The mercury mystery of South America Mercury sulfide, known as cinnabar, was mined in the Peruvian Andes as far back as 1400 BC, causing major atmospheric mercury pollution.
slices with a direct mercury analyzer. In n the early 1990s, Jerome Nriagu at compiling their data, Cooke and colthe University of Michigan sparked a leagues showed that, starting in AD 1554 controversy when he suggested that and continuing over the next 350 years, 196,000 tons of mercury were released into the atmosphere by the Spanish colonists’ mining activity in South America. Because mercury persists and circulates through the environment long after it’s released into the atmosphere, researchers began to search in Europe, North America, and New Zealand for this undocumented mercury pollution. But the analyses couldn’t confirm the mercury amounts Nriagu was suggesting. Now, Colin Cooke at the University of Alberta (Canada) and colleagues at the University of Connecticut and the Technical University of Braunschweig (Germany) have demonstrated that Colonial ruins around the Huancavelica mercury mine. lake sediments from a major mining region of Peru bear evidence of largethe Spanish presence in the region led to scale mercury pollution (Proc. Natl. Acad. excessive amounts of mercury being reSci. U.S.A. 2009, DOI 10.1073/ leased into the atmosphere. Measurements pnas.0900517106). Cooke and his team from the third lake confirmed that the found the pollution when they looked for pollution was spread beyond the immediit at its source: the South American mines. ate region of the mines. The investigators analyzed sediments But the biggest surprise came in disfrom three lakes in the Peruvian Andes. covering how long the mercury pollution Two were in the Huancavelica region, had been going on. “Our goal was to where the mines were rich in mercury suldocument the Spanish mercury mining fide, known as cinnabar, and the third was because it was historically recorded,” says 225 km away from the mining region. Cooke. “We suspected that [the mining] The samples were collected from the went back even earlier, but we didn’t lake beds by forcing a polycarbonate tube know how much earlier or how major it into the ground; each core was then exwould have been.” truded, cut into 1-cm slices, and freezeWhen the initial date for the mercury dried. The samples were subjected to deposits in the lake sediments came out as 210 1400 BC, the investigators thought the Pb measurements that dated the sediradiocarbon date was wrong. So they obments over the past 150 years. For older tained more dates and were astonished to dating, the investigators measured 14C find that those were consistent. The lake levels by accelerator MS. They quantified the total mercury amounts in the sediment sediment records showed mining pollu7132
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tion stretched over 3500 yearsOwhich meant that large-scale mining in the Andes was in full swing long before the Spanish showed up. Peaks in mercury release in 500 BC and AD 1450 corresponded to heavier mining by the Chavı´n and Inca peoples, respectively. The powdered red pigment called vermillion is produced from cinnabar, so Cooke says their discovery makes sense. “Archaeologists for years have been excavating skeletons, gold, and silver that had cinnabar on them as red paint. Archaeologists knew that these people were using cinnabar as far back as the earliest Andean civilizations,” he says. Nriagu has a different take on what Cooke and colleagues found. He doesn’t think that the mining itself generated the mercury pollution. He suspects the Incas were cooking moistened ores of gold or silver with mercury in a pot to amalgamate the precious metal, a process for which the Spanish have taken credit. Researchers now have to look for “evidence for ancient smelting of gold and silver around the Huancavelica mines,” he says. Cooke says his team has several different lines of research to pursue. They would like to fine-tune a mercury speciation method they have been developing called solid-phase mercury thermodesorption. They also want to return to South America to document how far and extensively the mercury-pollution effects were felt in the region. Cooke says the work will also help researchers “understand how mercury moves through the atmosphere and how it changes through time.” —Rajendrani Mukhopadhyay COLIN COOKE
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10.1021/AC901452H 2009 AMERICAN CHEMICAL SOCIETY
Published on Web 07/15/2009
