Transcriptional activation of stress genes and cytotoxicity in human liver carcinoma cells (HepG2) exposed to 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, and 2,6-dinitrotoluene

Ethyltoluenes Regulate Inflammatory and Cell Fibrosis Signaling in the Liver Cell Model

Crude oil naphtha fraction C9 alkylbenzenes consist of trimethylbenzenes, ethyltoluenes, cumene, and n-propylbenzene. The major fraction of C9 alkylbenzenes is ethyltoluenes (ETs) consisting of three isomers: 2-ethyltoluene (2-ET), 3-ethyltoluene (3-ET), and 4-ethyltoluene (4-ET). Occupational and environmental exposure to ETs can occur via inhalation and ingestion and cause several health problems. Exposure to ETs causes eye and upper respiratory tract irritation, coughing, gagging, vomiting, griping, diarrhea, distress, and depressed respiration. Previous studies suggest that ETs target the respiratory tract and liver and produce several lesions in the nose, lungs, and liver areas. In the current study, we investigated the impact of low concentrations of ETs on cell metabolism, cell inflammation, steatosis, and fibrosis signaling in liver cell models in vitro. Dose-dependent exposure of 2-ET, 3-ET, and 4-ET to HepaRG and hepatocellular carcinoma (HCC) HepG2 and SK-Hep1 cells affects cell survival/real-time proliferation and increases ROS production. ETs induce inflammatory CAT, SOD1, CXCL8, IL1B, HMOX1, NAT1 (3), and STAT3 gene expression. Exposure of 2-ET, 3-ET, and 4-ET to HepaRG and HCC HepG2 and SK-Hep1 cells affects mitochondrial respiration/cellular energetics and upregulates metabolic CYP1-A1, CYP1-A2, CYP2-D6, CYP2-E1, CYP3-A4, CYP3-B4, and VEGFA gene expression. However, no significant change in lipogenesis-related gene expression and modulation of cell steatosis was observed after ET exposure. Acute exposure to induvial ETs and in combination or chronic 2-ET exposure alone modulates cell fibrosis markers such as AST, FGF-23, Cyt-7 p21, TGFβ, TIMP2, and MMP2 in liver cell models, suggesting that ETs target liver cells and may dysregulate liver function.

Metabolic activation of 2,4,6-trinitrotoluene; a case for ROS-induced cell damage

The explosive compound 2,4,6-trinitrotoluene (TNT) is well known as a major component of munitions. In addition to its potential carcinogenicity and mutagenicity in humans, recent reports have highlighted TNT toxicities in diverse organisms due to its occurrence in the environment. These toxic effects have been linked to the intracellular metabolism of TNT, which is generally characterised by redox cycling and the generation of noxious reactive molecules. The reactive intermediates formed, such as nitroso and hydroxylamine compounds, also interact with oxygen molecules and cellular components to cause macromolecular damage and oxidative stress. The current review aims to highlight the crucial role of TNT metabolism in mediating TNT toxicity, via increased generation of reactive oxygen species. Cellular proliferation of reactive species results in depletion of cellular antioxidant enzymes, DNA and protein adduct formation, and oxidative stress. While TNT toxicity is well known, its ability to induce oxidative stress, resulting from its reductive activation, suggests that some of its toxic effects may be caused by its reactive metabolites. Hence, further research on TNT metabolism is imperative to elucidate TNT-induced toxicities.

Evaluation of a sequential anaerobic-aerobic membrane bioreactor system for treatment of traditional and insensitive munitions constituents

New energetic formulations containing insensitive high explosives (IHE), such as 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazole-5-one (NTO), and nitroguanidine (NQ) are being developed to provide safer munitions. The addition of IHE to munitions formulations results in complex wastewaters from explosives manufacturing, load and pour operations and demilitarization activities. New technologies are required to treat those wastewaters. The core objective of this research effort was to develop and optimize a dual anaerobic-aerobic membrane bioreactor (MBR) system for treatment of wastewater containing variable mixtures of traditional energetics, IHE, and anions. The combined system proved highly effective for treatment of traditional explosives (TNT, RDX, HMX), IHE (DNAN, NTO, NQ) and anions commonly used as military oxidants (ClO4-, NO3-). The anaerobic MBR, which was operated for more than 500 d, was observed to completely degrade mg L-1 concentrations of TNT, DNAN, ClO4- and NO3- under all operational conditions, including at the lowest hydraulic residence time (HRT) tested (2.2 d). The combined system generally resulted in complete treatment of mg L-1 concentrations of RDX and HMX to <20 μg L-1, with most of the degradation occurring in the anaerobic MBR and polishing in the aerobic system. No common daughter products of DNAN, TNT, RDX, or HMX were detected in the effluent. NTO was completely transformed in the anaerobic MBR, but residual 3-amino-1,2,4-triazole-5-one (ATO) was detected in system effluent. The ATO rapidly decomposed when bleach solution was added to the final effluent. NQ was initially recalcitrant in the system, but microbial populations eventually developed that could degrade >90% of the ∼10 mg L-1 NQ entering the anaerobic MBR, with the remainder degraded to <50 μg L-1 in the aerobic system. The dual MBR system proved to be capable of complete degradation of a wide mixture of munitions constituents and was resilient to changing influent composition.

