Interaction of pesticides with humic compounds and their metal complexes

Abstract

The interaction of pesticides with humic compounds (humic and fulvic acids) and with their metal complexes was studied potentiometrically and radiometrically, using the pesticides Aldicarb and Methomyl, and the herbicide Ametryne. The metal humate or fulvate complexes were prepared by precipitation of the complexes using Co2+, Zn2+, or Sr2+. The results indicated that Aldicarb, Methomyl, and Ametryne form stable complexes with humic acid (HA) and fulvic acid (FA). The complexation strength increases in the order Aldicarb ≤ Methomyl < Ametryne. The complexes of Aldicarb and Methomyl with HA and FA are stronger than the metal humate/fulvate complexes with Co2+, Zn2+, and Sr2+, and these pesticides displace the metal ions. Ametryne adds to the metal humate/fulvate by physical adsorption or ligand exchange. The complexation of Aldicarb and Methomyl with humic compounds causes the release of radionuclides (60Co, 65Zn, 90Sr) from the soil organic matter to the solution. The pH exerts a decisive effect on the complexation of the pesticides with humic compounds.