Formation, characteristics, and applications of environmentally persistent free radicals in biochars: A review

Complete degradation of polycyclic antibiotic methacycline by a micro/nanostructured biogenic Mn oxide composite from engineered Mn(II)-oxidizing Pseudomonas sp. MB04B

The misuse and improper disposal of methacycline (MTC), a widely used broad-spectrum antibiotic in human clinical settings and livestock production, poses significant threats to both human health and the ecological environment. In this study, a wild-type Mn(II)-oxidizing Pseudomonas strain MB04B was modified through multiple gene deletions, leading to a maximum 35% increase in Mn oxide deposit amount (MnODA) in the engineered strain MB04R-14, and accelerated formation of biogenic Mn oxide (BMO) aggregates, which exhibited the capability to degrade and detoxify MTC completely. After constructing a mini-Tn5 transposon insertion mutant library and screening for MnODA-increased mutants, a total of 10 target genes located in the corresponding mutant loci were identified using the high-efficiency thermal asymmetric interlaced PCR (hiTAIL-PCR) method. These genes were systematically knocked out singly or in multiple combinations, and the highest MnODA-promoted mutant (MB04R-14) was obtained, in which seven genes were knocked out. Following the characterization of the BMO aggregate complex formed in MB04R-14 as a micro-/nanostructured ramsdellite (MnO2) composite through means of several analysis methods, the complex was assessed for MTC degradation under laboratory trials. Complete MTC degradation was revealed after 24 h of treatment with the BMO complex, and the metal ions Mg2+, Cu2+, Ni2+, and Co2+ significantly inhibited MTC degradation efficiency. Liquid chromatography-mass spectrometry identified three intermediates in the degradation pathway, and a possible degradation-metabolic pathway of MTC by the BMO complex was proposed. Finally, the residual antibiotic activity, continuous degradation cycle performance, and treatment of MTC-containing hospital wastewater were evaluated.

IMPORTANCE

Due to the common usage and recalcitrance to degradation, methacycline is often found in various surface water and wastewater as a persistent antibiotic toxicant, posing significant risks to the environment and public health. By engineering a Pseudomonas strain, we developed a dynamic oxidative composite comprising engineered Pseudomonas cells and biogenic Mn oxides. This system not only enhances oxidative capacities but also accelerates the formation of biogenic Mn oxides, leading to the complete degradation of methacycline. The findings highlight the potential of engineered Pseudomonas strain as a sustainable solution for mitigating antibiotic pollution, thereby contributing to cleaner water resources and protecting ecosystems.

Formation and evolution of environmentally persistent free radicals in charcoal and soot generated from biomass materials

Environmentally persistent free radicals (EPFRs) are emerging pollutants that are highly reactive and toxic, posing potential health risks. Biomass burning is a significant source of EPFRs, but there has been a notable gap in research regarding the EPFRs present in charcoal and soot produced from the same combustion process. Our study detected EPFRs in both charcoal and soot, but there were significant differences in their characteristics. The EPFR concentrations in charcoal were much higher than that in soot, by approximately 2-4 orders of magnitude, suggesting that charcoal may be more chemically reactive. Differences in the formation mechanisms between charcoal and soot were found to result in variations in the characteristics of EPFRs observed in each material. Furthermore, the ability of EPFRs to generate reactive oxygen species (ROS) differed considerably between charcoal and soot. Charcoal exhibited a strong ability to produce ROS, including 1O2 and ·OH radicals, and the abundances of 1O2 was further enhanced (∼1.2 -2.1 times) after illumination. In contrast, only the 1O2 radical was found in soot produced at 300 °C. These findings enhanced our understanding of the environmental impact and potential toxicity of EPFRs, offering valuable insights for evaluating the risks associated with wildfires and agricultural burning.

Role of reactive oxygen species (ROS) on biochar enhanced chromium phytoremediation in the soil-plant system: Exploration on detoxification mechanism

Biochar, as an amendment to enhance phytoremediation of heavy metal contamination, can mediate reactive oxygen species (ROS) generation. However, the role of biochar-mediated ROS (BMR) during soil-plant phytoremediation remains inadequately understood. In this study, a combination of pot experiments, chemical extraction, and partial least squares path modeling (PLS-PM) was employed to investigate BMR dynamics and their influence on chromium (Cr) accumulation and detoxification in plants. Biochar addition promoted Cr removal efficiency and decreased ROS concentrations in soil, notably reaching the largest removal efficiency of 80.60 % and the lowest ROS concentration of 37.53 μmol/kg in BC-3 group at 90d. Decreased ROS concentrations in soil facilitated the plant absorbing water-soluble Cr (VI), adsorbed Cr (VI), and chromate-precipitated Cr (VI) in soil, and enhanced Cr accumulation in metabolically inactive compartments (cell walls and vacuoles). When biochar was added at concentrations of 2 % and 3 % (w/w), ROS concentrations in plant tissues decreased to signaling molecule thresholds. This reduction further stimulated antioxidant enzyme activity, promoted the reduction of Cr (VI) within subcellular organelles, and enhanced Cr cell wall fixation and vacuolar compartmentation, ultimately achieving their synergistic integration with Cr detoxification with accumulation. This study provides an in-depth understanding of BMR-related mechanisms during phytoremediation and valuable insights into strategies for enhancing mitigation of variable valence heavy metals in soils.

Persistent free radicals in the environment

Environmentally persistent free radicals (EPFRs) are environmental pollutants whose potential DNA damage and apoptosis toxicity may be mediated by reactive oxygen species (ROS). The currently available knowledge of their environmental characteristics and transformation mechanisms is not sufficient to understand the environmental behaviors and health effects of EPFRs and should be further expanded. This review offers a comprehensive review of the current state of EPFRs, including characterization methods, formation mechanisms, and environmental behavior of EPFRs. Electron paramagnetic resonance (EPR) spectroscopy directly probes EPFRs in environmental matrices. EPFRs can be simply categorized by g value, but structure confirmation solely by EPR is challenging because the complexity of environmental matrices results in the absence of a hyperfine splitting spectrum. Combined advanced EPR and multi-spectroscopic methods enable the structural identification of EPFRs in environmental samples. The environmental behavior and ecological impacts of EPFRs have been progressively studied. This review highlights the important role of EPFRs in natural environments and emphasizes the necessity of further research on EPFRs.

Recent advances in valorization of lignocellulosic waste into biochar and its functionalization for the removal of chromium ions

Lignocellulosic waste is a prevalent byproduct of agricultural and forestry activities which is an excellent feedstock for the preparation of biochar. This research area is of interest to the scientific community due to its potential in environmental remediation. In this regard, this review examines the latest advancements in transforming lignocellulosic waste into biochar and explores recent innovations in enhancing its functionality for chromium ion removal. It gives analysis on current methods for biochar production from lignocellulosic materials such as pyrolysis. Additionally focusing on improvements in production efficiency, structural properties, and surface modifications. The review also highlights various functionalization techniques, such as chemical activation and impregnation with metal oxides, that were innovated to improve adsorptive nature of biochar for chromium ions. While progress has been made, achieving scalability in lignocellulosic biochar production presents challenges, such as the high energy demands of pyrolysis, inconsistencies in feedstock quality, and the need for cost-effective functionalization methods. By summarizing recent research and technological progress, this paper aims to offer a clear perspective on the effectiveness of biochar derived from lignocellulosic waste in addressing contamination. Additionally, it discusses the ongoing challenges and future research directions needed to optimize biochar applications in environmental cleanup.

Three-dimensionally structured MoS2@biochar breaks through the bottleneck in antibiotic wastewater treatment: Greater efficiency and self-motivated oxidation pathway

Two-dimensional (2D) MoS2 has been widely used to remove antibiotics. However, low selectivity for antibiotic pollutants, dependence on applied energy and oxidant, and secondary contamination are still the bottlenecks of this system for treating antibiotic wastewater. In this study, we proposed a three-dimensional (3D) material (3MoS2/BMBC@MF) based on MoS2 and biochar with melamine sponge as the backbone. Compared with the 2D material (MoS2/BMBC), 3MoS2/BMBC@MF performed significantly better in enrofloxacin (ENR) removal, with an increase in the removal degree from 60.8 % to 88.1 %, and acted mainly through the degradation pathway rather than relying solely on the adsorption effect. It was shown that the direct oxidation process (DOP) behind the 3D materials is the key to the self-activated oxidation pathway. The three-dimensional structure enhances the generation and transfer pathways of persistent free radicals (PFRs) and electrons, realizing a multi-dimensional activation mechanism through its unique three-dimensional network, which greatly improves the redox capacity of the material. Upon exposure to pollutants, 3MoS2/BMBC@MF generates carbon-centered radicals of PFRs, which degrade ENR through mediated electron transfer. Coupled with the three-dimensional structure that contributes to the homogeneous dispersion of the active substances, dense steric active centers are formed in the grid skeleton by redox cycling of Mo ions to degrade antibiotics via DOP. Meanwhile, 3MoS2/BMBC@MF possesses good recyclability and maintains high efficiency in recycling. The structural design of this material not only enhances the removal efficiency and reduces the environmental impact, but also provides new potentials and solutions for practical water treatment of antibiotic contaminants.