Ultrasound-Assisted Mineralization of 2,4-Dinitrotoluene in Industrial Wastewater Using Persulfate Coupled with Semiconductors

Oxidative degradation of 2,4-dinitrotoluenes in aqueous solution was executed using persulfate combined with semiconductors motivated by ultrasound (probe type, 20 kHz). Batch-mode experiments were performed to elucidate the effects of diverse operation variables on the sono-catalytic performance, including the ultrasonic power intensity, dosage of persulfate anions, and semiconductors. Owing to pronounced scavenging behaviors caused by benzene, ethanol, and methanol, the chief oxidants were presumed to be sulfate radicals which originated from persulfate anions, motivated via either the ultrasound or sono-catalysis of semiconductors. With regard to semiconductors, the increment of 2,4-dinitrotoluene removal efficiency was inversely proportional to the band gap energy of semiconductors. Based on the outcomes indicated in a gas chromatograph-mass spectrometer, it was sensibly postulated that the preliminary step for 2,4-dinitrotoluene removal was denitrated into o-mononitrotoluene or p-mononitrotoluene, followed by decarboxylation to nitrobenzene. Subsequently, nitrobenzene was decomposed to hydroxycyclohexadienyl radicals and converted into 2-nitrophenol, 3-nitrophenol, and 4-nitrophenol individually. Nitrophenol compounds with the cleavage of nitro groups synthesized phenol, which was sequentially transformed into hydroquinone and p-benzoquinone.

2,4-Dinitrotoluene (DNT) Perturbs Yolk Absorption, Liver Development and Lipid Metabolism/Oxygen Transport Gene Expression in Zebrafish Embryos and Larvae

2,4-dinitrotoluene (2,4-DNT) is a common environmental pollutant, and was classified as a group 2B human carcinogenic compound by the International Agency for Research on Cancer. This study determined the toxic effects of 2,4-DNT exposure on zebrafish at the embryo-larvae stage, in terms of organ morphogenesis and the expression pattern of selected target genes related to lipid metabolism and oxygen transportation. The results showed that the 120-h post-fertilization LC50 of 2,4-DNT was 9.59 mg/L with a 95% confidence interval of 8.89-10.44 mg/L. The larvae treated with 2,4-DNT showed toxic symptoms including smaller body, less skin pigment production, yolk malabsorption, and disordered liver development. Further studies on the expression of genes related to lipid transport and metabolism, and respiration indicated that they were significantly affected by 2,4-DNT. It is concluded that 2,4-DNT exposure perturbed liver development and yolk absorption in early-life zebrafish, and disturbed the lipid metabolism /oxygen transport gene expression.

Mineralization of dinitrotoluenes in aqueous solution by sono-activated persulfate enhanced with electrolytes

Oxidative degradation of dinitrotoluenes (DNTs) in industrial wastewater was conducted by sono-activated persulfate process assisted with electrolytes. Experiments were carried out to elucidate the influence of various operating parameters on the sonolytic behavior, such as species and concentrations of electrolytes, ultrasonic power intensity, reaction temperature, dosage of oxygen and persulfate anions. The outcomes indicate that sulfate radicals serve as main oxidants in the sono-activated persulfate process, wherein MgSO₄ electrolyte obviously inhibits microbubble coalescence, leading to enhancement of cavitation strength and DNTs removal percentage. On addition of electrolytes, the increment of DNTs removal percentages was proportional to ionic strength of electrolytes. According to the results obtained from gas chromatograph-mass spectrometer (GC-MS), it is postulated that DNTs initially undergo denitration pathway with cleavage of nitro group into o-mononitrotoluene (MNT) or oxidation of methyl group followed with decarboxylation procedure into 1,3-dinitrobenzene (DNB), respectively. Due to electrolytes observed commonly in wastewater, the sono-activated persulfate process coupled with electrolytes is potentially applied to dispose wastewater effluent from toluene nitration processes.

Reduced metabolites of nitroaromatics are distributed in the environment via the food chain

Increased industrial processes have introduced emerging toxic pollutants into the environment. Phytoremediation is considered to be a very useful, economical and ecofriendly way of controlling these pollutants, however, certain pollutants can potentially travel through the food chain and accumulate at hazardous levels. Four isomers of dinitrotoluenes (DNT) were investigated and observed their potential toxicity towards A. thaliana. Two different aphid species (generalist and specialist) were allowed to feed on plants treated with DNTs and toxicity to aphids determined. Reduced metabolites of DNT (in both plant and aphids) were recovered and quantified through GC-MS analyses. 2,6-DNT was observed to be the toxic of the DNTs tested. Complete metabolism of DNTs to their reduced products was never achieved for higher concentrations. Regioselectivity was observed in the case of 2,4-DNT, with 4A2NT as the dominant isomer. Feeding aphids showed a similar toxicity pattern for DNT isomers as host plants. Metabolites were recovered from the body of aphids, demonstrating the potential transport of metabolites through the food chain. Plants show varied toxicity responses towards the DNT isomers. Aphids fed on A. thaliana plants treated with DNTs were shown to have ANTs present, which reflects the propagation of DNT metabolites through the food chain.

