Natural Attenuation of 2,4-Dichlorophenol in Fe-Rich Soil during Redox Oscillations: Anoxic-Oxic Coupling Mechanism.

Natural attenuation of organic contaminants can occur under anoxic or oxic conditions. However, the effect of the coupling anoxic-oxic process, which often happens in subsurface soil, on contaminant transformation remains poorly understood. Here, we investigated 2,4-dichlorophenol (2,4-DCP) transformation in Fe-rich soil under anoxic-oxic alternation. The anoxic and oxic periods in the alternating system showed faster 2,4-DCP transformation than the corresponding control single anoxic and oxic systems; therefore, a higher transformation rate (63.4%) was obtained in the alternating system relative to control systems (27.9-42.4%). Compared to stable pH in the alternating system, the control systems presented clear OH- accumulation, caused by more Fe(II) regeneration in the control anoxic system and longer oxygenation in the control oxic system. Since 2,4-DCP was transformed by ion exchangeable Fe(II) in soil via direct reduction in the anoxic process and induced ·OH oxidation in the oxic process, OH- accumulation was unbeneficial because it competed for proton with direct reduction and inhibited •OH generation via complexing with Fe(II). However, the alternating system exhibited OH--buffering capacity via anoxic-oxic coupling processes because the subsequent oxic periods intercepted Fe(II) regeneration in anoxic periods, while shorter exposure to O2 in oxic periods avoided excessive OH- generation. These findings highlight the significant role of anoxic-oxic alternation in contaminant attenuation persistently.

A Critical Review of Groundwater Table Fluctuation: Formation, Effects on Multifields, and Contaminant Behaviors in a Soil and Aquifer System.

The groundwater table fluctuation (GTF) zone is an important medium for the hydrologic cycle between unsaturated soil and saturated aquifers, which accelerates the migration, transformation, and redistribution of contaminants and further poses a potential environmental risk to humans. In this review, we clarify the key processes in the generation of the GTF zone and examine its links with the variation of the hydrodynamic and hydrochemistry field, colloid mobilization, and contaminant migration and transformation. Driven by groundwater recharge and discharge, GTF regulates water flow and the movement of the capillary fringe, which further control the advection and dispersion of contaminants in soil and groundwater. In addition, the formation and variation of the reactive oxygen species (ROS) waterfall are impacted by GTF. The changing ROS components partially determine the characteristic transformation of solutes and the dynamic redistribution of the microbial population. GTF facilitates the migration and transformation of contaminants (such as nitrogen, heavy metals, non-aqueous phase liquids, and volatile organic compounds) through colloid mobilization, the co-migration effect, and variation of the hydrodynamic and hydrochemistry fields. In conclusion, this review illustrates the limitations of the current literature on GTF, and the significance of GTF zones in the underground environment is underscored by expounding on the future directions and prospects.

Critical Functions of Soil Components for In Situ Persulfate Oxidation of Sulfamethoxazole: Inherent Fe(II) Minerals-Coordinated Nonradical Pathway.

Naturally occurring iron (Fe) minerals have been proved to activate persulfate (PS) to generate reactive species, but the role of soil-inherent Fe minerals in activating PS as well as the underlying mechanisms remains poorly understood. Here, we investigated sulfamethoxazole (SMX) degradation by PS in two Fe-rich soils and one Fe-poor soil. Unlike with the radical-dominant oxidation processes in Fe-poor soil, PS was effectively activated through nonradical pathways (i.e., surface electron-transfer) in Fe-rich soils, accounting for 68.4%-85.5% of SMX degradation. The nonradical mechanism was evidenced by multiple methods, including electrochemical, in situ Raman, and competition kinetics tests. Inherent Fe-based minerals, especially those containing Fe(II) were the crucial activators of PS in Fe-rich soils. Compared to Fe(III) minerals, Fe(II) minerals (e.g., ilmenite) were more liable to form Fe(II) mineral-PS* complexes to initiate the nonradical pathways, oxidizing adjacent SMX via electron transfer. Furthermore, mineral structural Fe(II) was the dominant component to coordinate such a direct oxidation process. After PS oxidation, low-crystalline Fe minerals in soils were transformed into high-crystalline Fe phases. Collectively, our study shows that soil-inherent Fe minerals can effectively activate PS in Fe-rich soils, so the addition of exogenous iron might not be required for PS-based in situ chemical oxidation. Outcomes also provide new insights into the activation mechanisms when persulfate is used for the remediation of contaminated soils.

