Ancient Romans Breathed in Enough Lead to Lower Their IQs, Study Finds. Did That Toxin Contribute to the Empire’s Fall?
At the same time as the Romans were building the Colosseum, they were also breathing in high amounts of toxic lead from silver mining and smelting operations. Hussain Didi via Wikimedia Commons under CC BY-SA 3.0 Did lead poisoning contribute to the fall of the Roman Empire? It’s a question historians have long debated, since the Romans sweetened their wine with lead acetate and sipped tap water that flowed through lead pipes. Now, new research suggests the Romans were also breathing in large amounts of lead from silver mining and smelting operations. The toxic metal polluting the air likely got into children’s blood, leading to “widespread cognitive decline,” researchers write in a new paper published Monday in the journal Proceedings of the National Academy of Sciences. Lead in the air might have caused an estimated 2.5- to 3-point drop in IQs throughout the Roman Empire, per the research. The new paper doesn’t solve the mystery of whether lead poisoning played a role in Rome’s downfall. But it does add new evidence to the debate. “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,” says Bruce Lanphear, a health scientist at Simon Fraser University in Canada who was not involved with the study, to NBC News’ Evan Bush. “It’s never just one thing.” Researchers say their findings also represent the first documented example of human-caused industrial pollution in history. To estimate lead pollution levels in ancient Rome, researchers turned to ice core samples taken from Greenland and Russia. For decades, scientists have been using large drills to penetrate Arctic ice sheets and extract columns of ice up to 11,000 feet long. These columns function like frigid time machines: As snowflakes fall, they capture chemicals and particles from the air. When the snow touches down in the Arctic, it compresses and solidifies into thin layers of ice—with those chemicals and particles still trapped inside. By studying these layers, scientists can effectively peer back in time. “You built up this layer cake year after year of environmental history,” study co-author Joe McConnell, a climate and environmental scientist at the nonprofit Desert Research Institute in Nevada, tells NBC News. The team looked at layers of Arctic ice that corresponded to the period between 500 B.C.E and 600 C.E. They saw an increase in lead pollution around the year 15 B.C.E., which lines up with the early years of the Roman Empire. Lead levels remained high until 180 C.E., which marks the end of a period of relative peace known as the Pax Romana. During the roughly 200-year stretch of the Pax Romana, the Romans were extracting and smelting a lot of silver to make coins. These processes are known to emit large amounts of lead into the atmosphere. “If you produce an ounce of silver, you’d have produced something like 10,000 ounces of lead,” McConnell tells the New York Times’ Katherine Kornei. Using the lead levels they found in the ice samples, the researchers were able to work backward and estimate how much lead the Romans must have been spewing into the air. Atmospheric modeling suggests between 3,300 and 4,600 tons of lead were released each year during the Pax Romana, per the New York Times. The scientists estimate that lead pollution was the worst in areas next to mining and smelting operations, reaching concentrations of at least 150 nanograms per cubic meter of air. The toxins would have also spread across Europe—they estimate average concentrations of lead air pollution were greater than 1 nanogram per cubic meter over the continent. Next, they used modern data to estimate how much lead would have built up in the blood of ancient Roman children. They were then able to extrapolate how these accumulations might have affected their IQ. The researchers focused on children in particular, because kids are especially vulnerable to the health consequences of lead exposure. Today, global health experts agree that no amount of lead is safe for kids. The heavy metal can build up in the body and cause health problems. In addition to lowering IQ, lead accumulation in children can lead to slowed growth, anemia, hearing problems, hyperactivity and behavior and learning problems. “We have actual data on IQ scores in kids with different blood-lead concentrations,” Deborah Cory-Slechta, a neurotoxicologist at the University of Rochester Medical Center who was not involved with the paper, tells the New York Times. Roman children likely had an extra 2.4 micrograms of lead per deciliter of blood from the empire’s air pollution. That correlates to a drop in IQ of between 2.5 and 3 points. Factoring in background lead exposure, their blood levels of lead may have been as high as 3.5 micrograms per deciliter, the researchers estimate. And that doesn’t take into account other sources of lead exposure, so the team’s findings are probably an underestimate, reports NBC News. For reference, American children had around 15 micrograms of lead per deciliter of blood during the 1970s, before lead paint and leaded gasoline were banned. Those levels likely resulted in a 9-point drop in IQ, per the New York Times. “A 2.5- to 3-point reduction in IQ may not sound like much but it was across the entire population and would have persisted for the nearly 180 years of the Pax Romana,” McConnell tells the Guardian’s Ian Sample. “I leave it to epidemiologists, ancient historians and archaeologists to determine if the levels of background atmospheric lead pollution and health impacts we have identified … were sufficient to change history.” But even factoring in these new findings, some experts remain skeptical that lead poisoning caused the Roman civilization to collapse around 476 C.E. “While the magnitude of exposure and the correlated blood lead levels were enough to negatively affect the cognitive function of that population, this is still a far cry from causing the downfall of the Roman Empire,” says Amy L. Pyle-Eilola, a pathologist at the Ohio State University who was not involved with the research, to New Scientist’s Christa Lesté-Lasserre. Caleb Finch, a neurobiologist at the University of Southern California who was not involved with the research, remains similarly unconvinced. “The conclusion of ‘widespread cognitive decline’ from an estimated three-IQ point decrease does not match the huge productivity of the Roman Empire, when lead production was maximal,” he tells Science’s Taylor Mitchell Brown. Get the latest stories in your inbox every weekday.
