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TECHNICAL REPORTS

Bioremediation and Biodegredation

Biotic and Abiotic Degradation of CL-20 and RDX in Soils

^a Analytical Services, Inc., 3532 Manor Dr., Suite 3, Vicksburg, MS 39180
^b U.S. Army Engineer Res. and Dev. Center, CEERD-EP, 3909 Halls Ferry Rd., Vicksburg, MS 39180
^c Pacific Northwest National Lab., P.O. Box 999 K3-61, Richland, WA 99354

^* Corresponding author (Fiona.H.Crocker{at}erdc.usace.army.mil)

Received for publication January 26, 2005. The caged cyclic nitramine 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is a new explosive that has the potential to replace existing military explosives, but little is known about its environmental toxicity, transport, and fate. We quantified and compared the aerobic environmental fate of CL-20 to the widely used cyclic nitramine explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in surface and subsurface soil microcosms. Soil-free controls and biologically attenuated soil controls were used to separate abiotic processes from biologically mediated processes. Both abiotic and biological processes significantly degraded CL-20 in all soils examined. Apparent abiotic, first-order degradation rates (k) for CL-20 were not significantly different between soil-free controls (0.018 < k < 0.030 d^–1) and biologically attenuated soil controls (0.003 < k < 0.277 d^–1). The addition of glucose to biologically active soil microcosms significantly increased CL-20 degradation rates (0.068 < k < 1.22 d^–1). Extents of mineralization of ¹⁴C–CL-20 to ¹⁴CO₂ in biologically active soil microcosms were 41.1 to 55.7%, indicating that the CL-20 cage was broken, since all carbons are part of the heterocyclic cage. Under aerobic conditions, abiotic degradation rates of RDX were generally slower (0 < k < 0.032 d^–1) than abiotic CL-20 degradation rates. In biologically active soil microcosms amended with glucose aerobic RDX degradation rates varied between 0.010 and 0.474 d^–1. Biodegradation was a key factor in determining the environmental fate of RDX, while a combination of biotic and abiotic processes was important with CL-20. Our data suggest that CL-20 should be less recalcitrant than RDX in aerobic soils.

Abbreviations: 2ADNT, 2-amino-4,6-dinitrotoluene • CL-20, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane • HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine • HPLC, high pressure liquid chromatography • k, first-order degradation rate constant • PLFA, phospholipid fatty acids • RDX, hexahydro-1,3,5-trinitro-1,3,5-triazine • TNT, 2,4,6-trinitrotoluene

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				K. T. Thompson, F. H. Crocker, and H. L. Fredrickson Mineralization of the Cyclic Nitramine Explosive Hexahydro-1,3,5-Trinitro-1,3,5-Triazine by Gordonia and Williamsia spp. Appl. Envir. Microbiol., December 1, 2005; 71(12): 8265 - 8272. [Abstract] [Full Text] [PDF]