Field trial demonstrating phytoremediation of the military explosive RDX by XplA/XplB-expressing switchgrass

Abstract

The explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a major component of munitions, is used extensively on military training ranges. As a result, widespread RDX pollution in groundwater and aquifers in the United States is now well documented. RDX is toxic, but its removal from training ranges is logistically challenging, lacking cost-effective and sustainable solutions. Previously, we have shown that thale cress (Arabidopsis thaliana) 2 engineered to express two genes, xplA and xplB, encoding RDX-degrading enzymes from the soil bacterium Rhodococcus rhodochrous 11Y can break down this xenobiotic in laboratory studies. Here, we report the results of a 3-year field trial of XplAB-expressing switchgrass (Panicum virgatum) conducted on three locations in a military site. Our data suggest that XplAB switchgrass has in situ efficacy, with potential utility for detoxifying RDX on live-fire training ranges, munitions dumps and minefields. Main textDuring World War II, RDX production peaked at 15,000 tons a month in the United States, and 7000 tons a month in Germany 1 . A major component in many munitions 1 , the demand for RDX is still high with a market size of $10.43 billion in 2018 2 . But RDX is toxic to soil organisms and humans, recalcitrant to degradation in the environment, and extremely mobile, readily moving into the groundwater [3][4][5][6][7] . These properties have resulted in the buildup of RDX in soil and groundwater to levels that have then threatened, or affected, human health, such as contamination of a sole source aquifer at Cape Cod 8 , and exposure of individuals to RDX in the Bickford Case in Utah 9 .Global RDX-contaminated areas are hard to map: historical explosives contamination is poorly recorded, and for reasons of security and political sensitivity, locations of current military sites are not openly documented. Extended Data Figure 1 maps global locations of explosives contamination, with examples of specifically RDX contamination additionally listed, and described in Supplementary Table 1. Supplementary Table 2 demonstrates the scale of RDX contamination in the United States. Contamination is not just limited to active military ranges, but includes decommissioned ranges, munitions dump sites and minefields; extensive RDX plumes emanate from manufacturing sites 8,9 .

The seizure‐inducing plastic explosive RDX inhibits the α1β2γ2 GABAA receptor

“…Due to these properties, RDX has been extensively employed in every major war since World War II and is also widely used for civilian purposes. In 2018 RDX had an estimated market of $10.4 billion 2 . RDX release as waste during manufacture, via explosion of ordinances, and during disposal of munitions constitutes an environmental concern for exposure of both humans and wildlife 2,3 .…”

“…In 2018 RDX had an estimated market of $10.4 billion. 2 RDX release as waste during manufacture, via explosion of ordinances, and during disposal of munitions constitutes an environmental concern for exposure of both humans and wildlife. 2,3 At 32 Environmental standard issued beer, soldiers supposedly could achieve increased inebriation, but often went on to develop seizures that required hospitalization.…”

“…2 RDX release as waste during manufacture, via explosion of ordinances, and during disposal of munitions constitutes an environmental concern for exposure of both humans and wildlife. 2,3 At 32 Environmental standard issued beer, soldiers supposedly could achieve increased inebriation, but often went on to develop seizures that required hospitalization. In a report from 1969, army physicians recognized RDX intoxication as the most common cause of generalized seizures in US service personnel in Vietnam.…”

“… 2 RDX release as waste during manufacture, via explosion of ordinances, and during disposal of munitions constitutes an environmental concern for exposure of both humans and wildlife. 2 , 3 At 32 Environmental Protection Agency (EPA) listed National Priority Sites, RDX has been found to leach into soil and groundwater and, in some cases, to induce seizures in fish, rodents, lizards, or birds. 3 , 4 , 5 There also is suggestive evidence of carcinogenic potential based on an EPA assessment performed in 2018.…”

Genome-Wide Identification of Switchgrass Laccases Involved in Lignin Biosynthesis and Heavy-Metal Responses

“…The overexpression of the switchgrass Cd-responsive gene PvBip1 in Arabidopsis significantly improved the plant’s Cd tolerance [ 23 ]. Additionally, the engineered switchgrass expressing xplA and xplB efficiently removed hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in a 3-year field trial [ 24 ].…”