Insensitive high-explosive compounds like 3-nitro-1,2,4-triazol-5-one (NTO) can contaminate soil and water at military sites. This study compared the ability of synthesized and commercial MnO2 materials to degrade the reduced daughter product of NTO, 3-amino-1,2,4-triazol-5-one (ATO), and characterized the solid-phase transformations that govern the products formed in continuousflow reactors. Synthetic birnessite degraded ATO fastest (k = 15.0 h- 1) but had poor hydraulic characteristics. Whereas the commercial material Pro-OXTM had a good degradation rate (k = 0.64 h- 1) and its granular morphology ensured good hydraulic performance. Results show ATO is oxidized by MnO2-type minerals to benign end-products (urea, NH4+, CO2(g), and N2(g)). Spent Mn oxides were fully regenerated using KMnO4 or NaOCl, restoring or even surpassing their original oxidative capacity. Further investigation of Pro-OX in packed-bed columns under a simulated wastewater treatment regime (1 mM ATO, empty bed contact time [EBCT]= 1 h) showed that the column reached breakthrough (C/C0 >= 0.05) at 2400 pore volumes (PVs), with a capacity to degrade 190 mg ATO g- 1. Under accelerated groundwater flow regime (0.1 mM ATO, EBCT= 24 h), the reactor removed ATO effectively for the duration of operation (660 PVs). After reacting with ATO, the Mn oxide material initially dominated by Mn(IV) (e.g., pyrolusite, ramsdellite, todorokite) was converted to Mn(III) minerals (e.g., groutite, manganite) and soluble Mn(II) (recovered in effluent) indicating reduction of MnO2 concurrent with ATO oxidation. Collectively, these findings demonstrate that MnO2 is a promising material for application in permeable reactive barriers or packed-bed filters to treat waters contaminated with ATO at military sites.

The insensitive munitions compound nitroguanidine (NQ) is used by the U.S. Army to avoid unintended explosions. However, NQ also represents an emerging contaminant whose environmental emissions can cause toxicity toward aquatic organisms, indicating the need for effective remediation strategies. Thus, we investigated the feasibility of treating water contaminated with NQ in continuous-flow columns packed with zero-valent iron (ZVI) or iron sulfide (FeS). Initially, the impact of pH on NQ transformation by ZVI or FeS was evaluated in batch experiments. The pseudo first-order rate constant for NQ transformation (k1, NQ) by ZVI was 8–10 times higher at pH 3.0 compared to pH 5.5 and 7.0, whereas similar k1, NQ values were obtained for FeS at pH 5.5–10.0. Based on these findings, the influent pH fed to the ZVI- and FeS-packed columns was adjusted to 3.0 and 5.5, respectively. Both reactors transformed NQ into nitrosoguanidine (NsoQ). Further transformation of NsoQ by ZVI produced aminoguanidine, guanidine, and cyanamide, whereas NsoQ transformation by FeS produced guanidine, ammonium, and traces of urea. ZVI outperformed FeS as a reactive material to remove NQ. The ZVI-packed column effectively removed NQ below detection even after 45 d of operation (490 pore volumes, PV). In contrast, NQ breakthrough (removal efficiency <85%) was observed after 18 d (180 PV) in the FeS-packed column. The high NQ removal efficiency and long service life of the ZVI-packed column (>490 PV) suggest that the technology is a promising approach for NQ treatment in packed-bed reactors and in situ remediation.

