The evidence for that change can still be found today.

It is embedded in human hair.

Hair Samples Trace Lead Exposure Back to 1916

Scientists at the University of Utah analyzed hair samples and discovered steep declines in lead levels going back more than a century. Their results show a clear downward trend beginning after environmental regulations were introduced.

“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 Metal That Was Useful and Dangerous

The study, published in PNAS, highlights how environmental protections have shaped public health outcomes. It also points out that some lead regulations are now being weakened by the Trump administration as part of a broader effort to loosen environmental safeguards.

“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 is harmful even at low concentrations. Despite these risks, it was widely used for decades because of its practical advantages. Lead was commonly used in pipes and added to paint to improve durability, speed drying, and create brighter colors. It was also blended into gasoline to improve engine performance by preventing pistons from “knocking.”

By the 1970s, the health dangers were well established, prompting the EPA to begin removing lead from paint, plumbing materials, gasoline, and other consumer products.

How Family Keepsakes Became Scientific Evidence

To find out whether these policy changes truly reduced lead exposure in people, Smith worked with geologist Diego Fernandez and Cerling. Fernandez and Cerling had developed methods to determine where animals lived and what they ate by analyzing the chemistry of hair and teeth.

The lead study grew out of earlier research funded by the university’s Center on Aging and the National Institutes of Health. That earlier work involved Utah residents who agreed to provide blood samples along with detailed family health information.

For the new research, participants were asked to submit hair samples from adulthood and from earlier in life. Some went a step further, locating hair preserved in family scrapbooks that dated back as much as a century. Altogether, the team collected hair from 48 individuals, creating a valuable record of lead exposure along Utah’s Wasatch Front, an area that once faced heavy 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 while the studies were underway.

Much of this region supported a major smelting industry throughout the 20th century, particularly in Midvale and Murray. Most of Utah’s smelters closed by the 1970s, around the same time the EPA began enforcing stricter limits on lead use.

Why Hair Preserves Lead So Well

The researchers analyzed the samples using mass spectrometry equipment 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.”

While blood tests offer a more precise snapshot of exposure at a specific moment, hair is far easier to collect and preserve. More importantly, it provides insight into past exposure for people who are now older 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.”

Leaded Gasoline Left a Clear Chemical Record

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

Before 1970, gasoline typically contained about 2 grams of lead per gallon. Although that amount may seem small, the scale of fuel consumption made it significant. With billions of gallons burned each year, this resulted in nearly 2 pounds of lead entering 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 fell sharply. Concentrations dropped from as high as 100 parts per million (ppm) to about 10 ppm by 1990. By 2024, average levels had fallen to less than 1 ppm.

The study, titled “Lead in archived hair documents decline in human lead (Pb) exposure since establishment of the US Environmental Protection Agency,” was published in PNAS, or Proceedings of the National Academy of Sciences. Support came from the Huntsman Cancer Foundation and the National Cancer Institute through a grant to the Utah Population Database and the University of Utah.