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Explosives and energetics continue to be prominent contaminants on many military installations. This research was undertaken to understand the extent to which microscale (10's of μm) particles are produced when macroscale residues are weathered by artificial precipitation. Initial experiments, in which artificial rainwater was applied drip-wise to single chunks of Composition B detonation residues from multiple heights, confirmed that microscale particles were produced during precipitation-driven aging, with 30% of the explosive mass collected detected as particulate Composition B (e.g., particles >0.45 μm in diameter). Follow-on experiments, during which multiple cm-sized residue chunks were subjected to realistic simulated precipitation, demonstrated an initial large pulse of particulate Composition B, followed by sustained production of microscale particles that represented 15–20% of recovered explosives. These findings indicate that the effective footprint of detonation residues likely increases as particulates are produced by the production and spreading of microscale particles across the soil surface. Combined with results published elsewhere that microscale particles can move into porous media to become a distributed source term, these findings point to the need for inclusion of these processes in explosive contaminant fate and transport modeling. [ABSTRACT FROM AUTHOR]

Highlights: [•] Weathering of mm-sized and microscale Comp B residues produced colloidal particles. [•] Colloidal particles migrated into and became entrained within porous media. [•] Higher dissolution was attributed to production and transport of colloidal particles. [Copyright &y& Elsevier]

Abstract: Energetic residues are scattered around active ranges due to the detonation events and dissolution is usually the first step for the entry of explosive compounds into the environment. The current models for describing the dissolution are subject to limitations in either model applicability or generality. This study attempted to develop a general model that is applicable to various types of energetic residues. Experimental data that were acquired from previous reports were used for testing the developed model. The results showed that the model captured well the dissolution processes of different types of energetic residues: 2,4,6-trinitrotoluene (TNT), Tritonal, Composition B, Octol, and Greener Insensitive Material (GIM). Moreover, it was observed that the mass transfer coefficients of TNT, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and/or octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) that were part of the energetic residues increased quantitatively with rising flow rates. In addition, the values of resistance coefficient, a model parameter, were negligible for the drop-impingement experiments, implying that under the conditions of rainfall and/or snowmelt flow, the surface attachment effect on the dissolution of energetic residues that rest on range soils is trivial. The study herein provides a general modeling approach for various types of energetic residues with additional insights in regards to their dissolution processes. [Copyright &y& Elsevier]

Abstract: The dissolution of the 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) from microscale particles (<250μm) of the explosive formulation Composition B was examined and compared to dissolution from macroscopic particles (>0.5mm). The dissolution of explosives from detonation soot was also examined. The measured mass transfer coefficients for the microscale particles were one to two orders of magnitude greater than the macroscopic particles. When normalized to particle surface area, mass transfer coefficients of microscale and macroscale particles were similar, indicating that the bulk dissolution processes were similar throughout the examined size range. However, an inverse relationship was observed between the particle diameter and the RDX:TNT mass transfer rate coefficient ratio for dry-attritted particles, which suggests that RDX may be more readily dissolved (relative to TNT) in microscale particles compared to macroscale particles. Aqueous weathering of larger Composition B residues generated particles that possessed mass transfer coefficients that were on the order of 5- to 20-fold higher than dry-attritted particles of all sizes, even when normalized to particle surface area. These aqueous weathered particles also possessed a fourfold lower absolute zeta-potential than dry-attritted particles, which is indicative that they were less hydrophobic (and hence, more wettable) than dry-attritted particles. The increased wettability of these particles provides a plausible explanation for the observed enhanced dissolution. The wetting history and the processes by which particles are produced (e.g., dry physical attrition vs. aqueous weathering) of Composition B residues should be considered when calculating mass transfer rates for fate and transport modeling. [Copyright &y& Elsevier]

Abstract: 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) are common contaminants around active military firing ranges. Dissolution of these compounds is usually the first step prior to their spreading in subsurface environments. Nevertheless, dissolution of individual TNT, RDX, and HMX under continuous flow conditions has not been well investigated. This study applied spectral confocal microscopy to observe and quantify the dissolution of TNT, RDX, and HMX (<100μm crystals) in micromodel channels. Dissolution models were developed to describe the changes of their radii, surface areas, volumes, and specific surface areas as a function of time. Results indicated that a model incorporating a resistance term that accounts for the surface area in direct contact with the channel surfaces (and hence, was not exposed to the flowing water) described the dissolution processes well. The model without the resistance term, however, could not capture the observed data at the late stage of TNT dissolution. The model-fitted mass transfer coefficients were in agreement with the previous reports. The study highlights the importance of including the resistance term in the dissolution model and illustrates the utility of the newly developed spectral imaging method for quantification of mass transfer of TNT, RDX, and HMX. [Copyright &y& Elsevier]

