Movement of TNT and RDX from composition B detonation residues in solution and sediment during runoff

Energetics used in military exercises can potentially contaminate ground and surface waters. This study was conducted to evaluate the movement of Composition B, a formulation that includes TNT (2,4,6-trinitrotoluene), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), in runoff. Mechanisms of transport we examined include movement of energetics dissolved in runoff, as particles and adsorbed to suspended sediment, and in infiltration. Rainfall simulations were conducted under controlled conditions with two rainfall rates (approximately 30 and 50 mm h-1), two soils with different infiltration capacities, and four energetic particle sizes (4.75-9.51 mm, 2.83-4.75 mm, 2-2.83 mm, and <2 mm). Particles remaining on the soil surface after rainfall were measured as well as energetics dissolved in runoff, in suspended sediment, and in infiltration. Greater concentrations of TNT than RDX and HMX were found dissolved in runoff due to its higher solubility and dissolution rates. We also found that particle transport in runoff increased with decrease in particle size. Smaller particle sizes also led to greater transport dissolved in solution. Relationships were found relating runoff and sediment yield to the transport of RDX and TNT. The results of this study allow improved prediction of Composition B transport in runoff and therefore its contamination potential.

Transport of insensitive munitions constituents, NTO, DNAN, RDX, and HMX in runoff and sediment under simulated rainfall

Insensitive munition constituents derived from residues of low order detonations and deposited on military training grounds present environmental risks. A series of rainfall simulation experiments on small soil plots examined the effect of precipitation, soil properties, and particle size on transport of IMX-104 munition components: NTO (3-nitro-1,2,4-triazol-5-one), DNAN (2,4-dinitroanisole), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and HMX (octahydro-1,3,5,7- tertranitro-1,3,5,7-tetrazocine). The primary pathways for rainfall driven transport were subsurface infiltration, off-site transport in solution, and transport in solid form including re-adsorption onto soil particles. The transport was solubility dependent with NTO moving mostly in solution, which was dominated by either runoff or infiltration depending on soil. DNAN, RDX, and HMX, were transported primarily in particulate form. The fine energetic fraction (<2 mm) showed the highest mobility, while the coarsest fraction (>4.75 mm) remained in-situ after rainfall. A simple linear model relating energetics transport with sediment yield and energetics particle size and was proposed. These findings provide the first comprehensive mass balance of munition constituents as affected by overland flow under rainfall. They improve our understanding of environmental fate of munitions, can further be used for predictive modelling, developing mitigation strategies, and regulatory compliance.

A laboratory rill study of IMX-104 transport in overland flow

The deposition of explosive contaminants in particulate form onto the soil surface during low-order detonations can lead to ground and surface water contamination. The vertical fate and transport of insensitive munitions formulation IMX-104 through soil has been thoroughly studied, however the lateral transport of explosive particles on the surface is less known. The objective of this research was to understand the impact of overland flow on the transport of IMX-104 constituent compounds 3-nitro-1,2,4-triazol-5-one (NTO), 2,4-dinitroanisole (DNAN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The effect of overland flow was examined in a rill flume using several flow rates (165-, 265-, and 300-mL min^-1) and IMX-104 particle sizes (4.75-9.51 mm, 2.83-4.75 mm, 2-2.83 mm, and <2 mm). We found that the smaller particles were transported more in solution and with the sediment compared to the larger particles, which had a higher percent mass remaining on the surface. As flow rate increased, there was an increase in the percent mass found in solution and sediment and a decrease in the percent mass remaining on the surface. NTO fate was dominated by transport in solution, while DNAN, RDX and HMX were predominantly transported with the sediment. This research provides evidence of the role of overland flow in the fate of energetic compounds.

Environmental Fate of 14C Radiolabeled 2,4-Dinitroanisole in Soil Microcosms

2,4-Dinitrosanisole (DNAN) is an insensitive munitions component replacing conventional explosives. While DNAN is known to biotransform in soils to aromatic amines and azo-dimers, it is seldom mineralized by indigenous soil bacteria. Incorporation of DNAN biotransformation products into soil as humus-bound material could serve as a plausible remediation strategy. The present work studied biotransformation of DNAN in soil and sludge microcosms supplemented with uniformly ring-labeled ¹⁴C-DNAN to quantify the distribution of label in soil, aqueous, and gaseous phases. Electron donor amendments, different redox conditions (anaerobic, aerobic, sequential anaerobic-aerobic), and the extracellular oxidoreductase enzyme horseradish peroxidase (HRP) were evaluated to maximize incorporation of DNAN biotransformation products into the nonextractable soil humus fraction, humin. Irreversible humin incorporation of ¹⁴C-DNAN occurred at higher rates in anaerobic conditions, with a moderate increase when pyruvate was added. Additionally, a single dose of HRP resulted in an instantaneous increased incorporation of ¹⁴C-DNAN into the humin fraction. ¹⁴C-DNAN incorporation to the humin fraction was strongly correlated (R² = 0.93) by the soil organic carbon (OC) amount present (either intrinsic or amended). Globally, our results suggest that DNAN biotransformation products can be irreversibly bound to humin in soils as a remediation strategy, which can be enhanced by adding soil OC.