REEVALUATION OF PARTITIONING AS A MECHANISM OF NON-IONIC CHEMICALS ADSORPTION IN SOILS

A critical evaluation of recent suggestions that the adsorption of nonionic organic compounds by soils can be well-correlated with the partition of the compounds between an aqueous and a nonpolar phase (usually 1-octanol), or with water solubility is presented. The physical basis proposed for these assumptions is that adsorption of nonionic organic compounds on soil organic matter is a ″partition″ process between the aqueous phase and a hydrophobic surface phase. The evidence presented in the literature for the dominance of a partition mechanism is insufficient to prove its general applicability. Theoretically, as well as practically, surface uptake cannot be simply defined as ″adsorption″ or ″partition″ , but rather there is a continuum of possible interactions starting with fixed site adsorption and ending with true partition between three-dimensional phases.