PHYTOREMEDIATION POTENTIAL OF VETIVER GRASS (CHRYSOPOGON ZIZANIOIDES L.) FOR 2,4,6-TRINITROTOLUENE (TNT) FROM SOIL: UREA-CATALYZED UPTAKE AND NITROREDUCTASE ENZYME MEDIATED TRANSFORMATION

2,4,6-Trinitrotoluene (TNT) is the most widely used explosive and a group C human-carcinogen. In our earlier studies vetiver grass, in the presence of urea as a chaotropic agent, showed high promise in removing TNT from both soil and water. The present study investigated the kinetics of TNT removal from soil, characterized the TNT uptake and translocation at agronomically recommended urea application rates, and investigated the potential transformation of TNT in vetiver and the possible biochemical mechanisms. Vetiver plants were allowed to grow in a sandy loam soil (Millhopper series) treated with different TNT (0,100mg kg^-1) and urea (0,125,350, and1000 mgkg^-1) concentrations. Kinetics of TNT removal from soil followed a pseudo first order reaction. Vetiver grass showed high uptake (>80%) and significant root-to-shoot translocation of TNT. Urea significantly enhanced (p<0.0001) the vetiver-TNT uptake from soil. Within the limits of agronomic fertilizer N application rates, 125 mg kg^-1 of urea was considered optimum for TNT uptake by vetiver grass (82% removal of TNT). However, increasing the urea rate to 1000 mg kg^-1 increased the TNT removal rate (91% removal of TNT). Major TNT metabolites, such as 2-ADNT, 4-ADNT and 1,3,5-TNB were detected in plant tissues. Presence of aminodinitrotoluenes in the TNT-treated-plants suggested the role of nitroreductase (NR) enzyme in the metabolic pathway of TNT. The NR-activity (nMg^-1h^-1) was higher in both root and shoot tissues of the TNT-treated-plants compared to the control plants. The NR-activity in the roots was significantly (p=0.007) enhanced by the increasing initial urea concentrations, whereas initial TNT treatment significantly (p=0.01) influenced the NR-activity in the shoot. The NR-activity in the shoot was >100 times higher than that of the root, indicating more phytodegradation of TNT in shoot tissues. This further corroborates our observation on the presence of higher levels of TNT metabolites in shoot as compared to the root tissues of vetiver grass.