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A new program from the US government’s Defense Advanced Research Agency, DARPA, is exploring new ways to reclaim soil contaminated with explosives and jet fuel, and it wants to do it in the most sustainable way possible: using biotech-modified plants.
According to the analysis, the US military will have to neutralize more than 1.2 million tons of explosive-contaminated soil at various bases and facilities. But if we project this need globally after a century of conflict, the world will need to dispose of billions of tons of soil contaminated with explosives and chemicals used by armies.
TNT, fast detonating explosive (RDX) and high melting point explosive (HMX) are the most common types of explosives found in soil. Each is a popular material used by the military, and due to inadequate handling and disposal practices, these materials and their derivatives pollute the environment to levels that threaten the health of people, livestock, wildlife and entire ecosystems. Pure. and Applied. Chemistry in a study published in the journal.
Ammunition factories, ammunition depots, testing centers, training centers leave behind a huge amount of fuel and chemicals – but the same thing happens to the battlefields in a literal sense – and change the safety and health of the soil and groundwater.
Governments around the world have been engaged in soil restoration for decades. The most common methods include burning, composting, and creating water-based soil sludge to break down chemicals. While these methods are effective, they are not environmentally friendly, require soil to be dug up and transported, and can cost a fortune. Moreover, apart from the composting process, the soil becomes unusable.
Significant research is also being carried out on recovery sites. Most often, lime is added to the soil. While the process is partly successful, it requires constant maintenance and regular access to water in order for the alkaline hydrolysis process to work. However, research by the US Army Corps of Engineers has raised serious environmental concerns. Simply put, the lime must remain moist, which requires a constant supply of water. Engineers also found that chemical degradation at the surface was successful, but deeper soil layers were not successfully decontaminated. In addition, the more lime and water we add to the soil, the more pollutants and acidity from the alkaline hydrolysis process enters the groundwater.
Governments have also tried tillage and the use of plant materials to control pollution with moderate success. However, the process requires constant human attention, which is not possible in many parts of the world. Compared to traditional remediation methods that require the physical removal of soil, biological remediation is much more environmentally friendly and efficient. The problem is that modern methods require a lot of soil preparation, transportation of nutrients and fertilizers, and a large number of workers. DARPA aims to eliminate all of this.
The agency’s latest program, Ceres, “aims to detoxify contaminants – spilled jet fuel-8 (JP-8) and trinitrotoluene, commonly known as TNT – from the soil by changing the behavior of plants and their associated microbial communities.” In other words, DARPA wants to automate plants and the microbial ecosystems they create to clean up the soil.
The area immediately surrounding the root system of a plant is called the rhizosphere, and this zone is where intense biological and chemical activity takes place. The rhizosphere is full of nutrients such as amino acids and organic acids, proteins and sugars that serve as food for a range of soil organisms. The plant provides nutrition for this microbiome around its root system, attracting all sorts of micro-organisms. These microorganisms feed each other, the plant itself and different layers of the ecosystem.
According to the Ceres proposal paper, the plan is to “create pristine rhizosphere communities and transform host plants into integrated, pollutant-specific, cleaner synthetic communities … that sense and respond to soil pollutants, and artificial plants maintain and improve decomposition of pollutants by rhizosphere communities”. By breaking the contract down into multiple tracks, DARPA hopes the new plant’s rhizosphere will be used to detect and break down chemical contaminants “to EPA-approved levels without dangerous by-products.”
Ceres is a four and a half year program divided into two phases of 24 months each. Contract applicants must demonstrate the ability to “isolate or assemble functional plant-microbial communities” and “optimize communities into synthetic communities through biological and environmental engineering.” To ensure that these biotech plants do not get out of hand, the bidder must also demonstrate that the plant and associated rhizosphere community can be easily removed once restoration is complete. Finally, the applicant must submit contaminated soil samples for plant testing from US military bases in the Eastern Forest, Plains, and Mediterranean in the United States.
DARPA will then hire an independent review team to verify the results. “Ceres will take advantage of what nature does for free and without intrusive research,” said Ceres program manager Dr. Paul Sheehan. “Theoretically, this could not be done at any cost other than planting seeds enriched with microbes designed to clean up the soil,” he added.
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