title: Evidence for nonlinear binding of PAHs to dissolved humic acids.
abstract: Binding of pyrene, fluoranthene, and phenanthrene to dissolved humic acids (HA) was determined by the fluorescence quenching (FQ) and complexation-flocculation (CF) methods. Determinations by the CF method, using varying contaminant concentrations and a constant HA concentration, yielded nonlinear Freundlich-type isotherms (n = 0.65-0.84). Experiments using both the CF and the FQ methods with varying HA concentrations and a constant contaminant concentration yielded curved "Stern-Volmer"-type plots that also indicate nonlinear binding. These findings suggest that linear partitioning or site complexation in the presence of excess available sites cannot fully describe the interactions of hydrophobic compounds with dissolved humic material. Site-specific hydrophobic interactions at limited interior or external molecular surfaces may be considered.
authors.affiliation: Faculty of Civil Engineering, Environmental and Water Resources Engineering, Technion, Haifa, Israel. yaelaor@netvision.net.il
authors.forename: Yael
authors.initials: Y
authors.lastname: Laor
authors.forename: Menahem
authors.initials: M
authors.lastname: Rebhun
mesh_terms: D006812:Humic Substances / Q000737:chemistry*; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D012995:Solubility; D014873:Water Pollutants
chemical_list: D006812:Humic Substances; D011084:Polycyclic Aromatic Hydrocarbons; D014873:Water Pollutants