Source apportionment of soil PTE in a northern industrial county using PMF model: Partitioning strategies and uncertainty analysis.

Positive matrix factorization (PMF) has commonly been applied for source apportionment of potentially toxic elements (PTE) in agricultural soil, however, spatial heterogeneity of PTE significantly undermines the accuracy and reliability of PMF results. In this study, a representative industrial-agricultural hub in North China (Xuanhua district, Zhangjiakou City) was selected as the research subject, multiple partition processing (PP) strategies and uncertainty analyses were integrated to advance the PMF modeling and associated algorithm mechanisms were comparatively discussed. Specifically, we adopted three methods to split the research area into several subzones according to industrial density (PP-1), population density (PP-2), and the ecological risk index (PP-3) respectively, to rectify the spatial bias phenomenon of PTE concentrations and to achieve a more interpretable result. Our results indicated that the obvious enrichment of Cd, Pb, and Zn was found in the agricultural soil, with Hg and Cd accounted for 83.49% of the overall potential ecological risk. Combining proper PP with PMF can significantly improve the modelling accuracy. Uncertainty analysis showed that interval ratios of tracer species (Cd, Pb, Hg, and Zn) calculated by PP-3 were consistently lower than that of PP-1 and PP-2, indicating that PP-3 coupled PMF can afford the optimal modeling results. It suggested that natural sources, fertilizers and pesticides, atmosphere deposition, mining, and smelting were recognized as the major contributor for the soil PTE contamination. The contribution of anthropogenic activities, specifically fertilizers and pesticides, and atmosphere deposition, increased by 1.64% and 5.91% compared to PMF results. These findings demonstrate that integration of proper partitioning processing into PMF can effectively improve the accuracy of the model even at the case of soil PTE contamination with high heterogeneity, offering support to subsequently implement directional control strategies.

Accumulation, potential risk and source identification of toxic metal elements in soil: a case study of a coal-fired power plant in Western China.

Coal-fired power plants (CPP) usually release massive numerous amounts of potentially toxic metal(loid)s (PTMs) into nearby ecosystems. There have been relatively few studies targeted on the ecological influences of PTMs related to the CPP in arid area. In this work, the distribution pattern, source apportionment and environmental risks of As, Cd, Cr, Hg, Pb and a couple of seldom monitored PTMs (Se, Zn, Co, Cu, Fe, Mn and Ni) in the soils near a coal electricity integration base were investigated in Hami, a city in northwestern China. Nemerow synthesis pollution index, geo-accumulation index and ecological risk index were used to assess pollution state of these PTMs in soils, and ordinary Kriging interpolation was used to analyze the spatial distribution for these elements. Methods of CA, PCA, CA and PAM were carried out for quantitative source analysis. The research outcome includes: (1) the contents of individual PTMs in most samples were greater than the background values, the pollution degrees of Se, Pb, Hg, Cd and As were significant, and some areas exceeded the warning threshold value; (2) the main sources of these PTMs were natural sources (35%), coal mine sewage (11%), atmospheric release during coal combustion (21%), dust generated from coal and combustion products (33%); (3) attention should be paid to the open-pit coal mines, shaft coal mines and ash dumps where the contents of metal elements were significantly polluted; and (4) wind is the main driving forces of PTMs migration in arid areas.

In vivo phytotoxic effect of yttrium-oxide nanoparticles on the growth, uptake and translocation of tomato seedlings (Lycopersicon esculentum).

The potential toxicity and ecological risks of rare-earth nanoparticles in the environment have become a concern due to their widespread application and inevitable releases. The integration of hydroponics experiments, partial least squares structural equation modeling (PLS-SEM), and Transmission Electron Microscopy (TEM) were utilized to investigate the physiological toxicity, uptake and translocation of yttrium oxide nanoparticles (Y2O3 NPs) under different hydroponic treatments (1, 5, 10, 20, 50 and 100 mg·L-1 of Y2O3 NPs, 19.2 mg·L-1 Y(NO3)3 and control) in tomato (Lycopersicon esculentum) seedlings. The results indicated that Y2O3 NPs had a phytotoxic effect on tomato seedlings' germination, morphology, physiology, and oxidative stress. The Y2O3 NPs and soluble YIII reduced the root elongation, bud elongation, root activity, chlorophyll, soluble protein content and superoxide dismutase and accelerated the proline and malondialdehyde in the plant with increasing concentrations. The phytotoxic effects of Y2O3 NPs on tomato seedlings had a higher phytotoxic effect than soluble YIII under the all treatments. The inhibition rates of different levels of Y2O3 NPs in shoot and root biomass ranged from 0.2% to 6.3% and 1.0-11.3%, respectively. The bioaccumulation and translocation factors were less than 1, which suggested that Y2O3 NPs significantly suppressed shoot and root biomass of tomato seedlings and easily bioaccumulated in the root. The observations were consistent with the process of concentration-dependent uptake and translocation factor and confirmed by TEM. Y2O3 NPs penetrate the epidermis, enter the cell wall, and exist in the intercellular space and cytoplasm of mesophyll cells of tomato seedlings by endocytic pathway. Moreover, PLS-SEM revealed that the concentration of NPs significantly negatively affects the morphology and physiology, leading to the change in biomass of plants. This study demonstrated the possible pathway of Y2O3 NPs in uptake, phytotoxicity and translocation of Y2O3 NPs in tomato seedlings.