Environments with elevated antimony (Sb) levels often result from industrial and mining activities, causing harm to ecosystems due to the inherent toxicity. Traditional treatments aim to eliminate or decrease Sb toxicity, yet they often result in the generation of secondary pollution. This study explores a novel approach for enhancing biological sulfate-reduction by biochar addition to cope with high Sb concentrations. Moreover, this research postulates sulfate-reduction bioprocess as a feasible alternative to obtain valuable antimony sulfide. The findings indicate that sulfate reduction effectively removes antimony, particularly at high concentrations, using a nonspecialized inoculum. Biochar plays a pivotal role in enhancing sulfate-reduction rates, reducing lag-phase periods, and enriching the microorganisms responsible for sulfate reduction. Interestingly, lower concentrations of Sb(III) (5-40 mg/L) and Sb(V) (5-100 mg/L) exhibited a lower removal percentage compared to higher concentrations of Sb(III) (80-500 mg/L) and Sb(V) (200-1000 mg/L). This phenomenon was attributed to the excess sulfide hindering the equilibrium of the first-order reaction at lower concentrations, while at higher concentrations, the reaction proceeded more rapidly. A combination of biochemical and physicochemical reactions facilitated the removal of >95 % Sb(III) and >97 % Sb(V) using biochar. Furthermore, various taxa displayed a significant logarithmic rate of change in their abundance, influenced by the application of biochar or the introduction of distinct antimony species. The biogenic sulfide generated through the sulfate reduction process reacted with the Sb species, resulting in the precipitation of stibnite (Sb2S3), Na3SbS3, and Na3SbS4. These precipitates are considered crucial precursors in electronic applications. In conclusion, this study constitutes a pioneering exploration of elevated antimony (Sb) concentrations under sulfate-reducing conditions, significantly contributing to an advancement of knowledge in the application of biological processes.

The need for effective technologies to remediate the insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) is emerging due to the increasing use by the US Army and environmental concerns about the toxicity and aqueous mobility of NTO. Reductive treatment is essential for the complete degradation of NTO to environmentally safe products. The objective of this study is to investigate the feasibility of applying zero-valent iron (ZVI) in a continuous-flow packed bed reactor as an effective NTO remediation technology. The ZVI-packed columns treated an acidic influent (pH 3.0) or a circumneutral influent (pH 6.0) for 6 months (ca. 11,000 pore volumes, PVs). Both columns effectively reduced NTO to the amine product, 3-amino-1,2,4-triazol-5-one (ATO). The column treating the pH-3.0 influent exhibited prolonged longevity in reducing NTO, treating 11-fold more PVs than the column treating pH-6.0 influent until the breakthrough point (defined as when 85% of NTO was removed). The exhausted columns (defined as when only 10% of NTO was removed) regained the NTO reducing capacity by reactivation using 1 M HCl, fully removing NTO. After the experiment, solid-phase analysis of the packed-bed material showed that ZVI was oxidized to iron (oxyhydr)oxide minerals such as magnetite, lepidocrocite, and goethite during NTO treatment. This is the first report on the reduction of NTO and the concomitant oxidation of ZVI in continuous-flow column experiments. The evidence indicates that treatment in a ZVI-packed bed reactor is an effective approach for the removal of NTO.

Nitroguanidine (NQ) is a constituent of gas generators for automobile airbags, smokeless pyrotechnics, insecticides, propellants, and new insensitive munitions formulations applied by the military. During its manufacture and use, NQ can easily spread in soils, ground, and surface waters due to its high aqueous solubility. Very little is known about the microbial biotransformation of NQ. This study aimed to elucidate important mechanisms operating during NQ anaerobic biotransformation. To achieve this goal, we developed an anaerobic enrichment culture able to reduce NQ to nitrosoguanidine (NsoQ), which was further abiotically transformed to cyanamide. Effective electron donors for NQ biotransformation were lactate and, to a lesser extent, pyruvate. The results demonstrate that the enrichment process selected a sulfate-reducing culture that utilized lactate as its electron donor and sulfate as its electron acceptor while competing with NQ as an electron sink. A unique property of the culture was its requirement for exogenous nitrogen (e.g., from yeast extract or NH4Cl) for NQ biotransformation since NQ itself did not serve as a nitrogen source. The main phylogenetic groups associated with the NQ-reducing culture were sulfate-reducing and fermentative bacteria, namely Cupidesulfovibrio oxamicus (63.1% relative abundance), Dendrosporobacter spp. (12.0%), and Raoultibacter massiliens (10.9%). The molecular ecology results corresponded to measurable physiological properties of the most abundant members. The results establish the conditions for NQ anaerobic biotransformation and the microbial community associated with the process, improving our present comprehension of NQ environmental fate and assisting the development of NQ remediation strategies.