2,4,6-Trinitrotoluene Induces Apoptosis via ROS-Regulated Mitochondrial Dysfunction and Endoplasmic Reticulum Stress in HepG2 and Hep3B Cells

2,4,6-trinitrotoluene (TNT) has been reported to cause numerous adverse effects. However, the detailed molecular mechanisms underlying TNT-induced liver toxicity need to be elucidated. In this study, we used HepG2 (p53wt) and Hep3B (p53null) cell lines to investigate the cytotoxic effects of TNT. At first, we found that TNT significantly decreased cell viability and induced DNA damage. Thereafter, through transcriptomic analysis, we observed that the diverse biological functions affected included mitochondrial dysfunction and endoplasmic reticulum (ER) stress. Mitochondrial dysfunction was evidenced by the loss of mitochondrial membrane potential, increased expression of cleaved-caspase-9&-3 and increased caspase-3/7 activity, indicating that apoptosis had occurred. In addition, the expressions of some ER stress-related proteins had increased. Next, we investigated the role of reactive oxygen species (ROS) in TNT-induced cellular toxicity. The levels of DNA damage, mitochondrial dysfunction, ER stress and apoptosis were alleviated when the cells were pretreated with N-acetyl-cysteine (NAC). These results indicated that TNT caused the ROS dependent apoptosis via ER stress and mitochondrial dysfunction. Finally, the cells transfected with CHOP siRNA significantly reversed the TNT-induced apoptosis, which indicated that ER stress led to apoptosis. Overall, we examined TNT-induced apoptosis via ROS dependent mitochondrial dysfunction and ER stress in HepG2 and Hep3B cells.

Species-specific differences in peroxisome proliferation, catalase, and SOD2 upregulation as well as toxicity in human, mouse, and rat hepatoma cells induced by the explosive and environmental pollutant 2,4,6-trinitrotoluene

2,4,6-Trinitrotoluene (TNT) has been widely used as an explosive substance and its toxicity is still of interest as it persisted in polluted areas. TNT is metabolized in hepatocytes which are prone to its toxicity. Since analysis of the human liver or hepatocytes is restricted due to ethical reasons, we investigated the effects of TNT on cell viability, reactive oxygen species (ROS) production, peroxisome proliferation, and antioxidative enzymes in human (HepG2), mouse (Hepa 1-6), and rat (H4IIEC3) hepatoma cell lines. Under control conditions, hepatoma cells of all three species were highly comparable exhibiting identical proliferation rates and distribution of their cell cycle phases. However, we found strong differences in TNT toxicity with the lowest IC₅₀ values (highest cell death rate) for rat cells, whereas human and mouse cells were three to sevenfold less sensitive. Moreover, a strong decrease in cellular dehydrogenase activity (MTT assay) and increased ROS levels were noted. TNT caused peroxisome proliferation with rat hepatoma cells being most responsive followed by those from mouse and human. Under control conditions, rat cells contained fivefold higher peroxisomal catalase and mitochondrial SOD2 activities and a twofold higher capacity to reduce MTT than human and mouse cells. TNT treatment caused an increase in catalase and SOD2 mRNA and protein levels in human and mouse, but not in rat cells. Similarly, human and mouse cells upregulated SOD2 activity, whereas rat cells failed therein. We conclude that TNT induced oxidative stress, peroxisome proliferation and mitochondrial damage which are highest in rat cells rendering them most susceptible toward TNT. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 989-1006, 2017.

Decomposition of nitrotoluenes in wastewater by sonoelectrochemical and sonoelectro-Fenton oxidation

Oxidative degradation of dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using electrochemical and electro-Fenton processes respectively, combined with ultrasonic irradiation, wherein a synergistic effect is observed. Experiments were carried out to elucidate the influence of various operating variables on the sonoelectrolytic behavior, such as electrode potential, sonoelectrolytic temperature, acidity of wastewater, oxygen dosage, and dosage of ferrous ions. It deserves to note that the nitrotoluene contaminants could be completely decomposed by sonoelectro-Fenton method, wherein hydrogen peroxide was in situ generated from cathodic reduction of oxygen, supplied partially by anodic oxidation of water. During the sonoelectrolytic process, in spite of existence of degassing phenomenon, the high yield of hydrogen peroxide was produced due to the significantly enhanced mass transfer rate of oxygen toward the cathode, caused by ultrasonic irradiation. Because higher removal efficiency of DNTs and TNT obtained at ambient conditions, it is believed that the sonoelectrolytic method is potentially applied to dispose wastewater from toluene nitration processes.

