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 Tłı̨chǫ man living in Behchokǫ̀, 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."

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.