How Plants Can Detect Chemical Weapons

Chemical warfare is high on the global defence agenda, especially after recent events in Syria, which showed how agents like the nerve gas sarin can be used in what was declared by the UN as a war crime—and how devastating their effects can be. But detecting the presence of chemical weapons is difficult, a task made harder by the potential ramifications of a positive (or false positive) result.

The use of chemical weapons is banned by the Chemical Weapons Convention, but in the wake of that incident it’s clear the threat of their use persists. (For its part, Syria wrote to the UN to say it would accede to the convention in December last year).

But to check compliance with the convention—or more importantly, detect non-compliance—you first have to collect evidence that chemical warfare agents have been used. One way to do that at the moment is to take soil samples and analyse them for compounds found in toxins like sarin, soman, and VX, all of which are considered weapons of mass destruction by the UN.

Now, researchers at the University of Central Lancashire and the UK’s Defence Science and Technology Laboratory (part of the Ministry of Defence) have suggested a new way of detecting chemical warfare agents that could be more effective and have the added advantage of removing them from contaminated soil. Their tool: mustard plants.

They found that mustard plants take up the chemical agents from the soil, and make what would have previously been undetectable levels of nerve agents detectable. Matthew Baker, who led the research at Lancashire, told me that the plats take up the chemicals just the same as they would absorb nutrients from the soil. The chemicals then last longer in the plant than they would in the soil, so the evidence sticks around for longer.

“It enables them to act as a time capsule to store nerve agents, which keeps it around longer for detection,” he said.

His team grew white mustard plants—which they chose because they can grow pretty much anywhere—in soil contaminated with VX, and reported their findings in a paper published in the Proceedings of the Royal Society A.

Samples of plants were taken, and evidence of the VX remained for as long as 45 days, the maximum length of time they waited. The VX itself had gone before then, but the researchers were able to detect the two chemical products it degrades into, which are difficult to find in soil alone. As a result, they suggested the plants could hold onto evidence of chemical weapons for longer than conventional soil-sampling methods.

Even better, their work suggested the plants could be used to actually remove traces of chemical weapons from the ground.

“You could draw the agent out of the soil, then burn the plants, and have the land back for arable use,” Baker told me. He said this would work regardless of whether the plants were there before a chemical attack, or planted afterwards (it grows very quickly).

While it’s not a recognised method of detecting or dealing with contamination yet, the paper suggests “green manures” like this could be used in the future to restore polluted sites. In the meantime, we still need to figure out exactly how to destroy the remaining stockpiles of chemical weapons.