A controversial report suggests that hundreds of known neurotoxins may be affecting the brains of children around the world and yet are loosely regulated because too high a standard of proof is required before stricter controls are considered.
Philippe Grandjean of the Harvard School of Public Health and co-author Philip J. Landrigan of the Mount Sinai School of Medicine compiled their list of more than 200 chemicals known to be neurotoxic to adults from government databases. For a handful of these chemicals—lead, methylmercury, polychlorinated biphenyls (PCBs), arsenic and toluene—there is also proof that they can harm fetal or child brain development, which has led to their tighter regulation. For example, as a result of these concerns lead was removed from gasoline and paint.
The authors argue that if a chemical is known to harm the brains of adults, then it has a good chance of harming the brain of a fetus or infant, and it is unwise to allow children to be exposed to these chemicals for years while scientists and lawmakers await final proof. Establishing a causal relation is difficult because each child may be exposed simultaneously to several substances and the effect of each may be small. But Grandjean says that developing brains are much more susceptible to toxicity than adult brains because affected neurons fail to migrate to their destinations. “This may be one reason why some effects appear to be permanent,” he notes.
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Not so, says Jean Harry, who leads the neurotoxicology group at the National Institute for Environmental Health Sciences. “The developing brain, while it's very sensitive, is elastic,” she explains. Furthermore, she points out that the placenta and the blood-brain barrier do provide some protection to the fetal brain. Although she does not dispute the importance of identifying and regulating dangerous chemicals, Harry says the authors do not credit regulatory agencies for their “large effort to address these concerns for susceptible populations.”