Evaluation of arsenic mineralogy and geochemistry in gold mine-impacted matrices: Speciation, transformation, and potential associated risks.

The risk of arsenic (As) contamination from gold mining is a long-term environmental concern for mines worldwide. Researchers have mainly focused on As contamination induced by tailings, however, less attention has been paid mineralogically to differentiate the fate of As among different As-bearing matrices. This paper presents a detailed study of the mineralogical and morphological features of three typical As-bearing matrices (waste rock, ores, and tailings) using bulk chemical, microscopic and spectroscopic analyses, and reveals the geochemical behavior of As in those matrices. Results from mineral composition identified by RoqSCAN revealed that the matrices were dominated by quartz, k-feldspar, albite, muscovite, and clay minerals, with subordinate ankerite, chlorite, smectite, hematite, arsenopyrite, pyrrhotite, apatite, pyrite, halite, and calcite. The sequential extraction scheme indicated that As in waste rock, ores and tailings was mainly hosted in arsenopyrite. Microscopic analysis observed that waste rock was significantly different from the ores and tailings in terms of mineralogical and morphological characteristics. For waste rock, from arsenopyrite to hematite, As content decreased from 46.12 wt% to 3.54 wt%. However, arsenopyrite presented as unweathered euhedral crystals or slight fragmentation in ores and tailings and a narrower oxidation rims than that of waste rock. The leaching test of SPLP showed that the highest As leaching was found in waste rock (0.246 mg/L) which was significantly higher than those in ores (0.080 mg/L) and tailings (0.148 mg/L). The As in waste rock displayed weaker geochemical stability than in ores and tailings, as supported by mineralogy analysis. Health risk assessment suggested waste rock had a higher health risk for both adults and children compared with ores and tailings. These findings reaffirm that understanding of As fate among different source materials is paramount for securing humans from As hazards. More must be done to decelerate the continuous oxidation of waste rock, thus mitigating As release into nature.

Evaluation of potential ecological risks in potential toxic elements contaminated agricultural soils: Correlations between soil contamination and polymetallic mining activity.

Extensive mineral exploitation activities in history have aggravated potential toxic elements (PTEs) contamination in agricultural soils in China. Comprehensive ecological risk assessment is of great significance to orientate the restoration of contaminated soils, especially for those with high background values and multiple sources. The study area is located in the major rice producing area of China. Historically, there was a silver mine and a lead-zinc mine in the area, which were successively closed during the investigation. The intensive mining activities caused serious PTEs pollution in the agricultural soils around the mining area. In this study, five PTEs (As, Cd, Cr, Hg and Pb) selected to assessed the potential of geoaccumulation index in assessing agricultural soil potential risk assessment by identifying ecological risk sources. 315 of soil samples collected in 2009, 2014, 2018 were comprehensively analyzed by single pollution index evaluation (single factor index, geoaccumulation index), comprehensive evaluation (Nemerow index, potential ecological risk index) and trend analysis. Single factor index analysis showed that geoaccumulation index considered the impact of natural diagenesis of background values and human activities on the environment, ensuring high evaluation accuracy comparing to other methods used in typical complex agricultural soils. The modified potential ecological risk index revealed that the high background area did not represent high risk area, which was consistent with the implementation effect of governance measures. This study can provide important insights for policymakers and environmental engineers to quantitatively recognize the soil pollution and the effectiveness of governance based on applicable and reasonable evaluation methods.

Distribution and migration characteristics of dinitrotoluene sulfonates (DNTs) in typical TNT production sites: Effects and health risk assessment.

