Temps de lecture :5 minutes
Imagine a region where the sun is hardly seen for months, while during other months the sun never sets, a region where snow and ice are essential to life. The Arctic is a beautiful but unforgiving and harsh environment that resembles a frozen desert. In the tundra area, which means “barren land”, the ground is permanently frozen and no trees can grow. Every possible advantage and fine-tuned adaptation is needed for animals and people to successfully call this region home. But amazingly, considering these conditions, the Arctic is a region full of life. It is the home to hares, lemmings, birds, wolverines, reindeer, caribou, musk oxen, seals, walrus, whales, arctic foxes, wolves, and polar bears. This region has been the home to people for many thousands of years, and is today inhabited by about 4 million people.
While the region may seem tough and well-isolated, it is also surprisingly fragile and connected to the rest of the planet. Despite its remote location, the Arctic is still affected by human activities including global pollution and climate change. Although some pollutants are found naturally in the region or come from local industry, many pollutants of concern are not produced or even widely used in the Arctic. Of special concern are the human-made industrial and agricultural chemicals that travel north largely via air and water currents. Highly volatile chemicals evaporate into the air, travel long distances, and eventually condense and reach the ground as rain or snow. Pollutants are also transported via ocean and river currents, melting sea-ice, and migratory species.
Although our knowledge is constantly improving, we are still far from fully understanding how chemicals impact the health of wild animals in their natural environments. While compelling studies are not proof of direct cause-and-effect relationships, they undoubtedly are reason for concern that chemicals are already harming arctic wildlife.
The main effects that have been studied in arctic wildlife thus far are disturbances of the hormone and immune systems, vitamin A levels, and bone mineral density, leading to various consequences.
The word hormone comes from the Greek word horman, meaning “to set in motion”. This is exactly what hormones do — they are chemical messengers that control almost every body function imaginable. Some chemicals can interfere with or mimic natural hormones.
Alterations in the immune system may result in reduced resistance to disease, increased virus levels and rates of disease transmission within and among populations.
Retinol, also known as vitamin A, is required by almost every tissue in the body, regulates growth and development and is essential for normal vision, reproduction, cell differentiation, and immunity.
Bone mineral density is a measure of the amount of calcium and the thickness of the bones. It is correlated with bone strength and the ability to bear weight. Some hormones (e.g. testosterone and estrogen) are known to regulate bone health.
The greatest concern is that contaminant mixtures may interact with other natural stressors in the Arctic, (e.g. climate change, habitat loss, reduced food supply) resulting in wildlife having reduced ability to successfully deal with every day challenges, (e.g. harsh winters, hibernation, feeding, nesting predation) leading to reduced reproductive capacity, increased likelihood of disease or even death, and population declines.
Increasing accumulation of chemicals up the food chain results in the highest chemical levels generally being found in top predators. Arctic mammals have several characteristics that make them vulnerable to chemical exposures: a large amount of body fat and fatty diets (many chemical are preferentially stored in fat), long periods of lactation during early development (resulting in large chemical transfers from the mother to the offspring via fatty milk), and long life spans resulting in chronic chemical exposures over many years.
Many fish and seafood species eaten by arctic mammals are also consumed by people (e.g. fish, crabs, squid, and mollusks). These mammals are, therefore, also important as sentinels for human exposures and health.
The Polar bears (Ursus maritimus) is the top arctic predator aside from humans. Polar bears are known to preferentially eat the fatty blubber of their prey. Arctic-wide studies have confirmed polar bears are heavily contaminated with chemicals, especially organochlorines and PCBs. They are immunotoxic to polar bears, potentially leading to impaired resistance to fight infectious diseases, and hormone disruption is also a concern.
Recent studies show that eastern North America and western Europe are the likely source regions for PCB and perfluorinated acid leading to brominated flame retardants in polar bears.
Seals and Sea lions: in addition to pollution, climate change and commercial fishing, arctic seals face another threat — predation — as they share their habitat with humans, foxes, wolves, dogs, and polar bears.
