Preparation of deuterium-labeled biotransformation products of 2,4,6-trinitrotoluene.

Methods for the preparation of deuterium-labeled analogs to six prominent biotransformation products of the explosive 2,4,6-trinitrotoluene were developed. These are useful as reference standards for stable isotope dilution techniques and for solid state (2)H NMR spectroscopic studies. Although syntheses for most of the target compounds in protiated form had been reported in the past, most of those were found to be poorly suited for the preparation of the deuterated materials. Selective reduction of [(2)H5]trinitrotoluene furnished [(2)H5]-4,6-dinitro-2-hydroxylaminotoluene, [(2)H5]-2,6-dinitro-4-hydroxylaminotoluene, [(2)H5]-2-amino-4,6-dinitrotoluene, and [(2)H5]-4-amino-2,6-dinitrotoluene. The syntheses of [(2)H10]-2,2'-azo-4,4',6,6'-tetranitrotoluene and [(2)H10]-4,4'-azo-2,2',6,6'-tetranitrotoluene were accomplished by selective oxidation of [(2)H5]-2-amino-4,6-dinitrotoluene and [(2)H5]-4-amino-2,6-dinitrotoluene, respectively.

Acute toxicity evaluation of explosive wastewater by bacterial bioluminescence assays using a freshwater luminescent bacterium, Vibrio qinghaiensis sp. Nov.

The compositions of explosive wastewater generated from TNT (2,4,6-trinitrotoluene) purification stage were characterized by using UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), high performance liquid chromatograph (HPLC) and gas chromatograph/mass spectroscopy (GC/MS). The acute toxicity was evaluated by bacterium bioluminescence assay using a freshwater luminescent bacterium (Vibrio qinghaiensis sp. Nov.) and a marine luminescent bacterium (Photobacterium phosphoreum). The results showed that the wastewater's biodegradability was poor due to the high amount of chemical oxygen demand (COD). The main organic components were dinitrotoluene sulfonates (DNTS) with small amount of TNT, dinitrotoluene (DNT), mononitrotoluene (MNT) and other derivatives of nitrobenzene. It was highly toxic to luminescent bacteria P. phosphoreum and V. qinghaiensis sp. Nov. After reaction time of 15 min, the relative concentration of toxic pollutants (expressed as reciprocal of dilution ratio of wastewater) at 50% of luminescence inhibition ratio was 5.32×10(-4) for P. phosphoreu, while that was 4.34×10(-4) for V. qinghaiensis. V. qinghaiensis is more sensitive and suitable for evaluating the wastewater's acute toxicity than P. phosphoreum. After adsorption by resin, the acute toxicity can be greatly reduced, which is helpful for further treatment by biological methods.

Reproductive toxicity of nitroaromatics to the cricket, Acheta domesticus.

The effect of TNT (2,4,6-trinitrotoluene) and its metabolites, 2,4-dinitrotoluene (2,4-DNT), 2-amino-4,6-dinitrotoluene (2A-DNT), and 4-amino-2,6-dinitrotoluene (4A-DNT) on cricket (Acheta domesticus) reproduction was evaluated. We previously used crickets to assess the toxicity of a nitramine explosive (RDX) and its metabolites. It is common to find that while much information on the environmental impact of the parent compound is available in the literature, such is often not the case for the degradation metabolites of the parent compound. In some instances, these metabolites are as toxic (or more so) as the parent compound and we hypothesized that this might be the case for TNT. The presence of TNT and its metabolites in sand (10 microg/g) did not adversely affect cricket egg production, but adversely affected hatching of cricket eggs as compared to controls. However, there were no differences in hatching success among TNT and metabolite treatment groups. Hatching success of cricket eggs in soil or following topical exposure decreased as concentrations of TNT and its metabolites increased. The relative toxicity of TNT and its metabolites in soil generally followed the trend of TNT<2A-DNT<4A-DNT<2,4-DNT. In addition, toxicity appeared to be higher in sand than in sandy loam soil or in the topical exposure test. After 45 days of exposure in sandy loam soil, the EC(20) (20% effect concentration), EC(50) (50% effect concentration), and EC(95) (95% effect concentration) were 14, 116, and 10,837 microg/g for TNT: 1.7, 32, and 16,711 microg/g for 2A-DNT: 1.9, 9, and 296 microg/g for 4A-DNT: and 0.4, 5.7, and 1437 microg/g for 2,4-DNT. Overall, results suggest that parent TNT and metabolites are toxic to cricket eggs at relatively high concentrations and these toxic effects are manifested as a decrease in hatching success.

