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HIGH LEVELS OF PCB IN THE NORWEGIAN POPULATION OF POLAR BEARS
By Kristine Bull
of polychlorinated biphenyls (PCBs) in the Norwegian population of polar bears
(Ursus Maritimus) at
To see a figure about circumplar levels of PCB’s in polar bears please click on the below link: http://www.environment.no/templates/themepage____2800.aspx
bears are the largest terrestrial predator on the earth. They live in the
circumpolar north and scientist have estimated that there are about 22000-27000
animals today. 15000 of them live in
What are PCBs?
PCBs are group of synthetic chlorinated hydrocarbons which are not easily degraded. They are not flammable and have isolating qualities which made them very popular substances. They were used in several electric systems and as an additive in paint and plastics. There have been developed 209 different types of PCBs and their toxic properties vary depending on the number of chlorine-atoms and the structure of the molecule. Even though PCBs are illegal today it is estimated that 2000 billion kilograms have been produced and about 1/4th of it has already been released into the environment.
Spreading of PCBs
both trough air and water and are therefore found almost everywhere even though
most of it, 60%, is found in the oceans. The reason that the levels of PCBs are
higher in the Norwegian population than in the populations of
figure about the pathway of the
The animals take up PCBs through the air, through the feed and through the skin. PCBs are fat-soluble and will therefore accumulate in the animals fat-reserves.
bears are on the top of the food chain feeding mostly on seals. The levels of
PCBs multiply through the food chain and are therefore higher in the polar
bears compared to the other carnivorous animals at
Effects of PCBs
PCBs are toxins having several effects on the animals, the effects varies between the specific members of this group. In large doses it could cause acute death.
Norwegian scientists have discovered 7 polar bear females that have both male and female genitals, “O. Wiig (1998), Science, vol. 280 (1998), number 5372, page 2053”. They suspect that PCBs are the main reason for this development, through interfering with the hormone-regulating enzymes called P-450 cytochromes. The pseudohermaphrodites were not sterile since some of them had cubs.
PCBs have also an effect on the fertility of the animals. This is due to the fact that some of the molecules have a similar structure to hormones, and the can therefore mimic, block or disrupt the function of the naturally occurring hormones.
The author’s opinion
bears face several major threats due to human-interference. Not only are they
vulnerable to toxins released into the environment, but they also face
extinction due to melting of the sea ice in the
|Notes (if any) by Peter Kabai:|