Analysis of Hair Samples Reveals How Lead Exposure Fell Over Time

Scientists from the University of Utah have shown, through the analysis of human hair, how environmental lead exposure has declined dramatically since the early 20th century. The findings, published in PNAS, demonstrate that levels of lead—a neurotoxin associated with developmental harm in children—dropped sharply following the establishment of regulations by the Environmental Protection Agency (EPA) in 1970.

Senior author Ken Smith and his colleagues analyzed hair samples spanning nearly a century, collected from Utah residents and their ancestors. “We were able to show through our hair samples what the lead concentrations are before and after the establishment of regulations by the EPA,” Smith said. “Back when the regulations were absent, the lead levels were about 100 times higher than they are after the regulations.” Before 1970, Americans were exposed to lead through paint, pipes, industrial pollution, and most significantly, car exhaust. 

The team’s work focused on hair because it preserves signs of long-term environmental contact. Using mass spectrometry equipment, co-author Diego Fernandez confirmed that lead tends to accumulate on the hair’s surface, making it ideal for detecting historical exposure. “Because mass spectrometry is very sensitive, we can do it with one hair strand,” Fernandez said. First author Thure Cerling explained that hair reflects general environmental exposure even if it doesn’t precisely record blood levels: “It doesn't really record that internal blood concentration that your brain is seeing, but it tells you about that overall environmental exposure.”

Utah offered a distinctive opportunity for this research thanks to a culture of preserving family records. Many participants provided both contemporary and historical hair samples, some from scrapbooks dating back a hundred years. Altogether, the team examined samples from 48 individuals along the Wasatch Front, once home to active smelting industries in Midvale and Murray.

During most of the 20th century, gasoline contained roughly 2 grams of lead per gallon, translating to about 2 pounds of lead released into the environment per person each year. “It's an enormous amount of lead that's being put into the environment and quite locally,” Cerling said. Following the EPA’s introduction of regulations in the 1970s, lead levels in hair plummeted—from around 100 parts per million before regulation to roughly 10 by 1990, and less than one by 2024.