Impact of clay minerals and DOM on the competitive sorption/desorption of PAHs

Two model compounds were used to investigate sorptive phenomena of a siltysand soil under single and binary solute systems at different concentrations. In the sorption isotherms, the presence of phenanthrene (PHE) exhibited a statistically significant (P < 0.05) sorption competition over pyrene (PYR), regardless of the concentration. PYR influenced the PHE isotherms only when it was present at 15 mg/L. The concentration dependence in sorption competition was only evident for the more hydrophobic PYR. In the presence of PHE, the fraction of desorbed PYR was significantly increased with an increase in PYR concentration. PHE desorption enhancement was the most observable with the higher initial concentration (15 mg/L). However, the presence of PYR did not affect PHE desorption. This study found that, based on equivalent solid mass, soils containing only clay minerals sorbed 12.2% more PHE than soils with only soil organic matter (SOM) for 3 mg/L PHE. Clay minerals also impacted desorption as evidenced by a 65% decrease in desorbed PYR fraction compared with when the soil only contained SOM. The dissolved organic matter (DOM) amendment did not increase desorption. Instead, PHE desorption was significantly inhibited by the added DOM. For this study, co-sorption was found to be the mechanism for the inhibited desorption.