Multi-phase partitioning and co-solvent effects for polynuclear aromatic hydrocarbons (pah) in authentic petroleum- and creosote-contaminated soils

The residual oil phase, present at substantial levels in hydrocarbon-contaminated soils, was found to be the principal medium for retention of polynuclear aromatic hydrocarbons (PAH). Using authentic petroleum and creosote-contaminated soils containing 2–6% w/w solvent extractable matter, individual PAH were shown to exist in the oil phase at values between 84 and 95% w/w of the total mass of each compound in the system, with the exception of naphthalene (70% w/w). Evaluation of the phase partitioning of PAH in creosote-contaminated soil confirmed that PAH were predominantly in the creosote oil phase, with substantially lower proportions associated with soil organic matter and soil water. In the aqueous phase, solubility enhancement was observed for PAH with the degree of enhancement more evident for the hydrophobic PAH. A normalised solubility enhancement factor (ESF’) was derived to illustrate the combined effect of increased PAH solubility in the aqueous phase. Values of log ESF’ varied from −4.97 (naphthalene) to 0.09 (benzo[ghi]perylene). The findings suggest limitations exist for successful remediation of PAH contamination in the soils evaluated and indicate that the focus of remediation must be on the residual oil phase if total PAH are to be removed.