OF ALL the nasty ways people have devised to harm each other, chemical weapons are among the worst. But even they have varying levels of unpleasantness. Mustard gas blisters the skin and lungs but is an inefficient way of killing. Nerve agents such as sarin, soman and VX are much more deadly. These can linger for days, and only tiny amounts are needed to cause uncontrollable muscle spasms. Death by suffocation follows swiftly as the victim’s diaphragm stops working properly, and he cannot breathe.
In a world where the use of chemical weapons is supposed to be prohibited, finding out when and where they have been deployed is important. But that is not as easy as it sounds. Though nerve agents hang around long enough to be formidable weapons, they degrade in the presence of moisture into chemicals called alkyl methylphosphonic acids. These are reliable signals something bad has happened but they, in turn, break down into simple molecules that leave no clear signature of the original poison.
The result is that, within a month or two of an attack, concentrations of alkyl methylphosphonic acids left in the soil are too low for gas chromatography—the tool normally used to search for traces of nerve gas—to detect. What is needed is a way to concentrate the chemical signal. And a group of researchers from the University of Central Lancashire, in Britain, and the country’s Defence Science and Technology Laboratory, led by Matthew Baker, think they have one: the humble white mustard plant.
White mustard (named after the colour of its seeds, not its flowers) grows rapidly in many sorts of soils. That makes it suitable for deployment all over the world. The researchers’ crucial discovery, though, was that if the soil in which it is growing contains a nerve agent (they used VX) the plant will absorb it, metabolise it into alkyl methylphosphonic acids, and store those acids in its tissue. It will do so even when the agent’s level in the soil is too low for chromatography to detect the poison directly. The plant’s constant extraction of chemicals from the soil means the acids build up in it to a point where detection is possible. Regardless of soil type, Dr Baker found, evidence for the presence of VX could be extracted from plants at least 45 days after application. Bad guys beware.
This article was published in The Economist on July 19th 2014. See this link.