Ecotoxicological characterization of energetic substances using a soil extraction procedure

Uncovering the structure and function of specialist bacterial lineages in environments routinely exposed to explosives

Environmental contamination by hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX), and Octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX), the two most widely used compounds for military operations, is a long-standing problem at the manufacturing and decommissioning plants. Since explosives contamination has previously been shown to favour the growth of specific bacterial communities, the present study attempts to identify the specialist bacterial communities and their potential functional and metabolic roles by using amplicon targeted and whole-metagenome sequencing approaches (WMS) in samples collected from two distinct explosives manufacturing sites. We hypothesize that the community structure and functional attributes of bacterial population are substantially altered by the concentration of explosives and physicochemical conditions. The results highlight the predominance of Planctomycetes in contrast to previous reports from similar habitats. The detailed phylogenetic analysis revealed the presence of OTU's related to bacterial members known for their explosives degradation. Further, the functional and metabolic analyses highlighted the abundance of putative genes and unidentified taxa possibly associated with xenobiotic biodegradation. Our findings suggest that microbial species capable of utilizing explosives as a carbon, energy, or electron source are favoured by certain selective pressures based on the prevailing physicochemical and geographical conditions.

Copper promotes E. coli laccase-mediated TNT biotransformation and alters the toxicity of TNT metabolites toward Tigriopus japonicus

Although laccase is involved in the biotransformation of 2,4,6-trinitrotoluene (TNT), little is known regarding the effect of E. coli laccase on TNT biotransformation. In this study, E. coli K12 served as the parental strain to construct a laccase deletion strain and two laccase-overexpressing strains. These E. coli strains were used to investigate the effect of laccase together with copper ions on the efficiency of TNT biotransformation, the variety of TNT biotransformation products generated and the toxicity of the TNT metabolites. The results showed that the laccase level was not relevant to TNT biotransformation in the soluble fraction of the culture medium. Conversely, TNT metabolites varied in the insoluble fraction analyzed by thin-layer chromatography (TLC). The insoluble fraction from the laccase-null strain showed fewer and relatively fainter spots than those detected in the wild-type and laccase-overexpressing strains, indicating that laccase expression levels were interrelated determinants of the varieties and amounts of TNT metabolites produced. In addition, the aquatic invertebrate Tigriopus japonicus was used to assess the toxicity of the TNT metabolites. The toxicity of the TNT metabolite mixture increased when the intracellular laccase level in strains increased or when purified E. coli recombinant Laccase (rLaccase) was added to the culture medium. Thus, our results suggest that laccase activity must be considered when performing microbial TNT remediation.

Tracing the Cycling and Fate of the Explosive 2,4,6-Trinitrotoluene in Coastal Marine Systems with a Stable Isotopic Tracer, (15)N-[TNT]

2,4,6-Trinitrotoluene (TNT) has been used as a military explosive for over a hundred years. Contamination concerns have arisen as a result of manufacturing and use on a large scale; however, despite decades of work addressing TNT contamination in the environment, its fate in marine ecosystems is not fully resolved. Here we examine the cycling and fate of TNT in the coastal marine systems by spiking a marine mesocosm containing seawater, sediments, and macrobiota with isotopically labeled TNT ((15)N-[TNT]), simultaneously monitoring removal, transformation, mineralization, sorption, and biological uptake over a period of 16 days. TNT degradation was rapid, and we observed accumulation of reduced transformation products dissolved in the water column and in pore waters, sorbed to sediments and suspended particulate matter (SPM), and in the tissues of macrobiota. Bulk δ(15)N analysis of sediments, SPM, and tissues revealed large quantities of (15)N beyond that accounted for in identifiable derivatives. TNT-derived N was also found in the dissolved inorganic N (DIN) pool. Using multivariate statistical analysis and a (15)N mass balance approach, we identify the major transformation pathways of TNT, including the deamination of reduced TNT derivatives, potentially promoted by sorption to SPM and oxic surface sediments.

