Mothers’ Pesticide Levels Linked to Autism in Their Children

CC BY 2.0. An airplane spraying DDT over Baker County, Oregon, 1955 (Wikimedia Commons)

A new study provides the first biomarker-based evidence that maternal exposure to insecticides is associated with autism among their offspring.

One of the many problems with unleashing vast amounts of synthetic chemicals into the environment is that if they turn out to pose a threat, they can be banned, but they may persist in the environment for many many years to come. Such is the case with the infamous DDT. The miracle pesticide was banned in the United States in 1972 – and largely credited with starting the modern environmental movement – and then banned worldwide for agricultural use. (It is still used in some countries for vector control.)

Alas, DDT is a persistent organic pollutant that loves to linger in the environment, finding its way into food chains, and into us as well. The breakdown product of DDT is DDE; the CDC says that most of the population has detectable levels of DDE.

DDT breast cancer

Joe Wolf/Flickr/CC BY 2.0

And now, a new study finds an association with elevated levels of DDE in pregnant mothers with an increased risk of autism among their children.

The objective of the study was to test whether elevated maternal levels of persistent organic pollutants – specifically DDT and PCBs – were associated with autism in their offspring.

The researchers started with mother-child cases from a national birth cohort study, the Finnish Prenatal Study of Autism, which includes a million women in Finland who gave birth between 1987 and 2005. They looked at DDE levels in maternal serum samples drawn from more than 750 children with autism and matched them with 750 control subjects.

While they found no link between the PCBs, the DDT by-products told a different story. Mothers with elevated concentrations of DDE (defined as the 75th percentile or greater) were 32 percent more likely than women with lower levels to give birth to children who developed autism.

“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. “While these results indicate an association, they do not prove causation, although the findings persisted after controlling for confounding factors.”

The authors say that their findings “provide the first biomarker-based evidence that maternal exposure to insecticides is associated with autism among offspring.”

Even so, DDE is likely just "one piece of a puzzle," said study lead researcher Dr. Alan Brown, a professor of psychiatry and epidemiology at NYC's Columbia University Medical Center. "Very likely, you need other predisposing factors.”

Brown urges women who are pregnant or planning on it to consume organic produce, as well as wash fruits and vegetables to rinse off toxic residues, but "I wouldn't say it's cause for alarm," he told Live Science. "We showed that overall in autism, there was a modest increase in risk, but the vast majority of offspring who are exposed to the high levels still won't get autism."

I appreciate that that the authors don’t want to frighten people, but still, those findings are clearly enough cause for concern to think more carefully about what we’re putting into the environment.

The paper, "Association of Maternal Insecticide Levels With Autism in Offspring From a National Birth Cohort," was published in the American Journal of Psychiatry.