Sorption, diffusion, and desorption of alachlor in oxidized and reduced smectite membranes

Abstract

The fate of pesticides in the environment depends to a large extent on their interactions with clay mineral surfaces in soils and sediments. Most studies of these interactions typically employ batch suspension methods. Another method, which may be much faster and simpler, is to cast the clay into the form of a self-supporting film immobilized between two porous nitrocellulose filters. The objective of this study was to investigate the kinetics of alachlor transport through such a membrane. We found that at least two kinetic phases (rapid and slow) exist. Herbicide disappearance from donor solutions, its appearance in acceptor solutions (including time lag and the rate at steady state), and its retention by the membrane revealed that adsorption on the clay surface plays a prominent role in transmembrane transport processes. The oxidation state of structural Fe in the clay film changed the surface chemical properties of the clay and modified both the fast adsorption and slow transport of alachlor through the membrane. Transport through the reduced clay was accompanied by chemical alterations of alachlor. No chemical alterations were observed if the clay film was in its oxidized state.