James M. Brannon

Environmental fate of explosives

Waste disposal practices associated with military production of weapons, especially before and during World War II, have resulted in significant contamination of soils and ground water with high explosives such as TNT, RDX and HMX. Development of remediation and risk management strategies for these contaminated sites as well as development of approaches for sustainable use of active training and weapons testing sites require an understanding of how the energetic compounds interact with the environment. Factors affecting leaching and transport, microbial degradation, phytotoxicity and plant uptake, and invertebrate and vertebrate toxicity are determinants of ultimate environmental fate and hazard potential. In this article, we will summarize our current understanding of these interactions, identify significant data deficiencies, and briefly discuss the drivers of future research in this area.

Dissolution rates of three high explosive compounds: TNT, RDX, and HMX.

Incidental exposure to high explosive compounds can cause subtle health effects to which a population could be more susceptible than injury by detonation. Proper source characterization is a key requirement in the conduct of risk assessments. For nonvolatile solid explosives, dissolution is one of the primary mechanisms that controls fate and transport, resulting in exposure to these compounds remote from their source. To date, information describing dissolution rates of high explosives has been sparse. The objective of this study was to determine the dissolution rates of three high explosive compounds, 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), in dilute aqueous solutions as a function of temperature, surface area, and energy input. To determine each variables impact on dissolution rate, experiments were performed where one variable was changed while the other two were held constant. TNT demonstrated the fastest dissolution rate followed by HMX and then RDX. Dissolution rate correlation equations were developed for each explosive compound incorporating the three aforementioned variables, independently, and collectively in one correlation equation.

Monitored Natural Attenuation of Explosives

Explosives are subject to several attenuation processes that potentially reduce concentrations in groundwater over time. Some of these processes are well defined, while others are poorly understood. The objective of the project was to optimize data collection and processing procedures for evaluation and implementation of monitored natural attenuation of explosives. After conducting experiments to optimize data quality, a protocol was established for quarterly monitoring of thirty wells over a 2-year period at a former waste disposal site. Microbial biomarkers and stable isotopes of nitrogen and carbon were explored as additional approaches to tracking attenuation processes. The project included a cone penetrometry sampling event to characterize site lithology and to obtain sample material for biomarker studies. A three-dimensional groundwater model was applied to conceptualize and predict future behavior of the contaminant plume. The groundwater monitoring data demonstrated declining concentrations of explosives over the 2 years. Biomarker data showed the potential for microbial degradation and provided an estimate of the degradation rate. Measuring stable isotopic fractions of nitrogen in TNT was a promising method of monitoring TNT attenuation. Overall, results of the demonstration suggest that monitored natural attenuation is a viable option that should be among the options considered for remediation of explosives-contaminated sites.

Abiotic transformation of TNT in montmorillonite and soil suspensions under reducing conditions

Abstract Abiotic reduction of nitrobenzenes by Fe +2 adsorbed to various surfaces has been demonstrated by others. The objective of this study was to describe abiotic TNT transformation as a function of pH and confirm the possibility of an abiotic Fe +2 reduction pathway in reduced soils.Effects of pH on abiotic transformations of TNT were examined in buffered batch tests with montmorillonite and Fe +2 . Results indicated that TNT was rapidly reduced under abiotic conditions, with the rate of reduction highest at pH 8. Mass balance experiments indicated that unextractable or unknown transformation products were produced. Suppression of the abiotic Fe +2 reduction mechanism in anaerobic soil by complexing Fe +2 with EDTA demonstrated the presence of the pathway in a soil.

Aquifer Soil Cation Substitution and Adsorption of TNT, RDX, and HMX

1U.S. Army Engineering Research and Development Center, Environmental Laboratory, 3909 Halls Ferry Road, Vicksburg, MS 39180; 2DynTel Corporation, 350 Manor Dr., Vicksburg, MS 39180 these contaminants in aquifer soils and groundwater. The objective of this laboratory study was to determine the effects of changing composition of simulated groundwater on TNT, RDX, and HMX adsorption in low carbon aquifer soils. Batch shake tests using homo-ionic aquifer soils and clay minerals were used to determine the effects of cation composition on sorption. Results of batch shake tests showed that simulated groundwater cation composition substantially affected the sorption of TNT in aquifer soils. Saturation of the cation exchange sites with K+ and NH4 resulted in increased TNT sorption to the aquifer soils by up to 9780%. TNT adsorption by biionic K+:Ca++ aquifer soil increased until 40% saturation of the exchange sites was attained. Past this point, pronounced increases in adsorption were not observed until 100% saturation with K+ was reached. Changing the cation substitution on aquifer soils by saturation with either K+ or NH4 did not consistently increase the adsorption of RDX and HMX. TNT shows great potential for treatment using cation substitution, while this is not the case for nitramines. The production of 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-hexahydrotriazine (RDX), and octahydro-1,3,57-tetranitro1,3,5,7-tetrazocine (HMX) has resulted in significant contamination of soil and groundwater at ammunition plants. The development of remediation and risk management strategies requires an understanding of the environmental fate and transport processes affecting TNT, RDX, and HMX. The transformation and soil sorption are key process descriptors that must be quantified to effectively evaluate the environmental fate of

