Picloram and Thiram: 2 pesticides acting as heavy metals carriers portrayed by DPASV

Abstract

Comunicación presentada en el Program of the 59th Annual Meeting of the International Society of Electrochemistry, Seville, 2008, S10-P085:Page 141. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxilic acid) is a herbicide widely used, alone or in combination with other herbicides to control of weeds in crops of sugar cane, rice, pasture and wheat1. It can stay active for long time, depending on the type of soil, moisture and temperature. Thiram (N,N-dimethildithiocabamate) is a fungicide used for a control of a variety diseases in the crops of fruits, vegetables and ornamentals2. From an electrochemical point of view, the study of the redox behaviour of both pesticides on modified electrodes has been reported recently3. However, few works reported the interactions between metallic ions and pesticides and their properties in the environment, although these molecules usually present functional groups that can act as ligands. In this work, we studied the interaction between heavy metals (Zn, Cu, Pb and Cd) and the pesticides (picloram and thiram) using the Differential Pulse Anodic Stripping Voltammetry technique on Hg electrode (DPASV) which has shown efficient in the evaluation of the formation of complexes in natural samples4 through the competing role of Hg for metals with respect to ligands. Electrochemical measurements provided a simple means to evaluate the stoichiometry of the complexes, and Scatchard and Langmuir algorithms allowed the calculation of the conditional complexation constants for both systems in an acetate pH 4 buffered solutions. Studies carried out for both Zn and Cu with Picloram have shown that 1:1 complexes were formed in all instances. Calculated conditional stability constants are quite close (log K’ ~ 6) for both metallic species, Cu consistently yielding highest values.