There are several theories about what causes autism; one of those revolves around exposure to pesticides. A recent study adds weight to that particular theory, as researchers discovered that children whose mothers were exposed to the most commonly used pesticides were more likely to develop autism spectrum disorder (ASD).
Findings from the Research
The study included nearly 38,000 people, including 2,961 cases of autism.
Women who were pregnant and who lived within a 2,000-meter radius of an area where pesticides were heavily applied were found to be between 10-16% more likely to have a child diagnosed with ASD, compared to women who lived in areas farther away from sprayed areas.
The team looked at 11 different pesticides, including glyphosate, chlorpyrifos, diazinon, permethrin, and others (often used to control ticks). They discovered that children who were exposed in-utero were 30% more likely to be dually diagnosed with autism and intellectual disabilities. Exposure in the first year of life increased the risk of autism by as much as 50%, compared to those not exposed to certain pesticides.
The Pesticides Studied Have Caused Damage in the Past
The 11 pesticides chosen for the study were selected because past research has linked them to potentially harmful effects on development and brain development, including on animals still in the womb, Von Ehrenstein said. Human studies have also linked the pesticides to harm, but much of that research relied on smaller groups than the cohort in the current study.
Von Ehrenstein said the study shows that babies are particularly vulnerable to pesticide exposure at 2 key points in their development: while in utero and after birth. The researchers controlled for the effect of prenatal exposure after birth when they calculated the risk for exposure while the mothers were pregnant.
The findings suggest that children who are exposed to pesticides during the first year of life may have a greater risk of developing both autism and intellectual disabilities.
Von Ehrenstein said:
“Both prenatal and postnatal periods are vulnerable periods. And it doesn’t stop at birth.”
It’s possible that other environmental factors besides pesticide spraying played a role in the development of autism in those diagnosed with the disorder. However, the researchers adjusted for other factors, including air pollution, whether the mothers lived in rural or urban areas, and their socioeconomic status. The link remained robust after all of these factors were accounted for.
Amanda Bakian, co-author of an editorial that accompanied the study and an assistant professor in the division of child and adolescent psychiatry at the University of Utah, said: 
“Pesticide exposure alone is not the whole story. Other factors are clearly at play that makes some children more vulnerable to this exposure than others. And at this point, we don’t know what those are.”
When Possible, Go Organic
Von Ehrenstein notes that, unlike smoking or drinking alcohol, most people have no control over when and where pesticides are applied, and pregnant women may not realize they are being exposed. What’s more, people may be further exposed to pesticides by eating fruit and vegetables that have been treated by the chemicals. In that case, it’s possible to lower one’s exposure by choosing organic over traditionally-grown produce. 
In the end, Von Ehrenstein and her team hope their findings will lead to greater public awareness and policy changes regarding pest control that benefit human health.
“I would hope that these findings would make some policymakers think about effective public health policy measures to protect populations who may be vulnerable and living in areas that could put them at higher risk. Raising awareness in the public may be the way to eventually change practices and agricultural policies.”
The Autism Society of America also hopes the study will lead to more research. Executive director and CEO Scott Badesch commented:
“These types of studies are so important to help us understand the underlying mechanisms that may lead to autism spectrum disorders. We also urge further research like this that might lead to specific public health actions and interventions for individuals and families.”