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The significant influx of antibiotics into the environment represents ecological risks and threatens human health. Microbial degradation stands as a highly effective method for reducing antibiotic pollution. This study explored the potential of immobilized microbial consortia to efficiently degrade tetracycline. Concurrently, the suitability of different immobilization materials were assessed, with reed charcoal-immobilized consortia exhibiting the highest efficiency in removing tetracycline (92%). Similarly, wheat-bran-loaded bacterial consortia displayed a remarkable 11.43-fold increase in tetracycline removal compared with free consortia. Moreover, adding the carriers increased the nutrients, while the activities of both intracellular and extracellular catalases increased significantly post-immobilization, thus highlighting this enzyme's crucial role in tetracycline degradation. Finally, analysis of the microbial communities revealed the prevalence of Achromobacter and Parapedobacter, signifying their potential as key degraders. Overall, the immobilized consortia not only hold promise for application in the bioremediation of tetracycline-contaminated environment but also provide theoretical underpinnings for environmental remediation by microorganisms.

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With the widespread use of tetracycline antibiotics (TCs) and the application of manure fertilizer in farmland, TCs and their metabolites especially 4-epimers have been heavily detected in agricultural soil. However, existing studies have focused on the residual and environmental behavior of maternal TCs, and few studies have looked at the ecotoxicity of their 4-epimers in soil. In this study, the degradation and interconversion of tetracycline (TC), oxytetracycline (OTC) and their 4-epimers (4-epitetracycline, ETC; 4-epioxytetracycline, OTC) were revealed. Their effects on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) and bacterial community in soil were also investigated in comparison. The results showed that the 4-epimers could be substantially transformed to their parents and degraded as a whole. The degradation rates of four selected pollutants are followed: TC > OTC > ETC > EOTC. This indicated that when TCs entered the soil, part of TCs transformed into slower-degraded 4-epimers, and these 4-epimers could also be converted back to their antibiotic parents, causing the long-term residue of TCs in soil. When added to the soil alone, TC and OTC significantly promoted the proliferation of most ARGs and MGEs, among them, trb-C, IS1247 and IS1111 were the top three genes in abundance. ETC and EOTC had little effect at the beginning. However, as the 4-epimers continuously converted into their parents after one month of cultivation, ETC and EOTC treatments showed similar promoting effect on ARGs and MGEs, indicating that the effect of ETC and EOTC on soil resistome was lagged and mainly caused by their transformed parents. Nocardioides, unclassified_Rhizobiaceae, norank_Sericytochromatia, Microlunatus, Solirubrobacter and norank_67-14 were the most frequent hosts of ARGs, Most of which belong to the phylum Actinobacteria. Due to their large transformation to TCs, slow degradation rate and potential effects on soil microbes and ARGs, the harm of TCs' 4-epimers on soil ecosystem cannot be ignored.

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The loss of nitrogen in soil damages the environment. Clarifying the mechanism of ammonium nitrogen (NH4+-N) transport in soil and increasing the fixation of NH4+-N after N application are effective methods for improving N use efficiency. However, the main factors are not easily identified because of the complicated transport and retardation factors in different soils. This study employed machine learning (ML) to identify the main influencing factors that contribute to the retardation factor (Rf) of NH4+-N in soil. First, NH4+-N transport in the soil was investigated using column experiments and a transport model. The Rf (1.29 - 17.42) was calculated and used as a proxy for the efficacy of NH4+-N transport. Second, the physicochemical parameters of the soil were determined and screened using lasso and ridge regressions as inputs for the ML model. Third, six machine learning models were evaluated: Adaptive Boosting, Extreme Gradient Boosting (XGB), Random Forest, Gradient Boosting Regression, Multilayer Perceptron, and Support Vector Regression. The optimal ML model of the XGB model with a low mean absolute error (0.81), mean squared error (0.50), and high test r2 (0.97) was obtained by random sampling and five-fold cross-validation. Finally, SHapely Additive exPlanations, entropy-based feature importance, and permutation characteristic importance were used for global interpretation. The cation exchange capacity (CEC), total organic carbon (TOC), and Kaolin had the greatest effects on NH4+-N transport in the soil. The accumulated local effect offered a fundamental insight: When CEC > 6 cmol+ kg-1, and TOC > 40 g kg-1, the maximum resistance to NH4+-N transport within the soil was observed. This study provides a novel approach for predicting the impact of the soil environment on NH4+-N transport and guiding the establishment of an early-warning system of nutrient loss.