Pilot-scale in situ bioremediation of HMX and RDX in soil pore water in Hawaii

A nine-month in situ bioremediation study was conducted in Makua Military Reservation (MMR) in Oahu, Hawaii (USA) to evaluate the potential of molasses to enhance biodegradation of royal demolition explosive (RDX) and high-melting explosive (HMX) contaminated soil below the root zone. MMR has been in operation since the 1940's resulting in subsurface contamination that in some locations exceeds USEPA preliminary remediation goals for these chemicals. A molasses-water mixture (1 : 40 dilution) was applied to a treatment plot and clean water was applied to a control plot via seven flood irrigation events. Pore water samples were collected from 12 lysimeters installed at different depths in 3 boreholes in each test plot. The difference in mean concentrations of RDX in pore water samples from the two test plots was very highly significant (p < 0.001). The concentrations differences with depth were also very highly significant (p < 0.001) and degradation was greatly enhanced at depths from 5 to 13.5 ft. biodegradation was modeled as first order and the rate constant was 0.063 per day at 5 ft and decreased to 0.023 per day at 11 ft to 13.5 ft depth. Enhanced biodegradation of HMX was also observed in molasses treated plot samples but only at a depth of 5 ft. The difference in mean TOC concentration (surrogate for molasses) was highly significant with depth (p = 0.003) and very highly significant with treatment (p < 0.001). Mean total nitrogen concentrations also differed significantly with treatment (p < 0.001) and depth (p = 0.059). The molasses water mixture had a similar infiltration rate to that of plain water (average 4.12 ft per day) and reached the deepest sensor (31 ft) within 5 days of application. Most of the molasses was consumed by soil microorganisms by about 13.5 feet below ground surface and treatment of deeper depths may require greater molasses concentrations and/or more frequent flood irrigation. Use of the bioremediation method described herein could allow the sustainable use of live fire training ranges by enhancing biodegradation of explosives in situ and preventing them from migrating to through the vadose zone to underlying ground water and off-site.

Dissolution and sorption of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT) residues from detonated mineral surfaces

Composition B (Comp B) is a commonly used military formulation composed of the toxic explosive compounds 2,4,6-trinitrotoluene (TNT), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Numerous studies of the temporal fate of explosive compounds in soils, surface water and laboratory batch reactors have been conducted. However, most of these investigations relied on the application of explosive compounds to the media via aqueous addition and thus these studies do not provide information on the real world loading of explosive residues during detonation events. To address this we investigated the dissolution and sorption of TNT and RDX from Comp B residues loaded to pure mineral phases through controlled detonation. Mineral phases included nontronite, vermiculite, biotite and Ottawa sand (quartz with minor calcite). High Performance Liquid Chromatography and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy were used to investigate the dissolution and sorption of TNT and RDX residues loaded onto the mineral surfaces. Detonation resulted in heterogeneous loading of TNT and RDX onto the mineral surfaces. Explosive compound residues dissolved rapidly (within 9 h) in all samples but maximum concentrations for TNT and RDX were not consistent over time due to precipitation from solution, sorption onto mineral surfaces, and/or chemical reactions between explosive compounds and mineral surfaces. We provide a conceptual model of the physical and chemical processes governing the fate of explosive compound residues in soil minerals controlled by sorption-desorption processes.

Soils contaminated with explosives: Environmental fate and evaluation of state-of-the-art remediation processes (IUPAC Technical Report)

An explosion occurs when a large amount of energy is suddenly released. This energy may come from an over-pressurized steam boiler, from the products of a chemical reaction involving explosive materials, or from a nuclear reaction that is uncontrolled. In order for an explosion to occur, there must be a local accumulation of energy at the site of the explosion, which is suddenly released. This release of energy can be dissipated as blast waves, propulsion of debris, or by the emission of thermal and ionizing radiation. Modern explosives or energetic materials are nitrogen-containing organic compounds with the potential for self-oxidation to small gaseous molecules (N2, H2O, and CO2). Explosives are classified as primary or secondary based on their susceptibility of initiation. Primary explosives are highly susceptible to initiation and are often used to ignite secondary explosives, such as TNT (2,4,6-trinitrotoluene), RDX (1,3,5-trinitroperhydro-1,3,5-triazine), HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane), and tetryl (N-methyl-N-2,4,6-tetranitro-aniline).

Statistical factor-screening and optimization in slurry phase bioremediation of 2,4,6-trinitrotoluene contaminated soil

Since slurry phase bioremediation is a promising treatment for recalcitrant compounds such as 2,4,6-trinitrotoluene (TNT), a statistical study was conducted for the first time to optimize TNT removal (TR) in slurry phase. Fractional factorial design method, 2(IV)(7-3), was firstly adopted and four out of the seven examined factors were screened as effective. Subsequently, central composite design and response surface methodology were employed to model and optimize TR within 15 days. A quadratic model (R(2) = 0.9415) was obtained, by which the optimal values of 6.25 g/L glucose, 4.92 g/L Tween 80, 20.23% (w/v) slurry concentration and 5.75% (v/v) inoculum size were estimated. Validation experiments at optimal factor levels resulted in 95.2% TR, showing a good agreement with model prediction of 96.1%. Additionally, the effect of aeration rate (0-4 vvm) on TR was investigated in a 1-liter bioreactor. Maximum TR of 95% was achieved at 3 vvm within 9 days, while reaching the same removal level in flasks needed 15 days. This reveals that improved oxygen supply in bioreactor significantly reduces bioremediation time in comparison with shake flasks.

