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

Toxicity of nitrophenolic pollutant 4-nitroguaiacol to terrestrial plants and comparison with its non-nitro analogue guaiacol (2-methoxyphenol)

Phenols, and especially their nitrated analogues, are ubiquitous pollutants and known carcinogens which have already been linked to forest decline. Although nitrophenols have been widely recognized as harmful to different aquatic and terrestrial organisms, we could not find any literature assessing their toxicity to terrestrial plants. Maize (monocot) and sunflower (dicot) were exposed to phenolic pollutants, guaiacol (GUA) and 4-nitroguaiacol (4NG), through a hydroponics system under controlled conditions in a growth chamber. Their acute physiological response was studied during a two-week root exposure to different concentrations of xenobiotics (0.1, 1.0, and 10 mM). The exposure visibly affected plant growth and the effect increased with increasing xenobiotic concentration. In general, 4NG affected plants more than GUA. Moreover, sunflower exhibited an adaptive response, especially to low and moderate GUA concentrations. The integrity of both plant species deteriorated during the exposure: biomass and photochemical pigment content were significantly reduced, which reflected in the poorer photochemical efficiency of photosystem II. Our results imply that 4NG is taken up by sunflower plants, where it could enter a lignin biosynthesis pathway.

Toxicity of bisphenol A and p-nitrophenol on tomato plants: Morpho-physiological, ionomic profile, and antioxidants/defense-related gene expression studies

Bisphenol A (BPA) and p-nitrophenol (PNP) are emerging contaminants of soils due to their wide presence in agricultural and industrial products. Thus, the present study aimed to integrate morpho-physiological, ionic homeostasis, and defense- and antioxidant-related genes in the response of tomato plants to BPA or PNP stress, an area of research that has been scarcely studied. In this work, increasing the levels of BPA and PNP in the soil intensified their drastic effects on the biomass and photosynthetic pigments of tomato plants. Moreover, BPA and PNP induced osmotic stress on tomato plants by reducing soluble sugars and soluble proteins relative to control. The soil contamination with BPA and PNP treatments caused a decline in the levels of macro- and micro-elements in the foliar tissues of tomatoes while simultaneously increasing the contents of non-essential micronutrients. The Fourier transform infrared analysis of the active components in tomato leaves revealed that BPA influenced the presence of certain functional groups, resulting in the absence of some functional groups, while on PNP treatment, there was a shift observed in certain functional groups compared to the control. At the molecular level, BPA and PNP induced an increase in the gene expression of polyphenol oxidase and peroxidase, with the exception of POD gene expression under BPA stress. The expression of the thaumatin-like protein gene increased at the highest level of PNP and a moderate level of BPA without any significant effect of both pollutants on the expression of the tubulin (TUB) gene. The comprehensive analysis of biochemical responses in tomato plants subjected to BPA and PNP stress illustrates valuable insights into the mechanisms underlying tolerance to these pollutants.

Transgenic tobacco plants overexpressing a cold-adaptive nitroreductase gene exhibited enhanced 2,4-dinitrotoluene detoxification rate at low temperature

Plants encounter many environmental factors such as low and high temperatures during phytoremediation processes. In this study, our aim was to produce the transgenic tobacco plants by using a newly characterized bacterial nitroreductase, Ntr, which was active at a broad range temperature in order to detoxify 2,4-dinitrotoluene (2,4-DNT) at lower temperature. The presence of Ntr and its heterologous expression was verified in T1 transgenic plants and their growing ability were determined under toxic amount of 2,4-DNT (35 µM). Fresh weight and dry weight of transgenic plants were significantly higher than wild type (WT) under toxic 2,4-DNT at 22 °C, indicating higher growth capacity of the transgenics. Transgenic plants also showed a higher tolerance than WT when exposed to 2,4-DNT at 15 °C. Moreover, transformation rate of 2,4-DNT was gradually decreased through decreasing temperatures in WT media, however, it was increased through decreasing temperatures in transgenic plant TR3-25 media and it had the highest transformation rate (54%) of 2,4-DNT at 4 °C. Correlatively, 2,4-DNT treatment at 4 °C led to a significant decrease in H2O2 level in transgenic plants. Thus, transgenic plants overexpressing nitroreductase might have an important advantage for phytoremediation of toxic nitroaromatic compounds in field applications at low temperatures.

