Mercury contamination from small-scale mining

Women and children grinding the ore with mercury into small ball mills

In Columbian mining towns, artisanal miners are using mercury to extract gold from ore, putting themselves, their communities and the country’s food exports at risk for mercury contamination.

Typically a poverty-driven activity, artisanal mining provides a source of income for those with few other options. “These miners aren’t villains, they’re victims,” says UBC professor of mining engineering Marcello Veiga, who is the world’s leading researcher on mercury contamination and UN advisor on the global effects of artisanal gold mining. After 30 years in the field involving travel to about 40 countries, he knows that hazardous extraction methods aren’t restricted to Columbia. There are roughly 15 million artisanal gold miners living in 80 countries – men, women and children – whose activities contaminate the environment with 1,000 tonnes of mercury each year.

Last year, Veiga and a research team investigated gold artisanal mining methods and mercury release pathways in 17 towns in the Columbian province of Antiquoia, where miners typically bring the ore back to town for processing because the presence of gold has attracted armed guerillas and paramilitary activity.

The extraction process involves grinding the ore with mercury into small ball mills called cocos. Before discarding the waste product, which contains most of the mercury, the miners soak it with cyanide to recover any residual gold. This produces highly toxic mercury-cyanide, which is then discarded into the local creeks, potentially affecting farms located downstream. As of yet, not much is known about the impact this practice is having on the environment and food chain. Colombia’s central and regional governments as well as the UN are involved in the research project, and one of the goals is to demonstrate to miners practical alternatives that are cleaner and safer.

Veiga explains that it’s the town residents who face the most immediate and extreme danger of exposure because of the mercury released directly into the air during the refinement process. Mercury is a toxin that can damage the brain and kidneys. Air quality measurements reveal mercury levels 10 times the limit set by the World Health Organization. “We found these levels and higher to be common in busy main streets with stores and schools, and with residential neighbourhoods nearby,” reports Veiga. The study was led by UBC PhD mining engineering student Paul Cordy.

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