Using phytoremediation for the removal of 2,4,6-trinitrotoluene

Explosives and explosive-related materials are used in many capacities, which include mining, surface quarrying, construction and demolition, and weapons manufacturing. While explosives, such as 2,4,6-trinitrotoluene (TNT), have acted as useful avenues for the advancement of human civilization, there is a side to TNT that we rarely think about, let alone discuss: what happens to TNT after an explosion? Not all TNT is consumed during an explosion. In fact, the after-explosion TNT residues are considered pollutants that settle over millions of acres at waste sites, mining areas and conflict (war) zones. These residues are very toxic to animals, but also degrade the biodiversity in soils and severely disrupt plant foliar growth and root systems. In order to remediate these contaminated soils researchers often use phytoremediation, or the use of plants as a “filter,” to removed pollutants from soil and water medias.

In light of these issues, a recent article from The Christian Science Monitor (CSM) titled “Mutant plant munches TNT, could help solve cleanup problems,” discusses a study from the United Kingdom’s University of York recently published in Science that makes use of a mutated relative of the cabbage plant, Arabidopsis thaliana, to remediate TNT-contaminated soils. In the study, led by Rylott and Bruce, Arabidopsis was selected due to its greater root growth in the presence of TNT, thereby being more tolerant to TNT presence than most plants and a better candidate for TNT detoxification by living plant organisms. The researchers mutated a gene in the plant strain to cause a deficiency of a specific enzyme, monodehydroascorbate reductase (MDHAR6), which protects plants from oxidative stress. This enzyme generates a superoxide from TNT, which as, a reactive oxygen species, would oxidize and breakdown plant material (figure below). While the principal investigators expected the mutation would increase the performance of enzymes in the plant to detoxify TNT, the mutation instead did not produce any MDHAR6, thereby making TNT completely harmless to the plant. This increases the mutant plant’s tolerance and maintains its uptake of TNT in contaminated soils. The tolerance of the mutant Arabidopsis is specific only to TNT.

The CSM article, which is largely a summary of the peer-reviewed article, does however contribute further statements from the researchers. The researchers state that there are still a few speed bumps that need to be taken care of in the follow up research, namely the confirmation that TNT remains inactive after death and decomposition of the plant material. But they are hopeful in the article, stating he is “..fairly confident that the TNT’s been locked up in the this material…it’s incredibly difficult to extract the transformed TNT once it’s been taken up into the plant.” The articles goes on to say that the greatest issue lies in public acceptance of using these mutants to remediate soils, since there is a general public aversion to using genetically modified organisms (or GMOs).

I felt as if the journal article stated the issues with using the modified Arabidopsis very well, that is, the fixation of TNT within the plant media during decomposition of the material. However, if the TNT is not fixated, this could create disposal issues. If not fixated, TNT will continue to be present in affected areas through the plant life cycle, and other disposal methods, such as burning,  may not be applicable here due to the nature of the pollutant. Overall, I found the CSM article very representative of the peer-reviewed journal article and appreciated that it was straight science in layman’s terms without any leaning politics or “sensationalizing” incorporated by the CSM author.