title: Effects of dissolved carboxylates and carbonates on the adsorption properties of thiuram disulfate pesticides.
abstract: The adsorption of thiram and disulfiram onto alpha-Al2O3 and montmorillonite clay has been studied in the presence of small carboxylate anions, bicarbonate, formate, and oxalate. At natural concentrations, HCO3- enhances dramatically the adsorption of both pesticides on alpha-Al2O3 and clay. An analogous significant enhancement of pesticide adsorption is also observed in the presence of formate and oxalate. Density functional theory calculations demonstrate that in solution a stable molecular complex between one molecule of thiram and one molecule of HCO3- is formed with interaction energy -35.6 kcal/mol. In addition, two H20 molecules further stabilize it by an interaction energy of -3.6 kcal/mol. This clustering [thiram- HCO3- -2H2O] leads to a change of the electronic structure and the ultraviolet-visible spectrum of thiram that is observed experimentally. Surface complexation modeling shows that the molecular cluster [thiram-HCO3- -2H2O], which bears a total net charge of -1, is responsible for the observed enhanced adsorption on the charged surface of alumina and clay at pH below their points of zero surface charge. The results reveal a novel pervasive role of carboxylate anions and particularly HCO3- on the adsorption of dithiocarbamate pesticides in natural waters.
authors.affiliation: Laboratory of Physical Chemistry, Department of Environmental and Natural Resources Management, University of Ioannina, Seferi 2, 30100 Agrinio, Greece.
authors.forename: Panagiota
authors.initials: P
authors.lastname: Stathi
authors.forename: Konstantinos C
authors.initials: KC
authors.lastname: Christoforidis
authors.forename: Athanasios
authors.initials: A
authors.lastname: Tsipis
authors.forename: Dimitra G
authors.initials: DG
authors.lastname: Hela
authors.forename: Yiannis
authors.initials: Y
authors.lastname: Deligiannakis
mesh_terms: D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D001546:Bentonite / Q000737:chemistry; D002254:Carbonates / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D000077215:Clay; D004787:Environmental Pollution / Q000517:prevention & control; D006863:Hydrogen-Ion Concentration; D010575:Pesticides / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013859:Thiocarbamates / Q000737:chemistry*; D013893:Thiram / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D002254:Carbonates; D002264:Carboxylic Acids; D010575:Pesticides; D013859:Thiocarbamates; D013893:Thiram; D001546:Bentonite; D000537:Aluminum Oxide; D000077215:Clay