The military is switching over to insensitive munitions compounds (IMCs) to avoid unintentional detonations during handling and use of explosives. 3-nitro-1,2,4-triazol-5-one (NTO) is an important component of IMCs. NTO may contaminate the subsurface due to its high aqueous solubility. Thus, there is a need to develop remediation technologies for the treatment of NTO-containing (waste) water. This study demonstrated that zero-valent iron (ZVI) reductively transformed NTO to its daughter product, 3-amino-1,2,4-triazol-5-one. The pseudo first-rate constant (k1) of NTO reduction by micron-sized ZVI at pH 3 was 192.6 h−1. Kinetic degradation experiments performed at different pH values showed that ZVI did not effectively reduce NTO at pH 6 (k1 = 0.6 h−1) or higher. The rapid NTO reduction in acidic conditions may be due to dissolution of iron precipitates on the ZVI surface. Additional experiments were conducted to assess the effectiveness of various depassivating pretreatments with deionized water, acetic acid, hydrochloric acid, or bicarbonate. Treatment with 1 M HCl for 15 min was the most effective depassivation method for a ZVI material containing a thick passivating layer (ca. 880 nm), achieving 84.0

Antimony (Sb) is a toxic and carcinogenic metalloid that can be present in contaminated water generated by mining operations and other industrial activities. Dissimilatory Sb(V) reduction to Sb(III) under anaerobic conditions by prokaryotic microbial communities has been reported; however, the fate of antimony in anaerobic wastewater treatment systems is poorly understood. This study investigated the potential of six different inoculum sources to reduce Sb(V) under anaerobic conditions and correlated the Sb(V) reduction rate with the microbial community composition. Microbial reduction of Sb(V) to Sb(III) by all the inoculum sources tested was observed in anaerobic incubations using hydrogen as an electron donor after a month. The highest reduction rate observed was 12.5 mg Sb per gram of volatile suspended solids per day. In some inocula, not only Sb reduction was observed, but also a decrease in the total Sb concentration, suggesting the precipitation of Sb(III). Metagenomic analysis revealed high variability in the community diversity associated with the origin of the inoculum. For the family taxonomic category, the three inocula that showed the highest Sb reduction potential were characterized by the presence of the Bacillaceae family.

3-Nitro-1,2,4-triazol-5-one (NTO) is an ingredient of new safer-to-handle military insensitive munitions formulations. NTO can be microbially reduced to 3-amino-1,2,4-triazol-5-one (ATO) under anaerobic conditions if an electron donor is available. Conversely, ATO can undergo aerobic biodegradation. Previously, our research group developed an anaerobic enrichment culture that reduces NTO to ATO. A second culture could aerobically mineralize ATO. This study aimed to combine anaerobic/aerobic conditions within a down-flow perlite/soil column for simultaneous NTO reduction and ATO oxidation. Acetate biostimulation was investigated to promote oxygen depletion and create anaerobic micro-niches for NTO reduction, whereas perlite increased soil porosity and oxygen convection, allowing ATO oxidation. Two columns packed with a perlite/soil mixture (70:30, wet wt.%) or 100% perlite were operated aerobically and inoculated with the NTO- and ATO-degrading cultures. Initially, the influent consisted of ∼280 μM ATO, and after 30 days, the feeding was switched to ∼260 μM NTO and ∼250 μM acetate. By progressively increasing acetate from 250 to 4000 μM, the NTO removal gradually improved in both columns. The perlite/soil column reached a 100% NTO removal after 4000 μM acetate was supplemented. Additionally, there was no ATO accumulation, and inorganic nitrogen was produced, indicating ATO mineralization. Although NH4+ was produced following ATO oxidation, most nitrogen was recovered as NO3− likely via nitrification reactions. Microbial community analysis revealed that phylotypes hosted in the enrichment cultures specialized in NTO reduction (e.g., Geobacter) and ATO oxidation (e.g., Hydrogenophaga, Ramlibacter, Terrimonas, and Pseudomonas) were established in the columns. Besides, the predominant genera (Azohydromonas, Zoogloea, and Azospirillum) are linked to nitrogen cycling by performing nitrogen fixation, NO3− reduction, and nitroaromatics degradation. This study applied a bulking agent (perlite) and acetate biostimulation to achieve simultaneous NTO reduction and ATO oxidation in a single column. Such a strategy can assist with real-world applications of NTO and ATO biodegradation mechanisms.