Polymer-oligopeptide composite coating for selective detection of explosives in water.

The selective detection of a specific target molecule in a complex environment containing potential contaminants presents a significant challenge in chemical sensor development. Utilizing phage display techniques against trinitrotoluene (TNT) and dinitrotoluene (DNT) targets, peptide receptors have previously been identified with selective binding capabilities for these molecules. For practical applications, these receptors must be immobilized onto the surface of sensor platforms at high density while maintaining their ability to bind target molecules. In this paper, a polymeric matrix composed of poly(ethylene-co-glycidyl methacrylate) (PEGM) has been prepared. A high density of receptors was covalently linked through reaction of amino groups present in the receptor with epoxy groups present in the co-polymer. Using X-ray photoelectron spectroscopy (XPS) and gas-chromatography/mass spectroscopy (GC/MS), this attachment strategy is demonstrated to lead to stably bound receptors, which maintain their selective binding ability for TNT. The TNT receptor/PEGM conjugates retained 10-fold higher TNT binding ability in liquid compared to the lone PEGM surface and 3-fold higher TNT binding compared to non-specific receptor conjugates. In contrast, non-target DNT exposure yielded undetectable levels of binding. These results indicate that this polymeric construct is an effective means of facilitating selective target interaction both in an aqueous environment. Finally, real-time detection experiments were performed using a quartz crystal microbalance (QCM) as the sensing platform. Selective detection of TNT vs DNT was demonstrated using QCM crystals coated with PEGM/TNT receptor, highlighting that this receptor coating can be incorporated as a sensing element in a standard detection device for practical applications.

Structure and reactivity of TNT and related species: application of spectroscopic approaches and quantum-chemical approximations toward understanding transformation mechanisms.

This paper presents our latest findings regarding the structure and reactivity of the nitroaromatics, TNT and selected derivatives, within their environmental context. We also demonstrate the useful and proactive role of combined computational chemistry and spectroscopy tools in studying competing transformation mechanisms, particularly those with toxic potential. TNT and selected derivatives were reacted via alkaline hydrolysis as well as via free radical initiators through monochromatic irradiation and through Fenton reactions in complex competing transformation mechanisms. Only alkaline hydrolysis produced consistent and effective transformation intermediate and final products in this research. However, irradiation of the product generated by alkaline hydrolysis at 450 nm (wavelength of maximum absorption) caused complete disappearance of the spectra.

TNT biodegradation and production of dihydroxylamino-nitrotoluene by aerobic TNT degrader Pseudomonas sp. strain TM15 in an anoxic environment.

Anaerobic bacteria have been used to produce 2,4-dihydroxylamino-nitrotoluene (2,4DHANT), a reductive metabolite of 2,4,6-trinitrotoluene (TNT). Here, an aerobic TNT biodegrader Pseudomonas sp. strain TM15 produced 2,4DHANT as evidenced by the molecular ion with m/z of 199 identified from LC-TOFMS analyses. TNT biodegradation with a high cell concentration (10(9) cells/ml) led to a significant accumulation of 2,4DHANT in the culture medium, as well as hydroxylamino-dinitrotoluenes (HADNTs), although these products were not accumulated when a low cell concentration was used; also, the accumulation of diamino-nitrotoluene and of an unidentified metabolite were observed in the culture medium with the high cell concentration (10(10) cells/ml). 2,4DHANT overproduction was a function of the aeration speed since cultures with low aeration speeds (30 rpm) had a 19-fold higher DHANT productivity than those aerated with high speeds (180 rpm); this indicates that molecular oxygen was related to the formation of 2,4DHANT. The quantification of dissolved oxygen (DO) in the media demonstrated that the productivity of 2,4DHANT was increased at low DO values. Moreover, supplying oxygen to the culture media produced a remarkable decrease of 2,4DHANT accumulation; these results clearly indicate that high 2,4DHANT production was a consequence of the oxygen deficit in the culture medium. This finding is useful for understanding the TNT biodegradation (bioremediation technology) in an anoxic environment.

Determination of TNT and its metabolites in water samples by voltammetric techniques.

