Before the Environmental Protection Agency (EPA) was established in 1970, we lived amid widespread lead contamination. Exposure to this toxic metal came from many sources: industrial emissions, lead-based paint, aging water pipes and, most significantly, automobile exhaust.

Lead is a potent neurotoxin that accumulates in human tissue and has been linked to developmental delays in children, as well as long-term health consequences across the lifespan.

Levels of lead in the environment have dropped dramatically over the past half-century, and new research shows just how profound that change has been.

Before 1970, when gasoline contained roughly two grams of lead per gallon and released enormous amounts into the air, hair samples showed concentrations as high as 100 parts per million (ppm).

The findings come from examining human hair, strand-by-strand. To track human lead exposure over more than a century, scientists at the University of Utah analyzed archived and contemporary hair samples. Their findings reveal a decline in lead levels beginning in the mid-20th century that dropped at a gallop after federal regulations took hold in the 1970s.

“We were able to show through our hair samples what the lead concentrations are before and after the establishment of regulations by the EPA,” researcher Ken Smith, a demographer and distinguished professor emeritus of family and consumer studies at the University of Utah, said in a press release. “And back when the regulations were absent, the lead levels were about 100 times higher than they are after the regulations.”

Lead was widely used for years because it's malleable, durable and chemically useful. This explains why exposure was once so pervasive. For instance, manufacturers added lead to paint to improve coverage and speed drying; they used it in pipes for plumbing; and blended it into gasoline to prevent engine knocking and improve performance.

As one of the weightiest of the heavy metals, lead shares toxic properties with mercury and arsenic, building up in the body even at low levels.

By the 1970s the dangers of lead were undeniable. Scientific evidence tied exposure to neurological damage, especially in children, prompting the EPA to begin phasing lead out of gasoline, paint, pipes and other consumer products. The Utah study set out to document whether those policy decisions translated into real reductions in human exposure.

To do this, Smith partnered with geologist and geophysicist Diego Fernandez and biogeochemist Thure Cerling, both at the University of Utah. The work built on an earlier National Institutes of Health-funded project that had recruited Utah residents willing to provide blood samples and detailed family health histories.

Manufacturers added lead to paint to improve coverage and speed drying; they used it in pipes for plumbing; and blended it into gasoline to prevent engine knocking and improve performance.

For the new study, participants were asked to contribute hair samples — both their own and, in some cases, hair from parents and grandparents preserved in family scrapbooks.

In total, the researchers analyzed hair from 48 individuals, spanning more than 100 years. Many samples came from Utah's Wasatch Front, a region that once supported a thriving smelting industry. These communities experienced heavy industrial lead emissions until most smelters closed in the 1970s, coinciding with federal environmental crackdowns.

The team measured lead concentration in strands of hair using mass spectrometry, a scientific technique that identifies and quantifies the chemical composition of materials. Because lead accumulates on a hair's surface and is not lost over time, hair serves as a useful way of tracing lead exposure. While it does not perfectly reflect internal blood levels, it offers a rare window into historical environmental exposure, especially for individuals who are now elderly or deceased.

The results of the study closely mirror the timeline of leaded gasoline's rise and fall. Before 1970, gasoline contained roughly two grams of lead per gallon, releasing enormous amounts into the air. Hair samples from that era showed concentrations as high as 100 parts per million (ppm). By 1990, levels had dropped to about 10 ppm. In 2024, they measured less than 1 ppm.

Before environmental regulations reshaped daily life, lead was everywhere in America — on the roads, in homes and, as it turns out, embedded in our bodies. But in the end, these humble hair samples tell a powerful story. When science informs policy, the benefits can be measured not just in laws passed, but in lives protected.

The study is published in PNAS.