Biotransformation of 2,4-dinitrotoluene by the beneficial association of engineered Pseudomonas putida with Arabidopsis thaliana

2,4-dinitrotoluene (2,4-DNT) is a priority environmental xenobiotic pollutant which has toxic, mutagenic, and carcinogenic properties. Thus, its biodegradation by applying recent approaches such as taking advantage of plant-bacteria interactions is crucial. In this work, the genes from Burkholderia sp. R34, necessary for 2,4-DNT degradation, were integrated into wild-type Pseudomonas putida (P. putida) KT2440 genome, and this strain, named KT.DNT, was inoculated to soil in in vitro conditions. To estimate the disappearance of 2,4-DNT in contaminated soil, samples were taken from different time intervals, extracted and analyzed using high-performance liquid chromatography (HPLC). Biotransformation of 2,4-DNT increased gradually and the degradation in soil after 14-days of treatment with the bacterium was found to be the 97.1%, indicating that the engineered strain could be a remarkable candidate for in situ bioremediation of 2,4-DNT-contaminated sites. In addition, in vitro interaction of this bacterium with a model plant, Arabidopsis thaliana (A. thaliana), enhanced lateral root and root hair formation together with dry root weight. Moreover, the initial 2,4-DNT concentration was decreased to 68% within 2 h with the plant-associated KT.DNT in liquid culture. Hence, the usage of this bacterium with plants could also be a promising application for the 2,4-DNT biotransformation.

Ecotoxicity of 2,4-dinitrotoluene to cold tolerant plant species in a sub-Arctic soil

Decades of live-fire training exercises have left millions of acres of military training lands contaminated with various munitions constituents such as dinitrotoluene. Those that pose a threat to higher organisms due to their toxicity and mobility in the soil are of particular concern. Plants aid in the biodegradation and phytoextraction of contaminants, and site-specific ecotoxicity determinations are critical to inform effective remediation strategy. These ecotoxicity determinations are lacking in cold-adapted plants and would be very informative for contaminated training lands in cold regions. Therefore, we conducted a phytotoxicity study to determine the median effective concentration (EC₅₀) of 2,4-dinitrotoluene (2,4-DNT) to four native Alaskan plant species in a sub-Arctic soil at two different temperatures. Plant species investigated were white spruce (Picea glauca), field locoweed (Oxytropis campestris), bluejoint grass (Calamagrostis canadensis), and Jacob's ladder (Polemonium pulcherrimum). Seedling emergence, fresh plant mass, and dry plant mass were used to model plant response to 2,4-DNT contamination. White spruce was most tolerant to 2,4-DNT contamination (EC₅₀ = 130.8 mg kg^-1) and field locoweed was least tolerant (EC₅₀ = 0.38 mg kg^-1). In general, Arctic plant species were more vulnerable to 2,4-DNT when compared to plant types native to temperate or tropical regions.

Inhibition of soil microbial activity by nitrogen-based energetic materials

We investigated individual toxicities of the nitrogen-based energetic materials (EMs) 2,4-dinitrotoluene (2,4-DNT); 2-amino-4,6-dinitrotoluene (2-ADNT); 4-amino-2,6-dinitrotoluene (4-ADNT); and nitroglycerin (NG) on microbial activity in Sassafras sandy loam (SSL) soil, which has physicochemical characteristics that support very high qualitative relative bioavailability for organic chemicals. Batches of SSL soil for basal respiration (BR) and substrate-induced respiration (SIR) assays were separately amended with individual EMs or acetone carrier control. Total microbial biomass carbon (biomass C) was determined from CO₂ production increases after addition of 2500 mg/kg of glucose-water slurry to the soil. Exposure concentrations of each EM in soil were determined using US Environmental Protection Agency method 8330A. Basal respiration was the most sensitive endpoint for assessing the effects of nitroaromatic EMs on microbial activity in SSL, whereas SIR and biomass C were more sensitive endpoints for assessing the effects of NG in soil. The orders of toxicity (from greatest to least) were 4-ADNT > 2,4-DNT = 2-ADNT > NG for BR; but for SIR and biomass C, the order of toxicity was NG > 2,4-DNT > 2-ADNT = 4-ADNT. No inhibition of SIR was found up to and including the greatest concentration of each ADNT tested in SSL. These ecotoxicological data will be helpful in identifying concentrations of contaminant EMs in soil that present acceptable ecological risks for biologically mediated processes in soil. Environ Toxicol Chem 2017;36:2981-2990. Published 2017 Wiley Periodicals Inc. on behalf of SETAC.This article is a US government work and, as such, is in the public domain in the United States of America.

