Association of benzo(a)pyrene with dissolved organic matter: Prediction of Kdom from structural and chemical properties of the organic matter

The affinity of dissolved organic matter (DOM) for binding a polycyclic aromatic hydrocarbon, benzo(a)pyrene (BaP), was measured for 11 surface and ground waters and a commercial humic acid. The hydrophobic-acid (HbA) and hydrophobic-neutral (HbN) compositions of the DOM, solution absorptivity at 270nm (ABS₂₇₀), and DOM molar volumes were determined. Waters enriched in HbA material had a larger molar volume and higher aromatic content (as indicated by the ABS₂₇₀). There was a good correlation between the size and HbA content of the DOM from the different sources and the K_dom for binding BaP. An excellent predictive relationship (r² = 0.9) was demonstrated between the ABS₂₇₀ of a water and the K_dom for binding BaP. Based on these results, it is suggested that binding of BaP to DOM depends not only on the hydrophobicity of DOM, but also on the existence of an open structure within the DOM to provide access of the aqueous solute to hydrophobic domains within the DOM.