Surfactant Solubilization of Polycyclic Aromatic Hydrocarbon Compounds in Soil-Water Suspensions

Polycyclic aromatic hydrocarbons (PAH) are hydrophobic compounds readily sorbed onto soil; the addition of surfactants to soil-water systems may solubilize PAH compounds by incorporation of the PAH in surfactant micelles. The solubilization of anthracene, phenanthrene and pyrene was evaluated in soil-water suspensions with several nonionic and anionic surfactants. The most effective surfactants were nonionic octyl- and nonyl- phenylethoxylates with 9 to 12 ethoxylate units. At soil-water mass ratios of about 1:7 to 1:2, greater than 0.1% by volume surfactant dose was required in order to initiate solubilization, with doses of 1% by volume resulting in 70 - 90% solubilization. The soil-water partition coefficient for anthracene was reduced by two orders of magnitude with 1% by volume phenylethoxylate surfactant. The solubilization of anthracene, phenanthrene and pyrene in soil-water systems occurs at surfactant doses, [C_surf], much greater than the clean water surfactant critical micelle concentration. A surfactant-soil solubilization coefficient is derived as C_aq(s)/S, where C_aq(s) is the observed aqueous solubility of PAH in the presence of surfactant, and S is the specific sorption of PAH onto soil. C_aq(S)/S is shown to be proportional to C_surf-CMC_eff, where CMC_eff is the effective critical micelle concentration in the presence of soil. Additional information is needed on the sorption characteristics of surfactant on soil in order to describe more fully the PAH-surfactant solubilization process.