Hydrochar of Prunus persica: green promoter of radical species to degrade methylene blue with visible irradiation

The creation of new materials based on metal-free catalysts represents a sustainable alternative in the treatment of water contaminated with dyes. In this context, the use of agro-industrial wastes for the creation of hydrochars with applications in environmental water remediation is an attractive and green option for metal-free catalysts for visible heterogeneous photocatalysis. In this study, hydrochars derived from agro-industrial waste of Prunus persica (peach pit) and their application in visible photodegradation of dyes were performed. The evaluation of the temperature and reaction time of hydrochars showed that 180 °C and 3 h yielded the highest photocatalytic activity and lower energy requirements in their preparation. The electron paramagnetic resonance (EPR) characterization evidenced the presence of persistent free radicals of the oxygen-centered radical type and, together with the oxygenated groups present in the carbonaceous structure of the hydrochar, promoted the generation of radical species such as superoxide and hydroxyl radicals. The visible photodegradation experiments of methylene blue (MB) demonstrated a high degradation efficiency of 92.9% using the following conditions: Ci = 10 mg/L, pH 7.0, hydrochar dosage: 50 mg, V: 50 mL, 120 min of irradiation time, and white-LED irradiation source. In addition, the generation of radicals •OH, O2-•, and 1O2, was demonstrated, as well as the potential use of the hydrochars for photodegradation in tap water and effluent of wastewater treatment plant matrices. Finally, the valorization of Prunus persica biomass through hydrochar production offers a promising avenue for water treatment and a route for the revalorization of agro-industrial waste.

Adsorption-desorption properties and control mechanism of aromatic organophosphate esters on biochar-mineral complexes

With the widespread application of biochar, biochar-mineral complexes are formed in large quantities in the environment. However, there are few reports on their adsorption and desorption mechanisms for organophosphate esters (OPEs). In this study, biochar-mineral complexes (MBC@FH and MBC@F) were prepared through co-ball-milling with biochar and minerals (α-FeO(OH) and Fe2O3). The properties of pristine biochar and MBC@FH/F were compared, and the adsorption-desorption mechanisms of OPEs on all biochar materials were analyzed. The results showed that MBC@FH/F complexes have a larger specific surface area, more oxygen-containing functional groups, stronger aromaticity, and larger pore structures, but less persistent free radicals than pristine biochar. MBC@FH/F complexes exhibited lower secondary kinetic adsorption rate constant (k2), higher intraparticle diffusion rate constant (k1p) and adsorption capacity than pristine biochar. Hydrophobic interactions controlled the adsorption of TPhP and TPPO on MBC@FH/F complexes, and π-π interactions, pore filling, hydrogen bonding also participated in the adsorption process. MBC@F had higher aromaticity than MBC@FH, thus having stronger adsorption capacity than MBC@FH. The large spatial volume of TPPO inhibited its diffusion on biochar materials, demonstrating a smaller adsorption amounts than TPhP. The desorption was only observed for TPhP, while no desorption occurred for TPPO. The retention amount of TPhP on MBC@FH/F was represented by subtracting the desorption amount from their adsorption amount, which increased by 1.22-6.98 times, reaching 4.48-41.07 mg/g. In addition, the desorption hysteresis decreases with increasing pore diameter of MBC@FH/F. This study illustrated that the formation of biochar-mineral complexes may be more conducive to the adsorption of OPEs.

Dynamic formation mechanism of persistent free radicals driven by water-phase oxidation-dependent heterogeneity of the carbon-silicon coupling structure in biochar

The formation of persistent free radicals (PFRs) in biochar (BC) is closely related to the structural characteristics and reactivity of BC, which have toxic effects on the environment. However, the mechanisms driving PFRs formation through structural evolution during oxidative aging of BC remain unclear. Herein, we propose a novel dynamic mechanism for BC-PFRs formation driven by oxidation-dependent heterogeneity in carbon-silicon coupling structures by evaluating their heterogeneous correlations, sequential responses, and synergistic relations. The sequential destruction of the "outer carbon-middle silicon-inner carbon" spatial layer and the transformation of molecular components caused by continuous oxidation of BC contributed to the formation of BC-PFRs with two concentration peaks. Moreover, two-dimensional correlation spectroscopy combined with infrared spectroscopy and high-resolution mass spectrometry revealed the sequential responses of carbon-silicon functional groups in BC (Si-O-Si groups → silicon enclosed structures → carbon groups) and BC-derived dissolved organic molecules (lipid-/aliphatic-/carbohydrate-like molecules → lignin-/tannin-like molecules → condensed aromatic molecules), leading to the staged formation of BC-PFRs. High molecular-weight lignin-/tannin-like and condensed aromatic molecules in the carbon layer contributed to BC-PFRs formation, whereas crystalline silicon components hindered the oxidative degradation of inner aromatic carbon and subsequent PFRs formation. Our findings help elucidate potential environmental behaviors and risks associated with BC-PFRs.

Effect of lignin carbon material on phosphorus solubilisation performance of Bacillus megaterium

Secondary salinisation significantly compromises soil quality because of the over-application of chemical fertilisers. The combined application of biochar and microorganisms enhanced soil physicochemical properties and improved soil remediation efficiency. However, different types of biochar had varying effects on microbial growth and reproduction. A phosphate-solubilising bacterial agent (BM-LPC) was obtained by low-temperature carbonisation/activation lignin-based porous carbon (LPC) in situ culture/adsorption Bacillus megaterium (BM). The maximum soluble phosphorus capacity of BM-LPC was 744.29 mg/L when 1 % LPC was added. This was a 22 % increase compared with BM alone. The maximum adsorption of BM by LPC was 3.66 × 109 colony-forming units (CFU)/g. At 150 days, the viable bacterial count of BM-LPC was 2.09 × 109 CFU/g. The abundances of -OH, -COOH, -NH2, and CO groups on the surface of LPC provided a stable environment for BM, which in turn, enhanced the solubilisation of phosphorus and extended the viability of BM. The findings of this study can help increase the added value of industrial lignin and provide a theoretical basis for soil remediation research.

Beyond the Bench: Contextualizing the Impacts of Char Redox Properties on Biogeochemical Cycling and Microbial Ecosystem Services

The electrochemical properties of chars have been recently described, positioning chars as active participants in microbial redox processes through functional groups, aromatic structures, redox-active metals, and radicals. While bench-scale studies have advanced mechanistic understanding of char's behavior and potential effects, translating these findings to complex ecosystems remains challenging. This is mainly due to the complexities of microbial communities and the unique properties of various ecosystems. Factors like char aging and patina formation, and environmental parameters including oxygen and moisture availability, pH, and organic matter content can significantly affect char electrochemical properties and microbial interactions. This highlights the need for a broader understanding of char redox processes to predict and effectively manage unintended environmental impacts or enhance beneficial effects. Long-term monitoring of complex systems amended with char is also needed to determine whether char accumulation has long-term redox effects on microbial ecosystem services, including biogeochemical cycling. Predictive understanding of these processes would inform the production of chars to enhance beneficial processes such as increased soil productivity, and provide new opportunities for engineered environmental remediation. Here, we summarize how char redox properties affect well-defined microbial systems and discuss key factors that determine whether the effects of char redox properties are enhanced or attenuated in complex systems. We also identify critical knowledge gaps about chars' role in microbial redox processes that are important for environmental sustainability and postulate that managing char's redox properties, such as electron donating, accepting, or conducting ability, is an emerging opportunity to influence microbial ecosystem services.

Upcycling Waste Biomass to Biochar: Feedstocks, Catalytic Mechanisms, and Applications in Advanced Oxidation for Wastewater Decontamination

Advanced oxidation technology plays an important role in wastewater treatment due to active substances with high redox potential. Biochar is a versatile and functional biomass material. It can be used for resource management of various waste biomasses. In addition, carbonaceous materials are commonly used to enhance the synergistic mechanisms of advanced oxidation processes, because of their good electrical conductivity and metal-free leaching. Biochar produced from waste biomass through pyrolysis has catalytic potential, is cost-effective, and is environmentally friendly. It is commonly used to activate hydrogen peroxide, persulfate, ozone, photocatalysis, and other systems for degrading organic pollutants in water. This review provides a summary of the feedstocks, pyrolysis conditions, and modification methods used in biochar production. It also described the effects of these factors on the yield, structure, and active sites of the biochar. The review summarized the mechanisms of various catalytic systems and their applications in wastewater decontamination, as well as their potential for practical application. Eventually, the limitations of this current technique and the outlook for future research were noted.

