STIMULATIVE PHYTOREMEDIATION OF 2,4,6-TRINITROTOLUENE (TNT) FROM SOIL USING VETIVER GRASS (CHRYSOPOGON ZIZANIOIDES L.) : A GREENHOUSE STUDY

Low aqueous solubility of nitroaromatic compounds results in limited plant uptake, which is a major constraint in developing an effective phytoremediation system for 2, 4, 6-trinitrotoluene (TNT). To overcome this limitation, we propose a novel stimulative-phytoremediation technique using urea, a common nitrogen fertilizer, as a chaotropic agent to enhance the solubility of TNT in soil solutions.The presentgreenhouse soil-column study investigated the fate of various concentrations of TNT in soil (0, 50, 100, 200 mg kg^-1) for a period of six months. The migration of TNT in theleachate in the presence or absence of vetiver grass and the optimum chaotropic dose of urea (325 mg kg-1)was studied. Results showed that 80% of TNT and monoaminodinitrotoluenes (ADNTs) were retained in soil after 6 months in the plant-free TNT amended control soil columns. Complete removal of TNT was achievedin the vetiver-urea treatments within 6mo, up to 100 mg kg^-1 initial TNT concentration. Urea significantly enhanced the TNT removal at all TNT concentrations. Significantly higher TNT and its metabolites were found in the leachate in plant-free-controls than in the leachate in presence of both plants and urea.Along with TNT and ADNTs, dinitrotoluenes (2,4-DNT and 2,6-DNT), were found in the plant-free TNT amended controls which raises high concern as both of these compounds exhibit higher toxicity than TNT in in-vivo studies (LD₅₀ in rat = 270 and 180 mg kg^-1, respectively) and are classified as group B human carcinogens. These compounds were not detected in the leachate in presence of vetiver, because of the quick uptake of TNT and its metabolites by vetiver grass. The current study indicates that chaotropically-enhanced phytoremediation using vetiver grass is a promising technique for the cleanup of TNT-contaminated soils.