Researchers have found the earliest evidence of air pollution buried deep inside the layers of ice sitting on top of the Andes Mountains in southern Peru.

A team of researchers at the Byrd Polar and Climate Research Center of the Ohio State University has extracted an ice core from the 1,200-year-old Quelccaya Ice Cap. The core, which was taken from the layer dating back to the Spanish occupation of Latin America during the 16th century, shows traces of lead and other chemicals that were produced in the silver mines of Potosi in what is now present-day Bolivia.

This, the researchers believe, is the first clear evidence of human-caused air pollution in South America even before the rise of the Industrial Revolution.

In 16th-century South America, the Spanish conquistadors forced the native Incas to work in the silver mines on top of the mountains of Potosi, which was the largest source of silver in the world at the time. Although the Incas knew how to refine silver, the conquistadors introduced a new technology that would speed up the production of silver.

This new technology is amalgamation, which involved grinding silver ore into powder form before mixing with mercury. Lead powder emerged as a by-product of amalgamation, and clouds of lead-heavy dust went up into the atmosphere as part of the new process. Some of those clouds were carried by the winds across the lands and eventually settled on the Quelccaya Ice Cap some 500 miles northwest of Potosi, which explains the high concentration of lead in the ice core.

"This evidence supports the idea that human impact on the environment was widespread even before the industrial revolution," says researcher Paolo Gabrielli.

In fact, historical evidence from the colonial era shows political officials were aware of the impact of mining activities on humans and the environment. For instance, history professor Kendall Brown of Brigham University in Utah, who is not connected to the study, tells LiveScience in an email that Francisco de Toledo, viceroy of Peru from 1569 to 1581, ordered the silver miners at Potosi to build higher chimneys for their amalgamators to reduce risk of contamination.

Using a mass spectrometer, the researchers found high concentrations of lead, antimony, arsenic, bismuth, molybdenum, and other lead particulates in the ice core. Although the researchers found small amounts of these chemicals from before the Spanish rule, which can be attributed to natural contamination sources such as volcanic eruptions, they discovered unusually large amounts of chemicals deposited just before 1600 and up until the early 1800s, when the South American countries declared independence from Spain.

"The fact that we can detect pollution in ice from a pristine high altitude location is indicative of the continental significance of this deposition," says Gabrielli. "Only a significant source of pollution could travel so far and affect the chemistry of the snow on a remote place like Quelccaya."

Still, the researchers concede the level of air pollution during the Spanish Conquest is far lower than the pollution generated during the 20th century, during which miners began conducting their operations in open pits and people started burning fossil fuels for energy.