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Last Update: 2008-05-08   Source: Star Projects
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Mercury falling

The distant Arctic is often thought of as pure and untouched. Yet it has been discovered that the food chain in the Arctic is contaminated with the deadly heavy metal mercury – from the bottom of the food chain through to humans. In the Svalbard archipelago, about half way between the North Pole and the coast of Norway, European Scientists are investigating how and why such concentrated deposits of mercury are settling upon the ice-sheets and glaciers of the Arctic.

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The primary sources of atmospheric mercury include mining and industrial combustion. With the right chemical, physical and geographical conditions, the mercury comes to fall over the Arctic region. The mercury is initially harmless until it reacts with specific forms of bacteria and fungi. It then becomes a highly toxic compound called methyl-mercury. The toxic mercury can filter through into the ocean as the snow and ice melts. In the water the mercury is absorbed by plankton, where its journey through the food chain begins. The term "bio-accumulable" describes a property mercury has, in which its concentration in organisms increases as it continues up the food chain. Estimates suggest that the marine life in some Arctic fjords have methyl-mercury concentrations a thousand times that of the water. As a result, the risk to humans at the top of the food chain is large enough that some Nordic countries released warnings against eating too much of some North Atlantic fish.

One step in the biological investigation is to find the types of bacteria with which mercury reacts to form the toxic methyl-mercury. Snow samples are taken in the Arctic and filtered to isolate the bacteria. At a micro-biology laboratory in central France at least 11 different types of Arctic bacteria are being investigated. After the bacteria have been identified, they are grown in a culture medium and then frozen. The researchers wish to find out how much mercury is absorbed by the bacteria and then establish what kinds of chemical reactions take place to form methyl-mercury.

A dangerous characteristic of mercury is that, after having entered, it will not leave the human body. Often the mercury becomes attached to proteins in the nervous system, leading to motor-disorders. In the brain, the mercury will lead to memory and more serious motor problems.

Similar mercury-related health and environmental risks are to be found in the French Alps. Researchers travel 2700 metres above sea-level to Lake Bramant, below the Saint Sorlin glacier. Here samples are being taken from snow of various depths, the ice below and from the water underneath the ice. Although not to the same extent seen in the Arctic, the problem of high mercury concentration has been proven to exist here as well. In the snow there is about 12 nanograms of mercury per litre, while 1 nanogram per litre is found in the water, where the mercury is more diluted. There is also a known correlation that the alpine lakes of higher altitude are absorbing more mercury. The impact of these changes will be evident for generations to come. The state of Lake Bramant today, for example, reflects the impact of the industrial revolution.

The Zeppelin Mountain weather station in Svalbard lies 474 metres above sea-level and measures three types of atmospheric mercury. The amount of mercury falling over the North Pole is estimated at 300 tons each year. But much more work in atmospheric monitoring is still required to understand the whole cycle of mercury: how much is deposited, re-emitted into the atmosphere, or how much ends up in the fjords. It is not only important to answer these questions, but to act upon the scientific research before any irreversible damage is done.


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