The insensitive munitions (IM) 2,4-dinitroanisole (DNAN) and nitroguanidine (NQ) have been used in newly developed explosives as a replacement for the more sensitive munition, 2,4,6-trinitrotoluene (TNT). These new formulations are less sensitive to external shocks, for example heat or strikes, and as such they are safer to store, transport and use in battle conditions. The objective of this research was to quantify the rate and extent to which IM can be transformed by combined biological and chemical reactions with iron and Fe(III)-reducing microorganisms.
The work was an investigation of chemical and biological degradation of DNAN and NQ by ferrous iron or hydroquinones using several metabolically diverse microorganisms: Geobacter metallireducens strain GS-15, Shewanella oneidensis strain MR-1, Rhodobacter sphaeroides, and Clostridium geopurificans strain MJ1. Fe(III), as the most common element found in subsurface environment, can be employed for in-situ remediation when Fe(III)-reducing microorganisms are active and generating Fe(II). Humic material present in the aquifer can also be used to promote degradation of insensitive munitions, hence quinone/hydroquinone couple was used in the study to represent this group. Fe(III) reducers, such as Geobacter and Shewanella, are ubiquitous and competitive for available substrates, which makes them suitable for explosives bioremediation.
Experimental results showed that DNAN can be readily reduced by chemical and biological processes at pH 7 within 24 hours, and at pH 8 and 9 in the order of minutes. At pH 6, organic ligands had to be used to stimulate degradation. DNAN and the highly energetic explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are used together in one of the newly developed explosive formulations and their mixture can be degraded by the same chemical and biological reactions. NQ was less susceptible to reductive degradation and it was most easily degraded at alkaline pH by organically complexed Fe(II) within several days; therefore, NQ may persist in the anoxic subsurface environments.
While the new munitions have not yet been detected outside of military test ranges, this work helps to evaluate environmental risks associated with potential contamination. The major benefit is the capacity to use a ubiquitous respiratory process, Fe(III) reduction, as the basis for a remediation strategy that uses both the biological and chemical electron transport processes as mechanisms.