10.1 Trends in cadmium and mercury in caribou kidneys

Last Updated: 
May 26, 2015

 

This indicator measures the levels of selected heavy metals (cadmium and mercury) in caribou herds across the Northwest Territories (NWT).

Cadmium and mercury in the NWT environment come from both natural and industrial sources. They are absorbed by vegetation and move up the food chain when the vegetation is eaten by herbivores such as caribou. Both metals can accumulate in caribou liver and kidneys. High levels of heavy metal accumulation could cause health problems for caribou and people eating caribou.

Ongoing monitoring of levels and changes in contaminants in caribou is an important part of a national program monitoring contaminants in Arctic wildlife and the environment to ensure that caribou remains a safe and healthy food source.

Information for this indicator is obtained from research conducted under the national Northern Contaminants Program, with field sampling done with assistance from Environment and Natural Resources, Aurora College, the Sahtu Renewable Resources Board, local hunters and other partners.

Some monitoring of contaminants has also been done in moose in the NWT. In the past, an advisory has been issued for moose in the southern Mackenzie Mountains in the Dehcho region. 

Taking samples from caribou, NWT.
Taking samples from caribou, NWT.

NWT focus

Caribou are an important food source in communities across the NWT. Caribou and moose meat, including liver and kidney, are a significant part of traditional Dene/Metis diets1.

The concentration of cadmium and mercury in caribou kidneys is measured to monitor whether caribou populations are healthy in terms of contaminant loads, to see if contaminant exposure is changing over time, and to make sure caribou remain a safe and healthy food choice for northerners. Monitoring levels of heavy metals in animals across the north is important to help people better understand natural background levels and exposure to metals in the environment, as well as to better understand changes in contaminants entering the NWT environment through local or global man-made sources2.

In the NWT, contaminant levels have been monitored in all major barren-ground caribou herds, and the Norhtern Contaminants Program (NCP) has chosen the Bluenose-East and Beverly herds to serve as sentinel herds over time. Sentinel herds are populations more closely studied to provide an indicator of the health of all populations of caribou. The Bathurst herd is designated a key herd by CARMA (CircumArctic Rangifer Monitoring and Assessment Network) and contaminant levels in the Bathurst herd have been monitored by the Government of the NWT and its community partners in recent years under the CARMA program.

Current view: status and trend

Mercury

The level of mercury in the kidneys of NWT caribou is very low and does not pose a health risk to either caribou or people who eat caribou. Both the meat and organs of NWT caribou are safe to eat. 

There are naturally occurring sources of mercury in the Arctic environment, and the levels of mercury found in caribou often reflect exposure to these background levels. The primary source of mercury exposure from human activities results from long-range atmospheric transport of mercury from other parts of the world3. Sources of mercury include mining, milling and smelting of mercury-containing ores, coal-burning plants, municipal wastewater treatment plants, pulp and paper mills and fungicides. Mercury is a toxic element that accumulates in brain and kidney tissue, and can affect neurological functions and cause poor growth, and kidney damage.

Increasing mercury levels have been seen in other Arctic wildlife species, in the North, particularly marine mammals, perhaps as a result of an increasing available atmospheric mercury combined with changes in the naturally occurring cycle of mercury in the Arctic environment4.  

Mercury in kidneys, NWT, 1992-2008
Mercury level in kidneys of NWT caribou herds, 1992-2008. Threshold for potential effects on caribou is calculated at 130.5 ppm5.

Cadmium

The levels of cadmium in NWT caribou are not of concern for caribou health, and caribou remain a safe and healthy food choice for northern people. 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) but the levels of cadmium in NWT caribou kidneys are generally low.

Quote from Larter and Nagy 20006:

"The World Health Organization recommends the cadmium intake should not exceed 72 mg per day or 26,280 mg per year. The average caribou kidney weights 250 g wet wt (...). Given the mean cadmium level 42.6 mg per gram and the mean water content is 77% (of Bluenose caribou kidneys), an individual would have to consume 10.64 entire kidneys per year in order to exceed the recommended level. Subsistence hunters do not harvest the average caribou; they harvest young animals. Conservatively, we suggest that hunters realistically harvest animals -6 years of age and therefore would have to consume 13.2 entire kidneys per year in order to exceed the recommended level. An average family of five would harvest six to eight caribou annually for subsistence purposes. Assuming all kidneys were available and in their entirety that would provide 16 kidneys for five individuals for annual consumption."

Cadmium is found naturally in the environment. Wildlife exposure to cadmium reflects regional and local differences of the type of rocks and soil in the area. In some areas, human activity may also be a source of cadmium. 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 zinc7. Long-range atmospheric transport can distribute this cadmium to other places in the environment. Lichens and some other plants absorb cadmium directly from the air and pass it on to the animals 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 the level of cadmium in kidneys for study animals would have to be at like 150 ppm dry weight before some health effects were detected8 on animals--for example, caribou. The levels measured in the NWT are well below this threshold3.

Age-corrected cadmium level in kidneys of NWT caribou herds, 1992-2008
Age-corrected cadmium level in kidneys of NWT caribou herds, 1992-2008. Sub-lethal effects threshold according to Outridge et al. (1994) noted at 150 ppm

Looking forward

It is expected that the level of contaminants in terrestrial mammals will remain low, although the global trend of increasing mercury levels warrants ongoing long-term monitoring. Researchers are discovering new contaminants in the North, such as PBDEs which are found in flame retardants and fabric treatments. The Northern Contaminants Program tests for a range of contaminants. If new pollutants of concern are detected or increase, they will be monitored to understand how they are being brought to the North and what they mean to the Arctic environment.

If a new contaminant appears in the NWT that has an effect on wildlife and is of concern to people, it could be included in the State of the Environment Report.

Looking around

The Northern Contaminants 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 and Moose Contaminant Monitoring Program is a collaborative study being done in the NWT, Nunavut and the Yukon to measure contaminant levels in selected caribou herds across the north over time to track changes in contaminant levels.

This project is coordinated by a contaminants specialist in collaboration with wildlife biologists and community members in each jurisdiction. Samples are collected in collaboration with local hunters and community organizations, coordinated by biologists within the GNWT and the NCP, and tested for contaminant levels by a specialized analytical laboratory (Environment Canada’s National Laboratory for Environmental Testing).

Terrestrial mammals in the NWT are generally found to have lower concentrations of pollutants than animals from more southern species or species that are part of the marine ecosystem3. Renal mercury in caribou does not appear to be increasing in the Porcupine herd (Yukon)4.

Cadmium levels are naturally higher in the southern Yukon. Analysis of caribou teeth from 5,000 years ago indicate that one caribou herd from the Southeast Yukon had higher cadmium levels then compared to the 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 cadmium in soil and make it available to herbivores.

Technical notes

Part per million (ppm) = µg/g. Scheuhammer's5 threshold potential effects on health of study animals for mercury is 30 ppm wet weight. A conversion factor of 77% water in kidney6 as used to report in dry weight.

For more information

Contact us

Found an error or have a question? Contact the team at NWTSOER@gov.nt.ca.


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. Larter, N.C., J.A> Nagy, and B.T. Elkin. 2008 In Prep. A change in radionuclide and heavy metal concentrations found in the kidneys of "Bluenose" caribou over time.  

Ref. 3. 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. 4. Mary Gamberg, unpublished data.

Ref. 5. 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. 6. 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

Ref. 7. Jaworski, J.F. 1980. Executive Reports: Effects of chromium, alkali halides, arsenic, asbestos, mercury, cadmium in the Canadian environment. National Research Council of Canada.

Ref. 8. 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