Pesticide Exposure and Risk of Autism

July 27, 2012

This week’s “Got Questions?” answer is from Alycia Halladay, Ph.D., Autism Speaks former director of research for environmental sciences.

While I was pregnant, I came in contact with a pesticide that has now been removed from the market. Could this have been one of the reasons my child has autism?

I often get this or similar questions about exposure to pesticides. While scientists are just beginning to scratch the surface of this issue, a recent article co-written by an Autism Speaks-funded investigator reviewed the scientific literature on pesticides and autism.

Before I get into the details of that review, I want to stress something important. Although studies have found links between pesticide exposure of pregnant women and increased risk of autism in their children, the cause of autism cannot be blamed on pesticides alone.  Pesticides are one of many environmental risk factors that may contribute to autism spectrum disorder (ASD). 

We know that a combination of genetic and environmental factors causes autism. (In rare cases, it can result from genes alone.) Exposure to pollutants is one potential environmental factor under study. These chemicals include pesticides, flame-retardants, plasticizers and industrial chemicals. As I discussed in a previous blog, researchers also use the term environmental to refer to nonchemical factors. These include the age of the mother or father at time of conception and fever or infections during pregnancy.

While we know that many environmental factors can contribute to autism, we can’t yet say whether any one of them carries more risk than do others. Each person’s genes can produce greater vulnerability to some risk factors over others.

As Janie Shelton, Irva Hertz-Picciotto, Ph.D., and Isaac Pessah, Ph.D., point out in their review article, a large nationwide survey of U.S. adults found that an estimated 80 to 100 percent of women have detectable levels of pesticides in their urine or blood. This study doesn’t link pesticides to any specific illnesses or disability. However, it builds a strong case that people should do what they can to minimize pesticide exposure.

Their review goes on to outline the epidemiological evidence of a link between certain pesticides and autism. One study found that pregnant women who lived near farms with high pesticide use have an increased risk of having a child with ASD. Another study found that pregnant women with higher levels of pesticides in their urine have an increased risk of having a child with developmental disorders.

Both studies looked at high-level exposures over extended periods. We know that, in general, repeated high exposures increase harm. We don’t fully understand the effects of low-level exposures or of a single high-level exposure in humans.

However, using animal models, researchers are gaining a better understanding of how pesticides cause harmful changes in the developing brain. We are also learning more about specific gene-pesticide interactions. For example, mutations of an autism-associated gene called reelin have been associated with exaggerated autism-like behaviors in animals exposed to pesticides. We’ve also learned that pesticides can impair cell structures called mitochondria, which provide our cells with vital energy. We also know that mitochondrial dysfunction is much more common in persons with autism than in the general population.

These findings don’t definitively link pesticides to ASD. But taken together, they show that pesticide exposure can affect the developing brain in ways that may lead to autism.

So what advice can we offer? We know that exposures to potentially toxic chemicals during pregnancy threaten the developing child’s health. To the extent possible, women who are pregnant or trying to conceive should become aware of such chemicals in their food, water and general environment. To the extent possible, they should take steps to reduce or eliminate exposures.

 You can find more information about avoiding chemical exposures at the Columbia Center for Children’s Environmental Health webpage for families. 

To help reduce potentially harmful chemical exposures, Autism Speaks has joined the Safer Chemicals Healthy Families coalition, which is working to improve government regulation of pollutants.

Editor’s note: As an organization and community, Autism Speaks considers environmental risk factors a high-priority area of research. Using this Autism Speaks Grant Search, you can explore many related Autism Speaks studies.

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