Skip navigation

Calls to Action

More Evidence Linking Pesticide Exposure to Autism

Autism more common among children whose moms lived near treated fields during pregnancy; experts redouble advice to avoid exposure
June 23, 2014

A new study finds increased rates of autism among the children of women who lived close to pesticide-treated fields during pregnancy. The association was strongest when the exposures occurred during the second and third trimesters.

The report, by researchers at the University of California-Davis MIND Institute, appears today in the journal Environmental Health Perspectives. It comes out of the ongoing Childhood Risk of Autism from Genetics and the Environment (CHARGE) study.

”This is the third epidemiological study from California to associate prenatal pesticide exposure with autism,” comments Alycia Halladay, Autism Speaks senior director for environmental and clinical sciences. “It reinforces the advice of public health experts and doctors to minimize exposure to these chemicals during pregnancy.” Autism Speaks was not directly involved in the study. However, it funds a broad range of CHARGE investigations into environmental factors that increase or decrease autism risk. (Follow the link to learn more.)

The UC-Davis investigators examined public records on commercial pesticide applications and linked this information to the addresses of approximately 1,000 CHARGE families. Most lived in California’s Sacramento Valley, Central Valley or the greater San Francisco Bay area. Nearly a third lived within a mile of a pesticide application site.

The degree of risk varied depending on when during pregnancy the mothers’ pesticide exposure occurred. For example, living within a mile of organophosphate pesticide applications at any time during pregnancy was associated with a 60 percent increased risk that a child would develop autism. However, when the exposure occurred during the third trimester, the increased risk was still higher - double that of children whose mothers lived more than a mile from treated areas. And the risk tripled when the mother’s exposure involved one particular organophosphate pesticide – chlorpyrifos – during her second trimester. Again, the increased risk is relative to that for children whose moms lived more than a mile from pesticide-application sites during pregnancy.

Exposure to another class of pesticides – pyrethroids – approximately doubled the risk of autism or developmental delay if exposure occurred immediately before conception or in the third trimester.

Exposures to pesticides may be particularly harmful during pregnancy because prenatal brain development is so sensitive to disturbance, says senior investigator Irva Hertz-Picciotto. Pesticides, in particular, tend to be neurotoxic. As such, they may interfere with the complex processes of brain development and brain-cell signaling, she says.

Clear advice to avoid contact
The report’s lead author, Janie Shelton, was a UC Davis graduate student at the time of the study. She now works as a consultant to the United Nations. "While we still must investigate whether certain sub-groups are more vulnerable to exposures to these compounds than others, the message is very clear,” she says. “Women who are pregnant should take special care to avoid contact with agricultural chemicals whenever possible."

In 2012, Shelton authored “Tipping the balance of autism risk: potential mechanisms linking pesticides and autism,” summarizing what is known about why prenatal exposure to pesticides can contribute to autism. (Follow the link to read the full report.)

Other research from the CHARGE Study has emphasized the importance of maternal nutrition during pregnancy, particularly the use of prenatal vitamins, in reducing autism risk. CHARGE receives funding from the National Institute of Environmental Health Sciences, the Environmental Protection Agency, the MIND Institute and Autism Speaks.

Autism Speaks supports a wide range of research on environmental risk factors for autism. To learn more about these research projects, click here. Learn more about Autism Speaks Environmental Factors in Autism Initiative here. This research is made possible by Autism Speaks community of families, volunteers and donors.

Dr. Halladay provided comment on this study in Scientific American. Read the article here.