2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO), two components of insensitive munitions, may contaminate the aqueous environments. However, assessment of degradation pathways of DNAN and NTO may be difficult because the products are either unknown, common in nature (e.g., nitrite, nitrate, ammonium, N2O), or are difficult to measure. Here, we developed and validated the compound-specific carbon and nitrogen isotope analysis (13C- and 15N-CSIA) methodologies to better understand the transformation mechanisms, as well as to track the fates of DNAN and NTO, in the environment. The GC-IRMS method we developed for DNAN yielded method detection limits (MDLs) of 150 ng for δ13C and 1,500 ng for δ15N with a precision of ± 0.2 ‰. Because photolysis may be an important mechanism for DNAN and NTO degradation in surface waters and wastewater treatment processes, isotope fractionation was evaluated under both UV-A and UV-C wavelengths. For DNAN, normal 13C fractionation (εC = -3.34‰) but inverse 15N fractionation (εN = +12.30‰) was observed under UV-A (λ ~ 350 nm) irradiation. Interestingly, the opposite was observed under UV-C (λ ~ 254 nm) irradiation, with inverse 13C fractionation (εC = +1.45‰) and normal 15N fractionation (εN = - 3.79‰). For NTO, the MDL of our low-temperature derivatization/GC-IRMS method was 788 ng for both C and N isotope ratio analyses, yielding a precision of ±0.3‰ for both δ13C and δ15N values in good agreement (within ± 0.1‰) with δ13C and δ15N values determined by elemental analyzer-IRMS. During UV irradiation of NTO, we observed normal 15N fractionation (εN = -7.58 ‰ under UV-A and εN = -6.63 ‰ under UV-C) and negligible 13C fractionation. We also examined the role of Cl- in photolysis of DNAN and NTO under UV-C irradiation in a high salinity solution. Reactive halogen species (RHSs, i.e., Cl● and Cl2●-) attacked the amino group during deamination/chlorination of ATO (i.e., NTO reduced product), or during chlorination of NTO. However, during the photolysis of DNAN in the presence of Cl-, RHSs seemingly attacked the benzene ring preferentially via denitration/chlorination, while reactive oxygen species attacked the benzene ring at a different C site (C1) via SN2Ar. These results indicate that DNAN and NTO may act as photosensitizers and produce nitrite, nitrate, and ammonia during UV-induced degradation by sunlight in surface water environments and by UV-C irradiation in wastewater treatment processes.

Understanding the photochemical transformation mechanisms of insensitive munitions DNAN and NTO via 13C- and 15N- compound-specific isotope analysis

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.