Desorption of nitramine and nitroaromatic explosive residues from soils detonated under controlled conditions

Potentially toxic nitroaromatic and nitramine compounds are introduced onto soils during detonation of explosives. The present study was conducted to investigate the desorption and transformation of explosive compounds loaded onto three soils through controlled detonation. The soils were proximally detonated with Composition B, a commonly used military explosive containing 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). Gas-exchangeable surface areas were measured from pristine and detonated soils. Aqueous batches of detonated soils were prepared by mixing each soil with ultrapure water. Samples were collected for 141 d and concentrations of Composition B compounds and TNT transformation products 2-amino-4,6-dinitrotoluene (2ADNT), 4-amino-2,6-dinitrotoluene (4ADNT), and 1,3,5-trinitrobenzene (1,3,5-TNB) were measured. The RDX, HMX, and TNT concentrations in detonated soil batches exhibited first-order physical desorption for the first, roughly, 10 d and then reached steady state apparent equilibrium within 40 d. An aqueous batch containing powdered Composition B in water was sampled over time to quantify TNT, RDX, and HMX dissolution from undetonated Composition B particles. The TNT, RDX, and HMX concentrations in aqueous batches of pure Composition B reached equilibrium within 6, 11, and 20 d, respectively. Detonated soils exhibited lower gas-exchangeable surface areas than their pristine counterparts. This is likely due to an explosive residue coating on detonated soil surfaces, shock-induced compaction, sintering, and/or partial fusion of soil particles under the intense heat associated with detonation. Our results suggest that explosive compounds loaded to soils through detonation take longer to reach equilibrium concentrations in aqueous batches than soils loaded with explosive residues through aqueous addition. This is likely due to the heterogeneous interactions between explosive residues and soil particle surfaces.

Role of soil interstitial water in the accumulation of hexahydro-1,3,5-trinitro-1,3,5-triazine in the earthworm Eisenia andrei

The uptake of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from soil by the earthworm Eisenia andrei was examined by using the equilibrium partitioning (EqP) theory and a three-compartment model including soil (S), interstitial water (IW), and earthworms (E). The RDX concentrations were measured using U.S. Environmental Protection Agency (U.S. EPA) Method 8330A and high-performance liquid chromatography (HPLC). The S-IW studies were conducted using four natural soils with contrasting physicochemical properties that were hypothesized to affect the bioavailability of RDX. Each soil was amended with nominal RDX concentrations ranging from 1 to 10,000 mg/kg. The HPLC analysis showed that the IW extracted from soil was saturated with RDX at 80 mg/kg or greater soil concentrations. The calculated S-IW coefficient (K(p)) values for RDX ranged from 0.4 to 1.8 ml/g soil, depending on the soil type, and were influenced by the organic matter content. In the IW-E studies, earthworms were exposed to nonlethal RDX concentrations in aqueous media. The uptake of RDX by the earthworms correlated well (r(2) = 0.99) with the dissolved RDX concentrations. For the E-S studies, earthworms were exposed to RDX-amended soils used in the S-IW studies. The bioconcentration factors (BCF; ratios of E-to-IW RDX concentrations) were relatively constant ( approximately 5) up to 80 mg/kg soil RDX concentrations, which encompass the RDX saturation limit in the interstitial water of the tested soils. At this concentration range, the RDX uptake from interstitial water was likely dominated by passive diffusion and could be used as an indicator of bioavailability. Other mechanisms may be involved at greater RDX soil concentrations.

Investigating the fate of nitroaromatic (TNT) and nitramine (RDX and HMX) explosives in fractured and pristine soils

Explosives compounds, known toxins, are loaded to soils on military training ranges predominantly during explosives detonation events that likely fracture soil particles. This study was conducted to investigate the fate of explosives compounds in aqueous slurries containing fractured and pristine soil particles. Three soils were crushed with a piston to emulate detonation-induced fracturing. X-ray diffraction, energy-dispersive X-ray spectrometry, gas adsorption surface area measurements, and scanning electron microscopy were used to quantify and image pristine and fractured soil particles. Aqueous batches were prepared by spiking soils with solutions containing 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 2,4-dinitrotoluene (2,4-DNT). Samples were collected over 92 d and the concentrations of the spiked explosives compounds and TNT transformation products 2-amino-4,6-dinitrotoluene (2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT) were measured. Our results suggest soil mineralogical and geochemical compositions were not changed during piston-induced fracturing but morphological differences were evident with fractured soils exhibiting more angular surfaces, more fine grained particles, and some microfracturing that is not visible in the pristine samples. TNT, 2,4-DNT, RDX, and HMX exhibited greater analyte loss over time in batch solutions containing fractured soil particles compared to their pristine counterparts. 2ADNT and 4ADNT exhibited greater concentrations in slurries containing pristine soils than in slurries containing fractured soils. Explosives compound transformation is greater in the presence of fractured soil particles than in the presence of pristine soil particles. Our results imply fractured soil particles promote explosive compound transformation and/or explosives compounds have a greater affinity for adsorption to fractured soil particle surfaces.

