Novel microbial consortia facilitate metalliferous immobilization in non-ferrous metal(loid)s contaminated smelter soil: Efficiency and mechanisms.

Exposure to toxic metals from nonferrous metal(loid) smelter soils can pose serious threats to the surrounding ecosystems, crop production, and human health. Bioremediation using microorganisms is a promising strategy for treating metal(loid)-contaminated soils. Here, a native microbial consortium with sulfate-reducing function (SRB1) enriched from smelter soils can tolerate exposures to mixtures of heavy metal(loid)s (e.g., As and Pb) or various organic flotation reagents (e.g., ethylthionocarbamate). The addition of Fe2+ greatly increased As3+ immobilization compared to treatment without Fe2+, with the immobilization efficiencies of 81.0% and 58.9%, respectively. Scanning electronic microscopy-energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed that the As3+ immobilizing activity was related to the formation of arsenic sulfides (AsS, As4S4, and As2S3) and sorption/co-precipitation of pyrite (FeS2). High-throughput 16S rRNA gene sequencing of SRB1 suggests that members of Clostridium, Desulfosporosinus, and Desulfovibrio genera play an important role in maintaining and stabilizing As3+ immobilization activity. Metal(loid)s immobilizing activity of SRB1 was not observed at high and toxic total exposure concentrations (220-1181 mg As/kg or 63-222 mg Pb/kg). However, at lower concentrations, SRB1 treatment decreased bioavailable fractions of As (9.0%) and Pb (28.6%) compared to without treatment. Results indicate that enriched native SRB1 consortia exhibited metal(loid) transformation capacities under non-toxic concentrations of metal(loid)s for future bioremediation strategies to decrease mixed metal(loid)s exposure from smelter polluted soils.

Photolysis of the Insensitive Explosive 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB).

The explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is of particular interest due to its extreme insensitivity to impact, shock and heat, while providing a good detonation velocity. To determine its fate under environmental conditions, TATB powder was irradiated with simulated sunlight and, in water, under UV light at 254 nm. The hydrolysis of particles submerged in neutral and alkaline solutions was also examined. We found that, by changing experimental conditions (e.g., light source, and mass and physical state of TATB), the intermediates and final products were slightly different. Mono-benzofurazan was the major transformation product in both irradiation systems. Two minor transformation products, the aci-nitro form of TATB and 3,5-diamino-2,4,6-trinitrophenol, were detected under solar light, while 1,3,5-triamino-2-nitroso-4,6-dinitrobenzene, 1,3,5-triamino-2,4-dinitrobenzene and mono-benzofuroxan were produced under UV light. The product identified as 3,5-diamino-2,4,6-trinitrophenol was identical to the one formed in the dark under alkaline conditions (pH 13) and in water incubated at either 50 °C or aged at ambient conditions. Interestingly, when only a few milligrams of TATB were irradiated with simulated sunlight, the aci-isomer and mono-benzofurazan derivative were detected; however, the hydrolysis product 3,5-diamino-2,4,6-trinitrophenol formed only much later in the absence of light. This suggests that the water released from TATB to form mono-benzofurazan was trapped in the interstitial space between the TATB layers and slowly hydrolyzed the relatively stable aci-nitro intermediate to 3,5-diamino-2,4,6-trinitrophenol. This environmentally relevant discovery provides data on the fate of TATB in surface environments exposed to sunlight, which can transform the insoluble substrate into more soluble and corrosive derivatives, such as 3,5-diamino-2,4,6-trinitrophenol, and that some hydrolytic transformation can continue even without light.

Photodegradation of bis(1H-tetrazol-5-yl)amine (H2BTA), a high nitrogen content tetrazole-based energetic compound in water.

