Synergistic mitigation of atrazine-induced oxidative stress on soybeans in black soil using biochar and Paenarthrobacter sp. AT5

Atrazine, a widely used herbicide in modern agriculture, can lead to soil contamination and adverse effects on specific crops. To address this, we investigated the efficacy of biochar loaded with Paenarthrobacter sp. AT5 (an atrazine-degrading bacterial strain) in mitigating atrazine's impact on soybeans in black soil. Bacterially loaded biochar (BBC) significantly enhanced atrazine removal rates in both unplanted and planted soil systems. Moreover, BBC application improved soybean biomass, photosynthetic pigments, and antioxidant systems while mitigating alterations in metabolite pathways induced by atrazine exposure. These findings demonstrate the effectiveness of BBC in reducing atrazine-induced oxidative stress on soybeans in black soil, highlighting its potential for sustainable agriculture.

Rare Earth Element Adsorption to Clay Minerals: Mechanistic Insights and Implications for Recovery from Secondary Sources

The energy transition will have significant mineral demands and there is growing interest in recovering critical metals, including rare earth elements (REE), from secondary sources in aqueous and sedimentary environments. However, the role of clays in REE transport and deposition in these settings remains understudied. This work investigated REE adsorption to the clay minerals illite and kaolinite through pH adsorption experiments and extended X-ray absorption fine structure (EXAFS). Clay type, pH, and ionic strength (IS) affected adsorption, with decreased adsorption under acidic pH and elevated IS. Illite had a higher adsorption capacity than kaolinite; however, >95% adsorption was achieved at pH ∼7.5 regardless of IS or clay. These results were used to develop a surface complexation model with the derived binding constants used to predict REE speciation in the presence of competing sorbents. This demonstrated that clays become increasingly important as pH increases, and EXAFS modeling showed that REE can exist as both inner- and outer-sphere complexes. Together, this indicated that clays can be an important control on the transport and enrichment of REE in sedimentary systems. These findings can be applied to identify settings to target for resource extraction or to predict REE transport and fate as a contaminant.

Improved energy recovery from yard waste by water-starved hydrothermal treatment: Effects of process water and pressure

This study investigated the feasibility of a high-loading process with less water consumption for the valorization of wet biomass waste through hydrothermal carbonization (HTC) with and without N2 pressurization from the views of water saving, carbon utilization, and energy recovery. The results revealed that reducing the liquid-to-solid ratio from 10 to 2.5 significantly improved carbon storage in hydrochar due to preferential carbon sequestration as the solid phase (59.9%) instead of being lost in the liquid phase (∼10%). The pressurized HTC process resulted in a higher stability hydrochar through the devolatilization of secondary char that was less stable, yet resulted in ∼10% 15% more carbon transformation to the gas phase. A cost-benefit analysis further demonstrated the potential of the high-loading HTC process for enhancing energy recovery while minimizing energy consumption during hydrochar production from high-moisture yard waste.

Adsorption of antibiotics onto low-grade charcoal in the presence of organic matter: Batch and column tests

Antibiotics contaminate diverse ecosystems and threaten human health. In ecosystems including water, sediment, and soil, the amount of antibiotics present is tiny compared to the amount of natural organic matter. However, most studies have ignored the co-presence of natural organic matter in the adsorption of target antibiotics. In this study, we quantitatively evaluated the effect of co-presenting natural organic matter on the adsorption of sulfamethazine (SMZ) through batch and column experiments using low-grade charcoal, an industrial by-product. SMZ was used as a model antibiotic compound and humic acid (HA) was used to represent natural organic matter. The co-presence of 2000 mg/L HA (400 times the concentration of SMZ) lowered the adsorption rate of SMZ from 0.023 g/mg·min to 0.007 g/mg·min, and the maximum adsorption capacity from 39.8 mg/g to 15.6 mg/g. HA blocked the charcoal's pores and covered its surface adsorption sites, which dramatically lowered its capacity to adsorb SMZ. Similar results were obtained in the flow-through column experiments, where the co-presence of natural organic matter shortened the lifetime of the charcoal. As a result, the co-presence of a relatively high concentration of natural organic matter can inhibit the adsorption of SMZ and likely other antibiotic compounds, and thus the presence of natural organic matter should be accounted for in the design of adsorption processes to treat antibiotics in water.

Arbuscular Mycorrhizal Fungi Drive Organo-Mineral Association in Iron Ore Tailings: Unravelling Microstructure at the Submicron Scale by Synchrotron-Based FTIR and STXM-NEXAFS

Arbuscular mycorrhizal (AM) fungi play an important role in organic matter (OM) stabilization in Fe ore tailings for eco-engineered soil formation. However, little has been understood about the AM fungi-derived organic signature and organo-mineral interactions in situ at the submicron scale. In this study, a compartmentalized cultivation system was used to investigate the role of AM fungi in OM formation and stabilization in tailings. Particularly, microspectroscopic analyses including synchrotron-based transmission Fourier transform infrared (FTIR) and scanning transmission X-ray microspectroscopy combined with near-edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS) were employed to characterize the chemical signatures at the AM fungal-mineral and mineral-OM interfaces at the submicron scale. The results indicated that AM fungal mycelia developed well in the tailings and entangled mineral particles for aggregation. AM fungal colonization enhanced N-rich OM stabilization through organo-mineral association. Bulk spectroscopic analysis together with FTIR mapping revealed that fungi-derived lipids, proteins, and carbohydrates were associated with Fe/Si minerals. Furthermore, STXM-NEXAFS analysis revealed that AM fungi-derived aromatic, aliphatic, and carboxylic/amide compounds were heterogeneously distributed and trapped by Fe(II)/Fe(III)-bearing minerals originating from biotite-like minerals weathering. These findings imply that AM fungi can stimulate mineral weathering and provide organic substances to associate with minerals, contributing to OM stabilization and aggregate formation as key processes for eco-engineered soil formation in tailings.

Extractability and phytotoxicity of heavy metals and essential elements from plastics in soil solutions and root exudates

Plastic waste is increasing and is a serious environmental problem. Among the threats associated with plastics is the release of contaminants into the environment. This study aimed to evaluate the efficiency of metals release from plastics (low-density polyethylene (LDPE), polyethylene terephthalate (PET), and polypropylene (PP)) as affected by different soil solution types, artificial root exudates, and distilled water. The extent of metal release varied depending on the type of solution and plastic used. Metals were leached most effectively from plastics in soil solutions, followed by root exudates, and least effectively by distilled water. LDPE released the highest concentrations of Cu and Na into solution, PP released the greatest amount of Fe, and PET released the most Cr. The efficiencies of Mg and Zn release from the plastics (PP and PET) varied by solution type. Among the plastics studied, LDPE exhibited the strongest ability to adsorb metals, such as Fe, Cr, Mg, and Zn from soil solutions. The amount of metal released from the plastics was also dependent on pH, dissolved organic carbon (DOC) concentrations, and the electrical conductivity (EC) of the solutions. Moreover, plastic extracts were found to have negative effects on germination and growth in Lepidium sativum.

Machine learning based prediction and experimental validation of arsenite and arsenate sorption on biochars

Arsenic (As) contamination in water is a significant environmental concern with profound implications for human health. Accurate prediction of the adsorption capacity of arsenite [As(III)] and arsenate [As(V)] on biochar is vital for the reclamation and recycling of polluted water resources. However, comprehending the intricate mechanisms that govern arsenic accumulation on biochar remains a formidable challenge. Data from the literature on As adsorption to biochar was compiled and fed into machine learning (ML) based modelling algorithms, including AdaBoost, LGBoost, and XGBoost, in order to build models to predict the adsorption efficiency of As(III) and As(V) to biochar, based on the compositional and structural properties. The XGBoost model showed superior accuracy and performance for prediction of As adsorption efficiency (for As(III): coefficient of determination (R2) = 0.93 and root mean square error (RMSE) = 1.29; for As(V), R2 = 0.99, RMSE = 0.62). The initial concentrations of As(III) and As(V) as well as the dosage of the adsorbent were the most significant factors influencing adsorption, explaining 48 % and 66 % of the variability for As(III) and As(V), respectively. The structural properties and composition of the biochar explained 12 % and 40 %, respectively, of the variability of As(III) adsorption, and 13 % and 21 % of that of As(V). The XGBoost models were validated using experimental data. R2 values were 0.9 and 0.84, and RMSE values 6.5 and 8.90 for As(III) and As(V), respectively. The ML approach can be a valuable tool for improving the treatment of inorganic As in aqueous environments as it can help estimate the optimal adsorption conditions of As in biochar-amended water, and serve as an early warning for As-contaminated water.

