Detailed sorption isotherms of polar and apolar compounds in a high-organic soil

Sorption isotherms of 13 apolar liquids and solids and polar solids-six in unprecedented detail-are used to evaluate a polymer-based model for natural organic matter. While ail isotherms are nonlinear, the "running" Freundlic h exponent n varies markedly with concentration. The isotherms show linear- scale inflection consistent with the presence of flexible (deformable) poro sity as predicted by the glassy polymer-based Extended Dual-Mode Model (EDM M). The EDMM assumes dissolution and hole-filling domains in the organic so lid, with provision for sorbate-caused plasticization of the solid and "mel ting" of the holes. Features of the EDMM are illustrated for chlorinated be nzenes in poly(vinyl chloride). The solutes fall into categories of "hard" (aliphatics and 2,4-dichlorophenol) and "soft" (chlorinated benzenes, 2-chl oronitrobenzene) according to their ability to plasticize organic matter. C omparison of domain coefficients at infinite dilution reveals that organic solutes have a modestly greater affinity for holes than dissolution sites ( by 0.1-0.6 log unit), as expected by the polymer model. Sorption of CHCl3 s hows time-dependent hysteresis diminished at high concentrations by the pla sticizing effect. Sorption of CHCl3 also shows a type of hysteresis for gla ssy solids known as the "conditioning effect" in which high loading of sorb ate increases hole population upon its removal and thus leads to enhanced u ptake and nonlinearity when a second sorption is performed. A Polanyi-based , fixed-pore filling model applied to the adsorption component of the isoth erms gave widely variant volumetric pore capacity, contrary to its own stip ulations, and could not explain the hysteresis.