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ADHD Linked to Pesticide Exposure before Birth


Exposure to pesticides called organophosphates before birth appears to be linked to the development of attention deficit hyperactivity disorder (ADHD) in children, according to a new study. Scientists at the University of California, Berkeley, report their findings in the journal Environmental Health Perspectives.

Pesticide Exposure
Overall, 888 million pounds of pesticides are applied to crops in the United States each year, according to the Pesticide Action Network. That breaks down to equal nearly 3 pounds per year for each woman, man, and child in America. Children in the United States consume an average of five servings of pesticide residue in food and water daily. Organophosphates are nerve agents that disrupt brain chemicals called neurotransmitters, especially acetylcholine, which has a critical role in short-term memory and attention.

Pesticide Study
In the new study, investigators followed more than 300 children who are part of the Center for the Health Assessment of Mothers and Children of Salinas study led by Brenda Eskenazi, UC Berkeley professor of epidemiology and of maternal and child health. The Assessment is evaluating the association between environmental exposures and reproductive health.

Eskenazi and her colleagues were “especially interested in prenatal exposure because that is the period when a baby’s nervous system is developing the most.” The mothers and children in the study are Mexican-Americans who live in an agricultural community and who are thus more likely to be exposed to pesticides than the general population. However, the pesticides assessed in the study are widely available and commonly used.

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The investigators tested for six metabolites of organophosphate pesticides in mothers two times during pregnancy and in their children several times after birth. The children were then evaluated at ages 3.5 and 5 years for symptoms of attention disorders and ADHD.

The investigators found that prenatal levels of organophosphate metabolites were significantly associated with attention difficulties at age 5, and that the impact was more evident among boys. Specifically, for each tenfold increase in prenatal pesticide metabolite levels, there was a fivefold greater risk of a child scoring high on the evaluation, suggesting a higher likelihood that the child had ADHD.

Eskenazi points out that this study, as well as others, including a recent Harvard University study that observed higher rates of ADHD among school-aged children exposed to organophosphate pesticides, raise red flags.

“These studies provide a growing body of evidence that organophosphate pesticide exposure can impact human neurodevelopment, particularly among children,” she warns. Lead author Amy Marks, an analyst at UC Berkeley’s School of Public Health at the time of the study, noted “there is reason to be cautious, especially in situations where exposure may coincide with critical periods of fetal and child development.”

The investigators at UC Berkeley will continue to follow the children in their study. For now, organophosphate pesticides join a list of other environmental toxins, including phthalates, polyfluoroalkyl chemicals (PFCs) and lead, that appear to have an impact on children and to be associated with ADHD and other neurodevelopmental challenges.

Marks B et al. Environmental Health Perspectives 2010; DOI: 10.1289/ehp.1002056
Pesticide Action Network