A new nationwide study of U.S. children links pesticide exposure to increased risk of attention-deficit hyperactivity disorder.

The study, published in the journal Pediatrics and conducted by scientists at Harvard University and the University of Montreal, measured pesticide levels in the urine of 1,139 children in the United States. The researchers found that exposure to organophosphate pesticides “at levels common among U.S. children may contribute to ADHD prevalence,” the study authors reported. Organophosphate pesticides are used in agricultural and residential settings. Certain conventionally grown fruits and vegetables have tested positive for pesticide residue, according to the Washington, D.C.-based Environmental Working Group.

The researchers couldn’t prove that pesticides cause ADHD.

“Previous studies have shown that exposure to some organophosphate compounds cause hyperactivity and cognitive deficits in animals,” said lead author Maryse F. Bouchard of the University of Montreal Department of Environmental and Occupational Health and the Sainte-Justine Hospital Research Center in a release. “Our study found that exposure to organophosphates in developing children might have effects on neural systems and could contribute to ADHD behaviors, such as inattention, hyperactivity, and impulsivity.”

The study is the first to look at risks among children with average levels of pesticide exposure.

According to the study, approximately 40 organophosphate pesticides are registered with the U.S. Environmental Protection Agency for use in the United States. The EPA considers food, drinking water, and residential pesticide use the key sources of exposure. The National Academy of Sciences considers diet to be the major source of exposure to pesticides for infants and children.

The EWG recently released its updated Dirty Dozen—a list of 12 fruits and vegetables highest in pesticide residue. This is where going organic really pays off.Celery, peaches, strawberries, apples and blueberries ranked as the top five for pesticide residue.

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Tags: ADHD, Environmental Working Group, EPA, pesticides