Researchers have examined three ice core records to identify lead pollution levels in the Arctic between 500 BCE through 600 CE. Lead isotopes allowed the authors to identify mining and smelting operations throughout Europe as the likely source of pollution during this period. Advanced computer modeling of atmospheric movement then produced maps of atmospheric lead pollution levels across Europe. Combined with research linking lead exposure to cognitive decline, the scientists also identified a 2.5-to-3 point reduction in intelligence quotient throughout the Roman Empire.
“This is the first study to take a pollution record from an ice core and invert it to get atmospheric concentrations of pollution and then assess human impacts,” said Dr. Joe McConnell, a researcher at the Desert Research Institute.
“The idea that we can do this for 2,000 years ago is pretty novel and exciting.”
“Our research changed our understanding of the Roman era by finding precise linkages between the lead pollution records and historical events such as population declines associated with periodic plagues and pandemics,” said Dr. Andrew Wilson, a historian at the University of Oxford.
Ancient lead pollution stemmed largely from silver mining, whereby the lead-rich mineral galena was melted down to extract silver.
For every ounce of silver obtained, this process produced thousands of ounces of lead — much of which was released to the atmosphere.
In adults, high levels of lead exposure are linked to infertility, anemia, memory loss, cardiovascular disease, cancer, and reduced immune response, among other impacts.
In children, even low levels of exposure have been connected to reduced IQ, concentration challenges, and reduced academic success.
While U.S. CDC considers a blood lead level of 3.5 µg/dl the point for medical intervention for children, there is no level of lead exposure without risk.
“Lead is known to have a wide range of human health impacts, but we chose to focus on cognitive decline because it’s something we can put a number on,” said Dr. Nathan Chellman, a researcher at the Desert Research Institute.
“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.”
In the study, the team found that atmospheric lead pollution began during the Iron Age and reached a peak during the late 2nd century BCE at the height of the Roman Republic.
It then declined sharply during the 1st century BCE, during the crisis of the Roman Republic, before increasing around 15 BCE following the rise of the Roman Empire.
Lead pollution remained high until the Antonine Plague from 165 to the 180s CE, which severely affected the Roman Empire.
It wasn’t until the High Middle Ages in the early 2nd millennium CE that lead pollution in the Arctic exceeded the sustained high levels of the Roman Empire.
According to the research, more than 500,000 tons of lead were released to the atmosphere during the nearly 200-year height of the Roman Empire.
“Although ice core records show that Arctic lead pollution was up to 40-fold higher during the highest historical peak in the early 1970s, the insight gained from this study demonstrates how humans have been impacting their health for thousands of years through industrial activity,” Dr. McConnell said.
The study was published in the Proceedings of the National Academy of Sciences.
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Joseph R. McConnell et al. 2025. Pan-European atmospheric lead pollution, enhanced blood lead levels, and cognitive decline from Roman-era mining and smelting. PNAS 122 (3): e2419630121; doi: 10.1073/pnas.2419630121