Research shows humans, not geology, source of high arsenic levels in Yellowknife

New research debunks a lingering belief that "natural arsenic" significantly contributes to high levels of the toxic substance around Yellowknife.

For many years, elevated levels have been attributed to natural bedrock geology, but geology experts from Queen's University say it's not so.

"The high values are due to pollution from human impact … Most of the emissions are from the roasters at Giant and Con [mines]," said Dr. Heather Jamieson, a professor and geology expert from Queen's. 

During more than half a century of mining, 19,000 tonnes of toxic arsenic trioxide dust went up the stacks of smelters at the Giant and Con gold mines and settled on the once-pristine land and lakes in and around Yellowknife.

The gold mining industry began in the late 1930s. Giant Mine closed in 2004, leaving a toxic legacy that has deeply changed the lives of people in N'Dilo.

The new study establishes a much lower figure for naturally occurring arsenic — five times less than previous estimates for the Yellowknife region.

They used tools that can distinguish particles of arsenic trioxide released from Giant Mine and Con Mine roaster stacks from natural arsenic in soil samples. 

Jamieson said the sampling work was done by two masters students who collected 479 soil samples which were then analyzed under a scanning electron microscope at the university.

It found arsenic trioxide in 80 per cent of samples as far as 30 kilometres from Yellowknife and researchers say this substance is a marker of mining activity.

"Within about 15 kilometres of Yellowknife, arsenic is predominantly hosted in arsenic trioxide … which is an arsenic mineral that's associated with mining emissions in the region," said Michael Palmer, the study's lead author and manager of the North Slave Research Centre at Yellowknife Aurora Research Institute.

"Understanding how the landscape will recover, how arsenic is dispersed and when that is going to happen is a very important and challenging question," he said. 

When the researchers were preparing to dig into the state of soil around Yellowknife, they met with Yellowknives Dene, with elders and the N.W.T.'s lands department, said Palmer.

"We really wanted to get a sense of where people wanted information from," said Palmer.

The study published in the international research journal Science of the Total Environment, calls for further research, such as where arsenic accumulates on the land and how long it will last, said Palmer.

"If we think of … the recovery of this landscape," he said, "future work should be devoted to understanding how much arsenic is still washing off the landscape from these soils into lakes and rivers. And what's its ultimate fate when it ends up in lakes and rivers?" 

'Definitely from mining emissions'

In the last year, Yellowknives Dene have held a demonstration at Giant Mine to demand a federal apology for the impacts to culture and life through loss of access to traditional lands.

The First Nation says a recent federal response to a petition that garnered more than 32,000 signatures simply "repeats talking points they presented to media before [YKDFN] had our first meeting with senior officials in January 2021."

They say the response fails to reflect over three months of discussions between the Yellowknives Dene and government representatives.

Giant Mine poisoned areas used by the Yellowknives Dene for harvesting, berry picking and other cultural activities, all infringements for which they've never been compensated. 

While science has dug into the question of arsenic distribution since the 1970s, it hasn't, until now, scientifically proven that the arsenic levels are caused by human activity. 

"There are certain arsenic minerals that are definitely from mining emissions versus other minerals that are predominantly natural," said Palmer.