Scientists have announced that they have discovered traces of air pollution from Spanish silver mines inside the Andean ice cap.

Evidence of metal-rich smog was discovered in Peru, but is thought to have been produced hundreds of miles away in modern-day Bolivia by the silver mines of Potosí. The industrial history of Potosí has seen it named a UNESCO World Heritage site, writes Megan Gannon of NBC.

Traces Of Conquistador Air Pollution In Peruvian Ice

Colonial-era technology

Before the Spanish arrived, the Inca had been mining silver for generations, but under colonial rule Potosi became the largest source of silver in the world. By the 17th century Potosí, which sits at an altitude of approximately 13,120 feet, was home to around 160,000 colonists and 13,500 indigenous people, who were forced to mine for silver. The boom in silver extraction was largely due to technology which the Spanish introduced in 1572.

Amalgamation led to faster production times, and involved grinding silver ore, which contains high levels of lead, before combining it with mercury. During the grinding process it seems likely that dust containing lead was released into the atmosphere, before apparently being carried 500 miles to the Quelccaya Ice Cap in the south of Peru.

Air pollution: Chemical analysis of the ice cap

Scientists were studying climactic changes when they made the discovery during the extraction of an ice sample in 2003. The sample is known as an ice core, and involves pulling out a section of the ice cap to analyze changes in its composition over time.

The differences in the sample from colonial times were not obvious to the naked eye, but chemical analysis showed that lead levels increased significantly just before 1600. Levels of lead remained largely consistent until the early 19th century, which saw a decline in mining activity due to the Latin American Wars of Independence.

The study revealed that colonial mining activity led to far less air pollution than during the 20th century. During this time mining operations involved huge open pits, pollution from which combined with the burning of fossil fuels and led to significant changes in the South American atmosphere, according to researcher Paolo Gabrielli of Byrd Polar and Climate Research Center at Ohio State University.

The findings were published in the Proceedings of the National Academy of Sciences.