Le rapport sur l’état de l’environnement 2022 est un document technique destiné à un usage interne. Il n’est disponible qu’en anglais.

Introduction

The Northwest Territories (NWT) has very low levels of pollution compared to many parts of the world. It is important for people in the NWT to know whether their environment and food are safe and healthy.

The Environmental Protection Act defines a contaminant as:

“any noise, heat, vibration or substance and includes such other substance as the Minister may prescribe that, where discharged into the environment,

(a) endangers the health, safety or welfare of persons,

(b) interferes or is likely to interfere with normal enjoyment of life or property,

(c) endangers the health of animal life, or

(d) causes or is likely to cause damage to plant life or to property”. 

 

This focal point includes indicators about substances that have been introduced into the environment (contaminant) that endanger the health, safety or welfare of animal, and may be harmful to humans.  Potentially harmful substances that are naturally present in the environment (e.g. mercury, arsenic) are not considered contaminants even though they can be harmful depending on the amount and length of exposure. Types of contaminants found in the northern Canada include petroleum hydrocarbons, persistent organic pollutants (POPs), heavy metals and radionuclides.

At this time, this focal point tracks the number of spills of hazardous substances reported in the NWT as well as potential contaminants in caribou, moose, and fish.

Air quality and the level of contaminants in the atmosphere are reported in the Air focal point, and information about contaminants in water is reported in the Water focal point.

8.1. Trends in spills of hazardous materials

This indicator tracks the number and type of hazardous material spills in the NWT, which provides information on risk to the environment.

Hazardous materials include contaminants, such as petroleum hydrocarbons and metals. Spills are reported within 24 hours, investigated and information on each event is compiled.

The Department of Environment and Climate Change (ECC) has maintained a database of all hazardous material spills reported in the NWT since 1971. Information for this indicator is obtained from the Hazardous Materials Spill Database and analysis undertaken for the annual Northwest Territories Spills Report.

This indicator was prepared by the Government of the Northwest Territories, Department of Environment and Climate Change, using information obtained the Environmental Protection and Waste Management Division.  

 

NWT Focus

Petroleum Hydrocarbons

Petroleum degrades very slowly in cold climates which can increase the risk of exposure to wildlife and plants. Petroleum spills are primarily associated with the transport and storage of fuels. Petroleum is transported using tanker trucks on the highway and the winter road systems. Petroleum is also transported to remote communities and industrial sites using barges along the waterways. Once delivered the product is stored in large quantities for use in vehicles, furnaces, electrical generators and other industrial needs. (Ref 1)

Mine/Drilling Waste (waste rock, tailings, impacted mine water)

Mining processes create a significant amount of waste rock and tailings. This material must be managed appropriately to protect the downstream aquatic environment. Dust from dry tailings ponds must also be managed as it can be distributed to surrounding land and water by wind.

The potential for contamination may also be associated with the weathering of mine rock exposed during the mining activities (iron pyrite and other sulphur bearing minerals) to atmospheric oxygen in the presence of moisture leading to acid weathering reactions. These reactions could lead to acid rock drainage. This leachate is a potential long-term source of metals to the environment where they can be taken up by plants and animals.

The discharge of drilling wastes and accidental spills of petroleum are the primary sources of environmental contamination that occurs during oil and gas activities. Waste drilling fluids are commonly disposed of into sumps adjacent to the drilling rig. The waste fluids can contain various pollutants ranging from metal salts to petroleum hydrocarbons. (Ref 1)

 

Current View: status and trend

In 2020, 212 spills were reported (Figure 1). There were 122 spills less than 100 litres or 100 kilograms, or 58%. These spills are considered small and consistently make up the majority of the spills reported in the NWT each year. They usually result from blown hydraulic lines or leaks from heavy equipment, haul trucks or smaller industrial vehicles leaking engine and transmission fluids.

Figure 1. Number of spills reported by year from 1990-2020

 

Wastewater, which includes sewage, mine tailings and other types of contaminated water, accounted for 23% of reported spills in 2020 (Figure 2). The remaining spills are fuel oil and various chemicals, such as antifreeze and glycol-based products for vehicles, lube oil and other hydrocarbons.

Figure 2. Number of spills by product for 2020

Reported spills in 2020 by sector are 23% from mining; 31% from federal, territorial and municipal government activities; 12% from oil and gas exploration and development; 15% from private activities; 3% from transportation; and 16% from unknown or other parties.

Since the release of the Homeowners’ Guide to Oil Tanks (Guide) and the requirement for new residential fuel oil tanks to be double walled in 2010, the number of spills reported from residential fuel oil tanks (defined as tanks under 1,136 litres) have shown a continuous downward trend Figure 3.

The Guide was developed to inform individual homeowners and commercial building and property owners of the potential environmental and financial liabilities associated with a fuel oil spill. It also provides some simple, practical steps that can minimize the chances of a spill.

Figure 3. Number of spills from residential fuel oil tanks

 

Looking forward

Changes in the number of spills of hazardous materials occurring each year correlate to changes in the NWT’s resource-based economy. Trends in spills larger than 100 litres can rapidly decrease with reduced activities in the mining, oil and gas sectors. However, efforts to reduce the number of potential spills with more efficient prevention and education programs continue.

Developing clean-up technologies in extremely cold and remote environments remains a challenge. A petroleum spill from a barge or tanker in Arctic fresh and marine waters has the potential to create a major environmental disaster. The current technology for cleaning up petroleum spills is not advanced enough to fully remove oil from frozen water bodies. Tanker trucks also pose a threat to the Arctic environment as they travel northern highways and ice roads. A spill from a tanker truck can impact the adjacent terrestrial and aquatic environments. (Ref 1)

 

Looking around

The Northwest Territories/Nunavut Spills Working Group was established to foster a cooperative and one-window approach to spill response in the North. This group ensures a comprehensive regulatory coverage of all spills in the NWT between federal and territorial governments and the Inuvialuit Land Administration.

Internationally, ECC is also a member of the Arctic Council's Emergency Prevention Preparedness and Response (EPPR) working group. This working group focuses on risk analysis and guidance documentation but is currently pausing all official meetings.

 

Find out more

More details are available on the NWT Hazardous Materials Spill Database and in the annual reports.

 

References

Ref.1. Environmental Protection. Government of the Northwest Territories. 1998. Pressures on the Arctic ecosystem from human activities. GNWT-ECC.

 

8.2 Trends in contaminants in wildlife

This indicator measures the levels of selected heavy metals (cadmium and mercury) in barren-ground caribou and moose in the Northwest Territories (NWT).

Cadmium and mercury in the environment come from both natural sources and human activities. Long-range atmospheric transport of cadmium and mercury can bring these contaminants from industrial sources outside of the NWT, in addition to natural locally occurring sources of both of these metals. They are absorbed by vegetation that is eaten by caribou and moose, and accumulate in the liver and kidneys, and to a lesser extent in the muscle.

This indicator was prepared by the Government of the Northwest Territories, Department of Environment and Climate Change, using information obtained the Wildlife and Fish Division and management partners.

 

NWT Focus

Caribou and moose are an important food source in communities across the NWT. These species, including liver and kidney, are a significant part of traditional Dene, Métis and Inuit diets (Ref. 1, 2).

The concentration of cadmium and mercury in kidneys is measured to monitor exposure to these two metals in the tissues of harvested species, changes over time, and possible impacts on wildlife health. This indicator also provides some insights into natural background levels of these metals in the environment, and changes in contaminants entering the NWT environment through local or global man-made sources (Ref. 3).

 

Current View: status and trend

In the NWT, contaminants have been monitored in many of the barren-ground caribou herds over time through work by ECC and the federal Northern Contaminants Program.

