Abiotic Transformations in Water, Sediments, and Soil

The importance of abiotic transformations to the fate of pesticides in the environment became widely recognized only recently. Even in a medium in which intense biological activity takes place, such as soil, abiotic transformations can be important. Under some conditions, such as those that may occur below the root zone, abiotic transformations can dominate the fate of pesticides. Abiotic transformations of pesticides have been reviewed by several investigators (e.g., Melnikov, 1971; Kearny & Kaufman, 1969; Morrill et al., 1982). In these publications, the pesticides were classified according to their chemical structure, demonstrating that transformations are based on functional groups of the pesticide. In the present chapter, the abiotic transformations will be described in terms of the specific environment in which they occur. Numerous transformations occur in the homogeneous phases, especially in the liquid phase. Other transformations occur in the interface between phases. These include reactions that are heterogeneously catalyzed and those that occur in solution under the influence of the electric field of charged surfaces. Crosby (1970), in a review on abiotic transformations in the soil, presented some examples of both surface-enhanced reactions and reactions that take place in the bulk liquid phase. It is often difficult to determine whether a pesticide undergoes abiotic or biotic transformations. In the case of many pesticides, significant biological and chemical degradation takes place simultaneously (Wolfe et al., 1980). For example, Deuel et ale (1985) reported such a situation for carbaryl degradation in flooded rice (Oryza sativa L.) fields. Barug and Vonk (1980) re-