The Sorption of Nonionic Organic Solutes to Humic Acid‐Mineral Complexes: Effect of Cosolutes

Abstract

AbstractIn binary isotherms, pyrene and naphthalene sorption were enhanced by the presence of anthracene as a cosorbate. Sorption enhancement was observed at low fractional organic carbon content (foc) (<3 × 10−5) and diminished foc increased. The addition of cosolutes to low foc systems (<3 × 10−5) appeared to aid the transition from adsorption/condensation type surface interactions to an interaction more like partitioning. It is postulated that observed sorption enhancement in higher foc systems (= 3 × 10−5) was due to an increase in effective foc resulting from cosolute sorption. The presence of a cosolute did not affect systems where partitioning was already the primary process. If partitioning was not occurring, the addition of a cosolute reduced the surface excess of the solute by competing for adsorption sites. This competition occurred until surface organic C increased to a sufficient concentration to promote partitioning. This research indicates that the use of Koc values derived from Kow data in low foc systems significantly underestimate the interactions of nonionic organic solutes with low organic C surfaces.