Removal of dinitrotoluenes in wastewater by sono-activated persulfate

Oxidative degradation of dinitrotoluenes (DNTs) in wastewater was performed using persulfate anions combined with ultrasonic irradiation, wherein a synergistic effect is observed. The batch-wise experiments were carried out to elucidate the influence of various operating parameters on sono-activated persulfate oxidation, including ultrasonic power intensity, persulfate anion concentration, reaction temperature and acidity of wastewater. It is noteworthy that the nitrotoluene contaminants could be almost completely eliminated by virtue of sono-activated persulfate oxidation, wherein sulfate radicals serve as principal oxidants, of which amounts are significantly enhanced via addition of sodium sulfate. Based on the results given by gas chromatograph-mass spectrometer (GC-MS), it is postulated that the methyl group of DNTs preliminarily underwent oxidation pathway into dinitrobenzoic acid, followed by decarboxylation to form 1,3-dinitrobenzene (DNB). In sum, the sono-activated persulfate oxidation is a promising method for treatment of nitrotoluenes in wastewater.

Effects of 2,4-dinitrotoluene exposure on enzyme activity, energy reserves and condition factors in common carp (Cyprinus carpio)

In this study relative condition factor (RCF) and hepatosomatic index (HSI) as well as the available energy reserves of common carp (Cyprinus carpio) by 2,4-DNT semi-static bioassay were determined and linked to effects of enzymes in liver tissues. Fish were exposed at sublethal concentrations of 2,4-DNT (0.13 μg/L, 0.1, 0.5, 1.0mg/L) for 7 and 15 d. Based on the results, there was no significant change in all parameters measured in fish exposed to 2,4-DNT at environmental related concentration, but 2,4-DNT stress in fish exposed to higher concentrations reflected the significant changes of physiological and biochemical responses. 2,4-DNT stress resulted in EROD activity induction in the liver, and the levels of EROD activity ranged from 0.39- to 1.83-fold higher than control. For GK, Na(+)/K(+)-ATPase, and GST, these enzyme activity continued to decline after exposure to 0.1, 0.5 and 1.0mg/L 2,4-DNT, whereas the trend on GK and Na(+)/K(+)-ATPase was more obvious than GST. Through principal component analysis, effects by 2,4-DNT-stress in each test group were distinguished. Additionally, indications of a trade-off between metabolic cost of toxicant exposure and processes vital to the survival of the organism were seen at the enzyme activity level as well as on higher levels of biological organization.

Removal of dinitrotoluenes and trinitrotoluene from industrial wastewater by ultrasound enhanced with titanium dioxide

Oxidative degradation of dinitrotoluenes (DNTs) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using ultrasonic irradiation combined with titanium dioxide (TiO(2)). The batch-wise experiments were carried out to elucidate the influence of various operating parameters on the sonolytic behavior, including power intensity, TiO(2) dosage, acidity of wastewater, reaction temperature and oxygen dosage. It is worthy to note that the nitrotoluene contaminants could be almost completely eliminated by sonochemical oxidation enhanced significantly with the addition of TiO(2) due to the supply of adsorbent and/or excess nuclei. High destruction rate of nitrotoluenes could be achieved by increasing the acidity of wastewater and decreasing the reaction temperature. According to the result given by pyrolysis/gas chromatograph-mass spectrometer (Pyrolysis/GC-MS), it is postulated that DNTs adsorbed on TiO(2) preliminarily undergo denitration pathway to o-mononitrotoluene (MNT) or oxidation pathway to 1,3-dinitrobenzene (DNB), respectively. Further, based on the spectra obtained from GC-MS, it is proposed that DNTs dissolved in wastewater proceed with similar reaction pathways as those adsorbed on TiO(2). Besides, oxidative degradation of 2,4,6-TNT results in the formation of 1,3,5-trinitrobenzene (TNB). Apparently, the sonolytic technique established is promising for direct treatment of wastewater from TNT manufacturing process.

