Reductions in the apparent soil-water partition coefficients (Kd (*)) for 28 polychlorinated biphenyls (PCBs) caused by the surfactant sodium dodecylsulphate (SDS) in the aqueous phase were studied. Above the critical micelle concentration (CMC) of the surfactant, Kd (*) was reduced by 2-3 orders of magnitude, but even far below CMC at environmentally relevant surfactant concentrations significant reductions in Kd (*) were observed. The plot of the soil-water partition coefficient (Kd) divided by Kd (*) versus the concentration of SDS allowed for the calculation of monomer (Kmn (oc)) and micellar (Kmc (oc)) surfactant-water partition coefficients normalized to organic carbon for each PCB congener. Kmn (oc) values were comparable with published values for the partition of PCBs between natural dissolved organic matter and lake water. Kmc (oc) values were up to 30 times higher than Kmn (oc) values and comparable with published octanol-water distribution coefficients. The findings of the present study underline the potential of surfactants at concentrations below their CMC to mobilize otherwise strongly bound hydrophobic compounds in soil-water systems.

The soil/water partition coefficient (Kd) of hexachlorobenzene (HCB) ranged from 220 1/kg to 1800 1/kg for eight soils having a wide range of physico-chemical properties. Kd normalised to soil organic carbon (Koc) was found to be 28000 ± 4800 1/kg. Anionic surfactant dodecylsulphate (DS) present at concentrations above the critical micellar concentration (CMC) caused reductions in the apparent soil/water partition coefficient (Kd (*)) in the range of 3-26 times for most soils and up to 36-91 times for sandy soils. Below CMC, at environmentally relevant surfactant concentrations, Kd (*) was reduced by a factor of 1-13. For clay and calcareous soils significant adsorption/complexation/precipitation of DS occurred. At the lowest DS concentration this produced a two-fold increase in Kd (*). At increasing DS concentrations this effect was shielded by the solubihzing effect from DS. Monomer (Kmn) and micellar (Kmc) surfactant/water partition coefficients for HCB were determined to be, 980 ± 190 1/kg and 21000 ± 1600 1/kg, respectively.