Soil decontamination of 2,4,6- trinitrotoluene by alfalfa (Medicago sativa)

Present study investigate the toxicity effect of 2,4,6-trinitrotoluene (TNT) on a terrestrial plant, alfalfa (Medicago sativa) in artificial soils. In this study, TNT toxicity assessment was performed on spiked silica with this nitroaromatic compound by determination of the percent of emergence and shoots and roots biomasses at the concentration range of 3.2-10000 mg kg(-1) Dry Weight (DW). The emergence was reduced by 22-32% after 5 days of exposure at TNT concentrations up to 100 mg kg(-1) DW; shoot and root biomasses were reduced by 48-50 and 63-74%, respectively after 30 days exposure at TNT concentrations < or = 32 mg kg(-1) DW. Concentrations higher than 100 mg kg(-1) DW can not be tolerated at all. Concentrations of TNT and its metabolites in silica, root and shoot were measured by High-Performance Liquid Chromatography (HPLC). Analyses of TNT spiked soil extracts reveal hat during alfalfa cultivation for 30 days, TNT was partially transformed at the extent of 15-27%. This transformation decreased at higher TNT soil concentrations. TNT is taken up and metabolized by plants to its downstream derivatives.

Effects of HMX-lead mixtures on reproduction of the earthworm Eisenia andrei

High metal (e.g., Pb) concentrations are typically found in explosive-contaminated soil, and their presence may increase, decrease, or not influence toxicity predicted on the basis of one explosive alone (e.g., HMX). Nevertheless, few data are available in the scientific literature for this type of multiple exposure. Soil organisms, such as earthworms, are one of the first receptors affected by the contamination of soil. Therefore, a reproductive study was conducted using Eisenia andrei in a forest-type soil. Both HMX and Pb decreased reproduction parameters (number of total cocoons, hatched cocoons, and surviving juveniles) individually. Based on the total number of cocoons, HMX was more toxic in a forest soil than Pb, with EC(50) of 31 mg kg(-1), and 1068 mg kg(-1), respectively. The slope of the concentration-response curve was significantly greater in the case of Pb, which is consistent with the possibility that the two compounds do not act on the same target site. The response-addition model was used to predict the response of earthworms and to test for interaction between the two contaminants. The predicted toxicity was not significantly different than the observed toxicity, implying that Pb and HMX were considered noninteractive compounds. The combined action of Pb-HMX may be described, therefore, as dissimilar-noninteractive joint action in a forest soil. The results illustrate the relevance of considering the presence of metals in the risk assessment of explosive-contaminated sites because metals can add their toxicity to explosives. Extension of this study to other types of soil and other metals would improve the understanding of toxicity at these sites.

Pressurized liquid extraction with water as a tool for chemical and toxicological screening of soil samples at army live-fire training ranges

Significant discrepancies in the results of risk assessments based on chemical and toxicity analyses of soils may arise through differences in the efficiency of the extraction or leaching methods used. A rapid technique that may be used in the screening phase of live-fire training ranges and suitable for extracting explosive residues is pressurized liquid extraction (PLE) with water. Therefore, PLE and the commonly used batch leaching method EN-124 57-2 were compared for their utility to extract specific residues from soil samples collected from the Canadian Forces Base (CFB) Petawawa, Ontario. After extraction the cytotoxicity of the samples were assessed in the L-929 growth inhibition assay. The PLE method yielded extracts suitable for direct use in the toxicity assay within 20 min as compared to 24h for the batch leaching method. Analysis of the extracts showed that the PLE water extracts tended to give higher recoveries of explosive residues and the resulting exposure concentrations were confirmed by higher cytotoxicities. Furthermore, gas chromatography-mass spectrometry analyses showed that the samples contained significant amounts of several munition-related stabilizers and plasticizers of toxicological significance in addition to the analysed explosive residues. In conclusion, PLE using water is a promising extraction technique for both chemical and toxicological screening of soil samples from areas that may be contaminated with explosive residues.

