Pollutants in Arctic foxes

Last updated 8 December 2022

In Svalbard, the Arctic fox (Vulpes lagopus) is a top predator and carrion eater feeding on the terrestrial and marine food chains. The Arctic fox is exposed to high levels of pollutants. Monitoring of Arctic foxes in Svalbard shows a significant decline in organic pollutants that are regulated internationally, while mercury shows a rising trend.

Status and trend

Geographical trend

Levels of PCBs and chlordanes were higher in Arctic foxes in Svalbard compared to Arctic foxes in Canada and Alaska. In contrast, levels of mercury and hexachlorocyclohexane (HCH) were higher in Arctic foxes in North America and Iceland compared to Svalbard. No geographical trend was found for dichlorodiphenyldichloroethylene (DDE) and hexachlorobenzene (HCB) in Arctic foxes. The geographical trends for organic pollutants in Arctic foxes correspond to the trends found in polar bears and seals.

Species trends

Levels of PCBs and chlorinated pesticides in Arctic foxes from Svalbard are similar to those found in polar bears, while levels of perfluorinated compounds and mercury are significantly lower.

Time trends

Levels of polychlorinated biphenyls (PCBs), chlorinated pesticides and polybrominated diphenyl ethers (BDE) in Arctic foxes show an average decline from the late 1990s to 2018. Comparison with previous studies shows that PCB levels measured in the liver of Arctic foxes from Svalbard remained stable and high from 1973–74 until the end of the 1990s.

Levels of perfluorooctaxosulfonate (PFOS) in Arctic foxes also declined from the late 1990s. The decline of the sum of long-chain perfluorinated carboxylic acids (PFCA) in the period 1997-2020 has been somewhat slower than the decline of PFOS.

It is important to note that, although an average, statistically significant, decline in levels of several pollutants in Arctic foxes has been measured from the 1990s until now, the levels vary between years.

It is important to be aware that different analytical methods have been used for the samples analysed before and after 1997, and that there is no information on the age and body condition of Arctic foxes in the earlier studies.

Results of analyses of mercury in Arctic foxes from Svalbard showed an average increasing, but not significant, time trend in the period 1997-2013.  

Effect of climate-related change on diet and access to food

In studies published in the period 2015-2019, time trends of pollutants in Arctic foxes from Svalbard have been investigated in relation to climate-related changes in diet and food availability.

The studies showed that the concentration of all pollutants was higher in Arctic foxes with a marine diet, such as seabirds, their eggs and seal carcasses, compared to Arctic foxes with preferentially terrestrial diets such as reindeer carcasses. The studies also showed that increased access to reindeer carcasses, which often occurs in winters with heavy rain on snow, results in lower concentrations of HCB, PFCA and mercury in Arctic foxes. Furthermore, it was found that the concentration of β-HCH, PFOS and mercury in Arctic foxes from Svalbard increased with increasing sea ice cover in the fjords, which resulted in increased access to marine prey.

When changes in eating habits and food availability between years were included in the statistical analyses of time trends in Arctic foxes, the models showed that changes in eating habits and food availability had from moderate to no effect in the measured trends. This means that time trends in pollutant levels in Arctic foxes are mainly related to emission patterns and levels in the environment in general, and variation in diet is less important in time trends of pollutants.  However, the mercury levels adjusted for eating habits and food availability rose faster (7% per year) than the measured levels (3.5% per year).

Causal factors

The main reason for the decline in levels of most of the so-called legacy organic pollutants in Arctic foxes is that their manufacture and use are regulated nationally and internationally.

Efforts to regulate PCBs and chlorinated herbicides began at the end of the 1970s and the international ban on the substances under the Stockholm Convention came into force in 2004. The main sources of releases of these substances have therefore stopped.

The reason they are still found in the environment is because they are stable, and can recirculate and be concentrated up the food chain.

