Maryse Bouchard says the study found that exposure could play a part in behaviors such as inattention and hyperactivity. But she also says the study does not prove that the chemicals cause the disorder.

MARYSE BOUCHARD: "We can’t affirm that exposure to pesticides is causing A.D.H.D. We would need a different type of study to say that."

The researchers say forty organophosphate pesticides are registered with the United States government. The chemicals are used to protect fruits and vegetables. They are also used to poison insects in other places such as homes.

Lynn Goldman is an environmental health scientist at Johns Hopkins University School of Public Health in Maryland. She notes that the use of pesticides, including organophosphates, is widespread in developing countries. Children come in contact with high levels of pesticides through farming.

LYNN GOLDMAN: "And those kids have much more serious, much more severe neurological problems. So we do see evidence of effects in those populations globally."

The study was published in the journal Pediatrics.

And that's the VOA Special English Health Report, written by Caty Weaver with Jessica Berman. I’m Steve Ember.