Study finds elevated levels of arsenic and mercury in Yellowknife lakes

Posted on Wednesday, April 6, 2016

Mining contributes significantly to Canada’s economy, but its long-term sustainability depends on responsible environmental practices. In Yellowknife, which is home to half the population of the Northwest Territories, gold mining has produced a legacy of pollution that remains a public health concern.

A study led by researchers from the University of Ottawa and published today in PLOS ONE found that most small lakes within a 15-to-20 km radius of the mines in Yellowknife contain arsenic in concentrations that exceed drinking water guidelines and levels required for protecting aquatic life. Large lakes (>100 hectares) had lower arsenic levels than small lakes, likely because large lakes receive more water from rain and snow.

From 1949 to 1999, the Giant Mine and Con. Mines produced 7 million ounces of gold, which helped build the early economy of the Northwest Territories, but these mines released large quantities of harmful contaminants, including arsenic, antimony and sulfur into the local environment.

“The legacy of five decades of gold mining is still very present on the surrounding landscape, more than 10 years after the mines ceased operations,” said lead author Adam Houben, a researcher with the Department of Biology at the University of Ottawa.

“There is a halo of high arsenic in lake water, centered on the gold mines in Yellowknife. We have no doubt that gold mining is the source of this high arsenic,” added Dr. Jules Blais, Professor of Biology and Environmental Toxicology at the University of Ottawa, who directed the research effort.

The area that features lakes with elevated arsenic levels spans over 700 square kilometers and is centred on the Giant Mine. In the past, most research on arsenic in water near Yellowknife was confined to the lease site occupied by the mine, but this study shows that the area affected by high arsenic levels extends well beyond the mine’s lease property and encompasses the City of Yellowknife.

This study shows that arsenic levels in lake waters near Yellowknife are often twenty times higher than the amounts considered acceptable for the protection of aquatic life, and ten times higher than drinking water guidelines, often at concentrations exceeding 100 micrograms per liter in areas within five kilometers of the mine.  

The researchers also found that levels of methyl mercury, a toxic form of mercury produced by bacteria, are elevated in the studied lakes near the gold mines. Methyl mercury can accumulate in food chains, leading to accumulation in fish that are consumed by people. The authors suggest that the roaster stack’s high sulfur emissions, which stimulated the growth of these bacteria, may be responsible for the methyl mercury in the lakes near the gold mines.

“To date, most of the studies have focused on arsenic; however, we show here the significant cumulative effects of pollution leading to unexpected concentrations of methyl mercury,” said Houben. “This stresses the need for sustained environmental monitoring in the mining industry.”

“These studies are important because they give us an opportunity to develop more sustainable mining practices,” said Blais. “We need to keep learning from our past mistakes so we don’t repeat them.”

Collaborative work is ongoing between academic and government research partners to further investigate issues related to arsenic in lakes of the Yellowknife region.

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