The manufacture and use of newer pollutants such as BDE-47 and PFOS have been restricted in the last 15 years. Tetra-BDE, penta-BDE, hexa-BDE, hepta-BDE and PFOS were included in the Stockholm Convention in 2009, while deca-BDE was included in 2017. It has been proposed to include long-chain perfluorinated carboxylic acids in the Stockholm Convention and production has declined in many countries, but many PFCA precursors are not currently regulated.

Global mercury emissions have been stable over the past 30 years. In 2017, the global Minamata Convention on Mercury, designed to reduce mercury emissions, was signed.

Consequences

Temporal trends of pollutants in apex predators are not only influenced by discharge patterns and regulations, but also by variations in the presence of various prey, which, in turn, are influenced by rapid changes in the climate in the Arctic. As recently shown above, climate-related changes in Arctic foxes’ diet and access to prey may affect pollutant levels in Arctic foxes from Svalbard to some extent.

In addition, changes in physical factors, such as increased precipitation and reduced sea ice cover, can lead to increased deposition of specific pollutants from air to soil and sea, and increased evaporation from sea to air. Melting sea ice will contain pollutants that can be absorbed into the food chain.

PCBs and chlorinated herbicides (particularly oxychlordane) make up the greater part of the pollutant burden in Arctic foxes. The levels in Arctic foxes are still high, and comparable with those in polar bears. In common with many other arctic animals, Arctic foxes have seasonal variations in their body condition. As summer approaches, they burn the body fat they have in winter as a natural adaptation from winter to summer conditions, and may repeatedly through the winter also lose body weight when they find insufficient food and must fall back on their fat reserves.

Periods of hunger and consumption of body fat are natural for the Arctic fox, but the process may be critical because pollutants stored in fatty tissue are released into the blood stream when the fat is consumed. The pollutants will then be available to be taken up in vital organs like the liver and brain.

The Arctic fox also has high levels of PCB metabolites. This is because the Arctic fox is very efficient at converting PCBs to more water-soluble variants. The purpose of such conversion processes is to convert contaminants into other compounds that are more easily dissolved in water, and can hence be excreted from the body. But, in the process, metabolites of PCBs are also produced, which remain in the body, and these compounds are actually more toxic than the original ones.

Very little is known about the effects the high levels of pollutants might have on, for example, a nursing fox and her cubs, or a fox that fails to find food and must fall back on its fat reserves in winter. The effects of pollutants on Arctic foxes have been experimentally studied in studies feeding whale blubber to farmed foxes and sled dogs in Greenland. In the exposed foxes and dogs, pollutant burdens correspond to comparable or lower levels than we see in Arctic foxes from Svalbard today. These studies found changes in levels of testosterone, vitamin A, vitamin E and thyroid hormone, and in kidney tissue, thyroid tissue and liver weight in the exposed animals compared to the control group. At the same time, no significant differences in liver tissue, bone mineral density and sperm quality were observed. It is therefore likely that the pollutant levels have negative effects on the health of Arctic foxes.

Comparing levels of mercury in Arctic foxes to threshold limits for effects in mink indicates that the health of Arctic foxes from Svalbard is not affected by mercury.

About the monitoring

The Arctic fox is uppermost in the food chain in Svalbard, both on land and in the marine ecosystem, thus putting it at risk of taking up pollutants. High levels of POPs have been found in several sets of samples, initially from 1973–74, most recently in 2012–13. In particular, high levels of oxychlordane and highly chlorinated PCBs, including PCB-153 and PCB-180, were found.

Mapping of pollutants in Arctic foxes in Alaska, Canada and Norway has shown that Arctic foxes from Svalbard have the highest levels of pollutants. Negative effects of exposure to pollutants have been demonstrated in controlled studies on farmed foxes, where the foxes were exposed to similar pollutant burdens, or lower levels, than we see in Arctic foxes in Svalbard today. This is worrying for the Arctic fox population in Svalbard, and further monitoring is therefore necessary.

The overall pollutant burden on Arctic foxes may also be affected by climate change, which further reinforces the importance of monitoring levels of pollutants in Arctic foxes.

Further reading