Mercury Pollution's Oldest Traces Found in Peru
for National Geographic magazine
|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.
The new study suggests the reverse: that both mining and metallurgy might spur the rise of complex society.
Preferential access to exotic goods such as cinnabar and gold would have supported the rise of early leaders, Cooke said.
Yale University archaeologist Richard Burger said Cooke's research supports his hypothesis that trade in cinnabar contributed to the rise of the Chavín culture.
Since the Chavín herded llamas, Burger said, they would have been able to haul vermilion throughout the Andes.
"This [new research] was an independent body of evidence that never occurred to me, and it independently confirms the hypothesis," Burger said.
The Chavín, and later the Inca, covered themselves in vermilion for ceremonial purposes, Burger said. The pigment was also used to decorate gold objects such as burial masks.
By 1450, long after the Chavín had collapsed and as the Incas were expanding their reach, levels of mercury pollution in the lakes had spiked more than tenfold and the type of pollution recorded there shifted from cinnabar dust to mercury vapor, Cooke's study shows.
This suggests the mercury was being heated, though it's unclear why.
Cooke said there is no evidence that the Inca were using mercury as part of the silver or gold extraction process. Rather, he said, they may have been experimenting with how to produce vermilion paint more efficiently.
"They are actually driving the mercury out of the [cinnabar] ore and into a gas phase, and that is recorded as a shift in the kind of pollution that's registered both in the sediments and how far that pollution is traveling," Cooke said. He and his team found traces of vapor in lakes several hundred miles from the main Huancavelica mine, while cinnabar dust settled only within a few miles of the mine.
Burger said the increase in pollution from that period makes sense, because the Inca Empire encompassed an area more than three times as large as the Chavín territory and because vermilion pigments played a large societal role in Inca rituals and burials. As a result, mining would have grown substantially during Inca times.
But Burger believes the shift from dust to vapor likely correlates with the transition to colonial mining practices, which included smelting, even though the radiocarbon dates suggest that transition happened about a century before Spanish arrival. "Radiocarbon dates are really not sufficiently precise to distinguish between the late Inca and the early colonial," Burger said.
Jerome Nriagu, an environmental chemist at the University of Michigan who has compiled historical documents on the colonial use of mercury in Peru, said Cooke's study suggests mercury could have been used in silver production in pre-colonial times, especially during Inca rule. If so, the mercury pollution from smelting would have been lethal to the miners, he said. Cinnabar dust is lower in toxicity.
The three-millennia-long mercury mining tradition at Huancavelica—including a 450-year colonial history that earned the mine its nickname Mina de la Muerte (Mine of Death)—has likely left behind a poisonous legacy in this central Peruvian highland region, Cooke believes.
"We haven't done any direct measurements of mercury in fish or blood-mercury levels in the residents or anything, but I would suspect it is probably one of the more polluted regions in the world," Cooke said.
Today the known mercury pollution from centuries past "should be of some concern," the University of Michigan's Nriagu said.
According to Nriagu, mercury emissions averaged about 600 tons per year during Peru's colonial period, when mercury was used in silver amalgamation. That amount is "approximately equivalent to current emissions from China," Cooke notes in his new study.
Further research will be needed to determine the environmental effects of ancient Peru's obsession with this toxic substance.
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