Square-wave voltammetry with the hanging drop mercury electrode as the working electrode was used for the determination of ultratraces of explosives in aqueous solution. It was shown that the strong pressure dependence of the pneumatically controlled multimode electrode system of a conventional Metrohm apparatus could be compensated by an additional pressure regulation, through which the pressure variations could be decreased when switching from deaeration to the static measurements. By using square-wave voltammetry with this electrode system after this modification the limits of detection for 2,4,6-trinitrotoluene (TNT) and other TNT-metabolites could be decreased down to 0.2 microg L(-1) when using a measurement time of 6 min. Also a simultaneous determination of TNT and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was shown to be possible over a wide linear range and the detection limits then were 2.2 microg L(-1) for TNT and 25 microg L(-1) for RDX. By applying the highly stable and adjustable pressure as mentioned before, the calibrations could be kept stable over a period of up to 1 week.

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.

A hybrid quantum dot-antibody fragment fluorescence resonance energy transfer-based TNT sensor.

We demonstrate the use of luminescent QDs conjugated to antibody fragments to develop solution-phase nanoscale sensing assemblies, based on fluorescence resonance energy transfer (FRET) for the specific detection of the explosive 2,4,6-trinitrotoluene (TNT) in aqueous environments. The hybrid sensor consists of anti-TNT specific antibody fragments attached to a hydrophilic QD via metal-affinity coordination. A dye-labeled TNT analogue prebound in the antibody binding site quenches the QD photoluminescence via proximity-induced FRET. Analysis of the data collected at increasing dye-labeled analogue to QD ratios provided an insight into understanding how the antibody fragments self-assemble on the QD. Addition of soluble TNT displaces the dye-labeled analogue, eliminating FRET and resulting in a concentration-dependent recovery of QD photoluminescence. Sensor performance and specificity were evaluated.

Homogeneous immunoassay for detection of TNT and its analogues on a microfabricated capillary electrophoresis chip.

A homogeneous immunoassay for TNT and its analogues is developed using a microfabricated capillary electrophoresis chip. The assay is based on the rapid electrophoretic separation of an equilibrated mixture of an anti-TNT antibody, fluorescein-labeled TNT, and unlabeled TNT or its analogue. The band intensities of the free fluorescein-labeled TNT and of the antibody-antigen complex reveal the relative equilibrated concentrations. Titration of the anti-TNT antibody with a fluorescein-labeled TNT derivative yields a binding constant of (3.9 +/- 1.3) x 10(9) M(-1). The dissociation rate constant of the complex is determined by kinetic capillary electrophoresis using a folded channel and a rotary scanner to interrogate the separation at multiple time points. The dissociation rate constant is found to be 0.035 +/- 0.005 s(-1), and the resulting binding rate constant is (1.4 +/- 0.7) x 10(7) M(-1) s(-1). Binding constants of TNT and five of its analogues are determined by competitive assays: TNT (4.3 +/- 2.6) x 10(8) M(-1); 1,3,5-trinitrobenzene (5.1 +/- 3.3) x 10(7) M(-1); picric acid (7.5 +/- 4.4) x 10(6) M(-1); 2,4-dinitrotoluene (7.9 +/- 4.0) x 10(6) M(-1); 1,3-dinitrobenzene (1.0 +/- 0.7) x 10(6) M(-1); and 2,4-dinitrophenol (5.1 +/- 3.0) x 10(4) M(-1). TNT and its analogues can be assayed with high sensitivity (LOD 1 ng/mL) and with a wide dynamic range (1-300 ng/mL) using this chip-based method.

2,4,6-trinitrotoluene-induced reproductive toxicity via oxidative DNA damage by its metabolite.

Several epidemiological studies and animal experiments showed that 2,4,6-trinitrotoluene (TNT), a commonly used explosive, induced reproductive toxicity. To clarify whether the toxicity results from the interference of endocrine systems or direct damage to reproductive organs, we examined the effects of TNT on the male reproductive system in Fischer 344 rats. TNT administration induced germ cell degeneration, the disappearance of spermatozoa in seminiferous tubules, and a dramatic decrease in the sperm number in both the testis and epididymis. TNT increased the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in sperm whereas plasma testosterone levels did not decrease. These results suggest that TNT-induced toxicity is derived from direct damage to spermatozoa rather than testosterone-dependent mechanisms. To determine the mechanism of 8-oxodG formation in vivo, we examined DNA damage induced by TNT and its metabolic products in vitro. 4-Hydroxylamino-2,6-dinitrotoluene, a TNT metabolite, induced Cu(II)-mediated damage to 32P-labeled DNA fragments and increased 8-oxodG formation in calf thymus DNA, although TNT itself did not. DNA damage was enhanced by NADH, suggesting that NADH-mediated redox reactions involving TNT metabolites enhanced toxicity. Catalase and bathocuproine inhibited DNA damage, indicating the involvement of H2O2 and Cu(I). These findings suggest that TNT induces reproductive toxicity through oxidative DNA damage mediated by its metabolite. We propose that oxidative DNA damage in the testis plays a role in reproductive toxicity induced by TNT and other nitroaromatic compounds.