Deciphering the dual role of bacterial communities in stabilizing rhizosphere priming effect under intra-annual change of growing seasons

The rhizosphere priming effect (RPE) is a widely observed phenomenon affecting carbon (C) turnover in plant-soil systems. While multiple cropping and seasonal changes can have significant impacts on RPE, the mechanisms driving these processes are complex and not yet fully understood. Here, we planted maize in paddy soil during two growing seasons having substantial temperature differences [May-August (warm season, 26.6 °C) and September-November (cool season, 23.1 °C)] within the same calendar year in southern China to examine how seasonal changes affect RPEs and soil C. We identified sources of C emissions by quantifying the natural abundance of 13C and determined microbial metabolic limitations or efficiency and functional genes related to C cycling using an enzyme-based biogeochemical equilibrium model and high-throughput quantitative PCR-based chip technology, respectively. Results showed that microbial metabolism was mainly limited by phosphorus in the warm season, but by C in the cool season, resulting in positive RPEs in both growing seasons, but no significant differences (9.02 vs. 6.27 mg C kg-1 soil day-1). The RPE intensity remained stable as temperature increased (warm season compared to a cool season), which can be largely explained by the simultaneous increase in the abundance of functional genes related to both C degradation and fixation. Our study highlights the simultaneous response and adaptation of microbial communities to seasonal changes and hence contributes to an understanding and prediction of microbially mediated soil C turnover under multiple cropping systems.

Spatial and temporal variation in toxicity and inorganic composition of hydraulic fracturing flowback and produced water

Hydraulic fracturing for oil and gas extraction produces large volumes of wastewater, termed flowback and produced water (FPW), that are highly saline and contain a variety of organic and inorganic contaminants. In the present study, FPW samples from ten hydraulically fractured wells, across two geologic formations were collected at various timepoints. Samples were analyzed to determine spatial and temporal variation in their inorganic composition. Results indicate that FPW composition varied both between formations and within a single formation, with large compositional changes occurring over short distances. Temporally, all wells showed a time-dependent increase in inorganic elements, with total dissolved solids increasing by up to 200,000 mg/L over time, primarily due to elements associated with salinity (Cl, Na, Ca, Mg, K). Toxicological analysis of a subset of the FPW samples showed median lethal concentrations (LC50) of FPW to the aquatic invertebrate Daphnia magna were highly variable, with the LC50 values ranging from 1.16% to 13.7% FPW. Acute toxicity of FPW significantly correlated with salinity, indicating salinity is a primary driver of FPW toxicity, however organic components also contributed to toxicity. This study provides insight into spatiotemporal variability of FPW composition and illustrates the difficulty in predicting aquatic risk associated with FPW.

Exogenous Electroactive Microbes Regulate Soil Geochemical Properties and Microbial Communities by Enhancing the Reduction and Transformation of Fe(III) Minerals

Electroactive microbes can conduct extracellular electron transfer and have the potential to be applied as a bioresource to regulate soil geochemical properties and microbial communities. In this study, we incubated Fe-limited and Fe-enriched farmland soil together with electroactive microbes for 30 days; both soils were incubated with electroactive microbes and a common iron mineral, ferrihydrite. Our results indicated that the exogenous electroactive microbes decreased soil pH, total organic carbon (TOC), and total nitrogen (TN) but increased soil conductivity and promoted Fe(III) reduction. The addition of electroactive microbes also changed the soil microbial community from Firmicutes-dominated to Proteobacteria-dominated. Moreover, the total number of detected microbial species in the soil decreased from over 700 to less than 500. Importantly, the coexistence of N-transforming bacteria, Fe(III)-reducing bacteria and methanogens was also observed with the addition of electroactive microbes in Fe-rich soil, indicating the accelerated interspecies electron transfer of functional microflora.

Copper exposure does not alter the ability of intertidal sea cucumber Cucumaria miniata to tolerate emersion during low tide

Intertidal animals experience cycles of tidal emersion from water and are vulnerable to copper (Cu) exposure due to anthropogenic toxicant input into marine waters. Both emersion and Cu toxicity can cause damage to physiological processes like aerobic metabolism, ammonia excretion, and osmoregulation, but the interactions of the combination of these two stressors on marine invertebrates are understudied. Mixed effects of 96 h of low and high Cu exposure (20 and 200 μg/L) followed by 6 h of tidal emersion were evaluated on the intertidal sea cucumber Cucumaria miniata. The respiratory tree accumulated the highest concentrations of Cu, followed by the introvert retractor muscle, body wall, and coelomic fluid. Emersion affected accumulation of Cu, perhaps by inhibiting excretion. 200 μg/L of Cu increased lactate production in the respiratory tree, indicative of damaged aerobic metabolism. Cu diminished ammonia excretion, but emersion increased oxygen uptake and ammonia excretion upon re-immersion. The combination of the two stressors did not have any interactive effects on metabolism or ammonia excretion. Neither Cu exposure nor emersion altered ion (sodium, potassium, calcium, magnesium) content of the coelomic fluid. Overall, results of this study suggest that Cu exposure does not alter C. miniata's high tolerance to emersion, and some potential strategies that this species uses to overcome environmental stress are illuminated.

Uranium surface processes with sandstone and volcanic rocks in acidic and alkaline solutions

Understanding the behaviour of uranium waste, for disposal purposes, is crucial due to the correlation between pH values and the disposal of distinct types of waste, with low level waste typically associated with acidic pH values, and higher and intermediate level waste commonly related to alkaline pH values. We studied the adsorption of U(VI) on sandstone and volcanic rock surfaces at pH 5.5 and 11.5 in aqueous solutions with and without bicarbonate (2 mM HCO₃^-) using XAS and FTIR. In the sandstone system, U(VI) adsorbs as a bidentate complex to Si at pH 5.5 without bicarbonate and as uranyl carbonate species with bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbs as monodentate complexes to Si and precipitates as uranophane. With bicarbonate at pH 11.5, U(VI) precipitated as a Na-clarkeite mineral or remained as a uranyl carbonate surface species. In the volcanic rock system, U(VI) adsorbed to Si as an outer sphere complex at pH 5.5, regardless of the presence of bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbed as a monodentate complex to one Si atom and precipitated as a Na-clarkeite mineral. With bicarbonate at pH 11.5, U(VI) sorbed as a bidentate carbonate complex to one Si atom. These results provide insight into the behaviour of U(VI) in heterogeneous, real-world systems related to the disposal of radioactive waste.

