Mutant Plants Suck TNT Out of Soil, Could Clean Polluted Land

Munitions like TNT pollute a vast amount of land, and a mutant plant could help remediate the soil. Here, mines, rockets and bombs, the equivalent of 750 kilograms of TNT, explode outside Kabul. Patrick De Noirmont / REUTERS

For more than a century, scientists have now and again tried to find a good way to degrade trinitrotoluene, or TNT—without, you know, exploding it. The chemical compound is really effective at blowing things up. But it strongly resists being broken down. It's highly toxic and once released into soil, it basically sits there, killing plants. There is no simple way to remediate land contaminated with the substance, says Neil Bruce, a plant biologist at England's University of York.

And this is no small problem. When bombs are detonated, for example on artillery ranges, there is often left-over TNT. In the United States, there are more than 38,000 square miles contaminated by "munitions constituents" including TNT, a sizable area that is—believe it or not—larger than the state of Maine.

Now, scientists have both identified the mechanism by which TNT kills plants, and found a mutant plant strain that is resistant to and can effectively absorb the explosive. In a study published today in the journal Science, Bruce and colleagues found that TNT interacts with a specific plant enzyme to continually and cyclically produce a highly toxic compound called superoxide.

The mutant plant on the right is resistant to TNT. The normal one of the left is poisoned by the explosive, which is typically toxic to plants. Liz Rylott

They then identified a mutant strain of Arabidopsis, a widely studied model plant, that is deficient in this enzyme. This mutant appears identical in every way to normal plants—same growth rate, size, and all that—but is resistant to TNT. This type of plant is not genetically modified, but rather produced by treating plants with mutagens and screening their offspring for resistance to TNT; this process could hypothetically be carried out to find similar mutants in grasses and other species that could be grown on large tracts of contaminated land, Bruce says.

Once plants take up TNT, they render much of it nontoxic, or at least much less toxic, Bruce says. Such mutants could also be genetically modified to break down other explosives, like a chemical called RDX, that often occur in the same places as TNT, says Stuart Strand, a plant biologist at the University of Washington who wasn't involved in the study. RDX is a particular concern since it's highly toxic and listed as a "possible human carcinogen" by the Environmental Protection Agency, and is also water soluble (unlike TNT).

The study could also help "design other herbicides with chemical similarity to TNT," says Jerry Schnoor, a researcher at the university of Iowa who wasn't involved with the paper. This is an exciting new avenue to explore, he says, since no new herbicidal "targets," or mechanisms, have been commercialized since the 1980s. Bruce says he is currently in talks with agrochemical companies about the possibility of commercializing the work.

A bomb exploding, contaminating the land with TNT. A newfound mutant plant strain can suck up the explosive. Eddy Doust
Mutant Plants Suck TNT Out of Soil, Could Clean Polluted Land | Tech & Science