On the influence of surfactants on the mobility of contaminants.
The adsorption behavior of orthic luvisol and the solubilizing potential of 3 different types of com. sodium dodecyl sulfate (SDS) was examd. in batch expts. 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 2 different adsorption mechanisms of dodecyl sulfate (DS) to the surface lead to the appearance of an adsorption max. in the adsorption isotherms for the lower soil, which is caused by the formation of a double layer. Behind the max., the double layer is destroyed by the transition of the surfactant aggregates in soln. The surfactant employed in these expts. mobilizes the hydrophobic PCBs better than water. Below the CMC (crit. micelle concn.) 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 soln. is achieved.
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