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

Residues of the herbicide glyphosate (N-phosphonomethylglicine) and its mai n metabolite, aminomethylphosphonic acid (AMPA), were determined in a fores t soil in north-west Spain, previously treated with 5 and 8 1 ha(-1) of gly phosate. Both Products were monitored in the solid and liquid soil phases f or an 8-week period after the treatment. Soil samples were extracted by KH, PO,. Concentrated extracts and liquid phase samples were derivatized with 9 -fluorenylmethyl chloroformate (FMOC) before determination by HPLC using an anion exchange column and spectrofluorometric detection. The treated soil peaked at 6.9 mug g(-1) of glyphosate, whereas soil water samples peaked at 0.74 mug ml(-1) of glyphosate. One month after the treatment, both glyphos ate and AMPA concentrations in soil and water samples were almost negligibl e. AMPA peaked at 0.77 mug ml(-1) in soil water samples. Glyphosate and AMP A exhibited high vertical mobility in the treated soil, quickly reaching hi gh concentrations in subsurface horizons where the degradation is slower. ( C) 2001 Elsevier Science B.V. All rights reserved.