Monitoring of contaminants has also occurred for moose in the Dehcho region of the NWT from 2005 to 2007 and again between 2011 and 2016. Monitoring for contaminants in moose was conducted in the South Slave region during the mid 2010s. Findings from these programs are summarized below.

 

Mercury in Caribou

The level of mercury in the kidneys of NWT caribou is very low and does not pose a health risk to either caribou or the people who eat caribou (Figure 1). Mercury levels tend to be higher in caribou in the spring than fall and higher in females compared to males. Both the meat and organs of NWT caribou are safe to eat.

Figure 1. Mercury level in kidneys of NWT caribou populations, 1991-2018 (Ref. 8). Threshold for potential effects on caribou is calculated at 130.5 ppm (Ref. 9).

 

Mercury levels did not change significantly over time in the Qamanirjuaq caribou population (2006-2018) and declined slightly in Porcupine caribou (1.5%/year; 1991-2017) (Ref. 10). Increasing mercury levels have been seen in some other northern wildlife species, particularly marine mammals and fish. This could be a result of increasing available atmospheric mercury in some ecosystems combined with changes in the naturally occurring cycle of mercury in the Arctic environment (Ref. 9). For more information about mercury in fish, see Pressure – Contaminants: Indicator 8.3.

The primary anthropogenic source of mercury exposure is long-range atmospheric transport from other parts of the world (Ref. 3). Sources of mercury include mining, milling and smelting of mercury-containing ores, the use of mercury in small scale artisanal gold mining, coal-burning plants, municipal wastewater treatment plants, pulp and paper mills and fungicides. Human activities have increased total atmospheric mercury concentrations by about 450% above natural levels (Ref. 3). Mercury is a toxic element that can concentrate in brain, liver, and kidney tissue, and to a lesser extent, in muscle tissue, with higher concentrations bioaccumulating in animals (or humans) higher up on the food chain. It can affect neurological function and cause poor growth, and kidney damage. The developing fetus and child are most at risk as their nervous systems are being formed and can be adversely affected by mercury accumulation.

 

Cadmium in caribou

The levels of cadmium caribou in the NWT are not of concern for caribou health, and caribou remain a safe and healthy food choice. Cadmium levels vary considerably with age (increasing levels in older animals), season (higher in spring than in fall), and sex (higher in female vs. male caribou) (Ref. 11), but the levels of cadmium in NWT caribou kidneys are generally low (Figure 2).

Wildlife exposure to cadmium reflects regional and local differences of the type of rocks and soil in the area, as well as local and long-range sources of cadmium from human activities. Industrial uses of cadmium include production of cadmium-plated metal, nickel-cadmium batteries, pigment and plastic stabilizers, and mining and refinement of copper, lead and zinc (Ref. 11). Long-range atmospheric transport can distribute this cadmium to other places. Lichens absorb cadmium directly from the air and pass it on to the caribou that feed on the lichen. Cadmium can accumulate in long-lived herbivores such as caribou, but levels seen in the NWT are not high enough to be harmful to their health. Studies show that sublethal effects of cadmium occur at 150 ppm in kidneys (Ref. 9). The levels measured in the NWT are well below this threshold (Ref. 8).

Figure 2. Cadmium level in kidneys of NWT caribou populations, 1991-2018 (Ref. 8). Sub-lethal effects threshold noted at 150 ppm (Ref. 12).

 

Contaminants in moose

Monitoring of metals and persistent organic pollutants in moose from the Dehcho Region and South Slave Regions of the NWT occurred to identify levels of these contaminants in an important traditional food source (Ref. 13, 14, 15, 16). As part of a moose health monitoring program in the South Slave region, the liver and kidney of 15 moose harvested between 2009 and 2013 were analyzed for 14 elements (Ref. 17).

Tissue samples from moose harvested in the Mackenzie and Liard valleys were provided by local harvesters. Analyses of these samples provided baseline information on the levels of 32 elements in kidney, liver, and muscle tissues (see the element list in Table 1).

Levels of most elements including arsenic, lead, mercury, selenium, zinc, and radionuclide levels were low and not of concern for the health of the animals.

Table 1: List of elements and detection limits (DLs) analyzed in moose tissues in the 2007 and 2016 analyses, reported in wet weight (ww). All elements were sampled in 2007 and 2016, except these marked by * were sampled only in 2016. (Ref. 15)

Element	DL (mg/kg ww)	Element	DL (mg/kg ww)
Aluminum (Al)	0.02	Magnesium (Mg)*	0.1
Antimony (Sb)	0.001	Manganese (Mn)	0.005
Arsenic (As)	0.002	Mercury (Hg)	0.002
Boron (B)*	0.05	Molybdenum (Mo)	0.001
Barium (Ba)	0.005	Nickel (Ni)	0.005
Beryllium (Be)	0.0001	Palladium (Pd)	0.01
Bismuth (Bi)	0.0001	Platinum (Pt)	0.001
Cadmium (Cd)	0.0001	Potassium (K0	0.2
Calcium (Ca)*	0.2	Rubidium (Rb)	0.001
Cesium (Cs)	0.0005	Selenium (Se)	0.01
Chromium (Cr)	0.001	Silver (Ag)	0.0001
Cobalt (Co)	0.0002	Strontium (Sr)	0.005
Copper (Cu)	0.01	Thallium (Tl)	0.0001
Gallium (Ga)	0.0001	Tin (Sn)	0.01
Iron (Fe)	0.05	Uranium (U)	0.0001
Lanthanum (La)	0.0001	Vanadium (V)	0.001
Lead (Pb)	0.001	Zinc (Zn)	0.01
Lithium (Li)	0.01

Liver samples from the Dehcho (n=7) and South Slave (n=7) were tested for the presence of persistent organic pollutants (POPs) including polychlorinated biphenyls (PCBs), DDT related compounds, toxaphene, brominated diphenyl ethers (PBDEs) and perfluorinated alkyl substances (PFASs). PFASs were the most prominent POP and Decabromodiphenyl ether (BDE-209) the most prominent PBDE, similar to that found in other arctic and subarctic herbivores. Both are generally particle-borne and relatively non-volatile.

The overall concentrations of major groups of POPs in the NWT were consistently low. Interestingly, concentrations of POPs were higher in moose harvested in the Dehcho than in the South Slave (Ref. 14) but sample sizes were small. The reasons for this difference are unknown.

Non-resident hunters provided tissue samples from moose harvested in the southern Mackenzie Mountains from 2007- to 2009 and 2011 to 2016. Additional muscle and kidney samples were collected from moose harvested in the Mackenzie Mountains from 2010 to 2013 (Ref. 5).

The levels of cadmium in the organs of moose harvested in the Mackenzie Mountains were approximately 10 times higher than that of moose harvested in the valleys. This was attributed to natural mineralization of soils, then bioaccumulation of cadmium by willows in an area with high geologic sources of this element (Ref. 6), resulting in enhanced uptake in the moose diet (Ref. 4, 5), Cadmium levels in Mackenzie Mountain moose kidneys were often >30 mg/kg wet weight, in the range of kidney dysfunction (Ref. 18, 19) yet there was no histological evidence to show cadmium toxicity was impairing moose kidney function (Ref. 5).

Elevated levels of cadmium in moose kidney in the southern Mackenzie Mountains led to advisories from GNWT Department Health and Social Services to limit consumption of moose kidneys from that area (Ref. 6). The advisory was renewed in 2017, and a consumption limit of 56 g of liver or 37 g of kidney per month of moose organs from that region was recommended (Ref. 7).

Mercury concentrations in moose organs (Ref. 15) were considerably lower than those reported for barren-ground caribou (Ref. 20). There was no trend in mercury concentrations in moose between 2007 and 2009 and 2011 and 2016.

