Imma Perfetto
Cosmos science journalist
Air pollution from large-scale mining and smelting at the height of the Roman Empire would have caused widespread cognitive declines, new research has found.
The study examined measurements of lead pollution in 3 Arctic ice cores dating from 500 BCE to 600 CE, an era spanning the rise of the Roman Republic through to the fall of the Roman Empire.
Researchers used computer models of atmospheric movement to map atmospheric lead pollution across Europe to estimate exposure levels and human health impacts.
Based on modern epidemiological understanding of the effects of childhood blood lead levels, they suggest there would likely have been reductions in IQ levels of at least 2 to 3 points during the Pax Romana – the 200-year height of the 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,” says Joe McConnell of Desert Research Institute (DRI) in the US, lead author of the study in Proceedings of the National Academy of Sciences (PNAS).
“The idea that we can do this for 2,000 years ago is pretty novel and exciting.”
In the past 150 years, humans have been exposed to atmospheric lead largely from the burning of fossil fuels, and from leaded petroleum especially since the 1920s.
“As lead pollution has declined during the last 30 years, it has become more and more apparent to epidemiologists and medical experts just how bad lead is for human development,” says McConnell.
It is now understood that any level of lead exposure is damaging to human health. This is especially the case for children, for which low-level exposure is linked to reduced intelligence quotient (IQ), concentration, and academic abilities.
“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,” says study coauthor Nathan Chellman of DRI.
According to the study, human exposure to lead arose through many potential routes during antiquity, including water pipes, utensils and pottery, toys, ornaments, cosmetics, and even intentional ingestion. It was also in the air.
“All Europeans, their livestock, and agricultural fields were exposed for centuries to background atmospheric lead pollution resulting from the large-scale mining and processing of lead/silver ores that underpinned the Greek and Roman economies,” the researchers write in the paper.
“This background lead pollution in air and soil may have been the most significant exposure route in rural, nonelite populations.”
The study found that atmospheric lead pollution 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, a period of political instability and social unrest.
This pollution increased again at about 15 BCE following the rise of the Roman Empire and remained high until the Antonine Plague (165-180s CE). The study estimates that 500 kilotons of lead were released to the atmosphere during this nearly 200-year period.
