The radiation resistance and cobalt biosorption activity of yeast strains isolated from the Lanyu low-level radioactive waste repository in Taiwan

The ubiquitous nature of microbes has made them the pioneers in radionuclides adsorption and transport. In this study, the radiation resistance and nuclide biosorption capacity of microbes isolated from the Lanyu low-level radioactive waste (LLRW) repository in Taiwan was assessed, the evaluation of the possibility of using the isolated strain as biosorbents for ⁶⁰Co and Co (II) from contaminated aqueous solution and the potential impact on radionuclides release. The microbial content of solidified waste and broken fragments of containers at the Lanyu LLRW repository reached 10⁵ CFU/g. Two yeast strains, Candida guilliermondii (CT1) and Rhodotorula calyptogenae (RT1) were isolated. The radiation dose necessary to reduce the microbial count by one log cycle of CT1 and RT1 was 2.1 and 0.8 kGy, respectively. Both CT1 and RT1 can grow under a radiation field with dose rate of 6.8 Gy/h, about 100 times higher than that on the surface of the LLRW container in Lanyu repository. CT1 and RT1 had the maximum ⁶⁰Co biosorption efficiency of 99.7 ± 0.1% and 98.3 ± 0.2%, respectively in ⁶⁰Co aqueous solution (700 Bq/mL), and the ⁶⁰Co could stably retained for more than 30 days in CT 1. Nearly all of the Co was absorbed and reached equilibrium within 1 h by CT1 and RT1 in the 10 μg/g Co (II) aqueous solution. Biosorption efficiency test showed almost all of the Co (II) was adsorbed by CT1 in 20 μg/g Co (II) aqueous solution, the efficiency of biosorption by RT1 in 10 μg/g of Co (II) was lower. The maximum Co (II) sorption capacity of CT1 and RT1 was 5324.0 ± 349.0 μg/g (dry wt) and 3737.6 ± 86.5 μg/g (dry wt), respectively, in the 20 μg/g Co (II) aqueous solution. Experimental results show that microbial activity was high in the Lanyu LLRW repository in Taiwan. Two isolated yeast strains, CT1 and RT1 have high potential for use as biosorbents for ⁶⁰Co and Co (II) from contaminated aqueous solution, on the other hand, but may have the impact on radionuclides release from LLRW repository. - Highlights: • Two yeast strains (CT1 and RT1) isolated from Lanyu LLRW repository could survive and grow under a dose rate of 6.8 Gy/h. • CT1 and RT1 absorbed nearly 100% of Co (II) and reached equilibrium within 1 h in 10 μg/g cobalt (II) aqueous solution. • CT1 effectively removed ⁶⁰Co to yield concentrations that met sewage monthly average discharge standard of ⁶⁰Co