Autism and Pesticides: The Research Behind the Controversial Link

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The First Suggestion - 2005

There has not yet been a large body of research looking for a connection between autism and pesticides. The first study to find anything of relevance was conducted in 2005 by an Italian team of researchers. The study, carried out at the University Campus Bio-Medico, compared native autistic Italian children to those who were from the United States, assuming that US children would be exposed to higher levels of organophosphate pesticides (OPs), such as diazinon and chlorpyrifos.

Through comparing the two regions, which are known for their low and high levels of OPs respectively, the researchers suggested that they had found indirect evidence that being exposed to OPs may cause genetically vulnerable fetuses to later show autistic tendencies. Their predictions were found to be correct, and they accepted their hypothesis that “concurrent genetic vulnerability and environmental OP exposure may possibly contribute to autism pathogenesis in a sizable subgroup of North American individuals.” In other words, they believe that pesticides may indeed contribute to the development of autism.

Preliminary Studies - 2007

In October 2007, a US study published in Environmental Health Perspectives built on that foundation. The autism rates in the US, and in California specifically, had been climbing drastically, leading to what some have termed “the autism crisis.” The California Department of Health study looked at 365 children on the autism spectrum and 6,975 who were not, all of them living in Central Valley, CA. It compared the exposure to pesticides of these children’s mothers during their first trimester, based on how far they lived from fields sprayed with OPs - specifically endosulfan and dicofol. Women who lived within 500 meters of the OP-sprayed fields were six times more likely of having children with autism than those who lived farther from the fields.

Although the researchers at the Department of Health emphasized that the results were preliminary and that more research is required to corroborate them, they maintain that the study’s results suggested that the condition of about 7% of all of the autistic children in the Central Valley was connected to pesticide exposure.

Refining the Studies - 2009 and Beyond

As autism rates in California continued to rise, the state produced more research about possible links between autism and pesticides. The UC Davis M.I.N.D. Institute conducted a study that found that the rising rates of autism in California since 1990 could not be explained by various technical issues, such as the migration into California of families who already had autistic children, the autism diagnoses of children with milder forms of the condition, or the earlier intervention and diagnosis of autism in recent years.

This study correlated the autism numbers between 1990 and 2006 with birth records, making sure to exclude children from outside of California. Their results suggest that less than a tenth of the increase could be due to different methods of diagnosis, and only 24% of the increase could be due to diagnosis at an earlier age. The rest of the increase must be due to either genetics or the environment (such as pesticides). And as Dr. Hertz-Picciotto, one of the researchers of the study, says, “There’s genetics and there’s environment. And genetics don’t change in such short periods of time."

So why haven’t they done more studies on autism and pesticides? One big component is a lack of funding. According to Dr. Hertz-Picciotto, research that looks into the genetic causes of autism have ten to twenty times the research dollars of research that looks into possible environmental causes. With time, however, additional research will map out whether there truly is a connection between autism and pesticides.

Autism and Pesticides References

Beyond Pesticides. “Autism Rates Tied to Environmental Factors, Not Changing Diagnoses.”

Beyond Pesticides. “Pesticides Linked to Rising Autism Rates.”

Autism Help. “Causes of Autism.”

PubMed. “Paraoxonase Gene Variants Are Associated with Autism in North America, But Not in Italy.”

This post is part of the series: Research About Autism

This series contains several articles about autism research, including causes and treatments of this condition.

  1. Point and Counterpoint: Using Chelation for Autistic Kids
  2. The Pros and Cons of Chelation Autism Therapy
  3. Using Conversation Starters for Kids with Autism
  4. Do Pesticides Contribute to Autism?
  5. Thimerosal and MMR Vaccinations: Is there a Relationship to Autism?