Worldwide, neurodevelopmental disabilities such as autism, attention-deficit hyperactivity disorder (ADHD), dyslexia, and other cognitive impairments affect millions of children. Some of these disorders are steadily increasing. For example, the rates of autism and ADHD are soaring. According to an international team of researchers, the number of industrial chemicals known to be related to autism has more than doubled over the past seven years. The findings were published in the March edition of the journal Lancet Neurology.
The researchers have been studying industrial chemicals that injure the developing brain for almost a decade. In 2006, they conducted a literature review and identified five industrial chemicals as developmental neurotoxicants: lead, methylmercury, polychlorinated biphenyls, arsenic, and toluene. They note that, since 2006, studies have identified six additional toxins that cause neurodevelopmental disabilities: manganese, fluoride, chlorpyrifos, dichlorodiphenyltrichloroethane (DDT), tetrachloroethylene, and the polybrominated diphenyl ethers.
Chemicals such as manganese and fluoride, which are commonly present in drinking water, are rarely found in high enough concentrations in the US to pose a health threat; however, other chemicals on the list are much often present in the environment in harmful levels. For example, chlorpyrifos is an organic pesticide; 10 years ago it was banned for household use; however, it is still extensively used in agriculture and can be found in many fruits and vegetables. Tetrachloroethylene, which has been linked to damaging neurological function and increased risk of psychiatric disorders, is a common solvent used in dry cleaning. Another chemical on the list, polybrominated diphenyl ethers, is a flame retardant that is frequently present in couches. The pesticide DDT is now banned in the US due to human health risks, it is still present in imported fruits and vegetables, as well as in soil and water throughout the nation.
The aforementioned chemicals are far more harmful to the brains of developing fetuses, infants, and young children. During the first several weeks of pregnancy, the embryo forms the cells that eventually go on to become the brain and spinal cord. Those cells divide, multiply and migrate, forming many millions of connections with surrounding cells; thus, they form the pathways that form the body’s central nervous system. If a chemical finds its way into the developing brain, it either destroys brain cells or disrupts cell division or cell migration; thus, those connections are lost and brain formation is incomplete. As a result, the affected child has a lower IQ and reduced attention span.
The researchers note that the increase in disorders such as autism and ADHD correlates well with the increased production and release into environment of synthetic chemicals over last 40 to 50 years. The study presents direct evidence that the industrial chemicals previously listed have been linked to neurologic problems in children.”
At present, the US has no system that can screen the potential health effects of industrial chemicals before they enter the marketplace. The investigators note that, to reduce the levels of dangerous problems in the environment, this problem must be addressed. Therefore, they propose a global prevention strategy. Untested chemicals should not be presumed to be safe to brain development; furthermore, chemicals presently in use and all new chemicals should be tested for developmental neurotoxicity. They recommend the urgent formation of a new international clearinghouse to coordinate these efforts and to develop preventive measures.
The researchers are affiliated with the Department of Environmental Medicine, University of Southern Denmark (Odense, Denmark), the Department of Environmental Health, Harvard School of Public Health (Boston, MA),and Icahn School of Medicine at Mount Sinai (New York, NY).