Atrazine Sorption by a Mineral Soil: Processes of Labile and Nonlabile Uptake

Abstract

A microfiltration−HPLC technique which was recently introduced is applied to the study of the uptake of atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) by a mineral soil, Green Belt BG 843. The uptake can be partitioned into labile and nonlabile contributions. Each process shows a saturation limit consistent with a “complexation site” model of atrazine binding. The indications of a definite and low stoichiometry of uptake capacity is a key result of this analysis. The labile sorption capacity, θc, is 0.40 × 10-6 mol g-1. At 25 °C an equilibrium constant, K1, for the labile sorption is 3.0 × 104 M-1, and the apparent diffusion coefficient for nonlabile uptake is 8.8 × 10-11 cm2 s-1, corresponding to a first-order rate constant of 9.6 × 10-7 s-1. Preliminary indications are that the capacity of nonlabile binding sites is <10-4 mol g-1. Keywords: Atrazine−soil interactions; on-line HPLC microextraction; bound residues; intraparticle diffusion; sorption capacity; sorption mechanisms