Quirks & Quarks

Genetically modified grass can suck toxic explosives out of the ground

A new study has found that modifying two genes in switchgrass allows it to metabolize a toxic chemical compound in explosives.

New study shows GM grass can completely degrade the chemicals found in the plastic explosive C-4

Study co-author Tim Cary seen here explaining the GM switchgrass test site to visitors at the military training ground in New York. (Neil Bruce/Liz Rylott/University of York)

Researchers have genetically modified a wild grass to metabolize toxic pollutants left behind by military explosives. This is the first time that genetically modified plants have been successfully used to clean up organic pollutants.

"It's a huge problem," Liz Rylott told Quirks & Quarks host Bob McDonald. "We have huge areas of military land that contain explosives from munitions [and] residues, as hot spots scattered across the training ranges."

After decades of research, Rylott and her co-authors were able to modify switchgrass to completely degrade the chemical compound RDX, an explosive which was heavily used in the Second World War and continues to be used today in munitions like the plastic explosive C-4.

"RDX is made of carbon and nitrogen and oxygen," Rylott said. "The plant uses these elements to grow back and produce more more plant biomass. It's completely destroyed."

The study was published in the journal Nature.

Explosive chemicals seep into groundwater

In the U.S., more than 10 million hectares of military land are contaminated with pollutants from munitions. RDX is a major contributor. It can persisit in the enviornment for many decades without breaking down naturally.

"We've got levels of RDX and other types of explosives that date back to the Second World War," said Rylott, a senior researcher and lecturer at the University of York.

The RDX is not in danger of exploding, but it is known to easily permeate the soil and has led to widespread pollution of groundwater. RDX is thought to be toxic to both animals and humans.

"It's a pretty nasty thing. It's a potential carcinogen. So it's really nasty stuff. And the groundwater levels in some areas are now threatening drinking water supplies. It's really not something that we want there," said Rylott. 

An explosives ordinances demolition technician attaches C-4 explosives to a fragmentation bomb in Afghanistan. RDX is the chemical compound that gives C-4 its explosive power, and its use has resulted in widespread pollution of groundwater. (Joe Raedle/Getty Images)

The researchers turned to switchgrass, a hardy plant commonly used to battle soil erosion, because they needed a perennial plant that could withstand the unique environmental challenges of a military training ground. 

"They've selected particular cultivars of these grasses to be very resistant to tank traffic, and to be literally being blown off the face of the training range and landing back down and growing again and to be incredibly robust," said Rylott.

'Batman and Robin combo' to tackle RDX

Rylott and her team went to areas with heavy RDX contamination and collected bacteria from the soil. Then, they were able to isolate two genes in the bacteria that had evolved specifically to degrade RDX.

"Plants aren't able to do very much with RDX themselves. They can take it up, but they don't break it down," said Rylott. "Bacteria alone can't do the job even though they're present. So we want to combine the plants and the bacteria like a kind of Batman and Robin combo to address this problem."

Once the genes had been introduced into the switchgrass, it was able to draw up RDX from the soil and successfully degrade it in the test area to non-detectable levels over the course of three years.

"It worked just beautifully," she said. "We were unable to detect the RDX in there."

Dr. Liz Rylott setting up a test site with genetically modified switchgrass. (University of York/Liz Rylott)

Rylott says the genetically modified plants are not a threat to non-modified native grasses.

"The only thing that this grass has in it that's different to the native grasses that are already there are these two genes. And the only advantage is if there's RDX around, they'd be able to break it down," she said.

Next, she hopes that this technology can be used to degrade other organic pollutants.

"Very sadly, there are a lot of them out there: PCBs, dioxins or organochlorine pesticides, for example," she said. "And this is the kind of technology that I think we need to address them."


Produced and written by Amanda Buckiewicz.

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