On military live fire training ranges, troops practice firing artillery shells, drop bombs on old tanks or derelict buildings and test the capacity of new weapons.
But those explosives and munitions leave behind toxic compounds that have contaminated millions of acres of U.S. military bases 鈥� with an estimated cleanup bill ranging .
In a published online Nov. 16 in , 91探花 and University of York researchers describe new transgenic grass species that can neutralize and eradicate 鈥� a that has been widely used in explosives since World War II.
91探花engineers introduced two genes from bacteria that learned to eat RDX and break it down into harmless components in two perennial grass species: switchgrass (Panicum virgatum) and creeping bentgrass (Agrostis stolonifera). The best-performing strains removed all the RDX from a simulated soil in which they were grown within less than two weeks, and they retained none of the toxic chemical in their leaves or stems.
It is the first reported demonstration of genetically transforming grasses to supercharge their ability to remove contamination from the environment. Grasses are hearty, fast-growing, low-maintenance plants that offer practical advantages over other species in real-world cleanup situations.
鈥淭his is a sustainable and affordable way to remove and destroy pollutants on these training ranges,鈥� said senior author and 91探花professor of civil and environmental engineering , whose lab focuses on taking genes from microorganisms and animals that are able to degrade toxic compounds and engineering them into useful plants.
鈥淭he grasses could be planted on the training ranges, grow on their own and require little to no maintenance. When a toxic particle from the munitions lands in a target area, their roots would take up the RDX and degrade it before it can reach groundwater,鈥� Strand said.
RDX is an organic compound that forms the base for many common military explosives, which can linger in the environment in unexploded or partially exploded munitions. In large enough doses, it has been shown to cause seizures and organ damage, and it鈥檚 currently as a potential human carcinogen.
Unlike other toxic explosives constituents such as TNT 鈥� which binds to soils and tends to stay put 鈥� RDX dissolves easily in water and is more prone to spread contamination beyond the limits of a military range, manufacturing facility or battleground.
鈥淧articles get scattered around and then it rains,鈥� Strand said. 鈥淭hen RDX dissolves in the rainwater as it moves down through the soil and winds up in groundwater. And, in some cases, it flows off base and .鈥�
Wild grass species do remove RDX contamination from the soil when they suck water up through their roots, but they don鈥檛 significantly degrade it. So when the grasses die, the toxic chemical is re-introduced into the landscape.
Co-authors and , biotechnology professor and research scientist, respectively, at the University of York and colleagues had previously isolated enzymes found in bacteria that evolved to use the nitrogen found in RDX as a food source. That digestion process has the added benefit of degrading the toxic RDX compound into harmless constituents.
The bacteria themselves aren鈥檛 an ideal cleanup tool because they require other food sources that aren鈥檛 always present on military training ranges. So Bruce and Rylott tried inserting the bacterial genes into plant species commonly used in laboratory settings. Those experiments proved that the new plant strains were able to remove RDX contamination much more successfully than their wild counterparts.
鈥淐onsidering the worldwide scale of explosives contamination, plants are the only low cost, sustainable solution to cleaning up these polluted sites,鈥� said Bruce.
The 91探花team of civil and environmental engineers spent eight years working to express the same genes in plant species that could stand up to real-world use. They needed a hearty perennial species that grows back year after year and that has strong root systems that can bounce back after fires.
Grasses fit that bill, but they are more difficult to manipulate genetically. In particular, the 91探花engineers had to build into their gene constructs robust monocot 鈥減romoters鈥� 鈥� or regions of DNA that cause a particular gene to be expressed 鈥� for the process to work in grass species.
鈥淔or cleaning up contaminated soils, grasses work best, but they鈥檙e definitely not as easy to transform, especially since flexible systems to express multiple genes in grasses have not been used before,鈥� said first author and acting 91探花instructor .
The research team also found another unexpected side benefit: because the genetically modified grasses use RDX as a nitrogen source, they actually grow faster than wild grass species.
Next steps for the 91探花research team include limited field trials on a military training range to test how the strains perform under different conditions. Wider use would require USDA approval to ensure that the genetic modifications pose no threat to wild grass species.
鈥淚 think it would be ecologically acceptable because the genes we鈥檝e introduced degrade real pollutants in the environment and cause no harm,鈥� Strand said. 鈥淔rom my perspective, this is a useful technology that鈥檚 beneficial to the environment and has the potential to remove dangerous legacy contamination from decades of military activity.鈥�
The research was funded by U.S. Department of Defense. Co-authors include 91探花civil and environmental engineering research techs Ryan Routsong and Quyen Nguyen.
For more information, contact Strand at sstrand@uw.edu or 206-543-5350.
Grant numbers: SERDP ER-1498, ESTCP ER-201436