Perfluorooctane Sulfonamide Induced Autotoxic Effects on the Zebrafish Immune System.

Perfluorooctane sulfonamide (PFOSA) is an immediate perfluorooctanesulfonate (PFOS) precursor (PreFOS). Previous studies have shown PFOSA to induce stronger toxic responses compared to other perfluorinated compounds (PFCs). However, the specific nature of PFOSA-induced toxicity, whether autonomous or mediated by its metabolite PFOS, has not been fully elucidated. This study systematically investigates the immunomodulatory effects of PFOSA and PFOS in zebrafish (Danio rerio). Exposure to PFOSA compromised the zebrafish's ability to defend against pathogenic infections, as evidenced by increased bacterial adhesion to their skin and reduced levels of the biocidal protein lysozyme (LYSO). Moreover, PFOSA exposure was associated with disruptions in inflammatory markers and immune indicators, along with a decrease in immune cell counts. The findings from this study suggest that the immunotoxicity effects of PFOSA are primarily due to its own toxicity rather than its metabolite PFOS. This conclusion was supported by dose-dependent responses, the severity of observed effects, and multivariate analysis. In addition, our experiments using NF-κB-morpholino knock-down techniques further confirmed the role of the Nuclear factor-κappa B pathway in mediating PFOSA-induced immunotoxicity. In conclusion, this study reveals that PFOSA impairs the immune system in zebrafish through an autotoxic mechanism, providing valuable insights for assessing the ecological risks of PFOSA.

New Insight into the Natural Detoxification of Cr(VI) in Fe-Rich Surface Soil: Crucial Role of Photogenerated Silicate-Bound Fe(II).

Photoexcitation of natural semiconductor Fe(III) minerals has been proven to generate Fe(II), but the photogeneration of Fe(II) in Fe-rich surface soil as well as its role in the redox biogeochemistry of Cr(VI) remains poorly understood. In this work, we confirmed the generation of Fe(II) in soil by solar irradiation and proposed a new mechanism for the natural reductive detoxification of Cr(VI) to Cr(III) in surface soil. The kinetic results showed that solar irradiation promoted the reduction of Cr(VI) in Fe-rich soils, while a negligible Cr(VI) reduction was observed in the dark. Fe(II), mainly in the form of silicate-bound Fe(II), was generated under solar irradiation and responsible for the reduction of Cr(VI) in soils, which was evidenced by sequential extraction, transmission electron microscopy with electron energy loss spectroscopy, and electron transfer calculation. Photogenerated silicate-bound Fe(II) resulted from the massive clay-iron (hydr)oxide associations, consisting of iron (hydr)oxides (e.g., hematite and goethite) and kaolinite. These associations could generate Fe(II) under solar irradiation either via intrinsic excitation to produce photoelectrons or via the ligand-to-metal charge transfer process after the formation of clay-iron (hydr)oxide-organic matter complexes, which was proven by photoluminescence spectroscopy and X-ray photoelectron spectroscopy. These findings highlight the important role of photogenerated Fe(II) in Cr(VI) reduction in surface soil, which advances a fundamental understanding of the natural detoxification of Cr(VI) as well as the redox biogeochemistry of Cr(VI) in soil.

Converting coastal silt into subgrade soil with biochar as reinforcing agent, CO2 adsorbent, and carbon sequestrating material.

