In order to enhance the safety of explosives, the military has been gradually transitioning from using TNT explosives to storing more stable explosives such as 2,4-dinitroanisole (DNAN). However, a university in the UK has discovered that the toxins produced by DNAN can accumulate in plants over the long term, affecting both plants and potentially impacting humans through the food chain.
TNT used to be the primary component of military ammunition worldwide, known for its high explosiveness and poor stability. Many countries later replaced TNT with the “insensitive munition” DNAN. DNAN is a low sensitivity organic compound that is not explosive on its own; it must be mixed with other explosive chemicals in certain proportions to become an explosive with 90% of the explosive power of TNT.
The latest research conducted by Neil Bruce, a professor in the Department of Biology and the Director of the Centre for Novel Agriculture Products at the University of York, UK, revealed that the toxins produced by DNAN after explosion can accumulate in plants, persist, and impact both plants and soil. The effects of DNAN may have long-lasting consequences.
Previous studies have found that TNT, after detonation, produces a specific enzyme called “monodehydroascorbate reductase 6” (MDHAR6), which reduces TNT to nitro free radicals. These radicals can oxidize TNT, turning it into superoxide radicals that react with DNA and cell membranes, leading to cell damage. Similarly, DNAN exhibits comparable effects on plants.
To assess the actual impacts of the toxins from DNAN and TNT on plants, the University of York research team conducted experiments by spraying solutions with different concentrations of DNAN and TNT on a plant species called “Arabidopsis thaliana” (thale cress) to observe their effects on plant growth.
Thale cress is a flowering plant native to Eurasia and Africa, commonly considered a weed that grows along roadsides and other areas. However, it is widely used in genetic studies related to phototropism, chloroplast positioning, stomatal aperture, and other fundamental plant research.
The results showed that the higher the concentrations of both explosives, the more negative impact on plant growth. When thale cress was treated with the lowest concentration (50 µM) of DNAN and TNT, only DNAN significantly reduced the plant’s weight. Furthermore, while TNT toxins in plants could be depleted within 24 hours, DNAN could persist longer, indicating its potential for chronic plant poisoning.
In order to evaluate the effects of MDHAR6 produced by DNAN on plants, the research team planted genetically modified thale cress and wild-type thale cress in soil contaminated with DNAN (100 mg/kg). The findings revealed that soil containing DNAN significantly affected wild-type thale cress but had a lesser impact on genetically modified thale cress.
Beyond these experiments, the researchers also discovered that DNAN is resistant to decomposition in plants and soil, often persisting in plant roots and leaf tissues.
The researchers from the University of York pointed out that while TNT may cause localized acute toxicity in plant roots, this toxicity can be rapidly mitigated through transformation. However, DNAN exhibits mobility within plants, accumulating in root and shoot tissues, thereby posing a risk for exposure through herbivores and the broader food chain, potentially impacting the environment significantly.
They further noted that their previous research successfully utilized genetically modified plants to remediate contamination levels in plant tissues caused by military TNT explosives, but currently, there is no natural method to counteract or reduce the presence of DNAN residues.
Professor Bruce expressed to the university’s press office, “TNT produces a critical plant enzyme after detonation, which reacts with the plant to generate highly reactive superoxides, causing severe cell damage. We have genetically modified plants to be immune to pollutant effects. Unfortunately, there is currently no natural way to counteract the toxic effects of DNAN; even trace amounts can impact plants. Not only does it accumulate throughout the plant system, but it can also be easily ingested by animals, giving the toxin a chance to spread through the food chain.”
Dr. Liz Rylott, a co-author of the study and researcher at the University of York’s Department of Biology, stated, “With increasing global conflicts and the continual advancement of military explosives, we may witness widespread contamination. This underscores the urgent need to develop feasible strategies to aid in plant restoration.”
“We currently do not know the toxicity threshold of DNAN in humans, so we hope that our latest research will prompt immediate actions to address the issues linked to DNAN production,” she added.
This study was published in the journal “Nature Plants” on November 28 and was funded by the Strategic Environmental Research and Development Program (SERDP) of the US Department of Defense, with assistance from researchers at the US Army Engineer Research and Development Center (ERDC) and the US Army Corps of Engineers.