[extract]

The study is small and limited to the greater Salt Lake City region of Utah. But it shows how physical mementos such as locks of hair stashed in scrapbooks for decades can reveal how our environment has changed over time.

Researchers gathered 47 hair samples dated from 1916 to 2024 and called in Diego Fernandez, a geochemist at the University of Utah, to analyze the lead content in the hair. The analysis didn’t distinguish between lead in the sheathlike cuticle that surrounds a hair and that found in the hair itself. The former would have been picked up from contaminated air, and the latter would have stemmed from the consumption of contaminated food or water.

The trend over time is stunning. Peak lead rates occurred in samples from the 1960s, when lead was enriched by some 120 times compared with 2020–2024 samples. But since the 1960s, lead exposure rates steadily plummeted.

The decline occurred alongside the formation of the Environmental Protection Agency in 1970 and the passage of landmark legislation, including the Clean Air Act and the Clean Water Act, in the same decade, although the researchers also note that the greater Salt Lake City region had been home to two smelting facilities that closed during that period.

Still, the decline is stunning. “I think it’s kind of a showstopper for showing the power of environmental protections,” Smith says.