Alkaline hydrolysis of the cyclic nitramine explosives RDX, HMX, and CL-20 : New insights into the degradation pathways obtained by the observation of novel intermediates

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX, I) and octahydro- 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) hydrolyze at pH > 10 to form end products including NO\u2082\u207b, HCHO, HCOOH, NH\u2083, and N\u2082O, but little information is available on intermediates, apart from the tentatively identified pentahydro-3,5-dinitro-1,3,5-triazacyclohex-1-ene (II). Despite suggestions that RDX and HMX contaminated groundwater could be economically treated via alkaline hydrolysis, the optimization of such a process requires more detailed knowledge of intermediates and degradation pathways. In this study, we hydrolyzed the monocyclicnitramines RDX, MNX (hexahydro-1-nitroso-3,5-dinitro-1,3,5- triazine), and HMX in aqueous solution (pH 10-12.3) and found that nitramine removal was accompanied by formation of 1 molar equiv of nitrite and the accumulation of the key ring cleavage product 4-nitro-2,4-diazabutanal (4-NDAB, O\u2082NNHCH\u2082NHCHO). Most of the remaining C and N content of RDX, MNX, and HMX was found in HCHO, N\u2082O, HCOOH, and NH\u2083. Consequently, we selected RDX as a model compound and hydrolyzed it in aqueous acetonitrile solutions (pH 12.3) in the presence and absence of hydroxypropyl-\u3b2-cyclodextrin (HP-\u3b2-CD) to explore other early intermediates in more detail. We observed a transient LC-MS peak with a [M-H] at 192 Da that was tentatively identified as 4,6-dinitro-2,4,6-triaza-hexanal (O\u2082NNHCH\u2082- NNO\u2082CH\u2082NHCHO, III) considered as the hydrolyzed product of II. In addition, we detected another novel intermediate with a [M-H] at 148 Da that was tentatively identified as a hydrolyzed product of III, namely, 5-hydroxy-4-nitro- 2,4-diaza-pentanal (HOCH\u2082NNO\u2082CH\u2082NHCHO, IV). Both III and IV can act as precursors to 4-NDAB. In the case of the polycyclic nitramine 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12- hexaazaisowurtzitane (CL-20), denitration (two NO\u2082\u207b) also led to the formation of HCOOH, NH\u2083, and N\u2082O, but neither HCHO nor 4-NDAB were detected. The results provide strong evidence that initial denitration of cyclic nitramines in water is sufficient to cause ring cleavage followed by spontaneous decomposition to form the final products.NRC publication: Ye

Sorption and stability of the polycyclic nitramine explosive CL-20 in soil

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 (Kd (0.33% TOC) 2.4 L kg-1; Kd (20% TOC) = 311 L kg-1). Sorption to minerals (Fe2O3, silica, kaolinite, montmorillonite, illite) was very low (0 < Kd < 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; Kd = 15 L kg-1; 8% loss) < clay soil from St. Sulpice, QC, Canada (CSS) (pH = 8.1; Kd = I L kg-1; 82% loss) < sandy soil provided by Agriculture Canada (SAC) (pH = 8.1, Kd = 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.Peer reviewed: YesNRC publication: Ye

Bioaccumulation of the synthetic hormone 17a-ethinylestradiol in the benthic invertebrates Chironomus tentans and Hyalella azteca

