The Wismut GmbH Schlema-Alberoda operation, once one of the largest uranium mines globally, left a hazardous legacy in what was then Soviet East Germany. Following its closure in 1990, coinciding with Germany’s reunification, the site has undergone extensive and expensive remediation.
Since the mine’s closure, it filled with water, necessitating ongoing treatment. The radioactive nature of raw uranium means that exposure, such as through drinking contaminated water, poses significant health risks to humans and other organisms.
Interestingly, the uranium-rich waters of the abandoned mine support a microbial ecosystem. Recent scientific findings have shown that these microbes can stabilize uranium under specific conditions.
The study was conducted by microbiologists and resource ecologists from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany and the University of Granada in Spain. Their findings were published in Nature Communications.
Microbiologist Evelyn Krawczyk-Bärsch of HZDR notes, “Our group’s investigations had already revealed that bacteria can use uranium dissolved in water for their metabolism when they have access to glycerol as a food source.”
She further explains that their research demonstrated, for the first time, how bacteria with glycerol as a carbon source can transform dissolved toxic uranium into a stable chemical form.
The research team, led by Krawczyk-Bärsch, began their study with water samples from the Wismut GmbH Schlema-Alberoda mine’s treatment plant inlet.
HZDR microbiologist Antonio Newman-Portela states, “We wanted to create natural conditions for the bacterial community already existing in the mine water because at a depth of approximately 2,000 meters there is usually little or no oxygen in the mine.”
Upon incubating the bacteria with glycerol, the researchers found that the bacteria converted uranium into a pentavalent state.
In this pentavalent form, uranium has an unusual oxidation state of +5, which alters its bonding behavior, making it easier to incorporate into stable minerals.
Newman-Portela explains that normally, uranium has a valency of 4 or 6, and while pentavalent uranium is known, it is rare and typically unstable.
In the presence of bacteria, pentavalent uranium combines with iron and oxygen to form FeU(V)O4, a known compound yet unfamiliar in natural formations involving bacteria.
After 130 days of incubation, Newman-Portela reports that only about five percent of the uranium remained dissolved in the samples.
The bacteria not only integrated uranium into their cell walls, but a significant portion of this uranium existed in the pentavalent state, facilitating the formation of FeU(V)O4, particularly when the samples were dried and exposed to oxygen.
Uranium contamination is a widespread concern, affecting surface and groundwater in countries like the United States, India, Canada, France, South Africa, and Australia, often surpassing the recommended limit of 0.03 milligrams per liter.
This prompts the question: could bacteria offer a solution?
For over thirty years, bioremediation has been studied as a cost-effective alternative to traditional physico-chemical water treatment methods, as the authors of the study note.
Field studies utilizing biological methods have shown significant uranium reduction while preventing the creation of secondary sludge.
These bacteria might become valuable allies in addressing nuclear contamination issues, not only in Germany but also worldwide.
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The authors conclude that the processes identified, though derived from a specific geochemical scenario, have broader implications for other contaminated waters.
However, as Krawczyk-Bärsch mentions, further research is needed to understand how effectively bacteria can render uranium harmless for remediation purposes.
The findings were published in Nature Communications.
This article was fact-checked by Carly Cassella and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
