On the influence of surfactants on the mobility of contaminants

Abstract

The adsorption behavior of Orthic Luvisol and the solubilizing potential of three different products of sodium dodecyl sulfate (SDS) was examined in batch experiments. Two PCBs were used as representative pollutants for persistent, hydrophobic substances. For the soil surface layer, adsorption occurs at the hydrophobic tail of the surfactant, whereas for the other horizons adsorption is located at the hydrophilic head group. These two different adsorption mechanisms of dodecyl sulfate (DS) to the surface lead to the appearance of an adsorption maximum in the adsorption isotherms for the lower soil, which is caused by the formation of a double layer. Behind the maximum, the double layer is destroyed by the transition of the surfactant aggregates in solution. The surfactant employed in these experiments mobilizes the hydrophobic PCBs better than water. Below the cmc (critical micelle concentration) mobilization of the PCBs is caused by surfactant monomers due to detergent effect, and above the cmc by insertion in surfactant aggregates. The vesicle-like droplets of a dispersed lamellar phase are able to solubilize more PCB than spherical micelles, which are formed as soon as the double cmc in solution is achieved.