Selection of scFv phages specific for chloramphenicol acetyl transferase (CAT), as alternatives for antibodies in CAT detection assays

Reporter gene assays are commonly used in applied toxicology to measure the transcription of genes involved in toxic responses. In these reporter gene assays, transgenic cells are used, which contain a promoter-operator region of a gene of interest fused to a reporter gene. The transcription of the gene of interest can be measured by the detection of the reporter protein. Chloramphenicol acetyl transferase (CAT) is frequently used as a reporter protein in mammalian reporter gene assays. Although CAT can be measured by different detection systems, like enzymatic and immune assays, most of these tests are expensive, time-consuming and labor-intensive. The excellent characteristics of phages, like their high affinity and specificity, their fast, cheap and animal-friendly manufacturing process with low batch-to-batch variations and their stability, make them appropriate as alternatives for antibodies in detection assays. Therefore, in this study single-chain variable fragment (scFv) phages were selected with affinity for CAT. Several scFv phages were selected that showed affinity towards CAT in a screening ELISA. Surface plasmon resonance analyses showed that the tested scFv phages have an affinity for CAT with a dissociation constant (K(d)) around 1 µM. The selected scFv phages in this study could be used as capture elements in a highly sensitive sandwich ELISA to detect CAT concentration as low as 0.1 ng ml⁻¹ or 4 pM. This low detection limit demonstrates the potential of the scFv phages as an alternative for capturing antibodies in a highly sensitive detection test to measure CAT concentrations in reporter gene assays.

Sulfur mustard toxicity: history, chemistry, pharmacokinetics, and pharmacodynamics

Sulfur mustard (SM) and similar bifunctional agents have been used as chemical weapons for almost 100 years. Victims of high-dose exposure, both combatants and civilians, may die within hours or weeks, but low-dose exposure causes both acute injury to the eyes, skin, respiratory tract and other parts of the body, and chronic sequelae in these organs are often debilitating and have a serious impact on quality of life. Ever since they were first used in warfare in 1917, SM and other mustard agents have been the subjects of intensive research, and their chemistry, pharmacokinetics and mechanisms of toxic action are now fairly well understood. In the present article we review this knowledge and relate the molecular-biological basis of SM toxicity, as far as it has been elucidated, to the pathological effects on exposure victims.

Analysis of common and specific mechanisms of liver function affected by nitrotoluene compounds

Background

Nitrotoluenes are widely used chemical manufacturing and munitions applications. This group of chemicals has been shown to cause a range of effects from anemia and hypercholesterolemia to testicular atrophy. We have examined the molecular and functional effects of five different, but structurally related, nitrotoluenes on using an integrative systems biology approach to gain insight into common and disparate mechanisms underlying effects caused by these chemicals.

Methodology/Principal Findings

Sprague-Dawley female rats were exposed via gavage to one of five concentrations of one of five nitrotoluenes [2,4,6-trinitrotoluene (TNT), 2-amino-4,6-dinitrotoluene (2ADNT) 4-amino-2,6-dinitrotoulene (4ADNT), 2,4-dinitrotoluene (2,4DNT) and 2,6-dinitrotoluene (2,6DNT)] with necropsy and tissue collection at 24 or 48 h. Gene expression profile results correlated well with clinical data and liver histopathology that lead to the concept that hematotoxicity was followed by hepatotoxicity. Overall, 2,4DNT, 2,6DNT and TNT had stronger effects than 2ADNT and 4ADNT. Common functional terms, gene expression patterns, pathways and networks were regulated across all nitrotoluenes. These pathways included NRF2-mediated oxidative stress response, aryl hydrocarbon receptor signaling, LPS/IL-1 mediated inhibition of RXR function, xenobiotic metabolism signaling and metabolism of xenobiotics by cytochrome P450. One biological process common to all compounds, lipid metabolism, was found to be impacted both at the transcriptional and lipid production level.

Conclusions/Significance

A systems biology strategy was used to identify biochemical pathways affected by five nitroaromatic compounds and to integrate data that tie biochemical alterations to pathological changes. An integrative graphical network model was constructed by combining genomic, gene pathway, lipidomic, and physiological endpoint results to better understand mechanisms of liver toxicity and physiological endpoints affected by these compounds.

Sonochemical decomposition of dinitrotoluenes and trinitrotoluene in wastewater

Mineralization of dinitrotoluenes (DNT) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted under ultrasonic irradiation. The batch-wise experiments were carried out to elucidate the influence of various operating parameters on the sonolytic behavior, including power intensity, acidity of wastewater, reaction temperature and oxygen dosage. It is remarkable that the nitrotoluenes contained could be almost completely decomposed by the sonochemical oxidation method, wherein the pyrolytic reaction was responsible for the destruction of organic compounds. During the sonication tests, the influence of reaction temperature on the degradation of nitrotoluenes is the most significant, followed by power intensity, acidity of wastewater and oxygen dosage. Based on the spectra obtained from gas chromatograph/mass spectrometer (GC/MS), it is suggested that 2,4,6-TNT is preliminarily denitrated to 2,6-DNT. The denitration of 2,6-DNT and/or 2,4-DNT results in the formation of o-mononitrotoluene, which proceeds with the cleavage of nitro group into toluene, followed by oxidation of methyl group and decarboxylation. In this study, it is believed that the sonolytic technique established is promising for wastewater disposal in toluene nitration processes.