Explosives: fate, dynamics, and ecological impact in terrestrial and marine environments

An explosive or energetic compound is a chemical material that, under the influence of thermal or chemical shock, decomposes rapidly with the evolution of large amounts of heat and gas. Numerous compounds and compositions may be classified as energetic compounds; however, secondary explosives, such as TNT, RDX, and HMX pose the largest potential concern to the environment because they are produced and used in defense in the greatest quantities. The environmental fate and potential hazard of energetic compounds in the environment is affected by a number of physical, chemical, and biological processes. Energetic compounds may undergo transformation through biotic or abiotic degradation. Numerous organisms have been isolated with the ability to degrade/transform energetic compounds as a sole carbon source, sole nitrogen source, or through cometabolic processes under aerobic or anaerobic conditions. Abiotic processes that lead to the transformation of energetic compounds include photolysis, hydrolysis, and reduction. The products of these reactions may be further transformed by microorganisms or may bind to soil/sediment surfaces through covalent binding or polymerization and oligomerization reactions. Although considerable research has been performed on the fate and dynamics of energetic compounds in the environment, data are still gathering on the impact of TNT, RDX, and HMX on ecological receptors. There is an urgent need to address this issue and to direct future research on expanding our knowledge on the ecological impact of energetic transformation products. In addition, it is important that energetic research considers the concept of bioavailability, including factors influencing soil/sediment aging, desorption of energetic compounds from varying soil and sediment types, methods for modeling/predicting energetic bioavailability, development of biomarkers of energetic exposure or effect, and the impact of bioavailability on ecological risk assessment.

Toxicity of hexahydro-1,3,5-trinitro-1,3,5-triazine to larval zebrafish (Danio rerio)

Hexahydro-1,3,5-trinitro-1,3,5-triazine, a cyclonitramine commonly known as RDX, is used in the production of military munitions. Contamination of soil, sediment, and ground and surface waters with RDX has been reported in different places around the world. Acute and subacute toxicities of RDX have been relatively well documented in terrestrial vertebrates, but among aquatic vertebrates the information available is limited. The objective of this study was to characterize the acute toxicity of RDX to larval zebrafish. Mortality (LC50) and incidence of vertebral column deformities (EC50) were two of the end points measured in this study. The 96-h LC50 was estimated at 22.98 and 25.64 mgl(-1) in two different tests. The estimated no-observed-effective-concentration (NOEC) values of RDX on lethality were 13.27+/-0.05 and 15.32+/-0.30 mgl(-1); and the lowest-observed-effective-concentration (LOEC) values were 16.52+/-0.05 and 19.09+/-0.23 mgl(-1) in these two tests, respectively. The 96-h EC50 for vertebral deformities on survivors from one of the acute lethality tests was estimated at 20.84 mgl(-1), with NOEC and LOEC of 9.75+/-0.34 and 12.84+/-0.34 mgl(-1), respectively. Behavioral aberrations were also noted in this acute toxicity study, including the occurrence of whirling movement and lethargic behavior. The acute effects of RDX on survival, incidence of deformities, and behavior of larval zebrafish occurred at the high end of the most frequently reported concentrations of RDX in aquatic environments. The chronic effects of RDX in aquatic vertebrates need to be determined for an adequate assessment of the ecological risk of environmental RDX.

Assessment of a 2,4,6-trinitrotoluene-contaminated site using Aporrectodea rosea and Eisenia andrei in mesocosms

Polynitro-organic compounds such as 2,4,6-trinitrotoluene (TNT) can be released into the environment from production and processing facilities and military firing ranges as well as through field use and disposal practices. Based on laboratory toxicity data, TNT has lethal (at >/=260 mg TNT/kg dry soil) and sublethal effects (at >/=59 mg TNT/kg dry soil) to the earthworm. However, field studies are needed to relate exposure of organisms to explosives in mixed-contaminated soil under field conditions and to define effects-based ecotoxicologic benchmarks for TNT-contaminated soil. In the present study, the lethal and sublethal effects of a 10-day in situ exposure at a TNT-contaminated field site using mesh-bag mesocosms were assessed. In addition to the survival end point, the biomarkers of earthworm exposure and effect-including tissue residues, lysosomal neutral red retention time (NRRT), and total immune activity (TIA)-were measured. Concentrations of TNT in soil mesocosms ranged from 25 to 17,063 mg/kg. Experiments indicated a trend toward decreasing survival of caged Aporrectodea rosea and Eisenia andrei as the concentration of TNT and total nitroaromatic compounds increased. E. andrei tolerated higher concentrations of TNT (up to 4050 mg/kg dry soil) in mesocosms than did indigenous earthworms, who survived only at </=1146 mg TNT/kg. Earthworms E. andrei and A. rose survived in 67% and 75% of TNT-contaminated mesocosms, respectively, compared with references groups. NRRT was significantly decreased in surviving earthworms from the contaminated areas compared with those from the reference site. TIA was not affected by field exposure to TNT. Earthworm tissue concentrations of TNT metabolites 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene were not correlated with TNT soil concentrations. In addition, higher tissue concentrations of TNT metabolites were observed at concentrations ranging from 116 to 130 mg TNT/kg soil. The results showed that earthworm exposure in TNT-contaminated soil produced both lethal and sublethal effects in the field. The results of study indicated that mesocosm experiments would be useful to assess the toxicity of a site and to characterize the overall effects of contaminants. However, mesocosm experiments present special considerations (e.g., abiotic factors, exposure period) when used at heterogenous sites, and data must be interpreted with caution.