Mitigation of arsenic release by calcium peroxide (CaO2) and rice straw biochar in paddy soil

Biochar has a great potential in the stabilization of soil heavy metals; however, the application can actually enhance the mobility of Arsenic (As) in soil. Here, a biochar-coupled calcium peroxide system was proposed to control the increase in As mobility caused by biochar amendment in paddy soil environment. The capability of rice straw biochar pyrolyzed at 500 °C (RB) and CaO₂ to control As mobility was evaluated by incubation for 91 days. CaO₂ encapsulation was performed for pH control of CaO₂, and As mobility was evaluated using a mixture of RB + CaO₂ powder (CaO₂-p), and RB + CaO₂ bead (CaO₂-b), respectively. The control soil solely and RB alone were included for comparison. The combination of RB with CaO₂ exhibited remarkable performance in controlling As mobility in soil, and As mobility decreased by 40.2% (RB + CaO₂-p) and 58.9% (RB + CaO₂-b) compared to RB alone. The result was due to high dissolved oxygen (6 mg L^-1 in RB + CaO₂-p and RB + CaO₂-b) and calcium concentrations (296.3 mg L^-1 in RB + CaO₂-b); oxygen (O₂) and Ca²⁺ derived from CaO₂ is able to prevent the reductive dissolution and chelate-promoted dissolution of As bound to iron (Fe) oxide by biochar. This study revealed that the simultaneous application of CaO₂ and biochar could be a promising way to mitigate the environmental risk of As.

Copper toxicity does not affect low tide emersion tolerance of Mytilus galloprovincialis

Intertidal mussels are well adapted to withstand emersion from water during low tide, but they may be intermittently exposed to waterborne toxicants such as copper, which targets physiological processes including metabolism, ammonia excretion, and osmoregulation. To determine if copper exposure damages intertidal organisms' ability to tolerate tidal emersion, Mediterranean mussels (Mytilus galloprovincialis) were exposed to copper for 96 h followed by 6 h of emersion. Oxygen uptake increased after copper exposure which suggests that copper accumulation caused moderate stress in the mussels, but ammonia excretion and anaerobic metabolism were unaffected by mixed copper and emersion exposures. Shell composition analyses indicate that cycles of copper exposure and tidal emersion may affect bivalve shell growth, but copper deposition into shells may decrease the metal's overall toxicity. Results suggest that copper does not damage M. galloprovincialis's tolerance to tidal emersion, and insight is provided into the mussel's ability to overcome mixed stressor exposures.

Water footprint of shale gas development in China in the carbon neutral era

The production of shale gas in China has repercussions for the global energy landscape and carbon neutrality. However, limited and threatened water resources may hinder the expansion of shale-derived natural gas, one of China's most promising development prospects. Coupling historical trends with policy guidance, we project that baseline water stress will intensify in two-thirds of China's provinces in the next decade. By 2035, annual water use for shale gas hydraulic fracturing activities is likely to increase to 16-35 million m³, with 13.8-23.7 million m³ of wastewater produced annually to extract 38-48 billion m³ of gas from ∼4800 shale gas wells. Analysis suggests that this projection is based on previously underestimated geological constraints (e.g., deep continental facies) in shale gas development in China. Nevertheless, forecasts suggest that the water footprint of shale development will become impossible to ignore, particularly in drought-stricken areas, indicating the potential risk of competition for water among shale development, domestic use, food production, and ecological protection. Meanwhile, the annual wastewater management market will increase to $0.2 billion by 2035. Our study suggests a critical need to direct attention to the (shale) energy-water nexus and develop multi-pronged policies to facilitate China's transition to carbon neutrality.

Selective Extraction of Critical Metals from Spent Lithium-Ion Batteries

Selective and highly efficient extraction technologies for the recovery of critical metals including lithium, nickel, cobalt, and manganese from spent lithium-ion battery (LIB) cathode materials are essential in driving circularity. The tailored deep eutectic solvent (DES) choline chloride-formic acid (ChCl-FA) demonstrated a high selectivity and efficiency in extracting critical metals from mixed cathode materials (LiFePO₄:Li(NiCoMn)_1/3O₂ mass ratio of 1:1) under mild conditions (80 °C, 120 min) with a solid-liquid mass ratio of 1:200. The leaching performance of critical metals could be further enhanced by mechanochemical processing because of particle size reduction, grain refinement, and internal energy storage. Furthermore, mechanochemical reactions effectively inhibited undesirable leaching of nontarget elements (iron and phosphorus), thus promoting the selectivity and leaching efficiency of critical metals. This was achieved through the preoxidation of Fe and the enhanced stability of iron phosphate framework, which significantly increased the separation factor of critical metals to nontarget elements from 56.9 to 1475. The proposed combination of ChCl-FA extraction and the mechanochemical reaction can achieve a highly selective extraction of critical metals from multisource spent LIBs under mild conditions.

Environmental impact of metal halide perovskite solar cells and potential mitigation strategies: A critical review

Metal halide perovskite solar cells (PSCs) have gained extensive attention in the field of solar photovoltaic technology over the past few years. Despite being a remarkable alternative to fossil fuels, solar cells may have detrimental effects on the environment and human health owing to the use of toxic materials during manufacturing. Although modern metal-halide-based PSCs are stable and have encapsulation to prevent the release of potentially toxic materials into the environment, their destruction due to strong winds, hail, snow, landslides, fires, or waste disposal can result in the exposure of these materials to the environment. This may lead to the contamination of soil and groundwater, and uptake of potentially toxic elements by plants, subsequently affecting humans and other living organisms via food chain contamination. Despite worldwide concern, the environmental and ecotoxicological impacts of metal-halide-based PSCs have not been comprehensively surveyed. This review summarizes and critically evaluates the current status of metal-halide-based PSC production and its impact on environmental sustainability, food security, and human health. Furthermore, safe handling and disposal methods for the waste generated from metal-halide-based PSCs are proposed, with a focus on recycling and reuse. Although some studies have suggested that the amount of lead released from metal halide PSCs is far below the maximum permissible levels in most soils, a clear conclusion cannot be reached until real contamination scenarios are assessed under field conditions. Precautions must be taken to minimize environmental contamination throughout the lifecycle of PSCs until nontoxic and similarly performing alternative solar photovoltaic products are developed.

Persisting Effects in Daphnia magna Following an Acute Exposure to Flowback and Produced Waters from the Montney Formation

Hydraulic fracturing extracts oil and gas through the injection of water and proppants into subterranean formations. These injected fluids mix with the host rock formation and return to the surface as a complex wastewater containing salts, metals, and organic compounds, termed flowback and produced water (FPW). Previous research indicates that FPW is toxic to Daphnia magna (D. magna), impairing reproduction, molting, and maturation time; however, recovery from FPW has not been extensively studied. Species unable to recover have drastic impacts on populations on the ecological scale; thus, this study sought to understand if recovery from an acute 48 h FPW exposure was possible in the freshwater invertebrate, D. magna by using a combination of physiological and molecular analyses. FPW (0.75%) reduced reproduction by 30% and survivorship to 32% compared to controls. System-level quantitative proteomic analyses demonstrate extensive perturbation of metabolism and protein transport in both 0.25 and 0.75% FPW treatments after a 48 h FPW exposure. Collectively, our data indicate that D. magna are unable to recover from acute 48 h exposures to ≥0.25% FPW, as evidence of toxicity persists for at least 19 days post-exposure. This study highlights the importance of considering persisting effects following FPW remediation when modeling potential spill scenarios.

Latent impacts on juvenile rainbow trout (Oncorhynchus mykiss) cardio-respiratory function and swimming performance following embryonic exposures to hydraulic fracturing flowback and produced water

Technologies associated with hydraulic fracturing continue to be prevalent in many regions worldwide. As a result, the production of flowback and produced water (FPW) - a wastewater generated once pressure is released from subterranean wellbores - continues to rise in regions experiencing fracturing activities, while waste management strategies attempt to mitigate compounding burdens of increased FPW production. The heightened production of FPW increases the potential for release to the environment. However, relatively few studies have directly investigated how ecosystems and organisms may be latently affected long after exposures occur. The current study examines rainbow trout exposed in ovo at select critical cardiac developmental time points to differing dilutions and lengths of time (acute versus chronic) to determine how FPW-mediated exposure in ovo may alter later cardiac function and development. After exposure, we allowed fish to grow for ∼ 8 months post-fertilization and measured fish swimming performance, aerobic scope, and cardiac structure of juvenile trout. Acute 48 h embryonic 5% FPW exposure at either 3 days post-fertilization (dpf) or 10 dpf significantly reduced later swimming performance and aerobic scope in juvenile trout. In ovo exposure to 2.5% FPW at 3 dpf yielded significant decreases in these metrics as well, while exposing trout to 2.5% FPW at 10 dpf did not induce as significant effects. Morphometric analyses of heart muscle tissue in all treatments decreased compact myocardium thickness. Chronic 1% FPW in ovo exposure for 28 days induced similar reductions in swimming performance, aerobic scope, and decreased compact myocardium thickness as acute exposures. Overall, our results demonstrate that FPW exposure during egg development ultimately results in persistently impaired heart morphology and resulting physiological (swimming) performance.

