The competitive adsorption of phenanthrene and benzo[a]pyrene by fractionated soil particles in individual and coexistence pollution

Two polycyclic aromatic hydrocarbons (PAHs), benzo[a]pyrene (BaP) and phenanthrene (Phe), were added alone and in combination to unfractionated and fractionated soil (fine sand, silt, clay) in batch equilibrium experiments to determine their adsorption. The maximum adsorption capacity increased with initial concentrations for both PAHs, with a stronger increase for BaP. The BaP adsorption capacity was promoted by coexistence of Phe, but Phe adsorption capacity was inhibited by coexistence of BaP. Their adsorption isotherms during coexistence best fitted the Freundlich equation, giving a lesser fit with a linear equation that improved by coexistence. The n of the Phe isotherm in coexistence with BaP wasclose to 1 for the fine sand and silt. The adsorption of Phe and BaP was strongest in clay, followed by fine sand and then silt. Single Phe adsorption in clay was 23.82∼61.33 % higher than in fine sand and silt, and for BaP it was 5.78∼8.35 % higher. In silt, the Phe adsorption efficiency was reduced by 39.73 % in coexistence with BaP, while the BaP adsorption efficiency improved with 19.69 % in coexistence. Coexistence triggered a mechanistic redistribution: it weakened Phe partitioning, while it strengthened BaP surface adsorption. The adsorption behavior of these PAHs in coexistence for different soil fractions provides insights for optimal remediation strategies of PAH-contaminated soils.