Half of U.S. adults were exposed to harmful lead levels as kids, study finds

A black-and-white photo of packed parking lots in downtown L.A.
Downtown Los Angeles parking lots fill up on Sept. 13, 1979. More than 170 million people born in the U.S. who were adults in 2015 were exposed to harmful levels of lead as children, a new study estimates.
(Wally Fong / Associated Press)

More than 170 million U.S.-born people who were adults in 2015 were exposed to harmful levels of lead as children, a new study estimates.

Researchers from Florida State University and Duke University used census information and data on levels of lead in the blood and consumption of leaded gasoline to examine the breadth of early-childhood exposure in the U.S. between 1940 and 2015.

In a paper published Monday in the Proceedings of the National Academy of Sciences, the researchers estimated that half the U.S. adult population in 2015 had been exposed to lead levels surpassing five micrograms per deciliter — the Centers for Disease Control and Prevention’s threshold for harmful lead exposure at the time.


The scientists also found that 90% of children born in the U.S. between 1950 and 1981 had blood lead levels higher than the CDC threshold. And the researchers found a significant impact on cognitive development: Exposure to lead in early childhood resulted in an average 2.6-point drop in IQ.

The more stringent standard announced by the Centers for Disease Control and Prevention will more than double the number of kids with worrisome levels of the toxic metal in their blood.

The researchers examined only lead exposure caused by leaded gasoline, the dominant form of exposure from the 1940s to the late 1980s, according to data from the U.S. Geological Survey. Leaded gasoline for on-road vehicles was phased out starting in the 1970s and banned in 1996.

The study’s lead author, Michael McFarland, an associate professor of sociology at Florida State University, said the findings were “infuriating” because it was long known that lead exposure was harmful, based on anecdotal evidence throughout history.

Though the U.S. has in recent decades implemented tougher regulations to protect against lead poisoning, the public health impacts of exposure could last for several decades, experts told the Associated Press.

“Childhood lead exposure is not just here and now. It’s going to impact your lifelong health,” said Abheet Solomon, a senior program manager at the United Nations Children’s Fund.

In addition to its impacts on cognitive development, lead exposure in early childhood increases the risk of developing hypertension and heart disease, experts said.

“I think the connection to IQ is larger than we thought, and it’s startlingly large,” said Ted Schwaba, a researcher at the University of Texas at Austin who studies personality psychology and was not part of the study. Schwaba said the study’s use of an average to represent the cognitive impacts of lead exposure could result in an overestimation of effects in some people and an underestimation in others.

Previous research on the relationship between lead exposure and IQ found a similar impact, though over a shorter study period.

Bruce Lanphear, a health sciences professor at Simon Fraser University in Vancouver, said his 2005 study found that the initial exposure to lead was the most harmful when it comes to loss of cognitive ability as measured by IQ.

“The more tragic part is that we keep making the same ... mistakes again,” Lanphear said. “First it was lead, then it was air pollution. ... Now it’s PFAS chemicals and phthalates [chemicals used to make plastics more durable]. And it keeps going on and on.

“And we can’t stop long enough to ask ourselves, ‘Should we be regulating chemicals differently?’”