Oxidative metabolism of 2,4,6-trinitrotoluene in aquatic phytoremediation systems of Myriophyllum aquaticum
Bhadra, R; Spanggord, RJ; Wayment, DG; Hughes, JB; Shanks, JV
Investigations into the activity of oxidative pathway(s) of TNT metabolism in plants are reported. As shown here, oxidative metabolism constitutes significant metabolic fate of TNT. The studies were conducted with sediment-free, 6- to 24-liter,'natural' aquatic systems of Myriophyllum aquaticum. Following the exposure of plants to dissolved TNT, oxidized TNT-metabolites were isolated from the 'spent' aqueous media by a combination of extraction procedures. Several compounds unique from the reduction products of TNT were identified and characterized by HPLC-UV, H-1- and C-13-NMR spectroscopy and mass spectroscopy, and confirmed independently 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, and 2,4-dinitro-6-hydroxytoluene. They provide conclusive evidence of oxidation of the ring-substituted methyl-group and of aromatic hydroxylation. It is possible that oxidative transformations precede nitroreduction 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 oxidized products identified here. Following a 12-day exposure of M. aquaticum to TNT, oxidized TNT-metabolites accumulated as follows: 2-amino-4,6-dinitrobenzoic acid, 4.4%; 2,4-dinitro-6-hydroxy-benzyl alcohol, 8.1%; 2-N-acetoxyamino-4,6-dinitrobenzaldehyde, 7.8%; and 2,4-dinitro-6-hydroxytoluene, 15.6%. The implications of these findings on the analysis of environmental fate and on phytoremediation strategies for explosives are significant.