Biodegradation of 2,4-dinitrotoluene by different plant species

Over the past century, rapid growth of population, mining and industrialization significantly contributed to extensive soil, air and water contamination. The 2,4-dinitrotoluene (2,4-DNT), used mostly as explosive, belongs to the hazardous xenobiotics. Soils and waters contaminated with 2,4-DNT may be cleaned by phytoremediation using suitable plant species. The ability of crop plants (hemp, flax, sunflower and mustard) to germinate and grow on soils contaminated with 2,4-DNT was compared. Stimulation of their growth was found at 0.252 mg/g 2,4-DNT. The lethal concentration for the growth for these species was around 1 mg/g. In hydropony, the above mentioned species were able to survive 200 mg/l 2,4-DNT, the concentration close to maximal solubility of 2,4-DNT in water. Metabolism of 2,4-DNT was tested using suspension culture of soapwort and reed. The degradation products 2-aminonitrotoluene and 4-aminonitrotoluene were found both in the medium and in the acetone extract of plant cells. The test showed that the toxicity of these metabolites was higher than the toxicity of the parent compound, but 2,4-diaminotoluene, the product of next reduction step, was less toxic in the concentration range tested (0-200 mg/l).

Ecotoxicological assessment of a high energetic and insensitive munitions compound: 2,4-dinitroanisole (DNAN)

The high explosive nitroaromatic 2,4-dinitroanisole (DNAN) is less shock sensitive than 2,4,6-trinitrotoluene (TNT), and is proposed as a TNT replacement for melt-cast formulations. Before using DNAN in munitions and potentially leading to environmental impact, the present study examines the ecotoxicity of DNAN using selected organisms. In water, DNAN decreased green algae Pseudokirchneriella subcapitata growth (EC50 = 4.0mg/L), and bacteria Vibrio fischeri bioluminescence (Microtox, EC50 = 60.3mg/L). In soil, DNAN decreased perennial ryegrass Lolium perenne growth (EC50 =7 mg/kg), and is lethal to earthworms Eisenia andrei (LC50 = 47 mg/kg). At sub-lethal concentrations, DNAN caused an avoidance response (EC50 = 31 mg/kg) by earthworms. The presence of DNAN and 2-amino-4-nitroanisole in earthworms and plants suggested a role of these compounds in DNAN toxicity. Toxicity of DNAN was compared to TNT, tested under the same experimental conditions. These analyses showed that DNAN was equally, or even less deleterious to organism health than TNT, depending on the species and toxicity test. The present studies provide baseline toxicity data to increase the understanding of the environmental impact of DNAN, and assist science-based decision makers for improved management of potential DNAN contaminated sites.

Multiple environmental stressors elicit complex interactive effects in the western fence lizard (Sceloporus occidentalis)

Evaluation of multiple-stressor effects stemming from habitat degradation, climate change, and exposure to chemical contaminants is crucial for addressing challenges to ecological and environmental health. To assess the effects of multiple stressors in an understudied taxon, the western fence lizard (Sceloporus occidentalis) was used to characterize the individual and combined effects of food limitation, exposure to the munitions constituent 2,4,6-trinitrotoluene (TNT), and Plasmodium mexicanum (lizard malaria) infection. Three experimental assays were conducted including: Experiment I--TNT × Food Limitation, Experiment II--Food Limitation × Malaria Infection, and Experiment III--TNT × Malaria Infection. All experiments had a 30 day duration, the malaria treatment included infected and non infected control lizards, food limitation treatments included an ad libitum control and at least one reduced food ration and TNT exposures consisting of daily oral doses of corn oil control or a corn oil-TNT suspension at 5, 10, 20, 40 mg/kg/day. The individual stressors caused a variety of effects including: reduced feeding, reduced testes mass, anemia, increased white blood cell (WBC) concentrations and increased mass of liver, kidney and spleen in TNT exposures; reduced cholesterol, WBC concentrations and whole body, testes and inguinal fat weights given food limitation; and increased WBC concentrations and spleen weights as well as decreased cholesterol and testes mass in malaria infected lizards. Additive and interactive effects were found among certain stressor combinations including elimination of TNT-induced hormesis for growth under food limitation. Ultimately, our study indicates the potential for effects modulation when environmental stressors are combined.