Pros and Cons of Biochar to Soil Potentially Toxic Element Mobilization and Phytoavailability: Environmental Implications

While the potential of biochar (BC) to immobilize potentially toxic elements (PTEs) in contaminated soils has been studied and reviewed, no review has focused on the potential use of BC for enhancing the phytoremediation efficacy of PTE-contaminated soils. Consequently, the overarching purpose in this study is to critically review the effects of BC on the mobilization, phytoextraction, phytostabilization, and bioremediation of PTEs in contaminated soils. Potential mechanisms of the interactions between BC and PTEs in soils are also reviewed in detail. We discuss the promises and challenges of various approaches, including potential environmental implications, of BC application to PTE-contaminated soils. The properties of BC (e.g., surface functional groups, mineral content, ionic content, and π-electrons) govern its impact on the (im)mobilization of PTEs, which is complex and highly element-specific. This review demonstrates the contrary effects of BC on PTE mobilization and highlights possible opportunities for using BC as a mobilizing agent for enhancing phytoremediation of PTEs-contaminated soils.

Molecular dynamics simulation study of covalently bound hybrid coagulants (CBHyC): Molecular structure and coagulation mechanisms

Covalently-bound organic silicate-aluminum hybrid coagulants (CBHyC) have been shown to efficiently remove low molecular weight organic contaminants from wastewater. However, the interaction dynamics and motivations during the coagulation of contaminant molecules by CBHyC are limited. In this study, a molecular dynamics (MD) simulation showed that CBHyC forms core-shell structure with the aliphatic carbon chains gather inside as a core and the hydrophilic quaternary ammonium-Si-Al complexes disperse outside as a shell. This wrapped structure allowed the coagulant to diffuse into solutions easily and capture target contaminants. The adsorption of anionic organic contaminants (e.g., diclofenac) onto the CBHyC aggregates was driven equally by van der Waals forces and electrostatic interactions. Cationic organic contaminants (e.g., tetracycline) were seldom bound to CBHyC because of substantial repulsive forces between cationic molecules and CBHyC. Neutrally-charged organic molecules were generally bound through hydrophobic interactions. For adenine and thymine deoxynucleotide, representatives of antibiotic resistance genes, van der Waals forces and electrostatic interaction became the dominant driving force with further movement for adenine and thymine, respectively. Driving forces between target contaminant and coagulant directly affect the size and stability of formed aggregate, following the coagulation efficiency of wastewater treatment. The findings of this study enrich the database of aggregation behavior between low molecular weight contaminants and CBHyC and contribute to further and efficient application of CBHyC in wastewater treatment.

Embryonic cardio-respiratory impairments in rainbow trout (Oncorhynchus mykiss) following exposure to hydraulic fracturing flowback and produced water

During hydraulic fracturing, wastewaters - termed flowback and produced water (FPW) - are created as a by-product during hydrocarbon extraction. Given the large volumes of FPW that a single well can produce, and the history of FPW release to surface water bodies, it is imperative to understand the hazards that hydraulic fracturing and FPW pose to aquatic biota. Using rainbow trout embryos as model organisms, we investigated impacts to cardio-respiratory system development and function following acute (48 h) and sub-chronic (28-day) FPW exposure by examining occurrences of developmental deformities, rates of embryonic respiration (MO₂), and changes in expression of critical cardiac-specific genes. FPW-exposed embryos had significantly increased rates of pericardial edema, yolk-sac edema, and tail/trunk curvatures at hatch. Furthermore, when exposed at three days post-fertilization (dpf), acute 5% FPW exposures significantly increased embryonic MO₂ through development until 15 dpf, where a switch to significantly reduced MO₂ rates was subsequently recorded. A similar trend was observed during sub-chronic 1% FPW exposures. Interestingly, at certain specific developmental timepoints, previous salinity exposure seemed to affect embryonic MO₂; a result not previously observed. Following acute FPW exposures, embryonic genes for cardiac development and function were significantly altered, although at termination of sub-chronic exposures, significant changes to these same genes were not found. Together, our evidence of induced developmental deformities, modified embryonic MO₂, and altered cardiac transcript expression suggest that cardio-respiratory tissues are toxicologically targeted following FPW exposure in developing rainbow trout. These results may be helpful to regulatory bodies when developing hazard identification and risk management protocols concerning hydraulic fracturing activities.

Pyrolyzed biomass-derived nanoparticles: a review of surface chemistry, contaminant mobility, and future research avenues to fill the gaps

Nanoparticles are abundant in the subsurface, soil, streams, and water bodies, and are often a critical control on elemental speciation, transport and cycling in the natural environment. This review provides an overview of pyrolyzed biomass-derived nanoparticles (PBNPs), their surface properties and reactivity towards aqueous species. We focus specifically on biochar-derived nanoparticles and activated carbon-derived nanoparticles which fall under our classification of PBNPs. Activated carbon-iron (nano)composites are included in some instances where there are significant gaps in literature because of their environmental relevance. Increased use of activated carbon, along with a resurgence in the manufacture and application of biochar for water treatment and soil amendment, has generated significant concerns about the mobility and toxicity of PBNPs derived from the bulk material in environmental applications. Recent examples are discussed to highlight current progress in understanding the influence of PBNPs on contaminant transport, followed by a critical discussion of gaps and future research directions.

Arsenic bioaccumulation and biotransformation in aquatic organisms

Arsenic exists universally in freshwater and marine environments, threatening the survival of aquatic organisms and human health. To elucidate arsenic bioaccumulation and biotransformation processes in aquatic organisms, this review evaluates the dissolved uptake, dietary assimilation, biotransformation, and elimination of arsenic in aquatic organisms and discusses the major factors influencing these processes. Environmental factors such as phosphorus concentration, pH, salinity, and dissolved organic matter influence arsenic absorption from aquatic systems, whereas ingestion rate, gut passage time, and gut environment affect the assimilation of arsenic from foodstuffs. Arsenic bioaccumulation and biotransformation mechanisms differ depending on specific arsenic species and the involved aquatic organism. Although some enzymes engaged in arsenic biotransformation are known, deciphering the complicated synthesis and degradation pathway of arsenobetaine remains a challenge. The elimination of arsenic involves many processes, such as fecal excretion, renal elimination, molting, and reproductive processes. This review facilitates our understanding of the environmental behavior and biological fate of arsenic and contributes to regulation of the environmental risk posed by arsenic pollution.

Complex impacts of hydraulic fracturing return fluids on soil microbial community respiration, structure, and functional potentials

The consequences of soils exposed to hydraulic fracturing (HF) return fluid, often collectively termed flowback and produced water (FPW), are poorly understood, even though soils are a common receptor of FPW spills. Here, we investigate the impacts on soil microbiota exposed to FPW collected from the Montney Formation of western Canada. We measured soil respiration, microbial community structure, and functional potentials under FPW exposure across a range of concentrations, exposure time, and soil types (luvisol and chernozem). We find that soil type governs microbial community response upon FPW exposure. Within each soil, FPW exposure led to reduced biotic soil respiration, and shifted microbial community structure and functional potentials. We detect substantially higher species richness and more unique functional genes in FPW-exposed soils than in FPW-unexposed soils, with metagenome-assembled genomes (e.g., Marinobacter persicus) from luvisol soil exposed to concentrated FPW being most similar to genomes from HF/FPW sites. Our data demonstrate the complex impacts of microbial communities following FPW exposure, and highlight the site-specific effects in evaluation of spills and agricultural reuse of FPW on the normal soil functions. This article is protected by copyright. All rights reserved.

