Lead Pollution Trapped in Greenland Ice Shows Rise and Fall of Ancient Societies

Ancient Rome's economy ran on mining silver, which produced airborne lead pollution carried all the way to Greenland. Dan Kitwood/Getty Images

The Romans left quite a legacy—their language is hidden in our words, their republic inspired the founders of modern governments, and the Greek architecture they adopted has shaped our own image of official buildings. Scientists have discovered a less savory inheritance: lead pollution encased in Greenland ice.

The pollution was caused by the metal mining that served as the basis of the civilization's economy. Air currents carried the pollution north, putting Roman economic history on ice, a new paper published in the journal Proceedings of the National Academy of Sciences details. The paper pegs the ancient lead pollution record more precisely than any previous study.

"The idea that we have a record of economic activity that has an uncertainty of one or two years is a whole different ballgame," first author Joseph McConnell, a hydrologist at the Desert Research Institute in Nevada, told Newsweek.

Researchers studied 1,300 feet of an almost 2-mile-long ice core collected in Greenland in the mid-1990s. McConnell and his team regularly collect their own ice cores, but only up to about 650 feet. The section that McConnell and his colleagues analyzed covers 1235 B.C. to A.D. 1257, almost 2,500 years that includes the entire span of the Roman republic and empire.

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They took the borrowed ice core and first melted away the outermost layers to avoid any contamination. That process left behind a series of skinny ice sticks each about 3 feet long, which the team could be sure would give them accurate data.

"It's ice that's never touched humans, never seen modern air," McConnell said of the center of the massive original core, which took about three years to extract.

From that pristine ice, the scientists made an eye-watering 21,000 measurements of lead levels, about nine for every year in the sample. The measurements allowed them to create a finely tuned timeline of lead emissions rising and falling.

Those lead emissions were produced as Romans—often, but not exclusively, slaves—smelted ore to mine silver, which served as the basis of the economy. McConnell and his co-authors were able to cross-reference lead pollution with documentary sources on a nearly year-by-year basis. That confirmed, for example, the economic havoc wreaked by the massive Antonine Plague, a pandemic, perhaps of smallpox, that spread throughout the empire in A.D.165. It also led them to believe that the Roman Empire was economically stronger—and dirtier—than the much-lauded republic that inspired the founders of the U.S.

Those emissions never disappeared. Lead air pollution accumulates in the environment, which means ancient lead pollution can come back to bite us.

"The question that all historians, climate scientists, which are also pollution scientists, and public health scholars often ask is what is the cumulative effect of 2,000, 3,000 years of lead pollution on human health," Alexander More, a historian of climate at Harvard University who wasn't involved in the new research, told Newsweek.

More adds that studies like these can help scientists pinpoint how much lead is really "natural" and how much is produced by humans. He argues that they also suggest government agencies should re-evaluate lead limits since they aren't truly based on a time before pollution.

"What's interesting about a lot of the studies that have emerged in the last couple of decades is the magnitude of pollution," Aubrey Hillman, a geoscientist at the University of Louisiana at Lafayette who was not involved in the new research, told Newsweek. "Historical documents have allowed us to make estimates, but what these natural archives do is allow us to verify those estimates."

The technique could also allow scientists to more precisely pinpoint events in societies that left less voluminous records behind than the Romans did, Hillman said. She pointed to South American societies producing lead and mercury pollution before Europeans invaded—historians are quite sure it happened but would like to pin down more details about its magnitude and chronology.

"We always think of the Industrial Revolution as the time when people start polluting," Hillman said. "But more and more studies are showing that we have this long history of polluting."