Phytotoxicity and uptake of nitroglycerin in a natural sandy loam soil

Nitroglycerin (NG) is widely used for the production of explosives and solid propellants, and is a soil contaminant of concern at some military training ranges. NG phytotoxicity data reported in the literature cannot be applied directly to development of ecotoxicological benchmarks for plant exposures in soil because they were determined in studies using hydroponic media, cell cultures, and transgenic plants. Toxicities of NG in the present studies were evaluated for alfalfa (Medicago sativa), barnyard grass (Echinochloa crusgalli), and ryegrass (Lolium perenne) exposed to NG in Sassafras sandy loam soil. Uptake and degradation of NG were also evaluated in ryegrass. The median effective concentration values for shoot growth ranged from 40 to 231 mg kg(-1) in studies with NG freshly amended in soil, and from 23 to 185 mg kg(-1) in studies with NG weathered-and-aged in soil. Weathering-and-aging NG in soil did not significantly affect the toxicity based on 95% confidence intervals for either seedling emergence or plant growth endpoints. Uptake studies revealed that NG was not accumulated in ryegrass but was transformed into dinitroglycerin in the soil and roots, and was subsequently translocated into the ryegrass shoots. The highest bioconcentration factors for dinitroglycerin of 685 and 40 were determined for roots and shoots, respectively. Results of these studies will improve our understanding of toxicity and bioconcentration of NG in terrestrial plants and will contribute to ecological risk assessment of NG-contaminated sites.

Engineering plants for the phytoremediation of RDX in the presence of the co-contaminating explosive TNT

The explosive compounds hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT) are widespread environmental contaminants commonly found as co-pollutants on military training ranges. TNT is a toxic carcinogen which remains tightly bound to the soil, whereas RDX is highly mobile leaching into groundwater and threatening drinking water supplies. We have engineered Arabidopsis plants that are able to degrade RDX, whilst withstanding the phytotoxicity of TNT. Arabidopsis thaliana (Arabidopsis) was transformed with the bacterial RDX-degrading xplA, and associated reductase xplB, from Rhodococcus rhodochrous strain 11Y, in combination with the TNT-detoxifying nitroreductase (NR), nfsI, from Enterobacter cloacae. Plants expressing XplA, XplB and NR remove RDX from soil leachate and grow on soil contaminated with RDX and TNT at concentrations inhibitory to XplA-only expressing plants. This is the first study to demonstrate the use of transgenic plants to tackle two chemically diverse organic compounds at levels comparable with those found on contaminated training ranges, indicating that this technology is capable of remediating concentrations of RDX found in situ. In addition, plants expressing XplA and XplB have substantially less RDX available in aerial tissues for herbivory and potential bioaccumulation.

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).

Uptake and transformation of soil [14C]-trinitrotoluene by cool-season grasses

This study investigated the fate and uptake of [(14)C]-TNT from soil into orchardgrass (Dactylis glomerata), perennial ryegrass (Lolium perenne), and tall fescue (Festuca arundinacea) over a one year period in a greenhouse-controlled environment. Pots (n = 4 for each grass, containing 10 mg cold TNT/kg soil + 1.2 mg [(14)C]-TNT/kg soil and controls with no TNT) were exposed to light and temperature conditions typical of June at 45 degrees N for 369 days. Three plant harvests were made (63, 181, and 369 days), and soil and plant materials were monitored for [(14)C]-TNT and metabolite concentrations. The 11.2 mg/kg TNT dose was not phytotoxic to the plant species tested. Continual uptake of TNT into grass blades was observed over the one-year period, with a total accumulation of 1.3%, 0.9%, and 0.8% of the initial soil [(14)C]-TNT dose for orchard grass, perennial ryegrass, and tall fescue, respectively. All [(14)C]-TNT residue in plant material was incorporated as bound residue. At final harvest, radioactivity was concentrated most highly in the root > crown > blade for all species. Soil TNT was gradually reduced to aminodinitro-toluenes and then further to an unidentified metabolite(s). Overall, orchardgrass appeared to be the most efficient species at taking up TNT.

