ABSTRACT
Organic compounds in the vadose zone can undergo a variety of biological and chemical transformations. Biological transformations range from partial to complete (Atlas and Bartha, 1993). The complete breakdown of an organic compound to carbon dioxide and water is called mineralization, which is a process that provides energy for growth and reproduction of cells. Incomplete transformations can also provide energy to support cellular growth, but can result in accumulation of deadend intermediate products which are not further degraded. Cometabolism is a second type of incomplete transformation in which a partial oxidation of the substrate occurs but the degrading cell is not able to utilize the energy from the oxidation for growth. Finally, in some instances microbial transformations can result in polymerization or coupling of organic compounds leading to formation of products which are more complex and stable than the parent compound (Bollag, 1992).
