The Toxins That Threaten Our Brains, by James Hamblin


Leading scientists recently identified a dozen chemicals as being responsible for widespread behavioral and cognitive problems. But the scope of the chemical dangers in our environment is likely even greater. Why children and the poor are most susceptible to neurotoxic exposure that may be costing the U.S. billions of dollars and immeasurable peace of mind.

Forty-one million IQ points. That’s what Dr. David Bellinger determined Americans have collectively forfeited as a result of exposure to lead, mercury, and organophosphate pesticides. In a 2012 paper published by the National Institutes of Health, Bellinger, a professor of neurology at Harvard Medical School, compared intelligence quotients among children whose mothers had been exposed to these neurotoxins while pregnant to those who had not. Bellinger calculates a total loss of 16.9 million IQ points due to exposure to organophosphates, the most common pesticides used in agriculture.

Last month, more research brought concerns about chemical exposure and brain health to a heightened pitch. Philippe Grandjean, Bellinger’s Harvard colleague, and Philip Landrigan, dean for global health at Mount Sinai School of Medicine in Manhattan, announced to some controversy in the pages of a prestigious medical journal that a “silent pandemic” of toxins has been damaging the brains of unborn children. The experts named 12 chemicals—substances found in both the environment and everyday items like furniture and clothing—that they believed to be causing not just lower IQs but ADHD and autism spectrum disorder. Pesticides were among the toxins they identified.

“So you recommend that pregnant women eat organic produce?” I asked Grandjean, a Danish-born researcher who travels around the world studying delayed effects of chemical exposure on children.

“That’s what I advise people who ask me, yes. It’s the best way of preventing exposure to pesticides.” Grandjean estimates that there are about 45 organophosphate pesticides on the market, and “most have the potential to damage a developing nervous system.”

Landrigan had issued that same warning, unprompted, when I spoke to him the week before. “I advise pregnant women to try to eat organic because it reduces their exposure by 80 or 90 percent,” he told me. “These are the chemicals I really worry about in terms of American kids, the organophosphate pesticides like chlorpyrifos.”

For decades, chlorpyrifos, marketed by Dow Chemical beginning in 1965, was the most widely used insect killer in American homes. Then, in 1995, Dow was fined $732,000 by the EPA for concealing more than 200 reports of poisoning related to chlorpyrifos. It paid the fine and, in 2000, withdrew chlorpyrifos from household products. Today, chlorpyrifos is classified as “very highly toxic” to birds and freshwater fish, and “moderately toxic” to mammals, but it is still used widely in agriculture on food and non-food crops, in greenhouses and plant nurseries, on wood products and golf courses.

Landrigan has the credentials of some superhero vigilante Doctor America: a Harvard-educated pediatrician, a decorated retired captain of the U.S. Naval Reserve, and a leading physician-advocate for children’s health as it relates to the environment. After September 11, he made news when he testified before Congress in disagreement with the EPA’s assessment that asbestos particles stirred into clouds of debris were too small to pose any real threat. Landrigan cited research from mining townships (including Asbestos, Quebec) and argued that even the smallest airborne asbestos fibers could penetrate deeply into a child’s lungs.

Chlorpyrifos is just one of 12 toxic chemicals Landrigan and Grandjean say are having grim effects on fetal brain development. Their new study is similar to a review the two researchers published in 2006, in the same journal, identifying six developmental neurotoxins. Only now they describe twice the danger: The number of chemicals that they deemed to be developmental neurotoxins had doubled over the past seven years. Six had become 12. Their sense of urgency now approached panic. “Our very great concern,” Grandjean and Landrigan wrote, “is that children worldwide are being exposed to unrecognized toxic chemicals that are silently eroding intelligence, disrupting behaviors, truncating future achievements and damaging societies.”


The chemicals they called out as developmental neurotoxins in 2006 were methylmercury, polychlorinated biphenyls, ethanol, lead, arsenic, and toluene. The additional chemicals they’ve since found to be toxins to the developing brains of fetuses—and I hope you’ll trust me that these all are indeed words—are manganese, fluoride, chlorpyrifos, tetrachloroethylene, polybrominated diphenyl ethers, and dichlorodiphenyltrichloroethane.

