The Arctic at Risk:
A Circumpolar Atlas of Environmental Concerns
The Arctic at Risk:
Organochlorines contaminating the Arctic are those that have been produced in large quantities, were released to the environment and widely dispersed, and have made their way to the Arctic over long distances (Barrie et al., 1992). Typically these chemicals have low water solubility, so they are found preferentially in the atmosphere. In general, long-range atmospheric transport is favored when a pollutant occurs as a gas, is adsorbed onto small particles that have long atmospheric residence times and high biological and chemical stability (Barrie et al., 1992). Many of the organochlorines are semi-volatile: they exist in the vapor phase, on particles in the atmosphere, and adsorbed or dissolved on the earth's surface (Barrie et al., 1992). Because they become less volatile at low temperatures, they tend to deposit during winter, and enter the gas phase during summer. With time, they move farther and farther to the north, toward regions with the coldest temperatures. As a result, more volatile organochlorines predominate in the northern regions, while less volatile compounds are left behind in warmer latitudes (Muir and Norstrom, 1994). This is called the "cold trapping" or "cold condensation" hypothesis or effect (Ottar, 1981; Wania and Mackay, 1992 and 1993; Iwata et al., 1993). Continued releases of persistent volatile and semi-volatile chemicals to the environment at lower latitudes pose a threat to the Arctic ecosystem (Muir and Norstrom, 1994).
Because of cold condensation, Arctic waters are likely to serve as a major sink for organochlorines released around the world (Iwata et al., 1993). In fact, studies in Canadian lake sediments indicate that there is widespread low-level contamination of freshwater systems by organochlorines (Muir and Norstrom, 1994). The marine environment is also contaminated (Iwata et al., 1993).
Once ingested, organochlorines are stored in the fatty tissues of the body. For example, Stern et al. (1994) found that, on a wet-weight basis, PCB and DDT levels are 4 to 140 times higher in beluga blubber than in skin or kidney (which contain less fat). But if these values are converted to lipid weight--that is, are normalized by the amount of lipid each tissue contains--the concentrations between the different tissues are similar.
When fat tissues are metabolized--for example, when the organism begins to starve--organochlorines are mobilized, adding further stress.
Female excrete organochlorines during lactation (Addison and Smith, 1974), and therefore do not tend to bioaccumulate organochlorines in the same way that males do.
Polyclorinated Biphenyls (PCBs)
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