Article, Book Resources
Food Web and Bioaccumulation
- Grades: 6–8, 9–12
The idea that the impact one has on a local environment could be carried to impact an environment thousands of miles away is relatively new. However, as we learn more about global circulatory systems — atmospheric, river or ocean — we begin to understand the implications of what's known as transboundary pollution.
The Arctic region is viewed as a place of ice and snow and wind and cold, a place of darkness in winter and perpetual daylight in summer, and above all, a place untouched by civilization. This picture of a world apart is no longer completely valid. The Arctic is now recognized as very much a part of the world we all live in; it is impacted by our activities in the more industrial southerly latitudes of the planet.
We are becoming increasingly aware that our planet must be looked at globally. There is now fairly convincing evidence that we are impacting the systems of the entire world, and the Arctic seems to be particularly sensitive to those influences.
Long-distance transport of airborne particles has been documented around the world. For example, it is known that dust from the Gobi Desert of Mongolia travels far out into the Pacific Ocean. A Japanese research group in1971 observed dust pass over Japan from Asia and days later collect in Hawaii and Alaska. They concluded that a single surge of dust from the Gobi had drifted across the Pacific for well over10,000 kilometers.
The contamination of the Arctic marine food web by organochlorine compounds (OCs) and heavy metals has been brought to light during the last decade and is now a well-know phenomenon. OCs are anthropogenic (human caused) compounds that include pesticides such as lindane, chlorodane, endrin, dieldrin, toxaphene, hexachlorobenzene (HCB), and dichlorodiphenyl trichloroethane (DDT) and polychlorinated biphenyls (PCBs) to name a few. Many of the OCs are industrial or agricultural chemicals that have been banned in North America and Western Europe since the late 1970's. Despite the regulatory action, these compounds are still being emitted into the environment because of ongoing use in many parts of the world (for example: toxaphane is still sprayed on crops in India and China), as well as improper storage and disposal. Heavy metals are produced mainly by smelting, burning of fossil fuels, and waste incineration — common activities in our communities.
Unfortunately, nearly all of the OCs detected at southern latitudes have also been detected in the Arctic. Since the Arctic has few local sources of pollution, most of the contaminants affecting it have travelled many miles from low- and mid-latitude sources. Once released into the environment they reach the Arctic through the atmosphere, rivers, and ocean water currents. The hazard lies in the continuous accumulation of contaminants transported to the Arctic in a process know as bioaccumulation. After PCBs are spilled, or pesticides sprayed on crops, they evaporate in the atmosphere and their residue is carried long distances by prevailing winds. Pesticide-laden soils and organochlorines from industrial incinerators are also transported this way. Once deposited on land or water, they may re-evaporate and be on the move again.
Greenland is an example of the effects of transboundary pollution. It is a country of clean air and water situated far away from major industrial centers and with few local sources of pollution. Pollution from lower latitudes, however, is a growing concern. The major concern for human health is organic mercury. Mercury is concentrated in the food chain and reaches high levels in the traditional Greenlandic diet, which is composed mostly of marine mammals. Very high levels of blood mercury have been found in hunters and their families from northern Greenland, but toxic effects have so far not been observed.
So, while the Arctic world is still distant, there is a growing silent presence of contaminants in the food web whose sources are thousands of miles away. Understanding the earth's atmospheric, river and ocean circulatory systems is an important first step in understanding the impact we are, unknowingly, having on the Arctic region.
The Arctic Region Supercomputing Center has articles on global change and data they are collecting on contaminants. This information can be found when you open the folder called "newsletter." On gopher, you do a search using Veronica and look for the "Arctic Region Supercomputing Center." The site address is: http://www.arsc.edu. This center is at the University of Alaska.
A book we suggest is:
The Global Ecology Handbook: What You Can Do About the Environmental Crisis. (Practical Supplement the PBS Series "Race to Save the Planet"). The Global Tomorrow Coalition
The Food Web and Bioaccumulation
Contaminants such as heavy metals and organochlorine compounds (PCBs are an example) are transported from distant sources to the Arctic by atmospheric, river, and ocean currents. As the contaminants arrive in the Arctic via these pathways, they tend to settle into the lower end of the food web. Unfortunately, due to the extreme conditions of low temperatures and long periods of darkness, they do not "burn off" as easily as in the lower latitudes. One organochlorine, for example, has a "shelf life" of eight months in the lower latitudes but in the Arctic region lasts for 40 years.
There has been a good deal of research and concern recently regarding the presence of these contaminants in the various Arctic mammal species. In the Arctic, contaminants in sea water builds starting with zooplankton, increasing in concentration as they move through the fatty tissues of small, then larger fish to the seal and to the polar bear. The contaminants actually increase in concentration each time they move through the food web. This process is known as bioaccumulation. Bioaccumulation continues at each link in the food web, resulting in a bigger dose for animals at the higher end of the food web (polar bear, walrus, beluga whale). So the level of PCBs, for example, in polar bears is exorbitantly high.
Organochlorines are of critical concern since they accumulate in whale and seal blubber and caribou fat, all of which are considered a major food that has cultural and economic importance for the Inuit. Disturbing evidence of this bioaccumulation is the organochlorine pollutants that are appearing in the breast milk of Inuit women. This is especially of concern when the closest known sources of these contaminants are thousands of miles away from the Arctic region.
It is very important to understand the implications of the day-to-day activities we have in the more industrial parts of the world. While spraying our farms may help with the insects locally, the impact of the dissipating pesticides in the atmosphere is felt strongly in the Arctic. "Think globally and act locally" has never had a stronger meaning than when it comes to the Arctic.
The GRID office in Norway has information on environmental data on the Arctic: http://www.grida.no/prog/polar/add/index.htm
For those who are interested, the address of the Arctic Long Term Ecological Research Site project's Home Page is as follows: http://www.mbl.edu/html/ECOSYSTEMS/lterhtml/arc.html