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A previously unknown arsenic-loving bacterium may provide a way to keep one of Canada's most toxic sites from poisoning one of the country's largest lakes and river systems, a pair of British scientists say.

In a paper delivered yesterday in Dublin, researchers from University College London revealed they have discovered a microbe living deep within Yellowknife's Giant Mine, where 230,000 tonnes of arsenic left over from decades of gold mining lies underground.

The mine site, which the federal government is cleaning up, is right beside Great Slave Lake, the source of the Mackenzie River.

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Microbiologists Thomas Osborne and Joanne Santini examined samples of bacteria found on walls in the bowels of the mine and found microbes busily converting one type of arsenic to another.

"Arsenite is very difficult to remove from water, whereas arsenate is relatively easy to remove," Mr. Osborne said.

Similar bacteria are found all over the world, but these were the first able to work in such a cold environment.

"Before, all the bacteria that have been isolated grow in moderate and hot temperatures, from 20 to 35 degrees and above 50 degrees. We found bacteria that will grow below 10 degrees," he said. "You could theoretically use them to help remove arsenic completely from water."

Arsenic is highly soluble, and contaminated water that collects deep within the former mine has been one of the chief concerns about the site. Even before Giant stopped producing in 2005, water that dribbled into its lower depths was pumped out to keep it from seeping into ground water and eventually into Great Slave Lake.

The federal government has since announced a remediation plan that would freeze the entire mine like an enormous, inverted popsicle.

Refrigerating pylons would be sunk to the level of the lowest arsenic chamber to restore the permafrost destroyed by decades of mining. Thermal pumps, commonly used in the North to keep permafrost solid under a building's foundations, would then draw heat out to keep the ground frozen.

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Water would slowly be released back into the mine to freeze and immobilize the whole area.

The entire process would take 20 years. Estimates suggest it would cost taxpayers somewhere between $90-million and $120-million. Area residents aren't convinced the plan would work and have forced the government to hold environmental hearings on it.

Mr. Osborne suggests the new microbe could become part of the solution. "Research using [the microbe]in filters to remove arsenic is ongoing and that could be a very real possibility."

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