Aging features of metal(loid)s in biochar-amended soil: Effects of biochar type and aging method

Soil contamination with toxic metals and metalloids has become a major threat to global food security. Among various immobilization agents that can stabilize toxic metal(loid)s effectively, biochar is promising due to its ability to restore soil health. Yet the aging characteristics of biochar following its amendment in soil remain poorly explored. Therefore, this study used standard biochars to depict their aging effects on remediation of metal(loid)-contaminated soil. A total of 2304 observations were made, including 6 biochar feedstocks (rice husk, soft wood, oilseed rape straw, miscanthus straw, sewage sludge and wheat straw), 2 pyrolysis temperatures (550 °C, 700 °C), 8 metal(loid)s (Mn, Ni, Cu, Zn, As, Cd, Sb, Pb), 4 aging methods (natural aging, freeze-thaw cycling, wet-dry cycling, chemical oxidation with H₂O₂), and 6 sampling intervals. Sewage sludge biochars exhibited the highest resistance to both artificial and natural aging, which may be related to the abundant oxygen-containing functional groups that favor metal complexation, and poorly-developed pore structures that limit the access of natural aging forces. A distinct relationship between ash and temperature was observed, where for high-ash biochars, an increase in pyrolysis temperature indicated lower resistance to aging, while for low-ash biochars, elevated pyrolysis temperature led to higher resistance. The aging behaviors of Cu and Sb were quite similar, which were both highly susceptible to chemical oxidation-induced dissolved organic carbon (DOC) release. Wet-dry cycling and freeze-thaw cycling revealed aging patterns that were similar to those of naturally aged soils as confirmed by cluster analysis. Lab aging data were then compared with existing biochar field aging results. Contrasting long-term immobilization performances were found in different studies, which were attributed to various causes associated with both biochar property and climate. The results of this study provide fresh insights into the long-term risks in the management of metal(loid)-contaminated agricultural soils.

Effect of fulvic acid co-precipitation on biosynthesis of Fe(III) hydroxysulfate and its adsorption of lead

Iron (III) co-precipitation with dissolved organic matter (DOM) is pervasive in many natural environments. However, the effects of DOM on the formation of Fe(III) hydroxysulfate (FHS) and its environmental implications are poorly understood. In this study, fulvic acid (FA) was used as a model DOM compound, and experiments were devised to investigate the effects of FA on the formation of FHS. In addition, the Pb(II) adsorption capabilities of FHSs biosynthesized under various FA dosages, including kinetics and sorption isotherm experiments, were conducted. These experiments showed that co-precipitation of FA promoted the formation of Fe-FA composites, FA-doped schwertmannite, and small particles of jarosite. Co-precipitates are more enriched in carboxyl (-COOH) functional groups due to their preferential binding with FHS. The adsorption kinetics, isotherms and mechanisms of Pb onto the biosynthesized FHSs were then comprehensively characterized and modeled. Though the specific surface area decreased with increasing FA loading, the introduction of FA into FHSs increased Pb(II) adsorption, with the highest concentration of FA addition improving the removal capacity of Pb(II) to 91.54%. Kinetics studies and intra-particle diffusion models indicated that the adsorption of Pb(II) onto the FHSs was correlated with the number of active sites, and two adsorption steps: surface adsorption and the diffusion of Pb(II) in channels inside the biosynthesized FHSs, are suggested. The adsorption mechanism was attributed to cation exchange between Pb(II) and -OH and -COOH functional groups, and the co-precipitated FA provided additional sites for Pb(II) adsorption by FHS.

A common well pad does not imply common toxicity: Assessing the acute and chronic toxicity of flowback and produced waters from four Montney Formation wells on the same well pad to the freshwater invertebrate Daphnia magna

Large stores of previously inaccessible hydrocarbons have become available due to the development of hydraulic fracturing technologies. During the hydraulic fracturing process, a mixture of water and proprietary additives is injected into geologic formations to release trapped hydrocarbons. After fracturing, injected water and fluid from the target formation return to the surface as flowback and produced water (FPW), a potentially toxic byproduct of hydraulic fracturing activities. FPW is a complex mixture that contains chemical additives present in the initial injection fluid as well as salts, metals, and a variety of organic compounds. As a result, FPW composition can be highly variable across wells from different geological formations, methods of fracturing and well development, and well age. The present study sought to determine if FPW sourced from four wells (O, P, U, V) located on the same well pad within the Montney Formation have similar levels of acute and chronic toxicity to the freshwater invertebrate, Daphnia magna. Minimal differences in the estimated 48 h LC50 concentrations were observed among the studied wells. Long-term, 21 d exposures to ≤2% FPW revealed differences in the level of lethality between wells, including complete mortality in daphnids exposed to 2% well O by day 9. No sublethal effects were observed as a result of exposure to FPW from wells P, U or V; however, a large impairment of reproductive traits and molting behaviour were detected after exposure to 0.75% well O FPW. These results indicate that FPW sourced from wells on the same well pad cannot be considered the same in terms of chemical composition or toxicity, an important distinction to make for risk assessment practices.

Insights into the adsorption of pharmaceuticals and personal care products (PPCPs) on biochar and activated carbon with the aid of machine learning

The science-informed design of 'green' carbonaceous materials (e.g., biochar and activated carbon) with high removal capacity of recalcitrant organic contaminants (e.g., pharmaceuticals and personal care products (PPCPs)) is indispensable for promoting sustainable wastewater treatment. In this study, machine learning (ML) incorporating PPCPs and biochar properties as well as adsorption conditions were applied to build adsorption prediction models and explore the contributions of various biochar's inherent properties to their PPCPs adsorption capacity. The results demonstrated that the models developed by detailed biochar properties (e.g., surface functionality and hierarchical porous structure) from advanced microscopic and spectroscopic techniques were more accurate (i.e., the root-mean-square error decreased by 18-24%) than those by general information such as bulk elemental composition and total pore volume. The relative importance of surface carbon functionalities ranked in the order of C-O bond > CO bond > non-polar carbon for predicting the adsorption capacity. According to the partial dependence analysis, the average pore diameters of adsorbents that were larger than the maximum diameter of PPCPs molecules by 1.5-fold to 2.5-fold favored the PPCPs adsorption. This study reveals new insights into the adsorption of PPCPs and provides a comprehensive reference for the sustainable engineering of biochar adsorbents for PPCPs wastewater treatment.

Suspended solids-associated toxicity of hydraulic fracturing flowback and produced water on early life stages of zebrafish (Danio rerio)

Hydraulic fracturing flowback and produced water (HF-FPW), which contains polyaromatic hydrocarbons (PAHs) and numerous other potential contaminants, is a complex wastewater produced during the recovery of tight hydrocarbon resources. Previous studies on HF-FPW have demonstrated various toxicological responses of aquatic organisms as consequences of combined exposure to high salinity, dissolved organic compounds and particle/suspended solids-bound pollutants. Noteworthy is the lack of studies illustrating the potentially toxic effects of the FPW suspended solids (FPW-SS). In this study, we investigated the acute and sublethal toxicity of suspended solids filtered from six authentic FPW sample collected from two fracturing wells, using a sediment contact assay based on early-life stages of zebrafish (Danio rerio). PAHs profiles and acute toxicity tests provided initial information on the toxic potency of the six samples. Upon exposure to sediment mixture at two selected doses (1.6 and 3.1 mg/mL), results showed adverse effects in larval zebrafish, as revealed by increased Ethoxyresorufin-O-deethylase (EROD) activity. Transcriptional alterations were also observed in xenobiotic biotransformation (ahr, pxr, cyp1a, cyp1b1, cyp1c1, cyp1c2, cyp3a65, udpgt1a1, udpgt5g1), antioxidant response (sod1, sod2, gpx1a, gpx1b) and hormone receptor signaling (esr1, esr2a, cyp19a1a, vtg1) genes. The results demonstrated that even separated from the complex aqueous FPW mixture, FPW-SS can induce toxicological responses in aquatic organisms' early life stages. Since FPW-SS could sediment to the bottom of natural wetland acting as a continuous source of contaminants, the current findings imply the likelihood of long-term environmental risks of polluted sediments on aquatic ecosystems due to FPW spills.