Tetrazoles have wide industrial applications, notably in the pharmaceutical industry. Tetrazole derivatives such as bis(1H-tetrazol-5-yl)amine (H2BTA) have recently been considered by the defense industry as high nitrogen composite propellants. Photodegradation studies under solar simulating conditions showed that H2BTA was partially degraded in water, while it was completely degraded under UV light at 254 nm. When H2BTA (0.35 mM) was irradiated with simulated sunlight at pH 3.65, there was a 1-day lag phase before the chemical started to degrade, reaching 43.5% degradation after 7 d. However, when pH increased to 5.76, it degraded without lag phase, suggesting that an HBTA- anion was involved in the initial degradation of the chemical. 5-Aminotetrazole (5-AT) was identified as a final degradation product and N-(1H-tetrazol-5-yl)formamide(T(5 yl)FA) and 1H-tetrazol-5-ylcarbamic acid (T(5 yl)CA) as intermediate products. At λ = 254 nm, H2BTA disappeared rapidly, resulting in the loss of 94% after 65 min. 5-AT was detected together with several transient products including N-(1H-tetrazol-5-yl)carbamohydrazonic acid (T(5 yl)CHA) and T(5 yl)FA. Kinetic studies and products analysis revealed that H2BTA photodegraded via two initial routes. One route (a) marked by the initial loss of HN3 and another (b) marked by the initial loss of N2. Route a) was characteristics for irradiation with simulated sunlight; however, routes a) and b) proceeded simultaneously under UV light. 5-AT eventually degraded to presumably give N2 and/or HN3 under UV light. Understanding the photodegradation pathway of H2BTA under simulated sunlight can help in providing the basis for natural attenuation assessment of the chemical in contaminated aquatic environments.

LC-MS analysis data of intermediate products used to construct photodegradation pathways for bis(1H-tetrazol-5-yl)amine (H2BTA).

The photolysis of bis(1H-tetrazol-5-yl)amine (H2BTA) in water was carried out in SolSim and Rayonet photochemical reactors equipped with solar simulating and ultraviolet lamps, respectively. The intermediary degradation products were monitored and tentatively identified by liquid chromatography - mass spectrometry (LC-MS). A quadrupole time-of-flight mass spectrometer (QTOF) was used to measure the mass-to-charge ratio (m/z) of the deprotonated molecular ions ([M - H]-) using electrospray ionization in negative mode (ESI-), thus making it possible to determine the number of C, H, N and O in the molecules. Four major degradation products, namely N-(1H-tetrazol-5-yl)formamide (T(5yl)FA), 1H-tetrazol-5-ylcarbamic acid (T(5yl)CA), N-(1H-tetrazol-5-yl)carbamohydrazonic acid (T(5yl)CHA) and 1H-tetrazol-5-amine (5-AT), have been identified after solar simulated and UV irradiation. This dataset is supplementary to the research paper "Photodegradation of bis(1H-tetrazol-5-yl)amine (H2BTA), a high nitrogen content tetrazole-based energetic compound in water" [1].

Impacts of Continuous Inflow of Low Concentrations of Silver Nanoparticles on Biological Performance and Microbial Communities of Aerobic Heterotrophic Wastewater Biofilm.

Attached-growth wastewater processes are currently used in water resource recovery facilities (WRRFs) for required upgrades due to an increase in influent loading or to reach more stringent discharge criteria. Yet, the distribution and long-term inhibitory effects of silver nanoparticles (AgNPs) in attached-growth biological wastewater processes and their impact on involved microbial communities are poorly understood at relevant, low concentrations. Retention, distribution, and long-term inhibitory effect of polyvinylpyrrolidone (PVP)-coated AgNPs were evaluated in bench-scale moving bed biofilm reactors (MBBRs), achieving soluble organic matter removal, over a 64 day exposure to nominal concentrations of 10 and 100 µg/L. Distributions of continuously added AgNPs were characterized in the influent, bioreactor, and effluent of MBBRs using single particle inductively coupled plasma mass spectroscopy (spICP-MS). Aerobic heterotrophic biofilms in MBBRs demonstrated limited retention capacity for AgNPs over long-term exposure, with release of AgNPs, and Ag-rich biofilm sloughed from the carriers. Continuous exposure to both influent AgNP concentrations significantly decreased soluble chemical oxygen demand (SCOD) removal efficiency (11% to 31%) and reduced biofilm viability (8% to 30%). Specific activities of both intracellular dehydrogenase (DHA) and extracellular α-glucosidase (α-Glu) and protease (PRO) enzymes were significantly inhibited (8% to 39%) with an observed NP dose-dependent intracellular reactive oxygen species (ROS) production and shift in biofilm microbial community composition by day 64. Our results indicated that long-term exposure to AgNPs in biofilm processes at environmentally relevant concentrations can impact the treatment process stability and the quality of the discharged effluent.

