FACTORS INFLUENCING THE ADSORPTION OF ATRAZINE ON MONTMORILLONITIC AND KAOLINITIC CLAYS

The herbicide atrazine, a member of the S-triazine family was reacted with a montmorillonitic and a kaolinitic clay, two soil constituents o f different mineralogical composition and with different adsorption pr operties. The clays were characterized by determination of the cation exchange capacity (CEC), the total and internal surface area and the p article size distribution. X-ray diffraction studies were made to acqu ire the mineralogical composition of the two clays. The influence of t he initial pesticide concentration the pH and the solid/liquid ratio o n the adsorption of atrazine was tested in a miniaturized approach, yi elding less than 5 ml of suspension per sampling. Freundlich adsorptio n isotherms were set up to determine the Freundlich k and 1/n values. Heal of adsorption DELTAH and the velocity of the establishment of a s teady state were determined. Furthermore, investigations on the desorb ability of the pesticide adsorbed were made. The montmorillonitic clay adsorbed a great amount of the pesticide in contrast to the kaoliniti c one. Montmorillonite reached apparent adsorption equilibrium within a few minutes while establishment of apparent equilibrium with kaolini te took some days. DELTAH varied between 10 and 50 kJ mol-1. Adsorptio n increased with higher herbicide concentrations and decreased with ri se in temperature Larger solid/liquid ratios diminished adsorption coe fficients. All experiments were carried out with dry as well as with w ater-saturated montmorillonitic clay, Desorption experiments showed th at only part of the herbicide adsorbed was desorbable by several subse quent water treatment steps. For the first time immunoassay technology in the form of an ELISA (enzyme-linked immunosorbent assay) selective for atrazine was applied to detect low concentrations of the analyte in the few milliliters of eluent obtained in this miniaturized approac h.