Metabolism and mineralization of hexahydro-1,3,5-trinitro-1,3,5-triazine inside poplar tissues (Populus deltoides x nigra DN-34)

Poplar tissue cultures and leaf crude extracts (Populus deltoides x nigra DN-34) were exposed to [U-14C]hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and incubated under light and in the dark. Poplar tissue cultures were able to partially reduce RDX to hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), regardless of the presence or absence of light. However, further transformation of RDX, MNX, and DNX required exposure to light and resulted in the formation of formaldehyde (CH2O), methanol (CH3OH), and carbon dioxide (CO2). Similarly, transformation of RDX by poplar leaf crude extracts required exposure to light. Neither reduction of RDX to MNX and DNX nor mineralization into CO2 were recorded in crude extracts, even when exposed to light, suggesting that both processes were light-independent and required intact plant cells. Control experiments without plant material showed that RDX was partially transformed abiotically, by the sole action of light, but to a lesser extent than in the presence of plant crude extracts, suggesting the intervention of plant subcellular structures through a light-mediated mechanism. Poplar tissue cultures were also shown to mineralize 14CH2O and 14CH3OH, regardless of the presence or absence of light. These results suggest that transformation of [U-14C]RDX by plant tissue cultures may occur through a three-step process, involving (i) a light-independent reduction of RDX to MNX and DNX by intact plant cells; (ii) a plant/light-mediated breakdown of the heterocyclic ring of RDX, MNX, or DNX into C1-labeled metabolites (CH2O and CH3OH); and (iii) a further light-independent mineralization of C1-labeled metabolites by intact plant cells. This is the first time that a significant mineralization of RDX into CO2 by light-exposed plant tissue cultures is reported.

Toxicity assessment of contaminated soils from an antitank firing range

Explosives are released into the environment at production and processing facilities, as well as through field use. These compounds may be toxic at relatively low concentrations to a number of ecological receptors. A toxicity assessment was carried out on soils from an explosive-contaminated site at a Canadian Forces Area Training Center. Toxicity studies on soil organisms using endpoints such as microbial processes (potential nitrification activity, dehydrogenase activity, substrate-induced respiration, basal respiration), plant seedling and growth (Lactuca sativa and Hordeum vulgare), and earthworm (Eisenia andrei) growth and reproduction were carried out. Results showed that 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) was the principal polynitro-organic compound measured in soils. Soils from the contaminated site decreased microbial processes and earthworm reproduction; whereas plant growth was not significantly reduced. Toxicity to aquatic organisms and genotoxicity were also assessed on soil elutriates using Microtox (Vibrio fischeri), growth inhibition of algae (Selenastrum capricornutum), and SOS Chromotest (Escherichia coli). Results indicated that soil elutriates were generally not toxic to bacteria (Microtox) and algae. However, genotoxicity was found in a number of soil elutriate samples. Thus, the explosive-contaminated soils from the antitank firing range may represent a hazard for the soil organisms. Nevertheless, the global toxicity might have partially resulted from HMX as well as from other (not identified) contaminants such as heavy metals.

Biodegradation of nitro-substituted explosives 2,4,6-trinitrotoluene, hexahydro-1,3,5-trinitro-1,3,5-triazine, and octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine by a phytosymbiotic Methylobacterium sp. associated with poplar tissues (Populus deltoides x nigra DN34)