Large amounts of coastal silt produced annually is urgent to be treated with a feasible strategy. This study converted it into subgrade soil by cement solidification for resource utilization. Biochar was used as exogenous additive for enhancing compressive strength of the product, simultaneously achieving carbon sequestration. Three biochars derived from peanut shells (PSBC), cow dung (CDBC) and sewage sludge (SSBC) at 300 °C, 500 °C and 700 °C pyrolysis, were added into raw materials with 1%, 2% and 5%, respectively. All biochars significantly improved the compressive strength of the subgrade soil by 20-110%. Biochar catalyzed cement hydration reactions to produce more Ca(OH)2, CaCO3 and calcium silicate hydrates (C-S-H gel). The catalytic capacity of different biochars followed the order of SSBC > PSBC > CDBC. Addition of 2% SSBC500 induced the greatest increase in 28 d-strength from only 1.0 MPa-2.1 MPa, which was due to that 500 °C biochar had a suitable specific surface area and porosity. Biochar facilitated CO2 capture (absorption) during the hydration reactions at the initial 48 h with 55-70 mg g-1. The high alkalinity and water holding capacity of biochar contributed to the absorption of CO2; the high content of minerals in SSBC compared to CDBC and PSBC promoted chemical conversion of CO2 to carbonate. Besides, the biochar itself as carbon rich material was encapsulated in the subgrade soil, which can be regarded as a long-term carbon sequestration strategy. Carbon budget analysis demonstrated that converting one ton dry silt into subgrade soil with addition of 2% biochar could increase CO2 sequestration from 11 kg to 36-94 kg. This study proposes a novel strategy of using biochar to strengthen the subgrade soil simultaneously achieve long-term carbon sequestration.

Medium-Low Temperature Conditions Induce the Formation of Environmentally Persistent Free Radicals in Microplastics with Conjugated Aromatic-Ring Structures during Sewage Sludge Pyrolysis.

Medium-low temperature pyrolysis is an effective method of retaining active components in sludge char. However, we found that incomplete cracking reactions resulted in residues of microplastics (MPs) remaining in the char; moreover, high levels of environmentally persistent free radicals (EPFRs) were detected in these MPs. Here, we investigated the temperature-dependent variations in the char-volatile products derived from sludge and MPs under different pyrolysis scenarios using multiple in situ probe coupling techniques and electron paramagnetic resonance spectroscopy, thereby identifying the sources of EPFRs and elucidating the corresponding formation-conversion mechanisms. The temperature was the key factor in the formation of EPFRs; in particular, in the 350-450 °C range, the abundance of EPFRs increased exponentially. Reactive EPFR readily formed in MPs with conjugated aromatic-ring structures (polyethylene terephthalate and polystyrene) at a temperature above 350 °C; EPFR concentrations were 5-17 times higher than those found in other types of polymers, and these radicals exhibited half-lives of more than 90 days. The EPFR formation mechanism could be summarized as solid-solid/solid-gas interfacial interactions between the polymers and the intermediate products from sludge pyrolysis (at 160-350 °C) and the homolytic cleavage-proton transfer occurring in the polymers themselves under the dual action of thermal induction and acid sites (at 350-450 °C). Based on the understanding of the evolution of EPFRs, temperature regulation and sludge components conditioning may be effective approaches to inhibit the formation of EPFRs in MPs, constituting reliable strategies to diminish the environmental risk associated with the byproducts of sludge pyrolysis.

Direct and Indirect Electron Transfer Routes of Chromium(VI) Reduction with Different Crystalline Ferric Oxyhydroxides in the Presence of Pyrogenic Carbon.

Electron transfer mediated by iron minerals is considered as a critical redox step for the dynamics of pollutants in soil. Herein, we explored the reduction process of Cr(VI) with different crystalline ferric oxyhydroxides in the presence of pyrogenic carbon (biochar). Both low- and high-crystallinity ferric oxyhydroxides induced Cr(VI) immobilization mainly via the sorption process, with a limited reduction process. However, the Cr(VI) reduction immobilization was inspired by the copresence of biochar. Low-crystallinity ferric oxyhydroxide had an intense chemical combination with biochar and strong sorption for Cr(VI) via inner-sphere complexation, leading to the indirect electron transfer route for Cr(VI) reduction, that is, the electron first transferred from biochar to iron mineral through C-O-Fe binding and then to Cr(VI) with Fe(III)/Fe(II) transformation on ferric oxyhydroxides. With increasing crystallinity of ferric oxyhydroxides, the direct electron transfer between biochar and Cr(VI) became the main electron transfer avenue for Cr(VI) reduction. The indirect electron transfer was suppressed in the high-crystallinity ferric oxyhydroxides due to less sorption of Cr(VI), limited combination with biochar, and higher iron stability. This study demonstrates that electron transfer mechanisms involving iron minerals change with the mineral crystallization process, which would affect the geochemical process of contaminants with pyrogenic carbon.

