Aminomethylphosphonic Acid and Glyphosate Adsorption onto Goethite:  A Comparative Study

Glyphosate is a non-selective, broad spectrum, post-emergent herbicide widely used in weed control. Aminomethylphosphonic acid (AMPA) is one of the main products of biodegradation of glyphosate in natural systems before its ultimate mineralization and also the breakdown product of more complex phosp...

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Bibliographic Details
Published in:Environmental science & technology 2005-01, Vol.39 (2), p.585-592
Main Authors: Barja, B. C, dos Santos Afonso, M
Format: Article
Language:English
Subjects:
Acids
Adsorption
Agronomy. Soil science and plant productions
Applied sciences
Biological and medical sciences
Biological and physicochemical properties of pollutants. Interaction in the soil
Comparative studies
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Fundamental and applied biological sciences. Psychology
Glycine - analogs & derivatives
Glycine - analysis
Glycine - chemistry
Glyphosate
Herbicides
Herbicides - analysis
Herbicides - chemistry
Iron - chemistry
Iron Compounds - chemistry
Isoxazoles
Minerals
Organophosphonates - analysis
Organophosphonates - chemistry
Pollution
Pollution, environment geology
Soil and sediments pollution
Soil and water pollution
Soil science
Temperature
Tetrazoles
Weeds
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Summary:Glyphosate is a non-selective, broad spectrum, post-emergent herbicide widely used in weed control. Aminomethylphosphonic acid (AMPA) is one of the main products of biodegradation of glyphosate in natural systems before its ultimate mineralization and also the breakdown product of more complex phosphonates such as nitrilotris(methylenephosphonic acid). The adsorption isotherms and surface coverage of AMPA and glyphosate (N-phosphomethylglycine, PMG) in aqueous suspensions of goethite as a function of pH were measured. Electrophoretic mobility curves for the PMG/goethite system were also determined. The ATR−FTIR interfacial spectra of the surface complexes of AMPA and PMG onto goethite were analyzed as a function of the pH and the surface coverage. The phosphonate moiety of these two ligands coordinates to the iron oxide surface with similar structures as the methylphosphonic acid despite the presence of the amino and/or carboxylate groups of their molecules. Two predominating complexes have been identified where the phosphonate group in PMG or AMPA bonds monodentately or bridges bidentately to the surface of iron oxide in an inner sphere mode, while the carboxylate and amino group are noncoordinated to the surface. The stability constants of the surface complexes ⋮FeOP(O)(OH)R, ⋮FeOP(O)2R, and (⋮FeO)2P(O)R were calculated using the constant capacitance model.
ISSN:0013-936X
1520-5851
DOI:10.1021/es035055q