The aim of this study was to investigate the change of Pu oxidation states due to interaction with aerobic bacteria and fungi
at low pH under laboratory conditions. Microorganisms were isolated from samples collected from the low-level radioactive
waste repository within the confines of Ignalina NPP. Abilities of the fungi (Absidia spinosa var spinosa Lendn. and Paecilomyces lilacinus Thom Samson) as well as Gram-positive bacteria (Bacillus mycoides and Micrococcus luteus) and Gram-negative bacterium I-m1 to transform the oxidation states of Pu under aerobic conditions were investigated. Oxidized
and reduced Pu was tested using two radiochemical procedures. The amount of reduced and oxidized Pu was determined by measuring
alpha activity after radiochemical separation. The results have shown that all bacteria and fungi can very slightly alter
oxidation states of Pu due to their microbial activity. All the microorganisms tested demonstrate quite a fast process of
Pu biosorption under the experimental conditions.