Using Arctic ice core samples, researchers estimate silver mining and smelting released enough lead during the Pax Romana to cause a 2.5- to 3-point drop in IQ
Did lead poisoning contribute to the fall of the Roman Empire? It’s a question historians have long debated, since the Romans sweetened their wine with lead acetate and sipped tap water that flowed through lead pipes.
Now, new research suggests the Romans were also breathing in large amounts of lead from silver mining and smelting operations.
The toxic metal polluting the air likely got into children’s blood, leading to “widespread cognitive decline,” researchers write in a new paper published Monday in the journal Proceedings of the National Academy of Sciences. Lead in the air might have caused an estimated 2.5- to 3-point drop in IQs throughout the Roman Empire, per the research.
The new paper doesn’t solve the mystery of whether lead poisoning played a role in Rome’s downfall. But it does add new evidence to the debate.
“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,” says Bruce Lanphear, a health scientist at Simon Fraser University in Canada who was not involved with the study, to NBC News’ Evan Bush. “It’s never just one thing.”
Researchers say their findings also represent the first documented example of human-caused industrial pollution in history.
To estimate lead pollution levels in ancient Rome, researchers turned to ice core samples taken from Greenland and Russia. For decades, scientists have been using large drills to penetrate Arctic ice sheets and extract columns of ice up to 11,000 feet long.
These columns function like frigid time machines: As snowflakes fall, they capture chemicals and particles from the air. When the snow touches down in the Arctic, it compresses and solidifies into thin layers of ice—with those chemicals and particles still trapped inside. By studying these layers, scientists can effectively peer back in time.
“You built up this layer cake year after year of environmental history,” study co-author Joe McConnell, a climate and environmental scientist at the nonprofit Desert Research Institute in Nevada, tells NBC News.
The team looked at layers of Arctic ice that corresponded to the period between 500 B.C.E and 600 C.E. They saw an increase in lead pollution around the year 15 B.C.E., which lines up with the early years of the Roman Empire. Lead levels remained high until 180 C.E., which marks the end of a period of relative peace known as the Pax Romana.
During the roughly 200-year stretch of the Pax Romana, the Romans were extracting and smelting a lot of silver to make coins. These processes are known to emit large amounts of lead into the atmosphere.
“If you produce an ounce of silver, you’d have produced something like 10,000 ounces of lead,” McConnell tells the New York Times’ Katherine Kornei.
Using the lead levels they found in the ice samples, the researchers were able to work backward and estimate how much lead the Romans must have been spewing into the air. Atmospheric modeling suggests between 3,300 and 4,600 tons of lead were released each year during the Pax Romana, per the New York Times.
The scientists estimate that lead pollution was the worst in areas next to mining and smelting operations, reaching concentrations of at least 150 nanograms per cubic meter of air. The toxins would have also spread across Europe—they estimate average concentrations of lead air pollution were greater than 1 nanogram per cubic meter over the continent.
Next, they used modern data to estimate how much lead would have built up in the blood of ancient Roman children. They were then able to extrapolate how these accumulations might have affected their IQ.
The researchers focused on children in particular, because kids are especially vulnerable to the health consequences of lead exposure. Today, global health experts agree that no amount of lead is safe for kids. The heavy metal can build up in the body and cause health problems. In addition to lowering IQ, lead accumulation in children can lead to slowed growth, anemia, hearing problems, hyperactivity and behavior and learning problems.
“We have actual data on IQ scores in kids with different blood-lead concentrations,” Deborah Cory-Slechta, a neurotoxicologist at the University of Rochester Medical Center who was not involved with the paper, tells the New York Times.
Roman children likely had an extra 2.4 micrograms of lead per deciliter of blood from the empire’s air pollution. That correlates to a drop in IQ of between 2.5 and 3 points.
Factoring in background lead exposure, their blood levels of lead may have been as high as 3.5 micrograms per deciliter, the researchers estimate. And that doesn’t take into account other sources of lead exposure, so the team’s findings are probably an underestimate, reports NBC News.
For reference, American children had around 15 micrograms of lead per deciliter of blood during the 1970s, before lead paint and leaded gasoline were banned. Those levels likely resulted in a 9-point drop in IQ, per the New York Times.
“A 2.5- to 3-point reduction in IQ may not sound like much but it was across the entire population and would have persisted for the nearly 180 years of the Pax Romana,” McConnell tells the Guardian’s Ian Sample. “I leave it to epidemiologists, ancient historians and archaeologists to determine if the levels of background atmospheric lead pollution and health impacts we have identified … were sufficient to change history.”
But even factoring in these new findings, some experts remain skeptical that lead poisoning caused the Roman civilization to collapse around 476 C.E.
“While the magnitude of exposure and the correlated blood lead levels were enough to negatively affect the cognitive function of that population, this is still a far cry from causing the downfall of the Roman Empire,” says Amy L. Pyle-Eilola, a pathologist at the Ohio State University who was not involved with the research, to New Scientist’s Christa Lesté-Lasserre.
Caleb Finch, a neurobiologist at the University of Southern California who was not involved with the research, remains similarly unconvinced.
“The conclusion of ‘widespread cognitive decline’ from an estimated three-IQ point decrease does not match the huge productivity of the Roman Empire, when lead production was maximal,” he tells Science’s Taylor Mitchell Brown.
Get the latest stories in your inbox every weekday.