CHARGE study links autism with prenatal exposure to pesticides

An 11-year study by investigators from California supports previous research that connects prenatal exposure to common pesticides with an increased risk of autism spectrum disorder (ASD). The finding, published in Environmental Health Perspectives, strengthens the evidence linking neurodevelopmental disorders with gestational pesticide exposures.

In the Childhood Autism Risks from Genetics and Environment (CHARGE) study, data on commercial pesticide application from the California Pesticide Use Report for 1997-2008 were linked to addresses of 970 women during pregnancy. Pounds of active ingredient applied for organophosphates, organochlorines, pyrethroids, and carbamates were aggregated within 1.25 km, 1.5 km, and 1.75 km buffer distances from the home in the population-based case-control study.

The goal of the study was to evaluate whether residential proximity to agricultural pesticides during pregnancy is associated with ASD or developmental delay (DD). Multinomial logistic regression was used to estimate the odds ratio (OR) of exposure comparing confirmed cases of ASD (n=486) or DD (n=168) with typically developing referents (n=316).

During pregnancy, approximately one-third of women in the study lived just under 1 mile from an agricultural pesticide application. Risk of ASD was 60% higher among offspring of women who lived in proximity to organophosphates at some point during gestation. The risk was highest for third-trimester exposures (OR=2.0, 95% confidence interval [CI] = 1.1, 3.6) and for chlorpyrifos applications that occurred in the second trimester (OR=3.3, 95% CI=1.5, .4). A higher risk of both ASD and DD was seen in children whose mothers had resided near pyrethroid insecticide applications just prior to conception or in the third trimester (ORs from 1.7 to 2.3). Risk of DD was increased in those near carbamate applications but the researchers did not identify a specific vulnerable period in pregnancy.

While noting that their data do not encompass all potential exposures to each of the compounds, the study authors concluded that “because of the observed associations in humans and direct effects on neurodevelopmental toxicity in animal studies, caution is warranted to avoid direct contact with pesticides during pregnancy.”

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