Ice cores from the Arctic made it possible to reconstruct lead pollution in ancient Rome
An international team of scientists with the participation of the University of Vienna examined three ice cores to determine lead pollution between 500 BCE and 600 CE in the Roman Empire. Lead has many negative effects on human health, one of which is a reduction in the intelligence quotient - the scientists focused on this in this study and were able to determine that lead pollution led to a reduction in IQ of 2 to 3 points among people in ancient Rome. The study has just been published in the renowned journal Proceedings of the National Academy of Sciences (PNAS).
Using huge drills, the scientists painstakingly extract ice columns up to 3,400 meters long, which penetrate further into the Earth’s history with every centimetre. Three such ice cores from the Arctic have now been examined for lead residues. The lead concentrations measured in the ice provide information about when and how much lead was deposited from the atmosphere. The study focused on the period from the rise of the Roman Republic to the fall of the Roman Empire, concentrating on the approximately 200-year heyday of the empire, the so-called Pax Romana - during which time the Roman Empire reached its greatest extent and covered large parts of Europe. And the highest concentrations of lead pollution also occurred during this Pax Romana. The ice cores are like postcards from the past, says hydrologist Joe McConnell from the Desert Research Institute (DRI) in the USA and lead author of the study. Gas bubbles trapped in the ice provide information about the atmosphere of past eras, while pollutants such as lead can be used to interpret mining and industrial activities or, as in this case, human health.
Lead pollution in antiquity is largely due to silver mining, in which the lead-containing mineral galena was melted down to extract silver. For every gram of silver extracted, this process produced several kilograms of lead, much of which was released into the atmosphere. This is where the team from the University of Vienna led by meteorologist Andreas Stohl came into play.
Stohl and his team provided the analyses on the distribution of lead in the atmosphere: "We have been working for many years with experts who analyze ice cores and support them with atmospheric transport modelling. This allows us to establish quantitative correlations between the sources of air pollution and its deposition in ice," explains Stohl from the University of Vienna.
Lead has many effects on human health, such as memory loss, infertility, cancer, difficulty concentrating or even a lower intelligence quotient (IQ). The scientists were able to determine a probable reduction in IQ value of at least 2 to 3 points in the European population. "A reduction in IQ of 2 to 3 points doesn’t sound like much, but if you apply that to the entire European population, it’s considerable," says Nathan Chellman, co-author
According to the research, more than 500 kilotons of lead were released into the atmosphere during the nearly 200-year heyday of the Roman Empire. Although ice core records show that lead levels in the Arctic were up to 40 times higher during the historic peak in the early 1970s, the findings of this study show how "humans have been affecting their health for thousands of years through industrial activities," McConnell said.
"There are not many groups in the world that collaborate with ice core experts on transport modeling like we do. We have therefore already published many interesting results. But calculating the air quality for the Pax Romana period was a completely new idea. As a meteorologist, I find it very exciting to be able to contribute to a better understanding of history and people’s health. Our study shows very well how rewarding interdisciplinary collaboration across many disciplines can be," says Stohl.
Original publication in PNAS:
Joseph R. McConnell, Andreas Stohl, et al: Pan-European atmospheric lead pollution, enhanced blood lead levels, and cognitive decline from Roman-era mining and smelting. 2025.
DOI: 10.1073/pnas.2419630121
