According to some scholars, toxic exposures contributed to the collapse of the Roman Empire. Roman rulers were poisoned by water cisterns and food containers fashioned from lead. These extreme exposures could have gradually made the Patrician families deranged and infertile – leaving no competent leaders to run the Empire. A similar fate seems to have befallen the Samurai regime in Japan. When bones from a castle burial were analyzed, lead concentrations in the children suggested severe lead poisoning. With damaged mental abilities, the Samurai descendants would likely have been incapable of dealing with political crisis, possibly contributing to the downfall of the Shogunate.

Today, our brains are being put to another extreme test, this time from a combination of toxic chemicals that includes mercury, arsenic, pesticides and persistent industrial compounds. The hidden threat that we now face is what I call chemical brain drain. It is insidious and silent, as it is usually not linked to any medical diagnosis, and it is serious, as the combined deficits are affecting the brains of a whole generation of children, upon whom our future relies.

Only recently has it become clear that the brain is extremely vulnerable, especially during its development in the womb and during infancy. In my early career, I encountered some surprises that medical school had not prepared me for, surprises that were fundamental to our understanding of the frailty of the human brain. According to the medical tradition, the fetus is well-protected inside the pregnant mother’s womb. But contrary to this comforting notion, the placenta allows many toxic chemicals to seep through, and some of these compounds can damage the brain’s sensitive developmental processes. The mother may escape unscathed, but for her child, such damage can be catastrophic.

Our highly sophisticated brains start out as a tiny strip of cells. A couple of weeks after conception, these cells are ready to multiply. At its peak, about 12,000 cells are generated every minute – 200 per second. Most do not remain in the same place, but move to specific locations within the developing brain. Overall, our brains develop by multiplication, migration, maturation and messaging – complex steps, each of which has to happen in a specific fashion, in the correct order and at the right time.

We are beginning to appreciate that this intricate timetable of closely connected and complex processes is very sensitive. If some disruption happens, brain development will be incomplete or abnormal, and there will be little, if any, time and opportunity for repair. Thus, the final product, our mature brain, will not express the full potentials that we inherited from our parents. Chemical damage that occurs early on will likely remain throughout our lifespan.

In the United States, one of every six children has a neurodevelopmental delay or a neurological disease. No one knows how many of those children faced environmental exposures that contributed to their problems. Chemical brain drain appears as a silent pandemic that is almost impossible to quantify. Economists have calculated that the value of lost IQ points in children exposed to chemical brain drainers worldwide are worth hundreds of billions of dollars per year. Having studied brain toxicity for 30 years, I realized that I must speak up. The adverse impacts on developing brains are serious enough to demand a loud response. In my book Only One Chance, I conclude: We get only one chance to generate a nervous system, so developing brains need vigorous protection.

So far, convincing proof of chemical brain drain is available for only a few well-researched chemicals. The best documentation available is for lead pollution, which has ruined the lives of countless children. While we were slowly gathering detailed scientific documentation, a whole generation of Americans, and children around the world, suffered loss of brain function due to the pollution from our careless use of lead in gasoline, paint and myriad consumer products. Only when the scientific evidence became truly overwhelming was a consensus finally reached that the public should be protected against this brain drainer. We are now discovering similar evidence about other chemicals, such as mercury, polychlorinated biphenyls (PCBs), arsenic, some solvents, certain pesticides, and other industrial compounds.

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But brain drain is not just a matter of a few annoying substances. When I scrutinized the scientific and medical literature, I was able to identify more than 200 industrial chemicals that had caused toxicity to the human brain one way or another, although mostly in poisonings of adults. Due to the vulnerability of developing brains, chemicals that are toxic to adult brains are probably even more of a threat to young brains – and at much lower doses. However, to scientifically document this chemical brain drain, evidence must be collated from meticulous studies of exposed children as they grow up.

Unfortunately, our research methods are inefficient tools to obtain the documentation we desire. Proper proof may take decades to gather for each individual chemical, one by one. Thus, useful knowledge has been accumulated only for a small number of the thousands of environmental chemicals, and for the others, we do not know the potential for causing brain drain. Our knee-jerk demand for proof leaves the brainpower of the next generation in harm’s way.

In the 1700s, the Duke of the German state of Württemberg decreed capital punishment for lead poisoning of his citizens. While that is unreasonably harsh, we need similar courage to act against chemical brain drain. A precautionary approach to regulating chemicals would seem appropriate. Still, the precautionary principle has been ridiculed by the American Chemistry Council (ACC) in statements such as: “It’s no secret that [ACC doesn’t] think the precautionary principle is either precautionary or a principle. It’s a blunt instrument being used by a number of organizations to essentially ban chemicals.” While we should not institute indiscriminate bans on chemicals, neither should we expose the next generation to likely brain drainers while we wait for significant damage to be documented.

We must learn from the past. The first confirmation in a rat model that methylmercury was toxic to the developing brain was published back in 1972. Yet children around the world are still exposed in the womb to levels of mercury that studies have shown reduce their mental abilities. We often suffer from “historical amnesia”, our common inability (or unwillingness) to learn from past experience. Now we have the luxury of looking back at the narrow-minded (and wrong) decisions that caused disasters like leaded gasoline, Minamata disease or Morinaga milk poisoning (arsenic). How will people in 20 years, or in 50, think about our lax attitude toward pesticides and other brain drainers and our miserable efforts to protect the brains of the next generation?

We use a specific part of our brains to plan for the future. Because some chemicals affect very specific brain functions, my recurring nightmare is that exposures during brain development are reducing our ability to plan for the future, leaving us unable to prevent even more chemical brain drain. It’s a vicious circle, and hopefully it is just a nightmare. But to quote Jonas Salk, “I have had dreams and I have had nightmares, but I’ve conquered my nightmares because I’ve had dreams.” Protection against chemical brain drainers should no longer be a dream. We need to make it happen.