 

Looking around

Terrestrial mammals in the NWT are generally found to have lower concentrations of pollutants than animals from more southern locations or species that are part of the marine ecosystem (Ref. 3).

Cadmium levels are naturally high in some areas of the Yukon and the southern Mackenzie Mountains shared by the Yukon and NWT (Ref. 21). Analysis of caribou teeth from 5,000 years ago indicate that the Carcross caribou herd from southern Yukon had higher cadmium levels than at present. This is likely due to a shift in habitat over that time. The area is still rich in cadmium, but no longer has an abundance of willows which tend to concentrate soil cadmium and make it available to herbivores.

Overall, the levels of elements in NWT moose were similar to those found in moose from other regions of Canada and Alaska. The overall concentrations of major groups of POPs found in moose from the NWT were consistently low and comparable to limited data available from Scandinavia (Ref. 22). Studies agree that the level of contaminants in moose is currently low and not of concern for the health neither of moose nor of those consuming moose organs (Ref. 23).

The Canadian Arctic Contaminants Assessment Report Series provide comprehensive result summaries on studies conducted in Arctic Canada, including in the NWT (Ref. 22).

 

Looking forward

Currently, contaminant levels are not a concern for caribou and moose health, but ongoing monitoring is important to assess for potential changes over time. If new pollutants of concern are detected or increase, consideration should be given to include them in ongoing monitoring to assess their source, levels and potential significance to wildlife, human, environmental health.

 

Find out more

• For more Information on the federal Northern Contaminants Program see http://science.gc.ca/eic/site/063.nsf/eng/h_67223C7F.html
• For more Information on Canadian Arctic Contaminants Assessment Reports see https://science.gc.ca/eic/site/063.nsf/eng/h_7FE5B2F8.html

For more information on contaminants in NWT species, see also the indicator Contaminants in fish.

 

Technical notes

The Northern Contaminant Program (NCP) is a national monitoring program that tracks contaminants in the air, water, wildlife and other parts of the Arctic environment. As part of this national initiative, the Arctic Caribou Contaminant Monitoring Program is a collaborative study in the NWT, Nunavut and the Yukon to measure contaminant levels in selected caribou populations across the north over time to track changes in contaminant levels.

Part per million (ppm) = µg/g=mg/kg.

Scheuhammer's (Ref. 9) threshold potential effects on health of study animals for mercury are 30 ppm wet weight. A conversion factor of 77% water in kidney (Ref. 6) was used to report concentrations in dry weight.

Threshold potential for renal cadmium toxicity is 30-60mg/kg (Ref. 18, 19).

References

Ref. 1.  Berti, P.R., O. Receveur, H.M. Chan, and H.V. Kuhnlein. 1998. Dietary exposure to chemical contaminants from traditional food among adult Dene/Metis in the western Northwest Territories, Canada. Environmental Research 76:131-142.

Ref. 2.  Kenny, T-A., M. Fillion, S. Simpkin, S.D. Wesche and H.M. Chan. 2018. Caribou (Rangifer tarandus) and Inuit Nutrition Security in Canada. EcoHealth 15:590-607.

Ref. 3.  UN Environment, 2019. Global Mercury Assessment 2018. UN Environment Programme, Chemicals and Health Branch Geneva, Switzerland.

Ref. 4.  Reimann, C., P. Englmaier, K. Fabian, L. Gough, P. Lamothe and D. Smith. 2015. Biogeochemical plant-soil interaction: Variable element composition in leaves of four plant species collected along a south-north transect at the southern tip of Norway. Science of the Total Environment 506/507:480-495. Available at: http://dx.doi.org/10.1016/j.scitotenv.2014.10.079

Ref. 5.  Larter, N.C., C.R. Macdonald, B.T. Elkin, X. Wang, N.J. Harms, M. Gamberg and D.C.G. Muir. 2016. Cadmium and other elements in tissues from four ungulate species from the Mackenzie Mountain region of the Northwest Territories, Canada. Ecotoxicology and Environmental Safety 132:9-17.

Ref. 6.  Larter, N.C. and K. Kandola. 2010. Levels of arsenic, cadmium, lead, mercury, selenium, and zinc in various tissues of moose harvested in the Dehcho, Northwest Territories. Circumpolar Health Supplement 7:351-355.

Ref. 7.  Health and Social Services, Government of the Northwest Territories. 2017. Moose organ consumption notice. Available at: www.hss.gov.nt.ca/sites/www.hss.gov.nt.ca/files/resources/moose-organ-co...

Ref. 8.  Gamberg, Mary, unpublished data.

Ref. 9. Scheuhammer, A.M. 1991. Effects of acidification on the availability of toxic metals and calcium to wild birds and mammals. Environmental Pollution 71:329-375.

Ref. 10. Macdonald, C. 2021. Temporal Trend Analysis of the Core Monitoring Program for the Northern Contaminants Program – 2021. Unpublished report. 66 pp.

Ref. 11. Gamberg, M., B. Braune, E. Davey, B. Elkin, P.F. Hoekstra, D. Kennedy, C. Macdonald, D. Muir, A. Nirwal, M Wayland and B. Zeeb. 2005. Spatial and temporal trends of contaminants in terrestrial biota from the Canadian Arctic. Sci Total Environment 351-352:148-164.

Ref. 12. Larter, N.C., and J.A. Nagy. 2000. A comparison of heavy metal levels in the kidneys of high Arctic and mainland caribou populations in the Northwest Territories of Canada. The science of the total environment 246:109-119. Note: Subsequent delineation of NWT barren-ground caribou subpopulations (Nagy et al. 2010) divided the Bluenose into Bluenose-East, Bluenose-West and Cape Bathurst subpopulations. The caribou sampled in Ref. 12 were from the Cape Bathurst subpopulation.

Ref. 13. Larter, N.C. 2009. A program to monitor moose populations in the Dehcho region, Northwest Territories, Canada. Alces 45:89-99.

Ref. 14. Larter, Nicholas C., Derek Muir, Xiaowa Wang, Danny G. Allaire, Allicia Kelly, and Karl Cox. 2017. Persistent Organic Pollutants in the Livers of Moose Harvested in the Southern Northwest Territories, Canada. Alces 53: 65–83.

Ref. 15. Larter, Nicholas C, Colin R. Macdonald, B.T. Elkin, D.C.G. Muir, and X. Wang. 2018. Analysis of Cadmium, Mercury and Other Elements in Mackenzie Valley Moose Tissues Collected from 2005 to 2016. File Report No. 152. Government of the Northwest Territories.

Ref. 16. Larter, Nicholas C, Colin R Macdonald, and N Jane Harms. 2018. Comparing Kidney Histology: Moose Harvested in the Mackenzie Valley Versus the Mackenzie Mountains. No. 272. Manuscript Report. Environment and Climate , Government of the Northwest Territories.

Ref. 17. Stasiak, I. 2014. A report on the South Slave moose health and monitoring program 2009-2013. ECC South Slave.

Ref. 18. Aughey, E., G.S. Fell, R. Scott and M. Black. 1984. Histopathology of early effects of oral cadmium in the rat kidney. Environmental Health Perspectives 54:153-161.

Ref. 19. Outridge, P.M., D.D. MacDonald, E. Porter, and I.D. Cuthbert. 1994. An evaluation of the ecological hazards associated with cadmium in the Canadian environment. Environ Rev 2:91-107.

Ref. 20. Gamberg, M., B. Braune, E. Davey, B. Elkin, P.F. Hoekstra, D. Kennedy, C. Macdonald, D. Muir, A. Nirwal, M. Wayland and B. Zeeb. 2005. Spatial and temporal trends of contaminants in terrestrial biota from the Canadian Arctic. Science of the Total Environment 351/352: 148-164. doi: 10.1016/j.scitotenv.2004.10.032.

