Table 9.

Examples of low electron donor and acceptor concentrations for important microbial processes in a repository environment.

Microbial group	Electron donor threshold (µmol L−1)	Electron acceptor threshold (µmol L−1)	Reference
Methanogens	4.0 × 10−4 hydrogen, 2.0 × 102 acetate	4.44 × 101 dissolved inorganic carbon	Chen et al. (2019), Jetten et al. (1992), Karadagli and Rittmann (2007), Chen et al. (2019)
Sulphate reducers	7 × 10−4 hydrogen, 4–6 for formate and acetate, and 5 × 10−1 for propionate	1 × 101 in seafloor sediments, <1.04 × 101 in petroleum-contaminated aquifer	Karadagli et al. (2023), Frank et al. (2015), Vroblesky et al. (1996), Glombitza et al. (2015)
Iron reducers	3 × 10−5 hydrogen	Iron reducers can use Fe3+ in solid material, e.g. ferrihydrite	Karadagli et al. (2023)