Commonwealth of Soil Health: How Do Earthworms Modify the Soil Microbial Responses to CeO2 Nanoparticles?

Soil ecotoxicological assays on nanoparticles (NPs) have mainly investigated single components (e.g., plants, fauna, and microbes) within the ecosystem, neglecting possible effects resulting from the disturbance of the interactions between these components. Here, we investigated soil microbial responses to CeO2 NPs in the presence and absence of earthworms from the perspectives of microbial functions (i.e., enzyme activities), the community structure, and soil metabolite profiles. Exposure to CeO2 NPs (50, 500 mg/kg) alone decreased the activities of enzymes (i.e., acid protease and acid phosphatase) participating in soil N and P cycles, while the presence of earthworms ameliorated these inhibitory effects. After the CeO2 NP exposure, the earthworms significantly altered the relative abundance of some microbes associated with the soil N and P cycles (Flavobacterium, Pedobacter, Streptomyces, Bacillus, Bacteroidota, Actinobacteria, and Firmicutes). This was consistent with the pattern found in the significantly changed metabolites which were also involved in the microbial N and P metabolism. Both CeO2 NPs and earthworms changed the soil bacterial community and soil metabolite profiles. Larger alterations of soil bacteria and metabolites were found under CeO2 NP exposure with earthworms. Overall, our study indicates that the top-down control of earthworms can drastically modify the microbial responses to CeO2 NPs from all studied biological aspects. This clearly shows the importance of the holistic consideration of all soil ecological components to assess the environmental risks of NPs to soil health.

Critical Impact of Nitrogen Vacancies in Nonradical Carbocatalysis on Nitrogen-Doped Graphitic Biochar.

Nitrogen-doped graphitic biochar (NBC) has boosted the development of nonradical peroxymonosulfate (PMS) activation in environmental remediation. However, the specific role of nitrogen species played in NBC-based nonradical carbocatalysis remains vaguely interpreted. To pinpoint the critical nitrogen speciation, a sophisticated thermo-mechanochemical manipulation was exploited to prepare a series of NBCs with similar dimensional structures and oxygen levels but different nitrogen species (i.e., dopants and vacancies). Different from conventional perspectives, nonradical NBC-based carbocatalysis was found to be preferably determined by the nitrogen vacancies more than their parent nitrogen dopants. Raman depth analysis evidenced that a complete transformation of nitrogen dopants into nitrogen vacancies could be achieved at 800 °C, where an excellent nonradical abatement of 4-chlorophenol (4-CH, 90.9% removal) was found for the NBC800 with a low PMS consumption (1.24 mM). According to PMS adsorption experiments, nitrogen vacancies exhibited the highest affinity toward the PMS molecules compared to nitrogen dopants, which accounted for the superior carbocatalysis. Electron paramagnetic resonance and Raman spectroscopic analyses indicated that the original PMS molecules were bound to positively charged nitrogen vacancies, and a robust metastable complex (*HSO5-) evolved subsequently via hydrogen abstraction by adjacent persistent free radicals. In situ Raman techniques could be adopted to estimate the level of nitrogen vacancies associated with the polarization of electron distribution. The flexible feature and practical prospects of nitrogen vacancy-based carbocatalysis were also observed in the remediation of simulated phenolic industrial wastewater. Overall, this study unravels the dilemma in the current NBC-based nonradical carbocatalysis and advances our understanding of nitrogen doping technology for next-generation biochar design.

