Citrate is a chelator which binds to certain transition metals and radioactive actinides. Stable complexes such as bidentate, tridentate (ligands with more than one atom bound) and polynuclear complexes (with several radioactive atoms) can be formed with citrate and radionuclides, which receive a microbial action. Anaerobically, Desulfovibrio desulfuricans and species of the genera Shewanella and Clostridium are able to reduce bidentate complexes of uranyl-citrate (VI) to uranyl-citrate (IV) and make them precipitate, despite not being able to degrade metabolically complexed citrate at the end of the process. In denitrifying and aerobic conditions, however, it has been determined that it is not possible to reduce or degrade these uranium complexes. Bioreduction do not get a head when they are citrate complex mixed metal complexes or when they are tridentate, monomeric or polynuclear complexes, since they become recalcitrant and persistent in the environment. From this knowledge exists a system that combines the degradation of radionuclide-citrate complex with subsequent photodegradation of remaining reduced uranyl-citrate (previously not biodegradated but sensitive to light), which allows for stable precipitates of uranium and also of thorium, strontium or cobalt from contaminated lands.