Adsorption and oxidation of 3-nitro-1,2,4-triazole-5-one (NTO) and its transformation product (3-amino-1,2,4-triazole-5-one, ATO) at ferrihydrite and birnessite surfaces

Abstract

The emerging insensitive munitions compound (IMC) 3-nitro-1,2,4-triazole-5-one (NTO) is currently being used to replace conventional explosives such as 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), but the environmental fate of this increasingly widespread IMC remains poorly understood. Upon release from unexploded solid phase ordinances, NTO exhibits high aqueous solubility and, hence, potential mobilization to groundwater. Adsorption and abiotic transformation at metal oxide surfaces are possible mechanisms for natural attenuation. Here, the reactions at ferrihydrite and birnessite surfaces of NTO and its biotransformation product, 3-amino-1, 2, 4-triazol-5-one (ATO), were studied in stirred batch reactor systems at controlled pH (7.0). The study was carried out at metal oxide solid to solution ratios (SSR) of 0.15, 1.5 and 15 g kg. The samples were collected at various time intervals up to 3 h after reaction initiation, and analyzed using HPLC with photodiode array and mass spectrometric detection. We found no detectable adsorption or transformation of NTO upon reaction with birnessite, whereas ATO was highly susceptible to oxidation by the same mineral, showing nearly complete transformation within 5 min at 15 g kg SSR to urea, CO and N. The mean surface-area-normalized pseudo-first order rate constant (k) for ATO oxidation by birnessite across all SSRs was 0.05 ± 0.022 h m, and oxidation kinetics were independent of dissolved O concentration. Both NTO and ATO were resistant to oxidation by ferrihydrite. However, NTO showed partial removal from solution upon reaction with ferrihydrite at 0.15 and 1.5 g kg SSR and complete loss at 15 g kg SSR due to strong adsorption. Conversely, ATO adsorption to ferrihydrite was much weaker than that measured for NTO.

Reductive Transformation of 3-Nitro-1,2,4-triazol-5-one (NTO) by Leonardite Humic Acid and Anthraquinone-2,6-disulfonate (AQDS)

“…ATO was stable in the presence of MES (pH 6.5), Tris (pH 8.0), and CAPSO (pH 10) buffers but was rapidly transformed in the presence of K 3 Fe­(CN) 6 , presumably through oxidation (Figure S6). The susceptibility of ATO to oxidation has been observed previously in both abiotic and biological systems. , …”

“…showed that ATO was less toxic than NTO to methanogenic archaea but highly toxic to Daphnia magna . Fortunately, ATO can be readily transformed into innocuous products such as N 2 , CO 2 , NH 3 , and urea, via either chemical oxidation by birnessite or biodegradation by Bacillus licheniformis and soil enrichment cultures . Therefore, reduction of NTO to ATO may represent not only a critical fate process but the first step to achieve complete mineralization of NTO.…”

Abiotic reduction of 3-nitro-1,2,4-triazol-5-one (NTO) and other munitions constituents by wood-derived biochar through its rechargeable electron storage capacity

“…Much research to date on the fate and treatment of NTO has focused on sorption 56–58 and biodegradation. 59–61 Because ATO can be readily mineralized to innocuous products such as CO 2 , NH 4 + , and N 2 , 62 reduction to ATO may be a first step to achieve complete NTO mineralization.…”

The Role of Manganese Dioxide in the Natural Formation of Organochlorines

“…Birnessite (δ-MnO 2 ) was synthesized according to a previously described method, and the solids were crushed using a mortar and pestle. The specific surface area was measured using a Micromeritics Gemini VII Surface Analyzer (Norcross, GA, USA) and determined to be 38.14 ± 0.46 m 2 g –1 using the multipoint calculation by the nitrogen adsorption Brunauer–Emmett–Teller (BET) method …”