The rampancy of developmental disorders such as attention deficit hyperactivity disorder (ADHD), autism and dyslexia has grown in recent years and researchers believe the changing environment has something to do with this.
In 2006, researchers had identified five industrial chemicals that may be contributing to children's cognitive deficits and attention problems. These chemicals include lead, methylmercury, polychlorinated biphenyls, arsenic and toluene.
In a new study published in The Lancet Neurology February 15, the same researchers has identified six more of what they have described as "global, silent pandemic of neurodevelopmental toxicity"-chemicals that are associated with developmental disorder in children. The newly identified neurotoxins include manganese, fluoride, chlorpyrifos, dichlorodiphenyltrichloroethane, tetrachloroethylene and polybrominated diphenyl ethers.
The chemicals manganese and fluoride, which are found in drinking water, can hamper normal brain development. An analysis of 27 studies of children who were exposed to fluoride in drinking water at high concentrations, for instance, has shown that fluoride may contribute to a seven-point drop, on average, in a child's IQ. Manganese, on the other hand, may contribute to lower math scores.
"The greatest concern is the large numbers of children who are affected by toxic damage to brain development in the absence of a formal diagnosis. They suffer reduced attention span, delayed development, and poor school performance. Industrial chemicals are now emerging as likely causes," said study author Philippe Grandjean, adjunct professor of environmental health at the Harvard School of Public Health in Boston.
The researchers also said that the effects are not just limited to loss of IQ points.
"Beyond IQ, we're talking about behavior problems -- shortening of attention span, increased risk of ADHD," said study co-author Philip Landrigan from Mount Sinai School of Medicine in New York. "We're talking about emotion problems, less impulse control, (being) more likely to make bad decisions, get into trouble, be dyslexic and drop out of school. ... These are problems that are established early, but travel through childhood, adolescence, even into adult life."
Despite the growing number of industrial chemicals associated with developmental problems, the authors said that more neurotoxins may not have been identified yet. "We postulate that even more neurotoxicants remain undiscovered. To control the pandemic of developmental neurotoxicity, we propose a global prevention strategy," they wrote.
Nonetheless, the researchers have suggested ways to mitigate the effects of harmful chemicals on children's growing brains. "The problem is international in scope, and the solution must therefore also be international," said Grandjean. "We have the methods in place to test industrial chemicals for harmful effects on children's brain development-now is the time to make that testing mandatory," they said.
