TNT transformation processes in sediment-free, “natural”, aquatic phytoremediation systems of Myriophyllum aquaticum were investigated with specific interest in oxidation products. Extraction procedures combining liquidliquid extractions and solid-phase extractions were developed for the isolation of the mostly acidic, oxidized TNT metabolites. Six compounds unique from the reduction products of TNT were isolated and characterized by UVvis, 1H, and 13C NMR spectroscopy, by mass spectroscopy, and by chemical synthesis where feasible. These compounds include 2-amino-4,6-dinitrobenzoic acid, 2,4-dinitro-6- hydroxy-benzyl alcohol, 2-N-acetoxyamino-4,6-dinitrobenzaldehyde, 2,4-dinitro-6-hydroxytoluene, and two binuclear metabolites unique from the customary azoxytetranitrotoluenes. The monoaryl compounds show clear evidence of oxidative transformations, methyl oxidation and/or aromatic hydroxylation. It is possible that oxidative transformation(s) preceded nitro reduction since studies on exposure of M.aquaticum to either 2-amino-4,6-dinitrotoluene or 4-amino- 2,6-dinitrotoluene did not yield any of the oxidation products identified here. The accumulation of oxidation products was significant: 2-amino-4,6-dinitrobenzoic acid, 4.4%; 2,4-dinitro-6-hydroxy-benzyl alcohol, 8.1%; 2-Nacetoxyamino- 4,6-dinitrobenzaldehyde, 7.8%; and, 2,4-dinitro- 6-hydroxytoluene, 15.6%. The binuclear metabolites accounted for an estimated 5.6%. This study is the first direct evidence for oxidative transformations in aquatic phytoremediation systems.