Implications of iron minerals in terrestrial anaerobic microbial redox processes for greenhouse and toxic gas emissions, and contaminant dynamics

Global concerns about increasing emissions of greenhouse gases (GHG), particularly methane (CH4) and nitrous oxide (N2O), and toxic hydrogen sulfide (H2S) gas from terrestrial and aquatic ecosystems warrant a comprehensive understanding of anaerobic microbial redox processes that contribute to these atmospheric emissions. Iron minerals that are widely distributed in natural environments mediate many anaerobic microbial metabolic processes that drive C, N, and S biogeochemical cycles, and create resilience in the terrestrial ecosystem against climate and other environmental changes. In this review, scientific information from recent research is gleaned to provide updated microbial pathways that reveal how Fe minerals, with their different properties and redox speciation, influence microbial redox processes in anaerobic environments (iron-, nitrate- and sulfate-reducing, and methanogenic conditions). These microbial processes have profound positive and negative environmental implications for GHG and H2S emissions in natural environments and also play a vital role in contaminant transformation. This review provides insights into mineral-microbe interactions and the importance of the physicochemical properties of minerals in defining these interactions. Comprehensive knowledge about these processes will help devise strategies to mitigate GHG and H2S emissions and biodegrade organic contaminants in natural and engineered environments.