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Despite extensive study, geochemical modeling often fails to accurately predict lead (Pb) immobilization in environmental samples. This study employs the Charge Distribution MUlti-SIte Complexation (CD-MUSIC) model, X-ray absorption fine structure (XAFS), and density functional theory (DFT) to investigate mechanisms of phosphate (PO4) induced Pb immobilization on metal (hydr)oxides. The results reveal that PO4 mainly enhances bidentate-adsorbed Pb on goethite via electrostatic synergy at low PO4 concentrations. At relatively low pH (below 5.5) and elevated PO4 concentrations, the formation of the monodentate-O-sharing Pb-PO4 ternary structure on goethite becomes important. Precipitation of hydropyromorphite (Pb5(PO4)3OH) occurs at high pH and high concentrations of Pb and PO4, with an optimized log Ksp value of -82.02. The adjustment of log Ksp compared to that in the bulk solution allows for quantification of the overall Pb-PO4 precipitation enhanced by goethite. The CD-MUSIC model parameters for both the bidentate Pb complex and the monodentate-O-sharing Pb-PO4 ternary complex were optimized. The modeling results and parameters are further validated and specified with XAFS analysis and DFT calculations. This study provides quantitative molecular-level insights into the contributions of electrostatic enhancement, ternary complexation, and precipitation to phosphate-induced Pb immobilization on oxides, which will be helpful in resolving controversies regarding Pb distribution in environmental samples.

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HYPOTHESIS: The competitive interaction of oxyanions and humic nanoparticles (HNPs) with metal (hydr)oxide surfaces can be used to trace the ligand and charge distribution of adsorbed HNPs in relation to heterogeneity, fractionation, and conformational change. EXPERIMENTS: Batch adsorption experiments of HNPs on goethite were performed in the absence and presence of phosphate. The size of HNPs was measured with size exclusion chromatography. The Ligand and Charge Distribution (LCD) model framework was further developed to describe the simultaneous interaction of HNPs and phosphate with goethite. FINDINGS: Preferential adsorption decreases the mean molar mass of adsorbed HNPs, independent of the phosphate presence, showing a linear dependency on the adsorbed HNPs fraction. Phosphate ion can be used as a probe to trace the distribution of functional groups and the variation in affinity of HNPs. The spatial distribution of adsorbed HNPs is driven by the potential gradients in the electrical double layer, which changes the conformation of the adsorbed HNPs. At the particle level, the adsorption of heterogeneous HNPs has an affinity distribution, which can be explained by the variation in molar mass (kDa) and density of the functional groups (mol kg-1) of the HNPs. The presented model can simultaneously describe the competitive adsorption of HNPs and phosphate in a consistent manner.

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Microplastics (MPs) in soil have attracted extensive attention as an emerging pollutant, and the transport of MPs is affected by their own physical and chemical properties, the chemical composition of soil solutions, and soil minerals. However, in the presence of oxides, the underlying mechanism for the transport of MPs in different ionic types and ionic strengths is still not fully understood. In this study, the effects of ionic type, ionic strength, and iron oxide on the transport of polystyrene microplastics (PSMPs) with different functional groups were investigated through stability experiments and transport experiments. The colloid transport model, CD-MUSIC model, and DLVO theory were used to explore the transport mechanism. The results showed that normalized concentrations (c/c0) of PSMPs were 0.99 in the NaH2PO4 background and 0.94 in the CaCl2 background, respectively, which indicated that the strongest stability of PSMPs was observed in the former and the weakest in the latter. Different ionic types had different effects on the transport of PSMPs. For the cations Na+ and Ca2+, Ca2+ strongly inhibited PSMPs transport in pure quartz sand because of the bridging effect and strong charge neutralization effect; the recovery rate of the PSMPs in the effluent was (43.83±1.71)%, and a first-order retention coefficient on the second kinetic Site-2 (k2a) was 1.54 min-1. The presence of iron oxide enhanced the inhibition, the recovery rate of the PSMPs in the effluent decreased to (6.04±0.40)%, and k2a increased to 5.33 min-1. For the anions Cl- and PO43-, the transport of PSMPs in pure quartz sand was dominated by surface electronegativity of PSMPs, and PSMPs exhibited lower electronegativity under Cl- background and thus showed higher recovery[(92.95±0.63)%] and lower k2a (0.19 min-1). However, in the presence of iron oxides, the Zeta potential of the quartz sand surface was the controlling factor for PSMPs transport. According to results of the CD-MUSIC model, PO43- could be easily adsorbed on the iron oxide surface to form innersphere complexes, which reduced the surface electronegativity of the iron-loaded quartz sand and enhanced the transport of PSMPs, higher recovery[(76.22±1.39)%], and lower k2a (0.66 min-1). Moreover, the species of the formed innersphere complex was controlled by the PO43- concentration, and different species of innersphere complexes had distinct negative surface charges. Higher surface electronegativity of the iron-loaded quartz sand was observed under higher PO43- concentration, which was not conducive to the transport of PSMPs. Further, the transport ability of PSMPs decreased with the increase in ionic strength. Finally, the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to calculate the variation in the primary barrier between PSMPs and the collector under the conducted experimental conditions, which helped better elucidate the transport behavior of PSMPs. The variation in the primary barrier was consistent with the transport ability of PSMPs, and a higher primary barrier indicated a larger repulsion between PSMPs and the collector, which was in favor of PSMPs transport.

