In this week’s Journal of the American Medical Association, reporter Bridget Kuehn summarizes two of the latest studies that have found an association in children between early exposure to pesticides and an increased risk of developing ADHD (attention-deficit hyperactivity disorder).
The news isn’t good for parents who already worry about such things.
Previous studies had linked ADHD with very high levels of childhood exposure to organophosphate pesticides, such as levels experienced by children living in farming communities that used these chemicals. But a recent study using data from the National Health and Nutrition Examination Survey (NHANES) found that even children who experience more typical levels of pesticide exposure, such as from eating pesticide-treated fruits and vegetables, have a higher risk of developing the disorder.
In addition, another research team linked low-level organochlorine exposure in utero to the development of ADHD-like behavior in children. In particular, they found that ADHD was associated with higher levels of intrauterine exposure to polychlorinated biphenyls (PCBs) and p,p’-dichloriphenyl dichloroethylene (a metabolite of the pesticide DDT). Both have been banned from production in the United States for decades but persist in the environment.
The first study that Kuehn refers to was published in May in Pediatrics. Researchers analyzed four years (2000-2004) of data on a representative sample of 1,139 children (aged 8 to 15 years) who took part in the National Health and Nutrition Examination Survey. About 10 percent (119) of the children met the diagnostic criteria for ADHD. The researchers also measured the organophosphate pesticide metabolites in all the children’s urine. (Organophosphates are among the most widely used pesticides in agriculture.) The children with the highest concentration of these metabolites were more likely to have been diagnosed with ADHD than those with the lowest concentrations. The risk for ADHD was 10 percent for those children with the lowest exposure and 20 percent for those with the highest.
The second study mentioned by Kuehn was published in April in the American Journal of Epidemiology. This study involved children born between 1993 and 1998 to mothers who lived near a PCB-contaminated harbor in Massachusetts. Researchers measured the levels of organochlorine pesticides in the children’s umbilical cord blood. Surprisingly, the measurements found that, despite the contamination of the harbor, the women had experienced a rather average level of exposure to PCBs. When the children were 8 years old, they were assessed for ADHD-like behavior. The study found that the children at greatest risk of developing ADHD-like behavior were those with the greatest prenatal exposure to the pesticides. As none of the umbilical cord blood tests had revealed excessive exposure to organochlorines, this finding suggested that even low-level pre-natal exposure to these chemicals might raise the risk of ADHD in children.
An important caveat: These studies found only an association, not a cause-and-effect, between pesticides and ADHD. And even if a link between pesticides and ADHD is confirmed, that doesn’t mean other factors aren’t also involved.
Still, parents may want to follow the advice that one of the study’s authors gave Kuehn: “It’s prudent for parents to try to reduce their children’s exposure to pesticides.” To help you get started (if you haven’t already), the St. Paul-headquartered Institute for Agriculture and Trade Policy has a great two-page tip sheet [PDF] on the topic.