Optimization of parameters and adsorption mechanism of thiabendazole fungicide by a montmorillonite of North Patagonia, Argentina

In the Valleys of the Negro and Neuquen Rivers (North Patagonia, Argentina), different pesticides are applied to fruits in the fields as well as in the packing plants. Thiabendazole (2-(thiazol-4-yl) benzimidazole, IUPAC chemical name) is widely used as post-harvest fungicide on fruits before packing and transportation. The surplus from the packing plants reaches the Limay and Neuquen Rivers, through open channels thereby contaminating the water bodies. A regional montmorillonite, selected by its physicochemical properties and high degree of tetrahedral substitution, was used to adsorb thiabendazole in order to reduce toxicity to a reference value. The adsorption was followed by UV spectrophotometry (gimel=298 nm) using batch equilibration, under various sets of conditions established by varying the following parameters: contact time, adsorbate/adsorbent ratio, pH and ionic strength. Concerning adsorption mechanism, this was elucidated based on studies by infrared spectroscopy and X-ray diffraction analysis and determinations of cation exchange mechanisms. Montmorillonite was able to completely remove the thiabendazole concentration found in industrial effluents. Moreover, no desorption was detected within 30 days after adsorption. (C) 2003 Elsevier B.V. All rights reserved.