Lead (Pb) sorption to hydrophobic and hydrophilic zeolites in the presence and absence of MTBE

The co-contamination of the environment by metals and organic pollutants is a significant concern, and one such example is lead (Pb) and methyl tert-butyl ether (MTBE) due to their historic use as fuel additives. Clinoptilolite is an abundant and efficient zeolite for metal removal, but the potential interference of co-existing organic pollutants on metal removal, such as MTBE, have rarely been discussed. In this study, a combination of batch sorption tests and synchrotron-based X-ray absorption spectroscopic analyses were employed to investigate Pb sorption mechanism(s) onto clinoptilolite in the presence and absence of MTBE. A comparison was made to synthetic ZSM-5 zeolite to gain insights into differences in Pb binding mechanisms between hydrophilic (clinoptilolite) and hydrophobic (ZSM-5) zeolites. Site occupancy and surface precipitation contributed equally to Pb removal by clinoptilolite, while surface precipitation was the main Pb removal mechanism for ZSM-5 followed by site occupancy. Despite the negligible effect of 100 mg/L MTBE on observed Pb removal from solution by both zeolites, a surface-embedded Pb removal mechanism, through the Mg site on clinoptilolite surface, arises when MTBE is present. This study provides an understanding of atomic-level Pb uptake mechanisms on zeolites, with and without co-contaminating MTBE, which aids in their application in water treatment at co-contaminated sites.

In-situ generation of reactive oxygen species using combination of electrochemical oxidation and metal sulfide

In-situ chemical oxidation (ISCO) is commonly practiced to degrade organic pollutants in various fields. However, ISCO is deteriorated the oxidation efficiency due to the non-selective and self-decomposition of reagents. Therefore, in-situ generation of oxidants is being proposed to compensate for the demerits of conventional ISCO. In this study, the aim is to suggest a novel in-situ generation system using the combination of electrochemical oxidation (EO) and pyrite oxidation. It is hypothesized that EO system can generate the oxygen species, which can activate the pyrite surface to produce more oxidants. We evaluated three systems (1) EO system (2) pyrite oxidation system (3) combined system using sulfanilamide as a common antibiotic. The EO system degraded completely sulfanilamide and generated 150 μM of H₂O₂ and 8 mg/L of DO even at 10 mA. In other words, EO system can directly oxidize the sulfanilamide and produce oxygen species. The pyrite system produced 204 and 24 μM of hydroxyl radicals at pH 3 under oxic and anoxic conditions, respectively, and 118 and 20 μM at pH 7. Pyrite oxidation can generate more reactive species in the presence of oxygen. The combined system enhanced the oxidation-rate constant to 1.5 times (from 0.2561 to 0.3502 h^-1). The additional supply of oxygen showed a higher oxidation rate to 1.5 and 1.3 times higher than single EO or pyrite oxidation, respectively. As a result, the co-presence of pyrite and oxygen shows a synergistic effect on the oxidation of the organic pollutant. Our results suggest that electrochemical generation of the oxygen species in the presence of pyrite is a promising technique to oxidize organic pollutants in groundwater.

Modification of ordered mesoporous carbon for removal of environmental contaminants from aqueous phase: A review

Contamination of water bodies by potentially toxic elements and organic pollutants has aroused extensive concerns worldwide. Thus it is significant to develop effective adsorbents for removing these contaminants. As a new member of carbonaceous material families (activated carbon, biochar, and graphene), ordered mesoporous carbon (OMC) with larger specific surface area, ordered pore structure, and higher pore volume are being evaluated for their use in contaminant removal. In this paper, modification techniques of OMC were systematically reviewed for the first time. These include nonmetallic doping modification (nitrogen, sulfur, and boron) and the impregnation of nano-metals and metal oxides (iron, copper, cobalt, nickel, magnesium, and rare earth element). Reaction conditions (solution pH, reaction temperature, sorbent dosage, and contact time) are of critical importance for the removal performance of contaminants onto OMC. In addition, the pristine and modified OMC have been investigated for the removal of a range of contaminants, including cationic/anionic toxic elements and organic contaminants (synthetic dye, phenol, and others), and involving different and specific mechanisms of interaction with contaminants. The future research directions of the application of pristine and modified OMC were proposed. Overall, this review can provide sights into the modification techniques of OMC for removal of environmental contaminants.

Simultaneous reduction and immobilization of Cr(VI) in seasonally frozen areas: Remediation mechanisms and the role of ageing

Among the toxic metals, hexavalent chromium [Cr(VI)] has attracted much attention due to its high mobility and toxicity, rendering considerable challenges for long-term remediation. In this study, the soil was collected from a dichromate contaminated industrial site in Liaoning Province, a seasonally frozen area in northern China, and subjected to frequent freeze-thaw cycles. Three additives, including (i) ferrous sulfate; (ii) calcium polysulfide; and (iii) combined biochar and calcium polysulfide were applied to reduce and immobilize Cr(VI) in the soils. The samples underwent 28 days of incubation followed by 16 freeze-thaw cycles. The toxicity characteristic leaching procedure (TCLP) and simulated acid rain leaching were adopted to test the remediation performances. It was observed that all three treatments can significantly reduce and immobilize Cr(VI) after short-term incubation, while biochar with abundant functional groups could adsorb and reduce Cr(VI) effectively. Notably, the concentration of Cr(VI) in TCLP leachates after incubation in combined treatment decreased by 67.87% and 37.27%, respectively, compared with the application of ferrous sulfate or calcium polysulfide alone. Freeze-thaw cycles induced the disintegration of soil particles and increased the risk of contaminant mobilization. Conversely, biochar particles has become finer and even produced nanoparticles with ageing, accompanied by the increase in oxygen-containing surface functional groups. Additionally, the specific surface area increased with the pyrolysis of biochar, which further enhanced the retention of soil colloidal particles and suppressed the migration of contaminants. Therefore, the cumulative release of Cr(VI) in the combined treatment (i.e., 10.97 ~ 32.97 mg/kg) was much lower than that of the other two treatments after freeze-thaw ageing. Overall, the combination of biochar and calcium polysulfide displayed advantages in the reduction and immobilization of Cr(VI), and offered a long-term, effective strategy for the remediation of Cr(VI) contaminated soils in cold regions.

A complex bioaccumulation story in flowback and produced water from hydraulic fracturing: The role of organic compounds in inorganic accumulation in Lumbriculus variegatus

Hydraulic fracturing creates large volumes of flowback and produced water (FPW). The waste is a complex mixture of organic and inorganic constituents. Although the acute toxicity of FPW to freshwater organisms has been studied, few have attempted to discern the interaction between organic and inorganic constituents within this matrix and its role in toxicity. In the present study, bioaccumulation assays (7-d uptake and 7-d elimination period) with FPW (1% dilution) were conducted with the freshwater oligochaete, Lumbriculus variegatus, to evaluate the toxicokinetics of inorganic elements. To evaluate the interacting role of organics, bioaccumulation of elements in unmodified FPW was compared to activated carbon treated FPW (AC-modified). Differences in uptake and elimination rates as well as elimination steady state concentrations between unmodified and AC-modified treatments indicated that the organics play an important role in the uptake and depuration of inorganic elements in FPW. These differences in toxicokinetics between treatments aligned with observed growth rates in the worms which were higher in the AC-modified treatment. Whether growth differences resulted from increased accumulation and changes in toxicokinetic rates of inorganics or caused by direct toxicity from the organic fraction of FPW itself is still unknown and requires further research.

