CL-20 is currently under consideration for wider military application by the Department of Defense (DoD). However, previous practices with similar nitramine explosives such as RDX and HMX have resulted in soil and groundwater contamination. To avoid similar environmental problems, DoD needs to predict the fate and transport of CL-20 in the environment before it is widely used. Data such as the physicochemical, biochemical, and ecotoxicological properties of CL-20, however, are limited, and novel approaches to determine the transformation/transport mechanisms and environmental effects of CL-20 are needed.
The objectives of this project were to (1) develop analytical methods to measure CL-20 and its degradation products in soil and water systems, (2) determine physicochemical properties, (3) determine aerobic and anaerobic biodegradation of CL-20 in soil and water, (4) determine enzymes responsible for initiating the degradation of CL-20, (5) conduct ecotoxicological tests to determine the effects of CL-20 on selected ecological receptors, and (6) determine sorption of CL-20 onto soil and its effect on biodegradation kinetics and toxicity mechanisms.
Researchers measured physicochemical parameters of CL-20, including water solubility (S), water/octanol partition coefficient (Kow), and sorption (Kd) onto various types of soil. Then they determined its stability in aged soil under different conditions (pH, organic matter, micro flora) and degradability with zero valent iron and towards light. Other laboratory experiments were conducted to determine biotic (microbial and enzymatic) degradation of CL-20 in water and soil systems using soil indigenous microorganisms or specific isolates (Pseudomonas sp., Clostridium sp., Phanerochaete chrysosporium, Irpex lacteus) and enzymes (dehydrogenase, nitroreductase). In parallel, several biological biochemical and biological assays were conducted to determine toxicity of the explosive towards various terrestrial, aquatic, and avian receptors.
An analytical method to measure CL-20 in soil and water was developed and validated by an interlaboratory study. Physicochemical parameters (Kow and S) were measured, and sorption/desorption data (Kd, Koc) were determined under various conditions (aging, T, and pH). CL-20 was found to sorb strongly onto the organic fraction of soils with sorption being reversible and governed by the type of organic matter. Liquid chromatography-mass spectrometry (LC/MS) and solid phase micro extraction-gas chromatography (SPME-GC) were used to identify degradation products, reaction kinetics, and stoichiometry. It was found that initial denitration caused by either iron, light, hydrolysis, bacteria, fungi, or enzymes led to the decomposition of CL-20 to give nitrite, ammonia, nitrous oxide, glyoxal, and formic acid. CL-20 was found to be non toxic to algae, higher plants, and soil micro flora, but toxic to earthworms and quails.
The knowledge gained in this project on the transport and transformation routes and toxicity of CL-20 can be used to help understand and predict fate and impact (toxicity mechanisms) of the chemical and inform decisions about its potential future use in military munitions.