Abstract

The overall objective was to improve the understanding of RDX transformation in plant tissues and the subsequent cycling of tissue-associated RDX and RDX daughter products among soil mineral and humic fractions following plant senescence. The hypothesis was that environmental risks from RDX at military training ranges can be reduced, and possibly eliminated, through a series of coupled processes involving plant uptake, plant enzyme mediated transformation, photodegradation in the plant, and finally humification of plant-tissue-associated RDX conjugates into soil organic matter after plant senescence and leaf drop. Although the effect of each individual process may be small, the combined effects of the processes taken as a system for sustainability may have a significant impact on RDX residues on surface soils. If so, they may lead to feasible range sustainability management practices. RDX is found in the soils and groundwater of bombing ranges and manufacturing sites. Plants of the family Lamiaceae were used to determine if either their enzymatic activities could accelerate the degradation of RDX once taken up from an aqueous solution. Plant tissue with higher chlorophyll content was found to contain higher concentrations of RDX, while the presence of anthocyanin appeared to have no impact. Of the four varieties of mint tested, chocolate mint, a variety of spearmint [Mentha spicata], had significantly lower RDX concentrations in its leaf tissues. Further research is needed to determine what processes are responsible for the reduced RDX content. Ascorbate, pH, and glutathione (GSH) were found to be statistically significant factors in the photodegradation of 2,4,6-trinitrotoluene (TNT), a process applicable to RDX. Ascorbate and pH increased the rate of TNT degradation, whereas GSH inhibited it. Photo-induced degradation of TNT occurs at approximately the same rate in extract-based solution. The results indicate that ascorbate and pH increase the rate of photolysis of TNT, whereas glutathione decreases it. In sufficiently reduced systems, RDX has been shown to attenuate, but the specific reactions and characterization of the residues that are produced have not been completely determined. Recent studies have demonstrated that both bacteria and fungi can also mineralize RDX, but, again, the pathways and intermediates formed are poorly understood. Because precedence has been established for RDX transformation, and explosives have been shown to bind covalently to soil humic fractions or organic material in compost, a humification approach may have significant utility in treating surface soils on impact and training ranges. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. ERDC/CRREL TR-13-4 iii

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