A paleolimnological perspective on industrial-era metal pollution in the central Andes, Peru

Scientists in the United States and Canada are reporting the first scientific evidence that ancient civilizations in the Central Andes Mountains of Peru smelted metals, and hints that a tax imposed on local people by ancient Inca rulers forced a switch from production of copper to silver.
Their study is scheduled for the May 15 issue of ACS' Environmental Science & Technology, a semi-monthly journal.

The University of Alberta's Colin A. Cooke and colleagues point out that past evidence for metal smelting, which involves heating ore to extract pure metal, was limited mainly to the existence of metal artifacts dating to about 1,000 A.D. and the Wari Empire that preceded the Inca. The new evidence emerged from a study of metallurgical air pollutants released from ancient furnaces during the smelting process and deposited in lake sediments in the area.

By analyzing metals in the sediments, the researchers recreated a 1,000-year history of metal smelting in the area, predating Francisco Pizarro and his Spanish conquistadors by 600 years. Their findings show that smelters in the Morococha region of Peru switched from production of copper to silver around the time that Inca rulers imposed a tax, payable in silver, on local populations.