Toxicity and bioaccumulation of reduced TNT metabolites in the earthworm Eisenia andrei exposed to amended forest soil

Phytotoxicity of nitroaromatic energetic compounds freshly amended or weathered and aged in sandy loam soil

The toxicities of 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitrobenzene (TNB), 2,4-dinitrotoluene (2,4-DNT), and 2,6-dinitrotoluene (2,6-DNT) to terrestrial plants alfalfa (Medicago sativa L.), Japanese millet (Echinochloa crusgalli L.), and perennial ryegrass (Lolium perenne L.) were determined in Sassafras sandy loam soil using seedling emergence, fresh shoot, and dry mass measurement endpoints. A 13-week weathering and aging of energetic materials in soils, which included wetting and drying cycles, and exposure to sunlight of individual soil treatments, was incorporated into the study design to better reflect the soil exposure conditions in the field than toxicity determinations in freshly amended soils. Definitive toxicity tests showed that dinitrotoluenes were more phytotoxic for all plant species in freshly amended treatments based on EC20 values for dry shoot ranging from 3 to 24mgkg(-1) compared with values for TNB or TNT ranging from 43 to 62mgkg(-1). Weathering and aging of energetic materials (EMs) in soil significantly decreased the toxicity of TNT, TNB or 2,6-DNT to Japanese millet or ryegrass based on seedling emergence, but significantly increased the toxicity of all four EMs to all three plant species based on shoot growth. Exposure of the three plant species to relatively low concentrations of the four compounds initially stimulated plant growth before the onset of inhibition at greater concentrations (hormesis).

Comparative and mixture sediment toxicity of trinitrotoluene and its major transformation products to a freshwater midge

The explosive trinitrotoluene (TNT) is a prevalent contaminant in many military installations worldwide. Limited knowledge of the comparative toxicity of sediment-associated TNT and related compounds contributes to uncertainty when assessing ecological risks in contaminated sites. Trinitrotoluene undergoes transformation when associated with soils and sediments and typically occurs as a mixture dominated by its reduction products. The objective of this study was to comparatively evaluate the single-compound toxicity of TNT and its major transformation products to the freshwater midge Chironomus tentans in 10-day exposures to sediment spiked with TNT, 2-aminodinitrotoluene (2-ADNT), 2,4-diaminonitrotoluene (2,4-DANT), or trinitrobenzene (TNB). In addition, the nature of the toxicological interactions of the latter compounds in a mixture was evaluated. Upon spiking to sediment, TNT and TNB rapidly degraded to reduced products, and disappearance of extractable compounds suggested irreversible binding to sediment particles. The high degree of transformation and reactivity occurring during 10 days at spiking concentrations as high as 4000 micromol/kg dry weight suggests that TNT and related compounds are unlikely to be encountered in fine-grained sediments at contaminated sites. Similar to previous investigations, the high reactivity of the spiked compound hampered determination of accurate toxic concentrations of TNT and related compounds, and of the nature of toxicological interaction of compounds in a mixture in this study. Sediment concentrations associated with decreased survival were similar for all four compounds, with the 10-d median lethal concentrations (LC50s) determined using initial concentrations ranging from 175 (2-ADNT) to 605 (2,4-DANT) micromol/kg dry weight. Sublethal decrease in growth was not observed for any compound. Results from the mixture experiment suggest additive interaction among TNT and related compounds in sediment exposures.

Comparative toxicokinetics of explosive compounds in sheepshead minnows

Juvenile sheepshead minnows Cyprinodon variegatus were exposed to the explosive compounds 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and to the TNT transformation products 2-aminodinitrotoluene (2-ADNT) and 2,4-diaminonitrotoluene (2,4-DANT) in five separate water-only experiments. A one-compartment model was used to characterize uptake (k(u)) and elimination (k(e)) rate constants and to estimate bioconcentration factors (BCFs). The compounds investigated in this study are weakly hydrophobic. Kinetically derived BCFs (9.6, 13.1, 0.5, 1.7, and 0.5 ml g(-1) for TNT, 2-ADNT, 2,4-DANT, RDX, and HMX, respectively) confirmed the expected low bioaccumulative potential of those compounds and the positive relationship between log BCF and log K(ow) (1.6, 2.0, 0.8, 0.9, and 0.2 for TNT, 2-ADNT, 2,4-DANT, RDX, and HMX, respectively). The uptake clearance (k(u)) was relatively slow for all compounds (7.3, 12.6, 1.3, 0.15, and 0.06 ml g(-1)h(-1) for TNT, 2-ADNT, 2,4-DANT, RDX, and HMX, respectively), and overall, it decreased with decreasing compound hydrophobicity. Elimination was extremely fast for the nitroaromatic compounds (0.77, 0.96, and 2.74 h(-1) for TNT, 2-ADNT, and 2,4-DANT, respectively), thus resulting in very short biological half-lives (<1 hour), but it was much slower for the cyclonitramines (0.09 h(-1) for RDX and 0.12 h(-1) for HMX). Although ADNTs were present in fish exposed to TNT, the parent compound was the dominant compound in tissues during the uptake and elimination exposures. The rates of metabolite formation (0.06 h(-1)) and elimination (0.16 h(-1)) were much slower than the rate of elimination of the parent compound (0.80 h(-1)). Because of the fast elimination rate of TNT and its transformation products and the exceedingly low bioaccumulative potential of RDX and HMX, exposure conditions likely associated with the presence of explosives in aquatic systems are unlikely to pose unacceptable risks to fish.