Solubilization of Naphthalene and Methyl-Substituted Naphthalenes from Crude Oil Using Biosurfactants

Glycolipids produced by Rhodococcus species H13-A and a representative synthetic surfactant Tween-80 (polyoxyethylene sorbitan monooleate) were used to demonstrate enhanced substrate “solubility” (aqueous-plus-micellar phase) in the presence of surfactants. Nascent concentrations of naphthalene and its methyl-substituted derivatives in crude oil were used as representative polycyclic aromatic hydrocarbons for the study. Both biosurfactant glycolipids from H13-A and Tween-80 lowered the surface tension of aqueous solutions from 72 to ∼30 dyn/cm. The two-ring aromatics showed a substantial increase in their apparent solubilities in the presence of surfactants; the increase being significantly greater for the biosurfactant as compared to the synthetic surfactant. The aqueous phase solubility enhancement was greater for the highly substituted derivatives as compared to the lesser substituted compounds. Higher toxicity levels, as seen by the lower EC 50 values, of the surfactant mixtures indicated enhanced partitioning of the petroleum contaminants in the aqueous phase. Higher initial EC 50 values for the biosurfactant meant that they exhibit lesser aqueous toxicity as compared to the synthetic surfactant. When compared on a toxicity per mass of PAH basis, the end point Tween-80 system was approximately 50% more toxic than the biosurfactant system.