Energetic contaminants inhibit plant litter decomposition in soil.

Individual effects of 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), nitroglycerin (NG), and 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) on litter decomposition, an essential biologically-mediated soil process, were assessed using Orchard grass (Dactylis glomerata) straw in Sassafras sandy loam (SSL) soil, which has physicochemical characteristics that support "very high" qualitative relative bioavailability for organic chemicals. Batches of SSL soil were separately amended with individual EMs or acetone carrier control. To quantify the decomposition rates, one straw cluster was harvested from a set of randomly selected replicate containers from within each treatment, after 1, 2, 3, 4, 6, and 8 months of exposure. Results showed that soil amended with 2,4-DNT or NG inhibited litter decomposition rates based on the median effective concentration (EC50) values of 1122 mg/kg and 860 mg/kg, respectively. Exposure to 2-ADNT, 4-ADNT or CL-20 amended soil did not significantly affect litter decomposition in SSL soil at ≥ 10,000 mg/kg. These ecotoxicological data will be helpful in identifying concentrations of EMs in soil that present an acceptable ecological risk for biologically-mediated soil processes.

Bioavailability and chronic toxicity of bismuth citrate to earthworm Eisenia andrei exposed to natural sandy soil.

The present study describes bioavailability and chronic effects of bismuth to earthworms Eisenia andrei using OECD reproduction test. Adult earthworms were exposed to natural sandy soil contaminated artificially by bismuth citrate. Average total concentrations of bismuth in soil recovered by HNO3 digestion ranged from 75 to 289mg/kg. Results indicate that bismuth decreased significantly all reproduction parameters of Eisenia andrei at concentrations ≥ 116mg/kg. However, number of hatched cocoons and number of juveniles seem to be more sensitive than total number of cocoons, as determined by IC50; i.e., 182, 123 and > 289mg/kg, respectively. Bismuth did not affect Eisenia andrei growth and survival, and had little effect on phagocytic efficiency of coelomocytes. The low immunotoxicity effect might be explained by the involvement of other mechanisms i.e. bismuth sequestered by metal-binding compounds. After 28 days of exposure bismuth concentrations in earthworms tissue increased with increasing bismuth concentrations in soil reaching a stationary state of 21.37mg/kg dry tissue for 243mg Bi/kg dry soil total content. Data indicate also that after 56 days of incubation the average fractions of bismuth available extracted by KNO3 aqueous solution in soil without earthworms varied from 0.0051 to 0.0229mg/kg, while in soil with earthworms bismuth concentration ranged between 0.310-1.347mg/kg dry soil. We presume that mucus and chelating agents produced by earthworms and by soil or/and earthworm gut microorganisms could explain this enhancement, as well as the role of dermal and ingestion routes of earthworms uptake to soil contaminant.

New Insights into the Photochemical Degradation of the Insensitive Munition Formulation IMX-101 in Water.

This study describes photolysis of the insensitive munition formulation IMX-101 [2,4-dinitroanisole (DNAN), NQ (nitroguanidine), and 3-nitro-1,2,4-triazol-5-one (NTO)] in aqueous solutions using a solar simulating photoreactor. Due to a large variance in the water solubility of the three constituents DNAN (276 mg L-1), NQ (5,000 mg L-1), and NTO (16,642 mg L-1), two solutions of IMX-101 were prepared: one with low concentration (109.3 mg L-1) and another with high concentration (2831 mg L-1). The degradation rate constants of DNAN, NQ, and NTO (0.137, 0.075, and 0.202 d-1, respectively) in the low concentration solution were lower than those of the individually photolyzed components (0.262, 1.181, and 0.349 d-1, respectively). In the high concentration solution, the molar loss of NTO was 4.3 times higher than that of NQ after 7 days of irradiation, although NQ was two times more concentrated and that NQ alone degraded faster than NTO. In addition to the known degradation products, DNAN removal in IMX-101 was accompanied by multiple productions of methoxydinitrophenols, which were not observed during photolysis of DNAN alone. One route for the formation of methoxydinitrophenols was suggested to involve photonitration of the DNAN photoproduct methoxynitrophenol during simultaneous photodenitration of NQ and NTO in IMX-101. Indeed, when DNAN was photolyzed in the presence of 15NO2-labeled explosive CL-20, we detected methoxydinitrophenols with an increase of 1 mass unit, indicating that denitration of DNAN and renitration of products simultaneously occurred. As was the case with DNAN, we found that guanidine, a primary degradation product of NQ, also underwent renitration in the presence of NTO and the photocatalyst TiO2. We concluded that the three constituents of IMX-101 can be photodegraded in surface water and that fate and primary degradation products of IMX-101 can be influenced by the interactions between the formulation ingredients and their degradation products.

