Sustainable Range Management of RDX and TNT by Phytoremediation with Engineered Plants

Decades of military activity on live-fire training ranges have resulted in the contamination of land and groundwater by recalcitrant high explosives, particularly TNT and RDX. TNT and its transformation products are highly toxic, but tend to bind strongly to clay and organic matter in soil, so are largely contained at the site of contamination. RDX, however, poses a major concern, because of its high mobility through the soil water table and consequent potential for contamination of groundwater. RDX contamination of training ranges is now proving to be a significant threat to drinking water sources. Currently, there are no cost-effective processes to contain RDX or remediate large areas of contaminated land on training ranges. The project responds directly to specific research objectives stated in SON number CUSON-06-04 including: i) sustained prevention of migration of surface and near surface soil contamination by energetic materials; ii) development of technologies applicable to large, potentially vegetated areas, directed at the long-term control of energetic materials through repeated applications; iii) sustainable technology; iv) inexpensive rapidly deployable technology; and v) adaptable to an unpredictable influx of contaminants. The objective of this project was to engineer transgenic grasses to remove and degrade RDX in the root zone of soil contaminated with explosives. The expression in plants of a novel, RDX-degrading cytochrome P450 gene, xp1A, was investigated. This enzyme, along with its redox partner (Xp1B), can degrade RDX to harmless metabolites. Since TNT often occurs as a co-contaminant alongside RDX, it was also necessary to engineer resistance to TNT, because this explosive is highly toxic to plants.