Many factors control and affect geochemical reactions.
Organic matter in ground water plays important roles in controlling geochemical processes by acting as proton donors/acceptors and as pH buffers, by affecting the transport and degradation of pollutants and by participating in mineral dissolution/precipitation reactions. Dissolved and particulate organic matter also may influence the availability of nutrients and serve as a carbon substrate for microbially mediated reactions. Numerous studies have recognized the importance of natural organic matter in the mobilization of hydrophobic organic species, metals and radionuclides. Many contaminants that scientists view as virtually immobile in aqueous systems can interact with dissolved organic carbon or colloidal organic matter, resulting in migration of hydrophobic chemicals far beyond distances predicted by structure/activity relationships. Although organic matter often is present in low concentrations in subsurface systems, this organic matter can exhibit significant reactivity with contaminants. In addition, these compounds are reactive substances that are potential precursors for the formation of disinfection by-products resulting from water treatment practices.