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TECHNICAL REPORTS

Organic Compounds in the Environment

Sorption and Stability of the Polycyclic Nitramine Explosive CL-20 in Soil

Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Avenue, Montréal, QC, Canada H4P 2R2

^* Corresponding author (Jalal.Hawari{at}cnrc-nrc.gc.ca).

Received for publication October 20, 2003. The polycyclic nitramine CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) is being considered for use as a munition, but its environmental fate and impact are unknown. The present study consisted of two main elements. First, sorption–desorption data were measured with soils and minerals to evaluate the respective contributions of organic matter and minerals to CL-20 immobilization. Second, since CL-20 hydrolyzes at a pH of >7, the effect of sorption on CL-20 degradation was examined in alkaline soils. Sorption–desorption isotherms measured using five slightly acidic soils (5.1 < pH < 6.9) containing various amounts of total organic carbon (TOC) revealed a nonlinear sorption that increased with TOC [K_d (0.33% TOC) = 2.4 L kg^–1; K_d (20% TOC) = 311 L kg^–1]. Sorption to minerals (Fe₂O₃, silica, kaolinite, montmorillonite, illite) was very low (0 < K_d < 0.6 L kg^–1), suggesting that mineral phases do not contribute significantly to CL-20 sorption. Degradation of CL-20 in sterile soils having different pH values increased as follows: sandy agricultural topsoil from Varennes, QC, Canada (VT) (pH = 5.6; K_d = 15 L kg^–1; 8% loss) < clay soil from St. Sulpice, QC, Canada (CSS) (pH = 8.1; K_d = 1 L kg^–1; 82% loss) < sandy soil provided by Agriculture Canada (SAC) (pH = 8.1, K_d = approximately 0 L kg^–1; 100% loss). The faster degradation in SAC soil compared with CSS soil was attributed to the absence of sorption in the former. In summary, CL-20 is highly immobilized by soils rich in organic matter. Although sorption retards abiotic degradation, CL-20 still decomposes in soils where pH is >7.5, suggesting that it will not persist in even slightly alkaline soils.

Abbreviations: CSS, clay soil from St. Sulpice • QC, Canada • FS, sandy forest soil provided by a local supplier • FSB, sandy forest soil from Boucherville, QC, Canada • GS, sandy garden soil obtained from a local supplier • HPLC, high performance liquid chromatography • K_d, distribution coefficient • K_F, Freundlich adsorption coefficient • K_oc, organic-carbon-normalized distribution coefficient • K_ow, n-octanol–water distribution coefficient • SAC, sandy soil provided by Agriculture Canada • SSL, Sassafras sandy loam • TOC, total organic carbon • VT, sandy agricultural topsoil from Varennes, QC, Canada

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