Explosive detonation causes an increase in soil porosity leading to increased TNT transformation

Abstract

Explosives are a common soil contaminant at a range of sites, including explosives manufacturing plants and areas associated with landmine detonations. As many explosives are toxic and may cause adverse environmental effects, a large body of research has targeted the remediation of explosives residues in soil. Studies in this area have largely involved spiking 'pristine' soils using explosives solutions. Here we investigate the fate of explosives present in soils following an actual detonation process and compare this to the fate of explosives spiked into 'pristine' undetonated soils. We also assess the effects of the detonations on the physical properties of the soils. Our scanning electron microscopy analyses reveal that detonations result in newly-fractured planes within the soil aggregates, and novel micro Computed Tomography analyses of the soils reveal, for the first time, the effect of the detonations on the internal architecture of the soils. We demonstrate that detonations cause an increase in soil porosity, and this correlates to an increased rate of TNT transformation and loss within the detonated soils, compared to spiked pristine soils. We propose that this increased TNT transformation is due to an increased bioavailability of the TNT within the now more porous post-detonation soils, making the TNT more easily accessible by soil-borne bacteria for potential biodegradation. This new discovery potentially exposes novel remediation methods for explosive contaminated soils where actual detonation of the soil significantly promotes subsequent TNT degradation. This work also suggests previously unexplored ramifications associated with high energy soil disruption.

Fig 1

SEM images of a) pre-blast landscape soil, b) post-blast landscape soil, c) pre-blast native soil, d) post-blast native soil, e) pre-blast Spearwood soil and f) post-blast Spearwood soil. In each of the post-blast soils illustrated in this figure, the explosive was detonated in contact with the soils. Newly-cleaved planes and fractures are visible within each post-blast soil. Note that the post-blast soils are displayed at a higher magnification than the pre-blast soils, to more clearly illustrate the detonation-induced damage to the soils. Source: Evelyne Delbos, James Hutton Institute.

Fig 2

μCT slices taken from a) a pre-blast landscape soil aggregate; b) a pre-blast native soil aggregate; and c) a pre-blast Spearwood sand grain. All aggregates measured 1–2 mm in diameter. Source: Holly Yu, Curtin University/University of Dundee.

Fig 3

Images of a landscape aggregate slice, showing a) the original slice; b) the slice after thresholding; c) the thresholded slice following the 'Create Selection' command; and d) the thresholded aggregate slice with solely its external edge selected.

Fig 4. Calculated average porosities from the pre- and post-blast landscape, native and Spearwood soil aggregates.

Error bars show standard deviations between three measurements.

Fig 5. Images taken from post-blast aggregates displaying large cracks throughout the aggregate structures (left to right: a native soil aggregate following explosive charge detonation in contact with soil; a native soil aggregate following explosive charge detonation over soil; a landscape soil aggregate following explosive charge detonation over soil).

Aggregate size 1–2 mm. Source: Holly Yu, Curtin University/University of Dundee.

Fig 6. TNT recoveries obtained from post-blast landscape and Spearwood soil samples and stored at 3 temperatures, extracting over 6 weeks.

Fig 7. Average (n = 2) TNT loss between the analysis time points used for this work, from spiked pre-blast and post-blast samples.

Fig 8. TNT recoveries obtained from post-blast native soil samples stored at 3 temperatures, extracting over 6 weeks.

Fig 9. 4-ADNT recovery from controlled detonation-spiked landscape, native and Spearwood soils stored at room temperature and extracted over 6 weeks.