Expectant mothers with higher levels of DDT pesticides in their bloodstream during the course of their pregnancy phase are likelier to have children who could be autistic, as per a research involving a study of more than a million pregnant ladies in Finland.
The study also looked at the risks associated with a class of industrial chemicals called polychlorinated biphenyls (PCBs) that were banned in 1979 in the United States and in 1985 in Europe, but no association with autism was found. Confusingly, a similarly designed 2016 study did find a link to PCBs and failed to identify one with DDT.
The finding sheds light on another potential cause of autism, a neurodevelopmental condition that affects communication, behavior and the ability to interact with others.
"We think of these chemicals in the past tense, relegated to a long-gone era of unsafe 20th Century toxins", says lead author Alan S. Brown, MD, MPH, professor of Epidemiology at Columbia University's Mailman School of Public Health and of Psychiatry at Columbia University Medical Center. "Very likely, you need other predisposing factors".
Brown's team found no correlation between the PCB by-product and autism.
Then, the researchers analyzed blood samples that had been taken from these children's mothers during early pregnancy. Now, scientists have evidence that the offspring of mothers exposed to DDT have a higher risk of developing autism.
Brown cautions that although there seems to be a link between autism and DDT exposure, the overall risk of having a child with the disorder is low-even among women with high DDT levels.
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"In addition, the odds of children having autism with intellectual disability were increased more than twofold with maternal DDE levels above this threshold", notes a statement from the American Psychiatric Association. The study does not now prove causation, although the researchers mentioned that "the findings persisted, even after controlling for compounding factors".
The researchers also tested the mothers' blood samples for PCBs (polychlorinated biphenyls), another class of environmental pollutants, but found that these substances were not associated with autism risk.
While DDT and PCBs were widely banned in many nations over 30 years ago, including the U.S. and Finland, they persist in the food chain because their breakdown occurs very slowly, as long as several decades, resulting in continuing exposure to populations. "Unfortunately, they are still present in the environment and are in our blood and tissues".
"What happened was DDT was sprayed in the air as an insecticide to kill mosquitoes, to kill bugs on fruits and vegetables".
Virtually everybody has some level of DDT and PCBs in their body. The breakdown product of DDT is DDE; the CDC says that most of the population has detectable levels of DDE.
Inutereo fetuses are exposed to higher levels of the chemicals too "because they kind of get concentrated when they go through the mom's blood to the placenta". "I would not say women should be concerned but it is important to be informed that at least this one chemical exposure is related to increased risk".