Widespread lead pollution from the Roman Empire's metals industry caused a cognitive decline across Europe, with researchers estimating a 2- to 3-point drop in IQ due to lead exposure, a recent study published in the Proceedings of the National Academy of Sciences (PNAS) suggests.
The study found that atmospheric lead pollution began during the Iron Age and peaked during the late second century BCE at the height of the Roman Republic, coinciding with the expansion of mining activities. Scinexx reported that during the nearly 200-year period of the Roman Empire, approximately 500 kilotonnes of lead were released into the atmosphere, contributing to health impacts.
Traces of the lead pollution were found in Arctic ice cores. Researchers analyzed ice cores drilled from the Arctic to track levels of airborne lead pollution back through Roman times, as noted by The Guardian. These ice cores serve as a frozen record of atmospheric conditions throughout history, preserving particles that circulated in the air during different periods.
Dr. Joe McConnell, a research professor and hydrologist at the Desert Research Institute in Nevada, applied his expertise in ice core analysis to assess samples from three different Arctic sites, leading to new insights into ancient lead pollution. "It's amazing that we were able to quantify atmospheric air pollution over Europe nearly 2,000 years ago and assess potential health impacts on the ancient Roman civilization," Dr. McConnell stated, as reported by Science Alert.
The researchers used advanced computer modeling to produce maps of atmospheric lead pollution levels across Europe, analyzing how lead spread from known Roman mining and smelting sites.
Lead pollution in antiquity largely stemmed from silver mining, where the lead-rich mineral galena was smelted to extract silver. The extraction and smelting of metals in the Roman Empire between 100 BCE and 200 CE contributed to lead emissions, likely causing a population-wide drop in IQ of about 2.5 to 3 points.
Nathan Chellman, a co-author and assistant research professor of snow and ice hydrology at DRI, highlighted the widespread impact of the pollution. "A 2 to 3 points lower IQ doesn't sound like much, but when you apply that to the entire European population, it's quite a lot," he said, according to Science Alert. The chronic exposure to lead would have affected the entire population over nearly 180 years of the Pax Romana, including the provinces of Gaul, North Africa, Iberia, and Britannia.
Lead is a well-established neurotoxin and remains a public health menace today, particularly harmful to infants and children. The American Centers for Disease Control and Prevention (CDC) consider a blood lead level of 3.5 µg/dl as the point for medical intervention for children, acknowledging that there is no safe amount of lead in the human body, according to NBC News.
In antiquity, there were several routes of lead exposure, including the use of glazed tableware, paints, cosmetics, and intentional ingestion, as well as utensils, cookware, water pipes, and wine. Popular Science reported that lead pipes and vessels delivered toxic particles directly to the elite and urban population.
The researchers determined that pollution from Roman silver smelters would have affected much of Europe, with increases in atmospheric lead levels noted in Arctic ice core data between 100 BCE and 200 CE, as reported by Newsweek. "Our findings demonstrate that anthropogenic emissions from industrial activities have resulted in widespread damage to human health for over two millennia, which is pretty profound in my view," Dr. McConnell added, according to The Guardian.
Scholars have debated lead poisoning's impact on Roman history for decades, with some arguing it played a role in the downfall of the Roman Empire.
Sean Scott, a chemist at Pacific Northwest National Laboratory, commented on the research methods. "It's interesting work, I agree with what they're trying to do," he said, according to Popular Science. However, he noted, "Once you make a leap from ice core to human blood, and then to intelligence quotient, that's going to have uncertainty."
Dr. McConnell acknowledged the limitations, saying, "It would be great if going forward the linkages between background air pollution, childhood blood lead levels, and health were better quantified," as reported by Popular Science.
An international team of researchers, including climatologists and epidemiologists from institutions in Denmark, the UK, the US, Canada, Austria, and Switzerland, wrote, "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," according to Science Alert.
The article was written with the assistance of a news analysis system.