Researchers urge action after study finds Yellowknife wildfires released 'significant' amount of arsenic

Wildfires near Yellowknife released a "significant"amount of arsenic into the air and water according to a recent study a finding one researcher says should be treated as a "wake up call."

The study, published in Environmental Research Letters in May, used public and open-access data to determine four fires near Yellowknife in 2023 known as the North Slave Complex released between 69 and 183 tonnes of arsenic into the air and water.

It says that's about half the arsenic wildfires around the world emit per year.

Natalie Plato, the deputy director of the Giant Mine remediation project, said earlier this year that how wildfire and arsenic interact isn't something her team knows a lot about.

Owen Sutton, a postdoctoral fellow at the University of Waterloo and lead author of the paper, said something similar to CBC on Wednesday that the science was new and "we don't know a lot about this sort of thing." As such, he said the findings were both a concern and a surprise.

With climate change expected to make wildfires more intense and severe Sutton hopes scientists, policy makers and land stewards will treat his findings as a call to action and will think more critically about how to mitigate the risk.

"There's a lot of places in the world that are dealing with both prevalent and severe wildfires and also legacy contamination from mining and smelting operations," he said. "Having a map of these particularly vulnerable areas would be really, really important for fire management."

John B. Zoe, a Tch man living in Behchok, spoke of the need for a tool like a map as well. He said the re-release of arsenic is something worth learning more about and talking about.

"Where is it, what effect is it having now?" he asked. "We also need to be taking an inventory of what's there right now and where exactly it is and where the strongest places where it's much more toxic than others."

Jules Blais, an environmental toxicology professor at the University of Ottawa who has studied arsenic around Yellowknife and who was not involved in Sutton's study, said the findings also spell out the importance of monitoring arsenic levels before, during and after a fire.

Blais spoke to CBC News last year as the fires encroached Yellowknife, warning that a significant release of arsenic into the air and water was possible. "This study basically confirms my warning," he said.

The report says wildfire activity closer to Yellowknife will put arsenic in the soil "at risk of an even larger catastrophic and unprecedented release."

Arsenic origins

Sutton and a pair of other researchers looked at an area with a 110-kilometre radius from Giant Mine, an old gold mine in Yellowknife that spewed arsenic trioxide into the air without any pollution controls between 1949 and 1951.

The mine then started to store that arsenic underground and it's still there all 237,000 tonnes of it to this day.

Although one of Canada's most toxic sites is at the heart of the research area, Sutton said "a lot" of the arsenic released into the air from wildfires in 2023 occurred naturally in the region's soil and bedrock.

Blais agrees there is naturally occurring arsenic around Yellowknife it's part of what led to gold mining in the first place, he said but he said he wouldn't characterize the arsenic released into the air in 2023 as naturally-occuring.

"Much of that arsenic that we see, that halo of arsenic [around Yellowknife] is from the roaster stack emissions," he said. Sutton said fires in 2023 did burn into this halo of arsenic, but they didn't burn very far.

"Our term 'naturally-occurring' was meant to distinguish arsenic from the regional geology from direct mine-related sources," Sutton explained in a follow up email. Beyond the halo, he said, arsenic concentrations return to "background levels" associated with what is naturally occurring in bedrock.

"When we added up all the arsenic released from the 2023 fires, the majority was from outside the halo," Sutton wrote.

"It just so happens that most of the wildfires have not burned into the areas that have very high concentrations from the mine. And that's why we think we need to start identifying these priority areas to protect," he said in an interview.

Outstanding questions

The researchers used publicly available data to make their estimates. Sutton said they took into account different geographical landscapes, the concentration of the arsenic in those areas, and how deeply fires burned into the ground.

One thing that researchers don't know, said Sutton, is how hot the fires were as they burned.

"Whether it's sort of a cool, smouldering fire or a flaming crown fire really influences how these compounds are released to the atmosphere or to the water," he said. That's why they chose to provide a range for the amount of arsenic researchers estimate was released.

"Even at the low end, we're still seeing a lot of arsenic," he said.

Where all that arsenic ended up a concern of John B. Zoe is another outstanding question. Sutton said it's one that warrants future study.

"If it is airborne and in the air, it can be blown a distance but then it might settle back down and it could be held in place for a long time," he said. Sutton said organic soil is "really good" at holding on to compounds like arsenic.

"If it goes into the water, it can also get stored again in other wetlands and depressions and basically little bowls in the landscape. There's plenty of those around the Yellowknife area."