to nerve function in both bugs and people.

Even at relatively low levels, organophosphates may be most hazardous to fetuses and young children, where healthy brain development depends on a carefully orchestrated sequence of biological events.

To protect kids, the EPA banned most residential uses of organophosphates in 2001, but they are still sprayed agriculturally on fruits and vegetables. They’re also used to control pests like mosquitos in public spaces like parks and golf courses. They can be absorbed through the lungs or skin or by eating them on food.

The new, government-funded studies, from researchers in New York and California, have charted environmental exposures in hundreds of women and their children through pregnancy and into their grade school years.

Though each study used a slightly different way to track the pesticide exposures, they all reached strikingly similar conclusions -- that many children exposed to higher levels of organophosphates during pregnancy than their peers are more likely to have lower IQs and may have more difficulty focusing on tasks or solving problems.

In one study, researchers even found that genetics appears to play a strong role in whether exposure to organophosphates will cause damage.  Mothers carrying a particular gene that slowed their ability to metabolize the pesticides were more likely to have children with brain deficits than mothers whose genes made them quick metabolizers.

Animal studies had previously demonstrated that organophosphates could scramble brain function and behavior in baby rats.

And last year, two studies found that children exposed to higher levels of organophosphate pesticides than their peers were more likely to be diagnosed with attention deficit hyperactivity disorder (ADHD).

“This combination of three long-term studies looking at everyday exposures in American subpopulations is notable,” says Sonya Lunder, a senior analyst at the Environmental Working Group, a nonprofit advocacy group. 

“There have only been a couple of studies like this in the U.S. before, and it really increases our level of concern. It’s a pretty sobering look at pesticide safety,” says Lunder, who was not involved in the research.

Checking Markers for Pesticide Exposure

Researchers at Columbia University looked at markers for exposure for particular organophosphate, chlorpyrifos, in blood samples taken from umbilical cords in 265 inner-city mothers and infants in New York City.

“Our measure is a direct measure of fetal exposure via fetal blood,” study researcher Virginia Rauh, ScD, a professor at Columbia University’s Mailman School of Public Health.