Exposure to heavy metals and other toxic chemicals, particularly flame retardants and pesticides, have collectively contributed to more than 1 million cases of intellectual disability in the US over the last two decades, new research finds.
Adverse outcomes from childhood exposure to lead and mercury have declined in recent years across the US in large part due to stricter regulations. However, exposure to harmful chemicals polybrominated diphenyl ethers (PBDEs) and Organophosphate pesticides (OPs) have overtaken heavy metals in recent years due to a lag in regulatory oversight.
PBDEs are used in a variety of products to decrease their flammability, like building materials, furnishings, textiles, among other things. The Environmental Protection Agency (EPA) notes the neurobehavioral effects of the chemicals on humans and other animals, as well as birds, fish, and invertebrates. They are not chemically bound to the products they are administered, which makes them more likely to leach out. OPs are a highly toxic insecticide that, up until the 21st century, were among the most widely used available. Both chemicals interfere with the thyroid and exposure at a young age has been linked to learning disabilities, autism, and other behavioral issues.
Researchers at the NYU Grossman School of Medicine studied the long-term neurological and economic impacts of exposure by analyzing PBDE, organophosphate, lead, and methylmercury levels found in blood samples from women of childbearing age and 5-year-old children. The data was obtained from the National Health and Nutrition Examination Survey conducted by the Centers for Disease Control and Prevention between 2001 and 2016. The team then reviewed previous studies to determine the economic burden of intellectual disability in the US.
Overall, IQ loss from exposure to toxic chemicals declined from 27 million IQ points in 2001 to 9 million IQ points in 2015. While this is a positive shift, the authors note that other PBDEs and OPs exposure has increased from 67 percent to 81 percent during the same study period. PBDE exposure was the greatest contributor to intellectual disability burden, resulting in a total of 162 million IQ points, followed by lead, OPs, and methylmercury, conclude the authors in the journal Molecular and Cellular Endocrinology.
"Our findings suggest that our efforts to reduce exposure to heavy metals are paying off, but that toxic exposures, in general, continue to represent a formidable risk to Americans' physical, mental, and economic health," said lead study investigator Abigail Gaylord, MPH, a doctoral candidate in the Department of Population Health at NYU Langone, in a statement. "Unfortunately, the minimal policies in place to eliminate pesticides and flame retardants are clearly not enough."
Nearly 2.2 million children across the nation were diagnosed with some form of intellectual disability linked with the substances over the study period in what the researchers say highlights a need for tightened regulations at the governmental levels. Overall, the researchers conclude that childhood exposures cost the US $7.5 trillion in lost economic productivity and other societal costs.
The study authors note that there are other chemicals that are more hazardous to the brain, which means impacts from similar chemicals may be worse than the study captures.