Evidence of air Pollution From Spanish Conquest of the Inca Found in Glacier Ice Cores

In the 16th century, during its conquest of South America, the Spanish Empire forced countless Incas to work extracting silver from the mountaintop mines of Potosí, in what is now Bolivia--then the largest source of silver in the world. The Inca already knew how to refine silver, but in 1572 the Spanish introduced a new technology that boosted production many times over and sent thick clouds of lead dust rising over the Andes for the first time in history.

Winds carried some of that pollution 500 miles northwest into Peru, where tiny remnants of it settled on the Quelccaya Ice Cap.

There it stayed--buried under hundreds of years of snow and ice--until researchers from The Ohio State University found it in 2003.

In the early online edition of the Proceedings of the National Academy of Sciences, they report discovery of a layer within a Quelccaya ice core that dates to the Spanish conquest of the Inca, contains bits of lead and bears the chemical signature of the silver mines of Potosí.

The core provides the first detailed record of widespread human-produced air pollution in South America from before the industrial revolution, and makes Quelccaya one of only a few select sites on the planet where the pre-industrial human impact on air quality can be studied today.

"This evidence supports the idea that human impact on the environment was widespread even before the industrial revolution," said Paolo Gabrielli, a research scientist at the Byrd Polar and Climate Research Center at Ohio State and corresponding author of the study.

Lonnie Thompson, Distinguished University Professor of earth sciences at Ohio State and co-author of the study, called the find "another keyhole into the past of human activity in that part of the world," and suggested that further investigation could ultimately help us better understand the fate of pollution circulating in the atmosphere today.

Previously, Thompson has called the Quelccaya ice cores a "Rosetta Stone" for gauging Earth's climate history. The samples were cut from ice that formed over 1,200 years as snow settled on the Peruvian Andes. Layer by layer, the ice captured chemicals from the air and precipitation during wet and dry seasons for all those years. Today, researchers analyze the chemistry of different layers to measure historical changes in climate.

For this study, the researchers used a mass spectrometer to measure the amount and type of chemicals present in the ice dating back to 800 AD. They looked for antimony, arsenic, bismuth, molybdenum and especially lead. That's because the refining process that the Spanish introduced to South America involved grinding silver ore--which contains much more lead than silver--into powder before mixing it with mercury in a process called amalgamation. So atmospheric pollution from silver production would chiefly contain traces of lead particulates.

The mass spectrometer revealed some spikes in the concentrations of these elements in the years before Spanish rule, but those layers all likely coincide with natural contamination sources, such as volcanic eruptions. Starting just before 1600, however, the Quelccaya ice began capturing much larger quantities of these elements, and the high amounts persisted until the early 1800s, when South American countries declared independence from Spain.

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