Antimony (Sb) is a toxic and carcinogenic metalloid that can be present in contaminated water generated by mining operations and other industrial activities. The toxicity of Sb (III) and Sb (V) to aerobic microorganisms remains limited and unexplored for anaerobic microorganisms involved in hydrogen (H2) and methane (CH4) production. This study aimed to evaluate the toxicity of Sb (III) and Sb (V) upon aerobic and anaerobic microorganisms important in biological wastewater treatment systems. Sb (III) was more toxic than Sb (V) independently of the test and environment evaluated. Under aerobic conditions maintained in the Microtox assay, Sb (V) was not toxic to Allivibrio fischeri at concentrations as high as 500 mg/L, whereas Sb (III) caused just over 50% inhibition at concentration of 250 mg/L after 5 min of exposure. In the respirometry test, for the specific oxygen uptake rate, the concentrations of Sb (III) and Sb (V) displaying 50% inhibition were 0.09 and 56.2 mg/L, respectively. Under anaerobic conditions, exposure to Sb (III) and Sb (V) led to a decrease in microorganisms activity of fermentative and methanogenic processes. The results confirm that the microbial toxicity of Sb depends on its speciation and Sb (III) displays a significantly higher inhibitory potential than Sb (V) in both aerobic and anaerobic environments.

Aryl-iodonium salts are utilized as photoacid generators (PAGs) in semiconductor photolithography and other photo-initiated manufacturing processes. Despite their utilization and suspected toxicity, the fate of these compounds within the perimeter of semiconductor fabrication plants is inadequately understood; the identification of photolithography products is still needed for a comprehensive environmental impact assessment. This study investigated the photolytic transformation of a representative iodonium PAG cation, bis-(4-tert-butyl phenyl)-iodonium, under conditions simulating industrial photolithography. Under 254-nm irradiation, bis-(4-tert-butyl phenyl)-iodonium reacted rapidly with a photolytic half-life of 39.2 s; different counter ions or solvents did not impact the degradation kinetics. At a semiconductor photolithography-relevant UV dosage of 25 mJ cm−2, 33% of bis-(4-tert-butyl phenyl)-iodonium was estimated to be transformed. Six aromatic/hydrophobic photoproducts were identified utilizing a combination of HPLC–DAD and GC–MS. Selected photoproducts such as tert-butyl benzene and tert-butyl iodobenzene had remarkably higher acute microbial toxicity toward bacterium Aliivibrio fischeri compared to bis-(4-tert-butyl phenyl)-iodonium. Octanol–water partition coefficients estimated using the Estimation Programs Interface Suite™ indicated that the photoproducts were substantially more hydrophobic than the parent compound. The results fill a critical data gap hindering the environmental impact assessment of iodonium PAGs and provide clues on potential management strategies for both iodonium compounds and their photoproducts.

