The photoinduced degradation of glyphosate (GLP) in the ferrioxalate system was investigated under irradiation with a 250 W metal halide lamp (lambda >= 365 nm). The efficiency of orthophosphates release, representing the photodegradation efficiency of GLP, increased with decreasing the initial concentrations of GLP and Fe(III)/oxalate ratios. At acidic pH value in the range of 3.5-5.0, higher efficiency of orthophosphates release up to 60.6% was achieved, while the efficiency dropped to 42.1% at pH 6.0. The photochemical process mainly involved the predominant species of iron(III), namely Fe(C2O4)(2)(-) and Fe(C2O4)(3)(3-) which lead to the formation of hydroxyl radicals in the presence of dissolved oxygen under UV-vis irradiation. Also, the complexation of GLP with Fe(III) obviously increased the light absorption of GLP and facilitated its degradation by direct photolysis. The ninhydrin test for primary amines showed that the GLP was attacked by hydroxyl radicals with C-N cleavage to yield aminomethylphosphonic acid (AMPA) and C-P cleavage to yield sarcosine. The photodegradation may be enhanced by the decomposition of reactive radicals produced through ligand-to-metal charge transfer (LMCT) of ferric-GLP complexes. (C) 2007 Elsevier B.V. All rights reserved.