Comparison of the Hydraulic Fracturing Water Cycle in China and North America: A Critical Review

There is considerable debate about the sustainability of the hydraulic fracturing (HF) water cycle in North America. Recently, this debate has expanded to China, where HF activities continue to grow. Here, we provide a critical review of the HF water cycle in China, including water withdrawal practices and flowback and produced water (FPW) management and their environmental impacts, with a comprehensive comparison to the U.S. and Canada (North America). Water stress in arid regions, as well as water management challenges, FPW contamination of aquatic and soil systems, and induced seismicity are all impacts of the HF water cycle in China, the U.S., and Canada. In light of experience gained in North America, standardized practices for analyzing and reporting FPW chemistry and microbiology in China are needed to inform its efficient and safe treatment, discharge and reuse, and identification of potential contaminants. Additionally, conducting ecotoxicological studies is an essential next step to fully reveal the impacts of accidental FPW releases into aquatic and soil ecosystems in China. From a policy perspective, the development of China's unconventional resources lags behind North America's in terms of overall regulation, especially with regard to water withdrawal, FPW management, and routine monitoring. Our study suggests that common environmental risks exist within the world's two largest HF regions, and practices used in North America may help prevent or mitigate adverse effects in China.

The kaolinite shuttle links the Great Oxidation and Lomagundi events

The ~2.22-2.06 Ga Lomagundi Event was the longest positive carbon isotope excursion in Earth's history and is commonly interpreted to reflect perturbations in continental weathering and the phosphorous cycle. Previous models have focused on mechanisms of increasing phosphorous solubilization during weathering without focusing on transport to the oceans and its dispersion in seawater. Building from new experimental results, here we report kaolinite readily absorbs phosphorous under acidic freshwater conditions, but quantitatively releases phosphorous under seawater conditions where it becomes bioavailable to phytoplankton. The strong likelihood of high weathering intensities and associated high kaolinite content in post-Great-Oxidation-Event paleosols suggests there would have been enhanced phosphorus shuttling from the continents into marine environments. A kaolinite phosphorous shuttle introduces the potential for nonlinearity in the fluxes of phosphorous to the oceans with increases in chemical weathering intensity.

Group versus individual exposure: Do methodological decisions in aquatic toxicology alter experimental results?

In aquatic toxicology, methods that are chosen for exposures have profound consequences on experimental outcomes and thus can skew policy initiatives. For example, as compared to single-organism exposures, toxicity test results of group exposures may be impacted by confounding factors such as social interactions between animals or individual variation in accumulation rates. To test for differences in organismal response between group and individual toxicological exposures, we exposed Daphnia magna to copper and subsequently compared the toxicity (median lethal concentration or LC50) between groups and individuals. Results suggested that water chemistry had a larger effect on experimental outcomes than the number of animals exposed in the same tank. Methodological decisions with respect to replication type can affect toxicity tests, and LC50s calculated using different exposure types (such as group and individual exposures) may not be comparable.

Changes to hepatic nutrient dynamics and energetics in rainbow trout (Oncorhynchus mykiss) following exposure to and recovery from hydraulic fracturing flowback and produced water

Hydraulic fracturing flowback and produced water (FPW) is a highly complex and heterogenous wastewater by-product of hydraulic fracturing practices. To date, no research has examined how FPW exposure to freshwater biota may affect energetic homeostasis following subsequent induction of detoxification processes. Rainbow trout (Oncorhynchus mykiss) were acutely exposed for 48 h to either 2.5% or 7.5% FPW, and hepatic metabolism was assessed either immediately or following a 3-week recovery period. Induction of xenobiotic metabolism was observed with an 8.8-fold increase in ethoxyresorufin-O-deethylase (EROD) activity after 48 h exposure to 7.5% FPW, alongside a 10.3-fold increase in the mRNA abundance of cyp1a, both of which returned to basal level after three weeks. Glucose uptake capacity was elevated by 6.8- and 12.9-fold following 2.5% and 7.5% FPW exposure, respectively, while alanine uptake was variable. Activity measurements and mRNA abundance of key enzymes involved in hepatic metabolism indicated that aerobic metabolism was maintained with exposure, as was glycolysis. Gluconeogenesis, as measured by phosphoenolpyruvate carboxykinase (PEPCK) activity, decreased by ~30% 48 h following 2.5% FPW exposure and ~20% 3 weeks after 7.5% FPW exposure. The abundance of pepck mRNA activity followed similar, yet non-significant, trends. Finally, a delayed increase in amino acid catabolism was observed, as glutamate dehydrogenase (GDH) activity was increased 2-fold in 7.5% FPW exposed fish when compared to saline  control fish at the 3-week time point. We provide evidence to suggest that although hepatic metabolism is altered following acute FPW exposure, metabolic homeostasis generally returns 3-weeks post-exposure.

Effect of temperature on phenanthrene accumulation from hydraulic fracturing flowback and produced water in rainbow trout (Oncorhynchus mykiss)

Hydraulic fracturing has become widely used in recent years to access vast global unconventional sources of oil and gas. This process involves the injection of proprietary mixtures of water and chemicals to fracture shale formations and extract the hydrocarbons trapped within. These injection fluids, along with minerals, hydrocarbons, and saline waters present within the formations being drilled into, return to the surface as flowback and produced water (FPW). FPW is a highly complex mixture, containing metals, salts and clay, as well as many organic chemicals, including polycyclic aromatic hydrocarbons such as phenanthrene. The present study sought to determine the effects of temperature on the accumulation of phenanthrene in rainbow trout (Oncorhynchus mykiss). This model organism resides in rivers overlapping the Montney and Duvernay formations, both highly developed formations for hydraulic fracturing. Rainbow trout acclimated to temperatures of 4, 13 and 17 °C were exposed to either 5% or 20% FPW, as well as saline mixtures representing the exact ionic content of FPW to determine the accumulation of radiolabelled ¹⁴C phenanthrene within the gill, gut, liver and gallbladder. FPW exposure reduced the overall accumulation of phenanthrene in a manner most often similar to high salinity exposure, indicating that the high ionic strength of FPW is the primary factor affecting accumulation. Accumulation was different at the temperature extremes (4 and 17 °C), although no consistent relationship was observed between temperature and accumulation across the observed tissues. These results indicate that several physiological responses occur as a result of FPW exposure and water temperature change which dictate phenanthrene uptake, particularly in the gills. Temperature (and seasonality) alone cannot be used to model the potential accumulation of polycyclic aromatic hydrocarbons after FPW spills.

Exposure to Hydraulic Fracturing Flowback Water Impairs Mahi-Mahi (Coryphaena hippurus) Cardiomyocyte Contractile Function and Swimming Performance

Publicly available toxicological studies on wastewaters associated with unconventional oil and gas (UOG) activities in offshore regions are nonexistent. The current study investigated the impact of hydraulic fracturing-generated flowback water (HF-FW) on whole organism swimming performance/respiration and cardiomyocyte contractility dynamics in mahi-mahi (Coryphaena hippurus-hereafter referred to as "mahi"), an organism which inhabits marine ecosystems where offshore hydraulic fracturing activity is intensifying. Following exposure to 2.75% HF-FW for 24 h, mahi displayed significantly reduced critical swimming speeds (U_crit) and aerobic scopes (reductions of ∼40 and 61%, respectively) compared to control fish. Additionally, cardiomyocyte exposures to the same HF-FW sample at 2% dilutions reduced a multitude of mahi sarcomere contraction properties at various stimulation frequencies compared to all other treatment groups, including an approximate 40% decrease in sarcomere contraction size and a nearly 50% reduction in sarcomere relaxation velocity compared to controls. An approximate 8-fold change in expression of the cardiac contractile regulatory gene cmlc2 was also seen in ventricles from 2.75% HF-FW-exposed mahi. These results collectively identify cardiac function as a target for HF-FW toxicity and provide some of the first published data on UOG toxicity in a marine species.