A Critical Review of an Environmental Risk Substance Induced by Aging Microplastics: Insights into Environmentally Persistent Free Radicals

Microplastics (MPs), as an emerging contaminants category, can undergo complex aging in a variety of environmental matrices in which the chemical bonds of polymer molecules can be broken to form free radicals. While the existence of free radicals in aged plastics has been known for over half a century, only recently has significant research on a new type of environmentally risky substance, namely environmentally persistent free radicals (EPFRs), present in aged MPs and their environmental effects, been started, but it is still in its infancy. To address these issues, this work examines EPFR generation on MPs and their environmental effect by reviewing publications from 2012 to 2023. The aging processes and mechanisms of MPs in the environment are first summarized. Then, the occurrence and formation mechanisms of EPFRs on aged MPs are specifically discussed. Additionally, the reactivity of EPFRs on aging MPs and their influencing factors are comprehensively considered, such as their physicochemical properties, oxygen content, and coexisting substances. Due to their reactivity, EPFRs can interact directly with some substances (e.g., p-nitrophenol and proteins, etc.) or induce the generation of reactive oxygen species, leading to diverse environmental effects, including pollutant transformation, biotoxicity, and health risks. Finally, research challenges and perspectives for EPFRs formation on aging MPs and related environmental implications are presented. Given the environmental fate and risk of MPs-EPFRs, our urgent call for a better understanding of the potential hazards of aged MPs is to help develop a sustainable path for plastics management.

MgO anchored N-doping biochar enhances the bensulfuron-methyl biodegradation by Acinetobacter YH0317: Higher reactive oxygen species level and bacterial viability

Bensulfuron-methyl (BSM) is a typical broad-spectrum sulfonylurea herbicide and the runoff of BSM residues from agricultural regions poses a significant threat to the ecosystem. Here we develop a bacteria-material hybrid system constructed by Acinetobacter YH0317 and Mg(NO3)2 modified biochar (MBC) for efficiently degrading BSM under various conditions including pH and temperature. Results showed that BSM biodegradation efficiency by YH0317&MBC (96.7 %) was significantly higher than YH0317&BC (79.5 %) and YH0317 (43.9 %) at 15 °C after 7 d of incubation. The addition of MBC significantly increased the reactive oxygen species (ROS) level, which was significantly higher than group YH0317. Moreover, the bacterial viability, extracellular polymeric substances (EPS) production, and membrane permeability of YH0317 were also enhanced with the addition of MBC. The electron paramagnetic resonance (EPR) and quenching experiments revealed that singlet oxygen (1O2) was the dominant active substance produced by MBC. The YH0317&MBC could effectively remove the BSM, and reduce the oxidative stress to soybean, which was beneficial to the growth of soybean through hydroponic experiment. This study establishes a microorganism-material system that efficiently removes BSM in aquatic environments and emphasizes the importance of ROS in pollution removal by the hybrid system.

Application of Biochar-Based Materials for Effective Pollutant Removal in Wastewater Treatment

With the growth of the global population and the acceleration of industrialization, the problem of water pollution has become increasingly serious, posing a major threat to the ecosystem and human health. Traditional water treatment technologies make it difficult to cope with complex pollution, so the scientific community is actively exploring new and efficient treatment methods. Biochar (BC), as a low-cost, green carbon-based material, exhibits good adsorption and catalytic properties in water treatment due to its porous structure and abundant active functional groups. However, BC's pure adsorption or catalytic capacity is limited, and researchers have dramatically enhanced its performance through modification means, such as loading metals or heteroatoms. In this paper, we systematically review the recent applications of BC and its modified materials for water treatment in adsorption, Fenton-like, electrocatalytic, photocatalytic, and sonocatalytic systems, and discuss their adsorption/catalytic mechanisms. However, most of the research in this field is at the laboratory simulation stage and still needs much improvement before it can be applied in large-scale wastewater treatment. This review improves the understanding of the pollutant adsorption/catalytic properties and mechanisms of BC-based materials, analyzes the limitations of the current studies, and investigates future directions.

A comprehensive review of antibiotic resistance gene contamination in agriculture: Challenges and AI-driven solutions

Since their discovery, the prolonged and widespread use of antibiotics in veterinary and agricultural production has led to numerous problems, particularly the emergence and spread of antibiotic-resistant bacteria (ARB). In addition, other anthropogenic factors accelerate the horizontal transfer of antibiotic resistance genes (ARGs) and amplify their impact. In agricultural environments, animals, manure, and wastewater are the vectors of ARGs that facilitate their spread to the environment and humans via animal products, water, and other environmental pathways. Therefore, this review comprehensively analyzed the current status, removal methods, and future directions of ARGs on farms. This article 1) investigates the origins of ARGs on farms, the pathways and mechanisms of their spread to surrounding environments, and various strategies to mitigate their spread; 2) determines the multiple factors influencing the abundance of ARGs on farms, the pathways through which ARGs spread from farms to the environment, and the effects and mechanisms of non-antibiotic factors on the spread of ARGs; 3) explores methods for controlling ARGs in farm wastes; and 4) provides a comprehensive summary and integration of research across various fields, proposing that in modern smart farms, emerging technologies can be integrated through artificial intelligence to control or even eliminate ARGs. Moreover, challenges and future research directions for controlling ARGs on farms are suggested.

Self-sacrificing and self-supporting biomass carbon anode-assisted water electrolysis for low-cost hydrogen production

Electrooxidation of renewable and CO2-neutral biomass for low-cost hydrogen production is a promising and green technology. Various biomass platform molecules (BPMs) oxidation assisted hydrogen production technologies have obtained noticeable progress. However, BPMs anodic oxidation is highly dependent on electrocatalysts, and the oxidation mechanism is ambiguous. Meanwhile, the complexity and insolubility of natural biomass severely constrain the efficient utilization of biomass resources. Here, we develop a self-sacrificing and self-supporting carbon anode (SSCA) using waste corncobs. The combined results from multiple characterizations reveal that the structure-property-activity relationship of SSCA in carbon oxidation reaction (COR). Theoretical calculations demonstrate that carbon atoms with a high spin density play a pivotal role in reducing the adsorption energy of the reactive oxygen intermediate (*OH) during the transition from OH- to *OH, thereby promoting COR. Additionally, the HER||COR system allows driving a current density of 400 [Formula: see text] at 1.24 V at 80 °C, with a hydrogen production electric consumption of 2.96 kWh Nm-3 (H2). The strategy provides a ground-breaking perspective on the large-scale utilization of biomass and low-energy water electrolysis for hydrogen production.

The interaction between biochar and earthworms: Revealing the potential ecological risks of biochar application and the feasibility of their co-application

Biochar's interaction with soil-dwelling organisms, particularly earthworms, is crucial in ensuring the effective and secure utilization of biochar in the soil. This review introduces the application of biochar in soil, summarizes how earthworms respond to biochar-amended soil and the underlying factors that can influence their response, discusses the synergistic and antagonistic impacts of earthworm activity on the efficacy of biochar, and considers the feasibility of applying them together. A review of existing research has identified uncertainty in the effect of biochar exposure on earthworms, with biochar derived from animal wastes, produced at higher pyrolysis temperatures, and used at higher doses of biochar having more negative effects on earthworms. Habitat modification, toxicity release, particle effects, and contaminant immobilization are underlying factors in how biochar affects earthworm indicators. While biochar in contaminated soils may alleviate the stress of pollutants on earthworms by decreasing their bioaccumulation, this remedial effect is not always effective. Additionally, earthworm bioturbation can enhance the migration, fragmentation, and oxidation of biochar, while also stimulating extracellular enzymes that convert biochar into 'vermichar'. Earthworms and biochar can synergize well to improve soil fertility and remediate soil organic pollution, yet exhibit contrasting roles in soil C sequestration and immobilizing heavy metals in soil. These findings highlight both the advantages and risks of their co-application. Therefore, when considering the use of biochar alone or with earthworms, it is crucial to thoroughly assess its potential ecotoxicity on earthworms and other soil organisms, as well as the influence of bioturbation, such as that caused by earthworms, on the effectiveness of biochar.

Cr(VI) bioreduction enhanced by the electron transfer between flavin reductase and persistent free radicals

Persistent free radicals (PFRs) in biochar are an important electron shuttle for mediating electron transfer, which has significant impact on the biogeochemical redox reactions. Although the influence of biochar on the extracellular electron transfer (EET) for redox cycle has been extensively studied, the molecular mechanism for promoting the EET with PFRs remains poorly understood. This study investigated the oxygen-centered PFRs-mediated Cr(VI) reduction by Shewanella oneidensis MR-1 (MR-1) and exhibited the molecular mechanism of electron transfer between flavin substances and PFRs. Results showed that the Cr(VI) bioreduction rate by MR-1 increased from 31% to 70% with the addition of biochar. Electrochemical results illustrated that biochar increased biocurrent generation in the Cr(VI) bioreduction process. 3D-EEM and LC/MS spectra indicated that MR-1 secreted the flavin mononucleotide (FMN) reductase that relied on the [H] to provide the electrons. Electron paramagnetic resonance spectra illustrated that PFRs in biochar accepted the electrons from FMN reductase and stored those bioelectrons. Because of the oxidation of FMN, the electron transfer from FMN reductase to PFRs would increase the intracellular reactive oxygen species, which further produced the extracellular ·O2-. The reduced PFRs released the bioelectrons, accelerating the Cr(VI) reduction by ·O2-. Together with the results of the mutant strains experiment, it was found that the EET by c-cytochrome and free radicals contributed to the Cr(VI) bioreduction by 7.1% and 92.9%, respectively. These findings revealed that the PFRs could participate in the EET process and promote the redox reactions, providing a new approach for enhancing the remediation of heavy metal pollution by microorganisms and suggesting the important role of PFRs in the electron transfer process.

