Lead pollution is thought to have caused a widespread decline in IQ in ancient Rome

Lead exposure has a variety of negative effects on human health, including affecting children’s cognitive development at even low levels. DRI researchers have previously identified periods of lead pollution across the Roman Empire using atmospheric pollution records found in Arctic ice cores. This new research builds on this discovery to determine the potential effects of lead pollution on the European populace.

published in January. 6 in Proceedings of the National Academy of Sciences, looked at three ice core records to determine the amount of lead pollution in the Arctic from 500 BCE to 600 CE. The study focuses on the Pax Romana, the roughly 200-year peak of the Roman Empire, but this period includes the rise of the Roman Republic through the fall of the Roman Empire.

By using lead isotopes, the researchers were able to pinpoint mining and smelting activities across Europe as the most likely cause of pollution during this time. This led to the creation of maps showing the levels of atmospheric lead pollution throughout Europe using sophisticated computer modeling of atmospheric movement. In addition to studies that link lead exposure to cognitive decline, the research team found that the European population likely had IQ declines of at least two to three points.

“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,” reports the study’s lead author, Joe McConnell, a research professor of hydrology at DRI. The notion that we were able to accomplish this 2,000 years ago is quite exciting and new. “.

Ice preserves historical records.

For decades, McConnell’s Ice Core Laboratory at DRI has been studying ice cores from regions where ice sheets have accumulated over millennia, such as Greenland and Antarctica.

Using massive drills, they meticulously remove ice columns up to 11,000 feet (3,400 meters) long, delving deeper and deeper into Earth’s past with every inch. With the help of well-dated volcanic eruption records, which mark the ice record like old postcards, McConnell’s team produces accurate timelines.

While pollutants like lead can be used to interpret mining and industrial activity, gas bubbles trapped in the ice provide information about the atmosphere of earlier times.

More than 20 years ago, McConnell applied techniques he had developed to more recent history to produce extremely detailed lead records in ice.

In an attempt to address unresolved historical issues, archaeologists and historians approached him after learning about this work with the goal of applying these novel methods to the Roman era.

As an ancient historian and co-author, Andrew Wilson of Oxford University says, “The resulting research changed our understanding of the era by finding precise linkages between the lead pollution records and historical events such as population declines associated with periodic plagues and pandemics.”.

an increasing awareness of the negative effects of lead pollution.

Silver mining, which involved melting down the lead-rich mineral galena to extract silver, was a major cause of ancient lead pollution. This process created thousands of ounces of lead for every ounce of silver that was obtained, with a large portion of that lead being released into the atmosphere.

Leaded gasoline emissions from automobiles were the main source of lead pollution in the 20th century. subsequently to the Clean Air Act’s passage in the U. S. . Since 1970, when leaded gasoline use was restricted, researchers have monitored the dramatic drop in lead levels in human blood. Nonetheless, scientists were able to monitor the effects of lead on health and cognitive development due to the widespread exposure, especially for children born between 1950 and 1985.

McConnell states that “epidemiologists and medical experts have become increasingly aware of just how bad lead is for human development as lead pollution has decreased over the last 30 years.”.

Among other effects, high levels of lead exposure in adults are associated with infertility, anemia, memory loss, cardiovascular disease, cancer, and weakened immune systems. Even minimal exposure levels in kids have been linked to lower IQs, difficulties focusing, and worse academic performance.

As the U.S. S. There is no level of lead exposure without risk, according to the Centers for Disease Control and Prevention (CDC), which considers a blood lead level of 3 to 5 µg/dl the threshold for medical intervention in children.

“We decided to concentrate on cognitive decline because it’s something we can quantify, even though lead is known to have a wide range of human health impacts,” says Nathan Chellman, co-author of the study and assistant research professor of snow and ice hydrology at DRI.

It may not seem like much, but when you consider that the entire European population is affected, a 2 to 3 point drop in IQ becomes significant. “.

The Iron Age saw the start of atmospheric lead pollution, which peaked in the late 2nd century BCE, at the height of the Roman Republic, according to the study. It then experienced a precipitous decline during the Roman Republic’s crisis in the first century BCE, before rising again around 15 BCE as the Roman Empire grew.

Until the Antonine Plague, which ravaged the Roman Empire from 165 to the 180s CE, lead pollution was still high. The prolonged high levels of lead pollution in the Arctic did not surpass those of the Roman Empire until the High Middle Ages in the early second millennium CE. Over 500 kilotons of lead were discharged into the atmosphere during the Roman Empire’s nearly 200-year peak, the study found.

The study’s findings highlight how “humans have been impacting their health for thousands of years through industrial activity,” notes McConnell, despite the fact that ice core records reveal that Arctic lead pollution was up to 40 times higher during the highest historical peak in the early 1970s.