SORPTION OF NONIONIC ORGANIC-COMPOUNDS IN SOIL-WATER SYSTEMS CONTAINING PETROLEUM SULFONATE OIL SURFACTANTS

The effects of petroleum sulfonate-oil (PSO) surfactants (commercial petronates) on sorption of representative nonionic organic contaminants naphthalene, phenanthrene, and 2,2',4,4',5,5'-hexachlorobiphenyl (2,2',4,4',5,5'-PCB) in an Oshtemo (B) soil-water system are presented in this report. In the range of petronate equilibrium aqueous concentrations from 0 to 170 mg L-1, we have observed a slight increase of the soil-water distribution coefficient (K) for naphthalene, a moderate decrease of K for phenanthrene, and a large (202-fold) decrease of K for 2,2',4,4',5,5'-PCB. Both aqueous and soil-sorbed PSO surfactant act as partition phases for NOCs. Solute partition coefficients between water and the PSO emulsions in the solution and soil-sorbed form, K(em) and K(sem), respectively, were determined. The K(em) values were consistently but only slightly larger (1.1-3 times) than K(sem), demonstrating that sorbed PSO is nearly as effective as aqueous-phase PSO emulsion as a partition phase for phenanthrene and 2,2',4,4',5,5'-PCB. The ratios of K(sem) to K(om) for phenanthrene and 2,2',4,4',5,5'-PCB were consistently about four, indicating that on a unit mass basis sorbed PSO is about four times more effective as a sorptive phase for these contaminants than natural soil organic matter. We have developed and evaluated a model that can predict accurately the apparent soil-water distribution coefficient of a nonionic organic compound at different petronate concentrations, by knowing the intrinsic distribution coefficient of the solute in the surfactant-free system and the soil-water distribution of the surfactant itself. These results suggest the utility of petronate surfactants for substantially increasing the aqueous-phase concentrations of poorly water-soluble organic contaminants present in soils.