Tracking Long-Lived Free Radicals in Dandelion Caused by Air Pollution Using Electron Paramagnetic Resonance Spectroscopy

Studies on particulate air pollution indicate that a new type of pollutant should be considered from mainly fossil fuel combustion and automobile exhaust emissions, i.e., environmentally persistent free radicals. These radicals, ubiquitous in the environment, have a long life span and are capable of producing harmful reactive oxygen species. Samples of dandelion were collected in 2020 and 2021 in spring and late summer. Roots, leaves, flower stalks, and inflorescences of Taraxacum sp. were collected from six sites with three plants each, along with monitoring of particulate matter air pollution. Four sites were located at streets with heavy traffic and two were control sites in the rural part of the city. The free radical content in each part of the plant was measured by electron paramagnetic resonance. The leaf was selected as the most appropriate part of the plant for the measurement of carbon-derived free radicals. The geff value and the total number of spins were calculated. Relationships were found between location, season, and measurements. The electron paramagnetic resonance spectrum consists of at least two components, which can be attributed to C-type radicals and mixed C + O radicals. Their increase in numbers in the fall seasons, compared to the spring seasons, is also noticeable. It has also been observed that leaves collected in autumn have a higher geff value, which is probably related to the higher amount of oxygen- and carbon-derived free radicals.

Coupled effects of Fenton-like systems with different concentrations of H2O2/Biochar on diethyl phthalate removal: Dominant role of environmental persistent free radicals (EPFRs)

To investigate the impact of different H2O2 concentrations on the Fenton-like systems of H2O2/biochar, this study examined the mechanism of the physical structure and environmental persistent free radicals (EPFRs) of biochar during diethyl phthalate (DEP) removal by the Fenton-like system. The peak-splitting method was utilized to differentiate EPFRs types in cotton stalk biochar produced at different temperatures. High-temperature environments promote π-electron delocalization, which facilitates phenyl π free radicals and σ-π oxygen-containing free radicals. By analyzing relationships between the removal rate K1 and removal constant Kobs of DEP with the structural properties of biochar, it was discovered that EPFRs concentrations in biochar had a significant positive correlation with K1 (r = 0.92) and Kobs (r = 0.97). Different H2O2 concentrations added to the biochar removal system resulted in varied DEP removal efficiency. Among them, CS500, CS550, and CS600 exhibited superior DEP removal efficiency when H2O2 concentration was 5 mM.

Fenton-conditioning of landfill leachate biological sludge enables biochar for efficient Cr(Ⅵ)removal: Occurrence of oxygen-centered free radicals

Fenton-conditioning is commonly used to improve dewatering ability for municipal biological sludge, however, its application in industries is scarce. In this study, biochar (FT-BC) was successfully synthesized from a Fenton-conditioned landfill leachate biological sludge under oxygen-limited. As compared to the corresponding blank and poly ferric-pretreated biochars (BC and PF-BC), moderate Fenton conditioning of the sludge could enable good removal performance for Cr (Ⅵ) by FT-BC. It was found that the oxygen central free radicals (OCFRs) on the biochar surface was intensively promoted due to Fenton electrophilic addition of ·OH onto the oxygen-containing functional groups in biomass. The amounts of OCFRs correlated positively well with the removal efficiency, indicating these persistent free radicals (PFRs)would mainly responsible for the reductive immobilization of Cr(VI)on the FT-BC surface. This study is expected to provide a new method for reclamation of industrial biological sludges with poor agglomeration by introducing simple Fenton pre-conditioning.

Environmentally persistent free radicals and other paramagnetic species in wildland-urban interface fire ashes

Wildland-urban interface (WUI) fires consume fuels, such as vegetation and structural materials, leaving behind ash composed primarily of pyrogenic carbon and metal oxides. However, there is currently limited understanding of the role of WUI fire ash from different sources as a source of paramagnetic species such as environmentally persistent free radicals (EPFRs) and transition metals in the environment. Electron paramagnetic resonance (EPR) was used to detect and quantify paramagnetic species, including organic persistent free radicals and transition metal spins, in fifty-three fire ash and soil samples collected following the North Complex Fire and the Sonoma-Lake-Napa Unit (LNU) Lightning Complex Fire, California, 2020. High concentrations of organic EPFRs (e.g., 1.4 × 1014 to 1.9 × 1017 spins g-1) were detected in the studied WUI fire ash along with other paramagnetic species such as iron and manganese oxides, as well as Fe3+ and Mn2+ ions. The mean concentrations of EPFRs in various ash types decreased following the order: vegetation ash (1.1 × 1017 ± 1.1 × 1017 spins g-1) > structural ash (1.6 × 1016 ± 3.7 × 1016 spins g-1) > vehicle ash (6.4 × 1015 ± 8.6 × 1015 spins g-1) > soil (3.2 × 1015 ± 3.7 × 1015 spins g-1). The mean concentrations of EPFRs decreased with increased combustion completeness indicated by ash color; black (1.1 × 1017 ± 1.1 × 1017 spins g-1) > white (2.5 × 1016 ± 4.4 × 1016 spins g-1) > gray (1.8 × 1016 ± 2.4 × 1016 spins g-1). In contrast, the relative amounts of reduced Mn2+ ions increased with increased combustion completeness. Thus, WUI fire ash is an important global source of EPFRs and reduced metal species (e.g., Mn2+). Further research is needed to underpin the formation, transformation, and environmental and human health impacts of these paramagnetic species in light of the projected increased frequency, size, and severity of WUI fires.

Evaluation of Rheological Properties of Asphalt Binder Modified with Biochar from Oat Hulls

In this study, the effect of biochar from oat hulls (BO) on the rheological properties of a PG 64-22 asphalt binder was evaluated using a full factorial design, which included the following factors: pyrolysis temperature (PT) (300 °C and 500 °C), BO particle size (<20 µm and <75 µm), and the amount of BO (2.5%, 5%, and 7.5%). First, the morphological and physicochemical properties of BO were analyzed by comparing it with graphite powder (CFG) and commercial activated carbon (CAC). The physicochemical properties of the modified asphalt binder were then evaluated using confocal laser microscopy, scanning electron microscopy (SEM-EDX), and Fourier-transform infrared spectroscopy (FTIR). Its storage stability was also evaluated. Subsequently, the rutting parameter G*/sin(δ) and the Fraass breaking point were analyzed to select asphalt binders that extended their viscoelastic range. The asphalt binders selected were those with 2.5%, 5%, and 7.5% BO, produced at a PT of 300 °C with a particle size <20 µm (BO300S). Next, the rheological properties of the selected samples were evaluated by testing for rotational viscosity, rutting parameter G*/sin(δ), multiple stress creep recovery (MSCR), fatigue parameter G*·sin(δ), and creep stiffness by bending beam rheometry (BBR). The rheological aging index according to rutting parameter G*/sin(δ) (RAI) was also evaluated. These tests were conducted in different states of the asphalt binder: original, short-term aged, and long-term aged. According to the results, the application of BO300S significantly increased the resistance of the asphalt binder to rutting and rotational viscosity, proportional to the amount added to the asphalt binder. Moreover, low modifier percentages improved fatigue resistance, outperforming CFG and CAC. In addition, it performs well at low service temperatures, registering better resistance than the control asphalt binders.

Recent advances and prospects of neonicotinoid insecticides removal from aquatic environments using biochar: Adsorption and degradation mechanisms

In recent years, neonicotinoid insecticides (NNIs), representing a new era of pest control, have increasingly replaced traditional classes such as organophosphorus compounds, carbamates, and pyrethroids due to their precise targeting and broad-spectrum efficacy. However, the high water solubility of NNIs has led to their pervasion in aquatic ecosystems, raising concerns about potential risks to non-target organisms and human health. Therefore, there is an urgent need for research on remediating NNI contamination in aquatic environments. This study demonstrates that biochar, characterized by its extensive surface area, intricate pore structure, and high degree of aromaticity holds significant promise for removing NNIs from water. The highest reported adsorption capacity of biochar for NNIs stands at 738.0 mg·g-1 with degradation efficiencies reaching up to 100.0 %. This review unveils that the interaction mechanisms between biochar and NNIs primarily involve π-π interactions, electrostatic interactions, pore filling, and hydrogen bonding. Additionally, biochar facilitates various degradation pathways including Fenton reactions, photocatalytic, persulfate oxidations, and biodegradation predominantly through radical (such as SO4-, OH, and O2-) as well as non-radical (such as 1O2 and electrons transfer) processes. This study emphasizes the dynamics of interaction between biochar surfaces and NNIs during adsorption and degradation aiming to elucidate mechanistic pathways involved as well as assess the overall efficacy of biochar in NNI removal. By comparing the identification of degradation products and degradation pathways, the necessity of advanced oxidation process is confirmed. This review highlights the significance of harnessing biochar's potential for mitigating NNI pollution through future application-oriented research and development endeavors, while simultaneously ensuring environmental integrity and promoting sustainable practices.

