Role of fungi in the biogeochemical fate of depleted uranium

The testing of depleted uranium (DU; a 97.25% U:0.75% Ti alloy) ammunition and its use in recent war campaigns in Iraq (1991 and 2003) and the Balkans (1995 and 1999) has led to dispersion of thermodynamically unstable DU metal into the environment [1–3]. Although less radioactive, DU has the same chemotoxicity as natural uranium and poses a threat to human populations [1]. Uranium tends to form stable aqueous complexes and precipitates with organic ligands [4], suggesting that living organisms could play an important role in geochemical transformations and cycling. Fungi are one of the most biogeochemically active components of the soil microbiota [5], particularly in the aerobic plant-root zone. Although the mutualistic symbiotic associations (mycorrhizas) of fungi with plants are particularly important in mineral transformations [5], fungal effects on metallic DU have not been studied. Here, we report that free-living and plant symbiotic (mycorrhizal) fungi can colonize DU surfaces and transform metallic DU into uranyl phosphate minerals.