Bacteria Found That Cleans Up Arsenic Contamination

The arsenic-eating bacteria was discovered at the Giant Mine, a large gold mine located at Yellowknife, Northwest Territories, in the Canadian sub-arctic. It contains over 230,000 metric tonnes of arsenic trioxide dust produced during the gold roasting process, making it one of the most polluted places on Earth.

This dust is water soluble and contains approximately 60 percent arsenic.

"Water seeps through the mine cracks carrying the arsenic with it as it drips down the walls," said Thomas Osborne from University College London, UK. "We discovered new types of bacteria living in biofilms on the walls of Giant Mine that consume arsenic compounds contained in the polluted water seeping through."

Arsenic is toxic to all living cells, and in people causes fatal cancers of the lung, liver, kidney and bladder. It also causes cirrhosis and gangrene, and on a wider scale seriously damages wildlife in fragile environments.

"Until now, no bacteria have ever been isolated that can thrive in cold temperatures and deal with arsenic contamination. The new bacteria we discovered function at temperatures from 20 degrees Celsius down as low as 4oC," said Osborne.

"These bacteria also live in a community called a biofilm, which means that we can build them into a new system to clean up contaminated areas by removing the arsenic from soil or drinking water, even in the cold far north and south, or in winter," he said.

Arsenic contamination is a global problem, with some countries, including Vietnam, West Bengal, Mexico, Canada, Argentina, Bangladesh and the United States, severely affected.

"The other exciting possibility that this opens up is that we can isolate the enzyme from these new strains of bacteria and develop an arsenic biosensor to use in cold environments. This will warn when traces of arsenic are escaping from areas like mine workings, industrial chemical facilities, or even laboratories, alerting us before pollution manages to get into watercourses or drinking water supplies," Osborne told his colleagues.

"We could also use it to test newly drilled wells in countries like Bangladesh where water supplies are known to be contaminated," he said.

Many organisms, including all plants and animals, ultimately get their energy from the sun via photosynthesis. But over the last few decades scientists have discovered more and more microbes that can get their energy directly from breaking down chemical bonds. This enables them to survive in extraordinary and dark environments such as deep inside the Earth or at the bottom of the coldest, deepest oceans, where previously no life was expected to exist at all.

The arsenic-contaminated Giant Mine in Yellowknife, NWT, Canada (Photo courtesy Environment Canada)

The mine produced more than seven million ounces of gold during its more than 50 years of operation. After the former owner of the mine went into receivership in 1999, the government of Canada through Indian and Northern Affairs Canada entered into an agreement with Miramar Giant Mine Ltd. to provide care and maintenance at the site. The company continued to mine gold until 2004 but the ore was processed off-site at Con Mine.

In 2005 Miramar Giant Mine Ltd. terminated this agreement, and the government of Canada entered into a cooperation agreement with the government of the Northwest Territories to remediate the site.

The remediation plan took several years to prepare and was completed in 2007. It was submitted to the Mackenzie Valley Land and Water Board as part of a water license application on October 19, 2007. The board is responsible for regulatory approval of the remediation plan under the Mackenzie Valley Resource Management Act.

The remediation plan calls for the long-term storage and maintenance of the 237,000 tonnes of arsenic trioxide dust stored as it is in sealed chambers and stopes underground by using the frozen block method.

The underground mining areas containing the arsenic trioxide dust would be fozen using an active freezing system similar to that used to freeze the ice in indoor rinks.

A super-cooled liquid will be circulated through a series of underground pipes to freeze the designated areas. This freezing will happen in stages over a 20 year period to ensure that the blocks are completely frozen. The blocks will then be kept frozen over the long-term by using thermosyphons - tall, metal tubular devices that draw and expel heat from the ground.

The remediation plan also outlines activities to demolish the more than 100 buildings and facilities on the surface of Giant Mine, and covering of the tailings ponds.

It remains to be seen whether the newly discovered arsenic-eating bacteria found in the Giant Mine will be added to the remediation plan.

Copyright Environment News Service (ENS) 2008. All rights reserved.