Lead pollution in ancient Rome may have dropped average IQ by up to 3 points, study finds

In ancient Rome, toxic lead was so pervasive in the air that it most likely dropped the average person’s IQ by 2.5 to 3 points, new research suggests.

The study, published Monday in the journal Proceedings of the National Academy of Sciences, amplifies long-standing questions about what role, if any, lead pollution played in the empire’s downfall.

The authors linked lead found in ice samples from Greenland to ancient Roman silver smelters and determined that the incredible amount of background pollution they produced would have affected much of Europe.

Using studies about lead exposure in modern society, the researchers were able to determine how much lead most likely ended up in Romans’ bloodstreams and the effects that would have had on their cognition.

Lead, a powerful neurotoxin, remains a public health menace today. There is no safe amount to have in your body. Exposure is associated with learning disabilities, reproductive problems, mental health issues and increased risk of hearing loss, among other effects.

The researchers behind the new study said the findings are the first clear example of widespread industrial pollution in history.

“Human or industrial activities 2,000 years ago were already having continental-scale impacts on human health,” said a lead author of the paper, Joe McConnell, a climate and environmental scientist at the Desert Research Institute, a nonprofit research campus in Reno, Nevada. “Roman-era lead pollution is the earliest unambiguous example of human impacts on the environment.”

The story of the ancient pollution was buried in the Greenland ice sheet.

The chemical composition of ice there and in other polar regions can yield key clues about what past environments were like. As snow falls, melts and compresses to form layers of ice, the chemicals trapped inside offer a kind of timeline.

“You built up this layer cake year after year of environmental history,” McConnell said.

By drilling, extracting and processing long cylinders of ice, scientists can measure qualities like the atmospheric carbon dioxide in past climates or, as in this case, lead concentrations over time.

The researchers analyzed three ice cores and found that lead concentrations rose and fell over roughly a millennium in ways that corresponded to key events in Rome’s economic history. The level rose, for example, when Rome organized control over present-day Spain and ramped up silver production in the region.

“For every ounce of silver you might produce, you might produce 10,000 ounces of lead,” McConnell said. “As you’re producing silver, the Romans were smelting and mining silver for their coinage, for their economy, and they were introducing a lot of lead into the atmosphere.”

During the smelting process, lead would attach to particles of dust in the atmosphere, McConnell said. A small fraction of those particles were blown and deposited in Greenland.

Once the researchers determined how much lead was concentrated in Greenland’s ice, they used climate modeling systems to figure out how much lead the Romans must have been emitting to pollute Greenland to the level observed.

Then the team analyzed modern-day information about exposure to lead and determined the health effects of the atmospheric lead present during the Pax Romana, a time of peace in the empire that lasted from 27 B.C.E. to A.D. 180.

The researchers found that the average lead exposure was about one-third of what it was in the United States in the late 1970s, when the use of leaded gasoline was at its peak and before the Clean Air Act. The Roman lead levels were roughly twice what American children are exposed to today, McConnell said.

The researchers think people living closest to silver mines in Iberia (modern-day Spain) would have had the most lead in their blood.

“Virtually nobody escaped,” McConnell said.

However, the results most likely do not speak to the full scope of lead’s health consequences in ancient Rome, because Roman people were exposed through other sources, including wine sweetened in lead-lined vessels, lead plumbing and lead drinking goblets.

Lead “was everywhere” in ancient Rome, said Dr. Bruce Lanphear, a lead expert and a professor of health sciences at Simon Fraser University in Canada, who was not involved in the study. So the new research is limited because it assesses only atmospheric lead, he said, which the authors acknowledge.

“Their estimates are likely to be an underestimate,” Lanphear said.

Still, the findings may invigorate ongoing debates over what effect lead had on the decline of ancient Rome, since the study offers evidence that exposure may, indeed, have played a role.

Historians and medical experts have for decades debated whether lead contributed to the empire’s downfall and to what degree. Researchers in the 1980s suggested that Rome’s elites were stricken with gout and erratic behavior because they drank copious amounts of lead-laced wine.

“I’m quite convinced lead was one of the factors that contributed to the decline of the Roman Empire, but it was only one factor. It’s never just one thing,” Lanphear said.

Joe Manning, a professor of history at Yale University, said most researchers think Rome fell for myriad reasons, including plagues, economic problems and shifts in climate. Manning said it is important to remember that ancient Rome was a tough place to survive, with life expectancies around 25 to 30 years.

“You do not want to go into a city in the ancient world under any circumstances. It’d be the last place you’d want to visit. They’re so dirty, disease-ridden, dysentery everywhere,” Manning said. “The lead is on top of really horrible sanitary conditions.”

This article was originally published on NBCNews.com