A pink-pigmented symbiotic bacterium was isolated from hybrid poplar tissues (Populus deltoides x nigra DN34). The bacterium was identified by 16S and 16S-23S intergenic spacer ribosomal DNA analysis as a Methylobacterium sp. (strain BJ001). The isolated bacterium was able to use methanol as the sole source of carbon and energy, which is a specific attribute of the genus Methylobacterium. The bacterium in pure culture was shown to degrade the toxic explosives 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazene (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine (HMX). [U-ring-(14)C]TNT (25 mg liter(-1)) was fully transformed in less than 10 days. Metabolites included the reduction derivatives amino-dinitrotoluenes and diamino-nitrotoluenes. No significant release of (14)CO(2) was recorded from [(14)C]TNT. In addition, the isolated methylotroph was shown to transform [U-(14)C]RDX (20 mg liter(-1)) and [U-(14)C]HMX (2.5 mg liter(-1)) in less than 40 days. After 55 days of incubation, 58.0% of initial [(14)C]RDX and 61.4% of initial [(14)C]HMX were mineralized into (14)CO(2). The radioactivity remaining in solution accounted for 12.8 and 12.7% of initial [(14)C]RDX and [(14)C]HMX, respectively. Metabolites detected from RDX transformation included a mononitroso RDX derivative and a polar compound tentatively identified as methylenedinitramine. Since members of the genus Methylobacterium are distributed in a wide diversity of natural environments and are very often associated with plants, Methylobacterium sp. strain BJ001 may be involved in natural attenuation or in situ biodegradation (including phytoremediation) of explosive-contaminated sites.

Lethal and subchronic effects of 2,4,6-trinitrotoluene (TNT) on Enchytraeus albidus in spiked artificial soil

The effects of 2,4,6-trinitrotoluene (TNT) exposure in spiked artificial soil on the survival and reproduction rate of the white potworm Enchytraeus albidus were studied. Based on the initial concentrations, TNT in freshly spiked soil decreased enchytraeid survival (21-day LC(50)=422+/-63 (SD)mg/kg, N=3) and fecundity (42-day EC(50)=111+/-34, N=4). Data also indicated that TNT was 5-10 times more lethal to juveniles than adults, and lethality was less pronounced in TNT-spiked soils aged for 21 days. A time-dependent decrease in the TNT concentrations, as well as a concomitant increase in the levels of 2- and 4-aminodinitrotoluene, was observed during the 42-day toxicity test. Taken together, TNT (or one of its metabolites) is more lethal to juvenile than adult enchytraeids. This effect may explain, at least in part, the ability of TNT to decrease fecundity as determined using the enchytraeid mortality-reproduction test.

Screening for soil toxicity and mutagenicity using luminescent bacteria--a case study of the explosive 2,4,6-trinitrotoluene (TNT)

The presented study explored the suitability of aquatic bioassays based on the marine luminescent bacterium Vibrio fischeri as screening indicators for soil toxicity and mutagenicity. The study consists of two parts: (i) determination of the bacterial toxicity and mutagenicity of the single substance 2,4,6-trinitrotoluene (TNT) and its primary reduced metabolites using three different luminescent bacteria assays and (ii) determination of the water-extractable toxicity and mutagenicity of soil samples taken at a former production plant for TNT showing complex contamination (TNT, metabolites of TNT, PAHs, and heavy metals). Resulting data indicate TNT to be predominantly responsible for the observed biological effects of soil leachates. A strategy for soil toxicity screening based on luminescent bacteria is proposed which may especially be applicable for the case of bioremediation of TNT-contaminated soils. Potentials and restrictions of this approach to soil toxicity assessment are discussed.

Effect of dust on the viability of Vibrio fischeri in the Microtox Test

The standard Microtox test involving the bioluminescent bacterium Vibrio fischeri is a frequently used ecotoxicological bioassay whose EC50, values have been correlated to acute toxicity parameters of vertebrates, to irritancy measures, and to cytotoxicity indices. The aims were to explore the dependence of light output on viable cell number, with the latter estimated with the naked eye using a colorimetric tetrazolium salt method, the effects of dust on the bioluminescence and cell viability, how the viability of the cells is affected after spills, and how spills can be sampled. The lower limit of the linear dynamic range of the light-emitting bacterium was first defined to be 3.7 x 10(7) cells/ mL, compared with 37 x 10(7) cells/mL in the Microtox assay. The effects of dust were then explored in the working range by the method of standard additions by adding 5-, 10-, and 20-mg amounts of Standard Reference Material Urban Dust 1649a. This simulated dust samples collected by a cordless vacuum technique involving a filter cassette. A mass of 20 mg dust totally inhibited the Microtox test at all times (5, 15, and 30 min). Masses of 5 and 10 mg dust lowered the luminescence significantly by 20 and 64%, respectively, after 30 min. However, the viability test was totally inhibited by 5 mg of dust. A spectrophotometric modification of the viability test using a wavelength of 508 nm was developed that was twice as sensitive as the naked eye test, and was as sensitive as the Microtox test. Mechanical shock involved with spilling and sampling bacterial reagent on hard surfaces killed the luminescent bacteria as shown by inhibition of luminescence. The optimum filter cassette for Microtox reagent collection was a 25-mm 1.00-microm PTFE filter in a 25-mm Delrin holder operated at 4.0 L/min, with a Tygon sampling probe.