Quantitative Soil Characterization for Biochar-Cd Adsorption: Machine Learning Prediction Models for Cd Transformation and Immobilization

Soil pollution with cadmium (Cd) poses serious health and environmental consequences. The study investigated the incubation of several soil samples and conducted quantitative soil characterization to assess the influence of biochar (BC) on Cd adsorption. The aim was to develop predictive models for Cd concentrations using statistical and modeling approaches dependent on soil characteristics. The potential risk linked to the transformation and immobilization of Cd adsorption by BC in the soil could be conservatively assessed by pH, clay, cation exchange capacity, organic carbon, and electrical conductivity. In this study, Long Short-Term Memory (LSTM), Bidirectional Gated Recurrent Unit (BiGRU), and 5-layer CNN Convolutional Neural Networks (CNNs) were applied for risk assessments to establish a framework for evaluating Cd risk in BC amended soils to predict Cd transformation. In the case of control soils (CK), the BiGRU model showed commendable performance, with an R2 value of 0.85, indicating an approximate 85.37% variance in the actual Cd. The LSTM model, which incorporates sequence data, produced less accurate results (R2=0.84), while the 5-layer CNN model had an R2 value of 0.91, indicating that the CNN model could account for over 91% of the variation in actual Cd levels. In the case of BC-applied soils, the BiGRU model demonstrated a strong correlation between predicted and actual values with R2 (0.93), indicating that the model explained 93.21% of the variance in Cd concentrations. Similarly, the LSTM model showed a notable increase in performance with BC-treated soil data. The R2 value for this model stands at a robust R2 (0.94), reflecting its enhanced ability to predict Cd levels with BC incorporation. Outperforming both recurrent models, the 5-layer CNN model attained the highest precision with an R2 value of 0.95, suggesting that 95.58% of the variance in the actual Cd data can be explained by the CNN model's predictions in BC-amended soils. Consequently, this study suggests developing ecological soil remediation strategies that can effectively manage heavy metal pollution in soils for environmental sustainability.

Negative impacts of perishable waste biochar to Escherichia coli and exploring potential damage factors

Agricultural application of pyrolysis‑carbonized perishable wastes can target reduction treatment and resource utilization of the wastes. However, potential undesirable impact has rarely been assessed. In this study, the adverse effect of perishable waste biochars (PWB) from different pyrolysis temperatures on Escherichia coli (E. coli) was explored and the potential risk factors were further analyzed. The results showed that PWBs pyrolyzed at 350, 500, and 650 °C inhibited the growth of E. coli, and PWB pyrolyzed at 500 °C showed the most inhibition. The exposure to PWB damaged the antioxidative system, as revealed by the concentration-dependent increasing of intracellular ROS. In addition, the toxicity at the gene level in terms of cell division and growth inhibition, the damage of cell membrane, antioxidant system disturbance, and DNA damage occurred, resulting in loss of the cell rules of morphology and eventual death. According to our results, the inhibitory effect on the growth of E. coli was mainly caused by PWB solids, accounting for >70 %. The membrane disruption and oxidative damage of E. coli by PWB were possibly induced by the direct physical interaction between cell and char particles. The growth of E. coli can be partly influenced by PWB extraction solutions that varied between PWB types, due to the differences in pH, released DOC and the production of extracellular ∙OH. The exploration of these potential hazards could provide new insights into the fate and toxicity of PWB in the environment and help guide the safe and sustainable applications for PWB.

Seasonal variations and sources of atmospheric EPFRs in a megacity in severe cold region: Implications for the influence of strong coal and biomass combustion

Environmentally persistent free radicals (EPFRs) can pose exposure risks by inducing the generation of reactive oxygen species. As a new class of pollutants, EPFRs have been frequently detected in atmospheric particulate matters. In this study, the seasonal variations and sources of EPFRs in a severe cold region in Northeastern China were comprehensively investigated, especially for the high pollution events. The geomean concentration of EPFRs in the total suspended particle was 6.58 × 1013 spins/m3 and the mean level in winter was one order of magnitude higher than summer and autumn. The correlation network analysis showed that EPFRs had significantly positive correlation with carbon component, K+ and PAHs, indicating that EPFRs were primarily emitted from combustion and pyrolysis process. The source appointment by the Positive Matrix Factorization (PMF) model indicated that the dominant sources in the heating season were coal combustion (48.4%), vehicle emission (23.1%) and biomass burning (19.4%), while the top three sources in the non-heating season were others (41.4%), coal combustion (23.7%) and vehicle emissions (21.2%). It was found that the high EPFRs in cold season can be ascribed to the extensive use of fossil fuel for heating demand; while the high EPFRs occurred in early spring were caused by the large-scale opening combustion of biomass. In summary, this study provided important basic information for better understanding the pollution characteristics of EPFRs, which suggested that the implementation of energy transformation and straw utilization was benefit for the control of EPFRs in severe cold region.

Reactive Oxygen Species (ROS)-Mediated Antibacterial Oxidative Therapies: Available Methods to Generate ROS and a Novel Option Proposal

The increasing emergence of multidrug-resistant (MDR) pathogens causes difficult-to-treat infections with long-term hospitalizations and a high incidence of death, thus representing a global public health problem. To manage MDR bacteria bugs, new antimicrobial strategies are necessary, and their introduction in practice is a daily challenge for scientists in the field. An extensively studied approach to treating MDR infections consists of inducing high levels of reactive oxygen species (ROS) by several methods. Although further clinical investigations are mandatory on the possible toxic effects of ROS on mammalian cells, clinical evaluations are extremely promising, and their topical use to treat infected wounds and ulcers, also in presence of biofilm, is already clinically approved. Biochar (BC) is a carbonaceous material obtained by pyrolysis of different vegetable and animal biomass feedstocks at 200-1000 °C in the limited presence of O2. Recently, it has been demonstrated that BC's capability of removing organic and inorganic xenobiotics is mainly due to the presence of persistent free radicals (PFRs), which can activate oxygen, H2O2, or persulfate in the presence or absence of transition metals by electron transfer, thus generating ROS, which in turn degrade pollutants by advanced oxidation processes (AOPs). In this context, the antibacterial effects of BC-containing PFRs have been demonstrated by some authors against Escherichia coli and Staphylococcus aureus, thus giving birth to our idea of the possible use of BC-derived PFRs as a novel method capable of inducing ROS generation for antimicrobial oxidative therapy. Here, the general aspects concerning ROS physiological and pathological production and regulation and the mechanism by which they could exert antimicrobial effects have been reviewed. The methods currently adopted to induce ROS production for antimicrobial oxidative therapy have been discussed. Finally, for the first time, BC-related PFRs have been proposed as a new source of ROS for antimicrobial therapy via AOPs.

Mechanistic and future prospects in rhizospheric engineering for agricultural contaminants removal, soil health restoration, and management of climate change stress

Climate change, food insecurity, and agricultural pollution are all serious challenges in the twenty-first century, impacting plant growth, soil quality, and food security. Innovative techniques are required to mitigate these negative outcomes. Toxic heavy metals (THMs), organic pollutants (OPs), and emerging contaminants (ECs), as well as other biotic and abiotic stressors, can all affect nutrient availability, plant metabolic pathways, agricultural productivity, and soil-fertility. Comprehending the interactions between root exudates, microorganisms, and modified biochar can aid in the fight against environmental problems such as the accumulation of pollutants and the stressful effects of climate change. Microbes can inhibit THMs uptake, degrade organic pollutants, releases biomolecules that regulate crop development under drought, salinity, pathogenic attack and other stresses. However, these microbial abilities are primarily demonstrated in research facilities rather than in contaminated or stressed habitats. Despite not being a perfect solution, biochar can remove THMs, OPs, and ECs from contaminated areas and reduce the impact of climate change on plants. We hypothesized that combining microorganisms with biochar to address the problems of contaminated soil and climate change stress would be effective in the field. Despite the fact that root exudates have the potential to attract selected microorganisms and biochar, there has been little attention paid to these areas, considering that this work addresses a critical knowledge gap of rhizospheric engineering mediated root exudates to foster microbial and biochar adaptation. Reducing the detrimental impacts of THMs, OPs, ECs, as well as abiotic and biotic stress, requires identifying the best root-associated microbes and biochar adaptation mechanisms.

A state-of-art review on the redox activity of persistent free radicals in biochar

Biochar-bound persistent free radicals (biochar-PFRs) attract much attention because they can directly or indirectly mediate the transformation of contaminants in large-scale wastewater treatment processes. Despite this, a comprehensive top-down understanding of the redox activity of biochar-PFRs, particularly consumption and regeneration mechanisms, as well as challenges in redox activity assessment, is still lacking. To tackle this challenge, this review outlines the identification and determination methods of biochar-PFRs, which serve as a prerequisite for assessing the redox activity of biochar-PFRs. Recent developments concerning biochar-PFRs are discussed, with a main emphasis on the reaction mechanisms (both non-free radical and free radical pathways) and their effectiveness in removing contaminants. Importantly, the review delves into the mechanism of biochar-PFRs regeneration, triggered by metal cations, reactive oxygen species, and ultraviolet radiations. Furthermore, this review thoroughly explores the dilemma in appraising the redox activity of biochar-PFRs. Components with unpaired electrons (particular defects and metal ions) interfere with biochar-PFRs signals in electron paramagnetic resonance spectra. Scavengers and extractants of biochar-PFRs also inevitably modify the active ingredients of biochar. Based on these analyses, a practical strategy is proposed to precisely determine the redox activity of biochar-PFRs. Finally, the review concludes by presenting current gaps in knowledge and offering suggestions for future research. This comprehensive examination aims to provide new and significant insights into the redox activity of biochar-PFRs.

