For related articles and more information, please visit OCA’s Health Resource page and our Organic Transitions page.

Babies whose moms lived within a mile of crops treated with widely used pesticides were more likely to develop autism, according to new research published today.

The study of 970 children, born in farm-rich areas of Northern California, is part of the largest project to date that is exploring links between autism and environmental exposures.

The University of California, Davis research – which used women’s addresses to determine their proximity to insecticide-treated fields – is the third project to link prenatal insecticide exposures to autism and related disorders.

One in every 68 U.S. children has been identified with an autism spectrum disorder.

“The weight of evidence is beginning to suggest that mothers’ exposures during pregnancy may play a role in the development of autism spectrum disorders,” said Kim Harley, associate director of University of California, Berkeley’s Center for Environmental Research and Children’s Health. She was not involved in the new study.

One in every 68 U.S. children has been identified with an autism spectrum disorder  –  a group of neurodevelopmental disorders characterized by difficulties with social interactions, according to the Centers for Disease Control and Prevention.

“This study does not show that pesticides are likely to cause autism, though it suggests that exposure to farming chemicals during pregnancy is probably not a good thing,” said Dr. Bennett Leventhal, a child psychiatrist at University of California, San Francisco who studies autistic children. He did not participate in the study.

The biggest known contributor to autism risk is having a family member with it. Siblings of a child with autism are 35 times more likely to develop it than those without an autistic brother or sister, according to the National Institutes of Health.

By comparison, in the new study, children with mothers who lived less than one mile from fields treated with organophosphate pesticides during pregnancy were about 60 percent more likely to have autism than children whose mothers did not live close to treated fields. Most of the women lived in the Sacramento Valley.

When women in the second trimester lived near fields treated with chlorpyrifos – the most commonly applied organophosphate pesticide – their children were 3.3 times more likely to have autism, according to the study, published in the journal Environmental Health Perspectives.

Chlorpyrifos, once widely used to kill insects in homes and gardens, was banned for residential use in 2001 after it was linked to neurological effects in children. It is still widely used on crops, including nut trees, alfalfa, vegetables and fruits.

“We need to understand how multiple exposures interact with each other and with genetics to understand all that is involved in the causes of autism.” –Alycia Halladay, Autism Speaks The study also is the first to report a link between pyrethroids and autism. Application of pyrethroids just prior to conception meant an increased risk of 82 percent, and during the third trimester, the risk was 87 percent higher.