The study, published TK in Proceedings of the National Academy of Sciences (PNAS), examined three ice core records to identify lead pollution levels in the Arctic between 500 BCE through 600 CE. This era spans the rise of the Roman Republic through the fall of the Roman Empire, with the study focusing on the approximately 200-year height of the Empire called the Pax Romana.
Postcards from the past
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 during this process, several kilograms of lead were produced, 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.
Distribution of lead in the athmosphere
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 analyse 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 negative effects on human health, one of which is a reduction in the intelligence quotient - the scientists focussed on this in this study and were able to determine that lead pollution led to a reduction in the IQ of people in ancient Rome by 2 to 3 points. “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,” says study coauthor Nathan Chellman, assistant research professor of snow and ice hydrology at DRI.
According to the research, more than 500 kilotonnes of lead were released into the atmosphere during the almost 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 modelling 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.
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
