A century of hair samples reveals how environmental guidelines helped slash People’ lead publicity by as much as 100 occasions.
Earlier than the Environmental Safety Company was created in 1970, lead air pollution was deeply embedded in on a regular basis American life. Communities have been uncovered by means of industrial exercise, lead-based paint, getting old water pipes, and most closely by means of car exhaust. Lead is a powerful neurotoxin that builds up within the physique over time and has been linked to developmental issues in kids. As environmental rules took impact, lead ranges within the atmosphere dropped sharply, adopted by a steep decline in human publicity.
The proof of that change continues to be seen at present.
It’s recorded in human hair.
Hair Samples Reveal a Century of Lead Publicity
College of Utah researchers analyzed hair samples and located dramatic reductions in lead ranges stretching again to 1916. These samples present a long-term organic file of environmental publicity.
“We have been in a position to present by means of our hair samples what the lead concentrations are earlier than and after the institution of rules by the EPA,” stated demographer Ken Smith, a distinguished professor emeritus of household and client research. “We’ve got hair samples spanning about 100 years. And again when the rules have been absent, the lead ranges have been about 100 occasions increased than they’re after the rules.”
A Helpful Steel With Critical Well being Prices
The outcomes, revealed at present (February 2) in PNAS, spotlight how environmental guidelines have performed a serious function in defending public well being. The examine additionally notes that some lead rules are actually being weakened by the Trump administration as a part of a broader effort to roll again environmental protections.
“We must always not overlook the teachings of historical past. And the lesson is these rules have been crucial,” stated co-author Thure Cerling, a distinguished professor of each geology and biology. “Generally they appear onerous and imply that trade can’t do precisely what they’d love to do after they wish to do it or as shortly as they wish to do it. However it’s had actually, actually constructive results.”
Lead is the heaviest of the heavy metals and, like mercury and arsenic, it accumulates in dwelling tissue and will be poisonous even at low doses. Regardless of these risks, lead was extensively used due to its sensible advantages. It was molded into water pipes, blended into paint to enhance sturdiness and shade, and added to gasoline to stop engine knocking.
By the Seventies, the well being dangers have been plain, prompting the EPA to start eradicating lead from paint, plumbing, gasoline, and different client merchandise.
Household Historical past Helps Scientists Monitor Air pollution
To find out whether or not these coverage adjustments really decreased human publicity, Smith teamed up with geologist Diego Fernandez and Cerling. Fernandez and Cerling had beforehand developed strategies to reconstruct the place animals lived and what they ate by inspecting the chemical make-up of hair and tooth.
This work expanded on an earlier examine supported by the college’s Heart on Getting older 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 decline in human lead (Pb) exposure since establishment of the US Environmental Protection Agency” 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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