Biological remediation of explosives and related nitroaromatic compounds.

Nitroaromatics form an important group of recalcitrant xenobiotics. Only few aromatic compounds, bearing one nitro group as a substituent of the aromatic ring, are produced as secondary metabolites by microorganisms. The majority of nitroaromatic compounds in the biosphere are industrial chemicals such as explosives, dyes, polyurethane foams, herbicides, insecticides and solvents. These compounds are generally recalcitrant to biological treatment and remain in the biosphere, where they constitute a source of pollution due to both toxic and mutagenic effects on humans, fish, algae and microorganisms. However, relatively few microorganisms have been described as being able to use nitroaromatic compounds as nitrogen and/or carbon and energy source. The best-known nitroaromatic compound is the explosive TNT (2,4,6-trinitrotoluene). This article reviews the bioremediation strategies for TNT-contaminated soil and water. It comes to the following conclusion: The optimal remediation strategy for nitroaromatic compounds depends on many site-specific factors. Composting and the use of reactor systems lend themselves to treating soils contaminated with high levels of explosives (e.g. at former ammunition production facilities, where areas with a high contamination level are common). Compared to composting systems, bioreactors have the major advantage of a short treatment time, but the disadvantage of being more labour intensive and more expensive. Studies indicate that biological treatment systems, which are based on the activity of the fungus Phanerochaete chrysosporium or on Pseudomonas sp. ST53, might be used as effective methods for the remediation of highly contaminated soil and water. Phytoremediation, although not widely used now, has the potential to become an important strategy for the remediation of soil and water contaminated with explosives. It is best suited where contaminant levels are low (e.g. at military sites where pollution is rather diffuse) and where larger contaminated surfaces or volumes have to be treated. In addition, phytoremediation can be used as a polishing method after other remediation treatments, such as composting or bioslurry, have taken place. This in-situ treatment method has the advantage of lower treatment costs, but has the disadvantage of a considerable longer treatment time. In order to improve the cost-efficiency, phytoremediation of nitroaromatics (and other organic xenobiotics) could be combined with bio-energy production. This requires, however, detailed knowledge on the fate of the contaminants in the plants as well as the development of efficient treatment methods for the contaminated biomass that minimise the spreading of the contaminants into the environment during post harvest treatment.

Mutation analyses of a series of TNT-related compounds using the CHO-hprt assay.

Trinitrotoluene (TNT) and related compounds were tested for induction of mutation in the CHO-hprt mutation assay. The parent compound, TNT, was consistently found to be mutagenic at concentrations above 40 microg ml(-1), whether or not S9 activating enzymes were added. Five TNT metabolites gave statistically significant but small increases in mutation frequency over solvent controls: 4-amino-2,6 dinitrotoluene, 2,4',6,6'-tetranitro-2',4-azoxytoluene, 2,2',6,6'-tetranitro-4,4'-azoxytoluene, 2',4,6,6'-tetranitro-2,4'-azoxytoluene and triaminotoluene. Clear dose-response relationships could not be established for the mutagenic response of these compounds. They are considered as very weak mutagens in this mammalian test system. Five compounds did not produce statistically significant mutation frequencies at the levels tested: 2-amino-4,6-dinitrotoluene, 2,4-diamino-6-nitrotoluene, 1,3,5-trinitrobenzene, 2,6-diamino-4-nitrotoluene and 4,4',6,6'-tetranitro-2,2'-azoxytoluene. The results indicate that none of the TNT metabolites tested pose a significant mutational health risk, at least as judged by the CHO-hprt assay.

Recent developments in formulating model descriptors for subsurface transformation and sorption of trinitrotoluene.