The ecotoxicity of zinc and zinc-containing substances in soil with consideration of metal-moiety approaches and organometal complexes.

Within Canada, screening-level assessments for chemical substances are required to determine whether the substances pose a risk to human health and/or the environment, and as appropriate, risk management strategies. In response to the volume of metal and metal-containing substances, process efficiencies were introduced using a metal-moiety approach, whereby substances that contain a common metal moiety are assessed simultaneously as a group, with the moiety of concern consisting of the metal ion. However, for certain subgroups, such as organometals or organic metal salts, the organic moiety or parent substance may be of concern, rather than simply the metal ion. To further investigate the need for such additional consideration, certain substances were evaluated: zinc (Zn)-containing inorganic (Zn chloride [ZnCl2] and Zn oxide) and organic (organometal: Zn diethyldithiocarbamate [Zn(DDC)2 ] and organic metal salts (Zn stearate [ZnSt] and 4-chloro-2-nitrobenzenediazonium tetrachlorozincate [BCNZ]). The toxicity of the substances were assessed using plant (Trifolium pratense and Elymus lanceolatus) and soil invertebrate (Folsomia candida and Eisenia andrei) tests in a sandy soil. Effect measures were determined based on total metal and total parent analyses (for organic substances). In general, the inorganic Zn substances were less toxic than the organometals and organic metal salts, with 50% effective concentrations ranging from 11 to >5194 mg Zn kg-1 dry soil. The data demonstrate the necessity for alternate approaches in the assessment of organo-metal complexes, with the organic moieties or parent substances warranting consideration rather than the metal ion alone. In this instance, the organometals and organic metal salts were significantly more toxic than other test substances despite their low total Zn content. Environ Toxicol Chem 2017;36:3324-3332. © 2017 Crown in the Right of Canada. Published by Wiley Periodicals Inc. on behalf of SETAC.

Desalinated drinking water in the GCC countries - The need to address consumer perceptions.

The Gulf Cooperation Council (GCC) countries consist of Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates. These countries depend mainly on seawater desalination to meet their water needs. Although great emphasis is given to characterize desalinated water for its physicochemical and microbial properties, e.g. presence of metals, other organic contaminants and for bacteria, sensorial characteristics including smell, taste and color have not received the same attention. This is possibly attributed to the fact that inhabitants of GCC States do not use desalinated tap water for drinking consumption, rather they depend on locally produced or imported bottled water where color, taste and odor are not problematic. To address the consumer needs and perceptions of drinking desalinated water in GCC countries, water quality standards and guidelines, should respond to the public concern about other sensorial characteristics (organoleptic properties) including taste, odor, and trigeminal sensations. Often the root causes of color and smell in water are attributed to the presence of organic and inorganic contaminants and to bacterial growth which is frequently accompanied by the production of metabolites and byproducts that are obnoxious. The unpleasant sensorial problems associated with desalinated drinking tap water may constitute the driving force for most people in GCC countries to depend on bottled water. To encourage people in the GCC countries to consume desalinated tap water, it is essential that water testing include measurements of physicochemical properties, biofilm presence and organoleptic parameters to improve overall water quality. This review highlights the contribution of organoleptics for consumers of desalinated tap water. It extends water quality research to be addressed by standards for organoleptic parameters in desalinated drinking water. Accordingly, consumer awareness and outreach campaigns should be implemented to encourage people to drink tap water in the GCC countries.

