New Study Links Pesticides and Autism

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Illustration courtesy U.S. Geological Survey
Chlorpyrifos, the pesticide most strongly linked to autism in a 2014 study, is applied to crops across the United States.

Pregnant women who live in close proximity to fields and farms where chemical pesticides are applied experience a 66 percent increased risk of having a child with autism spectrum disorder or developmental delay, a 2014 study by researchers at the University of California, Davis, MIND Institute has found.

Approximately 200 million pounds of pesticides are applied in California each year. This large study, published in Environmental Health Perspectives, examined associations between applications of pesticides during the study participants’ pregnancies and later diagnoses of autism and developmental delay in their children. Specific classes of pesticides studied were organophosphates, pyrethroids and carbamates.

For the study, researchers obtained study participants’ addresses during their preconception and pregnancy periods. They then overlaid the addresses on maps with the locations of agricultural chemical application sites based on pesticide-use reports, and categorized participants into different zones depending on whether they lived within 1.25 kilometers (km), 1.5 km or 1.75 km of application sites. Associations with children who developed autism or had delayed cognitive or other skills were higher the closer mothers lived to application sites, and lower the farther away they lived.

Different classes of pesticides had different effects. Organophosphates, particularly chlorpyrifos applications during the second trimester, were associated with an elevated risk of autism. Pyrethroids were moderately associated with autism, and carbamates were associated with developmental delay.

Researcher Irva Hertz-Picciotto cautions that we should find ways to reduce pesticide exposure, especially for pregnant women and young children. “We need to open up a dialogue about how this can be done, at both a societal and individual level,” she says. To read the full study on the link between pesticides and autism, go to the Environmental Health Perspectives website.