In this study, we examined the effect of a micelle-forming surfactant (Triton X-100) an the sorption of 1,1-bis(p-chlorophenyl)-2,2,2-trichlororethane (p,p'-DDT), 2,2',4,4',5,5'-hexachlorobiphenyl (2,2',4,4',5,5'-PCB), and 1,2,4-trichlorobenzene (1,2,4-TCB) in a soil-water system. At aqueous phase Triton X-100 concentrations (C-TX) below 200 mg L(-1) (approximately the critical micelle concentration, cmc, for Triton X-100), apparent soil-water distribution coefficients (K*) for each compound studied increased with increasing C-TX. At C-TX values above 200 mg L(-1), K* values decreased with increasing C-TX. Below the cmc, surfactant monomers in the aqueous phase are relatively ineffective as a partitioning medium for nonionic organic compounds (NOCs), while the sorbed surfactant molecules increase the sorptive capacity of the solid phase. Above the cmc, however, surfactant micelles in the aqueous phase begin to compete with the sorbed surfactant as an effective partitioning medium for the poorly water-soluble NOCs (e.g., p,p'-DDT), resulting in a 10-fold decrease in K* at a C-TX of about 600 mg L(-1). Two conceptual models were developed, which adequately described the functional dependence of K* an C-TX.
