Public health experts have identified 11 industrial chemicals as "developmental neurotoxicants" that are likely contributors to the rise of neurological disorders and deficits among young people worldwide, including autism and Attention Deficit and Hyperactivity Disorder (ADHD).
The chemicals are mainly toxic pollutants and byproducts such as arsenic and lead, which are released into the environment by coal plants and many other industrial operations, according to the report published in The Lancet Neurology on Friday.
One compound, fluoride, stood out from the list because it's treated as a desirable health supplement. Fluoride is deliberately added to the drinking water in hundreds of cities in the US and in other countries to help prevent dental decay.
The public health experts added fluoride to their list of 11 neurotoxicants because of studies showing excess consumption depresses IQs in children. This prompted the Fluoride Action Network, the leading American group opposed to fluoridation, to call for a reconsideration of fluoridation.
“In light of the new classification of fluoride as a dangerous neurotoxin, adding more fluoride to American’s already excessive intake no longer has any conceivable justification," said FAN executive director Paul Connett. "We should follow the evidence and try to reduce fluoride intake, not increase it.”
Dozens of American cities, from Oneida, NY, to Davis, CA, have rejected fluoridation in recent years. And many more, including Austin and New York City, have groups actively trying to roll back what they see as the potentially harmful fluoridation of their city water systems. These groups argue that the risk of neurological or other health damage from ingesting fluoride is not worth it, now that fluoride toothpastes and topical treatments can be used to protect teeth.
Fluoridation proponents say the risk is small, and the return, stronger teeth, still justified.
The report's authors, Drs. Phillippe Grandjean, an adjunct professor of Environmental Health at the Harvard School of Public Health and Philip J. Landrigan, Dean for Global Health at the Icahn School of Medicine at Mount Sinai in New York, decided upon their list of 11 neurotoxicants because each has been found to contaminate food, water or soil and to interfere with the vulnerable neurological systems of children. That makes these chemicals likely suspects for triggering the autism, attention-deficit disorder, dyslexia and other "cognitive impairments" that affect millions of children and are increasing in frequency.
In addition, many of these chemicals are known to cross the "blood-brain barrier" affecting the fetuses of expose mothers. Studies indicate that both types of exposure – prenatal and direct — can be harmful even at low levels because the developing human brain is especially sensitive to these chemicals prenatally and in early childhood.
The doctors acknowledge that it will be difficult to pinpoint the exact causes of the "pandemic" of cognitive difficulties besetting children around the world, but argue for the precautionary approach, which would reduce chemicals of concern even in the absence of "absolute proof" that they cause a specific health issue.
While genetics play a role in autism and other cognitive issues, "genetic factors seem to account for no more than perhaps 30-40 percent of all cases of neurodevelopmental disorders," the doctors wrote. "Thus, non-genetic, environmental exposures are involved in causation, in some cases probably by interacting with genetically inherited predispositions."
A CLOSER LOOK AT THE NEUROTOXICANTS
Five of the 11 chemicals cited in the Lancet review – the report is a compendium of the current science — had been identified in an earlier review by the team and published in 2006. Those were lead, methylmercury, polychlorinated biphenyls (PCBs), arsenic and toluene, and Grandjean and Landrigan updated their findings on those.
- Lead is well known for causing cognitive deficits and behavior problems in children who are exposed to high levels, which is why it was removed from gasoline and paint decades ago. However, it continues to enter the environment via industrial pollution. Recent international studies confirm the new thinking that "no safe level of exposure to lead exists," the Lancet article authors wrote.
- Similarly, methylmercury, which accumulates in the food chain as animals and marine live consume lead contaminated food and water, has been well documented to affect fetuses, even at low levels, which is why pregnant women are warned to limit their seafood and fish consumption. Prenatal exposures to methylmercury have been detected in children as old as 14, and have been shown to cause abnormal sensory stimulation responses in a child's brain, the researchers wrote.
- PCBs are found in hydraulic fluids, plasticizers, fire retardants and pesticides and can get into drinking water. The EPA reports that chronic exposure can affect the thymus gland and harm the immune and nervous systems.
