Nanometre-size products of uranium bioreduction.

One strategy that is being pursued to tackle the international problem of actinide contamination of soils, sediments and water is to use microbial activity to 'fix' these radionuclides into an insoluble form that cannot be readily dispersed. Here we show that uraninite (UO(2)) particles formed from uranium in sediments by bacterial reduction are typically less than 2 nanometres across and that the small size has important implications for uraninite reactivity and fate. Because these tiny particles may still be transported in an aqueous environment, precipitation of uranium as insoluble uraninite cannot be presumed to immobilize it.