Matthew C. Morley

Fate and Transport of High Explosives in a Sandy Soil: Adsorption and Desorption

Several areas of the Massachusetts Military Reservation (MMR) have soils with significant levels of high explosives (HE) contamination because of a long history of training and range activities (such as open burning, open detonation, disposal, and artillery and mortar firing). Site-specific transport and attenuation mechanisms were assessed in sandy soils for three contaminants of concern: the nitramine hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and the nitroaromatics 2,4-dinitrotolune (2,4-DNT) and 2,4,6-trinitrotoluene (TNT). For all three contaminants, linear distribution coefficients (Kd) were dependent on the fraction of organic carbon in soil. The nitroaromatics sorbed much more strongly than RDX in both soils. Over 120 hours, the desorption rate of RDX from field contaminated surface soil was much slower than its sorption rate, with the desorption Kd (1.5 L/kg) much higher than Kd for sorption (0.37 L/kg). Desorption of 2,4-DNT was negligible over 120 hours. Thus, applying sorption-derived Kd values for transport modeling may significantly overestimate the flux of explosives from MMR soils. Based on multiple component column transport tests, RDX will be the most mobile of these contaminants in MMR soils. In saturated columns packed with uncontaminated soil, RDX broke through rapidly, whereas the nitroaromatics were significantly attenuated by irreversible sorption or abiotic transformations.

Biodegradation of RDX and HMX Mixtures: Batch Screening Experiments and Sequencing Batch Reactors

Biodegradation is a potential treatment method for the high explosives RDX and HMX. In batch biodegradation tests, a facultative microbial consortium consumed the dissolved oxygen (DO) or reduced the oxidation-reduction potential (ORP) of the culture medium and biodegraded mixtures of RDX and HMX when supplied with various carbon and nitrogen sources. In batch tests with a mixture of carbon sources (glucose, glycerol, and succinic acid), RDX was reduced from 1.1 mg/L to below detectable levels within 4 days in the presence of 0.6 mg HMX/L. With ethanol as the carbon source, the culture degraded 90% of the initial 2.5 mg RDX/L over 8 days in the presence of 0.5 mg HMX/L. In batch mineralization tests, the culture converted 8 and 30% of the initial 14C-RDX to 14CO2 when supplied with ethanol and the mixed carbon sources, respectively. In both cases, a significant fraction of the initial 14C-RDX was converted to water-soluble 14C compounds, indicating triazine ring cleavage. However, mineralization was limit...

Evaluating Biodegradation as a Primary and Secondary Treatment for Removing RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine) from a Perched Aquifer

ABSTRACT Ground water beneath the U.S. Department of Energy (USDOE) Pantex Plant is contaminated with the high explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine). The authors evaluated biodegradation as a remedial option by measuring RDX mineralization in Pantex aquifer microcosms spiked with 14C-labeled RDX (75 g soil, 15 ml of 5 mg RDX/L). Under anaerobic conditions and constant temperature (16°C), cumulative 14CO2 production ranged between 52% and 70% after 49 days, with nutrient-amended (C, N, P) microcosms yielding the greatest mineralization (70%). The authors also evaluated biodegradation as a secondary treatment for removing RDX degradates following oxidation by permanganate (KMnO4) or reduction by dithionite-reduced aquifer solids (i.e., redox barriers). Under this coupled abiotic/biotic scenario, we found that although unconsumed permanganate initially inhibited biodegradation, > 48% of the initial 14C-RDX was recovered as 14CO2 within 77 days. Following exposure to dithionite-reduced solids, RDX transformation products were also readily mineralized (> 47% in 98 days). When we seeded Pantex aquifer material into Ottawa Sand that had no prior exposure to RDX, mineralization increased 100%, indicating that the Pantex aquifer may have an adapted microbial community that could be exploited for remediation purposes. These results indicate that biodegradation effectively transformed and mineralized RDX in Pantex aquifer microcosms. Additionally, biodegradation may be an excellent secondary treatment for RDX degradates produced from in situ treatment with permanganate or redox barriers.