Ref. 21. Hegel, T.M. and Russell, K. 2013. Status of northern mountain caribou (Rangifer tarandus caribou) in Yukon, Canada. Rangifer 33(2):59.

Ref. 22. Northern Contaminants Program. 2019. Canadian Arctic Contaminants Assessment Report Serie. Available at https://science.gc.ca/eic/site/063.nsf/eng/h_97658.html.

Ref. 23. Ratelle, M, Li, X., Laird, B.D. 2018. Cadmium exposure in First Nations communities of the Northwest Territories, Canada: smoking is a greater contributor than consumption of cadmium-accumulating organ meats. Env. Science: Processes and impacts. 20:1441-1453.

 

8.3 Status of Mercury and Other Contaminants in Fish

This indicator measures mercury concentrations in fish inhabiting the lakes, rivers, and the major river deltas (Slave River and Mackenzie River) of the Northwest Territories (NWT), and some additional analyses of fish from marine waters (Beaufort Sea).

Mercury can be toxic, and a guideline of 0.5 ppm (µg/g wet weight) has been established for the commercial sale of fish.

Mercury is a naturally occurring metal that exists in both inorganic and organic forms. Mercury is transformed from the inorganic form into the organic form, more commonly known as methyl mercury (MeHg), by a process called methylation (see technical notes). Bacteria are largely responsible for these transformations and conditions favorable for their growth include warmer temperatures, a rich organic substrate, and slightly acidic waters. Thus, mercury is more readily methylated in warmer than cold water bodies and in wetland and weedy regions of a lake or river than the offshore regions of lakes. The NWT contains thousands of water bodies of differing areas, depths, and water chemistry which contribute to the natural variability in mercury concentrations between such systems.

This indicator was prepared by Marlene Evans, Environment and Climate Change Canada (Saskatoon, SK) and reviewed by the Government of the Northwest Territories, Department of Environment and Climate Change.

 

NWT Focus

Information on mercury in fish is needed to support the commercial, domestic and sports fisheries in the NWT with respect to fish consumption (see technical notes on fish consumption advisories).

While mercury occurs naturally in the environment, human activity can affect both the concentration and form of that mercury. Historically mercury was used in many industrial processes such as chloro-alkali plants, including those that operated around pulp and paper mills, and was used in gold mining operations to extract gold from the ore. Mercury also has numerous uses including in medicines, cosmetics, light bulbs, thermometers, batteries, etc., many of which are being phased out. Large amounts of mercury are also released to the environment with coal burning and other anthropogenic activities, and such releases are believed to be responsible for increased concentrations of mercury in aquatic environments in remote regions (Ref.18, 21.).

The strongest evidence for such increases in mercury emissions has come from sediment and ice core studies which can examine trends over tens to hundreds of years (Muir et al. 2009) . The record of mercury concentrations in fish are generally limited to within the last 50 years.

Mercury concentrations can be high in fish in recently flooded lakes for reservoir formation. This occurs because conditions are created which result in an increase in mercury methylation rates as the flooded terrestrial vegetation enhances the growth of methylating bacteria. Mercury methylation occurs primarily in aquatic environments. Mercury concentrations can also be high in fish in lakes impacted by acidic emissions from coal burning and smelting operations. This is because mercury transformation by methylating bacteria is enhanced in somewhat acidic waters. Mercury concentrations are higher in predatory (piscivores) fish such as lake trout and northern pike than fish that eat invertebrates such as lake whitefish and suckers. Mercury concentrations also increase with fish age and length. (Ref. 22)

 

Current View: status and trends

 

Sampling efforts

Many observations have been made of mercury concentrations in fish in the NWT over the past 50 years. Some of the earliest measurements, beginning in the early 1970s, were made by the Canadian Food Inspection Agency, who measured mercury in small numbers of fish from lakes, rivers and delta sites in Canada, including the NWT (Ref. 4, 22). Sample size was small (generally <10) and fish age was not determined. These data were not published, and the program ended in the early 1990s. More measurements of factors influencing mercury concentration in fish (e.g., age) and larger sample sizes began to be made in the early 1990s as part of special studies conducted by the Department of Indian and Northern Affairs, (e.g., the multiyear Slave and Liard River studies) and industry (studies around dams such as the Taltson River and mining developments such as Giauque Lake (Discovery Mine)) (Ref. 4, 5,22).

Since the 1970s, mercury concentrations have been measured in more than 100 lakes, rivers, and deltas in the NWT. Lockhart et al. (2005) compiled much of the unpublished data generated between 1970 and 2002 and reported on average mercury concentrations in six species of fish by year, water body and, for some larger systems, sites within the lake or river. In total, they reported that 85 water bodies had been investigated at least once. In the late 1990s and early 2000s, the Northern Contaminants Program (NCP) began including mercury in its research and monitoring programs and since then there have been an increasing number of studies under NCP, the Cumulative Impact Monitoring Program (CIMP), the Slave River Delta partnership, industry monitoring, etc. Since then, the database has expanded to over 120 lakes with more in-depth studies conducted at many lakes. A second synthesis manuscript updating the Lockhart study is in preparation; several of the figures produced here are based on this ongoing synthesis which is being updated as the data base grows (Ref. 22).

Figure 1. Map showing the locations of the primary NWT lakes in which mercury concentrations have been determined in fish since the late 1990s. Mercury and organic contaminant trends are being monitored in Great Slave Lake (lake trout, burbot), the Mackenzie River at Fort Good Hope (burbot) and Great Bear Lake (lake trout). Map prepared by M. Evans, ECCC.

 

Highlights include:

• The majority of sampling from 1973 to 2021 has focused on lakes, and generally a single location within a lake. The notable exception is Great Slave Lake, which has a commercial fishery and various fishery zones in its western half and where lake trout and burbot are investigated at eastern and western locations. Most lakes have been sampled only once, giving a broad spatial characterization of average mercury concentrations in fish but a growing number of lakes are being monitored regularly as part of NCP and CIMP community-based monitoring programs including a series of lakes in the Deh Cho and the Tłı̨chǫ. Great Bear Lake, Great Slave Lake and several Dehcho lakes have a growing record as part of research-focused studies.
• The Mackenzie River at Fort Good Hope and the Slave River at Fort Smith are the most frequently sampled river sites, the former as part of the NCP biomonitoring program and the latter as part of various special studies, e.g., the Slave River baseline assessment study conducted from 1990 to 1994 (McCarthy et al. 1997), other periodic studies under NCP, the Slave River and Delta partnership and university led studies (Evans et al. 2005b, Carr et al. 2017, Tendler et al. 2020). Few measurements have been made in the Hay, Liard, Peel and other rivers in recent years.
• Several studies have been conducted on the Slave River delta as part of Slave River studies noted above. Information on mercury concentrations in fish in the Mackenzie River delta are more limited with Lockhart et al. (2005) reporting measurements made only in 1971, 1981 and 1989. Sea-run char have been measured for mercury on a number of occasions for stocks associated with community harvests or inland residence (Evans et al. 2015).
• Most of the measurements of mercury in fish have focused on predatory species, which have a greater likelihood of concentrations approaching or exceeding the 0.5 µg/g guideline, and lake whitefish, which are widely caught and important in the domestic and commercial fisheries (Figure 1). Consequently, mercury concentrations in cisco, longnose and white sucker have been measured in a smaller number of lakes.

(Figure 1). Consequently, mercury concentrations in cisco, longnose and white sucker have been measured in a smaller number of lakes.

Figure 2. The approximate number of lakes which common species of fish in the NWT have had mercury concentrations determined on at least one occasion over 1991-2017. Data are shown only to show broad patterns. Source: Ref.22.

