Unassuming fungi lock depleted uranium out of harm's way

Militaries used depleted-uranium munitions to penetrate hardened targets. Currently, contaminated battlefields can be partial decontaminated by physically collecting and disposing of fragments from shells. Trouble is, radioactive particles and dust from explosions remain in the soil, preventing full reclamation. Now, a research team in Scotland has established that common fungi can grow on and chemically lock away the offending uranium. As their hyphal filaments sprawled across fragments of depleted uranium, the tubules gradually became coated in a yellowy mineral. This, it turned out, locked the uranium into a chemical form inaccessible to biological organisms, and unlikely to dissolve into surface waters. At twice the density of lead, depleted uranium is added to weapons to give them extra force to penetrate targets, but the complete fallout from exploding missiles is impossible to collect physically. This means that hazardous radioactive uranium-235 in the material, which can cause kidney toxicity and has been linked with nerve damage and lung cancer, can persist in the environment for decades. “The fungal-produced minerals are capable of long-term uranium retention, so this may help prevent uptake of uranium by plants, animals and microbes,” says team leader Geoffrey Gadd of the University of Dundee. “It might also prevent the spent uranium from leaching out from the soil,” he says.

Essentially, the fungi form uranyl phosphate minerals which stabilize the uranium. “They change its chemistry from being highly chemically unstable and reactive metallic uranium to one of the most chemically stable forms, thus preventing uranium migration through the food chain,” says Gadd. Gadd says that any clean-up operation based on the fungi would be very low-tech. All that would be needed in practice would be to add moisture and nutrients to soil to help fungi flourish. “You can go to just about any soil, and you’d find fungi that would lock away uranium,” he says. “You could literally pick them from your own back garden.” He cautions that the minerals probably could not ever be considered harmless as they still contain uranium, and this could still be toxic if eaten. Nor have the Dundee team yet worked out a practical way to collect and dispose of the trapped uranium. The finding itself was a bonus in research mainly aimed at tracing the environmental fate of uranium. “Our work is only very preliminary,” he says. Ultimately, it might be possible to devise practical ways of using the fungi to decontaminate sites, Gadd says.