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A Toxic Situation: The Arsenic Trioxide Deposit in Yellowknife, NT

There is 237,000 tonnes of arsenic trioxide being stored underground in chambers underneath Yellowknife’s Giant Mine; it’s enough to kill the entire world a few times over, experts say.

The biggest danger humans face when it comes to arsenic trioxide is that it is highly lethal even small doses and is highly soluble — this particular deposit is sitting on the tenth largest lake in the world. Thirty-one bodies of water run into Great Slave Lake and it is drained by the Mackenzie River, which runs directly north into the Arctic Ocean.

Eight communities sit on the shores of Great Slave Lake, only one being situated on the East Arm, farther away from the contamination.

Arsenic dust was the cause of death of one Dene child in April 1951 — across the bay from Giant Mine on Latham Island — before regulations and preventative measures were put in place.

A current plan to solve the problem is to freeze the arsenic dust in chambers underground for the next 100 years using two methods, active and passive freezing.

Active freezing is similar to what’s used in keeping hockey rinks frozen. Passive freezing uses thermosyphons, which pull the warm air out of the ground using pressurized carbon dioxide.

The options of taking the arsenic trioxide out of the ground and leaving it where it is were weighed and tested before it was decided by The Giant Mine Remediation Project that leaving it where it is would be the safest way to take to the problem.

The next steps after freezing the underground chambers include taking down buildings, covering tailing ponds, fencing off pits and removing contaminated soil as well as treating Baker Creek, which runs through the site.

In a paper published by the Proceedings of the Royal Society in the United Kingdom, lead author Jules Blais of University of Ottawa estimated that one nearby lakes sediments from the 1960s contain up to three per cent arsenic.

In a phone interview, Blais said that the majority of the arsenic trioxide dust was spread from the roaster freely in the first ten years of production at the mine.

The team studied data taken from 25 lakes over a 25-kilometre radius of Yellowknife. The highest concentrations came from lakes in a four-kilometre radius of Giant Mine the highest concentration being more than 13 times the limit for safe drinking water and 27 times the limit for the protection of aquatic life.

“When we plotted arsenic in the lake water against distance from the mine we saw a huge exponential drop,” said Blais

A plan to research the lakes was originally for the purpose of climate change, but upon receiving the results the investigation “shifted,” said Blais.

“It started with a survey of lakes, we were analyzing water chemistry in lakes around Yellowknife and actually our initial study wasn’t even on arsenic, we were interested at the time in looking to see how lakes that are affected by various degrees of thawing permafrost.”

In an interview with Canadian Press, he stated that even in other highly contaminated places, Yellowknife’s Giant Mine and area is hugely impacted.

“That arsenic is there and it can’t be cleaned up, that fell onto the ground and it’s still there, it’s part of the regional chemistry now,” said Blais.

He said that his team was nearing the end of their three-year contract to study the contaminated area and that his biggest concerns were for people hunting and gathering on the land.

“We know people hunt and this information hasn’t been transferred to the animals, so we do have to be watchful of what the animals might be exposed to,” said Blais.

John Sandlos and Arn Keeling are the lead researchers working on a project investigating the relationship between mining and the Indigenous communities in Canada’s North.

“Many elders [of the Yellowknives’ Dene] clearly see the mines as the central agent of colonialism in the Yellowknife region, a progenitor of social, economic and ecological changes that dramatically altered the Yellowknives’ way of life based on hunting and trapping,” said a paper on Giant Mine’s history published in August 2012, titled Giant Mine: Historical Summary.

 The paper also spoke to the incident of the Dene child who died from arsenic poisoning and said that there were far more incidents that could be derived from the arsenic “crisis.”

“The number of the dead and dates often vary according to the speaker (and may indicate that more fatalities occurred than the young boy described in the archival record). Regardless, the Yellowknives elders and community leaders continually point to the tragic death and sickness of the 1950s as the most profound injustice associated with the gold mines,” it reads.

While remediation is underway for the mine, the site will remain a reminder for many of the measures humans must take to keep natural lands and the peoples associated with them safe.



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