If scientists were to measure only physical, or abiotic, elements, the Arctic environment would seem almost pristine, among the purest places on the planet. The Great Lakes, the Baltic, and the North Sea, for example, hold ten to one hundred times higher concentrations of PCBs than the Arctic Ocean. The air in Chicago contains a lot more PCBs than the air in Svalbard, Norway. So if the air they breathe and the water they drink and feed in are fairly clean, why do the bodies of the Arctic's people and top predators carry so much toxic trash? How contaminated an animal is depends not on where it lives but on what it eatsits place in the hierarchy of life, the food chain, or more accurately the food web. Capping a lush green and blue planet, the Earth's circumpolar north looks bleak and uninhabitable but in reality its 13 million square milesas vast as the entire continents of North America and Europe combinedbrim with an array of odd and hardy creatures, from ice-clinging, single-celled algae to polar bears, that can survive nowhere else on Earth. PCBs work their way through this ecosystem from the bottom up. They are absorbed first by sediment on the ocean floor and ice on the surface, and then they infiltrate single-celled plants that bloom during the spring, when light becomes available for photosynthesis. Each individual organism begins to build up the contaminants from its environmenta process called bioaccumulation. These plants, sometimes stretching into ten-foot-long filaments, are then grazed on by the ocean's zooplanktontiny, shrimplike crustaceans such as copepods. From there, the Arctic's food chain spreads into a vast, intricate web, reaching out in multiple directions. The copepods are eaten by cod, the cod are eaten by toothed whales such as narwhals, and the narwhals are eaten by Inuit hunters. Ringed seals eat the cod and then polar bears and human hunters eat the seals. Walrus feast on the copepods, people feast on the walrus. Seabirds eat cod, people eat the birds.
In the Arctic, you are what you eat. Because PCBs are not easily expelled from an animal's body, they accumulate therethis means that animals at the top of the food web have eaten all the contaminants consumed by their prey and their prey's prey. Arctic food ladders have as many as five rungs, and at each step up, the chemicals can magnify in concentration twentyfold or more in a phenomenon called biomagnification. Occupying the top rung are people and polar bears, which can carry millions, perhaps billions, of times more PCBs than the waters where they harvest their foods.
This trip through the food web, in most cases, occurs via the fat of animals. PCBs are not water-soluble, they are lipid-soluble, which means they are readily absorbed by tissues with a high fat content, and they cling there, rather than dissolving and flushing out of the body in liquids such as urine. "If you were to ask a PCB molecule where do you like to be, it would say it likes to be in the company of molecules similar to itself. As it looks around, the molecules that are closest in chemical nature to PCBs are fats, or lipids. So PCBs tend to accumulate in fat," says Donald Mackay of Trent University's Canadian Environmental Modelling Centre. In cold climates like the Arctic, sea mammals have an unusual propensity to produce fat. Their blubber is an insulating layer several inches thick, and their milk is mostly fat. Fat stores energy, but it also stores a variety of man-made chemicals, which makes Arctic mammals more susceptible to the buildup of contaminants than leaner animals in temperate zones. Making matters worse, many Arctic creatures experience seasonal cycles of fattening and starvation, and when they use up their fat reserves in winter, PCBs concentrate and migrate into their vital organs. Large Arctic predators such as polar bears and whales also tend to live longer than land animals so their bodies store many decades' worth of chemicals, increasing in concentration with their age.
Copyright © 2005 by Marla Cone. Reprinted with permission from Grove Atlantic, Inc. All rights reserved.
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