 

Overall Features of Mercury in Fish

A summary of mercury concentrations in fish in the lakes, rivers and deltas of the NWT are presented in a publication by Lockhart et al. (2005). These authors compiled mercury measurements made between 1991 and 2001 by various organizations including the Canadian Food Agency, the GNWT and federal government. First, these data show (Figure 2) that average mercury concentrations in fish that consume plankton and benthos such as cisco, longnose and white sucker, and lake whitefish are very low (generally ≤ 0.2 ppm). In contrast, lake-average concentrations are higher in predatory fish such as lake trout, northern pike, and walleye with fish in many lakes approaching or exceeding average concentrations of 0.5 ppm. While overall burbot mercury concentrations were lower from 1991 to 2005 than 2006 to 2017, different lakes were investigated in different years and so these data are not useful for assessing temporal trends.

Figure 3. Average mercury concentration in primary fish species investigated in NWT lakes over two time periods (Ref. 22)

 

Factors affecting mercury in fish

Several past and ongoing studies have investigated the factors affecting average mercury concentrations in fish in NWT lakes. One of the most important is lake size with average mercury concentrations in fish tending to be higher in small than large lakes (Figure 3). While there are several reasons for this, many of them relate to the fact that the transformation of inorganic to organic mercury occurs more readily in small lakes, which tend to be warmer, shallower, and have more dissolved and particulate organic matter that facilitates these transformations (Evans et al. 2005a). Fish growth rates, mercury concentrations in benthos and features such as watershed size and catchment characteristics also are important (Moslemi-Aqdam et al. 2021)

Figure 4. Average mercury concentrations in northern pike and lake trout for lakes of four size classes. Source: Ref.22.

 

Larger and older fish tend to have higher mercury concentrations than the smaller and younger fish within that species. In the NWT, predatory fish older than 10 years inhabiting small to medium size lakes often have mercury concentrations which exceed 0.5 ppm (Evans et al. 2005a). Mercury concentrations also tend to be lower in lakes that are fished regularly as the large and older fish are removed, lowering the average age and size of the remaining fish population. Fish also tend to grow faster in fished lakes because of reduced competition for food, also resulting in lower mercury concentrations. Remote lakes such as Lac Ste. Therese, south of Great Bear Lake, is seldom fished and hence has old fish (many 30 years and older) with high mercury concentrations. For example, during 1975 to 1990 the average mercury concentrations in lake trout, walleye and northern pike in Lac Ste. Therese generally ranged from 1.0-1.4 ppm (Ref. 22).

 

Mining activity and mercury in fish: There also are occasions where mercury concentrations are high in fish due to human activity. One such case is Giauque Lake, north of Yellowknife and the site of the Discovery mine which operated between 1946 and 1969. Mercury was used in the milling process and tailings were deposited into the lake between 1965 and 1968; waste material also was deposited on the landscape. In some situations, sulfur in tailings creates acidic conditions which enhance the mercury methylation rates with resulting high concentrations in fish such as in Giauque Lake. High concentrations of mercury in the sediment and other conditions associated with tailings resulted in round whitefish, lake trout, and northern pike having very high average mercury concentrations at 1.22, 3.79 and 1.75 µg/g respectively (Moore and Sutherland 1980).

In contrast, Giant Mine in Yellowknife used a roasting process to extract gold from the ore and so did not produce significant mercury contamination of the surrounding environment although arsenic contamination is significant (Cott et al. 2016). Other mines such as the lead zinc mine at Pine Point had no impact on mercury concentrations in fish in the Resolution Bay area (Evans et al. 1998) and compliance monitoring conducted by the diamond mines to date have shown no indication of mercury contamination of fish as a result of their activities (Ref. 22).

 

Reservoirs and mercury in fish: Reservoir creation, by flooding the landscape and transferring rich amounts of organic terrestrial material into the aquatic landscape results in a large increase in mercury methylation rates and an increase in mercury concentrations in fish. For example, Nonacho Lake was transformed into a reservoir in 1968 when a dam was placed on its outflow to provide additional water storage for the Twin Gorges Generating Station, installed in 1965. Average mercury concentrations in lake trout in 1978 were 1.06 ppm versus 0.54 ppm in 1986, 18 years after dam installation, were suggesting some recovery (Figure 4). Mercury concentrations in 2013 averaged 0.33 ± 0.27µg/g)) with further evidence of recovery from the initially high mercury concentrations that occurred after reservoir flooding ((Dewar 2016). Fish were old (19 ± 6 yr).

Figure 5. Mercury (mean ± 1 standard deviation) concentrations in lake trout measured from Nonacho Lake on various occasions after dam construction in 1968. Source: (Dewar 2016).

 

Mercury Trends in fish: Lake trout in Great Slave Lake

Mercury has been measured in lake trout in Great Slave Lake since 1993 under NCP, specifically from the commercial fishery which operates on the west side of the lake and from the domestic fishery at Lutsel K’e on the east side (Figure 5). Older data also exist from the monitoring of the commercial fish catch in the west side of the lake. Mercury concentrations are showing a small temporal trend of increase particularly when fish length is included as a variable in the statistical analyses (Evans et al. 2013). Mercury concentrations tended to be slightly higher in fish from the west than the east half of the lake, probably because the shallower and warmer waters in the west are more favorable for the transformation of inorganic mercury to organic mercury. Nevertheless, average mercury concentrations are well below commercial sale guidelines (below 0.5 ppm (µg/g)).

Figure 6. Trends in average mercury concentrations (mean ± 1 standard error) in lake trout harvested from two fisheries on Great Slave Lake. The commercial fishery operates out of Hay River, on the west side of the lake and Lutsel K’e is a small First Nation community on the east side. Also shown is the regression line. The turquoise dot is not included in the analyses as these fish are considered an outlier with no explanation for their high mercury concentration in terms of their length, age or trophic feeding. Source: Ref. 22.

Burbot monitored at Fort Resolution and Lutsel K’e on Great Slave Lake also are showing increasing trends of mercury when fish length is considered in statistical analyses (Figure 6) (Evans et al. 2013). Burbot monitored on the Mackenzie River from Fort Good Hope are showing an even stronger trend of mercury increase. This trend has been attributed to warming trends and increased productivity that, in part, facilitate the increased transformed of inorganic mercury to organic mercury (Carrie et al. 2010). Higher mercury concentrations in Mackenzie River than Great Slave Lake burbot are likely due to the warmer temperatures and the higher productivity of the ecosystems inhabited by Mackenzie River burbot than Great Slave Lake. A recent review of mercury concentrations in freshwater fish across western Canada and the United States concluded that mercury concentrations tend to be higher in fish in river than lake ecosystems (Eagles-Smith et al. 2016).

Figure 7. Trends in average mercury concentrations (mean ± 1 standard error) in burbot harvested from two fisheries on Great Slave Lake and one on the Mackenzie River. Also shown is the regression line. Source: Ref. 22, 33)

 

Other metals

While mercury has been the primary metal measured in fish, early studies measured other metals, mainly arsenic, cadmium and selenium (Ref. 23, 27). In recent years, with the advent of new technology, 30 or more metals can be measured simultaneously in the same sample analysis. Many metals such as copper, zinc, manganese, cobalt and vanadium are essential for human health.

