Transport of RDX and TNT from Composition-B Explosive During Simulated Rainfall

Abstract

A complete understanding of the fate of munitions constituents (MC) on U.S. Army training lands is needed to develop the fundamental framework for the contaminant transport, transformation and fate (CTT&F) model for predicting the impacts of training activities on the distribution of MC in the environment. Explosive compounds RDX, TNT, and HMX derived from Composition-B explosive are of particular concern due to their toxicity potential and widespread use. This study evaluated distribution of these compounds from particulate Composition-B (Comp-B) following simulated rainfall in soil and plant mesocosms. Initial studies evaluated dissolution of MC from Comp-B with mass of Comp-B to water ratios ranging from 0.0125% to 12.5% and found soluble RDX and TNT was limited to < 5 mg L-1. When Comp-B was agitated in suspended soil particles in runoff elutriates for 30 min, soluble RDX, HMX and TNT generally increased in clay, loam and sandy loam soils except for reduced RDX and no detectable HMX in sandy loam soil. Significantly lower soil calcium and/or higher iron in the sandy loam soil may have contributed to the reduced RDX and HMX. Rainfall simulations were conducted on soil plant mesocosms with bare upland soil, vegetated upland soil, and vegetated wetland soil in a flow through system to monitor fate and transport of MC from Comp-B placed on the bare upland soil. The purpose of this was to determine effects of vegetated buffer zones on MC transport during rainfall events. Soluble concentrations of RDX and HMX were detected in runoff discharge from the bare upland soil but were significantly reduced following discharge through upland and wetland vegetation. TNT exhibited the greatest reduction in overland flow through upland vegetation with no detectable concentrations in discharge from the wetland. RDX and TNT were distributed in soil following overland flow of simulated rainfall with the higher concentrations remaining near the source zone. Upland plants had RDX and HMX concentrations exceeding soil concentrations indicating the plant uptake was a major route of RDX and HMX removal from the system. Following continued plant interaction with the RDX, HMX and TNT laden soils, dormant vegetation contained higher concentrations of RDX and HMX which was subsequently leached from the tissue to non-detectable concentrations after three rainfall events. These results indicate that the fate and transport of RDX, HMX and TNT in surface water runoff may be controlled by a number of complex, interacting factors including various soil chemical and physical properties, plant uptake and adsorption, and seasonal influences on release from cellulose residues. Further research is needed to quantify kinetics of adsorption, uptake degradation and release in vegetated systems.