Grandjean and Landrigan note in their research that rates of diagnosis of autism spectrum disorder and ADHD are increasing, and that neurobehavioral development disorders currently affect 10 to 15 percent of births. They add that “subclinical decrements in brain function”—problems with thinking that aren’t quite a diagnosis in themselves—“are even more common than these neurobehavioral development disorders.”

In perhaps their most salient paragraph, the researchers say that genetic factors account for no more than 30 to 40 percent of all cases of brain development disorders:

Thus, non-genetic, environmental exposures are involved in causation, in some cases probably by interacting with genetically inherited predispositions. Strong evidence exists that industrial chemicals widely disseminated in the environment are important contributors to what we have called the global, silent pandemic of neurodevelopmental toxicity.

Silent pandemic. When public health experts use that phrase—a relative and subjective one, to be deployed with discretion—they mean for it to echo.

When their paper went to press in the journal The Lancet Neurology, the media responded with understandable alarm:

“A ‘Silent Pandemic’ of Toxic Chemicals Is Damaging Our Children’s Brains, Experts Claim” – Minneapolis Post, 2/17/14

“Researchers Warn of Chemical Impacts on Children,” –USA Today, 2/14/14

“Study Finds Toxic Chemicals Linked to Autism, ADHD” – Sydney Morning Herald, 2/16/14

When I first saw these headlines, I was skeptical. It wasn’t news that many of the chemicals on this list (arsenic, DDT, lead) are toxic. With each of these substances, the question is just how much exposure does it take to cause real damage. For instance, organophosphates aren’t something that anyone would categorically consider safe, in that they are poison. They kill insects by the same mechanism that sarin gas kills people, causing nerves to fire uncontrollably. But like asbestos, they are still legally used in U.S. commerce, with the idea that small amounts of exposure are safe. The adage “the dose makes the poison” may be the most basic premise of toxicology. And hadn’t we already taken care of lead? Didn’t we already know that alcohol is bad for fetuses? Wasn’t fluoride good for teeth?

I found that the real issue was not this particular group of 12 chemicals. Most of them are already being heavily restricted. This dozen is meant to illuminate something bigger: a broken system that allows industrial chemicals to be used without any significant testing for safety. The greater concern lies in what we’re exposed to and don’t yet know to be toxic. Federal health officials, prominent academics, and even many leaders in the chemical industry agree that the U.S. chemical safety testing system is in dire need of modernization. Yet parties on various sides cannot agree on the specifics of how to change the system, and two bills to modernize testing requirements are languishing in Congress. Landrigan and Grandjean’s real message is big, and it involves billion-dollar corporations and Capitol Hill, but it begins and ends with the human brain in its earliest, most vulnerable stages.

How Toxins Destroy Brains

About a quarter of your body’s metabolism goes toward operating and maintaining your brain. In order to process even basic information, billions of chemical signals are constantly being carried between neurons. The undertaking is so onerous that even though your brain is not moving (like, say, the powerful muscles in your legs), it uses around 10 times more calories per pound than the rest of you.

Most of that industrious brain and its 86 billion neurons were created in a matter of months. During the first few weeks of gestation, when your mother knew you only as morning sickness and you were a layer of cells huddled in one corner of her uterus, those cells lined up, formed a groove, and then closed to form a tube. One end of that tube eventually became your tiny spinal cord. The rest expanded to form the beginnings of your brain.

For a brain to develop properly, neurons must move to precise places in a precise sequence. They do so under the direction of hormones and chemical neurotransmitters like acetylcholine. The process is an intricate, fast-paced dance on a very tiny scale. Each nerve cell is about one hundredth of a millimeter wide, so it has to travel its own width 25,000 times just to move an inch—which some neurons in the cortex must. At any point, that cell can be knocked off course. Some of the neurotoxins Grandjean and Landrigan discuss have the potential to disrupt this journey, in a slight or serious fashion.

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