Hormesis effects and implicative application in assessment of lead-contaminated soils in roots of Vicia faba seedlings

Chemical analyses and biological methods were combined to investigate oxidative stress, hormesis effect and concerned mechanism in roots of Viciafaba seedlings grown in 0-2000 mg kg(-1) of Pb-treated soils after germination of 20d. The results showed that U-shaped dose response curves were displayed in superoxide radical (O2-) radicals, guaiacol peroxidase (POD) and ascorbate peroxidase (APX) activities, malondialdehyde (MDA) and carbonyl groups as well as activities of endoproteinase (EP) isoenzymes in the roots at low doses of extraneous Pb, indicating reduced oxidative stress and toxic effect. The inverted U-shaped curves were also exhibited in growth height, superoxide dismutase (SOD) and EP activities as well as inducible heat shock protein70 (HSP70) with the increasing extraneous Pb, indicative of enhanced oxidative stress. The enhancement in HSP70, carbonyl groups and EP activities confirmed intracellular proteotoxicity and proteolytic activity in the roots at higher doses of soil Pb. More interestingly, levels of inducible HSP70 were well correlated with those of growth heights (r=0.809, p<0.05), implying that HSP70 induction may be one of the mechanisms underlying the U-shaped growth curve of V. faba seedlings in the experiment. The results suggest that traditional threshold models ought to be combined with hormesis effect in assessment of Pb-polluted soils and the threshold dose range of Pb-treated soils is proposed rudimentally as 25-125 mg kg(-1).

Bioaccumulation of hexachlorobenzene in Eisenia foetida at different aging stages

The impacts of contact time on the extractability, the availability of hexachlorobenzene (HCB) in different soils (paddy soil, red soil, and fluvo-aquic soil) and bioaccumulation in earthworm Eisenia foetida were investigated under controlled conditions in laboratory. Results indicated that the aging rate of HCB displaying a biphasic character in different soils: a rapid aging in the first 60 d followed by a slow aging in the next 120 d incubation time. Moreover, most of extractable HCB (about 90%) decline occurred in the first 60 d after HCB was spiked into the soils. The aging rate of HCB in the paddy soil was higher than that in the fluvo-aquic soil or the red soil. The amount of HCB accumulated in the earthworms and its accumulative ability, expressed as a bioaccumulation factor (BAF), declined as the aging time increased from 1 to 180 d. Although the extractable HCB decreased with increasing residence time in soil, much of HCB could still be accumulated by earthworms (457.6-984.3 ng/g) through bioaccumulation, which poses a potential risk to soil ecological safety.

Effects, uptake, and fate of 2,4,6-trinitrotoluene aged in soil in plants and worms

The present study was aimed at providing data to be used at predicting exposure-based effects of 2,4,6-trinitrotoluene (TNT) aged in soil on endpoint organisms representing two trophic levels. These data can be used to define criteria or reference values for environmental management and conducting specific risk assessment. Long-term exposure tests were conducted to evaluate sublethal toxicity and uptake of aged soil-based explosives, with TNT as the main contaminant. In these tests, plants were exposed for 55 d, and biomass and explosives residues were determined. Worms were exposed for 28 and 42 d, and biomass, number, and tissue residues were determined. Biomass of Lolium perenne significantly decreased with soil-TNT concentration, and an effective concentration causing a 20% decrease in biomass (EC20) for TNT metabolites of 3.75 mg/kg was calculated. The concentrations of TNT metabolites in shoots and roots were significantly related to concentrations in soil, as were concentrations of hexahydro-1,3,5-trinitro-1,3,5 triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The mean bioconcentration factors, indicating the potential of a chemical to accumulate in an organism, were 0.9 for TNT metabolites, 71.8 for RDX, and 12.2 for HMX in L. perenne shoots. Biomass of Eisenia fetida adults significantly decreased with soil-TNT concentration, and an EC20 for TNT of 3.70 mg/kg was calculated. The TNT, RDX, and HMX levels in E. fetida were below detection.

