Kinetics of contaminant desorption from soil: comparison of model formulations using the Akaike information criterion

Desorption of organic contaminants from soil can be modeled by dividing the desorption time-concentration profile into three distinct regimes. These are characterized by desorption that occurs faster than the experimental sampling scheme, at a rate that is captured by it, and at a rate for which the duration of the experiment and data uncertainty obscures the rate. Batch desorption curves for atrazine and naphthalene on four soils were experimentally generated to demonstrate the existence of discrete observational desorption regimes. Nine mathematical models, each containing mechanisms formulated to describe at least one of the three regimes, were fit to each contaminant-soil combination using the Gauss-Newton method for parameter estimation. Each of the nine models was ranked using the small-sample-corrected Akaike information criterion (AICc). By interpretation of the AICc values, the atrazine desorption data were best described by three regimes, while the naphthalene desorption data were best described by two regimes. Furthermore, for a given number of regimes, we could find no general basis to suggest that a particular type of rate model (chemical, physical, kinetic, or statistical) is intrinsically superior over another.