Mercury Pollution's Oldest Traces Found in Peru

May 18, 2009

Demand for the mercury compound vermilion was strong enough to support a large-scale mercury mining industry in the Andes as far back as 1400 B.C., according to a new study (see pictures from the expedition).

A bright red pigment, vermilion was used in ancient Andean rituals and is frequently found adorning gold and silver ceremonial objects in ancient burials of kings and nobles in South America.

The find extends the record of New World mercury production back by more than 2,000 years and provides the first evidence of preindustrial mercury pollution, said geologist Colin Cooke, a Ph.D. student at Canada's University of Alberta and lead author of the study.

Mercury, a toxic heavy metal used to extract silver and gold from ore in a process called amalgamation, comes from the mineral cinnabar, which is crushed to make vermilion pigment.

Historical records kept by colonists from Spain, which ruled Peru from the 16th to 19th centuries, show that, by the late 16th century, liquid mercury was widely used to extract silver—one of the colonial economy's mainstays—from ore in the Andes.

Cooke and his colleagues initially had hoped to confirm only this colonial history of mercury mining by analyzing pollution in sediment cores they took from lakebeds near old mines in Huancavelica, Peru, a city of 40,000 located 140 miles (225 kilometers) southeast of Lima, and the world's second largest mercury deposit after Almadén, Spain.

Instead, Cooke said, "Once we radiocarbon-dated the cores, we realized it went back many, many centuries—a few millennia even—and that was pretty shocking. The idea that they were mining there as early as 1400 B.C. had never really been suggested before."

His team's findings are detailed in a paper to be published on May 19 in the journal Proceedings of the National Academy of Sciences. The National Geographic Society's Committee for Research and Exploration helped fund the research. (National Geographic News is part of the National Geographic Society.)

(Related: "Ancient Ore Mine Discovered in Peruvian Andes.")

Rise of Complex Society

Increasing levels of mercury pollution in sediments from two nearby lakes indicated the ancient mercury mining. The mining had started long before the Chavín culture—which Cooke described as "the cradle of complex Andean culture"—peaked, between 800 B.C. and 400 B.C. in central Peru.

"The traditional thinking has been that large-scale mining and metallurgy only begins after you get the emergence of large-scale societies that have social stratification and people can specialize in different crafts," Cooke said.

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