Transformation of 2,4,6-trinitrotoluene (TNT) by immobilized Phanerochaete chrysosporium under fed-batch and continuous TNT feeding conditions

The cometabolic transformation of 2,4,6-trinitrotoluene (TNT) by an immobilized Phanerochaete chrysosporium culture was investigated under different TNT and/or glycerol feeding conditions in a 5-L reactor. In the fed-batch feeding mode, as a result of four spiking events at an average feeding rate of 20 mg TNT L(-1) d(-1) and 250 mg glycerol L(-1) d(-1), the initial TNT transformation rate and the glycerol uptake rate of the 7-day-old immobilized cell culture were 2.41 mg L(-1) h(-1) and 16.6 mg L(-1) h(-1), respectively. Thereafter, the TNT fed into the reactor depicted a negative effect on the cell physiology of P. chrysosporium, i.e., both rates decreased constantly. At 32 mg TNT L(-1) d(-1) feeding rate, also in the presence of glycerol (200 mg L(-1) d(-1)), this effect on the fungal cell metabolism was even more significant. When TNT was fed alone at 3.7 mg L(-1) d(-1), it showed an initial 0.75 mg L(-1) h(-1) rate of TNT transformation, i.e., one-third the initial level observed in the presence of glycerol. In contrast, in the continuous feeding mode (dilution rate, D = 0.11 d(-1)), at 5.5 mg TNT L(-1) d(-1) and 220 mg glycerol L(-1) d(-1), the immobilized cell culture exhibited a constant TNT transformation rate for cultivation periods of 50 and 61 days, under uncontrolled and controlled pH conditions, respectively. Thereafter, during the latter experiment, 100% TNT biotransformation was achieved at 1,100 mg L(-1) d(-1) glycerol feeding rate. Immobilized cells (115-day-old), sampled from a continuous TNT feeding experiment, mineralized [(14)C]-TNT to a level of 15.3% following a 41-day incubation period in a microcosm.

Tween 80 enhanced TNT mineralization by Phanerochaete chrysosporium

The effect of a nonionic surfactant (Tween 80) on 2,4,6-trinitrotoluene (TNT) mineralization by the white-rot fungus Phanerochaete chrysosporium strain BKM-F-1767, was investigated in a liquid culture at 20, 50, and 100 mg TNT.L-1. The presence of 1% (w/v) Tween 80, at 20 mg.L-1 TNT, added to a 4-d-old culture, allowed the highest TNT mineralization level, that is 29.3% after 24 d, which is two times more than the control culture, without Tween 80 (13.9%). The mineralization of TNT resumed upon additional Tween 80 supplementation, consequently, 39.0% of the TNT was respired on day 68. Orbital agitation of the fungal culture was found detrimental to TNT mineralization, with or without Tween 80 in the culture medium. The surfactant also stimulated the growth of P. chrysosporium without any notable effect on either the glycerol consumption rate or the extracellular LiP and MnP activity levels. Respirometric assays highlighted some differences between the oxygen uptake rate of the fungal culture supplemented with or without Tween 80.

Acute toxicity of 2,4,6-trinitrotoluene in earthworm (Eisenia andrei)

2,4,6-Trinitrotoluene (TNT) is an worldwide recalcitrant environmental contaminant and is toxic to a number of organisms including humans. This study examines the acute effects (lethal and biomass changes) of TNT on the oligochaetes species Eisenia andrei, using the 3-day filter paper, and the 7- and 14-day direct contact spiked soil (OECD artificial and forest soil) toxicity tests. Studies using the filter paper test indicated that the lethality of TNT could be detected in the range 1.5 to 14.2 microg/cm(2), with significant biomass (body weight) changes occurring at the lowest concentration. Acute effects (lethality) could not be measured when earthworms were placed on filter paper containing a saturated aqueous solution of TNT. This may indicate that with these exposure conditions, TNT may have been adsorbed to the filter paper, and that this matrix should be saturated with TNT before becoming available to the earthworms. Spiked soil toxicity tests indicated that the E. andrei lethality by TNT was >1.5 times higher when earthworms were exposed to TNT-spiked forest soil (LOEC:260 mg/kg; LC(50) 14 days 222.4 mg/kg) than to spiked OECD artificial soil (LOEC:420 mg/kg; LC(50) 14 days: 364.9 mg/kg). The sublethal effect on biomass change at the selected TNT concentrations in soil was not significant compared to controls. Results indicate that the bioanalytical methods described in this article could be used as TNT toxicity assessment tools. This soil quality test method gives valuable information for the screening of soil toxicity.