The flooded depths of a Cold War uranium mine have yielded an unexpected discovery: bacteria that can convert dissolved radioactive uranium into a stable solid mineral, potentially offering a new way to tackle one of Europe’s largest environmental remediation challenges. Researchers from Germany’s Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and Spain’s University of Granada found that uranium mine bacteria—naturally occurring microbes in the Schlema-Alberoda mine—removed up to 96% of dissolved uranium from water samples in just 130 days. Their findings, published in Nature Communications in July 2026, reveal a biological process that transforms a highly mobile contaminant into a compound stable enough to persist for decades.
The discovery matters because the Schlema-Alberoda mine is not just any abandoned industrial site. It was Europe’s largest uranium operation, producing 231,000 tonnes of uranium for the Soviet nuclear program between 1946 and 1990. Its legacy includes 800 million tonnes of radioactive waste, a 7 billion euro cleanup bill, and a water treatment plant that must run indefinitely, with no end in sight. The bacteria living in that toxic water may change the calculus entirely.
Inside the Schlema-Alberoda Mine: A Cold War Legacy
From 1946 to 1990, the Soviet-German Wismut Company operated the Schlema-Alberoda mine in Saxony, extracting 231,000 tonnes of uranium and becoming the world’s fourth-largest producer. The uranium fueled the Soviet Union’s nuclear weapons and energy programs throughout the Cold War, making the mine a strategic asset of immense value. But the cost of extraction was staggering, and the environmental consequences would long outlast the geopolitical ones.
Mining low-grade ore generated roughly 800 million tonnes of waste rock, radioactive sludge, and overburden material, devastating approximately 10,000 square kilometers across the federal states of Saxony and Thuringia. Rivers were diverted, hillsides reshaped, and entire landscapes permanently altered. By the time the mine ceased operations, it had become the single largest environmental liability in the former East Germany.
When the mine closed in 1990 following German reunification, there was no transition plan. The underground workings, some extending nearly 2,000 metres below the surface, were gradually flooded in a controlled process that began in 1991. But flooding did not solve the contamination problem. Water moving through the old mine shafts continues to leach uranium, arsenic, and other heavy metals from the surrounding rock. Uranium concentrations in the untreated mine water remain around one milligram per liter, well above the discharge limits set by Saxon authorities.
Today, Wismut GmbH, the state-owned corporation charged with remediation, operates a treatment plant at the site that runs continuously. The process is straightforward but costly and endless. Water is pumped from the mine, aerated to strip out carbon dioxide, treated with alkaline chemicals, and filtered to remove precipitated contaminants. The result is large volumes of contaminated sludge that must be stored and managed separately, creating a secondary waste problem almost as daunting as the original one. The German government initially earmarked 6.4 billion euros for the Wismut cleanup—one of the largest environmental remediation programs ever undertaken. Current estimates place the total cost at 7 billion euros. And unlike most environmental remediation projects, this one has no projected completion date. The water must be treated for as long as it keeps flowing, potentially centuries.
How the Discovery Was Made
A research team led by scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), working with Wismut GmbH and the University of Granada in Spain, set out to study whether the native microbial community in the mine water could be harnessed to reduce uranium contamination. Their results, published in July 2026, exceeded expectations and opened a new front in the search for sustainable remediation strategies.
The researchers collected water samples from the inlet of the treatment plant and designed a laboratory experiment to closely replicate the conditions deep underground. At a depth of roughly 2,000 meters, the mine environment has little or no oxygen. The team sealed the water samples in bottles without oxygen and kept them in the dark to mimic the subterranean environment as faithfully as possible.
To stimulate the bacteria already living in the water, they added glycerol, a simple carbon-rich compound that is a basic component of plant and animal fats and is also formed when fungi decompose wood in nature. Glycerol was chosen deliberately. It is cheap and widely available as a byproduct of biodiesel production, and previous research had already shown that certain bacteria could use it to fuel uranium-reducing metabolic processes.
On day one of the experiment, the mine water appeared yellow, a telltale sign of dissolved uranium. Over the following weeks, something remarkable happened. The water gradually cleared, and a black precipitate began forming at the bottom of the bottles. After 130 days, the researchers measured the uranium concentration in the water and found it had dropped from 1 milligram per liter to just 0.04 milligrams per liter, a reduction of approximately 96 percent.
In control experiments where no glycerol was added or where the water was sterilized to kill the bacteria, uranium levels dropped by only 25 to 36 percent. The difference confirmed that the stimulated bacteria, not simple chemical precipitation, were responsible for the dramatic cleanup. “We suspected that the bacteria had incorporated the uranium into their cell walls,” said Antonio M. Newman-Portela, the study’s lead author and a former doctoral candidate at both HZDR and the University of Granada. Advanced microscopic and spectroscopic analysis confirmed exactly that. The uranium was accumulating in and around the bacterial cells, forming solid nanoparticles.
