Sorption-desorption of 1,2,4-trichlorobenzene on soil: Anionic surfactant and cationic polyelectrolyte effects

Anionic surfactants and cationic polymers are two classes of anthropogenic chemicals that are released to the environment in significant amounts. In particular, this occurs in the land disposal of sludges, potentially altering the terrestrial mobility of other contaminants such as hydrophobic organics. Thus, we examined the 1,2,4-trichlorobenzene (TCB) sorption-desorption on soil with sodium dodecyl sulfate (SDS) and/or a cationic polyelectrolyte (Percol 757) present. Initial experiments varying sorbent mass resulted in nonconstant partitioning and a nonlinear isotherm; a model of incomplete colloidal separation by centrifugation could not explain the nonlinearity. A proposed model quantifies this isotherm behavior with a BET isotherm equation related to the limiting sorption capacity of the organic matter phase, Q(om)(degrees). Additions of SDS and/or polyelectrolyte led to significant changes in TCB sorption. The SDS decreased TCB sorption significantly, but only with SDS exceeding the critical micelle concentration (CMC). The CMC value itself varied with electrolyte and soil presence. Increasing the SDS concentration above the CMC caused TCB desorption from soil. The SDS also increased residual colloidal solids, but primarily below the CMC. Percol 757 slightly increased TCP sorption. With polymer added to soil containing SDS, TCB sorption was unaffected until charge equivalence was approached, whereupon sorption increased severalfold. This trend reversed when the SDS exceeded the sum of the polymer equivalence and the CMC. These results are explained in terms of polymer-surfactant interactions. Environmental implications include effects on transport of hydrophobic organics resulting from sludge disposal on land.