Neurotoxins and the Developing Brain

We have long known that there is a critical period during a child’s development during which the brain is considerably more malleable than an adult’s brain. In other words, outside influences – both positive and negative – have a much greater impact on neuronal formation and function from gestation to the teenage years. Indeed, “By age two, almost all of the billions of brain cells that you will ever have are in their places.” With this in mind, new research regarding the neurotoxic effects of environmental chemicals in children is especially alarming.

One study, published earlier this year by Drs. Phillipe Grandjean and Philip J. Landrigan, analyze the detrimental impact of eleven common chemicals on the developing brain – something they have deemed a “silent pandemic.” These include, “lead, methylmercury, polychlorinated biphenyls, arsenic,…toluene…, fluoride, chlorpyrifos, dichlorodiphenyltrichloroethane, tetrachloroethylene, and the polybrominated diphenyl ethers.” These are “substances found in both the environment and everyday items like furniture and clothing…that they believe to be causing not just lower IQs but ADHD…, autism spectrum disorder…, [and] problems with thinking that aren’t quite a diagnosis in themselves.” You might be wondering what role genetics play in the development of these cognitive deficits, and it is important to weigh nature versus nurture. However, the study’s authors point out that, “Only about 30-40% of the cases of the disorders can be accounted for by genes alone, so environment must make up the other part.”

Many of the chemicals they listed as neurotoxic to children fall under the category of heavy metals. The mechanism by which heavy metals cause brain damage is multifaceted: they include the “disruption of neural cell migration from one part of the brain to another, as well as the formation of synapses (i.e., connections among cells)… [and interference] with neurotransmitters.”

Evidence also suggests that air pollution can cause detriment to young brains. One study measured the impact of “prenatal…exposure to [polcyclic aromatic hydrocarbons, or PAHs].” These are defined as “a group of over 100 different chemicals that are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances like tobacco or charbroiled meat.” The results found that several years after birth, the children exposed to high levels of PAHs during gestation tended to have a “lower verbal IQ and a lower full-scale IQ,” and were “associated with approximately a 5% lower mental development.”

The evidence shows that small things can make a big difference in two very important ways, the first of which is that the oft-repeated adage “the dose makes the poison” is not necessarily relevant when it comes to children. Dr. David Bellinger explains, “Are the blood lead levels of contemporary humans generally below the threshold of toxicity?… Let us hope so, but the conclusion that they are is based more on faith than on evidence.” Indeed, even relatively small changes in the amounts of chemicals can have an observable effect. For instance, several studies show that “as the level of PBDEs, a type of flame retardant, increases in pregnant women’s blood from 10 to 100 ppb, the IQ scores of their children drop by about 5 points.” Which reveals the second important way in which little things can engender major consequences: “Widespread exposure to a neurotoxin, like lead, that causes a 5-point drop in IQ across a population would result in a 57 per cent increase in the number of U.S. children who are challenged, from 6 million to 9.4 million…When you add the impact of another brain-damaging toxin, like flame retardants, the number of challenged kids would rise to over 11 million.”

Arguably the most effective way to protect developing brains’ from potential damage is to enact more stringent testing and regulation of chemicals. When it comes to our children, it seems wise to shape our actions according to the maxim, “Better safe than sorry.”

By Betty Vine 


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