Lead exposure has long been recognized for its detrimental effects on human health, particularly in children. Recent research conducted by scientists at the Desert Research Institute (DRI) suggests that lead pollution during the Roman Empire may have led to significant declines in IQ across Europe. This study, published in the Proceedings of the National Academy of Sciences (PNAS), utilized ice core records from the Arctic to trace lead pollution levels from 500 BCE to 600 CE.
The research focused on a period known as Pax Romana, approximately a 200-year span during the height of the Roman Empire. By analyzing lead isotopes, researchers were able to identify mining and smelting operations throughout Europe as primary sources of pollution. Using advanced computer modeling, they mapped atmospheric lead pollution levels across Europe and linked these findings to potential cognitive declines in the population.
“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 Joe McConnell, a research professor of hydrology at DRI and lead author of the study. The research indicates a likely reduction in IQ levels by at least 2 to 3 points among Europeans due to lead exposure.
McConnell's Ice Core Laboratory has been examining ice cores from Greenland and Antarctica for decades. These cores provide insights into Earth's past atmosphere through trapped gas bubbles and pollutants like lead. The methods developed by McConnell have helped link historical events such as population declines with periods of increased lead pollution.
Coauthor Andrew Wilson from Oxford University noted that this research changed understanding of historical events by linking them with precise pollution records. The ancient lead pollution primarily originated from silver mining activities, where large amounts of lead were released into the atmosphere.
In modern times, significant reductions in atmospheric lead have been observed following regulations like the U.S. Clean Air Act, which restricted leaded gasoline use. However, past exposure still allows scientists to track its impact on health and cognitive development.
“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,” said Nathan Chellman, assistant research professor at DRI.
The study highlights how industrial activities have impacted human health for millennia. More than 500 kilotons of lead were released into the atmosphere during Rome's peak years alone.
The full study titled "Pan-European atmospheric lead pollution, enhanced blood lead levels, and cognitive decline from Roman-era mining and smelting" is available in PNAS.