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

Department of Agronomy, The Ohio State Univ., Columbus, OH 43210

^* Corresponding author (onken{at}ude1.edu).

ABSTRACT

In 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 (f_oc) (<3 x 10^–5) and diminished f_oc increased. The addition of cosolutes to low f_oc systems (<3 x 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 f_oc systems (= 3 x 10^–5) was due to an increase in effective f_oc 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 K_oc values derived from K_ow data in low f_oc systems significantly underestimate the interactions of nonionic organic solutes with low organic C surfaces.

B.M. Onken, current address: Dep. of Plant and Soil Sciences, Univ. of Delaware, 149 Townsend Hall, Newark, DE 19717-1303.

Received for publication August 28, 1995.