How Romans pioneered silver recycling

Sampling a Roman Republican denarius for chemical analysis. (Image by the University of Liverpool).

Gold impurities in silver coins and lead pollution in Greenland ice show that the Romans were pioneers of recycling.

In a new paper, researchers at the University of Liverpool and the University of Warwick explain that extracting silver from ores and refining it at mints resulted in a lot of lead pollution. Ancient pollution entered the atmosphere, drifted across the Atlantic and left a pollution fingerprint in Greenland ice. However, there was a dramatic decline in lead pollution levels in the ice during the late Roman Republic, even though coins were still being produced.

The article notes that during the first and second centuries BC, Rome’s access to silver mines in Iberia and southern France was interrupted by conflict. Deliberate debasement of the denarii — the predominant silver coin of the Romans — with copper is often considered to show interruptions in silver production. Yet, despite slight dips in the fineness of silver coins, especially around the times of the Social and Civil Wars in the first century BC, this does not provide enough of an explanation for the drops in lead pollution.

To explain this phenomenon, researchers Matthew Ponting and Jonathan Wood point to the Romans recycling silver, often plundered following conflicts in Iberia and southern France, to make coins.

They analyzed how much gold was present in the coinage, given that all silver produced in antiquity contained small quantities of the yellow metal.

At around 120 BC, clusters of coins began appearing with very low levels of gold in them. The silver used for these coins also appears to have become part of the silver supply for coinage in the first half of the first century BC. Then, in 49 BC, a new infusion of silver with high levels of gold in it appeared to enter circulation.

Given that Julius Caesar returned to Rome from his battles with the Gauls in 49 BC, the researchers propose that this new silver in circulation was plundered by Caesar’s army.

“Debasing silver was one way to deal with fluctuations in the silver supply. Melting down existing silver, either yours or someone else’s, was another,” Wood said. “For the Romans, recycling coins would have been considerably less expensive than extracting new silver—a benefit for their finances, as well as for the environment.”