Pesticide exposure in womb linked to low IQ

Children exposed to high pesticide levels in the womb have lower average IQs than other kids, according to three independent studies released today in Environmental Health Perspectives.

The studies involved more than 400 children, followed from before birth through ages 6 to 9, from both urban and rural areas. Researchers were from the University of California-Berkeley, Columbia University in New York and Mount Sinai School of Medicine in New York.

The Berkeley study found that the most heavily exposed children scored an average of 7 points lower on IQ tests compared with children with the lowest pesticide exposures, lead author Brenda Eskenazi. says.

On IQ tests, the average score is around 100.

Even a difference of 2 or 3 points — the size of the IQ loss caused by lead, which is known to cause brain damage — can have an enormous impact, says pediatrician Aaron Bernstein of Children’s Hospital Boston.

That’s because a population’s IQ scores, when plotted on a graph, tend to fall along a bell-shaped curve. Shifting the entire curve down, even if just by a few points, causes a big jump in the number of kids with low intelligence and a dramatic loss in the number of super-smart ones, says Bernstein, who wasn’t involved in the study. That can sharply increase the number of kids needing remedial education, says Bruce Lanphear, a professor at Simon Fraser University in Vancouver, Canada, also not involved in the study.

Pesticide exposure after birth wasn’t linked to lower intelligence scores, suggesting that the harm caused by the chemicals is greatest during early pregnancy, when the brain is developing, notes Michael Lu, an obstetrician at the University of California-Los Angeles, also not involved in the study.

Such long-running studies are the strongest practical way to study potential harm from chemicals, Eskenazi says. The only way to definitively prove cause-and-effect would be to purposely expose half the kids in a study to pesticides, which would be unethical, she says.

Lanphear says earlier studies have linked the specific type of bug killer included in these studies, organophosphate pesticides, with attention deficit hyperactivity disorder (ADHD).

These pesticides are often used on crops, and people are exposed to them through eating fruits and vegetables, Eskenazi says. Two of the most commonly used organophosphate pesticides, including one measured in the Columbia study, are no longer used in homes.

Eskenazi says pregnant women should not shun fresh fruits and vegetables but should wash produce well or buy organic produce and, in general, limit the use of chemicals at home.