Comparative toxicogenomics of three insensitive munitions constituents 2,4-dinitroanisole, nitroguanidine and nitrotriazolone in the soil nematode Caenorhabditis elegans

Abstract

BackgroundEcotoxicological studies on the insensitive munitions formulation IMX-101 and its components 2,4-dinitroanisole (DNAN), nitroguanidine (NQ) and nitrotriazolone (NTO) in various organisms showed that DNAN was the main contributor to the overall toxicity of IMX-101 and suggested that the three compounds acted independently. These results motivated this toxicogenomics study to discern toxicological mechanisms for these compounds at the molecular level.MethodsHere we used the soil nematode Caenorhabditis elegans, a well-characterized genomics model, as the test organism and a species-specific, transcriptome-wide 44 K-oligo probe microarray for gene expression analysis. In addition to the control treatment, C. elegans were exposed for 24 h to 6 concentrations of DNAN (1.95–62.5 ppm) or NQ (83–2667 ppm) or 5 concentrations of NTO (187–3000 ppm) with ten replicates per treatment. The nematodes were transferred to a clean environment after exposure. Reproduction endpoints (egg and larvae counts) were measured at three time points (i.e., 24-, 48- and 72-h). Gene expression profiling was performed immediately after 24-h exposure to each chemical at the lowest, medium and highest concentrations plus the control with four replicates per treatment.ResultsStatistical analyses indicated that chemical treatment did not significantly affect nematode reproduction but did induce 2175, 378, and 118 differentially expressed genes (DEGs) in NQ-, DNAN-, and NTO-treated nematodes, respectively. Bioinformatic analysis indicated that the three compounds shared both DEGs and DEG-mapped Reactome pathways. Gene set enrichment analysis further demonstrated that DNAN and NTO significantly altered 12 and 6 KEGG pathways, separately, with three pathways in common. NTO mainly affected carbohydrate, amino acid and xenobiotics metabolism while DNAN disrupted protein processing, ABC transporters and several signal transduction pathways. NQ-induced DEGs were mapped to a wide variety of metabolism, cell cycle, immune system and extracellular matrix organization pathways.ConclusionDespite the absence of significant effects on apical reproduction endpoints, DNAN, NTO and NQ caused significant alterations in gene expression and pathways at 1.95 ppm, 187 ppm and 83 ppm, respectively. This study provided supporting evidence that the three chemicals may exert independent toxicity by acting on distinct molecular targets and pathways.Electronic supplementary materialThe online version of this article (10.1186/s12918-018-0636-0) contains supplementary material, which is available to authorized users.

Identifying degradation products responsible for increased toxicity of UV-degraded insensitive munitions

“…S1 and Supplemental Table S1). identified in the literature (Gersich and Hopkins, 1986;Xiang et al, 2010;Scott and Crunkilton, 2000) and further confirmed using analytical chemistry in the present study were determined. We used a combination of literature values for D. pulex as well as generation of new toxicity data for previously untested chemicals to provide context for the sum toxicity of UV-degraded NQ (Table 2).…”

“…The tubes were arranged in the outer ring of the carousel inside a Rayonet photoreactor (Model RPR-100, Southern New England Ultraviolet Co. Branford, CT) equipped with sixteen, 300 nm lightbulbs (RPR-3000A, Southern New England Ultraviolet Co.). Irradiation times were carefully controlled with a timer controller (Control Co. Webster, TX), and photon flux measured to be 1.38 ± 0.16 Â 10 À8 E per second by ferrioxalate actinometry (Goldstein and Rabani, 2008) where the formation of ferrous iron was monitored by UVevis spectroscopy (Cary 8454, Agilent, Santa Clara, CA) after chelation with FerroZine™.…”

“…One of the Army's insensitive munitions, IMX-101, consists of a mixture of 2e4 dinitroanisole (DNAN), nitrotriazolone (NTO), and nitroguanidine (NQ) and is being increasingly deployed as a replacement for conventional munitions across weapons platforms (Lee et al 2010;Williams et al, 2014). While the NQ parent compound is less toxic than TNT, RDX, DNAN and NTO in aquatic exposures (Gong et al, 2018;Gust et al, 2018;Gust et al, 2014;Gust et al, 2011;Lotufo et al, 2018;Stanley et al, 2015;Warner et al, 2012), the UV-degradation of NQ can generate products with higher toxic potency than the UV-degradation products of the other munitions constituents and nearly equal to those of TNT (Kennedy et al, 2015;Kennedy et al, 2017;Gust et al, 2017).…”

Accumulation of Insensitive Munition Compounds in the Earthworm Eisenia andrei from Amended Soil: Methodological Considerations for Determination of Bioaccumulation Factors

“…The compound DNAN also has the potential to undergo photochemical transformation (Taylor et al 2017a). It is toxic to a wide variety of aquatic species (Dodard et al 2013; Kennedy et al 2015; Stanley et al 2015; Gust et al 2018; Lotufo et al 2018) and to soil invertebrates (Dodard et al 2013; Gong et al 2018). Lotufo et al (2016) conducted bioaccumulation studies involving the uptake of DNAN by earthworms in amended soil and showed that the DNAN concentration in tissue exceeded the concentration of DNAN in soil.…”

“…It has excellent qualities as an explosive such as insensitivity and thermal and mechanical stability and is considered a potential insensitive replacement for hexahydro‐1,3,5‐triazine (RDX) in various formulations (Viswanath et al 2018). It has relatively low toxicity to tadpoles, fish, aquatic invertebrates, and soil nematodes and was found to be considerably less toxic than TNT and DNAN in comparative studies (Stanley et al 2015; Kennedy et al 2017; Pillard et al 2017; Gong et al 2018; Gust et al 2018; Lotufo et al 2018; Madeira et al 2018). The low log octanol–water partition coefficent K OW values predicted for NTO (from 0.89 to –1.19; Toghiani et al 2008) indicate a low propensity to adsorb to organic C through hydrophobic interactions.…”