Multi-species Aquatic Toxicity Assessment of 1-Methyl-3-Nitroguanidine (MeNQ).

Abstract

The Army is replacing traditional munitions with insensitive munitions (IM) resistant to accidental detonation. The aquatic toxicity of 1-methyl-3-nitroguanidine (MeNQ), which is being assessed for potential use in IM formulations, remains largely untested. The present study fills a number of critical data gaps for MeNQ aquatic toxicity by evaluating effects across two vertebrate and five invertebrate species. Specifically, responses in larval Pimephales promelas, Rana pipiens tadpoles, Chironomus dilutus, Lumbriculus variegatus, Hydra littoralis, Hyalella azteca, and Daphnia pulex were assessed in MeNQ exposures across various acute, subchronic, and chronic bioassays. Overall, survival was unaffected in most of the MeNQ exposures where significant lethal effects were only observed in D. pulex, H. littoralis, and C. dilutus and only at concentrations ≥ 2186mg/L. Significant sublethal effects on growth were observed for C. dilutus at 903mg/L and H. azteca at 1098mg/L in 10-d assays. Significantly decreased reproduction was observed at 2775mg/L for H. azteca in a chronic 35-d assay and at 174mg/L for D. pulex in the 11-d three-brood assay representing a sublethal effect one order of magnitude more sensitive than the effective lethal concentration for D. pulex (2987mg/L). Degradation of MeNQ in ultraviolet light (UV) greatly increased toxicity to D. pulex. Specifically, exposure to a MeNQ solution that was completely UV-degraded prior to D. pulex exposures resulted in an 11-d LC50 of 6.1mg/L and a 50% reduction in reproduction at 3.125mg/L, based on the original MeNQ parent-compound concentrations.