Polyaniline (PANI) and other amine-containing materials have recently been reported as high-affinity, selective adsorbents for per- and polyfluoroalkyl substances (PFAS) remediation, with surface area normalized adsorbed mass significantly exceeding that of granular activated carbon. However, most of these materials have low specific surface area (SSA), suggesting that increasing SSA could result in further enhancement of their ability to sequester PFAS. Herein, we employed a crosslinking method with paraformaldehyde (PFA) to improve the SSA and porous structure of PANI. Several characterization techniques, including elemental composition, N-2 adsorption-desorption, zeta potential titration, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy, confirmed the success of the crosslinking process. The characterization results demonstrated that crosslinking was a very effective method to synthesize hyper-crosslinked, permanently porous polymers with high SSA (490.3 m(2) g(-1) for crosslinked PANI_PFA_2.4 compared to 26.3 m(2) g(-1) for original PANI). Most importantly, crosslinked PANI presented rapid kinetics and high removal efficiency toward perfluorooctanoic acid (PFOA) at environmentally relevant concentrations, the maximum adsorption capacity of crosslinked PANI_PFA_2.4 (98.4 mg g(-1)) for PFOA remarkably exceeded that of PANI (41.1 mg g(-1)). Both PANI and crosslinked PANI showed higher sequestration for perfluorosulfonates than their corresponding perfluorocarboxylates, and adsorption increased with increasing fluorocarbon chain length. However, PANI_PFA_2.4 showed lower removal efficiency of multicomponent PFAS mixtures, relative to PANI, which is likely due to competitive PFAS adsorption and to the formation of narrow pores during crosslinking that were easily blocked by preferentially adsorbed long-chain PFAS molecules. The results in this study indicate that crosslinked PANI polymers are promising adsorbents for in situ remediation of PFAS-contaminated groundwater.

Remediation of water contaminated by per-and polyfluoroalkyl substances (PFAS) relies heavily on separation techniques. This work tested the adsorption of seven PFAS (including short-chain congeners) on polyaniline-derived polymers under simulated environmentally relevant conditions including a range of natural organic matter (NOM) and ion concentrations, mineral anionic and cationic species, and multi-component PFAS solutions. Results were benchmarked against commercial activated carbon and polymeric resin. The polymers poly-o-toluidine and polyaniline exhibited high PFAS removal efficiencies of over 98 and 75% of each PFAS in the compound mixture, respectively. The adsorption capacity of the polymers was comparable to that of activated carbon on a mass basis at low equilibrium concentrations (< 50 mu g L-1) and higher when adsorption was based on the surface area for the tested concentration range (1-1000 mu g L-1). The tailored polymers performed similar to or better than the activated carbon and resin in the presence of elevated NOM. In addition, the fast PFOA adsorption kinetics (6.20 and 4.92 g mg(-1) h(-1) for poly-o-toluidine and polyaniline, respectively), the low desorption of adsorbed PFAS to aqueous media, and the facile regeneration using methanol with 10 g kg(-1) NaCl at ambient temperature make these polymers ideal for flow-through sorption technology.

Nitroguanidine (NQ) is an emerging contaminant being used by the military as a constituent of new insensitive munitions. NQ is also used in rocket propellants, smokeless pyrotechnics, and vehicle restraint systems. Its un-controlled transformation in the environment can generate toxic and potentially mutagenic products, posing hazards that need to be remediated. NQ transformation has only been investigated to a limited extent. Thus, it is crucial to expand the narrow spectrum of NQ remediation strategies and understand its transformation pathways and end products. Iron-based reactive minerals should be investigated for NQ treatment because they are suc-cessfully used in existing technologies, such as permeable reactive barriers, for treating a wide range of organic pollutants. This study tested the ability of micron-sized zero-valent iron (m-ZVI), mackinawite, and commercial FeS, to transform NQ under anoxic conditions. NQ transformation followed pseudo-first-order kinetics. The re-action rate constants decreased as follows: commercial FeS > mackinawite > m-ZVI. For the assessed minerals, the NQ transformation started with the reduction of the nitro group forming nitrosoguanidine (NsoQ). Then, aminoguanidine (AQ) was accumulated during the reaction of NQ with m-ZVI, accounting for 86% of the ni-trogen mass recovery. When NQ was reacted with commercial FeS, 45% and 20% of nitrogen were recovered as AQ and guanidine, respectively, after 24 h. Nonetheless, NsoQ persisted, contributing to the N-balance. When mackinawite was present, NsoQ disappeared, but AQ was not detected, and guanidine accounted for 11% of the nitrogen recovery. AQ was ultimately transformed into cyanamide, whose dimerization triggered the formation of cyanoguanidine. Alternatively, NsoQ was transformed into guanidine, which reacted with cyanamide to form biguanide. This is the first report systematically investigating the NQ transformation by different iron-based reactive minerals. The evidence indicates that these minerals are attractive alternatives for developing NQ remediation strategies.

