Epsilon Open Archive

Abstract

For decades, the fate of trinitrotoluene (TNT) in soil environments has interested researchers around the world. Due to its toxicity and locally high concentrations in soils and sediments, a proper risk assessment requires detailed knowledge of the type of bonds formed between TNT (and its degradation products) and major soil components. In the work described in this thesis the effects of different soil constituents were investigated using a fractional factorial experimental design, and kinetic and equilibrium experiments. A major concern was the distribution of TNT between dissolved (DOM) and particulate soil organic matter (POM). Free TNT in solution, TNT bound to POM and to different size fractions of DOM were determined using ¹⁴C-labelled compounds, reversed-phase chromatography (RPC) and size-exclusion chromatography (SEC). The distributions of aniline, nitrobenzene and toluene between POM and DOM were also determined. These compounds have similar properties to TNT and its degradation products. The results conclusively showed that soil organic matter (SOM) is the most important variable for the binding of TNT and its degradation derivatives in acid, organic rich soils. In experiments involving γ-radiation, dialysis and varying concentrations of DOM and POM, it was shown that biologically mediated reductive degradation of TNT is crucial for the binding of TNT derivatives to DOM and POM. The reactive TNT derivatives mainly bind to DOM functional groups via a pH-dependent reaction. Smaller DOM molecules were found to be more reactive than larger ones. Non-degraded TNT was found to bind mainly to POM by a pH-independent hydrophobic partitioning process. Even though a relatively small fraction of TNT was bound to DOM in our experiments, compared to POM, continuous degradation of TNT over time will result in a large potential transport of TNT derivatives with DOM to ground and surface waters. The question remaining to be answered is: how bioavailable and toxic are TNT derivatives that are bound to DOM?