Influence of a nonionic surfactant (Triton X-100) on contaminant distribution between water and several soil solids

The influence of a nonionic surfactant (Triton X-100) on the contaminant di stribution coefficients in solid-water mixtures was determined for a number of relatively nonpolar compounds (contaminants) on several natural solids. The studied compounds consisted of BTEX (benzene, toluene, ethylbenzene, a nd p-xylene) and chlorinated pesticides (lindane, alpha-BHC, and heptachlor epoxide), which span several orders of magnitude in water solubility (S-w) ; the solid samples comprised a bentonite, a peat, and two other soils, whi ch cover a wide range of solid organic matter (SOM) content. The applied su rfactant concentrations (X) ranged from below the (nominal) CMC to 2-3 time s the CMC. For relatively water-soluble BTEX compounds, the distribution co efficients with surfactant (K-d*) all exceeded those without surfactant (K- d); the K-d*/K-d ratios increased with increasing S-w from p-xylene to benz ene on each solid at a given X, with increasing X for each compound on a so lid, and with decreasing solid SOM content for each compound over the range of X studied. For the less-soluble pesticides, the K-d*/K-d ratios exhibit ed a large increase with X for bentonite, a marginal change (increase or de crease) for a soil of 2.4% SOM, and a moderate-to-large decrease for two so ils of 14.8% and 86.4% SOM. These unique observations were rationalized in terms of the properties of the compound, the amount of surfactant sorbed on the solid, the enhanced solubilization of the compound by surfactant in wa ter, and the relative effects of the surfactant when adsorbed on minerals a nd when partitioned into SORI. (C) 2000 Academic Press.