A century-long analysis of human hair shows Americans’ lead exposure fell by up to 100 times after federal environmental regulations took effect, offering biological proof of the public health impact of pollution controls.
Before the Environmental Protection Agency was created in 1970, lead pollution was woven into daily life across the United States. The toxic metal came from factory emissions, lead-based paint, aging water pipes, and, most significantly, vehicle exhaust.
Lead is a potent neurotoxin that accumulates in the body and has been linked to developmental problems in children and long-term health damage in adults. As federal rules restricted its use, environmental lead levels dropped, followed by a sharp decline in human exposure.
Researchers say that transformation is preserved in an unexpected place: human hair.
Hair Samples Track Pollution Across Generations
Scientists at the University of Utah analyzed hair samples dating back to 1916 and found dramatic reductions in lead levels over time. The samples provide one of the longest biological records of environmental exposure yet assembled.
“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 Ken Smith, a demographer and distinguished professor emeritus of family and consumer studies. “Back when the regulations were absent, the Americans’ lead exposure levels were about 100 times higher than they are after the regulations.”
The findings were published Monday in the Proceedings of the National Academy of Sciences. The study comes as some lead-related rules face renewed scrutiny and weakening as part of broader efforts to roll back environmental protections.
“We should not forget the lessons of history,” said co-author Thure Cerling, a distinguished professor of geology and biology. “Those regulations have been very important. They have had really, really positive effects.”
Family Histories Create A Rare Record
To measure how policy changes affected people, Smith worked with geologist Diego Fernandez and Cerling, who previously developed techniques to trace environmental exposure by studying the chemical makeup of hair and teeth.
The research was built on an earlier project supported by the National Institutes of Health that collected blood samples and family health records from Utah residents. For the new study, participants submitted current hair samples and older ones saved from earlier in life.
Some families contributed hair preserved in scrapbooks from parents, grandparents, and earlier generations. In total, the team analyzed samples from 48 individuals, creating a rare snapshot of Americans’ lead exposure
along Utah’s Wasatch Front.
“The Utah part of this is so interesting because of the way people keep track of their family history,” Smith said. “I don’t know that you could do this in New York or Florida.”
The region once supported a large smelting industry, particularly in Midvale and Murray. Most of those facilities closed by the 1970s, around the same time federal rules sharply limited lead use.
Leaded Gas Decline Written In Hair
Using mass spectrometry, researchers found that hair preserves lead on its surface over long periods. While blood samples show short-term exposure, hair offers a window into past environmental conditions.
“The surface of the hair is special,” Fernandez said. Americans’ lead exposure is not lost over time. That makes it easier to reconstruct past exposure.”
The hair decline closely mirrors the phaseout of leaded gasoline after the EPA was established under President Richard Nixon. Before 1970, gasoline typically contained about two grams of lead per gallon.
With billions of gallons burned each year, that amounts to nearly two pounds of lead released into the environment per person annually. The metal entered the air from tailpipes, settled locally, and was inhaled or absorbed.
By 1990, lead concentrations in hair had fallen to about 10 parts per million, down from highs near 100. By 2024, average levels dropped below one part per million, even as gasoline use continued to rise.
“It’s written right into the hair,” Cerling said. “It shows how much cleaner the environment became once lead was taken out.”