 Unlike mercury, other metals do not strongly bioaccumulate in organisms and biomagnify in food webs. Nor are there concentration guidelines for these metals for the commercial sale of fish. Arsenic is an interesting metal, similar to mercury in that it occurs in an elemental, organic and inorganic form with inorganic arsenic being the toxic form. While arsenic concentrations are elevated in soils and sediments at some locations near Yellowknife due to emissions of arsenic trioxide from gold smelting operations, arsenic concentrations in fish caught from Yellowknife Bay were only about two times higher than in the main body of Great Slave Lake; consumption of these fish posed a negligible to very low risk health risk (Ref. 24). A recent study conducted under the Slave River and Delta partnership investigating a suite of 25 metal concentrations in five species of fish caught at various locations along the Athabasca River, Lake Athabasca, and the Slave River found that concentration of arsenic, selenium, thallium, and vanadium tended to be higher in fish caught from the Slave River than at upstream sites but that no health risk was posed from the consumption of these fish (Ref. 31).

 

Persistent organic contaminants

Persistent organic contaminants such as PCBs, DDT, and dieldrin are monitored in lake trout and burbot from Great Slave Lake and burbot from the Mackenzie River at Fort Good Hope under the Northern Contaminants Program, a program concerned with long-range atmospheric transport of chemicals (Figure 8.). Concentrations of these compounds have been declining since the early 1990s as a result of their decreased use globally (Ref. 32). Concentrations are several times lower than in regions such as the Great Lakes where some consumption advisories are in place. New classes of compounds, including flame retardants (PBDEs) and surfactants (PFACs) also are being analyzed as part of NCP monitoring on Great Slave Lake and the Mackenzie River at Fort Good Hope; lake trout are being monitored also at Great Bear Lake under the Chemical Management Program with Great Bear Lake serving as a reference lake for comparison against more developed regions in southern Ontario and Quebec (Ref. 33,34). Analyses are conducted on whole body basis and focus PBDEs, PFACs, mercury and other metals with mercury analyses also conducted on fillet.

Figure 8. Time trends in persistent organic contaminants in lake trout fillet (West Basin- Hay River commercial fishery East Arm at Lutsel K’e) and burbot liver (West Basin, Fort Resolution). Data are shown as the mean ± 1 standard error and are in wet weight. From Ref. 29.

 

Polynuclear aromatic hydrocarbons (PAHs)

PAHs are a class of compounds associated with combustion (pyrogenic) and oils (petrogenic) having natural and anthropogenic sources. Concentrations are naturally high in the sediments of the Mackenzie River delta because of natural sources of petrogenic inputs (Ref. 35,36). Oil seeps in the Norman Wells also are local sources of PAHs while Great Slave Lake receives PAHs in suspended sediments from the Athabasca and Peace River with highest concentrations offshore of the Slave River (Ref.37). PAH concentrations were measured in various species of fish in the 1990s as part of general surveys of contaminants in fish (Ref. 37,38). More recently PAHs have been measured in several species of fish in the Slave River at Fort Smith and Fort Resolution, complementing studies being conducted on the Athabasca River and focused on concerns raised with oil sands activities. (Ohiozebau et al. 2015, Ohiozebau et al. 2016, Evans et al. 2019). Concentrations tend to be higher in forage fish than large-bodied fish and slightly higher in large-bodied fish in the immediate oil sands area than at downstream locations including Fort Smith and Fort Resolution (Ref. 26,39) with no health risk posed by their consumption.

Shortly after the construction of the drill islands at Norman Wells on the Mackenzie River in the early 1980s, concerns were raised by local communities about the quality of burbot liver and investigations conducted, including PAH measurements in burbot liver, with inconclusive results (Ref.4.) A more recent study of the relationship between burbot liver quality and contaminant concentrations conducted in burbot from the Mackenzie River delta also was inconclusive with poorer liver quality tending to be associated with older fish with higher parasites loads; PAHs were not measured (Ref. 25).

 

Looking around

A recent Canada-wide review was conducted on mercury in fish in the Canadian environment as well as the Arctic (Depew et al. 2013a, Depew et al. 2013b, Chételat et al. 2015). In addition, a review was conducted on mercury in freshwater fish across western Canada and the United Sates ((Eagles-Smith et al. 2016). Overall, mercury concentrations are considered low in fish in northern Canada, particularly in comparison to developed areas such as southeastern Ontario. Another series of studies reported on a more than 40-year monitoring program of mercury concentrations in predatory fish in hundreds of Ontario lakes (Gandhi et al. 2014, Gandhi et al. 2015). These studies have shown roughly similar patterns as in the NWT with around 50% of walleye, lake trout and northern pike in the remote regions of the province having average mercury concentrations >0.5 µg/g and general trends of increase, potentially related to warming trends, although other factors may also be influential. Some lakes may be more vulnerable to increase than others, i.e., small, shallow lakes with large watersheds, as such systems are more sensitive to warming influences than large, deep lakes such as Great Slave and Great Bear (Evans et al. 2005a, Moslemi-Aqdam et al. 2021)t

The recognition that various human activities result in increased mercury concentrations in fish and other biota began to be reported in certain developed regions in Canadian provinces in the 1970s. Remedial actions were implemented, but mercury remains of concern including the long-range transport of mercury in the air from around the world. Furthermore, climate change potentially may enhance productivity and mercury methylation rates.

 

Looking forward

Sampling

With mercury analytical costs falling and many university and government research scientists having their own analyzers, sampling efforts are predicted to improve as additional analyses will be more readily performed as part of any research project on fish.

Other watersheds supporting commercial fisheries such as Trout Lake, Kakisa Lake and Tathlina Lake have multi-year mercury data records, including data collected as part of ongoing university-community studies. There are significant ongoing studies of Dehcho lakes in the Fort Simpson area, the Marian watershed and the Tłı̨chǫ Aquatic Ecosystem. These data are being evaluated as part of a new synthesis of mercury in NWT fish (Ref. 22).

 

Future trends

Future trends in mercury concentrations in fish require educated predictions. There is reason to be optimistic with substantial improvements nationally in the reduction of mercury released to the environment. This has been accomplished through shifts to cleaner fuels (than coal), improved operation of facilities such as pulp and paper mills and gold mines; and the reduction of the use of mercury products (e.g., in batteries and thermometers) in the environment. However, the scientific community is concerned that increasing temperatures may result in increased mercury concentrations in fish as more inorganic mercury in the environment is converted to methyl mercury and thus more easily bioaccumulated and biomagnified by top predators. Furthermore, increased mercury emissions from developing economies in Asia and artisanal gold production in southeastern Asia, Africa and South America may offset gains in improved emission controls in North America and Europe. This will be an area of active research and monitoring for years to come.

Other factors may result in a decrease in average mercury concentrations in fish in a lake. For lakes that are lightly fished, and fish are old and high in mercury concentrations, increased fishing pressures may reduce the average age of fish and hence average mercury concentrations. Increased fish growth rates due to less competition for food may also help dilute mercury concentrations in fish. However, if lakes become more productive and there are more small, bodied fish to be consumed, mercury concentrations could increase in fish such as lake trout that consume invertebrates (zooplankton) when small fish are scarce.

Mercury in fish will remain a topic of concern globally for decades to come. The ratification on the Minamata Convention of Mercury speaks to the global commitment to protect human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds to the environment. Hence, there is a continued strong need for monitoring programs to document changes in concentration over time at a location considering influencing factors such as fish age and length. There also is the need for research programs, which tend to be shorter in duration, to conduct more intensive studies to investigate specific questions.

 

Find out more

More information on mercury research and monitoring programs in the NWT can be found by visiting the Northern Contaminants Program at https://science.gc.ca/eic/site/063.nsf/eng/h_7A463DBA.html.

The Arctic Monitoring and Assessment Program (AMAP) also includes a number of relevant reports available at https://www.amap.no/ (Ref. 21).

