Brains terrify me.

There’s a reason I prefer to research microbes. They’ve got a single cell (usually). They’re massively important to sustaining life on the planet, but they’re pretty simple to understand as organisms.

Trying to figure out a brain, on the other hand, seems to me like asking for trouble.

The human brain is made up of 86 billion neurons, plus billions of attendant cells. It uses 20 percent of our energy. It controls our physical movements, stores our memories, and processes our thoughts.

I held a human brain once — lifted it out of a skull in a human dissection. Cradling it carefully in both hands, I marveled that this three-pound organ once held the essence of the deceased person before me. It was a profound moment in my scientific education.

But if the significance of the adult human brain is awe-inspiring, the balletic dance of the developing brain is miraculous. It’s precisely choreographed by millennia of evolutionary optimization and directed by a series of developmental signals that somehow transform a ball of cells into a thinking, functioning human brain.

Brain development is a process we still know little about. Yet its complexity and delicacy suggest that it may be susceptible to a variety of derailments. So we instruct women who may become pregnant to chow down on folic acid supplements and warn expecting mothers to eschew alcohol. New parents are asked to stimulate their child’s neurological development with conversation, reading, and educational toys.

It’s safe to say that baby brains are important to us.

So why, then, do we let tens of thousands of chemicals go untested into the environment, when we know that at least some of them pose serious neurological threats?

That’s the question that at least some pediatricians are asking in the face of mounting evidence of the harmful side effects of some of these chemicals.

More than two years ago, Dr. David Bellinger of Harvard Medical School calculated that environmental toxins caused a loss of 40 million IQ points in a population of just 25.5 million American children. Since each IQ point is worth more than $17,000 in lifetime earnings, that figure equates to a total economic loss of almost $700 billion.

And Bellinger’s work analyzed the neurological damage produced by only three (methylmercury, lead, and organophosphate pesticides) of potentially thousands of toxic compounds.

Wait. Doesn’t everyone know about lead poisoning? And surely people keep children away from pesticides, right?

The answer to the first question is yes, mostly, but only after decades of accumulating evidence finally convinced the Centers for Disease Control to lower the advisable limit of lead concentration in children’s blood.

As far as organophosphate pesticides go, many of them are fat-soluble. This means that once they enter the human body, they tend to stay there, accumulating over time. And one of their favorite places to reside is in human breast tissue, from where they ultimately make their way into fat- and protein-rich mother’s milk, fed to suckling infants at some of their most vulnerable stages of brain development.

Should mothers stop breast-feeding?

Absolutely not, say healthcare providers. The benefits — to nutrition, to the immune system and beyond — vastly outweigh the costs. Yet it’s nonetheless disturbing to think that such an intimate and pure act is now irrefutably marked by the chemical signature of modern times.

Breast milk contains traces of hundreds of different chemicals that permeate our everyday life. If we are lucky, most will prove harmless. But an unlucky few, like lead, will eventually prove to be carcinogens or neurotoxins, and we will wish, as with lead, that we’d caught on earlier.

The way America’s chemical regulations are designed, it’s unlikely we’ll ever get ahead of the game. Though the Toxic Substances Control Act of 1976 requires that the Environmental Protection Agency review all chemicals imported to or manufactured in the United States, only five of the 80,000 compounds regulated under the Act have been banned. And 60,000 compounds were grandfathered in under the act, never to be reviewed at all.

Attempts to reform the act languish on Congressional backburners. The latest attempt is a year old, languishing in its efforts to reconcile industry lobbying with the public good.

But ultimately, the problem with regulation in hindsight is that the burden of proof falls on regulators after the chemicals have been introduced to our environment, where they may remain in our very bodies for decades. As long as we embrace the promise of modern chemistry — and, indeed, it has provided many miracles — we will continue to subject ourselves to its darker shadow, often long after the chemical brain drain has begun.

 

Holly welcomes reader feedback at hollyvm “at” stanford.edu.