The role of superoxide anion to Cr(VI) reduction by pine biochar

It has been reported that Cr(VI) can be reduced by biochar because of its redox activity. Considering the anionic form of Cr(VI), we hypothesize that the reduction in aqueous phase is significant. However, the contribution of different reactive oxygen species in the biochar-Cr(VI) reaction system has not been distinguished. Herein, we quantitatively identified Cr(VI) adsorption and reduction in biochar systems. The reduction content of Cr(VI) was 1.5 times higher in untreated conditions than in anaerobic conditions. The disappearance of·O2- under anaerobic conditions illustrated that·O2- may be involved in the reduction of Cr(VI). Quenching of·O2- resulted in a decrease of Cr(VI) reduction by 34%, while 1O2 was negligible, probably due to the stronger electron-donating capacity of·O2-. The degradation of nitrotetrazolium blue chloride (quenching agent of·O2-) confirmed that the reduction process of·O2- mainly occurred in the liquid-phase. Boehm titration and quantification of·O2- further elucidated the significant correlation (P < 0.05) between phenolic groups and the formation of·O2-, which implied that phenolic groups acted as the primary electron donors in generating·O2-. This study highlights the importance of the liquid-phase reduction process in removing Cr(VI), which provides theoretical support for biochar conversion of Cr(VI).

Formation and biotoxicity of environmentally persistent free radicals in steelworks soil under thermal treatment

Thermal treatment are commonly used to address organic contaminated soils. In particular, the pyrolysis of organic substances can result in the creation of environmentally persistent free radicals (EPFRs). We investigated a steelworks site in Chongqing (China) to observe changes in EPFRs before and after thermal treatment. Our findings revealed that the EPFRs were carbon-centered radicals with a g-factor < 2.0030 and a spin density ranging from n.d.-5.23 × 1015 spins/mg. The formation of EPFRs was driving by polycyclic aromatic hydrocarbons (PAHs), Mn, Cu, and total organic carbon (TOC). Following the thermal treatment, the spin densities of EPFRs increased by a factor of 0.25 to 1.81, with maximum levels reached at 300 °C. High molecular weight PAHs exhibited high heat capacity, enabling the generation of more EPFRs. The thermal decay of EPFRs occurred in two stages, with the shortest 1/e lifetime lasting up to 16.8 h. Raising the temperature or prolonging time can significantly reduce EPFRs levels. Thermal treatment increased the generation of EPFRs, hydroxyl radicals (•OH) and superoxide radical (•O2-), leading to a decrease in bacterial luminescence. Specifically, •OH contributed to approximately 73% of the B. brilliantus inhibition. Our results highlight that the thermal treatment significantly enhance EPFRs concentrations, and the treated soil remained ecologically risky. The knowledge of the formation of EPFRs and their biotoxicity is shedding new light on the thermal treatment risk management.

Excess sludge-based biochar loaded with manganese enhances catalytic ozonation efficiency for landfill leachate treatment

This study developed an efficient and stable landfill leachate treatment process, which was based on the combination of biochar catalytic ozonation and activated sludge technology for intensive treatment of landfill leachate, aiming to achieve the standard discharge of leachate. The focus is to investigate the effect of manganese loading on the physicochemical properties of biochar and the mechanism of its catalytic ozonation. It was found that more surface functional groups (CO, Mn-O, etc.) and defects (ID/IG = 1.27) were exposed via the change of original carbon structure by loading Mn, which is conducive to the generation of lattice oxygen. Meanwhile, generating different valence states of Mn metal can improve the redox properties and electron migration rate, and encourage the production of reactive oxygen species (ROS) during the reaction process and enhance the catalytic efficiency. The synergistic action of microorganisms, especially denitrifying bacteria, was found to play a key role in the degradation of nitrogenous pollutants during the activated sludge process. The concentration of NH+4-N was reduced from the initial 1087.03 ± 9.56 mg/L to 9.05 ± 1.91 mg/L, while COD was reduced from 2290 ± 14.14 mg/L to 86.5 ± 2.12 mg/L, with corresponding removal rates of 99.17% and 99.20%, respectively. This method offers high efficiency and stability, achieving discharge standards for leachate (GB16889-2008). The synergy between Mn-loaded biochar and microorganisms in the activated sludge is key to effective treatment. This study offers a new approach to solving the challenge of waste leachate treatment.

Biochar-Derived Persistent Free Radicals: A Plethora of Environmental Applications in a Light and Shadows Scenario

Biochar (BC) is a carbonaceous material obtained by pyrolysis at 200-1000 °C in the limited presence of O2 from different vegetable and animal biomass feedstocks. BC has demonstrated great potential, mainly in environmental applications, due to its high sorption ability and persistent free radicals (PFRs) content. These characteristics enable BC to carry out the direct and PFRs-mediated removal/degradation of environmental organic and inorganic contaminants. The types of PFRs that are possibly present in BC depend mainly on the pyrolysis temperature and the kind of pristine biomass. Since they can also cause ecological and human damage, a systematic evaluation of the environmental behavior, risks, or management techniques of BC-derived PFRs is urgent. PFRs generally consist of a mixture of carbon- and oxygen-centered radicals and of oxygenated carbon-centered radicals, depending on the pyrolytic conditions. Here, to promote the more productive and beneficial use of BC and the related PFRs and to stimulate further studies to make them environmentally safer and less hazardous to humans, we have first reviewed the most common methods used to produce BC, its main environmental applications, and the primary mechanisms by which BC remove xenobiotics, as well as the reported mechanisms for PFR formation in BC. Secondly, we have discussed the environmental migration and transformation of PFRs; we have reported the main PFR-mediated application of BC to degrade inorganic and organic pollutants, the potential correlated environmental risks, and the possible strategies to limit them.

Phytoremediation of contaminated sediment combined with biochar: Feasibility, challenges and perspectives

The accumulation of contaminants in sediments is accelerated by human activities and poses a major threat to ecosystems and human health. In recent years, various remediation techniques have been developed for contaminated sediments. In this review, a bibliometric analysis of papers on sediment remediation indexed in the WOS database between 2009 and 2023 was conducted using VOSviewer. We describe the development of biochar and plants for sediment contaminant removal. However, the single processes of biochar remediation and phytoremediation can be impeded by (i) low efficiency, (ii) poor tolerance of plants towards pollutants, (iii) difficulty in biochar to degrade pollutants, and (iv) biochar aging causing secondary pollution. Fortunately, combination remediation, realized through the combination of biochar and plants, can overcome the shortcomings of their individual applications. Therefore, we suggest that the remediation of contaminants in sediments can be accomplished by combining biochar with macrophytes and considering multiple limiting factors. Here, we explore the challenges that co-remediation with biochar and macrophytes will face in achieving efficient and sustainable sediment remediation, including complex sediment environments, interaction mechanisms of biochar-macrophyte-microorganisms, emerging pollutants, and integrated life cycle assessments, which can provide references for combined biochar and plant remediation of sediments in the future.

Efficient reduction and adsorption of Cr(VI) using FeCl3-modified biochar: Synergistic roles of persistent free radicals and Fe(II)

Transition metal iron and persistent free radicals (PFRs) both affect the redox properties of biochar, but the electron transfer relationship between them and the coupling reduction mechanism of Cr(VI) requires further investigation. To untangle the interplay between iron and PFRs in biochar and the influences on redox properties, FeCl3-modified rice husk biochar (FBCs) was prepared and its reduction mechanism for Cr(VI) without light was evaluated. The FBCs had higher surface positive charges, oxygen-containing functional groups, and PFRs compared with pristine rice husk biochar (BC). Phenoxyl PFRs with high electron-donating capability formed in biochar. The pronounced electron paramagnetic resonance signals showed that the PFRs preferred to form at lower Fe(III) concentrations. While a high concentration of Fe(III) would be reduced to Fe(II) and consumed the formed PFRs. Adsorption kinetics and X-ray photoelectron spectroscopy analysis indicated that the FBCs effectively enhanced the Cr(VI) removal efficiency by 1.54-8.20 fold and the Cr(VI) reduction efficiency by 1.88-9.29 fold compared to those of BC. PFRs quenching and competitive reductant addition experiments revealed that the higher Cr(VI) reduction performance of FBCs was mainly attributed to the formed PFRs, which could contribute to ∼74.0% of Cr(VI) reduction by direct or indirect electron transfer. The PFRs on FBCs surfaces could promote the Fe(III)/Fe(II) cycle through single electron transfer and synergistically accelerate ∼52.3% of Cr(VI) reduction. This study provides an improved understanding of the reduction mechanism of iron-modified biochar PFRs on Cr(VI) in environments.