Minamata Convention can be found here: https://www.mercuryconvention.org/

 

Technical Notes

Fish bioaccumulate mercury from the water and their food, i.e., mercury concentration builds up over time unless there is a reduction in mercury concentrations in the fishes’ environment. Mercury concentrations also increase up the food web from animals at the base such as invertebrates (e.g., clams and worms) to small fish, to large fish at the top of the food web through a process called biomagnification. Thus, predatory fish such as lake trout and walleye have higher mercury concentrations than bottom feeding fish such as suckers and whitefish.

Mercury methylation is the process of replacing a hydrogen on an inorganic mercury compound with a methyl group (CH3) to form the toxic organic compound, methyl mercury (MeHg). This process of methylation is not unique to mercury; however, a methyl group is quite toxic when bonded with mercury.

The NCP began in 1992 and focused on the long-range atmospheric transport of persistent organic contaminants. During the mid-1990s, two scientific studies reported high mercury concentrations in fish (Shilts and Coker 1995, Stephens 1995) in remote lakes in the NWT prompting NCP to include mercury in its core biomonitoring programs in 1998. Archived samples were analyzed retroactively. A synthesis of the existing information of mercury in fish under the early NCP mercury program was conducted by Lockhart et al. (2005) and studies were conducted to investigate the factors contributing to high mercury levels in predatory fish in some NWT lakes ((Evans et al. 2005a).

The NCP has established two long-term fish biomonitoring sites in the NWT to assess trends in mercury and persistent organic contaminants. One site is on the Mackenzie River at Fort Good Hope where burbot are monitored annually and the record extends back to 1985. The second location is Great Slave Lake where lake trout and burbot are monitored and the record extends back to 1993 with older data from the commercial fishery also available. Other lakes are being investigated as part of other studies associated with NCP, including community-based monitoring studies, the Cumulative Impact Monitoring Program, and industry-required fish monitoring. Data are submitted to the GNWT Department Health and Social Services who assess this information and issue consumption advice notices for NWT lakes, if required.

 

Fish consumption

Advice on fish consumption is a complex matter as it depends on the frequency with which a species is consumed, the size of the fish, amount consumed, and whether the individual is a child or an adult, a man or a woman and/or a woman of childbearing years. For example, while the commercial sale guideline for fish is 0.5 ppm, fish such as fresh tuna and swordfish commonly exceed this guideline but can be sold commercially. This is because guidelines and risk assessment are based on a weekly consumption of the particular fish throughout a person’s lifetime. It can be reasonably assumed that the vast majority of people are not eating fresh marlin, an expensive and hard to capture fish, on a weekly basis throughout their lifetime.

With this in mind, more complex lake/river specific consumption guidelines are issued by provincial and territorial agencies for various water bodies, based on fish species and their lengths, assumptions of various meal sizes, and separate advice for children versus adults and men versus women. Guidelines are advice to reduce mercury intake. Such guidelines generally recommend the consumption of fish lower down in the food web like lake whitefish and suckers over predatory fish and, when predatory fish are consumed, to choose smaller rather than larger predatory fish.

 

References

Ref. 1.  Evans, M. S., W. L. Lockhart, L. Doetzel, G. Low, D. Muir, K. Kidd, G. Stephens, and J. Delaronde. 2005. Elevated mercury concentrations in fish in lakes in the Mackenzie River Basin: The role of physical, chemical, and biological factors. Science of the Total Environment 351-352:479-500.

Ref. 2.  Shilts, W. W., and W. B. Coker. 1995. Mercury anomalies in lake water and in commercially harvested fish, Kaminak Lake area, district of Keewatin, Canada. Water, Air, and Soil Pollution 80:881-884.

Ref. 3.  Stephens, G. R. 1995. Mercury concentrations in fish in a remote Canadian Arctic lake. Water, Air, and Soil Pollution 80:633-636.

Ref. 4.  Lockhart, W. L., G. A. Stern, G. Low, M. Hendzel, G. Boila, P. Roach, M. S. Evans, B. N. Billeck, J. DeLaronde, S. Friesen, K. Kidd, S. Atkins, D. C. G. Muir, M. Stoddart, G. Stephens, S. Stephenson, S. Harbicht, N. Snowshoe, B. Grey, S. Thompson, and N. DeGraff. 2005. A history of total mercury in edible muscle of fish from lakes in northern Canada. Science of the Total Environment 351-352:427-463.

Ref. 5.  McCarthy, L. H., G. R. Stephens, D. M. Whittle, J. Peddle, S. Harbicht, C. LaFontaine, and D. J. Gregor. 1997. Baseline studies in the Slave River, NWT, 1990-1994: Part II. Body burden contaminants in whole fish tissue and livers. Science of the Total Environment 197:55-86.

Ref. 6.  Evans, M. S., D. Muir, W. L. Lockhart, G. Stern, M. Ryan, and P. Roach. 2005. Persistent organic pollutants and metals in the freshwater biota of the Canadian Subarctic and Arctic: An overview. Science of the Total Environment 351–352:94-147.

Ref. 7.  Carr, M. K., T. D. Jardine, L. E. Doig, P. D. Jones, L. Bharadwaj, B. Tendler, J. Chételat, P. Cott, and K. E. Lindenschmidt. 2017. Stable sulfur isotopes identify habitat-specific foraging and mercury exposure in a highly mobile fish community. Science of the Total Environment 586:338-346.

Ref. 8.  Evans, M. S., D. C. G. Muir, J. Keating, and X. Wang. 2015. Anadromous char as an alternate food choice to marine animals: A synthesis of Hg concentrations, population features and other influencing factors. Science of the Total Environment 509-510:175-194.

Ref. 9.  Moore, J. W., and D. J. Sutherland. 1980. Mercury concentrations in fish inhabiting two polluted lakes in northern Canada. Water Research 14:903-907.

Ref. 10. Cott, P. A., B. A. Zajdlik, M. J. Palmer, and M. D. McPherson. 2016. Arsenic and mercury in lake whitefish and burbot near the abandoned Giant Mine on Great Slave Lake. Journal of Great Lakes Research 42:223-232.

Ref. 11. Evans, M. S., J. F. Klaverkamp, and L. Lockhart. 1998. Metal studies of water, sediments and fish from the Resolution Bay area of Great Slave Lake: studies related to the decommissioned Pine Point mine. National Water Research Institute.

Ref. 12. Dewar, D. 2016. Taltson Water License AEMP & SEMP Requirements. File MV2011L4-0002. Reports submitted to the Mackenzie Valley Land and Water Board. Northwest Territories Power Corporation Hay River, NWT.

Ref. 13. Evans, M., D. Muir, R. B. Brua, J. Keating, and X. Wang. 2013. Mercury trends in predatory fish in Great Slave Lake: the influence of temperature and other climate drivers. Environmental Science & Technology 47:12793-12801.

Ref. 14. Carrie, J., F. Wang, H. Sanei, R. W. Macdonald, P. M. Outridge, and G. A. Stern. 2010. Increasing Contaminant Burdens in an Arctic Fish, Burbot (Lota lota), in a Warming Climate. Environmental Science & Technology 44:316-322.

Ref. 15. Eagles-Smith, C. A., J. T. Ackerman, J. J. Willacker, M. T. Tate, M. A. Lutz, J. A. Fleck, A. R. Stewart, J. G. Wiener, D. C. Evers, J. M. Lepak, J. A. Davis, and C. F. Pritz. 2016. Spatial and temporal patterns of mercury concentrations in freshwater fish across the Western United States and Canada. Science of the Total Environment 568:1171-1184.

Ref. 16. Depew, D. C., N. M. Burgess, and L. M. Campbell. 2013. Spatial patterns of methylmercury risks to common loons and piscivorous fish in Canada. Environmental Science and Technology 47:13093-13103.

