About 2,000 years ago,
the Roman Empire was thriving. But there was something sinister in the air. Literally. This may have been the world's first case of widespread industrial pollution.
Widespread airborne lead pollution affected health and intelligence, researchers report Monday, Jan. 6, in the scientific journal Proceedings of the National Academy of Sciences.
For about two centuries beginning in 27 B.C., a period of relative stability and prosperity known as the Pax Romana (Latin for "Roman world"), the empire stretched across Europe, the Middle East, and North Africa. Its economy relied on the minting of silver coins, which required enormous mining operations.
But mining silver from the bowels of the earth produces large amounts of lead, says Joseph McConnell, an environmental scientist at the Desert Research Institute, a nonprofit group based in Nevada, and lead author of the new study. "If you mine an ounce of silver, you get about 10,000 ounces of lead," he says.
And lead has many negative effects on the human body. "There is no safe level of lead exposure," says Deborah Corey-Slechta, a neurotoxicologist at the University of Rochester Medical Center who was not involved in the study.
Dr. McConnell and his colleagues found lead in layers of ice collected in Russia and Greenland that date back to the time of the Roman Empire. The team hypothesized that lead was released into the atmosphere during mining in Rome, moved by air currents, and eventually fell as snow in the Arctic.
The lead levels measured by Dr. McConnell and his colleagues were extremely low - about one molecule of lead per trillion molecules of water. But the ice samples were collected thousands of kilometers away from southern Europe, and the lead concentration must have dissipated greatly after such a long journey.
To estimate the amount of lead originally released by Roman mining operations, the researchers worked backwards. Using powerful computer models of the planet's atmosphere and making assumptions about the mining locations, the team varied the amount of lead emitted according to the concentration they measured in the ice.
In one case, the scientists assumed that all silver mining occurred at a historically important mining site in southwestern Spain known as Rio Tinto. In another case, they assumed that silver mining was evenly distributed across dozens of sites.
The research team estimated that Roman silver mining operations emitted between 3,300 and 4,600 tons of lead into the atmosphere each year.
The researchers then estimated how all that lead was dispersed throughout the Roman Empire. "
We ran the model forward to see how these emissions would be distributed," Dr. McConnell says. Once they had data on atmospheric lead concentrations, the researchers used modern data to estimate how much lead might have gotten into people's blood
in ancient Rome.
Photo: kazgazeta.kz
Dr. McConnell and his colleagues focused on infants and children. Young people are particularly susceptible to ingestion and inhalation of environmental lead, says Dr. Bruce Lanphear, a public health physician at Simon Fraser University in British Columbia who was not involved in the study. "Children, especially infants, eat more and breathe more," he says.
According to Dr. Cory-Slecht, in recent decades, blood lead levels in children have been correlated with a range of physical and mental health indicators, including IQ. "We have actual data on IQ scores in children with different blood lead concentrations," he says.
McConnell's team calculated that children in much of the Roman Empire must have received between 2 and 5 extra micrograms of lead per deciliter of blood, and such levels correspond to a drop in IQ of about 2 to 3 points.
By comparison, in American children in the 1970s before the phase-out of leaded gasoline and leaded paint, average blood lead levels increased by about 15 micrograms per deciliter of blood. The corresponding average decrease in IQ was about 9 points.
However, lead exposure may have had other negative effects on the Romans. Elevated blood lead levels have also been linked to a higher incidence of premature births and decreased cognitive function in old age. "Clead follows you throughout your life," says Dr. Lanphear.
Some scholars have suggested that lead poisoning played an important role in the decline of the Roman Empire. However, this idea has been called into question, at least when it comes to water contaminated by lead pipes. A 2014 study found that while the pipes that supplied water in Rome raised lead levels, the water was unlikely to have been truly harmful.
According to Hugo Delille, a geoarchaeologist at the French National Center for Scientific Research who was not involved in the study, these new findings make sense. "They confirm the extent of lead contamination from Roman mining and metallurgical activities," he says.
Dr. McConnell says the study also confirms the damage to the population that Roman mining caused. "As far as I know, this is the earliest example of widespread industrial pollution," he says.