Destruction of nitrotoluenes in wastewater by Electro-Fenton oxidation

Electrolytic degradation of dinitrotoluenes (DNTs) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted by Electro-Fenton's reagents. The batch-wise experiments were carried out to elucidate the influence of various operating variables on the electrolytic behavior, including electrode potential, oxygen dosage, electrolytic temperature, acidity of wastewater and dosage of ferrous ions. It deserves to note that the nitrotoluenes contained could be completely decomposed by Electro-Fenton's reagents, wherein hydrogen peroxide was in situ generated from cathodic reduction of oxygen, supplied mainly by anodic oxidation of water. During the electrochemical process, the influence of electrolytic temperature on the degradation of nitrotoluenes is the most significant, followed by electrode potential, acidity of wastewater and oxygen dosage. Based on the spectra analyzed by gas chromatograph/mass spectrometer (GC/MS), it is proposed that initial denitration of 2,4-DNT and/or 2,6-DNT gives rise to formation of o-mononitrotoluene, which undergoes the cleavage of nitro group into toluene, followed by oxidation of methyl group to benzoic acid and subsequent decarboxylation. It is believed that the electrolytic method established is potentially applied to dispose wastewater from toluene nitration processes in practice.

Recovery of nitrotoluenes in wastewater by solvent extraction

Toluene extraction was utilized to recover 2,4-dinitrotoluene (DNT), 2,6-DNT, and 2,4,6-trinitrotoluene (TNT) from wastewater of toluene nitration process. The batch-wise experiments were performed to elucidate the influence of various operating variables on the extracting behavior, including extracting temperature, volume ratios of solvent versus wastewater, agitation time, acidity of wastewater, and extraction stages. It was found that recovery of total organic compounds (TOC) was significantly elevated with increasing extraction temperature. Besides, high volume ratio of toluene/wastewater (2.0) and wastewater acidified to lower pH value enhanced the recovery percentage of TOC, in which extractable tendency was as follows: 2,6-DNT>2,4-DNT>2,4,6-TNT. It is worth noting that the nitrotoluenes in wastewater would be almost completely recovered using three sequential stages toluene extraction at the agitation time of 12min and pH 3.0. It is apparent that this established method is promising for the treatment of wastewater from toluene nitration processed industrially.

Phytotoxicity and phytoremediation of 2,6-dinitrotoluene using a model plant, Arabidopsis thaliana

Biochemical and genetic studies of xenobiotic metabolism in the model plant Arabidopsis have significant potential in providing information for phytoremediation. This paper presents the toxicity of 2,6-dinitrotoluene (2,6-DNT) to Arabidopsis under axenic conditions, the fate and transformation of 2,6-DNT after uptake by the plant, and the effect of a putative glutathione S-transferase (GST), which is highly induced by 2,4,6-trinitrotoluene (TNT) in the previous study, on the detoxification of 2,6-DNT. 2,6-DNT had toxic effects on the growth of Arabidopsis based on whole seedling as well as root growth assays. Using [U- 14C]2,6-DNT, the recovery was over 87% and less than 2% accounted for the mineralization of 2,6-DNT in axenic liquid cultures during the 14d of exposure. About half (48.3%) of the intracellular radioactivity was located in the root tissues in non-sterile hydroponic cultures. 2-Amino-6-nitrotoluene (2A6NT) and two unknown metabolites were produced as transformation products of 2,6-DNT in the liquid media. The metabolites were further characterized by proton NMR spectra and the UV-chromatograms when the plant was fed with either 2,6-DNT or 2A6NT. In addition, polar unknown metabolites were detected at short retention times from radiochromatograms of plant tissue extracts. The GST gene of the wild-type of Arabidopsis in response to 2,6-DNT was induced by 4.7-fold. However, the uptake rates and the tolerance at different concentrations of 2,6-DNT and TNT were not significantly different between the wild-type and the gst mutant indicating that induction of the GST gene is not related to the detoxification of 2,6-DNT.

Cytotoxicity of dinitrotoluenes (2,4-dNT, 2,6-DNT ) to MCF-7 and MRC-5 cells

DNTs are considered possibly carcinogenic to humans (Group 2B) because there is inadequate evidence in humans for carcinogenicity though there is sufficient evidence in experimental animals. In this study, MCF-7 (breast) and MRC-5 (lung) cells were exposed to a serial dilution of 2,4 and 2,6 DNTs (control, 1–500 ppm) in 96 well tissue culture plates. After various time intervals (24, 48, 72 and 96 hrs) the plates were washed, and 100 μl fluorescein diacetate solution (10 μg/ml in PBS) was added column wise to each well, and incubated at 37°C for 30–60 min before reading the fluorescence with a spectrofluorometer at excitation and emission wavelengths of 485 and 538 nm respectively. Spectrofluorometeric readings were converted to percentages of cell survival. Regression analysis was conducted to determine the relationship between cell survival and exposed concentration. Linear equations derived from the regression analysis were used to calculate the LC ₅₀ values. Results indicated that 2,6 DNT as more toxic to breast cells; LC₅₀ values were 445 and 292 ppm at 24 and 48 hours respectively compared to 2,4 DNT showing LC₅₀ values of 570 and 407 ppm at 24 and 48 hours, respectively. No significant differences in toxicity existed between the two chemicals with regard to lung cells. Contrary to the above observation, 2,4 DNT was more toxic to breast cells; LC₅₀ values were 407 and 238 ppm at 24 and 48 hours respectively compared to lung cells showing LC₅₀ values of 527 and 402 ppm at 24 and 48 hours respectively. No significant difference existed for 2,6 DNT between the two cell lines. Lungs cells were more resistant to the two chemicals.

