Pesticide exposure during pregnancy increases autism risk.

reside1A new study originating from the University of California, Davis, has given more credence to research which has linked pesticide exposure to a number of health conditions including autism. This study determined that women who lived in close proximity to field and farms with heavy pesticide use were two thirds more likely to have a child with autism spectrum disorder and other developmental delays. The neurological damage was worse when the exposure occurred during the second and third trimesters of pregnancy. The research published in the Journal of Environmental Health Perspectives, examined associations between specific classes of pesticides, including organophosphates, pyrethroids and carbamates.

“This study validates the results of earlier research that has reported associations between having a child with autism and prenatal exposure to agricultural chemicals in California,” said lead study author Janie F. Shelton, a UC Davis graduate student who now consults with 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: Women who are pregnant should take special care to avoid contact with agricultural chemicals whenever possible.”

In California approximately 200 million pounds of active pesticides are applied each year. Several studies have linked the toxic qualities of pesticide use to various neurological disorders. This study examined commercial pesticide applications using the California Pesticide Use Report and linking the data to the residential addresses of approximately 1,000 participants in the Northern California-based Childhood Risk of Autism from Genetics and the Environment (CHARGE) Study.

The research participants include families with children between 2 and 5 diagnosed with autism or developmental delay or with typical development and the researchers used questionnaires to obtain study participants’ residential addresses during the pre-conception and pregnancy periods. The addresses were overlaid on maps with the locations of agricultural chemical application sites based on the pesticide-use reports to determine residential proximity. The study also examined which participants were exposed to which agricultural chemicals. Twenty-one chemical compounds were identified in the organophosphate class, including chlorpyrifos, acephate and diazinon. The second most commonly applied class of pesticides was pyrethroids, one quarter of which was esfenvalerate, followed by lambda-cyhalothrin permethrin, cypermethrin and tau-fluvalinate. Eighty percent of the carbamates were methomyl and carbaryl.

“We mapped where our study participants’ lived during pregnancy and around the time of birth. In California, pesticide applicators must report what they’re applying, where they’re applying it, dates when the applications were made and how much was applied,” Hertz-Picciotto said. “What we saw were several classes of pesticides more commonly applied near residences of mothers whose children developed autism or had delayed cognitive or other skills.”

“In that early developmental gestational period, the brain is developing synapses, the spaces between neurons, where electrical impulses are turned into neurotransmitting chemicals that leap from one neuron to another to pass messages along. The formation of these junctions is really important and may well be where these pesticides are operating and affecting neurotransmission,” Hertz-Picciotto said.

The researchers recommend dialogues at a societal and individual level to reduce the risk of maternal exposure to chemical pesticides. “If it were my family, I wouldn’t want to live close to where heavy pesticides are being applied,”Hertz-Picciotto said.

The researchers did not address the pesticide residue issue found on genetically modified crops that are modified to be resistant to certain pesticides.


Janie F. Shelton, Estella Marie Geraghty, Daniel J. Tancredi, Lora D. Delwiche, Rebecca J. Schmidt, Beate Ritz, Robin L. Hansen, Irva Hertz-Picciotto. Neurodevelopmental Disorders and Prenatal Residential Proximity to Agricultural Pesticides: The CHARGE Study. Environmental Health Perspectives, 2014; DOI: 10.1289/ehp.1307044

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