Autism Linked to Maternal Exposure to DDT, Study Finds

Though the organic pollutants DDT (dichlorodiphenyltrichloroethane) and PCBs (polychlorinated biphenyls) were banned in the U.S. and many other countries more than 30 years ago, these toxic compounds can persist in the environment for decades. According to a study published today in AJP in Advance, maternal exposure to DDT is associated with an increased risk of autism in children, particularly autism with significant intellectual disability. There was no association between maternal exposure to PCBs and autism.

While several studies have established a connection between environmental pollutants and autism, “few studies have examined an association between prenatal exposure to toxins and autism, and among these, most have been based on ecologically, rather than serologically, documented exposures,” Alan Brown, M.D., M.P.H., of Columbia University Medical Center and colleagues wrote. The researchers used blood samples from mothers to assess DDT and PCB exposure, providing the first biomarker-based evidence for this connection.

The researchers obtained their data from the Finnish Maternity Cohort, which has archived serum samples from more than 1 million pregnant women since 1983. Using national health registries, they next identified 778 diagnoses of autism among children born to these mothers between 1987 and 2005. These 778 mother-child pairs were matched 1:1 with pairs that included a child without autism, and blood samples from all 1,556 mothers were analyzed for PCBs and the DDT metabolite p,p′-DDE.

The average level of p,p′-DDE in the mothers of children with autism was 1,032 pg/mL and 811 pg/mL in corresponding control subjects. The average level of PCBs was 1,022 pg/mL in mothers of children with autism and 999 pg/mL in controls.

Mothers with the highest concentrations of p,p′-DDE (top 25% of p,p′-DDE levels) were 32% more likely than those with lower p,p′-DDE levels to have a child with autism, and the odds of having a child diagnosed with autism with intellectual disability was more than double. There was no association between total levels of maternal PCBs and autism.

The authors proposed two reasons for why DDT appeared to be linked with autism while maternal exposure to PCB did not. First, DDT exposure is also known to increase the risk of both premature birth and small birthweight—two known autism risk factors. Second, DDT can reduce the production of androgen receptors, another autism risk factor.

To read more about environmental risk factors for mental illness, see Chapter 9: Poisons and Toxins in the Textbook of Neuropsychiatry and Clinical Neurosciences.

(Image: iStock/banprik)

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