Effects of Sorption on Reduction Kinetics

Although molecular descriptors that measure the ability of chemicals to accept electrons (e.g., one-electron reduction potentials) have been used successfully to predict relative reaction rates in well-defined homogeneous systems, their use for 

Although these observations suggest that sorption inhibits reduction, removal of the sediment by filtration generally results in loss of reactivity, suggesting that the reducing agent or agents is associated with the solid phase (i.e., the reductants are either part of the sediment or derived from the sediment). To explain this apparent 

Plot of the log of the observed rate constant versus the log of the distribution coefficient, K j, for substituted azobenzenes in an anaerobic sediment-water system. From Weber and Wolfe (1987). Reprinted by permission of the Society for Environmental Toxicology and Chemistry. 

Returning to our initial example of DDT, based on DDT s extremely large sediment-water partition coefficient, this model suggests that DDT is strongly sorbed to the nonreactive sink (k2 k.2) and that transport to reactive sites on the 

Our accumulated knowledge concerning reductive transformations in environmental systems suggests that natural surfaces (e.g., sediments, soils, mineral oxides) play crucial roles in these processes. This is in stark contrast to hydrolysis reactions for which surface effects are limited to a relatively small number of chemicals that have unique functionality. Clearly, the ability to understand, and thus predict reaction rates for reductive transformations in environmental systems will be dependent on our ability to delineate the role that natural surfaces play in the overall process. 

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