Meet the Microbes: Desulfovibrio and the Two-Stage Cleanup Crew
The mine water is not home to a single bacterial species but to an entire microbial ecosystem that has adapted to an extreme environment with high metal concentrations and almost no oxygen—not unlike the microbial life discovered 2.4 kilometers underground in Earth’s deep biosphere, where organisms survive under similarly extreme conditions. Among the key players identified in the study are bacteria belonging to the genus Desulfovibrio, a group of sulfate-reducing bacteria well known to microbiologists for their ability to transform metals—a capacity also seen in metal-eating bacteria discovered in other extreme environments.
What makes the process work is a two-stage microbial partnership. In the first stage, certain bacteria ferment the glycerol, breaking it down into simpler organic acids and hydrogen gas. In the second stage, Desulfovibrio and related sulfate-reducing bacteria consume those breakdown products as fuel. As they do, they also alter the chemistry of the surrounding water, reducing sulfate to sulfide and changing the oxidation state of dissolved metals, including uranium.
The enzymatic machinery behind uranium reduction in Desulfovibrio has been studied for decades, with research identifying cytochrome c3 as a critical electron carrier in the reduction pathway. A key protein is cytochrome c3, a periplasmic electron carrier that transfers electrons to uranium, converting it from a soluble to an insoluble form. While no single enzyme is solely responsible, cytochrome c3 appears to be a critical part of the electron transport chain. The researchers also observed that the stimulated bacteria consumed nearly all of the dissolved iron in the water and about two-thirds of the sulfate. These geochemical shifts are not side effects. They are integral to the immobilization process. The uranium does not simply get reduced. It becomes chemically bound with iron and oxygen to form a remarkably stable mineral.
Pentavalent Uranium: The ‘Impossible’ Chemical State
In chemistry, the term “valency” describes how many chemical bonds an atom can form. Uranium almost always appears in nature with a valency of four, known as tetravalent uranium or U(IV), or six, known as hexavalent uranium or U(VI). Hexavalent uranium dissolves readily in water and can travel long distances through groundwater, which is why it poses such a contamination risk. Tetravalent uranium, by contrast, tends to form insoluble minerals like uraninite that stay put.
There is a third state, pentavalent uranium or U(V), with a valency of five. Chemists have long known U(V) exists, but it was considered so unstable that it would almost immediately transform into either U(IV) or U(VI) in any natural environment. Finding it in significant quantities inside a real mine was not expected, and it overturns a long-held assumption about uranium chemistry in the environment.
“Uranium usually occurs with a valency of 4 or 6. Pentavalent uranium does exist, but it is rare or only transient. Until now, it had been seen in an unstable oxidation state,” Newman-Portela explained. “So, the findings of our study were extremely surprising because in the biomass analyzed from our experimental runs, an unusually high proportion of the uranium identified was also pentavalent uranium.”
The pentavalent uranium combined with iron and oxygen to form a compound with the chemical formula FeU(V)O4.
This compound does not yet have a common name, because until recently, scientists barely knew it existed. It was first identified in a 2020 study of soil from parts of Croatia contaminated by depleted uranium ammunition used during the Balkan conflicts of the 1990s. In that soil, FeU(V)O4 had remained stable for more than 25 years despite being exposed to atmospheric oxygen the entire time.
The HZDR team confirmed something even more surprising. When they dried the bacterial biomass from their experiments and exposed it to oxygen, the amount of FeU(V)O4 actually increased. Far from destroying the pentavalent uranium, oxygen appeared to help lock it into the stable mineral form. “Our study has revealed for the first time that bacteria supplied with glycerol as a carbon source can convert toxic uranium dissolved in water into a stable chemical compound,” said Dr. Evelyn Krawczyk-Bärsch, a scientist in HZDR’s Terrestrial Microbiology research group and co-author of the study.
What This Means for Mine Cleanup
The current method of treating the Schlema-Alberoda mine water is effective but fundamentally unsustainable. Water must be continuously pumped, aerated, chemically treated, and filtered, generating enormous volumes of contaminated sludge that require their own long-term storage. The process consumes significant energy and resources, and because contaminated water will continue flowing through the mine for the foreseeable future, there is no off switch.
Bacterial bioremediation offers a radically different approach. Instead of extracting and treating water above ground, the idea is to stimulate the bacteria already living in the mine to immobilize uranium where it sits, reducing or eliminating the need for perpetual active treatment. The comparison below illustrates the differences between the two approaches.
| Factor | Current Chemical Treatment | Potential Bacterial Bioremediation |
|---|---|---|
| Method | Pump, aerate, add alkaline chemicals, filter precipitates | Stimulate native bacteria with glycerol in situ |
| Waste Generated | Large volumes of contaminated sludge requiring long-term storage | Solid uranium minerals trapped in stable form |
| Energy Input | High, continuous pumping and aeration | Low, passive process once stimulated |
| Cost | 7 billion euros and counting | Potentially far lower (glycerol is cheap biodiesel waste) |
| Endpoint | None, treatment must continue indefinitely | Potential long-term stabilization of uranium in place |
| Status | Operational since 1990s | Laboratory proof-of-concept only |
The researchers themselves are careful to temper expectations. “We still have to investigate to what extent bacteria might help to render uranium harmless for remediation purposes,” Krawczyk-Bärsch cautioned. The experiments were conducted in sealed laboratory bottles with carefully controlled conditions. Translating those results to a 2,000-meter-deep flooded mine with complex hydrogeology is an entirely different challenge.
