How Exactly Does Lead Exposure Harm the Brain?

By now, many of the effects of lead exposure are well understood by scientists and nonscientists alike. We know that lead is a neurotoxin that can cause serious damage to the brain and nervous system. We know that lead exposure is especially dangerous to the developing brains of children, including fetuses still in the womb. We know that there’s no such thing as a “safe” level of lead in the human body—even trace amounts of it in children’s bloodstreams can lead to a host of negative outcomes, including delayed growth and cognitive development, learning problems, behavioral problems, lower IQ scores, and hyperactivity.

We also know that the primary way that lead is getting into people’s bodies today is through lead pipes used for drinking water. Once it enters the bloodstream, this toxic metal quickly makes its way to the brain. But what happens once it gets there?

The calcium connection: How lead gets into the brain

Lead enters the body most commonly through ingestion or inhalation. It was banned as a paint additive for residential use in 1978, and, thanks in large part to action taken by NRDC in the early 1970s, lead was completely phased out of gasoline in the mid-1990s. But according to a 2021 NRDC survey of the water industry, lead is still found in anywhere from 9.7 million to 12.8 million service lines, which are the small pipes that connect the water mains running under or along the street to your home and other buildings. These pipes bring drinking water to about 22 million people, and with it, lead that is unwittingly consumed—disproportionately by people of color and people from low-income households.

To understand how lead causes brain damage, you must understand the role in the brain of another well-known element on the periodic table: calcium. Calcium is essential in the building of healthy brains because it helps neurons communicate with other neurons. Brain cells send chemical and electrical signals through the infinitesimally small spaces, called synapses, between them, and playing a key part in this communication is a protein known as the brain-derived neurotrophic factor (BDNF). The brain requires calcium to produce BDNF, which helps stimulate the growth and differentiation of neurons—including those that are key to the development of memory, learning, and other cognitive activities. So when calcium shows up at a synapse, openings aptly named calcium channels “recognize” it and allow it to enter the neuron.

The presence of lead at the synapse, however, disrupts this process. And lead does this in the most insidious of ways: through deception. “Basically, lead ‘looks’ like calcium and can be transported in the brain through the same ways that calcium is,” says Dr. Jennifer Lowry Sample, a specialist in pediatric toxicology who spent more than 20 years caring for lead-exposed children at Children's Mercy Kansas City and the University of Missouri–Kansas City School of Medicine. She says that once lead enters the synapse, “it’s taken up by calcium channels and binds to the receptors that calcium should be binding to.” Or to put it another way, lead sneaks into the brain disguised as calcium, and then closes the door behind itself.

When lead blocks the uptake of calcium in this way, the connections between brain cells that rely on it, and the BDNF it produces, begin to deteriorate. “If the exposure to lead is so overwhelming that calcium cannot be used and cell functions are damaged, the effects in those processes may be irreversible,” Sample says.

Why children are at the greatest risk from lead exposure

Lead is harmful to all humans, and adults are certainly not immune to its toxicity. Lead exposure in adults can result in cardiovascular disease, elevated blood pressure, and problems with kidney and reproductive functions, among other ailments. But those most susceptible to the effects of lead are young children.

Why? The simple answer is that the brains of young people grow at a far faster rate than the brains of adults. A child’s brain, in fact, develops more during the first five years of life than it does during any other period. At birth, a baby’s brain is about a fourth the size of what it will eventually become. The brain typically doubles in size during the child’s first year, and reaches 90 percent of its adult size by the age of five.

Behind all of that incredibly rapid growth is an equally rapid rate of neural connections—a million of them zapping away per second, on average, in a child under three. So even the smallest amount of lead flowing into the brain of an infant or a toddler has much more opportunity to gum up synaptic connectors and weaken neurotransmission. Weaker signals between neurons can stunt brain development, which manifests itself in the symptoms of lead toxicity in children.

“Even at chronic, low levels of exposure, children have had speech delays and learning disabilities, where they have a harder time in school with reading comprehension and math skills,” says Sample, who has witnessed these consequences firsthand. “Some children have behavioral changes due to their inability to focus on tasks in school.”

What we need to do to protect children from lead

The best way to lessen lead’s pernicious effect on brain development is to eliminate all avoidable lead exposures, including replacing the lead in our woefully outdated drinking water infrastructure. President Biden has acknowledged as much, observing in speeches that lead exposure is extremely widespread; indeed, a 2022 study found that more than half of the U.S. population was exposed to high levels of lead in early childhood. His administration has also vowed to replace every single lead service line in the country within 10 years: an ambitious but achievable task with cooperation from state and local governments. And according to a recently published NRDC report, the full removal of lead service lines would save the nation $37 billion in annual health-care costs.

In the meantime, another potent weapon in this battle would be for the U.S. Environmental Protection Agency to strengthen the Lead and Copper Rule through moves such as requiring water utilities to pay for lead pipe removal, improving tap water testing, and lowering the lead level at which utilities must take action, from 15 parts per million (ppb) to 5 ppb.

Lead exposure interferes with the most important period of brain development in a person’s life, potentially robbing them of the future they would otherwise have. We have the ability to get rid of lead pipes by the end of the decade. Under any definition of environmental justice, doing so is a must.

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