- Arsenic gets into drinking water from treated wood, paints, mining and other industrial processes (or breakdowns, such as the recent coal ash containment leaks in to the Dan River in North Carolina). Long-term exposure "may have an increased risk of cancer," according to the EPA and studies show it can impair cognitive function in children.
- Toluene, a solvent found in paints, varnishes, lacquers and glues, has been associated with the development of asthma and acts on the central nervous system. Acute toxic exposure can cause seizures and a loss of balance; chronic exposure can decrease cognitive abilities, damage skin, cause anemia and impair bone formations.
The new report, Neurobehavioural Effects of Developmental Toxicity, added six more chemicals that interfere with brain development: manganese, fluoride, chlorpyrifos, dichlorodipenyltrichloroethane (DDT), tetrachloroethylene and polybrominated diphenyl ethers (PBDEs).
- Manganese is a metal that's a useful dietary ingredient, but only at low doses. While it's a naturally occurring metal, excess amounts get into food and water from the runoff of manganese-containing pesticides, industrial waste and landfill leaching. Studies show that excessive consumption by children correlated with reduced achievement in math and increased hyperactivity. One study found that school-aged children living near manganese mining and processing facilities with airborne manganese concentrations showed diminished intellectual function and impaired motor skills.
- Fluoride, another naturally occurring compound, is consumed in excess when children get it in treated drinking water and also in certain foods and fruit juices, that have recently been found to contain higher levels of fluoride. The US Centers for Disease Control and the American Dental Association endorse adding fluoride to drinking water because it strengthens tooth enamel. But in 2011, the US Health and Human Services lowered its recommended level of fluoride in water after a study found many American children showed mottling on their teeth, indicating they were getting too much fluoride. The Lancet researchers included fluoride because a meta-analysis of 27 studies of children exposed to high levels of fluoride in drinking water, mainly in China, found that it lowered their IQs by an average of seven points. Critics of fluoridation in the US and around the world have been fighting to stop the practice, arguing that modern science shows it does more harm than good and that children's teeth can be adequately protected with topical fluoride applications from toothpaste and at the dentist's office.
- Chlorpyrifos, an organophosphate pesticide, has been shown to lead to a small head circumference in babies born to exposed mothers. This indicates that the chemical affects brain growth, and "neurobehavioural deficits that have persisted to at least 7 years of age," the Grandjean and Landrigan wrote.
- DDT and its related metabolite, DDE, continue to cause problems in the environment. Even though the highly toxic DDT was banned in the US and other developed nations decades ago, it is still used in other parts of the world, such Africa where it is sprayed to fight mosquito-borne malaria. Furthermore, it persists in the environment for decades. One study cited linked DDE to delayed development in toddlers.
- Tetrachloroethylene (TCE) is a solvent, which studies show has been correlated with hyperactivity and aggressive behavior in children born to mothers who were exposed while pregnant and working as operating room nurses or on the factory floor. It's no longer used as an anesthetic, though its use as an industrial degreaser has contributed to groundwater contamination in certain areas. It is present at hundreds of Superfund sites and has been found seeping into buildings from contaminated soil. TCE also is an acknowledged carcinogen.
- Polybrominated diphenyl ethers (PBDEs) have been used as flame retardants in upholstered furniture, TV and computer casings and dozens more products. Epidemiological studies in Europe and the US "have shown neurobehavioral deficits in children with increased prenatal exposures to these compounds." The research is emerging, the scientists wrote, but PBDEs "should be regarded as hazards to human neurobehavioral development, although attribution of relative toxic potentials to individual PBDE cogeners is not yet possible. [i.e., they cannot draw a definite line from one type of PBDE to a specific disorder]" Some types of PBDEs have been phased out, but have been replaced by related chemicals. Environmentalists are highly concerned about these synthetic chemicals because they persist in soils, house dust and landfills.
"To control the pandemic of developmental neurotoxicity, we propose a global prevention strategy," Grandjean and Landrigan wrote. "Untested chemicals should not be presumed to be safe to brain development, and chemicals in existing use and all new chemicals must therefore be tested for developmental neurotoxicity."
They proposed an international clearinghouse could test chemicals, share data, develop protective policies and identify new chemicals that pose a threat to the human brain.
(Top photo: Harvard.edu)