Pesticide Adsorption and Degradation Properties as Influenced by Iron Oxidation State in Clay Minerals

Abstract

Reduction of structural Fe in the clay greatly increased the adsorption and produced substantial degradation of all pesticides. When reacted with chemically treated clays, the total amount of atrazine removed from solution by the reduced clay was much greater than by the oxidized or reoxidized clays. Similar behavior was observed for the other pesticides studied. Hydroxyatrazine was the only atrazine degradation product found in the reduced clay, and no degradation was detected in the presence of oxidized or reoxidized clays. Fourteen alachlor degradation products were produced by the reduced clay suspensions, whereas only two appeared in the oxidized clay. For trifluralin and ethalfluralin, many more degradation products appeared in the reduced clay than in the oxidized or reoxidized clay. Similar trends were observed using clays in which microorganisms rather than inorganic chemicals served as the reducing agent, although the difference between reduced and reoxidized was less than that in the chemical treatments. These differences may be due to interaction between the pesticide and residual bacterial fragments or nutrients from the microbial inoculum. Preliminary desorption studies revealed that most of the adsorbed atrazine, alachlor, and their degradation products could be removed from the clay by simple dilution in water.