A new study published in the American Journal of Psychiatry found a link between pregnant mothers exposed to the pesticide DDT and increased risks of giving birth to autistic children. Autism is a disorder characterized by impaired social interaction, problems with communication, and restricted and repetitive behavior. The study utilized blood serum obtained from over one million pregnant women in Finland to arrive at its conclusions.

The research was conducted by scientists from Columbia University and the University of Turku in partnership with the National Institute for Health and Welfare in Finland. The authors of the study relied on data provided by the Finnish Prenatal Study of Autism which is a countrywide birth cohort study on the effects of DDT on pregnant women.

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According to the World Health Organization (WHO), one in 160 children has some level of autism. It is believed autism is caused by a combination of genetic and environmental factors which many now include prenatal exposure to pesticides such as DDT. The pesticide is banned in several countries, but prior use in such countries suggests a possible link between DDT use and autism risks in children. Even after banning DDT, the pesticide remains a problem because it lingers for decades in the soil and water, contaminating crops and wildlife for decades after first use.

The blood serum database used by the researchers was put together from 1987 to 2005. The scientists sampled 1,300 children diagnosed with autism and took a study population of 778, together with the mothers of the children. These 778 autistic children and their mothers formed one group, while another group of 778 children who do not have autism and their mothers were used as a control group and compared against one another based on date and place of birth, sex and residence at the time of birth.

The scientists compared the blood samples of both groups and analyzed the blood for polychlorinated biphenyls (PCBs) and DDT byproducts. Though both DDT and PCBs have been linked to cancer, PCB’s showed no association with autism. However, the DDT analysis found that pregnant mothers with high levels of DDT byproducts have a 32 percent higher chance of giving birth to autistic children. Additionally, mothers with elevated levels of DDT byproducts were twice as likely to have children with autism who also had intellectual disabilities.

“This just confirms that banning it was a good idea,” said Tracey Woodruff, a student of reproductive health and environment at the University of California, San Francisco. An epidemiologist at McGill University in Montreal, Canada, Jonathan Chevrier couldn’t agree more. According to him, “At this point, essentially the entire planet is contaminated with DDT.”

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