Mixtures of environmental organocontaminants may present a risk of immune toxicity to wild seals. A recent study provided the first evidence that, in addition to persistent organic chemicals, exposure to metals (lead, tin, aluminum, chromium, nickel) may also be impacting the health of harbor seals (Phoca vitulina).
PCBs were also associated with the probability of california sea lions (Zalophus californianus) dying with cancer.
The Saimaa ringed seals (Phoca hispida saimensis) population is in decline. Between 1981 and 2000, mercury and organochlorine contaminants were measured in these seals. However, levels of some organochlorines in the blubber of ringed seals from NWT, Canada, have not changed significantly between 1981 and 2000.
Grey seal (Halichoerus grypus) adults have lesions of the female reproductive organs, intestines, kidneys, adrenal glands, and skulls that illustrate the negative impacts high levels of chemicals can have on seals.
In addition to chemicals, threats upon stellar sea lions (Eumetopias jubatus) include nutritional stress due to changes in fish availability to lower fat fish, competition with commercial fisheries for food, human caused deaths, increased predation, and climate change. While exposure to PCBs and DDTs may be declining, sea lion habitats and prey are contaminated with additional chemicals and hazards including radioactivity, solvents, and chemical weapon dumps.
Beluga whales: the word “cetacean” comes from the Latin word cetus, meaning “whale or sea monster”. The word beluga means “the white one” in Russian and the beluga is also known as the “singing whale” or “sea canary” because of its underwater noises.
Despite an end to wide-scale hunting, since the 1970s the Belugas population has declined. Several factors, including chronic exposure to toxic chemicals are likely the cause. The bodies of some belugas from the Saint Lawrence estuary in Canada are so contaminated that their carcasses are treated as toxic waste.
Belugas prefer shallow coastal waters and swim up river inlets where pollutants are concentrated, as a result they can be studied as models of long-term exposure to chemicals and can be used to predict health problems that could emerge in highly exposed wildlife and human populations over time.
Many chemicals that are attracted to fat (PCBs, organochlorine pesticides) and taken up and excreted in egg yolks. As is the case for mammals through lactation, in birds chemical exposures to the embryo during the most critical early development phase also occur.
Exposure to several different chemicals result in changes in adult male sexual behavior, altered neurotransmitters, impaired reproductive and immune related end points, and altered steroid hormones.
Contaminants can interfere with hormones and decrease bone deposition, resulting in less calcium for the eggs. Organochlorines (PCBs, DDE, dieldrin) have been linked to decreased parent attentiveness during egg incubation, impaired courtship behavior, and neurological effects (impaired avoidance behavior) in birds.
Organochlorines are correlated with thyroid hormone ratios in male glaucous gulls (Larus hyperboreus). In birds, thyroid hormones regulate metabolism, growth, weight, nervous system function, feathers, egg hatching, molting, and reproduction. Therefore, any hormonal alteration is of concern.
A study showed that gulls are bioaccumulating fluorochemicals, to an extent that there is the potential for altered biological processes.
The evidence thus far for arctic species demonstrates considerable changes that are very likely influenced or caused by chemical exposures. Some of these alterations are potentially quite serious (e.g. immune suppression, hormone disturbances, altered behavior). Chemical exposures are especially of concern for wildlife when one considers that many species are already facing other concurrent and serious threats to survival and, in some cases, large population declines.
Additional studies are needed to assess effects from chemical mixtures, which are the norm in nature.
The accumulating evidence thus far is certainly enough to show that a move towards more precautionary chemical legislation must be carefully considered and that additional funding should be provided for wildlife toxics research.
WWF does not argue that pollutants are the only or even the most important threat facing arctic species. However, we insist the time to act to improve chemical legislation is long overdue especially when this can be done in a way that has minimal economical impact and in fact has the potential for great economic and environmental savings.
Many arctic peoples are also known to be heavily contaminated. In order to avoid a repeat of the chemical mistakes of the past we need improved chemical safety now.
Extracts from rapport de WWF International Arctic Programme et WWF-DetoX, 2006