The Fate and Transport of Munitions Residues in Contaminated Soil

Principal Investigators
S.D. Comfort, P.J. Shea, D.L. McCallister, and W.L. Powers, University of Nebraska-Lincoln

Abstract

Goals: Goals are to establish accurate predictions of desorption kinetics of munitions residues by elucidating changes in sorption characteristics over time; to characterize transport properties of both freshly added and aged RDX, TNT, and principal degradates; and to predict the fate and transport of munitions residues over time with a computer transport model.

Rationale: Past disposal practices of munitions production facilities have resulted in contamination of terrestrial and aquatic ecosystems. Efforts to date have documented the extent of contamination and estimated potential migration routes. To predict the fate and transport of munitions in soils, an accurate description of the adsorption-desorption process is critical.

Approach: Investigators hypothesize that munitions residues residing in soils for extended periods may be more tightly bound into a soil organic fraction and that this bound fraction may be more important in predicting the long-term fate and transport of munitions residues. The proposed research will elucidate the transformations, mechanisms, and reversibility of munitions residues in soils with traditional sorption experiments and diffuse reflectance (FTIR) spectroscopy. The validity of using transport equations that assume instantaneous equilibrium, isotherm linearity, and adsorption-desorption singularity in field contaminated soils will also be tested. The proposed research will characterize the sorption of munitions residues in soil and provide improved predictions on desorption kinetics.

Status: Results from TNT sorption and transport experiments indicate that TNT sorption, transport, and degradation are concentration-dependent. Researchers found that assumptions of linear adsorption and singular adsorption-desorption, commonly used in transport modeling, are likely invalid for predicting TNT transport in highly contaminated soils. Transport experiments indicated that the fate of TNT in soil is highly dependent upon concentration. Further experiments provide strong evidence for the formation of bound residues of TNT degradates to surface and subsurface soil. Due to reduced availability, this process provides one possible pathway for practical detoxification of TNT residues. Experiments provide strong evidence for denitrification of TNT by P. savastanoi, and investigators have determined environmental conditions favoring this degradation pathway. Chemical (abiotic) treatments of Fenton oxidation and metal reduction have an excellent potential to remediate munitions-contaminated soil and water. Using these two techniques, soils with TNT and RDX contamination in excess of 1000 mg kg-1 were successfully remediated below the remediation goals established for the Nebraska Ordnance Plant. The most common pathway for microbial transformation of nitroaromatics is by reduction of nitro groups to amino groups via nitroso and hydroxylamino intermediates. Results from a kinetic study of adsorption and abiotic transformation of TNT in the presence of clay minerals and iron metal indicate that adsorption of TNT to both vermiculite and iron is very rapid. This project is in its third year.

Clients/Users: This research will be of use to those in munitions production facilities, U.S. Department of Defense, and others.

Key words: fate and transport, munitions, soil, adsorption, diffuse reflectance spectroscopy.

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