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DDT linked to an increase in autism risk in new study

Columbia University Medical Center researchers found that mothers with higher exposure to the banned pesticide had an increased risk of a child developing autism.

The discontinued pesticide DDT is linked to an increased risk of autism, according to a new study out of Columbia University Medical Center.


The study, published today in the American Journal of Psychiatry, found that a mother's exposure to DDT increased the risk of her child developing autism spectrum disorder.

The study builds on previous evidence that the environmental toxic is linked to developmental impacts in children exposed in utero, and is significant as autism rates keep growing in the U.S. and researchers don't yet know what causes the disorder. Approximately one in 59 kids in the U.S. has autism—up from one in 150 in the year 2000.

DDT was an insecticide heavily used in the 1940s to 1960s but banned in 1972 in the US because of its impact on wildlife and concerns over its effect on fertility, immune systems, hormones and brain development.

The chemical takes a while to break down and accumulates in fatty tissue, so even though it has been banned for decades, people are still exposed through food—mostly seafood, Kristen Lyall, professor at the Drexel Autism Institute at Drexel University, told EHN. Lyall was not involved in the new study.

In the study, researchers matched 778 cases of childhood autism with maternal blood samples in Finland. The mothers' blood samples were tested for DDE, a metabolized form of DDT, and for another banned toxic—polychlorinated biphenyls (PCBs). Women with the highest levels of exposure to DDE were 32 percent more likely to have a child with autism.

The association between the increased risk and higher maternal exposure of DDE was significant for boys but not girls. Autism is about 4 times more common in US boys, according to federal data.

There was no link between PCB exposure and autism rates.

Why the link?

It's not clear why DDE increases the risk of autism but the researchers suggested two reasons.

The first is because maternal exposure to DDT has previously been linked with premature birth and smaller children—both risks for later developing autism.

The second reason is that DDE has an effect on androgens, which are male sex hormones. DDE exposure has been shown to cause problems with androgens' abilities to bind to their receptors, Dr. Alan Brown, lead author of the new study and a professor of psychiatry and epidemiology at Columbia University Medical Center, told EHN.

Like Brown, Lyall has also looked at DDT and PCBs and autism risks, but her study, which was published in 2017 in Environmental Health Perspectives, found opposite results to Brown's. In her study, it was the PCBs, not DDT, that were linked to an increase in autism.

Both Brown and Lyall are quick to point out that both studies need to be repeated and neither definitively means the chemicals caused the disorders.

Brown also pointed out the differences between Lyall's study and his. Brown's studied women and children in Finland and had a much larger population than Lyall's population, which was based in California, he said. The differences in population may attribute to the disparate findings, he said.

"It tells us about the importance about studying different populations, and then to home in on what might be different about this population to tell us even more about autism," Brown said.

Brown said the lingering legacy from DDT and PCBs should serve as cautionary tales for other compounds.

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