Coupling indigenous biostimulation and phytoremediation for the restoration of 2,4,6-trinitrotoluene-contaminated sites

In-situ bioremediation has been highly promising in degrading nitroaromatics in soil, e.g., 2,4,6-trinitrotoluene (TNT). The case of TNT is examined here as a representative nitroaromatic compound that belongs to a suite of explosive residue types scattered throughout the European Union and other areas of the world. Differences in cost-effectiveness and TNT degradation rates between existing methods have spurred extensive debate in bioremediation research of explosive-contaminated sites. Rhizoremediation (plant inoculation with a specific microorganism), including genetic modification of plant/tree species, has been treated as the next best remediation method due to excellent performance in the lab. However, recent data collected in the field do not support the initial enthusiasm, showing in many cases, no statistical difference between (non-)transgenic rhizoremediation and phytoremediation (use of wild plant types). Obviously, the role of indigenous rhizospheric microorganisms has been underestimated, impeding our progress towards identifying the critical components of the optimum bioremediation scheme. Future research directions to enhance the indigenous microbial activity in the plant rhizosphere via addition of chemical amendments, such as, nutrients (fertilizers), and/or chaotropic agents (urea) could improve the overall efficiency of existing phytoremediation schemes.