Aquatic toxicity of photo‐degraded insensitive munition 101 (IMX‐101) constituents

Abstract

Insensitive munitions are desirable alternatives to historically used formulations, such as 2,4,6-trinitrotoluene (TNT), because of their so-called insensitivity to unintended detonation. The insensitive munition IMX-101 is a mixture of 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ). Environmental releases of munitions may be from production wastewaters or training; these munitions may be exposed to ultraviolet (UV) light. Therefore, it is useful to understand the relative toxicity of IMX-101 and its constituents both before and after photodegradation. The intent of the present study was to generate relative hazard information by exposing the standard ecotoxicological model Ceriodaphnia dubia to each insensitive munition constituent individually and to IMX-101 before and after the exposure solution was irradiated in a UV photoreactor. Without photodegradation, DNAN was more toxic (median lethal concentration [LC50] = 43 mg/L) than the other 2 constituents and it contributed predominantly to the toxicity of IMX-101 (LC50 = 206 mg/L) based on toxic units. Toxicity was observed only at high levels of NQ (LC50 = 1174 mg/L) and pH-adjusted NTO (LC50 = 799 mg/L). The toxicity of IMX-101 is lower than literature-reported TNT toxicity. Photodegradation efficiency was greater at lower insensitive munition concentrations. The observed degradation was greatest for NQ (42-99%), which in turn corresponded to the greatest relative increase in toxicity (100-1000-fold). Modest percent of degradation (4-18%) and increases in phototoxicity (2-100-fold) were observed for NTO and DNAN. Photodegraded NQ products were the predominant source of toxicity of photodegraded IMX-101. Future work involves research to enable analytical and computational confirmation of the specific degradation compounds inducing the observed photoenhanced toxicity. Environ Toxicol Chem 2017;36:2050-2057. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Comparative Toxicological Evaluation of UV‐Degraded versus Parent‐Insensitive Munition Compound 1‐Methyl‐3‐Nitroguanidine in Fathead Minnow

“…Even though UV treatment clearly caused increased toxicity of MeNQ in fathead minnows (Table ), the magnitude of increased toxicity is lower than has been reported for UV‐degraded NQ in previous experiments (Gust et al ; Kennedy et al ; Moores et al ). Kennedy et al () reported a 73‐fold lower LC50 for UV‐treated NQ compared with NQ parent compound in C. dubia . Moores et al () demonstrated the greatest increase in toxicity yet observed for UV‐degraded NQ, where 90% UV degradation of NQ elicited a 1240‐fold increase in toxicity in Daphnia pulex .…”

“…Information on subchronic or chronic toxicity of NQ to fathead minnows was not found in the available literature; therefore, future studies comparing the chronic toxicity of parent MeNQ and NQ including concentrations approaching their limit of solubility in water are warranted to determine if these compounds elicit lethal and sublethal effects in fathead minnows. (Table 3), the magnitude of increased toxicity is lower than has been reported for UVdegraded NQ in previous experiments Kennedy et al 2017;Moores et al 2020b). Kennedy et al (2017) reported a 73-fold lower LC50 for UV-treated NQ compared with NQ parent compound in C. dubia.…”

“…Moores et al () demonstrated the greatest increase in toxicity yet observed for UV‐degraded NQ, where 90% UV degradation of NQ elicited a 1240‐fold increase in toxicity in Daphnia pulex . Comparatively, the effect of UV‐degraded NQ was perhaps less severe in fish compared with cladocerans, where 69.2% UV degradation of NQ caused a 17‐fold increase in toxicity in larval zebrafish (Gust et al ), whereas 7% UV degradation of NQ elicited an 85‐fold increase in toxicity for D. pulex (Kennedy et al ).…”

Biotransformation and photolysis of 2,4-dinitroanisole, 3-nitro-1,2,4-triazol-5-one, and nitroguanidine

“…37 Overall, DNAN is the most toxic of the IHE constituents. 38 The toxicity of DNAN, and two of its amino derivatives towards nitrifiers, aerobic heterotrophs, methanogens and the bioluminescent bacterium, Aliivibrio fischeri has been investigated. 24 The results indicated that reduction to diaminoanisole (uncommon under aerobic conditions) was required to lower DNAN toxicity.…”

“…52 Finally, a study of photolysis of IMX-101 and the individual constituents indicates a 100-times increase in toxicity of NTO to Ceriodaphnia dubia after photolysis, but questions remain about the underlying cause of the toxicity increase. 38…”