About 2,000 years ago, the Roman Empire was thriving. However, there was something ominous in the air. literally.
Widespread pollution in the form of airborne lead is taking a toll on health and intelligence, researchers reported Monday in the Proceedings of the National Academy of Sciences.
During a period of relative stability and prosperity known as the Pax Romana, beginning in 27 BC and lasting about two centuries, the empire spread across Europe, the Middle East, and North Africa. Its economy depended on silver coinage, which required extensive mining operations.
But extracting silver from the earth produces large amounts of lead, said Joseph McConnell, an environmental scientist at the Nevada-based nonprofit Desert Research Institute and lead author of the new study. . “For every ounce of silver produced, 10,000 ounces of lead are produced.”
And lead has various negative effects on the human body. “There is no such thing as a safe level of lead exposure,” said Deborah Corey Slecta, a neurotoxicologist at the University of Rochester Medical Center who was not involved in the study.
Dr. McConnell and his colleagues detected lead in layers of Roman ice collected in Russia and Greenland. The researchers speculated that lead entered the atmosphere from Roman mining operations, traveled on air currents, and eventually fell out of the atmosphere as arctic snow.
The levels of lead that Dr. McConnell and his collaborators measured were very low, approximately one lead-containing molecule per trillion molecules of water. But the ice samples were collected thousands of miles from southern Europe, and the lead concentrations would have been highly dispersed after such a long journey.
To estimate the amount of lead originally emitted by Roman mining activity, the researchers worked backwards. Using powerful computer models of Earth's atmosphere and assumptions about the location of the mine site, the team varied the amount of lead emitted to match the environment. The concentrations they measured in ice. In one case, they assumed that all the silver production took place in a historically important mine in southwestern Spain known as Rio Tinto. In another case, silver mining was estimated to be evenly distributed over dozens of locations.
The researchers calculated that Rome's silver mining operations release between 3,300 and 4,600 tons of lead into the atmosphere each year. The researchers then estimated how all that lead was scattered throughout the Roman Empire.
“We ran the model forward to see how these emissions were distributed,” Dr. McConnell said.
With these atmospheric lead concentrations in hand, the researchers then used modern data to estimate the amount of lead that would have entered the bloodstream of people in ancient Rome.
Dr. McConnell and his colleagues focused on infants and children. Dr. Bruce Lanphear, a public health physician at Simon Fraser University in British Columbia who was not involved in the study, said young people are particularly susceptible to ingesting lead from the environment through ingestion or inhalation. “For every pound, children, especially young children, eat more and breathe more.”
In recent decades, lead levels in children's blood have been correlated with a number of physical and mental health indicators, including IQ, says Dr. Cory Slecta. “We have real data on IQ scores for children with different blood lead concentrations.”
Using these modern relationships, Dr. McConnell and his team estimated that most children in the Roman Empire would have ingested about 2 to 5 micrograms more lead per deciliter of blood. Such a level corresponds to an IQ drop of approximately 2 or 3 points.
For comparison, in the 1970s, before leaded gasoline and paint were phased out, American children's blood lead levels increased by about 15 micrograms per deciliter of blood on average. Ta. Their corresponding average IQ drop was about 9 points.
However, exposure to lead would have had other negative effects on the Romans as well. Elevated blood lead levels have also been linked to an increased incidence of preterm birth and decline in cognitive function in the elderly. “It stays with you for the rest of your life,” Dr. Lanphear said.
Some scholars hypothesize that lead poisoning played an important role in the decline of the Roman Empire. But that idea is being questioned, at least when it comes to water contaminated by lead pipes. A 2014 study showed elevated lead levels in pipes used to distribute water in Rome, but it was unlikely that the water was truly harmful.
Hugo Delisle, a geoarchaeologist at France's National Center for Scientific Research who was not involved in the study, said these new discoveries make sense. “They confirm the extent of lead contamination resulting from Roman mining and metallurgical activities.”
Dr McConnell said the study also gave Roman mining dubious honors. “To my knowledge, this is the earliest example of widespread industrial pollution,” he said.