Differential photodegradation processes of adsorbed polychlorinated biphenyls on biochar colloids with various pyrolysis temperatures

Despite the crucial role of photodegradation in the environmental transformation of organic pollutants, the photodegradation process of organic pollutants irreversibly absorbed on biochar colloids (BCCs) remains poorly understood. This study investigated the photodegradation processes and mechanisms of 2,4,4'-trichlorobiphenyl (PCB28) adsorbed on BCCs released from bulk biochars derived from bamboo chips at pyrolysis temperatures of 300, 500, and 700 °C. Results show that BCCs-adsorbed PCB28 could be degraded under simulated solar illumination (95-105 mW·cm-2) but at decreased photodegradation rates compared to the dissolved PCB28. The inhibition effect of BCCs on the PCB28 photodegradation increased with increasing pyrolysis temperature. After adsorptive binding to BCCs, the half-life of PCB28 (0.1 mg/L) was prolonged from 2.65 h for the dissolved PCB28 alone in deionized water to 7.48, 40.67, and 81.82 h in the presence of BCC300, BCC500, and BCC700 (5.0 mg/L), respectively. Mechanistically, the photodegradation of adsorbed pollutants was regulated by the photogenerated free radicals and surface functional groups of the low-temperature BCCs, as well as the defects and direct electron transfer capabilities of the high-temperature BCCs; PCB28 adsorbed on the low-temperature BCCs accepted electrons from persistent free radicals under light illumination, which led to PCB28 dechlorination, followed by ring-opening oxidation through hydroxyl radical attack, ultimately resulting in progressive mineralization; singlet oxygen caused preferential ring opening of adsorbed PCB28 on the high-temperature BCCs, preceding dechlorination. The photodegradation of BCCs-adsorbed PCB28 remained significant though more or less being inhibited under the effects of water pH, ionic strength, dissolved organic matters (humic acid and fulvic acid), and in natural water samples. These findings contribute to a better understanding of the structural properties of BCCs that impact phototransformation processes of adsorbed pollutants and facilitate an accurate assessment of the environmental risk associated with biochar application.

Pristine and modified biochar applications as multifunctional component towards sustainable future: Recent advances and new insights

Employing biomass for environmental conservation is regarded as a successful and environmentally friendly technique since they are cost-effective, renewable, and abundant. Biochar (BC), a thermochemically converted biomass, has a considerably lower production cost than the other conventional activated carbons. This material's distinctive properties, including a high carbon content, good electrical conductivity (EC), high stability, and a large surface area, can be utilized in various research fields. BC is feasible as a renewable source for potential applications that may achieve a comprehensive economic niche. Despite being an inexpensive and environmentally sustainable product, research has indicated that pristine BC possesses restricted properties that prevent it from fulfilling the intended remediation objectives. Consequently, modifications must be made to BC to strengthen its physicochemical properties and, thereby, its efficacy in decontaminating the environment. Modified BC, an enhanced iteration of BC, has garnered considerable interest within academia. Many modification techniques have been suggested to augment BC's functionality, including its adsorption and immobilization reliability. Modified BC is overviewed in its production, functionality, applications, and regeneration. This work provides a holistic review of the recent advances in synthesizing modified BC through physical, chemical, or biological methods to achieve enhanced performance in a specific application, which has generated considerable research interest. Surface chemistry modifications require the initiation of surface functional groups, which can be accomplished through various techniques. Therefore, the fundamental objective of these modification techniques is to improve the efficacy of BC contaminant removal, typically through adjustments in its physical or chemical characteristics, including surface area or functionality. In addition, this article summarized and discussed the applications and related mechanisms of modified BC in environmental decontamination, focusing on applying it as an ideal adsorbent, soil amendment, catalyst, electrochemical device, and anaerobic digestion (AD) promoter. Current research trends, future directions, and academic demands were available in this study.

Biochar modulating soil biological health: A review

Biochar can be used for multifunctional applications including the improvement of soil health and carbon storage, remediation of contaminated soil and water resources, mitigation of greenhouse gas emissions and odorous compounds, and feed supplementation to improve animal health. A healthy soil preserves microbial biodiversity that is effective in supressing plant pathogens and pests, recycling nutrients for plant growth, promoting positive symbiotic associations with plant roots, improving soil structure to supply water and nutrients, and ultimately enhancing soil productivity and plant growth. As a soil amendment, biochar assures soil biological health through different processes. First, biochar supports habitats for microorganisms due to its porous nature and by promoting the formation of stable soil micro-aggregates. Biochar also serves as a carbon and nutrient source. Biochar alters soil physical and chemical properties, creating optimum soil conditions for microbial diversity. Biochar can also immobilize soil pollutants and reduce their bioavailability that would otherwise inhibit microbial growth. However, depending on the pyrolysis settings and feedstock resources, biochar can be comprised of contaminants including polycyclic aromatic hydrocarbons and potentially toxic elements that can inhibit microbial activity, thereby impacting soil health.

New Features of Laboratory-Generated EPFRs from 1,2-Dichlorobenzene (DCB) and 2-Monochlorophenol (MCP)

The present research is primarily focused on investigating the characteristics of environmentally persistent free radicals (EPFRs) generated from commonly recognized aromatic precursors, namely, 1,2-dichlorobenzene (DCB) and 2-monochlorophenol (MCP), within controlled laboratory conditions at a temperature of 230 °C, termed as DCB230 and MCP230 EPFRs, respectively. An intriguing observation has emerged during the creation of EPFRs from MCP and DCB utilizing a catalyst 5% CuO/SiO2, which was prepared through various methods. A previously proposed mechanism, advanced by Dellinger and colleagues (a conventional model), postulated a positive correlation between the degree of hydroxylation on the catalyst's surface (higher hydroxylated, HH and less hydroxylated, LH) and the anticipated EPFR yields. In the present study, this correlation was specifically confirmed for the DCB precursor. Particularly, it was observed that increasing the degree of hydroxylation at the catalyst's surface resulted in a greater yield of EPFRs for DCB230. The unexpected finding was the indifferent behavior of MCP230 EPFRs to the surface morphology of the catalyst, i.e., no matter whether copper oxide nanoparticles are distributed densely, sparsely, or completely agglomerated. The yields of MCP230 EPFRs remained consistent regardless of the catalyst type or preparation protocol. Although current experimental results confirm the early model for the generation of DCB EPFRs (i.e., the higher the hydroxylation is, the higher the yield of EPFRs), it is of utmost importance to closely explore the heterogeneous alternative mechanism(s) responsible for generating MCP230 EPFRs, which may run parallel to the conventional model. In this study, detailed spectral analysis was conducted using the EPR technique to examine the nature of DCB230 EPFRs and the aging phenomenon of DCB230 EPFRs while they exist as surface-bound o-semiquinone radicals (o-SQ) on copper sites. Various aspects concerning bound radicals were explored, including the hydrogen-bonding tendencies of o-semiquinone (o-SQ) radicals, the potential reversibility of hydroxylation processes occurring on the catalyst's surface, and the analysis of selected EPR spectra using EasySpin MATLAB. Furthermore, alternative routes for EPFR generation were thoroughly discussed and compared with the conventional model.

Persistent free radicals on biochar for its catalytic capability: A review

Biochar is an economical carbon material for water pollution control, which shows great promise to be applied in the up-scale wastewater remediation processes. Previous studies demonstrate that persistent free radicals (PFRs) on biochar are critical to its reactivity for wastewater remediation. A series of studies have revealed the important roles of PFRs when biochar was applied for organic pollutants degradation as well as the removal of Cr (VI) and As (III) from wastewater. Therefore, this review comprehensively concludes the significance of PFRs for the catalytic capabilities of biochar in advanced oxidation processes (AOPs)-driven organic pollutant removal, and applied in redox processes for Cr (VI) and As (III) remediation. In addition, the mechanisms for PFRs formation during biochar synthesis are discussed. The detection methods are reviewed for the quantification of PFRs on biochar. Future research directions were also proposed on underpinning the knowledge base to forward the applications of biochar in practical real wastewater treatment.

Inactivation of harmful cyanobacteria Microcystis aeruginosa by Cu2+ doped corn stalk biochar treated with different pyrolysis temperatures

In this study, biochars (BCs) derived from corn stalk treated at various pyrolysis temperatures (350-950 °C) were prepared and then loaded with Cu2+ to form highly efficient algaecide, i.e. Cu2+-doped BC composites (Cu-BCs). The results showed BCs pyrolyzed at higher temperatures suppressed the growth of Microcystis aeruginosa in the order of BC550 ≫ BC750 > BC950, while BC350 accelerated cell growth due to the release of inorganic nutrients. The difference could be attributed to the physicochemical characteristics, including specific surface area, adsorption capacity of nutrients and the presence of particularly persistent free radicals. Furthermore, Cu-BCs exhibited the improved inactivation performance, but the 72 h growth inhibition rates and reaction activities of Cu-BCs were still influenced by the Cu2+ loading ratio and pyrolysis temperature. These results, reported for the first time, demonstrated the algae inactivation efficiency of pristine BCs, and Cu-BCs were principally manipulated by the biochar pyrolysis temperature.

