Reevaluation of Partitioning as a Mechanism of Nonionic Chemicals Adsorption in Soils

Abstract

Abstract 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. For example, systems in which a distinct hydrophobic phase at the solid surface does not exist are shown to exhibit the uptake behavior presumed to characterize partition. 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.