Sorption of glyphosate and Cu(II) on a natural fulvic aced complex: Mutual influence

The mutual influence of the pesticide glyphosate (Gps) and copper on their adsorption on a natural metal-fulvic acid complex (M-FA) has been studied. The complex was extracted from a podsol and contains 22.16% Fe and 7.54% Al. High adsorption of Gps on M-FA is observed, but it decreases slightly in the presence of Cu(II) in solution. This is due to formation of very strong metal-Gps complexes, either with the added Cu or with Fe and Al desorbed from the M-FA complex. These complexes have a lower tendency to be adsorbed than the free Gps. Al and Fe desorption is more marked as higher is the concentration of Cu and GPS in solution, due to the decrease of equilibrium pH, to their displacement from the FA complex by Cu2+ ions and to ligand exchange of Gps for FA in the complex. In contrast, the adsorption of Cu increases as the concentration of Gps increases, since the formation of Gps complexes with Al and Fe in solution originates vacant positions on M-FA, facilitating copper adsorption.