Cytotoxicity and expression of c-fos, HSP70, and GADD45/153 proteins in human liver carcinoma (HepG2) cells exposed to dinitrotoluenes

Dinitrotoluenes (DNTs) are byproducts of the explosive trinitrotoluene (TNT), and exist as a mixture of 2 to 6 isomers, with 2,4-DNT and 2,6-DNT being the most significant. The main route of human exposure at ammunition facilities is inhalation. The primary targets of DNTs toxicity are the hematopoietic system, cardiovascular system, nervous system and reproductive system. In factory workers, exposure to DNTs has been linked to many adverse health effects, including: cyanosis, vertigo, headache, metallic taste, dyspnea, weakness and lassitude, loss of appetite, nausea, and vomiting. Other symptoms including pain or parasthesia in extremities, abdominal discomfort, tremors, paralysis, chest pain, and unconsciousness have been documented. An association between DNTs exposure and increased risk of hepatocellular carcinomas and subcutaneous tumors in rats, as well as renal tumors in mice, has been established. This research was therefore designed targeting the liver to assess the cellular and molecular responses of human liver carcinoma cells following exposure to 2,4-DNT and 2,6-DNT. Cytotoxicity was evaluated using the MTT assay. Upon 48 hrs of exposure, LC₅₀ values of 245 ± 14.72μg/mL, and 300 ± 5.92μg/mL were recorded for 2,6-DNT and 2,4-DNT respectively, indicating that both DNTs are moderately toxic, and 2,6-DNT is slightly more toxic to HepG₂ cells than 2,4-DNT. A dose response relationship was recorded with respect to the cytotoxicity of both DNTs. Western blot analysis resulted in a significant expression (p<0.05) of the 70-kDa heat shock protein in 2,6-DNT-treated cells compared to the control cells and at the 200 μg/mL dose for 2,4-DNT. A statistically significant expression in c-fos was also observed at the 200 and 250 μg/mL treatment level for 2,4- and 2,6-DNT, respectively. However, no statistically significant expression of this protooncogene-related protein was observed at the doses of 0, 100, or 300 μg/mL or within the dose range of 0–200 μg/mL for 2,6-DNT. The 45-kDa growth arrest and damage protein was significantly expressed at the dose range of 200 – 250μg/mL for 2,6-DNT and at the dose range of 200 – 400μg/mL for 2,4-DNT. Expression of 153-kDa growth arrest and DNA damage protein was significant at the 100, 200, and 250μg/mL doses for 2,6-DNT and at the 200 μg/mL dose for 2,4-DNT. Overall, these results indicate the potential of DNTs to induce cytotoxic, proteotoxic (HSP70), and genotoxic (GADD45/153) effects, as well as oxidative stress and pro-inflammatory reactions (c-fos).

Cancer of the urinary bladder in highly exposed workers in the production of dinitrotoluenes: a case report

Technical dinitrotoluene (consisting of 2,4- and 2,6-dinitrotoluene isomers) has been widely used as explosives. Both technical isomers are mutagenic in Salmonella typhimurium TA98 strains and carcinogenic in rodents. 2,4-dinitrotoluene shows a dose-dependency of malignant tumors of the kidneys, liver, and mammary glands in rats and mice. In this case report, we discuss a cluster of three cases of urothelial cancer amongst a group of about 60 workers exposed to dinitrotoluenes. The workers were employed in the manufacturing of nitrotoluene explosives in the former German Democratic Republic. The cases occurred within a period of 12 years (1990-2002) leading to a 15.9 fold higher incidence of cancer of the urinary bladder than of the federal state where the chemical factory was located. The observation of the cluster of urothelial cancer in persons highly exposed to nitrotoluenes underlines the putative human carcinogenicity of dinitrotoluenes with the human urothelium as a relevant target tissue.