Photo-oxidation of Micro- and Nanoplastics: Physical, Chemical, and Biological Effects in Environments

Micro- and nanoplastics (MNPs) are attracting increasing attention due to their persistence and potential ecological risks. This review critically summarizes the effects of photo-oxidation on the physical, chemical, and biological behaviors of MNPs in aquatic and terrestrial environments. The core of this paper explores how photo-oxidation-induced surface property changes in MNPs affect their adsorption toward contaminants, the stability and mobility of MNPs in water and porous media, as well as the transport of pollutants such as organic pollutants (OPs) and heavy metals (HMs). It then reviews the photochemical processes of MNPs with coexisting constituents, highlighting critical factors affecting the photo-oxidation of MNPs, and the contribution of MNPs to the phototransformation of other contaminants. The distinct biological effects and mechanism of aged MNPs are pointed out, in terms of the toxicity to aquatic organisms, biofilm formation, planktonic microbial growth, and soil and sediment microbial community and function. Furthermore, the research gaps and perspectives are put forward, regarding the underlying interaction mechanisms of MNPs with coexisting natural constituents and pollutants under photo-oxidation conditions, the combined effects of photo-oxidation and natural constituents on the fate of MNPs, and the microbiological effect of photoaged MNPs, especially the biotransformation of pollutants.

Persistent free radicals generated from a range of biochars and their physiological effects on wheat seedlings

Biochar is a promising soil conditioner and environmental remediation material. However, the amount, type, and environmental effect and risk of persistent free radicals (PFRs) associated with biochar need to be better understood. Thus, this study characterized PFRs in a range of biochar types and their effects on the growth and oxidative stress of wheat seedlings. Among the biochars prepared by pyrolysis of different types of biomass at 500 °C, the concentrations of PFRs in cow dung and egg shell biochar were the highest and the lowest, respectively. They both increased with artificial weathering treatment but decreased with aging. The dominant types of biochar PFRs were transformed from carbon-centered to oxygen and carbon/oxygen-centered free radicals with weathering. The amount and type of biochar PFRs in mixtures of biochar and soil varied with soil type and biochar dose. After 30 d incubation in different soil-biochar mixtures, measures of wheat plant germination and growth and antioxidant enzyme activity showed increases at lower biochar doses but decreases at higher doses. Catalase activity was 38.1 % greater at 20 g·kg-1 biochar dosage and 25.2 % less at 80 g·kg-1 dosage, on average. In contrast, leaf malondialdehyde content and staining by Evans Blue, both indicators of plant cell membrane damage, generally increased with increasing biochar dosages. Finally, soil hydrolase enzyme activity also displayed an inverted U-shaped dose response. The toxicity indicators showed an increasing trend with higher PFR concentrations in the soil-biochar combinations. While these findings provide evidence for significant potential agricultural and ecological risks associated with the application of biochar due to PFRs damage, it also points to ways that these risks could be mediated such as through biochar dosage restrictions and pre-aging. This study provides new insights into the potential toxicological mechanism and ecological risks associated with the application of biochar in agricultural and environmental settings.

A bibliometric analysis of emerging contaminants (ECs) (2001-2021): Evolution of hotspots and research trends

Emerging contaminants (ECs) have attracted increasing attention in the past two decades because of their ubiquitous existence and high environmental risk. Understanding the progress of research and the evolution of hot topics is critical. This study provides a bibliometric review, along with a quantitative trend analysis of approximately 8000 publication records dated from 2001 to 2021. Wider distribution in various subjects was discovered in terms of publication numbers, indicating a strong tendency for EC research to become an interdisciplinary topic. Visualization of term co-occurrence analysis revealed that the ECs study went through three stages over time: identification and detection, traceability and risk, and process and control. Quantitative trend analysis revealed that antibiotics, microplastics, endocrine disrupting chemicals (EDCs), per/poly-fluoroalkyl substances (PFAS), pesticides, heavy metals, and nanoparticles are attracting increasing attention, whereas conventional pharmaceuticals, persistent organic pollutants, and materials such as benzotriazole, diclofenac, bisphenol A, carbamazepine, triclosan, and titanium dioxide exhibit a downward trend. PFAS and EDCs are considered potential future core hotspots for the hysteretic rise in research attention compared with conventional ECs. Furthermore, analysis of research linkage and the developing stages of ECs could be possible approach to determine the evolution of hotspots in ECs study. This study provides objective and comprehensive insights into the research landscape of ECs, which may shed light on future developmental directions for researchers interested in this field.

Waste-derived nanobiochar: A new avenue towards sustainable agriculture, environment, and circular bioeconomy

The greatest challenge for the agriculture sector in the twenty-first century is to increase agricultural production to feed the burgeoning global population while maintaining soil health and the integrity of the agroecosystem. Currently, the application of biochar is widely implemented as an effective means for boosting sustainable agriculture while having a negligible influence on ecosystems and the environment. In comparison to traditional biochar, nano-biochar (nano-BC) boasts enhanced specific surface area, adsorption capacity, and mobility properties within soil, allowing it to promote soil properties, crop growth, and environmental remediation. Additionally, carbon sequestration and reduction of methane and nitrous oxide emissions from agriculture can be achieved with nano-BC applications, contributing to climate change mitigation. Nonetheless, due to cost-effectiveness, sustainability, and environmental friendliness, waste-derived nano-BC may emerge as the most viable alternative to conventional waste management strategies, contributing to the circular bioeconomy and the broader goal of achieving the Sustainable Development Goals (SDGs). However, it's important to note that research on nano-BC is still in its nascent stages. Potential risks, including toxicity in aquatic and terrestrial environments, necessitate extensive field investigations. This review delineates the potential of waste-derived nano-BC for sustainable agriculture and environmental applications, outlining current advancements, challenges, and possibilities in the realms from a sustainability and circular bioeconomy standpoint.

Biochar amendment combined with partial root-zone drying irrigation alleviates salinity stress and improves root morphology and water use efficiency in cotton plant

An adsorption experiment and a pot experiment were executed in order to explore the mechanisms by which biochar amendment in combination with reduced irrigation affects sodium and potassium uptake, root morphology, water use efficiency, and salinity tolerance of cotton plants. In the adsorption experiment, ten NaCl concentration gradients (0, 50, 100, 150, 200, 250, 300, 350, 400, and 500 mM) were set for testing isotherm adsorption of Na+ by biochar. It was found that the isotherms of Na+ adsorption by wheat straw biochar (WSP) and softwood biochar (SWP) were in accordance with the Langmuir isotherm model, and the Na+ adsorption ability of WSP (55.20 mg g-1) was superior to that of SWP (47.38 mg g-1). The pot experiment consisted three factors, viz., three biochar amendments (no biochar, WSP, and SWP), three irrigation strategies (deficit irrigation, partial root-zone drying irrigation - PRD, full irrigation), and two NaCl concentrations gradients (0 mM and 200 mM). The findings indicated that salinity stress lowered K+ concentration, root length, root surface area, and root volume (RV), but increased Na+ concentration, root average diameter, and root tissue density. However, biochar amendment decreased Na+ concentration, increased K+ concentration, and improved root morphology. In particular, the combination of WSP and PRD increased K+/Na+ ratio, RV, root weight density, root surface area density, water use efficiency, and partial factor productivity under salt stress, which can be a promising strategy to cope with drought and salinity stress in cotton production.

Role of modeling and artificial intelligence in process parameter optimization of biochar: A review

Enhancement of crop yield, conservation and quality upgradation of soil, and efficient water management are the main objectives of sustainable agriculture and mitigating climate change's impact on agriculture. In recent days, biochar, obtained via thermochemical alteration of biomass is becoming a powerful agent for soil and water quality improvement, carbon sequestration, greenhouse gas emission reduction, and heavy metal adsorption. The present study predominantly focuses on various process parameters related to biochar preparation through pyrolysis, their impact on biochar production as well as physicochemical characteristics, and the optimization of such process parameters. Different designs of the experiment (DOE) and optimization techniques including traditional and non-traditional optimizations are discussed in the current review, along with their applicability and shortcomings. Since the biochar preparation process is tedious and energy-consuming, the present review will help to understand the importance of optimization in preparing biochar, thereby leading to a better way to prepare biochar.

Household characteristics associated with environmentally persistent free radicals in house dust in two Australian locations

The association between air pollution and adverse health outcomes has been extensively studied, and while oxidative stress in likely to be involved, the underlying mechanism(s) remain unclear. Recent studies propose environmentally persistent free radicals (EPFRs) as the missing connection between air pollution and detrimental health impacts. However, the indoor environment is rarely considered in EPFR research. We measured EPFRs in household dust from two locations in Australia and investigated household characteristics associated with EPFRs. Random forest models were built to identify important household characteristics through variable importance plots and the associations were analysed using Spearman's rho test. We found that age of house, type of garage, house outer wall material, heating method used in home, frequency of extractor fan use when cooking, traffic related air pollution, frequency of cleaning and major house renovation were important household characteristics associated with EPFRs in Australian homes. The direction of association between household characteristics and EPFRs differ between the locations. Hence, further research is warranted to determine the generalisability of our results.