Persulfate Oxidation of Sulfamethoxazole by Magnetic Iron-Char Composites via Nonradical Pathways: Fe(IV) Versus Surface-Mediated Electron Transfer.

Despite the vital roles of reactive radical species in the coupled iron-carbon composite/persulfate (PS) system for eliminating pollutants, nonradical contributions are typically overlooked. Herein, we developed two efficient magnetic iron-char composites via low-temperature (BCFe-400) and high-temperature (BCFe-700) pyrolysis. The two composites activated PS through nonradical pathways for sulfamethoxazole (SMX) degradation. In the BCFe-400/PS system, high-valent iron Fe(IV) was the dominant active species for the oxidation, evidenced by methyl phenyl sulfoxide-based probe tests, Mössbauer spectroscopy, and in situ Raman analyses with kinetic evaluation. In the BCFe-700/PS system, surface-mediated electron transfer dominated the oxidation, and the nonradical regime was probed by the electrochemical test and in situ Raman analysis. Furthermore, the BCFe-400/PS system maintained high efficiency in continuous degradation of SMX due to the feasible Fe2+generation toward Fe(IV) formation. In the BCFe-700/PS system, the stability of the system was limited due to the hindered electron transfer between the surface reactive complex (i.e., BCFe-700-PS*) and SMX, and thermal treatment would help recover the reactivity. Both BCFe-400/PS and BCFe-700/PS systems exhibited high performances for SMX removal in the presence of chloride and humic acid and in real water matrixes (e.g., seawater, piggery wastewater, and landfill leachate), exhibiting the great merits of the nonradical system. Overall, the study would provide new insights into PS activation by iron-loaded catalysts to efficiently degrade pollutants via nonradical pathways.

Elucidating Toxicodynamic Differences at the Molecular Scale between ZnO Nanoparticles and ZnCl2 in Enchytraeus crypticus via Nontargeted Metabolomics.

Much effort has been devoted to clarifying the comparative toxicity of ZnO nanoparticles (NPs) and Zn ions; however, little is known about their toxicodynamic processes at the metabolic level. Here, we investigated the acute (2d) and chronic (7d) effects to a soil species, Enchytraeus crypticus, of two sublethal doses of ZnO-NPs and ZnCl2 (10 and 30 mg/L Zn) using ultrahigh performance liquid chromatography-quadrupole-time-of-flight/mass spectrometry-based metabolomics. The metabolomics analysis identified 99, 128, 121, and 183 significantly changed metabolites (SCMs) in E. crypticus exposed to ZnO-NPs for 2d, ZnCl2 for 2d, ZnO-NPs for 7d, and ZnCl2 for 7d, respectively, suggesting that ZnCl2 induced stronger metabolic reprogramming than ZnO-NPs, and a longer exposure time caused greater metabolite changes. Among the SCMs, 67 were shared by ZnO-NPs and ZnCl2 after 2d and 84 after 7d. These metabolites were mainly related to oxidative stress and antioxidant defense, membrane disturbance, and energy expenditure. The targeted analysis on physiological and biochemical responses further proved the metabolic observations. Nevertheless, 32 (33%) and 37 (31%) SCMs were found only in ZnO-NP treatments after 2 and 7d, respectively, suggesting that the toxicity of ZnO-NPs cannot be solely attributed to the released Zn ions. Metabolic pathway analysis revealed significant perturbations of galactose metabolism, amino sugar and nucleotide sugar metabolism, and glycerophospholipid metabolism in all test groups. Based on involvement frequency, glucose-1-phosphate, glycerol 3-phosphate, and phosphorylcholine could serve as universal biomarkers for exposure to different Zn forms. Four pathways perturbed by ZnO-NPs were nanospecific upon acute exposure and three upon chronic exposure. Our findings demonstrated that metabolomics is an effective tool for understanding the molecular toxicity mechanism and highlighted that time-series measurements are essential for discovering and comparing modes of action of metal ions and NPs.

Effective Modeling Framework for Quantifying the Potential Impacts of Coexisting Anions on the Toxicity of Arsenate, Selenite, and Vanadate.