Several practical questions remain unanswered. How much glycerol would be needed at field scale, and how would it be delivered and distributed through kilometers of flooded tunnels? What happens to the uranium-laden bacteria over decades? Could the uranium remobilize if conditions change, for example if the mine floods with oxygenated rainwater? These are the questions the HZDR team aims to address in future work.
Despite the unknowns, the study represents a proof of principle with genuine significance—much like how certain microbes can protect the environment by transforming toxic compounds through natural metabolic processes. The bacteria are already there. They are not genetically modified or artificially introduced. They simply need the right food source to do what evolution has equipped them to do, and that simplicity is precisely what makes the approach so compelling.
Beyond Germany: The Global Uranium Contamination Problem
The Schlema-Alberoda mine is not an isolated case. Uranium contamination of surface water and groundwater is a widespread and persistent problem in every country with a history of uranium mining or processing. The United States, India, Canada, France, South Africa, and Australia all have sites where uranium concentrations in water exceed the World Health Organization guideline of 0.03 milligrams per liter.
In the United States alone, the Environmental Protection Agency estimates that abandoned uranium mines across the Navajo Nation and the western states have left behind more than 500 contaminated water sources. Many of these sites are remote, economically depressed, and technically challenging to remediate. Traditional pump-and-treat remediation, where contaminated water is extracted, treated above ground, and discharged, generates enormous volumes of secondary waste and is often economically unfeasible for low-priority or hard-to-reach locations. Alternative approaches, such as shockwave-based decontamination, have shown promise but remain similarly early-stage.
Microbial bioremediation has been explored for decades as a lower-cost, lower-waste alternative. Field studies using biological methods, such as injecting nutrients to stimulate native bacteria, have demonstrated substantial uranium reduction without generating secondary sludge. The challenge has always been ensuring that the immobilized uranium stays immobilized. The discovery of FeU(V)O4, with its demonstrated 25-year stability under real-world conditions, strengthens the case that biological remediation can produce lasting results. The paper’s authors are explicit about the broader applicability of their findings. “Although derived from a single geochemical scenario, the processes identified here are broadly applicable to other contaminated waters,” they write.
Frequently Asked Questions
What bacteria were discovered in the uranium mine?
The microbial community includes several types of bacteria, with Desulfovibrio, a genus of sulfate-reducing bacteria, playing a key role. These are naturally occurring microbes, not genetically engineered or artificially introduced. They have adapted over time to survive in the extreme environment of the flooded mine, which has almost no oxygen and high concentrations of uranium and other heavy metals.
How do the bacteria trap uranium?
When provided with glycerol as a food source, the bacteria metabolize it and, in the process, alter the chemical state of dissolved uranium. They convert soluble hexavalent uranium (U(VI)) into pentavalent (U(V)) and tetravalent (U(IV)) forms, which are far less mobile. The pentavalent uranium combines with iron and oxygen to form FeU(V)O4, a solid mineral that essentially locks the uranium in place. Much of the uranium accumulates on bacterial cell walls as nanoparticles.
Can this method clean up all radioactive contamination?
No. The process specifically targets dissolved uranium in water, not other radioactive elements or solid radioactive waste. It is most relevant to groundwater and mine water contaminated by uranium mining and processing. Other contaminants present in the mine water, such as arsenic, would require separate treatment approaches.
Is the treated water safe to drink?
The study reduced uranium to very low levels, from 1 milligram per litre to 0.04 milligrams per litre, but the experiments were conducted in sealed laboratory bottles, not in a real drinking water system. Making water safe for human consumption would require additional treatment steps and rigorous testing. The research remains at the proof-of-concept stage and is not yet ready for deployment in public water supplies.
When could this be used in real mine cleanup operations?
There is no specific timeline. The HZDR research team plans to continue investigating the underlying biochemical and geochemical processes, with field trials likely years away. Several practical challenges must be solved first, including how to deliver glycerol at scale through kilometres of flooded mine workings and how to ensure the uranium remains permanently immobilized over geological timescales.
Conclusion
The bacteria living in the flooded darkness of the Schlema-Alberoda mine did not evolve to solve a human problem. They adapted to survive in an environment that would kill most living things, and in doing so, they developed metabolic pathways that happen to immobilize one of the most persistent contaminants of the nuclear age. The discovery does not mean radioactive pollution can suddenly be made to disappear. It means there is a lower-waste, lower-energy tool worth developing further, one that nature has already tested in the most unforgiving of laboratories.
The Cold War left Europe with environmental debts that will take generations to repay. At Schlema-Alberoda, where the cleanup bill runs to billions of euros and the treatment plant has no off switch, a microscopic ally may help lighten that load. The next step is to find out whether what worked in a bottle can work in a mine.
The research was published in the journal Nature Communications (Newman-Portela et al., 2026, DOI: 10.1038/s41467-026-72560-z).
