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.

Heavy-metal uptake by a high cation-exchange-capacity montmorillonite: the role of permanent charge sites

“…The surface charge of montmorillonite suspensions were evaluated by two methods: potentiometric acid -base titrations (Schulthess and Sparks, 1986;Stathi et al, 2006;Giannakopoulos et al, 2006) and mass titration (Giannakopoulos et al, 2006;Bourikas et al, 2003).…”

Eliminating the matrix effects of dissolved carbon dioxide and carbonate in extraction of triclosan and chlorophenols in environmental waters by hollow fiber supported liquid membrane

“…During the HFSLM extraction of target weak organic acids, the dissolved carbon dioxide and carbonate that are widely present in environmental waters are co-extracted by partitioning in the form of CO 2 or H 2 CO 3 into the liquid membrane and then trapping into the acceptor as carbonate. 12 Given the high concentration of dissolved carbon dioxide and carbonate (at mM level) 13 in comparison to the target analytes (at nM level), the trapping of dissolved carbon dioxide and carbonate in the basic acceptor might signicantly reduce the acceptor pH and therefore the extraction efficiency of the target analytes. As the dissolved carbon dioxide and carbonate in reagent water used to prepare standard solutions are negligible, the reduced extraction efficiency of target analytes resulted from the relatively high contents of dissolved carbon dioxide and carbonate in real environmental samples, giving rise to low recovery of analytes.…”

A general mechanism of interaction of carbonates with non-polar S-containing pesticides

“…In real soils, more than one mechanism may operate simultaneously. So far, several works have attempted to study and/or correlate the role of sorption in connection with the persistence of selected pesticides on soil (Sheng et al, 2001, Stathi et al, 2006. Sheng et al (2001) have reported an unusual nonlinear adsorption isotherm for Ethyl-Parathion on soil organic matter.…”

“…This isotherm non-linearity has been attributed, although not proven, to the presence of high surface area carbonaceous material and/or to specific interactions between pesticide and adsorbent (Sheng et al, 2001). Recently we have demonstrated that adsorption of two common dithiocarbamate pesticides, i.e., Thiram and Disulfiram, on soil components such as a-Al 2 O 3 or montmorillonite (Stathi et al, 2006) and humic acids (Stathi et al, 2007) is determined by carbonates at natural concentrations. Natural concentrations of HCO 3 − have been shown to either enhance drastically adsorption of the neutral dithiocarbamates on a-Al 2 O 3 and montmorillonite (Stathi et al, 2006) or to cause severe inhibition of their sorption on humic acid (Stathi et al, 2007).…”

“…Thiram form a stable anionic species [Thiram-HCO 3 − ] −1 in solution (Stathi et al, 2006(Stathi et al, , 2007. A combination of weak covalency plus a network of Hbonds have been shown to stabilize the complex [Thiram-HCO 3 − ] −1 .…”