Hardly any study has focused on the quantitative modeling of the toxicity of anionic metal(loid)s and their mixtures in the presence of potentially competing anions. Here, we designed a univariate experiment (420 treatments) to investigate the influence of various anions (phosphate, sulfate, carbonate, and OH-) on the toxicity of single anionic metal(loid)s (arsenate, selenite, and vanadate) and a full factorial mixture experiment (196 treatments) to examine the interactions and toxicity of As-Se mixtures at 4 phosphate levels. Standard root elongation tests with wheat (Triticum aestivum) were performed. A modeling framework, resembling the biotic ligand model (BLM) for cationic metals, was developed, extended, and applied to explain anion competitions and mixture effects. Carbonate significantly alleviated the toxicity of all three metal(loid)s. The toxicity of As was significantly mitigated by phosphate, while V toxicity was significantly relieved by OH-. The BLM-like model successfully explained more than 93% of the observed variance in toxicity. With the parameters derived from single-metal(loid) exposures, the developed BLM-toxic unit model reached an overall prediction performance of 78% in modeling the toxicity of As-Se mixtures at varying phosphate levels, validating the effectiveness of the model framework. It is concluded that by taking possible anion competitions and interactions into account, the BLM-type approaches can serve as promising tools for the risk assessment of single and mixed metal(loid)s contamination.

Coupling mixture reference models with DGT-perceived metal flux for deciphering the nonadditive effects of rare earth mixtures to wheat in soils.

The risk assessment of mixtures of rare earth elements (REEs) is hampered by a lack of fundamental understanding of their interactions in different soil types. Here, we assessed mixture interactions and toxicity to Triticum aestivum of Y and Ce in four different soils in relation to their bioavailability. Mixture toxicity was modelled by concentration addition (CA) and independent action (IA), in combination with different expressions of exposure: three equilibrium-based doses (total soil concentrations [M]tot, free ion activity in soil solution {M3+}, and the fraction (f) of metal ions bound to the biotic ligands (BLs)) and one kinetically controlled dose ([M]flux) metrics. Upon single exposure, REE toxicity was increasingly better described when using exposure expressions based on deepened understanding of their bioavailability: [M]flux > f > {M3+} > [M]tot. The mixture analyses based on [M]tot and {M3+} displayed deviations from additivity depending on the soil type. With the parameters derived from single exposures, the BLM approach gave better predictions of mixture toxicity (R2 ~ 0.70) than when using CA and IA based on either [M]tot or {M3+} (R2 < 0.64). About 30% of the variance in toxicity remained unexplained, challenging the view that the free metal ion is the main bioavailable form under the BLM framework based on thermodynamic equilibrium. Toxicity was best described when accounting for changes in the size of the labile metal pool by using a kinetically controlled dose metric (R2 ~ 0.80). This suggests that dynamic bioavailability analysis could provide a robust basis for modeling and reconciling the interplays and toxicity of metal mixtures in different soils.

Uptake of vegetable and soft drink affected transformation and bioaccessibility of lead in gastrointestinal track exposed to lead-contaminated soil particles.

Accidental ingestion of Pb-contaminated soil particles by direct hand-to-mouth activity or by swallowing airborne dust particles is important pathway of human exposure to Pb. Appropriate evaluation of Pb risk to human is important in determining whether the soil needs remediation or not, however, there is paucity of data about the dietary influences on Pb bioaccessibility (Pb-BA) and transformation in humans. This study chose two typical foods, spinach and cola, representing vegetable and soft drink, respectively, and investigated their effects on Pb species in gastrointestinal tract using the physiologically based extraction test. Results showed that ingestion of spinach and cola decreased the Pb-BA by 52%-94% in the gastric phase and by 38%-95% in the intestinal phase, respectively. The reduction of Pb-BA by spinach was attributed to the precipitation of Pb with phosphorus in spinach and the sorption of Pb by the generated hydrolysate and un-hydrolysate from spinach in gastrointestinal tract. Cola decreased Pb-BA mainly via formation of insoluble Pb phosphates precipitates. Analysis of X-ray diffraction and MINTEQ modeling demonstrated that the dissolved Pb was transformed to precipitated or sorbed Pb with intake of cola or spinach. Our findings suggest that dietary habit greatly influence the speciation and subsequent Pb-BA in the gastrointestinal tract, which should be incorporated into human health risk assessment of Pb-contaminated soil.

