Researchers investigated historic and current lead exposure by studying an unexpected part of the body: hair.
In a study published yesterday in the journal PNAS, researchers analyzed hair clippings from people in Utah (referred to as Utahns, if you can believe it) dating back to 1916. Lead levels before the creation of the United States’ Environmental Protection Agency (EPA) were significantly higher than afterward, according to their results, highlighting the importance of environmental regulations within the context of public health.
“We were able to show through our hair samples what the lead concentrations are before and after the establishment of regulations by the EPA,” Ken Smith, a demographer at the University of Utah and a co-author of the study, said in a university statement. “We have hair samples spanning about 100 years. And back when the regulations were absent, the lead levels were about 100 times higher than they are after the regulations.”
Hair lead
Lead is toxic to humans and unsafe in any amount of exposure. It deposits in living tissues and is associated with developmental issues. After its establishment in 1970, the EPA started transitioning away from the use of lead in things such as pipes, paint, and gasoline, and I don’t think it’s a coincidence that environmental lead levels decreased dramatically.
In the recent study, Smith and his colleagues received hair samples from 48 Utahns, including some particularly old ones retrieved from scrapbooks. These samples provide significant insight into lead levels on the state’s Wasatch Front, a densely populated area with a history of heavy industrial lead emissions. The 20th century saw a vigorous smelting industry in the region, though by the 1970s, a majority of the state’s smelters closed.
The researchers studied the hair with mass spectrometry, an approach researchers employ to pinpoint chemical compounds. While blood would give better insight into lead exposure, hair is simpler to deal with and sheds light on an individual’s exposures in the distant past.
“The surface of the hair is special. We can tell that some elements get concentrated and accumulated on the surface. Lead is one of those. That makes it easier because lead is not lost over time,” said Diego Fernandez, a co-author of the study and researcher at the University of Utah’s 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 on the surface mostly, but it could also be coming from the blood if that hair was synthesized when there was high lead in the blood.”
“It doesn’t really record that internal blood concentration that your brain is seeing, but it tells you about that overall environmental exposure,” explained Thure Cerling, a biology and geology professor at the university and also a co-author of the study. “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.”
Coincidence? I think not
The hair revealed a steep decrease in its lead concentration following the 1970s, despite the fact that people in the United States used more gasoline. A peak of 100 parts per million (ppm) fell to 10 ppm in 1990. Over 30 decades later, the level was below 1 ppm. The team’s results align with the decreases of lead in gasoline in the wake of the EPA.
“We should not forget the lessons of history. And the lesson is those regulations have been very important,” Cerling pointed out. “Sometimes they seem onerous and mean that industry can’t do exactly what they’d like to do when they want to do it or as quickly as they want to do it. But it’s had really, really positive effects.”
The study comes within the context of a significant drop in the EPA’s budget. This year, the agency’s budget is 54% lower than 2025.
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