Scientists have found that exposure to pesticide residues on vegetables and fruit may double a child's risk of attention deficit hyperactivity disorder (ADHD) a condition that causes inattention, hyperactivity, impulsivity or a combination of all three in children.
According to the U.S. Centers for Disease Control and Prevention, between three and seven percent of school age children in the United States have ADHD, which makes them impulsive and impairs concentration in the classroom.
In the study, researchers with the University of Montreal and Harvard University tested the urine of more than 1,100 children, between the ages of eight and 15, looking for breakdown products of organophosphate pesticides. 119 of the children in the study had been diagnosed with ADHD.
"What we saw was that the higher the level of pesticide residues in the urine, the higher the risk of ADHD in the children," said Maryse Bouchard, who led the team of researchers.
Investigators found the risk of ADHD was almost double in youngsters with higher levels of the most common breakdown metabolite, compared to children with nearly undetectable levels.
Researchers say 40 organophosphate pesticides are registered with the U.S. government.
Organophosphates are among the most widely used pesticides by growers to protect fruit and vegetables. Studies have showed that organophosphates cause hyperactivity and cognitive defects in laboratory animals, as well as neural changes.
Bouchard, who is with the University of Montreal's Department of Environmental and Occupational Health, says she is not surprised by the finding, although she cautions it is too early to draw any firm conclusions.
"We can't affirm that exposure to pesticides is causing ADHD," she added. "We would need a different kind of study to say that."
Lynn Goldman is with the Department of Environmental Health Sciences at Johns Hopkins University School of Public Health in Baltimore. Goldman says the use of pesticides, including organophosphates, is widespread in developing countries, where children are exposed to high levels of pesticides through farming.
"Those kids have much more serious, much more severe, neurological problems," said Goldman. "So, we do see evidence of effects in those populations globally."
Goldman says studies will probably now be conducted in other nations to determine how pesticides affect brain development in children.
A 2008 study of produce in the United States found organophosphate residues in 28 percent of frozen blueberry samples, 25 percent of fresh strawberry samples and 19 percent of celery samples.
The new study on pesticides and attention deficit hyperactivity disorder appears in the journal Pediatrics.