Study Strengthens Link Between Prenatal Pesticide Exposure and Autism

Pete Markham

Autism Spectrum Disorder (ASD) affects about 1 in 68 children in the United States, and a combination of genetic and environmental factors, along with complications during pregnancy have been associated with ASD diagnoses. A new study from the National Institute of Environmental Health Services has strengthened the link between prenatal exposure to agricultural pesticides and ASD. The study’s findings have been published in the journal Environmental Health Perspectives.

In 2003, University of California-Davis began the Childhood Autism Risks from Genes and Environment (CHARGE) study. This ongoing study seeks to identify causes and risk factors for ASD and other developmental delays (DD). This particular facet of the study explored prenatal exposure to agricultural pesticides, which have known neurotoxic effects. 

The researchers compared addresses during pregnancy to state records of applications of organochlorines, organophosphates, pyrethroids, and carbamates within 1.25 km, 1.5 km, and 1.75 km from those addresses. About a third of the 970 study participants lived within 1.5 km (0.9 miles) of pesticide applications during pregnancy. While proximity to any of the four classes of pesticide resulted in an increased risk of a child with ASD or DD, some of the chemicals presented a greater risk at different stages during pregnancy.

Proximity to organophosphates during prenatal development increased the risk of the child being diagnosed with ASD or DD by 60%, with exposure during the third trimester increasing the risk nearly threefold than earlier during development. However, exposure to chlorpyrifos, a subclass of organophosphates, conferred the greatest risk during the second trimester. Exposure to pyrethroids presented an increased risk before conception and during the third trimester. Prenatal exposure to carbamates resulted in an increased risk of ASD or DD, though the data did not indicate a particular time during development that was more affected by exposure. Too few volunteers in the study were exposed to organochlorines, so that data was excluded.

The researchers corrected for child ethnicity, maternal age, prenatal vitamin use, maternal education, differences in health insurance at birth, region, and maternal birth place, in order to account for other known confounders in ASD/DD diagnoses. It is also important to note that CHARGE participants are volunteers, and the type of mother seeking to participate in such a study is likely more proactive about the child’s health in the first place, and might not be indicative of the general population. However, these findings do support previous studies that have linked pesticide exposure to ASD and DD.

The study focused on where the pesticides were applied, not the diet of the mothers and how much or which pesticides were potentially ingested. The USDA has approved over 200 synthetic chemicals to be used in certified organic farming. Additionally, organic pesticides do not work as long and need to be reapplied more frequently than synthetics, which may pose a greater harm to the environment and also has negative effects on human health. Synthetic and organic pesticides can be washed off of produce with a commercial detergent (water alone will not work) or with a homemade mixture of white vinegar, baking soda, and water.

Future study will explore the specific genes and biological mechanisms affected by exposure to pesticides. The researchers recommend that women who are trying to conceive or who are pregnant should avoid direct contact with pesticides as much as possible to reduce risk of the fetus developing ASD or DD.

[Header image “An Air Tractor Doing Some Crop Dusting near the Farm” by Pete Markham via flickr, used in accordance with CC BY-SA 2.0]

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