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The degradation of organic pollutants and the adsorption of organic pollutants onto microplastics (MPs) in the environment have recently been intensively studied, but the effects of biocurrents, which are widespread in various soil environments, on the environmental behavior of MPs and antibiotic pollutants have not been reported. In this study, it was found that polylactic acid (PLA) and polyvinyl chloride (PVC) MPs accelerated the mineralization of humic substances in microbial electrochemical systems (MESs). After tetracycline (TC) was introduced into the MESs, the internal resistance of the soil MESs decreased. Additionally, the presence of MPs enhanced the charge output of the soil MESs by 40% (PLA+TC) and 18% (PVC+TC) compared with a control group without MPs (424 C). The loss in MP mass decreased after TC was added, suggesting a promotion of TC degradation rather than MP degradation for charge output. MPs altered the distribution of the highest occupied molecular orbitals and lowest unoccupied molecular orbitals of TC molecules and reduced the energy barrier for the TC hydrolysis reaction. The microbial community of the plastisphere exhibited a greater ability to degrade xenobiotics than the soil microbial community, indicating that MPs were hotspots for TC degradation. This study provides the first glimpse into the influence of MPs on the degradation of TC in MESs, laying a theoretical and methodological foundation for the systematic evaluation of the potential risks of environmental pollutants in the future.

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Bioelectric field is a stimulated force to degrade xenobiotic pollutants in soils. However, the effect of bioelectric field on microplastics (MPs) aging is unclear. The degradation behavior of polyvinyl chloride (PVC), polyethylene (PE) and polylactic acid (PLA) was investigated in an agricultural soil microbial electrochemical system in which bioelectric field was generated in-situ by native microbes. Based on the density function theory, the energy gaps between the highest and the lowest occupied molecular orbitals of the three polymers with periodic structure were 4.20, 7.24 and 10.09 eV respectively, and further decreased under the electric field, indicating the higher hydrolysis potential of PLA. Meanwhile, the mass loss of PLA in the closed-circuit group (CC) was the highest on day 120, reaching 8.94%, which was 3.01-3.54 times of that without bioelectric field stimulation. This was mainly due to the enrichment of plastic-degrading bacteria and a robust co-occurrence network as the deterministic assembly process, e.g., the abundance of potential plastic-degrading bacteria on the surface of PLA and PVC in the CC increased by 1.92 and 1.30 times, respectively, compared to the open-circuit group. In terms of functional genes, the xenobiotic biodegradation and metabolism capacity of plasticsphere in the CC were stronger than that in soil, and determined by the bioaccessibility of soil nitrogen and carbon. Overall, this study explored the promoting effect of bioelectric field on the degradation of MPs and reveled the mechanism from quantum chemical calculations and microbial community analysis, which provides a novel perception to the in-situ degradation of MPs.

