Long lingering pesticides may increase risk for autism: Study

Women who have high levels of a marker for a long-discontinued pesticide in their blood seem to have an increased risk of having a child with autism spectrum disorder (ASD), according to researchers from Columbia University Medical Center.

What is autism?

Autism is a complex disorder with largely unknown causes. It is identified by problems in communication, repetitive body movements and behaviors, and difficulty relating to people and events. There are existing risk factors, which we know are linked to increased chances of having a child with ASD, such as having a sibling with ASD, having older parents or having certain genetic conditions like Down Syndrome.

In this study, 1 million women in Finland had their blood drawn during pregnancy at three months, six months, and nine months. The researchers looked for levels of DDE (p,p'-dichlorodiphenyl dichloroethylene), a product of the pesticide DDT (dichlorodiphenyltrichloroethane). These chemicals are known to transfer across the placenta, meaning that they could potentially go to a fetus’ bloodstream. Though DDT has been banned in the United States since 1972, small amounts of it may still be found lingering in the soil.

What did the researchers find?

Researchers examined the blood samples from the database of 778 mothers who had children on the autism spectrum and compared them to the blood samples of 779 mothers who did not. The odds of autism among children were increased, by 32 percent, in mothers whose DDE levels were high (high was, comparatively, 75th percentile or greater). One thing to remember: This is not something mothers can control or guard against.

“This adds another piece to the puzzle in terms of the possible risk factors for autism,” said lead author Dr. Alan Brown, professor of psychiatry and epidemiology at Columbia University Medical Center and director of Program in Birth Cohort Studies at the New York State Psychiatric Institute, in an interview with ABC News. “Although we can’t prove that it is a cause, we are working towards learning more about how such environmental risks may be altering brain development and possibly increasing autism risk.”

Researchers also found that the odds of having children on the autism spectrum who also had an intellectual disability were increased more than two-fold when the mother’s DDE levels were high.

“We aware of the study and will carefully consider its findings," said the Federal Drug Administration (FDA) in a written statement to ABC News. "The Federal Drug Administration has action levels for DDT, and this pesticide is included in our monitoring program. The most recent report summarizes the results of FDA’s pesticide monitoring program and shows that the levels of pesticide chemical residues measured by FDA in the U.S. food supply are generally in compliance with the Environmental Protection Agency’s pesticide tolerances."

Brown said many women had some level of DDE and PCB in their blood, however, the vast majority did not have children with increased risk of autism spectrum disorder.

“I don’t think people should be alarmed by these findings," Brown added, "but it is something to be aware of."

Find more information on pesticides at the U.S. National Institute of Environmental Health Sciences website.

Aditi Vyas, M.D. specializes in radiology and occupational and environmental medicine and is a resident in the ABC Medical Unit.

Richa Kalra, M.D., is a resident physician specializing in psychiatry and working in the ABC News Medical Unit.