ABSTRACT
Microorganisms mediate the biotransformation of many different chemicals in the subsurface. Historically there has been much scientic debate over the relative contribution of abiotic and biotic chemical processes in the subsurface. Until the last 50 years, very little was known about microorganisms in groundwater, and thus abiotic transformations were thought to dominate. However, more recent research has contributed new knowledge about microbial life in the subsurface and this view has changed. While our understanding of subsurface microbiology and biogeochemistry is far from complete, biologically mediated reactions of both inorganic and organic compounds in groundwater are known to be signicant, and in many cases
control groundwater chemistry (Chapelle, 1993). With respect to the biotransformation of organic pollutants, microbially mediated reactions are by far the most important. e abiotic transformation of pollutants does occur (e.g., dehalogenation, polymerization, and hydrolysis reactions), however, the environmental signicance of these abiotic reactions relative to microbially mediated reactions is dicult to assess. is is partly due to the diculty in distinguishing between abiotic and biotic processes in situ. In addition, certain abiotic reactions are dependent on two environmental parameters that are oen controlled by microbial processes, redox, and pH. us these latter types of abiotic reactions are indirectly mediated by microorganisms as well.
