The Fate of Nitroaromatic (tnt) and Nitramine (rdx and Hmx) Explosives in Fractured and Weathered Soils

We investigated the fate of explosives compounds in slurries containing fractured and weathered soil particles. Three soils were crushed with a piston to emulate detonation-induced fracturing. We used X-ray diffraction, scanning electron microscopy and gas adsorption surface area measurements to quantify the mineralogies and surfaces of the weathered and fractured soil particles. Soil batch slurries were prepared by spiking the soils with waters containing TNT, 2,4-DNT, HMX and RDX. Batch samples were collected 10 times over 92 days and the concentrations of the four spiked explosives compounds and TNT breakdown products 2ADNT and 4ADNT were measured. TNT, 2,4-DNT, RDX, and HMX exhibited substantially greater analyte loss batch solutions containing crushed soils compared to their uncrushed, weathered counterparts. This suggests explosives compounds breakdown more readily in the presence of fresh mineral and soil particle surfaces than in the presence of weathered surfaces. Concentrations of TNT breakdown products 2ADNT and 4ADNT were slightly greater in the slurries containing weathered soils than in slurries containing crushed soils. We suspect this is because these compounds are breaking down more rapidly to diamino and triamino compounds in the crushed soil batches than in the weathered batches. Following the batch runs the weathered, unfractured soils contained lower TNT, 2,4-DNT, RDX, HMX,2ADNT, and 4ADNT concentrations than their crushed counterparts. This suggests enhanced transformation of explosives compounds in the crushed soils is not associated with enhanced adsorption onto mineral surfaces but, rather, is associated with degradation to tertiary breakdown products. Distribution Statement A: Approved for public release; distribution is unlimited. INTRODUCTION Artillery, mortars, hand grenades and small arms munitions contain nitroaromatic compounds like 2,4,6trinitrotoluene (TNT) and nitramines like 1,3,5hexahydro-1,3,5-trinitrotriazine (RDX) and 1,3,5,7tetrahydro-1,3,5,7-tetranitrotetrazocine (HMX) that interact with the soils onto which they are deposited. Explosives are known to adsorb to soil mineral surfaces and aquatic sediments (Brannon et al., 2002; Li et al., 2004; Eriksson et al., 2004). Training range soils with adsorbed explosives thus provide a long-term contamination issue at training, testing and manufacturing sites. The off-site migration of explosives either adsorbed to sediments or eluted from sediments provides a long-term risk. Reactions on mineral and organic particle surfaces at a range of scales control nitramine and nitroaromatic compound adsorption and transformation. Previous investigations of the fate of explosives in sediments have used weathered clays, silts and sands in a series of column and incubation studies (eg. Price et al., 2000 and the references therein). These samples provide a substrate that is well characterized but the rounded grains and general lack of fresh mineral surfaces offered by these weathered substrates provide a less reactive surface for adsorption than fractured or unweathered mineral surfaces. Explosives compounds are formulated based on their brisance, or ability to shatter materials which include targets and training range soil particles (Eremenko and Nesterenko, 1989; Pepekin and Gubin, 2007). These fractured soils are the primary transfer mechanism between explosives detonations and training range soils. It is widely known that fresh mineral