“Unmasking Ancient Rome: How Lead Pollution Diminished Intelligence Across an Empire”

Exposure to lead is linked to numerous health consequences in humans, with even modest levels affecting the cognitive development of young children. DRI researchers have previously utilized air pollution records preserved in Arctic ice cores to trace instances of lead contamination throughout the Roman Empire, and now new findings broaden this research to discern how this pollution potentially impacted the populace of Europe.

The research, published on Jan. 6 in Proceedings of the National Academy of Sciences, investigated three ice core records to ascertain lead pollution levels in the Arctic from 500 BCE to 600 CE. This timeframe reflects the ascent of the Roman Republic to the decline of the Roman Empire, with the study concentrated on the approximately 200-year peak of the Empire referred to as the Pax Romana.

Lead isotopes enabled the research team to pinpoint mining and smelting activities across Europe as the probable origin of pollution during this era. Sophisticated computer modeling of atmospheric circulation then produced visualizations of atmospheric lead contamination levels throughout Europe. Coupled with research correlating lead exposure to cognitive decline, the research team also estimated likely reductions in IQ levels of at least 2 to 3 points within the European populace.

“This is the inaugural study to extract a pollution record from an ice core and reverse-engineer it to derive atmospheric pollution concentrations, and subsequently evaluate human effects,” states Joe McConnell, research professor of hydrology at DRI and the principal author of the study. “The ability to accomplish this for 2,000 years ago is quite groundbreaking and thrilling.”

Preservation of historical records in ice

McConnell’s Ice Core Laboratory at DRI has dedicated decades to the examination of ice cores from regions like Greenland and Antarctica, where layers of ice have accumulated over thousands of years.

Utilizing massive drills, they meticulously retrieve ice columns extending as much as 11,000 feet (3,400 meters) in length, delving ever deeper into Earth’s historical narrative with each inch. McConnell’s team creates accurate timelines utilizing records of well-documented volcanic eruptions, which leave a mark on the ice record akin to postcards from eras gone by.

Gas bubbles encased in the ice provide a glimpse into the atmosphere of former epochs, while pollutants such as lead can be interpreted to deduce mining and industrial activities.

Over two decades ago, McConnell started devising methods to produce very detailed lead records within ice, applying them to more recent historical contexts.

When archaeologists and historians discovered this work, they sought his expertise, hoping to utilize these new methodologies in relation to the Roman period to uncover answers to persistent historical queries.

“The resultant research transformed our comprehension of the era by establishing precise connections between the records of lead pollution and historical occurrences such as population declines linked to intermittent plagues and pandemics,” remarks co-author and ancient historian Andrew Wilson from Oxford University.

A deepening awareness of the risks of lead pollution

Ancient lead pollution primarily originated from silver extraction, wherein the lead-rich mineral galena was processed to release silver. For every ounce of silver procured, this procedure generated thousands of ounces of lead, much of which was expelled into the atmosphere.

Throughout the 20th century, lead pollution was mainly attributed to the emissions from vehicles utilizing leaded gasoline. Following the enactment of the Clean Air Act in the U.S. in 1970, which imposed restrictions on the use of leaded gasoline, researchers have monitored the significant reduction of lead in human bloodstream. Nevertheless, the nationwide exposure, particularly among children born between 1950 and 1985, has enabled scientists to examine the repercussions of lead on health and cognitive growth.

“As lead pollution has significantly decreased over the last three decades, it has become increasingly evident to epidemiologists and medical professionals just how detrimental lead is to human development,” states McConnell.

In adults, substantial levels of lead exposure correlate with infertility, anemia, memory impairment, cardiovascular ailments, cancer, and diminished immune response, among other repercussions. Furthermore, in children, even minimal exposure levels have been associated with lowered IQ and concentration.challenges, and diminished educational achievement.

While the U.S. Centers for Disease Control and Prevention (CDC) identifies a blood lead level of 3.5 µg/dl as the threshold for medical action in children, they have asserted that there is no safe level of lead exposure.

“Lead is recognized for its extensive impacts on human health, but we opted to concentrate on cognitive decline as it’s quantifiable,” remarks study co-author Nathan Chellman, assistant research professor of snow and ice hydrology at DRI.

“A reduction of 2 to 3 IQ points may not seem significant, yet when applied to nearly the entire European population, it becomes a considerable issue.”

The research indicated that atmospheric lead pollution commenced during the Iron Age, peaking during the late 2nd century BCE at the zenith of the Roman Republic. It sharply decreased throughout the 1st century BCE, amid the crisis of the Roman Republic, before surging again around 15 BCE with the emergence of the Roman Empire.

Lead pollution remained elevated until the Antonine Plague from 165 to the 180s CE, which had a severe impact on the Roman Empire. It wasn’t until the High Middle Ages in the early 2nd millennium CE that lead pollution in the Arctic surpassed the sustained high levels experienced during the Roman Empire. The findings reveal that over 500 kilotons of lead were emitted into the atmosphere during the nearly 200-year peak of the Roman Empire.

Although ice core records indicate that Arctic lead pollution reached up to 40 times higher during the peak historical levels in the early 1970s, the insights derived from this study illustrate how “humans have been affecting their health for thousands of years through industrial activities,” states McConnell.