Highly Efficient Utilization of Nano-Fe(0) Embedded in Mesoporous Carbon for Activation of Peroxydisulfate.

Nanoscale zerovalent iron (nZVI) particles have received much attention in environmental science and technology due to their unique electronic and chemical properties. However, the aggregation and oxidation of nZVI brings much difficulty in practical application of environmental remediation. In this study, we reported a composite nano-Fe(0)/mesoporous carbon by a chelation-assisted coassembly and carbothermal reduction strategy. Nano-Fe(0) particles with surface iron oxide (Fe2O3·FeO) were wrapped with graphitic layers which were uniformly dispersed in mesoporous carbon frameworks. The unique structure made the nano-Fe(0) particles stable in air for more than 20 days. It was used as a peroxydisulfate (PDS) activator for the oxidation treatment of 2,4,6-trichlorophenol (TCP). The TOF value of MCFe for TCP degradation is nearly 3 times higher than those of FeSO4 and Fe2O3·FeO and nearly 2 times than that of commercial nZVI. The reactive oxygen species (ROS) including •SO4-, HO•, and •O2-, 1O2 are efficiently generated by PDS activation with MCFe. The PDS activation process by nano-Fe(0) particles was intrinsically induced by the ferrous ions (Fe(II)) continuously generated at the solid/aqueous interface. Namely, the nano-Fe(0) particles were highly efficiently utilized in sulfate radical-based advanced oxidation processes (SR-AOP). The porous structure also assists the absorption and transfer of TCP during the degradation process.

Kaolinite Enhances the Stability of the Dissolvable and Undissolvable Fractions of Biochar via Different Mechanisms.

Input of biomass-derived biochar into soil is recognized as a promising method of carbon sequestration. The long-term sequestration effect of biochar depends on the stability of both its dissolvable and undissolvable fractions in soil, which could be affected by their interactions with soil minerals. Here, walnut shell-derived biochar was divided into dissolvable and undissolvable fractions and then interacted with kaolinite. Stability of kaolinite-biochar associations was evaluated by chemical oxidation and biological degradation. At low dissolvable biochar concentrations, the association was mainly attributed to "Ca2+ bridging" and "ligand exchange", whereas "van der Waals attraction" was dominant at high concentrations. For the undissolvable biochar, kaolinite raised the activation energy of its surface by 22.1%, causing a reduction in biochar reactivity. By chemical oxidation, kaolinite reduced the C loss of total biochar by 42.5%, 33.1% resulting from undissolvable biochar and 9.4% from dissolvable biochar. Because of the presence of kaolinite, the loss of biodegradable C in total biochar was reduced by 49.4% and 48.2% from undissolvable fraction and 1.2% from dissolvable fraction. This study indicates that kaolinite can increase the stability of both dissolvable and undissolvable biochar, suggesting that kaolinite-rich soils could be a beneficial environment for biochar for long-term carbon sequestration.

Transformation and bioaccessibility of lead induced by steamed bread feed in the gastrointestinal tract.