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In this work, comparative study of paddy and upland soils were carried out to unravel mechanisms of enhanced soil organic carbon (SOC) sequestration in paddy soils using fractionation methods, 13C NMR and Nano-SIMS analysis, as well as organic layer thickness calculations (Core-Shell model). The results showed that although there is a strong increase in particulate SOC in paddy soils compared to that in the upland soils, the increase in mineral-associated SOC is more important, explaining 60-75% of SOC increase in the paddy soils. In the wet and dry alternate cycles of paddy soil, iron (hydr)oxides adsorb relatively small and soluble organic molecules (fulvic acid-like), promote catalytic oxidation and polymerization, thus accelerating formation of larger organic molecules. Upon reductive iron dissolution, these molecules are released and incorporated into existing less soluble organic compounds (humic acid or humin-like), which are coagulated and associated with clay minerals, becoming part of the mineral-associated SOC. The functioning of this "iron wheel" process stimulates accumulation of relatively young SOC into mineral-associated organic carbon pool, and reduces the difference in chemical structure between oxides-bound and clay-bound SOC. Further, the faster turnover of oxides and soil aggregates in paddy soil also facilities interaction between SOC and minerals. The formation of mineral-associated SOC may delay degradation of organic matter during both wet and dry period in the paddy field, therefore enhancing carbon sequestration in paddy soils.

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The contamination of greenhouse vegetable soils with antibiotics and antibiotic resistance genes (ARGs), caused by the application of livestock and poultry manure, is a prominent environmental problem. In this study, the effects of two ecological earthworms (endogeic Metaphire guillelmi and epigeic Eisenia fetida) on the accumulation and transfer of chlortetracycline (CTC) and ARGs in a soil-lettuce system were studied via pot experiments. The results revealed that earthworm application accelerated the removal of the CTC from the soil and lettuce roots and leaves, with the CTC content reducing by 11.7-22.8 %, 15.7-36.1 %, and 8.93-19.6 % compared with that of the control, respectively. Both earthworms significantly reduced the CTC uptake by lettuce roots from the soil (P < 0.05) but did not change the CTC transfer efficiency from the roots to leaves. The high-throughput quantitative PCR results showed that the relative abundance of ARGs in the soil and lettuce roots and leaves decreased by 22.4-27.0 %, 25.1-44.1 %, and 24.4-25.4 %, respectively, with the application of earthworms. Earthworm addition decreased the interspecific bacterial interactions and the relative abundance of mobile genetic elements (MGEs), which helped reduce the dissemination of ARGs. Furthermore, some indigenous soil antibiotic degraders (Pseudomonas, Flavobacterium, Sphingobium, and Microbacterium) were stimulated by the earthworms. The results of redundancy analysis indicated that the bacterial community composition, CTC residues, and MGEs were the main parameters affecting the distribution of ARGs, accounting for 91.1 % of the total distribution. In addition, the bacterial function prediction results showed that the addition of earthworms reduced the abundance of some pathogenic bacteria in the system. Overall, our findings imply that earthworm application can substantially reduce the accumulation and transmission risk of antibiotics and ARGs in soil-lettuce systems, providing a cost-effective soil bioremediation practice for addressing antibiotic and ARGs contamination to guarantee the safety of vegetables and human health.

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Atmospheric deposition is an essential cadmium (Cd) pollution source in agricultural ecosystems, entering crops via roots and leaves. In this study, atmospherically deposited Cd was simulated using cadmium sulfide nanoparticles (CdSN), and chili (Capsicum frutescens L.) was used to conduct a comparative foliar and root experiment. Root and foliar uptake significantly increased the Cd content of chili tissues as well as the subcellular Cd content. Scanning electron microscopy and high-resolution secondary ion mass spectrometry showed that Cd that entered the leaves via stomata was fixed in leaf cells, and the rest was mainly through phloem transport to the other organs. In leaf, stem, and root cell walls, Cd signal intensities were 47.4%, 72.2%, and 90.0%, respectively. Foliar Cd uptake significantly downregulated purine metabolism in leaves, whereas root Cd uptake inhibited stilbenoid, diarylheptanoid, and gingerol biosynthesis in roots. Root uptake contributed 90.4% Cd in fruits under simultaneous root and foliar uptake conditions attributed to xylem and phloem involvement in Cd translocation. Moreover, root uptake had a more significant effect on fruit metabolic pathways than foliar uptake. These findings are critical for choosing pollution control technologies and ensuring food security.

