It was during the period known as the Pax Romana, a time of stability in the Roman Empire that lasted for about two hundred years between 27 BC and 192 AD. Mining and smelting operations throughout Europe were likely a a source of lead contamination, which had its consequences on health.
Scientists from the Desert Research Institute (DRI) in Reno, Nevada, used Arctic ice core records to reconstruct atmospheric pollution in Ancient Rome. According to an article published in the journal Proceedings of the National Academy of Sciences (PNAS), they have linked this exposure to a reduction in human intelligence.
Lead exposure
Lead exposure is responsible for a variety of health impacts, and even relatively low levels affect the cognitive development of children. This is why the DRI team identified likely reductions in IQ levels of at least 2 to 3 points among the European population.
“This is the first study to take a record of pollution from an ice core and invert it to obtain atmospheric pollution concentrations to assess human impacts,” says Joe McConnell, lead author of the study.
The mineral galena is melted to extract silver
McConnell's Ice Core Laboratory at DRI has spent decades examining ice cores from places like Greenland and Antarctica, where layers of ice have accumulated for millennia. Using massive drills, they painstakingly extract ice columns up to 3,400 meters long.
Researchers then create precise chronologies using well-dated volcanic eruption records, which turn the data obtained from ice into postcards from the past. Trapped gas bubbles provide information about the atmosphere of ancient times, while contaminants like lead can be used to interpret mining and industrial activity.
Specialists began developing methods to create highly detailed lead records in ice over twenty years ago. When archaeologists and historians learned about this work, they approached it hoping to apply these new techniques to the Roman period, seeking answers to persistent historical questions.
“The resulting research changed our understanding of the era by finding precise links between lead pollution records and historical events such as population decline associated with periodic plagues and pandemics,” adds co-author Andrew Wilson from the University of Oxford.
A researcher from the Desert Research Institute with an ice core
Lead pollution in ancient times was largely originated in silver mining, which involved melting the lead-rich galena mineral to extract silver. For every ounce of silver obtained, this process produced thousands of ounces of lead, much of which was released into the atmosphere.
In the 20th century, for example, pollution was mainly due to emissions from vehicles burning leaded gasoline. After the approval of the Clean Air Act in the United States in 1970, which restricted the use of this type of fuel, researchers have traced the significant decrease in lead in human blood.
Impact on cognitive development
However, national-level exposure, particularly for children born between 1950 and 1985, allowed scientists to track the impact of lead on health and cognitive development. “As pollution has decreased, it has become increasingly evident how harmful this chemical element is for human development,” McConnell says.
In adults, high levels of exposure are linked to infertility, anemia, memory loss, cardiovascular diseases, cancer, and reduced immune response, among others. In children, even low levels of exposure have been associated with reduced IQ, concentration problems, and lower academic success.
Ice cores allow us to reconstruct atmospheric pollution
The Centers for Disease Control and Prevention in the United States, researchers say, consider a blood lead level of 3.5µg/dl to be the point for medical intervention for children. However, they have also pointed out that there is no safe level of lead exposure.
“Lead is known to have a wide range of impacts on human health, but we chose to focus on cognitive impairment because it's something we can quantify,” says Nathan Chellman, co-author of the study. “A reduction in IQ of 2 to 3 points may not seem like much, but when applied to virtually the entire European population, it becomes a significant issue,” he adds.
High lead contamination
The study indicates that atmospheric lead pollution began during the Iron Age and peaked in the late 2nd century BC, at the height of the Roman Republic. It then decreased significantly during the 1st century BC, amidst the Republic's crisis, before increasing around 15 BC following the rise of the Roman Empire.
Lead pollution remained high until the Antonine Plague, a smallpox epidemic that severely affected the Roman Empire from 165 to 180 AD. It wasn't until the High Middle Ages that lead contamination in the Arctic surpassed the elevated levels sustained during the Roman Empire.
According to DRI research, over the almost 200 years of the Roman Empire's peak, more than 500 kilotons of lead were released into the atmosphere. While ice core records show that pollution in the Arctic was up to 40 times higher during the highest historical peak in the early 1970s, the information obtained from this study demonstrates how “humans have been affecting their health for thousands of years through industrial activity,” McConnell concludes.
