Synergistic solubilization of polycyclic aromatic hydrocarbons by mixed anionic-nonionic surfactants

Water solubility enhancements of naphthalene (Naph), acenaphthylene (Acen), anthracene (An), phenanthrene (Phen) and pyrene (Py) by micellar solutions of single and mixed anionic-nonionic surfactants were measured and compared. Effects of typical inorganic ions, such as NH(4)(+), Na(+) and Mg(2+) coexisted with the organic pollutants (in soils) on water solubilities of polycyclic aromatic hydrocarbons (PAHs) in the presence of single and mixed surfactants were also investigated. Solubilities of PAHs in water are greatly enhanced in a linear fashion by each of Triton X-100 (TX100), Triton X-305 (TX305), Brij 35, and sodium dodecyl sulfate (SDS). Solubility enhancement efficiencies of surfactants above the critical micelle concentration (CMC) follow the order of TX100>Brij 35>TX305>SDS. PAHs are solubilized synergistically in mixed anionic-nonionic surfactant solutions, especially at low surfactant concentrations. The synergistic power of the mixed surfactants is SDS-TX305>SDS-Brij 35>SDS-TX100. Synergistic effect of a given mixed-surfactant solution on different PAHs also appears to be linearly related to the solute logK(ow). The noted synergism for the mixed surfactants is attributed to the formation of mixed micelles, the lower CMC of the mixed-surfactant solutions, and the increase of the solute's molar solubilization ratio or micellar partition coefficients (K(mc)) because of the lower polarity of the mixed micelles. Suitable quantity of inorganic cations can enhance the solubilization capacities of anionic-nonionic mixed surfactants, the effect being Mg(2+)>NH(4)(+)>Na(+). The water solubility of pyrene was slightly increased by anthracene and significantly increased by 1,2,3-TCB in the presence of SDS-Brij 35. Mixed surfactants may improve the performance of surfactant-enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus the remediation cost.