by Charlie Whittaker

Toxins and pollutants that are the by-products of industrial processes are one of the most serious environmental issues of the 21st century. They render land uninhabitable, pollute both water supplies and the atmosphere, and can cause a variety of costly and debilitating illnesses along with it. Removing these pollutants, from wherever it may be they accumulate, is usually a very costly and time intensive affair. Most processes rely on physical destruction of the matter they have contaminated. However, a great deal of work is going in to providing other avenues of opportunity for decontamination. One of these is phytoremediation.

Phytoremediation involves using plants to solve these very problems. In doing so, decontamination can be achieved without any need to excavate and transport contaminated material: the entire process of detoxification can be done on site, preventing irreversible destruction of the environment that can occur with other methods as well as reducing cost.

Phytoremediation is not a new idea, and many plants have already been utilised to remove toxic contaminants from the soil. Alpine pennygrass has been in use for a long time due to its ability to hyperaccumulate the poisonous metal cadmium. However, a new direction in the field is to utilise metabolic pathways found in other organisms, and then genetically engineer them into plants, with the potential to vastly increase the types of toxins plants can deal with.

RDX

RDX is a nitroamine based explosive widely used in both military and industrial application and which is far more powerful than TNT. First used during World War II, RDX is still used in the bulk of explosives employed today. Extensive military activity involving RDX over long periods of time has resulted in widespread and severe contamination of the soil with the material. This contamination affects both the land used during the military exercises, but also more concerningly, the groundwater contained beneath it. RDX is toxic; thus, this represents a substantial safety issue.

Natural degradation rates of RDX in the environment are low, and the strategies currently employed (such as incineration and composting of the soil) are incredibly expensive. However, nature has one trick up its sleeve. A number of different bacterial species were found that possessed metabolic pathways resilient enough to process and decontaminate the RDX molecules, rendering them harmless and providing the bacteria with a source of energy.

Credit: Alberto Salguero Quiles

Taking advantage of this, one group of scientists engineered the protein, called XplA/B, responsible for RDX degradation in bacteria, into the plant Arabidopsis thaliana. The plants were transformed, and demonstrated an incredible ability to grow in soils so concentrated in RDX to have killed plants not possessing the protein. The plants were able to take up these toxic explosives, and store them safely.

Ongoing work is looking at introducing these modified plants into decommissioned military operation sites. At the moment the concentrations of RDX in the soil are so high as to have killed off most if not all of the native species present there, as well as rendering the land uninhabitable. The hope is that, through the use of these plants, effective phytoremediation can occur, and the explosives can be removed from the soil.

This article originally appeared in Varsity
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Defusing the Biosphere: Plants, Explosives and Contaminated Battlefields

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