a b s t r a c t The present study investigated the bioaccumulation of the synthetic hormone 17a-ethinylestradiol (EE2) in the benthic invertebrates Chironomus tentans and Hyalella azteca, in water-only and spiked sediment assays. Water and sediment residue analysis was performed by LC/MS-MS, while biota extracts were analyzed using both LC/MS-MS and a recombinant yeast estrogen receptor assay. At the lowest exposure concentration, C. tentans accumulated less EE2 than H. azteca in the water-only assays (p ¼ 0.0004), but due to different slopes, this difference subsided with increasing concentrations; at the exposure concentration of 1 mg/L, C. tentans had a greater body burden than H. azteca (p ¼ 0.02). In spiked sediments, C. tentans had the greatest EE2 accumulation (1.270.14 vs. 0.570.05 mg/g dw, n ¼ 4). Measurements in H. azteca indicated a negligible contribution from the sediments to the uptake of EE2 in this species. These differences were likely due to differences in the behavior and life history of the two species (epibenthic vs. endobenthic). Water-only bioaccumulation factors (BAFs) calculated at the lowest exposure concentration were significantly smaller in C. tentans than in H. azteca (31 vs. 142, respectively; po0.0001). In contrast, the sediment bioaccumulation factor (BSAF) of C. tentans was larger than that of H. azteca (0.8 vs. 0.3; po0.0001). Extracts of the exposed animals caused a response in a recombinant yeast estrogen receptor assay, thus confirming the estrogenic activity of the samples, presumably from EE2 and its estrogenic metabolites. The results of the present study suggest that consumption of invertebrate food items could provide an additional source of exposure to estrogenic substances in vertebrate predators

Physico-chemical measurements of CL-20 for environmental applications : comparison with RDX and HMX

CL-20 is a polycyclic energetic nitramine, which may soon replace the monocyclic nitramines RDX and HMX, because of its superior explosive performance. Therefore, to predict its environmental fate, analytical and physico-chemical data must be made available. An HPLC technique was thus developed to measure CL-20 in soil samples based on the US Environmental Protection Agency method 8330. We found that the soil water content and aging (21 days) had no effect on the recoveries (>92%) of CL-20, provided that the extracts were kept acidic (pH 3). The aqueous solubility of CL-20 was poor (3.6 mg l-1 at 25 degreeC) and increased with temperature to reach 18.5 mg l-1 at 60 degreeC. The octanol-water partition coefficient of CL-20 (log KOW = 1.92) was higher than that of RDX (log KOW = 0.90) and HMX (log KOW = 0.16), indicating its higher affinity to organic matter. Finally, CL-20 was found to decompose in non-acidified water upon contact with glass containers to give NO2- (2 equiv.), N2O (2 equiv.), and HCOO- (2 equiv.). The experimental findings suggest that CL-20 should be less persistent in the environment than RDX and HMX.NRC publication: Ye

Sediment Contaminated with the Azo Dye Disperse Yellow 7 Alters Cellular Stress- and Androgen-Related Transcription in <i>Silurana tropicalis</i> Larvae

Azo dyes are the most commonly used type of dye, accounting for 60–70% of all organic dye production worldwide. They are used as direct dyes in the textile, leather, printing ink, and cosmetic industries. The aim of this study was to assess the lethal and sublethal effects of the disazo dye Disperse Yellow 7 (DY7) in frogs to address a knowledge gap regarding mechanisms of toxicity and the potential for endocrine disrupting properties. Larvae of <i>Silurana tropicalis</i> (Western clawed frog) were exposed to DY7-contaminated water (0 to 22 μg/L) and sediment (0 to 209 μg/g) during early larval development. The concentrations used included the range of similar azo dyes found in surface waters in Canada. A significant decrease in tadpole survivorship was observed at 209 μg/g while there was a significant increase in malformations at the two highest concentrations tested in sediment. In the 209 μg/g treatment, DY7 significantly induced <i>hsp70</i> (2.5-fold) and <i>hsp90</i> (2.4-fold) mRNA levels, suggesting that cells required oxidative protection. The same treatment also altered the expression of two androgen-related genes: decreased <i>ar</i> (2-fold) and increased <i>srd5a2</i> (2.6-fold). Furthermore, transcriptomics generated new hypotheses regarding the mechanisms of toxic action of DY7. Gene network analysis revealed that high concentrations of DY7 in sediment induced cellular stress-related gene transcription and affected genes associated with necrotic cell death, chromosome condensation, and mRNA processing. This study is the first to report on sublethal end points for azo dyes in amphibians, a growing environmental pollutant of concern for aquatic species