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Lead Pollution May Have Lowered IQs in Ancient Rome, Study Finds

The mass production of silver coins in the Roman Empire had an unintended effect: spewing so much lead into the atmosphere that it may have lowered citizens’ IQs.

ByNick Keppler|
Roman coins from the Hoxne hoard, buried in the 5th century in Hoxne, Suffolk, UK.
Roman coins from the Hoxne hoard, buried in the 5th century in Hoxne, Suffolk, UK. | CM Dixon/Print Collector/Getty Images

The Roman Empire was more lead-coated than a Baby Boomer’s childhood bedroom. 

The Romans had excess lead; it was a byproduct of the massive mining and smelting operations that produced the silver coins that were the cornerstone of their monetary system. Romans slathered lead on aqueducts and kitchen utensils and even used it as a wine sweetener. Some have cited mental and physical decline due to lead poisoning as a cause of the fall of the empire, though most historians agree that military overextension, political corruption, economic instability, and attacks by neighboring tribes are enough to explain the Western empire’s effective dissolution toward the end of the 5th century.

But the release of lead in the atmosphere did shave a few IQ points off Roman citizens, according to new research published in the journal Proceedings of the National Academy of Sciences.

Environmental scientists at the nonprofit Desert Research Institute examined cores of ice from the Arctic that formed from 500 BCE to 600 CE, a time that spans the rise of the Roman Republic; its transformation into the imperialistic and autocratic power that expanded through Europe, Western Asia, and North Africa; and its decline. 

Lead emissions traveled thousands of miles northward and imprinted patterns on ice as it formed. The researchers used computer modeling of atmospheric movement to produce maps of lead pollution levels across Europe throughout the time periods. Pollution peaked around 180 BCE, after Roman industry recovered from the Antonine plague. According to their research, more than 500 kilotons of lead were released during the 200-year height of the Roman civilization.

The researchers used another model, predicting the cognitive effects of so much lead, and concluded an average intelligence quotient (IQ) drop of two to three points from lead in the atmosphere alone.

Other studies suggest this loss of capacity is on par with that lost by Americans in the 20th century, thanks to lead in paint and gasoline, which was largely phased out in the 1970s. (People who were children in the ’60s, during the worst years of lead exposure, may have lost an average of six points.) 

In a statement on the new study, co-author Nathan Chellman explained, “An IQ reduction of two to three points doesn’t sound like much, but when you apply that to essentially the entire European population, it’s kind of a big deal.”

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