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This study aimed to obtain a better understanding on the environmental behavior of As in paddy soil and to reveal the influence mechanisms of different environmental factors on the availability of As in the soil solution. The effects of pH, calcium, and phosphate on the solubility and speciation distribution of As in the paddy soil collected from Zhuzhou of Hunan province were studied by combining the adsorption experiments with the NOM-CD model. The results showed that the minimum concentration of soluble As in the soil was at approximately a pH of 6.0, which was mainly affected by both electrical interactions and site competition between Ca2+, PO43-, As(Ⅲ), and As(Ⅴ). The adsorption of As onto soil particles could be increased by an increase in Ca2+ in the soil system, leading to the decrease in soluble As concentration. This effect became significant at a higher pH, because adsorbed Ca2+ increased the positive charge on (hydr)oxide surfaces. With phosphate addition, the reduction in As(Ⅴ) in the soil was inhibited at pH<5.5, whereas it was promoted at pH>5.5. Moreover, the concentration of soluble As(Ⅲ) and As(Ⅴ) in the soil solution was dramatically increased with the addition of phosphate owing to the competitive adsorption between As and phosphate. At a lower background of Ca2+, there was a higher fraction of As(Ⅲ) in the soil either with or without phosphate addition. This phenomenon might be caused by the higher bioavailability of phosphorus in soil at a lower concentration of Ca2+, which favors the dissimilatory reduction of As or iron (hydr)oxides. The results indicated that the NOM-CD model could predict the influence of pH, calcium, and phosphate on the solubility and speciation distribution of As in paddy soil and reveal its main mechanisms. Therefore, the NOM-CD model would provide the quantitative and scientific method for evaluating the risk of As in soils or other solid-water systems.

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The transport of ferrihydrite colloid (FHC) through porous media is influenced by anions (e.g., PO43-) and cations (e.g., Ca2+) in the aqueous environment. This study investigated the cotransport of FHC with P and P/Ca in saturated sand columns. The results showed that P adsorption enhanced FHC transport, whereas Ca loaded onto P-FHC retarded FHC transport. Phosphate adsorption provided a negative potential on the FHC, while Ca added to P-FHC led to electrostatic screening, compression of the electric double layer, and formation of Ca5(PO4)3OH followed by heteroaggregation at pH ≥ 6.0. The monodentate and bidentate P surface complexes coexisted, and Ca mainly formed a ternary complex with bidentate P (≡(FeO)2PO2Ca). The unprotonation bidentate P at the Stern 1-plane had a considerable negative potential at the Van der Waals molecular surface. Extending the potential effect to the outer layer of FHC, the potential at the Stern 2-plane and zeta potential exhibited a corresponding change, resulting in a change in FHC mobility, which was validated by comparison of experimental results, DFT calculations, and CD-MUSIC models. Our results highlighted the influence of P and Ca on FHC transport and elucidated their interaction mechanisms based on quantum chemistry and colloidal chemical interface reactions.

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Adsorption and transport of levofloxacin (LEV) and ofloxacin (OFL) enantiomers in a matrix containing goethite and natural organic matter (NOM) were investigated using batch and column experiments. In batch studies, competition and enantioselectivity were observed in the adsorption of LEV and OFL. Enantioselectivity upon adsorption was investigated by comparing changes in the enantiomer fraction (EF) (the ratio of LEV to the sum of LEV and OFL remaining in the solution) after and before adsorption. At pH < 7, there was hardly any selectivity in adsorption of OFL and LEV to goethite. At pH > 7, OFL showed a stronger adsorption than LEV to goethite, and this preference remained when NOM samples of Leonardite humic acid (LHA) and Elliott Soil fulvic acid (ESFA) were added. However, when Suwannee River NOM (SRNOM) was added, the preference was reversed, and LEV was adsorbed more strongly. In single systems, the presence of different types of NOM increased adsorption of LEV and OFL, especially LEV. In column studies, preloaded NOM decreased the transport of LEV and OFL through goethite-coated sand. The EF values in the effluent increased with retention time and reached the largest values (0.59-0.72) at around 1.5 pore volume (PV), and then decreased again, reaching a stable value at 5.0-30.0 PV. Both batch and column experiments showed that, fractionation of LEV and OFL occurred during adsorption and transport in the presence of NOM-goethite complexes, which would eventually affect their environmental fate.

