CHICAGO - An analysis of U.S. health data links children's attention-deficit disorder with exposure to pesticides used on produce.
Although the study couldn't prove that pesticides used in agriculture contribute to childhood learning problems, experts said the research is persuasive.
"I would take it quite seriously," said Virginia Rauh of Columbia University, who has studied prenatal exposure to pesticides but wasn't involved in the study.
More research will be needed to confirm the tie, she said.
Children may be more prone to the risks of pesticides because they're growing and they may consume more pesticide residue than adults relative to their body weight.
The study found detectable levels of pesticide compounds in the urine of 94 percent of the children.
The children with higher levels had increased chances of having ADHD, attention-deficit hyperactivity disorder, a common problem that causes students to have trouble in school.
The findings were published today in Pediatrics.
The children may have eaten food treated with pesticides, breathed them in the air, or swallowed them in drinking water.
Experts said it's likely children who don't live near farms are exposed through what they eat.
Lead author Maryse Bouchard of the University of Montreal said people can limit their exposure by eating organic produce.
One government report said celery, frozen blueberries, and strawberries had more pesticide residue than other foods.
A 2008 Emory University study found that in children who switched to organically grown fruits and vegetables, urine levels of pesticide compounds dropped to undetectable or close to undetectable.
Because of known dangers of pesticides in humans, the U.S. Environmental Protection Agency limits how much residue can stay on food. But the new study shows it's possible even tiny, allowable amounts of pesticide may affect brain chemistry, Ms. Rauh said.
The exact causes behind the children's reported ADHD are unclear.
Any number of factors could have caused the symptoms, and the link with pesticides could be by chance.
The new findings are based on one-time urine samples in 1,139 children and interviews with their parents to determine which children had ADHD.
The children, ages 8 to 15, took part in a government health survey from 2000 to 2004.
As reported by their parents, about 150 children in the study either showed the severe inattention, hyperactivity, and impulsivity characteristic of ADHD, or were taking medication to treat it.
The study dealt with one common type of pesticide called organophosphates.
Levels of six pesticide compounds were measured. For the most frequent compound detected, 20 percent of the children with above-average levels had ADHD.
In children with no detectable amount in their urine, 10 percent had ADHD.