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.
