How Arctic ice cores prove lead pollution may in Ancient Rome have caused empire-wide cognitive decline

RENO, Nev. — Lead pollution from Roman mining and metal production may have lowered intelligence levels across the vast Roman Empire nearly 2,000 years ago, new research suggests. Scientists from the Desert Research Institute in Nevada say their findings connect ancient industrial activities to widespread cognitive impairment.

By analyzing ice cores from the Arctic that preserved detailed records of atmospheric pollution, study authors determined that lead emissions from Roman silver mining and smelting operations reached levels high enough to potentially reduce IQ scores by 2.5 to 3 points throughout the Empire’s population during its peak period known as the Pax Romana (27 BCE to 180 CE).

“This is the first study to take a pollution record from an ice core and invert it to get atmospheric concentrations of pollution and then assess human impacts,” explains Joe McConnell, research professor of hydrology at DRI and lead author of the study, in a statement. “The idea that we can do this for 2,000 years ago is pretty novel and exciting.”

The primary source of this ancient lead pollution was silver mining. The process of extracting silver from lead-rich galena ore released significant amounts of lead into the atmosphere, a stark contrast to more recent lead pollution which primarily came from leaded gasoline emissions in the 20th century.

While scholars have long known that Romans were exposed to lead through water pipes, glazed pottery, and even intentional consumption, this study reveals that air pollution from industrial operations likely posed an even greater health risk to the general population. The study, published in the Proceedings of the National Academy of Sciences, found that lead concentrations in the air exceeded 150 nanograms per cubic meter near mining and smelting sites, with average increases of more than 1 nanogram per cubic meter across Europe.

To put these numbers in perspective, the researchers estimate that young children during Roman times had blood lead levels approximately 2.4 micrograms per deciliter above the natural background levels seen in pre-industrial societies. Today, health authorities consider there to be no safe level of lead exposure, with the U.S. Centers for Disease Control and Prevention recently lowering its reference level for intervention in children from 5 to 3.5 micrograms per deciliter.

“As lead pollution has declined during the last 30 years, it has become more and more apparent to epidemiologists and medical experts just how bad lead is for human development,” McConnell notes. Modern research has established that no level of lead exposure is safe, with the U.S. Centers for Disease Control and Prevention recently lowering its reference level for intervention in children from 5 to 3.5 micrograms per deciliter.

The cognitive effects of this pollution may have been particularly devastating because they impacted developing children. Modern research shows that lead exposure in early childhood can have lifelong consequences, affecting not just intelligence but also academic performance, concentration, and eventual lifetime earnings.

The study presents compelling evidence that industrial pollution may have affected brain development across the Roman world. By examining lead deposits preserved in Arctic ice cores and using sophisticated atmospheric modeling, the researchers reconstructed how lead emissions from Roman mining and smelting operations spread across Europe and North Africa.

The research process involved analyzing ice cores drilled from Arctic locations, where layers of ice have accumulated over millennia. These cores contained annual layers of snow that trapped and preserved lead particles carried by winds from southern Europe. By measuring lead concentrations in these layers, the scientists could track pollution levels year by year from 500 BCE to 600 CE.

The study explored two possible scenarios for how lead emissions spread. In one scenario, all emissions came from a single massive mining district in southwestern Spain called Rio Tinto. In the other, emissions were distributed among multiple known Roman mining sites across Europe. Both scenarios suggested widespread lead exposure at levels capable of impairing cognitive development.

Archaeological evidence supports these findings. Analysis of tooth enamel from Roman-era skeletal remains shows elevated lead levels were common, with only 4% of samples showing lead concentrations below what the researchers estimate for average background exposure from air pollution alone.

Intriguingly, the study suggests a possible link between lead pollution and one of the Roman Empire’s greatest catastrophes: the Antonine Plague that killed an estimated 5-10 million people between 165-180 CE. The researchers note that lead exposure can impair immune system function, and this widespread lead pollution immediately preceded the devastating epidemic.

Like the fall of Rome itself, the legacy of Roman lead pollution serves as a cautionary tale about the far-reaching and unintended consequences of industrial development. Two millennia before the Industrial Revolution, Roman mining and metallurgy created the first documented case of large-scale environmental lead contamination affecting human cognitive capacity across an entire civilization.

“Lead is known to have a wide range of human health impacts, but we chose to focus on cognitive decline because it’s something we can put a number on,” says study coauthor Nathan Chellman, assistant research professor at DRI. “An IQ reduction of 2 to 3 points doesn’t sound like much, but when you apply that to essentially the entire European population, it’s kind of a big deal.”