Enhanced Uptake and Biotransformation of 2, 4, 6-Trinitrotoluene by Vetiver Grass (Chrysopogon zizanioides) From Soil.

Potential migration of 2, 4, 6-trinitrotoluene (TNT) from contaminated military areas can cause serious soil and groundwater contamination. Presence of carcinogenic and mutatoxic TNT can prohibit residential and other uses of closed military sites unless effective remedial measures are taken. One of the major challenges in developing an effective phytoremediation system for TNT contaminated soil and water is limited plant-uptake of TNT resulting from the low solubility of TNT. The effectiveness of a common agrochemical urea as a chaotropic agent in increasing TNT extractability and uptake in plant-hydroponic-systems has been documented, but little is known about its performance in complex soil systems. The primary objectives of this greenhouse study were to i) characterize the TNT uptake and biotransformation by vetiver grass from a low organic matter containing soil,  and ii) evaluate the catalyzing effectiveness of urea as a chaotropic agent in enhancing TNT-uptake by vetiver grass. A sandy soil was spiked with 100 mg Kg^-1 TNT and spiked with four rates of urea (0, 125, 350, 1000 mg kg^-1). Urea concentrations were chosen to mimic the agronomic fertilizer nitrogen application rates (125 to 350 mg kg^-1). A 1000 mg kg^-1 urea concentration was chosen to comply with the previous hydroponic TNT-vetiver experiment. Vetiver grass reduced soil TNT concentrations (73%) in the absence of urea compared to the TNT amended no-plant controls (21%). Urea significantly enhanced (p<0.0001) the vetiver-TNT uptake from soil. Within the limits of agronomic fertilizer N application rate, 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 disappearance rate (91% removal of TNT). Major TNT metabolites, such as 2-ADNT, 4-ADNT and 1,3,5-TNB were detected in shoot tissues, suggesting TNT phytodegradation by vetiver grass.