Ultra-hydrophilic perand polyfluorinated sulfonates (PFSA) are increasingly scrutinized in recent years due to their ubiquitous occurrence, persistence, and aqueous mobility in the environment, yet analysis remains a challenge. This study developed methods for the analysis of trifluoromethanesulfonate, perfluorobutanesulfonate, 10-camphorsulfonate, and a di-fluorinated sulfonate utilizing mixed-mode liquid chromatography, where all analytes were adequately retained and separated. Chromatography and electrospray ionization parameters were optimized; instrumental limits of quantification for the anionic target analytes were in the range of 4.3 - 16.1 ng L-1. Solid phase extraction (SPE) methods were developed using Oasis WAX cartridges; SPE recoveries for the analytes ranged from 86% to 125%. Salinity and total organic carbon both impaired the SPE performance to different extents, depending on the respective analyte. Utilizing widely accessible instrumentation and materials, this is a single method to simultaneously analyze conceivably the most hydrophilic PFAS chemical, i.e., trifluoromethanesulfonate, and moderately hydrophobic PFSAs. (C) 2022 Published by Elsevier B.V.

Insensitive munitions compounds (IMCs), such as 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO), are replacing conventional explosives in munitions formulations. Manufacture and use of IMCs generate waste streams in manufacturing plants and load/assemble/pack facilities. There is a lack of practical experience in executing biodegradation strategies to treat IMCs waste streams. This study establishes a proof-of-concept that bacterial consortia can be designed to mineralize IMCs and co-occurring nitroaromatics in waste streams. First, DNAN, 4-nitroanisole (4-NA), and 4-chloronitrobenzene (4-CNB) in a synthetic DNAN-manufacturing waste stream were biodegraded using an aerobic fluidized-bed reactor (FBR) inoculated with Nocardioides sp. JS 1661 (DNAN degrader), Rhodococcus sp. JS 3073 (4-NA degrader), and Comamonadaceae sp. LW1 (4-CNB degrader). No biodegradation was detected when the FBR was operated under anoxic conditions. Second, DNAN and NTO were biodegraded in a synthetic load/assemble/pack waste stream during a sequential treatment comprising: (i) aerobic DNAN biodegradation in the FBR; (ii) anaerobic NTO biotransformation to 3-amino-1,2,4-triazol-5-one (ATO) by an NTO-respiring enrichment; and (iii) aerobic ATO mineralization by an ATO-oxidizing enrichment. Complete biodegradation relied on switching redox conditions. The results provide the basis for designing consortia to treat mixtures of IMCs and related waste products by incorporating microbes with the required catabolic capabilities.