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.

Effect of ozonation on anaerobic digestion sludge activity and viability.

The effect of ozonation of anaerobic digested sludge on methane production was studied as a means of increasing the capacity of municipal anaerobic digesters. Ozone doses ranging from 0 to 192 mg O3/g sludge COD were evaluated in batch tests with a bench scale ozonation unit. Ozonation initially, and temporarily, reduced biomass viability and acetoclastic methanogenic activity, resulting in an initial lag phase ranging from 0.8 to 10 days. Following this lag phase, ozonation enhanced methane production with an optimal methane yield attained at 86 mg O3/g COD. Under these conditions, the yield of methane and the rate of its formation were 52% and 95% higher, respectively, than those factors measured without ozonation. A required optimal ozone dose could be feasible to improve the anaerobic digestion performance by increasing the methane production potential with a minimum impact on microbial activity; thus, an optimal ozone dose would enable an increase in the capacity of anaerobic digesters.

Cysteamine broadly improves the anti-plasmodial activity of artemisinins against murine blood stage and cerebral malaria.

BACKGROUND: The potential emergence and spread of resistance to artemisinins in the Plasmodium falciparum malaria parasite constitutes a major global health threat. Hence, improving the efficacy of artemisinins and of artemisinin-based combination therapy (ACT) represents a major short-term goal in the global fight against malaria. Mice defective in the enzyme pantetheinase (Vnn3) show increased susceptibility to blood-stage malaria (increased parasitaemia, reduced survival), and supplementation of Vnn3 mutants with the reaction product of pantetheinase, cysteamine, corrects in part the malaria-susceptibility phenotype of the mutants. Cysteamine (Cys) is a small, naturally occurring amino-thiol that has very low toxicity in vivo and is approved for clinical use in the life-long treatment of the kidney disorder nephropathic cystinosis. METHODS: The ability of Cys to improve the anti-plasmodial activity of different clinically used artemisinins was tested. The effect of different CYS/ART combinations on malarial phenotypes (parasite blood-stage replication, overall and survival from lethal infection) was assessed in a series of in vivo experiments using Plasmodium strains that induce either blood-stage (Plasmodium chabaudi AS) or cerebral disease (Plasmodium berghei ANKA). This was also evaluated in an ex vivo experimental protocol that directly assesses the effect of such drug combinations on the viability of Plasmodium parasites, as measured by the ability of tested parasites to induce a productive infection in vivo in otherwise naïve animals. RESULTS: Cys is found to potentiate the anti-plasmodial activity of artesunate, artemether, and arteether, towards the blood-stage malaria parasite P. chabaudi AS. Ex vivo experiments, indicate that potentiation of the anti-plasmodial activity of artemisinins by Cys is direct and does not require the presence of host factors. In addition, potentiation occurs at sub-optimal concentrations of artemisinins and Cys that on their own have little or no effect on parasite growth. Cys also dramatically enhances the efficacy and protective effect of artemisinins against cerebral malaria induced by infection with the P. berghei ANKA parasite. CONCLUSION: These findings indicate that inclusion of Cys in current formulations of ACT, or its use as adjunct therapy could improve the anti-plasmodial activity of artemisinin, decrease mortality in cerebral malaria patients, and prevent or delay the development and spread of artemisinin resistance.

Development of a sensitive in vitro assay to quantify the biological activity of pro-inflammatory phorbol esters in Jatropha oil.

New health safety concerns may arise from the increasing production and use of Jatropha oil, a biodiesel feedstock that also contains toxic, pro-inflammatory, and co-carcinogenic phorbol esters. Based on the exceptional sensitivity of Madin-Darby canine kidney (MDCK) cells to the model phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a robust bioassay was developed to quantify the biological activity of Jatropha phorbol esters directly in oil, without sample extraction. We first verified that the characteristic response of MDCK cells to TPA was also observed following direct exposure to phorbol esters in Jatropha oil. We further confirmed that similarly to TPA, Jatropha oil's phorbol esters can activate protein kinase C (PKC). We then assessed the transcriptional response of MDCK cells to Jatropha oil exposure by measuring the expression of cyclooxygenase-2 (COX-2), a gene involved in inflammatory processes which is strongly upregulated following PKC activation. Based on the parameterization of a TPA dose-response curve, the transcriptional response of MDCK cells to Jatropha oil exposure was expressed in term of TPA toxic equivalent (TEQ), a convenient metric to report the inflammatory potential of complex mixtures. The sensitive bioassay described in this manuscript may prove useful for risk assessment, as it provides a quantitative method and a convenient metric to report the inflammatory potential of phorbol esters in Jatropha oil. This bioassay may also be adapted for the detection of bioactive phorbol esters in other matrices.

