A toxic legacy

For more than 50 years, the Giant Mine contaminated the air, land and water around Yellowknife with arsenic. Environmental toxicologists Jules Blais and Laurie Chan are monitoring the after-effects in nearby lakes and rivers.

Laurie Chan et Jules BlaisLaurie Chan and Jules Blais

“There is a halo of arsenic that we can detect in lakes up to 15 kilometres away from the Giant Mine. Our preliminary analysis is showing that arsenic concentrations in the lakes are exceeding levels that are required to protect aquatic life.”

– Jules Blais

From 1948 to 2004, seven million ounces of gold were extracted from the Giant Mine on the edge of Great Slave Lake in the Northwest Territories. But these vast riches had a deadly by-product: 237,000 tonnes of arsenic trioxide.

Eleven years ago, the governments of Canada and of the Northwest Territories signed an agreement to clean up the site. The Giant Mine Remediation Project, which aims to make surrounding land and water safe and to restore the landscape, is expected to cost nearly $1 billion. The site, located only six kilometres from Yellowknife, where half of the population of the Northwest Territories lives, includes 100 highly contaminated buildings, open pits, tailings ponds and contaminated soil.

The Giant Mine seen from the skyThe Giant Mine

University of Ottawa biology professor Laurie Chan, who holds a Canada Research Chair in Toxicology and Environmental Health, is a member of the Independent Peer Review Panel (IPRP) established by Aboriginal Affairs and Northern Development Canada (now Indigenous and Northern Affairs Canada) to provide technical advice to the government on choosing the best out of 56 options for the Giant Mine clean-up. In August 2014, all stakeholders agreed to the IPRP’s recommendation to use the Frozen Block Method to freeze the arsenic trioxide that is currently buried in underground containers. The process will keep the man-made toxins from seeping into the surrounding environment.

“It would be too difficult and risky to remove all the waste buried at the site. It would be like mining for arsenic,” says Chan, who continues to advise the remediation project on occupational and environmental health measures. “There’s ongoing concern among Yellowknife residents over arsenic exposure.”

Contaminant levels in the mine’s vicinity are being monitored, including arsenic levels in Arctic grayling in nearby creeks and water bodies, some of which are popular fishing spots. Chan is also designing a human health study to assess, in the coming years, the potential risk of exposure to arsenic among Yellowknife residents and in neighbouring First Nations communities.

In a similar vein, Chan’s colleague, professor of biology and environmental toxicology Jules Blais, the director of the Laboratory for the Analysis of Natural and Synthetic Environmental Toxicants, is examining arsenic levels in areas around the Giant Mine site. In 2014, he received a Natural Sciences and Engineering Research Council of Canada strategic project grant of $570,000 over three years to develop new tools for assessing legacy pollutants and their ecological consequences in lakes near N.W.T. mines.

“There is a halo of arsenic that we can detect in lakes up to 15 kilometres away from the Giant Mine,” says Blais. “We are looking exclusively beyond the mine property. Our preliminary analysis is showing that arsenic concentrations in the lakes are exceeding levels that are required to protect aquatic life.”

“We’re trying to understand why these aquatic systems haven’t recovered,” he adds.

Blais examines core samples of lake sediments to trace the environmental record back through hundreds of years. Clues in the layers, such as the shells of cladocera — tiny crustaceans that form a major part of the aquatic food chain — reveal the history of the lake over time, much like tree rings indicate warm and cold years.

Blais is trying to determine whether lake sediments are absorbing the arsenic and taking it out of the waters, or diffusing it. Early results show that arsenic levels in the sediment increased during the decades in which the Giant Mine roaster was melting ore to separate out the gold, particularly before emissions controls were put into place, and that cladocera died off in huge numbers during this period.

“Environmental studies are often like arriving at the scene of an accident. You realize there is a problem after the problem has happened. Our approach allows us to go back and reconstruct what changes took place and look at how the biota responded to past disturbances,” says Blais. “Our research aims to find better ways to learn from our past mistakes.”

Once published, this research will present a well-documented history of the levels of contaminants such as arsenic, mercury and sulphur dioxide, which will answer questions about what has happened since the mine ceased operations and how the contaminants have moved through the ecosystem. Ultimately, Blais hopes the research will inform future regulators.

“If regulators can better understand the effects of releasing these emissions, like sulphur and arsenic, into the environment, if they are provided with tools to better understand the environmental consequences, then they will be in a better position to regulate these emissions,” says Blais.

In the meantime, Chan secured a $1.65 million NSERC CREATE grant in 2014 to help train the next generation of environmental toxicologists at the University of Ottawa and three other Canadian universities. Among other things, students are taught how science contributes to regulating dangerous chemicals in the environment. It’s an important step in averting future environmental catastrophes of Giant Mine proportions.

This article was first published in Tabaret, March 2015.


by Mike Foster

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