Recent published data show that transformation and sorption are key processes involved in the subsurface transport of TNT. The state-of-the-art understanding of TNT soil transformation and sorption phenomena is summarized below: There is unequivocal evidence of reductive transformation of TNT in soils. However, soil properties affecting TNT transformation are only partially understood. Edaphic factors such as redox are probably important since highest reductive transformation rates occur under anaerobic conditions. TNT transformation products include 2A-DNT, 4A-DNT, 2,4-DANT, and 2,6-DANT. Azoxytoluenes have also been reported. Triaminotoluene may be an important TNT transformation product, but this product has not been routinely measured. TNT soil sorption is rapid and can be modeled as equilibrium controlled. Poor mass balances are difficult to interpret owing to lack of information on transformation products. Various irreversible disappearance mechanisms other than transformation to elutable transformation products are possible.

Capillary electrophoretic separation of TNT and its transformation products.

2,4,6-Trinitrotoluene (TNT), 2-aminodinitrotoluene (2ADNT), 4-aminodinitrotoluene (4ADNT), and diamino-6-nitrotoluene (DA6NT) in a variety of matrices (including chemical, microbial, and plant extract) were successfully separated and quantified using micellar electrokinetic capillary electrophoresis (MEKC). The method used a buffer solution of 20 mM in borax, 50 mM in sodium dodecyl sulfate (SDS), and of pH 8.5. Voltage applied across the capillary was 20 kV and temperature was maintained at 25 degrees C. Compounds eluted within approximately 6-11 min and were identified by both their migration times and spectra.

Phototoxicology. 1. Light-enhanced toxicity of TNT and some related compounds to Daphnia magna and Lytechinus variagatus embryos.

Many environmental pollutants interact with solar near-ultraviolet (nuv) light in a manner which greatly increases their toxic effects. The phenomenon of light-mediated toxicity (phototoxicity) is only now becoming generally recognized to any significant degree. Manufacture of, and loading munitions with, the explosive 2,4,6-trinitrotoluene (TNT) in past decades caused contamination of soils and sediments at levels exceeding 1000 ppm and of waters at levels near saturation (100 ppm). Manufacture of TNT produces numerous nitrated by-products, and most of these compounds, including TNT, can be metabolized by many species, including bacteria, fungi, plants, and mammals. This study investigated the phototoxicity of TNT, and 2,3-, 2,4-, 2,6-, and 3,4-dinitrotoluene (DNT) and -diaminotoluene (DAT), and the major metabolites 2-amino-4,6-dinitrotoluene (2A) and 4-amino-2,6-dinitrotoluene (4A), to Daphnia magna (acute toxicity) and Lytechinus variagatus (sea urchin) embryos (subacute, developmental toxicity). Most of the compounds were weakly toxic or nontoxic in the dark. All were phototoxic to sea urchins. In D. magna, 2,3- and 3,4-DNT/DAT and 4A were not toxic but were phototoxic, and 2A was toxic and phototoxic; the other isomers were not toxic or phototoxic to this species.

Toxicity and mutagenicity of 2,4,-6-trinitrotoluene and its microbial metabolites.

TNT (2,4,6-trinitrotoluene) of explosive grade is highly toxic to marine forms that included fresh water unicellular green algae (Selenastrum capricornutum), tidepool copepods (Tigriopus californicus), and oyster larvae (Crassostrea gigas), and mutagenic to Salmonella typhimurium. On the basis of mutagenic assays carried out with a set of histidine-requiring strains of the bacterium, TNT was detected as a frameshift mutagen that significantly accelerates the reversion rate of a frameshift tester, TA-98. In contrast, the major microbial metabolites of TNT appeared to be nontoxic and nonmutagenic.

Determination of the concentration of explosives in air by isotope dilution analysis.

The concentrations in air of dinitrotoluene (DNT), trinitrotoluene (TNT), nitroglycerin (NG), ethylene glycol dinitrate (EGDN), and pentaerythritol tetranitrate (PETN) were measured at 25 degrees C under equilibrium conditions, and that of cyclomethylene trinitramine (RDX) was measured at elevated temperature by means of an isotope dilution technique. Isotopically multi-labeled compounds were synthesized and used as diluents. Field ionization mass spectrometry was used to measure the abundance ratios of the unlabeled materials. The concentrations in air at 25 degrees C of DNT, TNT, NG, EDGN, PETN, and RDX are 184, 4, 31, 37,000, 7, and 0.8 ppb v/v, respectively. The data obtained may be used for the assessment of the required sensitivity of air-monitoring detection systems.