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Let them eat waste. Bacteria could not only thrive on nuclear waste dumped underground, but may immobilise it and make it safer.

Experiments have shown that certain microbes can make use of radionuclides such as uranium and neptunium in place of oxygen. In doing so, they convert them from soluble forms to insoluble forms, making them less mobile.

This should give us more confidence in waste disposal plans, says Jonathan Lloyd, a geomicrobiologist at the University of Manchester, UK, who presented the research at the annual meeting of the Microbiology Society in Edinburgh last week.


The UK has accumulated around 4.5 million cubic metres of nuclear waste, enough to fill Wembley stadium four times. Most of it is currently stored in ponds and silos at surface level at Sellafield in Cumbria. The government plans to dispose of the most highly active waste deep underground, in repositories encased in cement, but has yet to decide on a site.

These plans are designed to be safe based on physical and chemical barriers that will stop radioactive material from escaping for hundreds of thousands of years.

Too alkaline?

It had been thought that the presence of cement would result in conditions too alkaline for microbes to grow – it has a pH of around 11, similar to bleach. To see if this was true, Lloyd’s team studied a lime kiln site in the UK’s Peak District to see if microbes could be found growing in conditions similar to those that would be expected in a nuclear disposal site.

“We went to see if there was biology there and there was,” says Lloyd. “All the sorts of organisms we were interested in studying, we could find, and we found they could grow at pH values you would probably find developing around these cementitious waste forms.”

The radiation levels typically found at nuclear waste dumps don’t seem to pose a problem for bacteria either. In fact, it can help them by increasing the availability of certain nutrients.

“When we’ve studied microbial systems under similar doses to what you would have around these waste forms, it doesn’t kill them,” says Lloyd. “If anything, it actually stimulates the microbes down there.”

Work by Lloyd’s team and others has highlighted various ways bacteria can process waste products that make it less likely hazardous material will seep into the environment. Some nuclear waste contains cellulose, which can break down to form isosaccharinic acid (ISA) under alkaline conditions.

Nuclear leak

ISA can form a soluble complex with uranium, helping it to leak out of the waste repository. But bacteria seem to like using ISA as a carbon source and degrade it, keeping radionuclides in solid form – which means they stay in place.

Microbes may also help prevent radioactive gases escaping. Hydrogen gas produced by reactions in the repository could build up pressure that leads to radioactive gases escaping through fractures in the rock. But a recent study in a rock formation in Switzerland where repositories are planned found that microbes there can exploit hydrogen and thus keep the levels down.

“At the moment, safety case models are built on chemistry and physical containment. If you start including the biology, it means that those models are actually overly conservative, which is a good thing,” says Lloyd, who is part of an EU-funded consortium studying the impact of microbes on the safety of geological repositories.

Previous studies have largely focused on whether there will be any negative effects, and ignored any positive effects, says Joe Small of the National Nuclear Laboratory in Warrington, UK, another researcher in the consortium.

But a lot more research will have to be done before we can be sure these positive effects persist and outweigh any negative ones over the very long timescales involved in storing radioactive waste.

In the shorter term, the findings could be useful to us in other ways. The uranium-munching bacteria could help decontaminate drinking water, for instance. “It would be really nice to identify these organisms and harness this ability to clean up our messes,” says Lee Kerkhof at Rutgers University in New Jersey, who is studying microbes from an old uranium ore mill in Colorado.

Read more: Shocking state of world’s riskiest nuclear waste site

The attribution of statements in the third-from-last paragraph has been changed.