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.

Joint photomicrobial process for the degradation of the insensitive munition N-guanylurea-dinitramide (FOX-12).

N-Guanylurea-dinitramide (FOX-12) is a very insensitive energetic material intended to be used in the composition of next-generation insensitive munitions. To help predict the environmental behavior and fate of FOX-12, we conducted a study to determine its photodegradability and biodegradability. When dissolved in water, FOX-12, a guanylurea-dinitramide salt, also named GUDN, dissociated instantly to produce the dinitramide moiety and guanylurea, as demonstrated by high-performance liquid chromatography (HPLC) analysis. When an aqueous solution of FOX-12 was subjected to photolysis using a solar-simulated photoreactor, we found a rapid removal of the dinitramide with concurrent formation of N2O, NO2(-), and NO3(-). The second component, guanylurea, was photostable. However, when FOX-12 was incubated aerobically with the soil isolate Variovorax strain VC1 and protected from light, the dinitramide component of FOX-12 was recalcitrant but guanylurea degraded effectively to ammonia, guanidine, and presumably CO2. When FOX-12 was incubated with strain VC1 in the presence of light, both components of FOX-12 degraded, giving similar products to those described above. We concluded that the new insensitive explosive FOX-12 can be effectively degraded by a joint photomicrobial process and, therefore, should not cause persistent contamination of surface waters.

Sorption of 2,4-dinitroanisole (DNAN) on lignin.

The present study describes the use of two commercially available lignins, namely, alkali and organosolv lignin, for the removal of 2,4-dinitroanisole (DNAN), a chemical widely used by the military and the dye industry, from water. Sorption of DNAN on both lignins reached equilibrium within 10 hr and followed pseudo second-order kinetics with sorption being faster with alkali than with organosolv lignin, i.e. k2 10.3 and 0.3 g/(mg x hr), respectively. In a separate study we investigated sorption of DNAN between 10 and 40 degrees C and found that the removal of DNAN by organosolv lignin increased from 0.8 to 7.5 mg/g but reduced slightly from 8.5 to 7.6 mg/g in the case of alkali lignin. Sorption isotherms for either alkali or organosolv lignin best fitted Freundlich equation with enthalpy of formation, deltaH0 equaled to 14 or 80 kJ/mol. To help understand DNAN sorption mechanisms we characterized the two lignins by elemental analysis, BET nitrogen adsorption-desorption and 31P NMR. Variations in elemental compositions between the two lignins indicated that alkali lignin should have more sites (O- and S-containing functionalities) for H-bonding. The BET surface area and calculated total pore volume of alkali lignin were almost 10 times greater than that of organosolv lignin suggesting that alkali lignin should provide more sites for sorption. 31P NMR showed that organosolv lignin contains more phenolic -OH groups than alkali lignin, i.e., 70% and 45%, respectively. The variations in the type of OH groups between the two lignins might have affected the strength of H-bonding between DNAN and the type of lignin used.

Biodegradation of RDX nitroso products MNX and TNX by cytochrome P450 XplA.

