ABSTRACT
Reduction and oxidation processes exert an important control on the natural concentrations of O2, Fe2, SO4
2, H2S, CH4, etc. in groundwater. They also determine the fate of pollutants like nitrate leaching from agricultural fields, contaminants leaching from landfill sites, industrial spills, or heavy metals in acid mine drainage. Redox reactions occur through electron transfer from one atom to another and the order in which they proceed can be predicted from standard equilibrium thermodynamics. However, the electron transfer is often very slow and may only proceed at significant rates when mediated by bacterial catalysis. An example is the reduction of sulfate by organic matter which occurs both in aquifers and in marine sediments. The reaction is immeasurably slow abiotically, but microbes like Desulfovibrio sp. produce enzymes that catalyze the process and the reaction proceeds rapidly in natural environments.
