Can Chemicals Cause Autism?


Recent studies show that certain chemicals can increase the risk of autism. Researchers from the Drexel University have published evidence that some pesticides, banned in 1970, may still cause a significant risk of autism during pregnancy. The study showed that children born after being exposed to the highest levels of organochlorine chemicals during their mother’s pregnancy were roughly 80% more likely to be diagnosed with autism in comparison with individuals with the lowest levels of these chemicals.

Why do these chemicals appear in our bodies nowadays when it was banned in the United States in 1977? The truth is that these dangerous compounds have remained in the environment and have become absorbed in the fat of animals that we eat, leading to this exposure. The organochlorine chemicals can cross the placenta barrier and affect the fetus’ neurodevelopment during pregnancy.

“There’s a fair amount of research examining exposure to these chemicals during pregnancy in association with other outcomes, like birth weight—but little research on autism, specifically,” explained Kristen Lyall, Sc.D., assistant professor in Drexel University’s A.J. Drexel Autism Institute. “To examine the role of environmental exposures in risk of autism, it is important that samples are collected during time frames with evidence for susceptibility for autism—termed ‘critical windows’ in neurodevelopment. Fetal development is one of those critical windows.”

1,144 children, born in southern California between 2000 and 2003, took part in this research. The data was collected from mothers who had enrolled in California’s Expanded Alphafetoprotein Prenatal Screening Program. This program’s aim is to discover the birth defects during pregnancy. There were 3 groups of children: 545 who were diagnosed with ASD, 181 with intellectual disabilities but no autism diagnosis, and 418 with a diagnosis of neither.

To determine the level of exposure, blood tests were taken from the mothers in their second trimester. The blood tests were used to discover the presence of 2 different classes of organochlorine chemicals: polychlorinated biphenyls (PCBs, which were used as lubricants, coolants, and insulators in consumer and electrical products) and organochlorine pesticides (OCPs, which include chemicals like DDT). According to this, Dr. Lyall summarized, “Exposure to PCBs and OCPs is ubiquitous. Work from the National Health and Nutrition Examination Survey, which includes pregnant women, shows that people in the U.S. generally still have measurable levels of these chemicals in their bodies.”

The news is disturbing but Dr. Lyall added that, “adverse effects are related to levels of exposure, not just presence or absence of detectable levels. In our southern California study population, we found evidence for modestly increased risk for individuals in the highest 25th percentile of exposure to some of these chemicals.”

The researchers detected two compounds —PCB138/158 and PCB153—which can increase the risk of autism. Children with the highest in utero levels of these two forms of PCBs were between 79% and 82% more likely to have an autism diagnosis than those found to be exposed to the lowest levels. “The results suggest that prenatal exposure to these chemicals above a certain level may influence neurodevelopment in adverse ways,” Dr. Lyall concluded.

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