Enhanced rhizodegradation of munitions explosives and degradates by selected native grass species

Abstract

TNT (2,4,6-trinitrotoluene) and RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) are the two most widespread explosives in the world. The manufacture, use and disposal of explosives can result in environmental contamination, which has been reported as a threat to human health and ecosystems. Compared to highly expensive and inefficiently conventional remediation methods, phytoremediation has been considered as a cost-effective way to clean up contaminated sites. The objectives of this research are to: (1) evaluate the degradation kinetics of TNT and RDX in the rhizospheres of two selected native grass species; (2) investigate the synergic effects of TNT degradation in both rhizospheres by inoculating with known explosive degraders; and (3) investigate the effects of living plants on sustaining TNT degrader population (pnrA gene) and TNT degradation activities. Results suggested that the TNT was rapidly degraded into its major metabolites in both rhizospheres and control soil; the degradation of the TNT metabolites was significantly enhanced in the rhizosphere soils as compared with the control. However, the mineralization of TNT in all the treatments was limited (< 5%). In contrast, the degradation of RDX and its metabolites in the rhizosphere soils were significantly enhanced over the control. More than 13% RDX was mineralized in rhizosphere soils as compared to 5% in the control. Overall, EG appeared to be more effective for RDX degradation, while SW to be more suitable for TNT degradation. Inoculation of TNT degrader P. putida KT2440 to SW could enhance TNT degradation as compared to use SW alone.