Dynamics of glyphosate and aminomethylphosphonic acid in a forest soil in Galicia, north-west Spain

Residues of the herbicide glyphosate ŽN-phosphonomethylglicine. and its main metabolite, aminomethylphosphonic acid ŽAMPA., were determined in a forest soil in north-west Spain, previously treated with 5 and 8 l ha 1 of glyphosate. Both products were monitored in the solid and liquid soil phases for an 8-week period after the treatment. Soil samples were extracted by KH2PO4. Concentrated extracts and liquid phase samples were derivatized with 9-fluorenylmethyl chloroformate ŽFMOC. before determination by HPLC using an anion exchange column and spectrofluorometric detection. The treated soil peaked at 6.9 g g 1 of glyphosate, whereas soil water samples peaked at 0.74 g ml 1 of glyphosate. One month after the treatment, both glyphosate and AMPA concentrations in soil and water samples were almost negligible. AMPA peaked at 0.77 g ml 1 in soil water samples. Glyphosate and AMPA exhibited high vertical mobility in the treated soil, quickly reaching high concentrations in subsurface horizons where the degradation is slower.