Monitoring legacy arsenic in the Yellowknife area

Legacy Arsenic Human Health Risk Assessment

Legacy Arsenic Human Health Risk Assessment

Members of the public and Indigenous governments and Indigenous organizations expressed concern about what arsenic might be doing to their health, so the Government of the Northwest Territories Department of Environment and Climate Change, in partnership with the NWT Regional Office of Crown Indigenous Relations and Northern Affairs Canada, conducted a human health risk assessment (HHRA).

What did the HHRA measure?

The purpose of the HHRA was to measure potential exposure and assess the health risks for people living in cabins or houses on inland lakes in the area as well as people using the areas around Yellowknife, Ndilǫ, and Dettah for traditional and recreational activities. Arsenic exposure can cause cancer; therefore, this assessment looked at the risk of developing cancer from arsenic concentration in soil, indoor dust, water, sediment, and country foods in the area, that were above normal background levels. Arsenic and antimony were identified by study researchers, with input from Indigenous governments and Indigenous organizations and stakeholders, as the key contaminants to measure in this study in addition to a request from the Department of Health and Social Services to include mercury.

How does the Legacy Arsenic HHRA link to previous health and environmental studies?

The HHRA built upon the information we learned from the Giant Mine Remediation Project’s Human Health and Ecological Risk Assessment (HHERA). In other words, the risks associated with recreational and on the land activities were added to risks previously determined through the HHERA for people living in Yellowknife, Ndilo and Dettah. The results of this HHRA assessment reflect the risks for living in Yellowknife, Ndilǫ, or Dettah and the incremental risks associated with people using areas outside of their communities for recreational and traditional activities.

Short-term exposures from recreational activities such as hunting, harvesting, running, hiking, and swimming were studied. Exposure from eating fish and periodically drinking water from inland lakes in the area was also considered. Long term year-round exposure to residents living on or using inland lakes, including Vee, Landing, Ryan, Walsh, Banting, Prosperous, Madeline, Pontoon, Prelude, and River Lake were studied. A specific traditional land use (TLU) area was identified within a 25 km radius to the southeast of the Giant Mine site where current traditional land uses by local Indigenous peoples occur.


Arsenic exposure and associated risks of developing cancer were low.

Low risk means that the risk of getting cancer is similar to the risks from medical procedures such as annual x-rays at the dentist or having one CT scan.

Recreational Areas 

  • There is very low risk to people who live in Yellowknife, Ndilǫ, and Dettah, who enjoy all types of recreational areas within the study area and beyond. This includes fishing, hunting, harvesting, berry picking, swimming, boating, hiking, and camping.
  • There is very low risk to people living on the inland lakes, for example Vee, Landing, Ryan, Walsh, Banting, Prosperous, Madeline, Pontoon, Prelude, and River lakes, who eat country foods from the area.
  • Outside of the 10km area around the two mines, it is safe to eat mushrooms, except for mushrooms from the Tricholomataceae family including Tricholoma "pine" mushrooms, Clitocybe "common funnel" mushrooms and White Matsutake mushrooms. These mushrooms should not be eaten within 25km of the Giant and Con Mine, however, at distances of 25km and greater it is safe to eat mushrooms as long as mushrooms are properly identified. The same advice applies for chaga mushrooms harvesting in the area.

Traditional Land Use Areas

Risks are low for local Indigenous peoples who have a traditional lifestyle that includes hunting, fishing, and gathering within the study area and fishing from Great Slave Lake. Locally harvested country foods are a healthy, and often preferred, alternative to supermarket foods. The following activities represent a very low risk:

  • Eating fish from inland lakes, and Great Slave Lake in the study area, including their eyes, skin/fatty layer, and organs.
  • Eating berries from around the Yellowknife area. (However, it is still recommended to pick berries outside of10 km of the old Giant and Con mine sites. . 
  • Eating small mammals, land birds such as grouse or ptarmigan and waterfowl from around the Yellowknife area.
  • Eating fish that have been in Baker Creek is not a health concern. People can safely eat Arctic grayling caught in the Yellowknife area and within Great Slave Lake. 

Additional Analysis


There have been concerns expressed about swimming and wading on the shores of Ndilǫ and Latham Island and at Long Lake beach. The results from the HHERA determined that these activities pose a very low risk and can continue to be enjoyed safely. Children should not put mud or sediments in their mouths.


The GNWT Department of Health and Social Services (GNWT HSS) identified mercury as a constituent of interest in fish and requested that it be evaluated in the HHRA. The study determined that mercury concentrations in fish from all the inland lakes were below the Health Canada maximum limit of 0.5 mg/kg wet weight (ww) with the exception of 1 large northern pike from Mason Lake and 14 out of 18 northern pike from Lower Martin Lake. All lake whitefish in Lower Martin Lake were below the Health Canada maximum limit. GNWT HSS has issued an advisory for eating northern pike in Lower Martin Lake.

Ingraham Trail workers

At the request of the GNWT Department of Infrastructure, a separate evaluation was also completed to assess risks for outdoor workers along the Ingraham Trail/Highway 4, between Yellowknife and the Yellowknife River. The results tell us that workers are not at risk for arsenic exposure. Workers should always follow safe work practices, including wearing standard personal protection and using safety equipment.