Accumulation of trinitrotoluene (TNT) in aquatic organisms: part 1--Bioconcentration and distribution in channel catfish (Ictalurus punctatus)

Little is currently known regarding the toxicokinetics of TNT in fish. In the present study, the bioconcentration and distribution of trinitrotoluene (TNT) and TNT biotransformation products was investigated in juvenile channel catfish by exposing catfish to 14C-labeled TNT in water. Uptake experiments showed relatively fast rates (k(u)=10.1 ml g(-1) h(-1)) for TNT from the water; however, bioconcentration factors for TNT were low (0.79 ml g(-1)) due to rapid biotransformation and potential elimination of TNT. Accumulation of extractable radioactivity (TNT and all extractable biotransformation products) was much greater (BCF=10.5 ml g(-1)) than that for parent compound. TNT (parent compound) bioconcentrated to the greatest extent in the gills of the fish, while total radioactivity bioconcentrated to the greatest extent in the viscera. Residual portions of the fish that contained muscle and skin had lower concentrations of TNT than the whole fish, indicating that ingestion of fish fillets would result in decreased exposure to human consumers. Although the bioconcentration potential of TNT is very low, future research needs to be conducted to identify the biotransformation products that make up most of the radioactivity in exposed fish and evaluate their potential to promote toxicity.

Lead-induced cytotoxicity and transcriptional activation of stress genes in human liver carcinoma (HepG2) cells

Lead is a non-essential element that exhibits a high degree of toxicity, especially in children. Most research on lead has focused on its effects on organ systems such as the nervous system, the red blood cells, and the kidneys which are considered to be the primary targets of lead toxicity. However, the molecular mechanisms by which it induces toxicity, and carcinogenesis remain to be elucidated. In this research, we performed the MTT assay to assess the cytotoxicity, and the CAT-Tox assay to assess the transcriptional responses associated with lead exposure to thirteen different recombinant cell lines generated from human liver carcinoma cells (HepG2), by creating stable transfectants of mammalian promoter chloramphenicol (CAT) gene fusions. Study results indicated that lead nitrate is cytotoxic to HepG2 cells, showing LD50 values of 49.0 +/- 18.0 microg/mL, 37.5 +/- 9.2 microg/mL, and 3.5 +/- 0.7 microg/mL for cell mortality upon 24, 48 and 72 h of exposure, respectively; indicating a dose- and time-dependent response with regard to the cytotoxic effect of lead nitrate. A dose-response relationship was also recorded with respect to the induction of stress genes in HepG2 cells exposed to lead nitrate. Overall, six out of the thirteen recombinant cell lines tested showed inductions to statistically significant levels (p < 0.05). At 50 microg/mL of lead nitrate, the average fold inductions were: 2.1 +/- 1.0, 5.4 +/- 0.4, 12.1 +/- 6.2, 5.0 +/- 1.7, 2.5 +/- 1.3, and 4.8 +/- 4.5 for XRE, HSP70, CRE, GADD153, and GRP78, respectively. These results indicate the potential for lead nitrate to undergo biotransformation in the liver (XRE), to cause cell proliferation (c-fos), protein damage (HSP70, GRP78), metabolic perturbation (CRE), and growth arrest and DNA damage (GADD153). Marginal but not significant inductions were also obtained with the GSTYa (1.5 +/- 0.8), and GADD45 (5.7 +/- 8.1) promoters, and the NF-KB (2.0 +/- 1.7) response element, indicating the potential for oxidative stress. No significant inductions (p > 0.05) were recorded for CYP1A1, HMTIIA, p53RE, and RARE.

Environmental toxicology and health effects associated with dinitrotoluene exposure

Dinitrotoluenes (DNTs) are nitroaromatic compounds appearing as pale yellow crystalline solids at room temperature. Dinitrotoluenes exist as a mixture of 2 to 6 isomers, with 2,4-DNT, and 2,6-DNT being the most significant. About 500 persons are estimated to be potentially exposed yearly to 2,4-DNT and 2,6-DNT during the production of munitions and explosives. The main route of human exposure at ammunition facilities is inhalation, but dermal contact and inadvertent ingestion can also be substantial. In factory workers, exposure to DNTs has been linked to many adverse health effects, including cyanosis, vertigo, headache, metallic taste, dyspnea, weakness and lassitude, loss of appetite, nausea, and vomiting. Other symptoms including pain or parasthesia in extremities, abdominal discomfort, tremors, paralysis, chest pain, and unconsciousness have also been reported. The primary targets of DNT toxicity are the hematopoietic system (pallor, cyanosis, anemia, and leukocytosis), the cardiovascular system (ischemic heart disease), the nervous system (muscular weakness, headache, dizziness, nausea, insomnia, and tingling pains in the extremities) and the reproductive system (reduction of sperm counts, alteration of sperm morphology, and aspermatogenesis). An association between DNT exposure and increased risk of hepatocellular carcinomas and subcutaneous tumors in rats, as well as renal tumors in mice, has been established. Epidemiologic studies of DNT toxicity have been limited to small groups of workers who had been occupationally exposed at various ammunitions production facilities. Clearly defining the health effects of DNTs with a high degree of confidence has therefore been difficult because of the multigenic nature of occupational exposure. In an attempt to update the toxicologic profile of the DNTs, we hereby provide a critical review of the environmental and toxicologic pathology of DNTs, with a special emphasis on their potential implications for public health.