Anaerobic transformation of the explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) by microorganisms involves sequential reduction of N-NO(2) to the corresponding N-NO groups resulting in the initial formation of MNX (hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine). MNX is further reduced to the dinitroso (DNX) and trinitroso (TNX) derivatives. In this paper, we describe the degradation of MNX and TNX by the unusual cytochrome P450 XplA that mediates metabolism of RDX in Rhodococcus rhodochrous strain 11Y. XplA is known to degrade RDX under aerobic and anaerobic conditions, and, in the present study, was found able to degrade MNX to give similar products distribution including NO(2)(-), NO(3)(-), N(2)O, and HCHO but with varying stoichiometric ratio, that is, 2.06, 0.33, 0.33, 1.18, and 1.52, 0.15, 1.04, 2.06, respectively. In addition, the ring cleavage product 4-nitro-2,4,-diazabutanal (NDAB) and a trace amount of another intermediate with a [M-H](-) at 102 Da, identified as ONNHCH(2)NHCHO (NO-NDAB), were detected mostly under aerobic conditions. Interestingly, degradation of TNX was observed only under anaerobic conditions in the presence of RDX and/or MNX. When we incubated RDX and its nitroso derivatives with XplA, we found that successive replacement of N-NO(2) by N-NO slowed the removal rate of the chemicals with degradation rates in the order RDX > MNX > DNX, suggesting that denitration was mainly responsible for initiating cyclic nitroamines degradation by XplA. This study revealed that XplA preferentially cleaved the N-NO(2) over the N-NO linkages, but could nevertheless degrade all three nitroso derivatives, demonstrating the potential for complete RDX removal in explosives-contaminated sites.

Aerobic mineralization of nitroguanidine by Variovorax strain VC1 isolated from soil.

Nitroguanidine (NQ) is an energetic material that is used as a key ingredient of triple-base propellants and is currently being considered as a TNT replacement in explosive formulations. NQ was efficiently degraded in aerobic microcosms when a carbon source was added. NQ persisted in unamended microcosms or under anaerobic conditions. An aerobic NQ-degrading bacterium, Variovorax strain VC1, was isolated from soil microcosms containing NQ as the sole nitrogen source. NQ degradation was inhibited in the presence of a more favorable source of nitrogen. Resting cells of VC1 degraded NQ effectively (54 µmol h(-1) g(-1) protein) giving NH(3) (50.0%), nitrous oxide (N(2)O) (48.5%) and CO(2) (100%). Disappearance of NQ was accompanied by the formation of a key intermediate product that we identified as nitrourea by comparison with a reference material. Nitrourea is unstable in water and suffered both biotic and abiotic decomposition to eventually give NH(3), N(2)O, and CO(2). However, we were unable to detect urea. Based on products distribution and reaction stoichiometry, we suggested that degradation of NQ, O(2)NN═C(NH(2))(2), might involve initial enzymatic hydroxylation of the imine, -C═N- bond, leading first to the formation of the unstable α-hydroxynitroamine intermediate, O(2)NNHC(OH)(NH(2))(2), whose decomposition in water should lead to the formation of NH(3), N(2)O, and CO(2). NQ biodegradation was induced by nitroguanidine itself, L-arginine, and creatinine, all being iminic compounds containing a guanidine group. This first description of NQ mineralization by a bacterial isolate demonstrates the potential for efficient microbial remediation of NQ in soil.

Involvement of cytochrome c CymA in the anaerobic metabolism of RDX by Shewanella oneidensis MR-1.

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a cyclic nitramine explosive commonly used for military applications that is responsible for severe soil and groundwater contamination. In this study, Shewanella oneidensis MR-1 was shown to efficiently degrade RDX anaerobically (3.5 µmol·h(-1)·(g protein)(-1)) via two initial routes: (1) sequential N-NO(2) reductions to the corresponding nitroso (N-NO) derivatives (94% of initial RDX degradation) and (2) denitration followed by ring cleavage. To identify genes involved in the anaerobic metabolism of RDX, a library of ~2500 mutants of MR-1 was constructed by random transposon mutagenesis and screened for mutants with a reduced ability to degrade RDX compared with the wild type. An RDX-defective mutant (C9) was isolated that had the transposon inserted in the c-type cytochrome gene cymA. C9 transformed RDX at ~10% of the wild-type rate, with degradation occurring mostly via early ring cleavage caused by initial denitration leading to the formation of methylenedinitramine, 4-nitro-2,4-diazabutanal, formaldehyde, nitrous oxide, and ammonia. Genetic complementation of mutant C9 restored the wild-type phenotype, providing evidence that electron transport components have a role in the anaerobic reduction of RDX by MR-1.