Work

Indigenous bacterial adaptation and survival: Exploring the shifts in highly compacted bentonite over a 5-year long-term study for nuclear repository purposes

Year: 2025

Type: article

Abstract: Compacted bentonite is one of the most promising engineered barrier materials used in Deep Geological Repositories (DGR) of high-level radioactive waste encapsulated in metal canisters. Determining bentonite compaction density threshold for bacterial presence and activity has been a long-standing objective, due to their implications for canisters’ durability and, therefore, in the safety performance of DGR. This study provided new insights into the effect of dry density (1.5 and 1.7 g cm⁻³), acetate amendment, and long-term incubation (5 years) on the bentonite mineralogy as well as their bacterial community distribution and survival. Through Illumina sequencing, we demonstrated that higher dry density reduces the bacterial diversity with spore-forming bacteria such as Nocardioides , and Promicromonospora being predominant. Interestingly, Paracoccus and Pseudomonas were enriched in acetate-treated samples, suggesting the utilization of this carbon source and, consequently, supporting their viability and survival. In addition, spore-forming (e.g., Bacillus ) and desiccation-resistant (e.g., Arthrobacter ) microorganisms were isolated. X-ray diffraction and scanning electron microscopy analyses showed the stability of bentonite while indicating the probable formation of iron sulfides. These findings confirm the influence of bentonite compaction degree and long-term incubation on microbial viability and activity, highlighting their potential impact on the integrity and safety of future DGR. • Bentonite compaction degree and 5-year incubation affected microbial diversity. • Bacterial diversity decreased by increasing bentonite compaction density. • Spore-forming bacteria dominated the microbial community of highly compacted bentonite. • Enrichment of acetotrophic microbes confirmed bacterial viability over long-term incubation. • Iron sulfide precipitates indicated active sulfate-reducing bacteria in compacted bentonites.

Source: Journal of Hazardous Materials

DOI: 10.1016/j.jhazmat.2025.137526