Trace Element Mobilization in Soils by Glyphosate
Glyphosate, the most widely used herbicide in agriculture, has a strong tendency to sorb on minerals by bonding with surface metals through its metal-coordinating functional groups. However, this same chemical process can potentially mobilize sorbed trace metals by chelation and sorbed anions such as phosphate by displacement. The tendency for glyphosate to mobilize Cu and other elements was tested in soil leaching experiments by applying glyphosate alone or complexed with Cu to mineral and organic soil columns and measuring the concentrations of these elements in the leachates by inductively coupled plasma (ICP) spectrophotometry. Complexation with glyphosate inhibited Cu sorption on the soil columns, rendering this metal more mobile in both the mineral and organic soil. Glyphosate mobility was also enhanced when applied to the organic soil as the Cu complex, but this effect was not detected with the mineral soil. Glyphosate was adsorbed more completely on the organic soil than the mineral soil, suggesting a metal bridging mechanism to explain sorption of this anionic molecule. The application of a commercial Roundup spray to long-contaminated soils containing elevated concentrations of heavy metals and phosphate resulted in significant increases in the leaching of Cu, Zn, Al, Ni, P, Si, and As. No significant increases in elemental leaching were detected in mineral and organic soils with normal background concentrations of heavy metals and P. Batch equilibration studies confirmed the glyphosate-enhanced dissolution of Cu in Cu-contaminated soils, but reductions of free Cu2+ activity were measured only in uncontaminated soils. The results indicate that several elements, particularly Cu, Al, and P, could be mobilized within the thin surface layer of soils receiving a high effective rate of glyphosate during herbicide application.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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