Competitive adsorption of heavy metals by anaerobic ammonium-oxidizing (anammox) consortia

Anammox-based processes and microbial consortia have drawn extensive attention for their use in high-efficiency wastewater treatment technologies. Metals substantially affect the activity of anammox consortia and the quality of wastewater treatment plant effluent. Here, we explored the role of anammox consortia in terms of metals complexation in both single and multi-metal systems. Adsorption edges of single metal cations indicate that the adsorption preference was in the order: Pb(II) > Cd(II) > Cr(VI). A competitive effect was observed in multi-metal cations systems, with Pb(II) being preferably adsorbed and the degree of adsorption somewhat reduced in the presence of either Cd(II) or Cr(VI), while Cd(II) and Cr(VI) were easily exchanged and substituted by other metals. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) further suggest that the adsorption of Pb(II) and Cd(II) are as inner-sphere ion-exchange mechanisms, while Cr(VI) adsorption is mainly by outer-sphere complexation. Density functional theory (DFT) calculations highlight that Cd(II) and Pb(II) have different binding sites compared to Cr(VI), and the order of binding energy (E_bd) of three metal cations were Pb(II) > Cd(II) > Cr(VI). These calculations support the adsorption data in that Pb forms more stable complexes with anammox bacterial surface ligands. Surface complexation modelling (SCM) further predicted both the sorption of single metal cations and competitive adsorption of the three metals to anammox consortia, the exception being Cd at higher loadings. The results of this study highlight the potential role of anammox consortia in removing metal cations from wastewater in treatment systems.

Effects of aging and weathering on immobilization of trace metals/metalloids in soils amended with biochar

Biochar is an effective amendment for trace metal/metalloid (TMs) immobilization in soils. The capacity of biochar to immobilize TMs in soil can be positively or negatively altered due to the changes in the surface and structural chemistry of biochar after soil application. Biochar surfaces are oxidized in soils and induce structural changes through physical and biochemical weathering processes. These changes in the biochar surface and structural chemistry generally increase its ability to immobilize TMs, although the generation of dissolved black carbon during weathering may increase TM mobility. Moreover, biochar modification can improve its capacity to immobilize TMs in soils. Over the short-term, engineered/modified biochar exhibited increased TM immobilization capacity compared with unmodified biochar. In the long-term, no large distinctions in such capacities were seen between modified and unmodified biochars due to weathering. In addition, artificial weathering at laboratories also revealed increased TM immobilization in soils. Continued collection of mechanistic evidence will help evaluate the effect of natural and artificial weathering, and biochar modification on the long-term TM immobilization capacity of biochar with respect to feedstock and synthesis conditions in contaminated soils.

Redox-induced mobilization of Ag, Sb, Sn, and Tl in the dissolved, colloidal and solid phase of a biochar-treated and un-treated mining soil

The aim of this work was to study the redox-induced mobilization of Ag, Sb, Sn, and Tl in the dissolved, colloidal, and sediment phase of a mining soil treated and untreated with biochar as affected by the redox potential (E_H) -dependent changes of soil pH, dissolved organic carbon, Fe, Mn and S. The experiment was conducted stepwise at two E_H cycles (+200 mV → -30 mV → +333 mV → 0 mV) using biogeochemical microcosm. Silver was abundant in the colloidal fraction in both cycles, indicating that Ag might be associated with colloids under different redox conditions. Antimony, Sn and Tl were abundant in the colloidal fraction in the first cycle and in the dissolved fraction in the second cycle, which indicates that they are retained by colloids under oxic acidic conditions and released under reducing alkaline conditions. Release of dissolved Sb, Sn, and Tl was governed positively by pH, Fe, S, and dissolved aromatic compounds. Biochar mitigated Ag release, but promoted Sb, Sn, and Tl mobilization, which might be due to the wider range of E_H (-12 to +333) and pH (4.9-8.1) in the biochar treated soil than the un-treated soil (E_H = -30 to +218; pH = 5.9-8.6). Also, the biochar surface functional groups may act as electron donors for the Sb, Sn, and Tl reduction reactions, and thus biochar may play an important role in reducing Tl³⁺ to Tl⁺, Sb⁵⁺ to Sb³⁺, and Sn⁴⁺ to Sn²⁺, which increase their solubility under reducing conditions as compared to oxic conditions. Thallium and Sb exhibit higher potential mobility in the solid phase than Sn and Ag. Biochar increased the potential mobility of Sb, Sn, and Tl under oxic acidic conditions. The results improve our understanding of the redox-driven mobilization of these contaminants in soils.

Hydro-climate and biogeochemical processes control watershed organic carbon inflows: Development of an in-stream organic carbon module coupled with a process-based hydrologic model

Dissolved organic carbon (DOC) in surface waters directly influences the speciation, transport, and fate of heavy metals, as well as the partitioning of organic contaminants. However, the lack of process-based watershed-scale models for simulating carbon cycling and transport has limited the effective watershed management to control organic carbon fluxes to source waters and throughout the river systems. Here, a process-based in-stream organic carbon (OC) module was developed, coupled with the physically process-based Soil and Water Assessment Tool (SWAT), and linked with its existing soil carbon module to simulate dynamics of both particulate organic carbon (POC) and DOC. The advanced model simulates a large spectrum of OC processes from landscapes to stream networks throughout the watersheds. In-stream organic carbon processes related to POC and DOC as state variables are modeled in the water column, and the transformations between different carbon species and interactions between OC with algae are considered. The module's ability to simulate total organic carbon (TOC) loads was assessed, and the monthly and seasonal variations were captured over 14 years. Simulations for TOC loads suggested that spring snowmelt and summer rainfall runoff events are the main driving forces behind TOC export in the watershed. The parameter sensitivity analysis and dynamic reaction rate simulated in the streams suggested that TOC dynamics in the study area are controlled by both landscape and in-stream processes. The spatiotemporal analysis of the simulated TOC load showed that 55.8% of total terrestrial OC exports into the streams are removed due to in-stream POC settling and DOC mineralization, confirming the necessity of integrating terrestrial and aquatic OC processes for process understanding and for modelling and management of water quality at the watershed scale. The developed OC module is a potentially effective tool for simulating the OC cycle at the watershed scale and can be applied further to water treatment plans and watershed management.

Using CO2 as an Oxidant in the Catalytic Pyrolysis of Peat Moss from the North Polar Region

As global warming and climate change become perceived as significant, the release of greenhouse gases (GHGs) stored in the earth's polar regions is considered a matter of concern. Here, we focused on exploiting GHGs to address potential global warming challenges in the north polar regions. In particular, we used CO₂ as a soft oxidant to recover energy as syngas (CO and H₂) and to produce biochars from pyrolysis of peat moss. CO₂ expedited homogeneous reaction with volatile matters from peat moss pyrolysis, and the mechanistic CO₂ role resulted in the conversion of CO₂ and peat moss to CO at ≥530 °C. Steel slag waste was then used as an ex situ catalyst to increase reaction kinetics, addressing the issue of the role of CO₂ being limited to ≥530 °C, with the result where substantial H₂ and CO formation was achieved at a milder temperature. The porosity of biochars, a solid peat moss pyrolysis product, was modified in the presence of CO₂, with a significant improvement in CO₂ adsorption capacity compared to those achieved by N₂ pyrolysis. Therefore, CO₂ has the potential to serve as an initial feedstock in sustainable biomass-to-energy applications and biochar production, mitigating atmospheric carbon concentrations.