Azoles are a class of nitrogen-containing heterocyclic compounds that are widely used as metal corrosion inhibitors in different industrial processes and consumer products. These compounds are severely inhibitory towards microorganisms responsible for nitrification and can impair the efficiency of biological nitrogen removal in wastewater treatment plants. This study assessed the effect of chemical structure on the toxicity of simple azole compounds towards microbial nitrification with the aim of identifying substitution patterns leading to decreased inhibition. Nitrification inhibition by the widely used azoles, pyrazole and 1,2,4-triazole, and several of their derivatives with dimethyl-, diethyl-, carbonyl-, amino substituent groups was studied. The results indicated that, while pyrazole and 1,2,4-triazole were severely inhibitory towards nitrification, addition of dimethyl-and diethyl-substituents greatly lowered the toxicity response of these compounds. The fifty percent inhibition concentrations (IC50) of pyrazole and 1,2,4-triazole were very low, 0.07 and 0.11 mg L-1, respectively, indicating a high level of inhibition. In contrast, nitrification inhibition by the dimethyl- and diethyl -substituted azoles was at least 30-700 times lower compared to the unsubstituted parent compounds, and in the best case, 3,5-diethyltriazole was found to be completely non-toxic. Preliminary evaluation of the corrosion inhibition efficiency of the alkyl-substituted azole compounds under alkaline conditions was conducted electrochemically. All the azoles tested were able to inhibit copper corrosion to a significant extent. For the pyrazoles, the corrosion inhibition performance improved with the addition of dimethyl-and diethyl-substituents. The inhibition efficiency by pyrazole, 3,5-dimethylpyrazole and 3,5-diethylpyrazole was 71.5, 77.6 and 85.0%, respectively, with respect to the control with no inhibitor. In the case of triazoles, the corrosion inhibition efficiency was slightly lower for the alkyl-substituted triazoles (77.7% for 3,5-dimethyl-1,2,4-triazole and 82.9% for 3,5-diethyl-1,2,4-triazole) than for the unsubstituted 1,2,4-triazole (89.6%). An important implication of these results is the possibility of replacing conventional azole compounds by their non-toxic substituted counterparts in industrial applications. This would prevent inhibition of microbial nitrification without compromising the efficacy of the azoles as inhibitors of copper corrosion.

Insensitive munitions compounds (IMCs) are emerging nitroaromatic contaminants developed by the military as safer-to-handle alternatives to conventional explosives. Biotransformation of nitroaromatics via microbial respiration has only been reported for a limited number of substrates. Important soil microorganisms can respire natural organic matter (NOM) by reducing its quinone moieties to hydroquinones. Thus, we investigated the NOM respiration combined with the abiotic reduction of nitroaromatics by the hydroquinones formed. First, we established nitroaromatic concentration ranges that were nontoxic to the quinone respiration. Then, an enrichment culture dominated by Geobacter anodireducens could indirectly reduce a broad array of nitroaromatics by first respiring NOM components or the NOM surrogate anthraquinone-2,6-disulfonate (AQDS). Without quinones, no nitroaromatic tested was reduced except for the IMC 3-nitro-1,2,4-triazol-5-one (NTO). Thus, the quinone respiration expanded the spectrum of nitroaromatics susceptible to transformation. The system functioned with very low quinone concentrations because NOM was recycled by the nitroaromatic reduction. A metatranscriptomic analysis demonstrated that the microorganisms obtained energy from quinone or NTO reduction since respiratory genes were upregulated when AQDS or NTO was the electron acceptor. The results indicated microbial NOM respiration sustained by the nitroaromatic-dependent cycling of quinones. This process can be applied as a nitroaromatic remediation strategy, provided that a quinone pool is available for microorganisms.