Toxicity and uptake of cyclic nitramine explosives in ryegrass Lolium perenne

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) are cyclic nitramines used as explosives. Their ecotoxicities have been characterized incompletely and little is known about their accumulation potential in soil organisms. We assessed the toxicity and uptake of these explosives in perennial ryegrass Lolium perenne L. exposed in a Sassafras sandy loam (SSL) or in a sandy soil (DRDC, CL-20 only) containing contrasting clay contents (11% and 0.3%, respectively). A 21-d exposure to RDX, HMX or CL-20 in either soil had no adverse effects on ryegrass growth. RDX and HMX were translocated to ryegrass shoots, with bioconcentration factors (BCF) of up to 15 and 11, respectively. In contrast, CL-20 was taken up by the roots (BCF up to 19) with no translocation to the shoots. These studies showed that RDX, HMX, and CL-20 can accumulate in plants and may potentially pose a risk of biomagnification across the food chain.

Partitioning species variability from soil property effects on phytotoxicity: ECx normalization using a plant contaminant sensitivity index

Soil properties mitigate hazardous effects of contaminants through soil chemical sequestration and should be considered when evaluating ecological risk from terrestrial contamination. Empirical models that quantify relationships between soil properties and toxicity to ecological receptors are necessary for site-specific adjustments to ecological risk assessments. However, differential sensitivities of test organisms in dose-response studies may limit the utility of such models. We present a novel approach to toxicity estimation that partitions the effect of differential sensitivities of test organisms from that of soil chemical/physical properties. Five soils that ranged in selected properties were spiked with five concentrations of sodium arsenate. Bioassays were conducted where above ground dry matter growth and the corresponding tissue arsenic concentrations were evaluated for three terrestrial plants (Alfalfa, Medicago sativa L.; Perennial ryegrass, Lolium perrene L.; and Japanese millet, Echinochloa crusgalli L.). Estimates were combined into a plant contaminant sensitivity index (PCSI) and used to normalize phytotoxicity parameters to the most sensitive species (i.e., alfalfa) where necessary. Simple linear regression and ANCOVA indicated a 36.5% increase in the explanatory power of the modifying effects of soil properties on phytotoxicity when differential arsenate sensitivities were accounted for by PCSI (r(2) = 0.477-0.833). Normalization of ecotoxicity parameters by PCSI is a seemingly effective approach to quantify the modifying effects of soil properties on phytotoxicity endpoints when it is of interest to consider multiple plant species (or varieties within a species) with differential sensitivities to experimental contaminants.

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.

Detoxification of 2,4-dinitrotoluene by transgenic tobacco plants expressing a bacterial flavodoxin

Significant effort has been directed in recent times to the use of plants to extract and detoxify nitroaromatics from polluted industrial facilities. We have explored the possibility of overcoming the phytotoxicity of the highly toxic and recalcitrant nitroderivative 2,4-dinitrotoluene (2,4-DNT) by expressing a cyanobacterial flavodoxin (Fld) in tobacco plants. We demonstrate here that transformants accumulating Fld in plastids display a remarkable increase in the ability to tolerate, take up, and transform 2,4-DNT, as compared to their wild-type siblings. We also show that Fld mediates one-electron reduction of 2,4-DNT in the presence of oxygen and especially in anaerobiosis. Moreover, Fld-loaded chloroplasts are able to convert 2,4-DNT into its aminoderivatives in the presence of light. The results suggest that expression of Fld in landscape plants could facilitate effective cleanup of sites contaminated with this class of pollutants.

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.

Liquid chromatography/electrospray ionization tandem mass spectrometry analysis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)

A quantitative liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed for the analysis of the explosive, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). In negative ionization mode, HMX forms an acetate adduct ion [M + CH(3)COO](-), m/z 355, in the presence of a small amount of acetic acid in the mobile phase. The ESI collision-induced dissociation (CID) spectrum of m/z 355 was acquired and the transitions m/z 355 --> 147 and m/z 355 --> 174 were chosen for the determination of HMX in samples. Using this quantification technique, the method detection limit was 1.57 microg/L and good linearity was achieved in the range 5-500 microg/L. This method will help to unambiguously analyze environmentally relevant concentrations of HMX.