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To explore the responses of soil microbial communities to concentration gradients of antibiotic residues in soil, 32 soil samples were collected from a typical greenhouse vegetable production base in Northern China in 2019. The total concentrations of 26 antibiotic residues in these soil samples was 83.24-4237.93 µg·kg-1, of which metabolites of tetracyclines were 23.34-1798.80 µg·kg-1. The total concentrations in 32 samples were clustered into three levels (L: <100 µg·kg-1, M: 100-300 µg·kg-1, H: >300 µg·kg-1) to elucidate the impacts of antibiotic residues on the diversity, structure, composition, function and antibiotic resistome of soil microbial community. Results showed that higher concentration of antibiotic residues in soil was prone to decrease the diversity and shift the structure and composition of soil microbial community. Antibiotic resistome occurred in soils with antibiotic residues exceeding 300 µg·kg-1. Interactions among soil bacteria followed the order of H > L > M, consistent with the relative abundances of mobile genetic elements. Bacteroidetes and Firmicutes were the top attributors impacting the profile of antibiotics in soil. According to weighted comprehensive pollution index of risk quotient, in 28.1 % of soil samples the residual antibiotics presented high ecological risk, whereas in the rest of soil samples the ecological risk is medium. The results will enrich the database and provide references for antibiotic contamination control in soils of the region and alike.

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Nanoplastics (NPs) and natural organic matter (NOM) are ubiquitous and usually present simultaneously in the environment. Both NPs and NOM can be adsorbed to minerals such as iron-(hydr)oxides, with such interactions being important for controlling their fate in the environment. However, the quantification of NPs and NOM in mixtures remains challenging even under controlled conditions in laboratory studies. In this research, a UV-Vis method was established to quantify concentrations of NOM, such as humic acid (HA) and fulvic acid (FA), and polystyrene NPs (PSNPs) in mixtures. In addition, both original NOM samples and those recovered following adsorptive fractionation using an iron oxide (goethite, α-FeOOH) were mixed separately with PSNPs and their concentrations were further calculated via the developed UV-Vis method. The UV-Vis method performed well (recovery of 100 ± 16 %) with original NOM and PSNPs system at detection limits of 20.8 and 7.4 mgC L-1, respectively. Particularly, for original FA and PSNPs systems with carboxylic groups (PSNPs-COOH, 200 nm), a similar recovery rate could be obtained at detection limits of only 2.5 and 1.9 mgC L-1, respectively. For fractionated NOM and PSNPs systems, detection limits (31.2 mgC L-1 and 27.5 mgC L-1, respectively) are increased to reach the same accuracy. Furthermore, the UV-Vis method can be used to estimate the proportion of HA that is adsorbed to PSNPs. The relative errors are < 13.7 % when the mass ratios of PSNPs and HA was between 1.6:1 and 8:1 and HA concentration was higher than 4.6 mgC L-1. This method developed can be applied to future laboratory research to investigate the interaction between NOM, NPs, and minerals.

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The combination of biochar (BC) and iron minerals improves their pollutant adsorption capacity. However, little is known about the reactivity of BC-iron mineral composites regarding their interaction and change in the pore structure. In this study, the mechanism of cadmium (Cd) adsorption by BC-iron oxide composites, such as BC combined with ferrihydrite (FH) or goethite (GT), was explored. The synergistic effect of the BC-FH composite significantly improved its Cd adsorption capacity. The adsorption efficiencies of BC-FH and BC-GT increased by 15.0% and 10.8%, respectively, compared with that of uncombined BC, FH, and GT. The strong Cd adsorption by BC-FH was attributed to stable interactions and stereoscopic pore filling between BC and FH. The scanning electron microscopy results showed that FH particles entered the BC pores, whereas GT particles were loaded onto the BC surface. FTIR spectroscopy showed that GT covered a larger area of the BC surface than FH. After loading FH and GT, BC porosities decreased by 9.3% and 4.1%, respectively. Quantum chemical calculations and independent gradient mode analysis showed that van der Waals interactions, H-bonds, and covalent-like interactions maintained stability between iron minerals and BC. Additionally, humic acid increased the agglomeration of iron oxides and formed larger particles, causing additional aggregates to load onto the BC surface instead of entering the BC pores. Our results provide theoretical support to reveal the interfacial behavior of BC-iron mineral composites in soil and provide a reference for field applications of these materials for pollution control and environmental remediation.

