Effects of Cyclic Nitramines

Robidoux et al. [23] found no reduction in seedling emergence or biomass of lettuce (Lactuca sativa L.) and barley (Hordeum vulgare L.) at measured soil concentrations 

Cyclic nitramine compounds such as RDX and HMX appear to have different modes of action in plants compared to the nitroaromatic compounds. Their basic structure and behavior in plants are similar to those of the triazine herbicides such as atrazine and simazine, which inhibit photosystem II in photosynthesis [32], The inhibition of photosynthesis may also be one of the modes of toxicity of cyclic nitramines based on symptoms such as chlorosis, necrosis, yellow leaf spots, and anthocyanin expression [27], However, the mechanism(s) of phytotoxicity of cyclic nitramines have not been investigated thoroughly. 

---

Effects of Cyclic Nitramines on Microbial Activity in Soil... 

EFFECTS ON SOIL INVERTEBRATES 3.4.1 Effects of Cyclic Nitramines... 

The cyclic nitramine explosives RDX, HMX, and CL-20 did not adversely affect plants at concentrations tested hence no plant-based ETVs could be developed for these MC. Similarly, soil invertebrate-based ETV could not be developed for HMX weathered and aged in amended soil, because the EC20 value was established only for one test species, F. Candida. HMX did not adversely affect reproduction of either earthworms or potworms in weathered and aged treatments at concentrations tested. The greatest concentrations of cyclic nitramine explosives that were tested in these studies that produced no adverse effects on the test species are shown in Table 12.5 and Table 12.6 as reference values only these values should not be considered ETVs for the respective explosives. 

In some related work, Lear and co-workers prepared the powerful cyclic nitramine explosive Keto-RDX (102) from the nitrolysis-nitration of2-oxa-5-tert-butyltriazone(101). Pagoria and co-workers " conducted a full study on the effect of different nitrating agents on the yield of Keto-RDX (Table 5.6). 

The preceding discussion revealed that once an initial attack, whether biotic or abiotic, disturbed the cyclic nitramine (RDX, HMX, or CL-20), the subsequent degradation reactions are largely governed by the interactions of the newly formed intermediates with water to eventually produce N02, N20, NH3, HCHO, and HCOOH (Figures 2.2, 2.3, 2.5, and 2.6). Knowledge of the product distributions provides insight into the adverse effect of this family of explosives to various receptors in the environment. 

The wide use of nitro organic based energetic chemicals (NOCs), such as the aromatic TNT, and the nonaromatic cyclic nitramines RDX and HMX has resulted in the contamination of terrestrial and aquatic systems. Several reports (see Chapters 3-5 and 7-9 of this book) described the toxic and carcinogenic effects of explosives and their degradation products to various terrestrial, aquatic, and avian receptors. However, to determine the true identity of the chemicals that cause toxicity, the transport and transformation mechanisms of these chemicals must be understood. 

Assessment of the toxicity of nitroaromatic EMs to soil invertebrates has received considerably greater attention compared with cyclic nitramines. The effects of exposure... 

Cyclic nitramines RDX and CL-20 share neurobiological pathways in their toxic effects on earthworms. Gong et al. [83] observed that toxicity of CL-20 on the giant... 

A relatively broad variety of aquatic toxicity studies exists for nitro-substituted phenol, toluene, and benzene explosives and related compounds, but very little toxicological information is available for tetryl, cyclic nitramines, and the other energetic compounds discussed in this chapter. Several explosives, such as tetryl, are no longer manufactured and are, therefore, of diminishing environmental concern, although their persistence and the nature, stability, and toxicity of their breakdown products is not understood in sufficient detail and should be further investigated. A variety of other energetic compounds, for example, perchlorates, are used in military operations, and due to environmental concerns with their release, additional studies on their fate and effects in aquatic systems are recommended. 

AZTC and DATH are a similar pair of mixed azidomethyl nitramines, one of which is cyclic and the other acyclic. Both compounds decompose similarly (and somewhat anomalously for nitramines) liberating N2O and CH2O as the vastly dominant nitramine products [46,48]. Neither produces much NO2. From these results we conclude that cyclization has little effect on the gas product distribution, but it could influence the temperature at which thermal decomposition begins. 

---