Quicksilver & Gold: Mercury Pollution from Artisanal and Small-Scale Gold Mining

Abstract

In 2009 a mining engineer named Marcello Veiga set out to study mercury air pollution in a part of northwest Colombia called Antioquia Department. This mountainous, conflict-ridden state, where leftist guerillas routinely battle Colombian security forces, is an important center for artisanal and small-scale gold mining (ASGM). Miners isolate gold by mixing ores dug from the ground or from stream beds with mercury to form an amalgam. When the amalgam is burned, the elemental mercury vaporizes into a toxic plume while the gold stays behind. Veiga, who is also an associate professor at the University of British Columbia, was especially interested in air quality in and around specialized shops called entables that burn amalgam for a fee. Faced with threats of robbery in the field, local miners bring their ore to these entables for final processing. Five cities in Antioquia—Segovia, Remedios, Zaragoza, El Bagre, and Nechi—collectively house more than 300 entables, each of them a point source for inorganic mercury vapors that pollute the air of the region and beyond. Antioquia’s entables produce 10–20 metric tons of pure gold each year, so Veiga expected the air mercury levels would be high. Still, he was surprised when readings occasionally spiked over 999 µg/m3, the upper limit on his handheld mercury analyzer.1 That’s nearly 1,000 times the World Health Organization’s (WHO) air quality guideline of 1 µg/m3 for chronic exposure to inorganic mercury vapor2 and 3,000 times the U.S. Environmental Protection Agency reference concentration of 0.3 µg/m3 for chronic inhalational exposure to inorganic mercury.3 For centuries miners have used mercury to trap particles of precious metals. Artisanal and small-scale gold miners used an estimated 1,400 metric tons of mercury in 2011. About one-third of the mercury used is believed to go into the air while the rest ... The worst pollution was in the entables, even on their days off. But Veiga also detected inorganic mercury levels tens to hundreds of times higher than the WHO air quality guideline in city plazas, local neighborhoods, a bakery, and in front of an elementary school in Remedios, where readings ranged from 5 to 10 µg/m3. “These were the highest mercury levels I’d ever seen,” says Veiga, whose research experience in gold mining spans three decades in 40 countries. Mercury amalgamation has been used for centuries to process precious metals.4 Today, ASGM is the world’s second greatest source of atmospheric mercury pollution after coal combustion, according to the United Nations Environment Programme (UNEP).5 And with gold prices now exceeding US$1,600 per ounce (up from less than US$500 in the 1980s),6 ASGM is on the rise along with its mercury problem, Veiga says.