Despite the widespread utilization of onium salts as photoacid generators (PAGs) in semiconductor photolithography, their environmental, health, and safety (EHS) properties remain poorly understood. The present work reports the bioconcentration potential of five representative onium species (four sulfonium and one iodonium compound) by determining the octanol–water partition coefficient (POW) and lipid membrane affinity coefficient (KMA); microbial toxicity was evaluated using the bioluminescent bacterium Aliivibrio fischeri (Microtox bioassay). Four of the oniums exhibited varying degrees of hydrophobic (lipophilic) partitioning (log POW: 0.08–4.12; KMA: 1.70–5.62). A strong positive linear correlation was observed between log POW and KMA (KMA = log POW + 1.76, R2 = 0.99). The bioconcentration factors (log BCF) estimated from POW and KMA for the four oniums ranged from 0.13 to 3.67 L kg−1. Bis-(4-tert-butyl phenyl)-iodonium and triphenylsulfonium had 50% inhibitory concentrations (IC50) of 4.8 and 84.6 μM, whereas the IC50 values of the other three oniums were not determined because these values were higher than their aqueous solubility. Given the increased regulatory scrutiny regarding the use and potential health impacts from onium PAGs, this study fulfills critical knowledge gaps concerning the EHS properties of PAG oniums, enabling more comprehensive evaluation of their environmental impacts and potential risk management strategies.

As military applications of the insensitive munitions compounds (IMCs) 2,4-dinitroanisole (DNAN) and 3-nitro1,2,4-triazol-5-one (NTO) increase, there is a growing need to understand their environmental fate and to develop remediation strategies to mitigate their impacts. Iron (II) monosulfide (FeS) minerals are abundant in freshwater and marine sediments, marshes, and hydrothermal environments. This study shows that FeS solids can reduce DNAN and NTO to their corresponding amines under anoxic ambient conditions. The reactions between IMCs and the FeS minerals were surface-mediated since they did not occur when only dissolved Fe-(aq)(2+) and S-(aq)(2-) were present. Mackinawite, a tetragonal FeS with a layered structure, reduced DNAN mainly to 2methoxy-5-nitroaniline (MENA), which in turn was partially reduced to 2-4-diaminoanisole (DAAN). The layered structure of mackinawite provided intercalation sites likely responsible for partial adsorption of MENA and DAAN. Mackinawite entirely reduced NTO to 3-amino-1,2,4-triazol-5-one (ATO). The reduction of IMCs showed concurrent oxidation of mackinawite to goethite and elemental sulfur. A commercial FeS product, composed mainly of pyrrhotite and troilite, reduced DNAN to DAAN and NTO to ATO. At pH 6.5, DNAN and NTO transformation rates were 667 and 912 mu mol h(-1) m(-2), respectively, on the mackinawite surface and 417 and 1344 mu mol h(-1) m(-2), respectively, on the commercial FeS surface. This is the first report of the reduction of a nitro-heterocyclic compound (NTO) by FeS minerals. The evidence indicates that DNAN and NTO can be rapidly transformed to their succeeding amines in anoxic subsurface environments and aquatic sediments rich in FeS minerals.

The nitroheterocyclic 3-nitro-1,2,4-triazol-5-one (NTO) is an ingredient of insensitive explosives increasingly used by the military, becoming an emergent environmental pollutant. Cometabolic biotransformation of NTO occurs in mixed microbial cultures in soils and sludges with excess electron-donating substrates. Herein, we present the unusual energy-yielding metabolic process of NTO respiration, in which the NTO reduction to 3-amino-1,2,4-triazol-5-one (ATO) is linked to the anoxic acetate oxidation to CO2 by a culture enriched from municipal anaerobic digester sludge. Cell growth was observed simultaneously with NTO reduction, whereas the culture was unable to grow in the presence of acetate only. Extremely low concentrations (0.06 mg L-1) of the uncoupler carbonyl cyanide m-chlorophenyl hydrazone inhibited NTO reduction, indicating that the process was linked to respiration. The ultimate evidence of NTO respiration was adenosine triphosphate production due to simultaneous exposure to NTO and acetate. Metagenome sequencing revealed that the main microorganisms (and relative abundances) were Geobacter anodireducens (89.3%) and Thauera sp. (5.5%). This study is the first description of a nitroheterocyclic compound being reduced by anaerobic respiration, shedding light on creative microbial processes that enable bacteria to make a living reducing NTO.