Predicting the Mobility and Availability of Toxic Organic Chemicals

  • Z. Gerstl
Part of the Ecological Studies book series (ECOLSTUD, volume 73)


The behavior of organic chemicals in the unsaturated zone is governed by a variety of complex processes, the most important of which is adsorption. Adsorption of organic compounds can, and does, influence the mobility and biological activity of many chemicals (Leistra 1980). This is the direct result of the adsorption process which determines the distribution of the chemical in question between the aqueous phase and the soil solid phase (in the following discussion we shall disregard volatile compounds for the sake of simplicity). Adsorption can be defined as: the excess of solute concentration at the solid-liquid interface over the concentration in the bulk solution regardless of the nature of the interface region or of the interaction between the solute and the solid surface causing the excess (Mingelgrin and Gerstl 1983). Any process which proceeds at a more rapid rate in the soil solution than in the adsorbed state, such as transport, will be retarded as a result of adsorption. Conversely, reactions such as degradation can either be enhanced or impeded by adsorption depending on the exact nature of the degradation process. Surface catalyzed reactions, such as the degradation of parathion on kaolinite surfaces, will be enhanced by adsorption whereas solution phase reactions will be slowed down due to adsorption of one of the reactants. Accordingly, adsorption has received a tremendous amount of attention and any method which can reliably predict the adsorption of a solute will be of great importance to scientists and decision makers. An advanced method for predicting adsorption will be discussed below.


Aqueous Solubility Molecular Connectivity Molecular Connectivity Index Kaolinite Surface Organic Matter Distribution 
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© Springer-Verlag Berlin Heidelberg 1989

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  • Z. Gerstl

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