Did Lead Lower The IQs of Ancient Romans?

"Lead pollution in ancient Rome was so high that it dropped the population's IQ by around three points or more.

Elites were exposed to lead through water pipes, cooking pots, cosmetics and the syrups that sweetened their wine. But the most widespread exposure for Romans came from industrial pollution caused by the mining and smelting of metals used to make money.

Romans melted down galena, a lead-rich ore, to extract the silver needed for coins. Lead was a major byproduct of the process.

"For every ounce of silver you produce, you might produce thousands of ounces of lead," said Joseph McConnell, a climate and environmental scientist at the Desert Research Institute in Reno, Nev. "Nobody could escape it."

McConnell and his colleagues estimated the Romans' lead exposure and reported the rough drop in IQ that epidemiologists have associated with that level of exposure. The findings were published last month in the Proceedings of the National Academy of Sciences,

The researchers examined airborne lead that drifted north from ancient Rome and was preserved in ice cores extracted from Greenland and the Russian Arctic. The samples dated between 2,500 and 1,400 years ago -- an era that included the Roman Empire's rise and fall.

The team was able to match the chemical fingerprints of lead found in the cores to the isotopes of lead sources mined within the empire, McConnell said, and atmospheric modeling also showed the lead's drift. The work revealed that lead pollution peaked during the Pax Romana, a prosperous period when ancient Rome spanned portions of the Middle East, Europe and North Africa.

The researchers' models showed 3,300 tons to 4,600 tons of lead were emitted annually at the time, suggesting that ancient Romans had lead levels between 2 micrograms and 5 micrograms per deciliter of blood. Other research links that amount to a decline of around 3 IQ points.

In comparison, at the time the Clean Air Act of 1970 was passed to regulate lead and other airborne pollutants in the U.S., American children averaged about 15 micrograms of lead per deciliter of blood with an associated seven-point drop in IQ, according to Bruce Lanphear, a professor of health sciences at Simon Fraser University in British Columbia. He wasn't involved in the study.

Lead exposure is associated with increases in mortality, preterm births and anemia as well as reduced cognitive functioning, he said. For children, who are more vulnerable, lead is associated with IQ drops that persist over time.

Lanphear said the new study likely underestimates the amount of exposure that beleaguered the Romans, but the pervasiveness of lead underscores a popular theory that the pollutant might have played a role in the empire's decline.

"It gives more weight to the idea that lead was one of many risk factors that could have contributed," he said. "How consequential it was, of course, would be difficult to say."" [1]

1. REVIEW --- Science Shorts: Did Lead Lower The IQs of Ancient Romans? Woodward, Aylin. 
Wall Street Journal, Eastern edition; New York, N.Y.. 22 Feb 2025: C5.