An exploratory approach to modeling explosive compound persistence and flux using dissolution kinetics

Recent advances in the description of aqueous dissolution rates for explosive compounds enhance the ability to describe these compounds as a contaminant source term and to model the behavior of these compounds in a field environment. The objective of this study is to make predictions concerning the persistence of 2,4,6-trinitrotoluene (TNT) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in solid form both as individual explosive compounds and components of octol, and the resultant concentrations of explosives in water as a result of dissolution using three exploratory modeling approaches. The selection of dissolution model and rate greatly affect not only the predicted persistence of explosive compound sources but also their resulting concentrations in solution. This study identifies the wide range in possible predictions using existing information and these modeling approaches to highlight the need for further research to ensure that risk assessment, remediation and predicted fate and transport are appropriately presented and interpreted.

Fluoranthene KDOC in sediment pore waters

Abstract When calculating concentrations of truly dissolved hydrophobic organic contaminants (HOCs) in sediment pore water, a common assumption is that the partition coefficient between pore water and colloidal plus dissolved organic carbon (K DOC ) equals the partition coefficient between pore water and sediment total organic carbon (K OC ). This study examined the K DOC of fluoranthene in pore water from 11 sediments. Truly dissolved fluoranthene was separated from DOC-associated fluoranthene by partitioning on C-18 Sep Paks. Measured values of K DOC were not constant over the 11 sediments examined, and were over or underestimated by assuming that K DOC = K OC . Current models used to predict the fate of HOCs may require modification to account for the observed difference between K DOC and K OC .

The effects of sediment contact time on Koc of nonpolar organic contaminants

Abstract Mobility of nonpolar organic contaminants depends upon partitioning between sediment solids and interstitial water. The objective of this study was to measure the constancy of Koc values for polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs) over time. Two PCBs and one PAH were incubated and sampled periodically over a 6 month period. Results demonstrated that as time of contact increased, the value of Koc increased, reflecting a decrease in the truly dissolved contaminant concentration in the interstitial water. The data also showed a marked dependence of Koc on the source of organic carbon and a 2 to 17 fold deviation of measured Koc values from values predicted by empirical relationships. Therefore, empirical data may be the only truly reliable alternative for determining mobility potential of these contaminants.

Capping Contaminated Dredged Material

Abstract The ability of various uncontaminated cap materials of varying thicknesses to isolate contaminated dredged material from the water column was assessed in large (250 l.) reactor units using chemical and microbial tracers. Heavy metals, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and bacterial spores contained in the underlying contaminated dredged material were monitored in the overlying water column, clams ( Rangia cuneata ) suspended in the water, and burrowing polychaetes ( Nereis virens ). Tissue analysis of Rangia indicated that none of the 5 cm cap thicknesses tested was totally effective in preventing contaminant transfer to biota. However, cap materials consisting predominantly of clay and silt appeared more effective than sand in preventing contaminant transfer to biota. Rangia did not show elevated tissue concentrations of chemicals when contaminated sediment was covered with a 50 cm cap. However, chemical and microbial results indicated that Nereis breached both the 5 cm and 50 cm thicknesses of all cap materials tested.

Volatilization of Contaminants from Suspended Sediment in a Water Column during Dredging

Abstract Remedial dredging of contaminated bed sediments in rivers and lakes results in the suspension of sediment solids in the water column, which can potentially be a source for evaporation of hydrophobic organic compounds (HOCs) associated with the sediment solids. Laboratory experiments were conducted in an oscillating grid chamber to simulate the suspension of contaminated sediments and flux to air from the surface of the water column. A contaminated field sediment from Indiana Harbor Canal (IHC) and a laboratory-inoculated University Lake (UL) sediment, Baton Rouge, LA, were used in the experiments, where water and solids concentration and particle size distribution were measured in addition to contaminant fluxes to air. A transient model that takes into account contaminant desorption from sediment to water and evaporation from the water column was used to simulate water and sediment concentrations and air fluxes from the solids suspension. In experiments with both sediments, the total suspended solids (TSS) concentration and the average particle diameter of the suspended solids decreased with time. As expected, the evaporative losses were higher for compounds with higher vapor pressure and lower hydrophobicity. For the laboratory-inoculated sediment (UL), the water concentrations and air fluxes were high initially and decreased steadily implying that contaminant release to the water column from the suspended solids was rapid, followed by evaporative decay. For the field sediments (IHC), the fluxes and water concentrations increased initially and subsequently decreased steadily. This implied that the initial desorption to water was slow and that perhaps the presence of oil and grease and aging influenced the contaminant release. Comparison of the model and experimental data suggested that a realistic determination of the TSS concentration that can be input into the model was the most critical parameter for predicting air emission rates.