SYDNEY: Some bacteria have the capacity to stabilise uranium contaminated sites, and if they are used they could reduce the chances of these sites contaminating major waterways and ecosystems, U.S. scientists have said.
Of the millions of tonnes of bacteria living within the Earth’s subsurface, some are able to transform the oxidative state of uranium, which defines how the element will interact with oxygen to form various molecules. They change it from the radioactive, toxic and water soluble uranium (VI) to the less soluble, stationary and therefore less harmful uranium (IV) as part of their normal growth.
While this process is relatively well known and has been demonstrated numerous times, until now most studies have occurred in the lab without the added difficulties associated with working in the field. Namely, that uranium isn’t the only element that the bacteria affect.
Bacteria causes changes in other elements too
“Bacteria cause chemical changes in several elements, including iron and sulphur,” said Ken Kemner, a physicist with the U.S. Department of Energy’s Argonne National Laboratory, which is conducting the research.
“Those changes in the iron and/or sulphur geochemistry could cause the uranium to change between soluble and insoluble forms,” he said.
The Argonne scientists are studying bacteria at three uranium-contaminated research sites across the United States, one in Colorado and two others at the Pacific Northwest and Oak Ridge National Laboratories in Washington State and Tennessee, respectively. All are relics of the nuclear proliferation of the Cold War era, with the potential for contaminating major waterways.
Not yet ready to unleash on environment
Using the US Department of Energy’s Advanced Photon Source (APS) electron accelerator and storage system – which provides the brightest x-ray beams in the Western Hemisphere – the scientists have been able to study the transformation of uranium at the atomic level.
“The [researchers have] successfully demonstrated in some pilot studies that this really works,” Kemner said. “But we don’t understand it enough that we can go off into the environment and routinely employ the bacteria on a larger scale.”
According to Robert Anitori, a microbiologist at Oregon Health and Science University, “the importance of the research being performed by the Argonne group is that they are trying to understand what is going on in the field.”
Other bacteria, iron may work too
“This is unique, compared to the numerous previous studies in this area,” he said. “Their work will result in improvements in the efficiency and effectiveness of uranium-eating bacteria employed in contaminated sites.”
Anitori is currently working on a similar project using a nanoscale form of iron to clean up a uranium-contaminated site on the Columbia River in Washington State. He has also worked with the Australian Centre for Astrobiology, based at the University of New South Wales, on similar ‘extremophile’ bacteria inhabiting radioactive hot springs in South Australia’s Flinders Ranges.
According to Anitori, “the [Argonne] results are easily applicable in an Australian context, in that they would be easy to adapt to any uranium contaminated site.” One such example is the leakage of uranium-contaminated water from the Ranger uranium mine, located in the World Heritage-listed Kakadu National Park in Australia’s Northern Territory.
Kakadu under threat of contamination
In 2009 the Australian Office of the Supervising Scientist warned that the Ranger Uranium Mine was spilling the equivalent of three petrol tankers-worth of contaminated water into the ground each day. In total, there have been more than 150 leaks, spills and other problems at the site since it opened in 1981.
Earlier this year, news outlets reported that the water seeping out from beneath the dam at the Ranger mine has a uranium level of about 5,400 times greater than the natural background level.
While Australia has no nuclear weapons, and does not currently use uranium to generate electricity, it holds around 23% of the world’s uranium reserves, has three large-scale uranium mines and three nuclear reactors with the capacity to commercially produce radioisotopes for nuclear medicine and neutrons for research and irradiation of materials. Australia has also accumulated over 4000 cubic metres of low level and ‘short-lived’ intermediate level radioactive waste in the past 40 years.
The U.S. Department of Energy’s Argonne National Laboratory published two studies on the research in January and February this year. Both appeared in the US-based journal Environmental Science & Technology.
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The Argonne National Laboratory homepage
Abstract in Environmental Science & Technology
Second Abstract in Environmental Science & Technology