Old Hair Reveals How Toxic America Once Was

A century of hair samples shows how environmental rules helped slash Americans’ lead exposure by up to 100 times.

Before the Environmental Protection Agency was created in 1970, lead pollution was deeply embedded in everyday American life. Communities were exposed through industrial activity, lead-based paint, aging water pipes, and most heavily through vehicle exhaust. Lead is a powerful neurotoxin that builds up in the body over time and has been linked to developmental problems in children. As environmental regulations took effect, lead levels in the environment dropped sharply, followed by a steep decline in human exposure.

The evidence of that change is still visible today.

It is recorded in human hair.

Hair Samples Reveal a Century of Lead Exposure

University of Utah researchers analyzed hair samples and found dramatic reductions in lead levels stretching back to 1916. These samples provide a long-term biological record of environmental exposure.

“We were able to show through our hair samples what the lead concentrations are before and after the establishment of regulations by the EPA,” said demographer Ken Smith, a distinguished professor emeritus of family and consumer studies. “We have hair samples spanning about 100 years. And back when the regulations were absent, the lead levels were about 100 times higher than they are after the regulations.”

A Useful Metal With Serious Health Costs

The results, published today (February 2) in PNAS, highlight how environmental rules have played a major role in protecting public health. The study also notes that some lead regulations are now being weakened by the Trump administration as part of a broader effort to roll back environmental protections.

“We should not forget the lessons of history. And the lesson is those regulations have been very important,” said co-author Thure Cerling, a distinguished professor of both geology and biology. “Sometimes they seem onerous and mean that industry can’t do exactly what they’d like to do when they want to do it or as quickly as they want to do it. But it’s had really, really positive effects.”

Lead is the heaviest of the heavy metals and, like mercury and arsenic, it accumulates in living tissue and can be toxic even at low doses. Despite these dangers, lead was widely used because of its practical benefits. It was molded into water pipes, mixed into paint to improve durability and color, and added to gasoline to prevent engine knocking.

By the 1970s, the health risks were undeniable, prompting the EPA to begin removing lead from paint, plumbing, gasoline, and other consumer products.

Family History Helps Scientists Track Pollution

To determine whether these policy changes actually reduced human exposure, Smith teamed up with geologist Diego Fernandez and Cerling. Fernandez and Cerling had previously developed methods to reconstruct where animals lived and what they ate by examining the chemical makeup of hair and teeth.

This work expanded on an earlier study supported by the university’s Center on Aging and the National Institutes of Health. That project recruited Utah residents who agreed to provide blood samples and detailed family health records.

For the new research, participants were asked to submit hair samples from the present day as well as from earlier in their lives. Some contributors went even further, uncovering hair preserved in family scrapbooks from parents, grandparents, and even earlier generations. In total, the team collected samples from 48 individuals, creating a rare historical snapshot of lead exposure along Utah’s Wasatch Front, an area once heavily affected by industrial pollution.

“The Utah part of this is so interesting because of the way people keep track of their family history. I don’t know that you could do this in New York or Florida,” said Smith, who led the U’s Pedigree and Population Program at the Huntsman Cancer Center during the research.

Throughout much of the 20th century, the region supported a large smelting industry, particularly in Midvale and Murray. Most of these facilities closed by the 1970s, around the same period when federal rules sharply restricted the use of lead.

Why Hair Preserves a Chemical Record

The researchers analyzed the hair using mass spectrometry at a facility overseen by Fernandez.

“The surface of the hair is special. We can tell that some elements get concentrated and accumulated in the surface. Lead is one of those. That makes it easier because lead is not lost over time,” said Fernandez, a research professor in the Department of Geology & Geophysics. “Because mass spectrometry is very sensitive, we can do it with one hair strand, though we cannot tell where the lead is in the hair. It’s probably in the surface mostly, but it could be also coming from the blood if that hair was synthesized when there was high lead in the blood.”

Blood samples offer a more precise snapshot of what the body was experiencing at a given moment. Hair, however, is much easier to collect and store, and it provides valuable insight into exposures that occurred decades earlier, even for people who are now elderly or no longer alive.

“It doesn’t really record that internal blood concentration that your brain is seeing, but it tells you about that overall environmental exposure,” Cerling said. “One of the things that we found is that hair records that original value, but then the longer the hair has been exposed to the environment, the higher the lead concentrations are.”

The Fall of Leaded Gas, Written in Hair

The decline in lead found in hair closely matches the reduction of lead in gasoline after the EPA was established under President Richard Nixon.

Before 1970, gasoline typically contained about 2 grams of lead per gallon. While that amount may sound small, the scale of fuel consumption made it enormous. With billions of gallons burned each year, this translated into nearly 2 pounds of lead released into the environment per person annually.

“It’s an enormous amount of lead that’s being put into the environment and quite locally,” Cerling said. “It’s just coming out of the tailpipe, goes up in the air and then it comes down. It’s in the air for a number of days, especially during the inversions that we have and it absorbs into your hair, you breathe it and it goes into your lungs.”

After the 1970s, even as gasoline use continued to rise in the United States, lead levels measured in hair dropped sharply. Concentrations fell from as high as 100 parts per million (ppm) to about 10 ppm by 1990. By 2024, the average level had fallen to less than 1 ppm.

Reference: “Lead in archived hair documents a decline in lead exposure to humans since the establishment of the US Environmental Protection Agency” by Thure E. Cerling, Diego P. Fernandez and Ken R. Smith, 2 February 2026, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2525498123

The study was supported by the Huntsman Cancer Foundation and the National Cancer Institute through a grant to the Utah Population Database and the University of Utah.

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