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

The fate of pesticides in the environment depends to a large extent on thei r interactions with clay mineral surfaces in soils and sediments. Most stud ies of these interactions typically employ batch suspension methods. Anothe r method, which may be much faster and simpler, is to cast the clay into th e form of a self-supporting film immobilized between two porous nitrocellul ose filters. The objective of this study was to investigate the kinetics of alachlor transport through such a membrane. We found that at least two kin etic phases (rapid and slow) exist. Herbicide disappearance from donor solu tions, its appearance in acceptor solutions (including time lag and the rat e at steady state), and its retention by the membrane revealed that adsorpt ion on the clay surface plays a prominent role in transmembrane transport p rocesses. The oxidation state of structural Fe in the clay film changed the surface chemical properties of the clay and modified both the fast adsorpt ion and slow transport of alachlor through the membrane. Transport through the reduced clay was accompanied by chemical alterations of alachlor. No ch emical alterations were observed if the clay film was in its oxidized state .