Microorganism Cleans Up Toxic Groundwater

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"Within the DOE complex, uranium contamination of soils and groundwater is widespread because it was mined, milled, refined, purified, enriched, fabricated, and reprocessed with each step typically taking place at a different location," Fryberger said.

According to Lovley, exact figures on the extent of uranium-contaminated groundwater are difficult to come by, but he said, "It's massive."

"To try to clean up all existing uranium contaminated sites with current technology—the non-biological things—it would basically bankrupt the country," Lovley said. "The costs are too much. That's why we're looking for simpler and cheaper methods."

Is Geobacter the cheap and simple answer? The researchers are testing the microorganism at an abandoned uranium mining and mill site near the town of Rifle in western Colorado.

Field Tests

Geobacter are naturally present in the groundwater at the Rifle site, but they thrive mostly on iron oxide and their populations are relatively small.

From previous work Lovley and his colleagues know that Geobacter's favorite food is acetate—essentially vinegar. When acetate is abundant, Geobacter populations explode.

So the researchers drilled a few pipes into the ground at the Rifle test site and let the acetate slowly drip into the groundwater to encourage a population explosion. According to the scientists' theory, if the population explodes, the microbes will exhaust the iron oxide supply and turn their attention to the dissolved uranium.

To test this hypothesis, the researchers drilled a series of wells downstream from where they dripped the acetate and periodically took water samples. By the end of the 2003 field session, the scientists had refined their technique to the point of removing about 90 percent of the uranium from the groundwater.

Instead of digging down and removing the solid uranium, the scientists allow the solid, immobile form to stay in the ground. "As long as we stabilize these uranium-contaminated environments that are near a river, as long as it won't be carried to the river, people are going to be very happy," Lovley said.

To ramp up the technology, Lovley and his team are now developing a computer model that describes the way the microbes respond to different conditions in the environment. The team also recently sequenced the genome of Geobacter sulferreducens, which has provided insight to the way the microbe functions.

Fryberger, the DOE research director, said that she and her colleagues are "excited about Dr. Lovley's results from the old Rifle site. This work has shown that microbial immobilization of uranium can be accomplished outside of the laboratory."

One question for the Department of Energy going forward is the long-term stability of the immobilized uranium created by the microbial interactions.

Another concern raised by Arjun Makhijani, president of the Institute for Energy and Environmental Research in Takoma Park, Maryland, is the long-term effect of wide-scale applications of the microbes.

"We are not attending to unforeseen consequences of long-term changes in the organisms and what damage that might cause to the ecosystems," Makhijani said.

For more microbe news, scroll down for related stories and links.

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