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Excessive application of fertilizers has caused a high load of phosphorus (P) in the North China Plain. The fate of P and its effects on aquatic ecosystems depend on its chemical speciation in soils. However, few studies systematically investigated the transport and retardation of different P species in the fluvo-aquic soil. In this study, the transport of inorganic P (orthophosphate, PO4), organic P (phytic acid, PA) and particulate P (hydroxyapatite nanoparticles, nHAP) in the fluvo-aquic soil were investigated by column experiments, and their retardation from major soil components such as kaolin, CaCO3, Al2O3, and goethite (GT) was also investigated by monitoring breakthrough curves and fitting transport models. The transport of P species in fluvo-aquic soil followed the order of PO4 > PA > nHAP. A high fraction of increased clay and mineral particle-associated P (P-E) was observed for PO4 and PA; while significant Ca-associated P (P-Ca) for nHAP. Under the experimental conditions, both CaCO3 and GT were the most influential factors for PO4, PA, and nHAP retention. Goethite strongly inhibited PO4 transport due to its high PO4 adsorption capacity, while CaCO3 strongly inhibited PA transport due to its strong association with PA under alkaline conditions. Both CaCO3 and GT can severely inhibit nHAP transport due to the favorable electrostatic conditions as well as the Ca2+ bridging effect. These results indicated that CaCO3 played a key role in regulating the retention of organic P and particulate P in the calcareous soil, and also suggested the important role of Fe (hydr)oxides in controlling the transport of inorganic P, which could out-compete that of CaCO3.

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The redox process driven by anaerobic respiration is a link between matter conversion and energy exchange in soil biogeochemistry. Microbial extracellular electron transfer forming biocurrents is a force in element cycling and community living in soil. However, the effect of indigenous microorganisms generating biocurrents on soil quality is unclear. We found that soil biocurrent showed little adverse influence on soil pH, cation exchange capacity, and available nitrogen, phosphorus and potassium and deblocked sequestered organic matter (29%). In addition, the bioelectric field derived from biocurrent obviously forced the migration of mineral elements, which was a supplement to the theory of water-salt transport, providing a new perspective on element transport. Moreover, the soil biocurrent directly regulated the availability of Ca and Fe (increase of 7-fold), indicating that electron transfer plays an important role in weathering and mineralization and thus pedogenesis. From a microbial ecology point of view, the soil bacterial richness and diversity were perfectly restored to their original state when the biocurrent stopped; including bacterial functions; although a temporary enrichment of certain species was observed. The above results provide new insights into the interactions between electron transfer and soil quality and confirm the safety of soil bioelectrochemical technology.

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Soil microorganisms are biological factors involved in the farmland environment. The factors that shape soil microbial communities and how these are influenced by geographic location, planting pattern (open-field or greenhouse), and soil organic pollutants (phthalate esters, PAEs) remain poorly understood at large scales. Using 16 S rRNA gene and ITS sequencing, we characterized the soil microbiota in open-field and greenhouse soils in Hebei Province, China, and correlated their structure and composition to geographic location, planting pattern and PAEs. Compared with geographic location, planting pattern is more decisive for shaping soil microbes and has more significant effects on bacteria, and the effects are shaped by the number and types of core OTUs. PAEs participated in the shaping of soil microbial communities by altering the relative abundances of dominant microorganisms in the two planting patterns, and the effects of PAEs with high Kow were more significant. PAEs have a greater impact on bacteria than fungi in both planting patterns. Bacteria in the greenhouse soil were sensitive to the 9 kinds of PAEs detected, however in the open-field samples, mainly responded to PAEs with high Kow and rarely respond to PAEs with low Kow. DEHP and DBP, as two monomers with the highest concentration, have significant effects on dominant genera of microorganisms under both planting patterns, with inhibiting effect on bacteria and significantly promotion on fungi. Our study clarified the factors that have a substantial impact on soil microorganisms at the provincial scale and the mechanisms involved in shaping soil microbial community structure, as well as the significant impact of PAEs on soil microbial dominant microorganisms.

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