Accidental ingestion of contaminated soil has been recognized as an important pathway of human exposure to lead (Pb), especially for children through hand-to-mouth activities. Intake of food following the soil ingestion may affect the bioaccessibility of Pb in the gastrointestinal tract. In this study, the effect of steamed bread on the transformation and subsequent bioaccessibility of Pb in two soils was determined by the physiologically based extraction test (PBET). Two compounds, Pb(NO3)2 and PbCO3, were included in the evaluation for comparison. In the gastric phase, Pb bioaccessibility decreased as the steamed bread increased due to the sorption of Pb on the undissolved steamed bread, especially in PbCO3, Pb bioaccessibility decreased from 95.03% to 85.40%. Whereas in the intestinal phase, Pb bioaccessibility increased from 1.85% to 5.66% and from 0.89% to 1.80% for Pb(NO3)2 and PbCO3, respectively. The increase was attributed to the transformation of formed Pb carbonates into soluble organic-Pb complexes induced by the dissolved steamed bread at neutral pH as indicated by MINTEQ modeling. For the PbCO3-contaminated soil, the change in Pb bioaccessibility in both gastric and intestinal phases behaved like that in the pure PbCO3 compound, the steamed bread increased the bioaccessibility of Pb in the intestinal phase, but the decreased bioaccessibility of Pb was observed in the gastric phase after the steamed bread was added. However, in the soil contaminated with free Pb2+ or sorbed Pb forms, the steamed bread increased the Pb bioaccessibility in both gastric and intestinal phases. This was probably due to the higher dissolved organic carbon induced transformation of sorbed Pb (Pb sorbed by Fe/Mn oxides) into soluble Pb-organic complex. Results from this study indicated that steamed bread had an influence on the Pb speciation transformation, correspondingly affecting Pb bioaccessibility in the gastrointestinal tract.

Roles of Phosphoric Acid in Biochar Formation: Synchronously Improving Carbon Retention and Sorption Capacity.

Pretreatment of biomass with phosphoric acid (HPO) for biochar production was expected to improve carbon (C) retention, porosity structure, and the sorption ability of biochar. This study investigated the interaction of phosphorus with the C structure to elucidate the mechanisms by which HPO simultaneously captured C and created micropores. Sawdust was soaked in diluted HPO and dried for pyrolytic biochar generation at 350, 500, and 650°C. Results showed that HPO pretreatment resulted in 70 to 80% of biomass C retention in biochar, compared with only about 50% remaining without pretreatment. The specific surface area and total pore volume of the HPO-pretreated biochar were 930 m g and 0.558 cm g, respectively, compared with <51.0 m g and 0.046 cm g in the untreated biochar. The volume of micropores (<10 nm) increased from 59.0% to 78.4-81.9%. The presence of HPO shifted the decomposition temperature to a lower value and decreased the energy required for biomass decomposition. Micropore formation was via the insertion of P-O-P into the C lattice, leading to swelling and amplification of amorphous form and lattice defect of the C structure, as evidenced by Raman spectrum and small-angle X-ray scattering analysis. The crosslinking of P-O-P and C bonds resulted in greater biomass C retention in biochar. This biochar-phosphorus composite had a much higher sorption ability for Pb than the unmodified biochar, which was possibly dominated by phosphate precipitation and surface adsorption. This study provided a simple method to improve biochar properties and explored the multiple benefits of HPO in biomass pyrolysis.

The Interfacial Behavior between Biochar and Soil Minerals and Its Effect on Biochar Stability.

In this study, FeCl3, AlCl3, CaCl2, and kaolinite were selected as model soil minerals and incubated with walnut shell derived biochar for 3 months and the incubated biochar was then separated for the investigation of biochar-mineral interfacial behavior using XRD and SEM-EDS. The XPS, TGA, and H2O2 oxidation were applied to evaluate effects of the interaction on the stability of biochar. Fe8O8(OH)8Cl1.35 and AlCl3·6H2O were newly formed on the biochar surface or inside of the biochar pores. At the biochar-mineral interface, organometallic complexes such as Fe-O-C were generated. All the 4 minerals enhanced the oxidation resistance of biochar surface by decreasing the relative contents of C-O, C═O, and COOH from 36.3% to 16.6-26.5%. Oxidation resistance of entire biochar particles was greatly increased with C losses in H2O2 oxidation decreasing by 13.4-79.6%, and the C recalcitrance index (R50,bicohar) in TGA analysis increasing from 44.6% to 45.9-49.6%. Enhanced oxidation resistance of biochar surface was likely due to the physical isolation from newly formed minerals, while organometallic complex formation was probably responsible for the increase in oxidation resistance of entire biochar particles. Results indicated that mineral-rich soils seemed to be a beneficial environment for biochar since soil minerals could increase biochar stability, which displays an important environmental significance of biochar for long-term carbon sequestration.