The effects of physical form, moisture, humic acids, and mixtures on the photolysis of insensitive munitions compounds

The explosive formulations IMX-101 and IMX-104 are replacing conventional explosives in munitions, making them safer to transport and handle. However, munitions manufacturing and military training can lead to the environmental release of constituent insensitive munitions compounds (IMCs) such as 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ). These IMCs absorb ultraviolet light and transform photochemically into products with potentially greater toxicity. This study explores the effects of physical form, moisture, humic acids, and compound mixtures on the photolysis of solid and dissolved IMCs under UV-A (350 nm) and UV-B (300 nm) light. Irradiation of dry vs. moist solid IMC crystals yielded few measured products, and while photolysis rates were not significantly different, they were orders of magnitude slower than for aqueous IMCs. There was no significant difference in photolysis rates for aqueous IMCs irradiated with 0, 0.4, and 4 mg L^-1 humic acids, but 40 and 400 mg L^-1 humic acids inhibited NTO and enhanced NQ photolysis. In two- and three-component aqueous mixtures, DNAN photolysis was enhanced by NQ (at 300 and 350 nm) and NTO (at 350 nm); NTO photolysis was inhibited by DNAN and enhanced by NQ (both at 300 nm); and NQ photolysis was inhibited by both DNAN and NTO (both at 300 and 350 nm). The average quantum yields of the IMCs irradiated alone in solution were: 8.29 × 10^–5 (300 nm) and 6.26 × 10^–5 (350 nm) for DNAN; 5.76 × 10^–4 (300 nm) and 1.74 × 10^–4 (350 nm) for NTO; and 1.01 × 10^–2 (300 nm) and 1.14 × 10^–4 (350 nm) for NQ. Although organic and inorganic products were detected in the mixtures, an average of 15–35 % of the theoretical starting IMC masses (as nitrogen) was not accounted for. Overall, aqueous IMCs transformed 4–48 times faster than the solid IMCs, but the environmentally-relevant conditions tested were found to play a minor role in IMC photolysis.