Abstract: An evaluation of peat moss plus crude soybean oil (PMSO) for mitigation of explosive contamination of soil at military facilities was performed using large soil lysimeters under field conditions. Actual range soils were used, and two PMSO preparations with different ratios of peat moss:soybean oil (1:1, PO1; 1:2, PO2) were compared to a control lysimeter that received no PMSO. PMSO was applied as a 10cm layer on top of the soil, and Composition B detonation residues from a 55-mm mortar round were applied at the surface of each of the lysimeters. Dissolution of the residues occurred during natural precipitation events over the course of 18months. Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) emanating from the Composition B residues were significantly reduced by the PO2 PMSO material compared to the untreated control. Soil pore water RDX concentrations and RDX fluxes were reduced over 100-fold compared to the control plots at comparable depths. Residual RDX in the soil profile was also significantly lower in the PMSO treated plots. PO1 PMSO resulted in lower reductions in RDX transport than the PO2 PMSO. The transport of the RDX breakdown product hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) was also greatly reduced by the PMSO materials. Results were in general agreement with a previously developed fate and transport model describing PMSO effectiveness. These results demonstrate the potential effectiveness of the inexpensive and environmentally benign PMSO technology for reducing the subsurface loading of explosives at training ranges and other military facilities. [Copyright &y& Elsevier]

We report the ability of nickel-based catalysts to degrade explosives compounds in aqueous solution. Several nickel catalysts completely degraded the explosives, although rates varied. Nearly all of the organic explosive compounds tested, including 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), were rapidly degraded to below detection limits by a powdered nickel on an alumina-silicate support (Aldrich nickel catalyst). Perchlorate degradation was minimal (<25%). Degradation of TNT by Aldrich nickel catalyst resulted in apparent first-order kinetics. Significant gaseous 14C was released and collected in an alkaline solution (most likely carbon dioxide) from [14C]RDX and [14C]HMX, indicating heterocyclic ring cleavage. Significant gaseous 14C was not produced from [14C]TNT, but spectrophotometric evidence indicated loss of aromaticity. Degradation occurred in low ionic strength solutions, groundwater, and from pH 3 to pH 9. Degradation of TNT, RDX, and HMX was maintained in flow-through columns of Aldrich nickel catalyst mixed with sand down to a hydraulic retention time of 4h. These data indicate that nickel-based catalysts may be an effective means for remediation of energetics-contaminated groundwater. [Copyright &y& Elsevier]

Peat moss and soybean oil are proposed as potential amendments for mitigating the dissolved transport of energetic compounds from military training facilities. Laboratory column experiments were performed to evaluate the migration of 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) through peat moss and peat moss amended with soybean oil. Results indicated that uptake into the sorbents significantly reduced the migration of these compounds, and that uptake into the peat was mass transfer limited. Addition of the soybean oil had a negligible effect on the transport of RDX and HMX, but had a significant impact on the transport of TNT through the columns. The relatively large impact of soybean oil on TNT transport was due, in part, to enhanced biotransformation of TNT. The TNT biotransformation rate constant in the presence of soybean oil was approximately 10 times greater than in the presence of peat alone, and at least 10 times greater than the biotransformation rate constant of RDX or HMX. The presence of the soybean oil also increased the rate of TNT mass transfer to kinetically controlled sorption sites, resulting in an overall decrease in TNT flux from the peat plus soybean oil columns. A diffusion model incorporating the effects of liquid viscosity and soybean oil–water contaminant partitioning was shown to accurately describe the impact of soybean oil addition on the transport of energetic compounds, indicating that mass transfer limitations in peat moss are the result of liquid phase diffusion, and that the presence of nonaqueous phase liquids affect sorption kinetics. [ABSTRACT FROM AUTHOR]

Changes in the microbial community during bioremediation of explosives-contaminated soil in a molasses-fed bioslurry process were examined. Upon addition of molasses to laboratory-scale reactors, total culturable heterotrophs increased rapidly by three to four orders of magnitude. However, heat-shocked heterotrophs and the percentage of gram-positive bacterial isolates did not increase until the soluble concentrations of 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrobenzene (TNB) began to decrease. The number of identified phospholipid fatty acids (PLFA) and the total PLFA concentration also exhibited an immediate increase in response to molasses addition, while the concentration of branched PLFA, indicative of the gram-positive population, remained low until soluble TNT and TNB concentrations had significantly decreased. This same general relationship between explosives degradation and gram-positive-specific PLFA was observed during an experiment with a large field-scale bioslurry lagoon reactor. These results indicate that the gram-positive organisms, which have been shown to be severely impacted by even low concentrations of TNT and TNB [Current Microbiol. 35 (1997) 77; Environ. Toxicol. Chem. 17 (1998) 2185], are able to increase in concentrations after explosives compounds are reduced to non-inhibitory levels, and should therefore be able to reestablish themselves in remediated soils. [Copyright &y& Elsevier]