Prediction of Soil Sorption Coefficients Using a Universal Solvation Model

Using a database of 440 molecules, we develop a set of effective solvent descriptors that characterize the organic carbon component of soil and thereby allow quantum mechanical SM5 universal solvation models to be applied to partitioning of solutes between soil and air. Combining this set of effective solvent descriptors with solute atomic surface tension parameters already developed for water/air and organic solvent/air partitioning allows one to predict the partitioning of any solutes composed of H, C, N, O, F, P, S, Cl, Br, and I between soil and water. We also present linear correlations of soil/water partitioning with 1-octanol/water partition coefficients using the same database. The quantum mechanical calculations have the advantages that they require no experimental input and should be robust for a wide range of solute functionality. The quantitative effective solvent descriptors can be used for a better understanding (than with previously available models) of the sources of different partitioning phenomena in cases where the results exhibit significant fragment interactions. We anticipate that the model will be useful for understanding the partitioning of organic chemicals in the environment between water and soil or, more generally, between water and soil or sediments (geosorbents).