Ref. 17. Depew, D. C., N. M. Burgess, M. R. Anderson, R. Baker, S. P. Bhavsar, R. A. D. Bodaly, C. S. Eckley, M. S. Evans, N. Gantner, J. A. Graydon, K. Jacobs, J. E. LeBlanc, V. L. St. Louis, and L. M. Campbell. 2013. An overview of mercury concentrations in freshwater fish species: A national fish mercury dataset for Canada. Canadian Journal of Fisheries and Aquatic Sciences 70:436-451.

Ref. 18. Chételat, J., M. Amyot, P. Arp, J. M. Blais, D. Depew, C. A. Emmerton, M. Evans, M. Gamberg, N. Gantner, C. Girard, J. Graydon, J. Kirk, D. Lean, I. Lehnherr, D. Muir, M. Nasr, A. J. Poulain, M. Power, P. Roach, G. Stern, H. Swanson, and S. van der Velden. 2015. Mercury in freshwater ecosystems of the Canadian Arctic: Recent advances on its cycling and fate. Science of the Total Environment 509-510:41-66.

Ref. 19. Gandhi, N., S. P. Bhavsar, R. Tang, and G. B. Arhonditsis. 2015. Projecting fish mercury levels in the Province of Ontario, Canada and the implications for fish and human health. Environmental Science and Technology 49:14494-14502.

Ref. 20. Gandhi, N., R. W. K. Tang, S. P. Bhavsar, and G. B. Arhonditsis. 2014. Fish mercury levels appear to be increasing lately: A report from 40 years of monitoring in the province of Ontario, Canada. Environmental Science and Technology 48:5404-5414.

Ref. 21. AMAP/UN Environment. 2019. echnical Background Report for the Global Mercury Assessment 2018. Arctic Monitoring and Assessment Programme., UN Environment Programme, Chemicals and Health Branch, Geneva, Switzerland, Oslo, Norway.

Ref. 22. Evans, M. 2021. (Pers. Comm. ) Environment and Climate Change Canada (Saskatoon, SK).

Ref. 23.Braune, B., D. Muir, B. March, M. Gamberg, K. Poole, R. Currie, M. Dodd, W. Dusckenko, J. Eamer, B. Elkin, M. Evans, S. Grundy, C. Hebert, R. Johnstone, K. Kidd, B. Koenig, L. Lockhart, H. Marshall, K. Reimer, J. Sanderson, and L. Shutt. 1999. Spatial and temporal trends of contaminants in Canadian Arctic freshwater and terrestrial ecosystems: a review. Science of the Total Environment 230:145-207.

 

Ref. 24. Chételat, J., P. A. Cott, M. Rosabal, A. Houben, C. McClelland, E. B. Rose, and M. Amyot. 2019. Arsenic bioaccumulation in subarctic fishes of a mine-impacted bay on Great Slave Lake, Northwest Territories, Canada. PLoS One 14.

 

Ref. 25. Cott, P. A., A. L. Amos, M. M. Guzzo, L. Chavarie, C. P. Goater, D. C. G. Muir, and M. S. Evans. 2018. Can traditional methods of selecting food accurately assess fish health? Arctic Science 4:205-222.

 

Ref. 26. Evans, M. S., M. McMaster, D. C. G. Muir, J. Parrott, G. R. Tetreault, and J. Keating. 2019. Forage fish and polycyclic aromatic compounds in the Fort McMurray oil sands area: Body burden comparisons with environmental distributions and consumption guidelines. Environmental Pollution 255:113135.

 

Carr, M. K., T. D. Jardine, L. E. Doig, P. D. Jones, L. Bharadwaj, B. Tendler, J. Chételat, P. Cott, and K. E. Lindenschmidt. 2017. Stable sulfur isotopes identify habitat-specific foraging and mercury exposure in a highly mobile fish community. Science of the Total Environment 586:338-346.

Carrie, J., F. Wang, H. Sanei, R. W. Macdonald, P. M. Outridge, and G. A. Stern. 2010. Increasing Contaminant Burdens in an Arctic Fish, Burbot (Lota lota), in a Warming Climate. Environmental Science & Technology 44:316-322.

Chételat, J., M. Amyot, P. Arp, J. M. Blais, D. Depew, C. A. Emmerton, M. Evans, M. Gamberg, N. Gantner, C. Girard, J. Graydon, J. Kirk, D. Lean, I. Lehnherr, D. Muir, M. Nasr, A. J. Poulain, M. Power, P. Roach, G. Stern, H. Swanson, and S. van der Velden. 2015. Mercury in freshwater ecosystems of the Canadian Arctic: Recent advances on its cycling and fate. Science of the Total Environment 509-510:41-66.

Cott, P. A., B. A. Zajdlik, M. J. Palmer, and M. D. McPherson. 2016. Arsenic and mercury in lake whitefish and burbot near the abandoned Giant Mine on Great Slave Lake. Journal of Great Lakes Research 42:223-232.

Depew, D. C., N. M. Burgess, M. R. Anderson, R. Baker, S. P. Bhavsar, R. A. D. Bodaly, C. S. Eckley, M. S. Evans, N. Gantner, J. A. Graydon, K. Jacobs, J. E. LeBlanc, V. L. St. Louis, and L. M. Campbell. 2013a. An overview of mercury concentrations in freshwater fish species: A national fish mercury dataset for Canada. Canadian Journal of Fisheries and Aquatic Sciences 70:436-451.

Depew, D. C., N. M. Burgess, and L. M. Campbell. 2013b. Spatial patterns of methylmercury risks to common loons and piscivorous fish in Canada. Environmental Science and Technology 47:13093-13103.

Dewar, D. 2016. Taltson Water License AEMP & SEMP Requirements. File MV2011L4-0002. Reports submitted to the Mackenzie Valley Land and Water Board. . Northwest Territories Power Corporation Hay River, NWT.

Eagles-Smith, C. A., J. T. Ackerman, J. J. Willacker, M. T. Tate, M. A. Lutz, J. A. Fleck, A. R. Stewart, J. G. Wiener, D. C. Evers, J. M. Lepak, J. A. Davis, and C. F. Pritz. 2016. Spatial and temporal patterns of mercury concentrations in freshwater fish across the Western United States and Canada. Science of the Total Environment 568:1171-1184.

Evans, M., D. Muir, R. B. Brua, J. Keating, and X. Wang. 2013. Mercury trends in predatory fish in Great Slave Lake: the influence of temperature and other climate drivers. Environmental Science & Technology 47:12793-12801.

Evans, M. S., J. F. Klaverkamp, and L. Lockhart. 1998. Metal studies of water, sediments and fish from the Resolution Bay area of Great Slave Lake: studies related to the decommissioned Pine Point mine. National Water Research Institute.

Evans, M. S., W. L. Lockhart, L. Doetzel, G. Low, D. Muir, K. Kidd, G. Stephens, and J. Delaronde. 2005a. Elevated mercury concentrations in fish in lakes in the Mackenzie River Basin: The role of physical, chemical, and biological factors. Science of the Total Environment 351-352:479-500.

Evans, M. S., M. McMaster, D. C. G. Muir, J. Parrott, G. R. Tetreault, and J. Keating. 2019. Forage fish and polycyclic aromatic compounds in the Fort McMurray oil sands area: Body burden comparisons with environmental distributions and consumption guidelines. Environmental Pollution 255:113135.

Evans, M. S., D. Muir, W. L. Lockhart, G. Stern, M. Ryan, and P. Roach. 2005b. Persistent organic pollutants and metals in the freshwater biota of the Canadian Subarctic and Arctic: An overview. Science of the Total Environment 351–352:94-147.

Evans, M. S., D. C. G. Muir, J. Keating, and X. Wang. 2015. Anadromous char as an alternate food choice to marine animals: A synthesis of Hg concentrations, population features and other influencing factors. Science of the Total Environment 509-510:175-194.

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