Leaded Gasoline Dropped The IQ Of 170 Million Americans A 'Startling' Amount: Study

"I think the connection to IQ is larger than we thought, and it’s startlingly large."

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This is a general view of Mound Bayou, Miss. in 1970.
This is a general view of Mound Bayou, Miss. in 1970.
Photo: AP Photo/Jack Thornell (AP)

Leaded gasoline for cars finally disappeared from the Earth for good in 2021, but its affects will be with us for a long time.

A new study looked at the impact of exposure to leaded gasoline in the early childhood development of Americans between 1940 and 2015. Researchers published their findings Monday in the journal Proceedings of the National Academy of Sciences. From the Associated Press:

The scientists from Florida State University and Duke University 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 significant impact on cognitive development: on average, early childhood exposure to lead resulted in a 2.6-point drop in IQ.

The researchers only examined 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, then finally banned in 1996.

Study 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 of lead’s health impacts throughout history.


Sale of leaded gasoline for passenger cars was officially ended in the U.S. in 1996, but by the 1980s, most gas was unleaded. Less than 20 years ago, however, leaded gas was still on sale in 117 countries, the Smithsonian reports.

When leaded gasoline was invented in the 1920s by a General Motors engineer, the toxic effects of the fuel additive were well known. Lead was known to be poisonous for centuries (though that never slowed down humanity from using it.) Adding tetraethyl lead, or TEL, cheaply raised the octane of fuel and quieted knocking engines. It also would lead to instant lead poisoning when absorbed through the skin. It took decades for Caltech geochemist Clair Patterson to sufficiently raise the alarm over all the lead we were pumping into the air before anything was done. Researchers told AP that the results are consistent with other studies, and completely infuriating. From the AP:

Bruce Lanphear, a health sciences professor at Simon Fraser University in Vancouver who has researched lead exposure and IQ, said his 2005 study found 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,” he said.


Leaded gasoline didn’t just drop IQ points for half of Americans — it led to other health issues as well, such as heart disease and hypertension. Leaded gas was responsible for 1.2 million premature deaths per year, according to the United Nations. The lead expended by cars for those long decades is still with us today in the brains of millions of adults the world over.