Outdoor weathering and dissolution of TNT and Tritonal

Low-order detonations of military munitions scatter cm-sized chunks of high-explosives onto military range soils, where rainfall can dissolve and then transport the explosives to groundwater. We present 1 year of mass-loss data obtained from cm-sized chunks of the frequently used explosives TNT (2,4,6-trinitrotoluene) and Tritonal (an 80:20 mixture of TNT and aluminum flakes) exposed outdoors to weather and dissolve under natural conditions. The explosive chunks rested on glass frits in individual funnels and all precipitation interacting with them was collected and analyzed. Mass balance data reveal that TNT in the water samples accounts for only about one-third of the TNT lost from the chunks. The creation of photo-transformation products on the solid chunks, and their subsequent dissolution or sublimation, probably accounts for the other two-thirds. Although these products cannot, as yet, be quantified they are intrinsic to the outdoor weathering and fate of TNT-based explosives. TNT in our water samples was not photo-transformed. Thus, we used the yearlong, dissolved-mass time-series to validate a drop-impingement dissolution model for TNT. The model used measured rainfall and air temperature data as input, and the results agreed remarkably well with TNT dissolved-mass time-series measured for the year. This model can estimate annual TNT influx into range soils using annual rainfall and particle-size distributions. Nevertheless, large uncertainties remain in the numbers and sizes of TNT particles scattered on military ranges and the identities and fates of the photo-transformation products.