The production of 2,4,6-trinitrotoluene (TNT) produces a great deal of waste water, and dinitrotoluene sulfonates (DNTs) are the main pollutants in its waste. This paper presents a pilot investigation on the geochemical transformation of DNTs affected by historical wastewater spillage from a typical TNT production company in Northwest China. In the horizontal direction, DNTs diffused from the evaporation pond to the surrounding area of the site, and the concentration of DNTs in the evaporation pond surface soil exceeded 1000 mg/kg. The horizontal distribution of DNTs in the site showed a migration trend to the east and south of evaporation, which was consistent with the terrain of high northwest and low southeast of the site. Due to the high water solubility of pollutants, water flow is the main driving force for the horizontal distribution of DNTs. In the vertical direction, the concentration of pollutants gradually increased with the depth of the soil. DNTs are mainly adsorbed in the third layer (6.0-8.0 m). It can be seen that the accumulation of the 2,4-DNTs-3-SO3- is obviously larger than that of the 2,4-DNTs-5-SO3-, which may be related to the steric hindrance effect of sulfonic acid groups in the two isomers. Results showed DNTs distribution strongly linked to soil physicochemical properties and the migration of DNTs in soil exhibited obvious heterogeneity in time and space. The carcinogenic risks in surface soil (0-1.5 m) and lower soil (1.5-6.0 m, 6.0-8.0 m) are all higher than 1✕10-6; non-carcinogenic risk surface soil (0-1.5 m) is 4.011✕10, which is greater than 1, indicating that they may cause certain harm to the human body. Meanwhile, this study presented a pioneering investigation for the contamination and geochemical transfer of DNTs.

Input-output balance of cadmium in typical agriculture soils with historical sewage irrigation in China.

The gradual increase of cadmium (Cd) in soils has caused environmental and health risk, and it's important to study the accumulation trend to evoke the awareness of farmland safety management. This research during the period of March in 2017-2018 evaluated the input (irrigation, atmospheric deposition, fertilizer and pesticide application) and the output (runoff and seepage, grain and straw uptake) of Cd in contaminated farmland irrigated with sewage water in Hebei Province. The experimental results indicated sewage irrigation (51.03%), and atmospheric deposition (46.35%) were the main input pathways; Grain uptake (42.72%) and straw removal (50.71%) played a major role in output fluxes. The input-output balance (net transport fluxes) of Cd in the farmland were estimated to be +3621.68 ~ +8899.78 mg·(ha·yr)-1 under different conditions (sewage irrigation with straw returning/straw removal, clean water irrigation with straw returning/straw removal), representing there was a Cd inputting in the farmland during the study. Even in the case of the lowest net transport fluxes, the annual increase of Cd concentration in soils reached to 0.0014 mg/kg. Therefore, it's necessary to take action that cutting off those pathway inputs into farmland ecosystems, such as monitoring the water quality of irrigation water sources, applying fertilizer and pesticide properly. Furthermore, attentions need to be paid to the Cd input into the farmland and environmental risks that may arise while returning straw to the field for improving soil fertility and crop production.

Benzene homologues contaminants in a former herbicide factory site: distribution, attenuation, risk, and remediation implication.

Benzene homologues often used as organic raw materials or as detergents in chemical industry are prone to accidental release into the environment which can cause serious long-term soil pollutions. In a large former herbicide factory site, we investigated 43 locations for benzene homologues contaminations in soil, soil gas, and groundwater and studied the hydrogeological conditions. An inverse distance weighted interpolation method was employed to determine the pollutants three-dimensional spatial distribution in the soils. Results showed that benzene homologues residues were mainly originated from the herbicide production workshop and that the pollution had horizontally expanded at the deeper soil layer. Contaminants had already migrated 15 m downward from ground surface. Contaminant phase distribution study showed that NAPL was the primary phase (> 99%) for the pollutants accumulated in the unsaturated zone, while it had not migrated to groundwater. The primary mechanism for contaminant transport and attenuation included dissolution of "occluded" NAPL into pore water and pollutant volatilization into soil pore space. Risk assessment revealed that the pollutants brought unacceptable high carcinogenic and non-carcinogenic risks to public health. In order to convert this former chemical processing factory site into a residential area, a remediation to the polluted production workshop sites is urgently required.

Reducing Arsenic Concentration in Panax notoginseng via Contaminant Immobilization in Soil Using Fe-Ce Oxide.

(Burk.) F.H. Chen, a valuable Chinese medicine, is currently confronted with arsenic (As) contamination in China due to soil pollution. Our previous research demonstrated that Fe(0) and zeolite had a certain inhibitory effect on As accumulation in . In order to further reduce As accumulation in the plant, a synthetic iron material (Fe-Ce oxide [FC]) with high As adsorption capacity was tested for As remediation. In the study, after FC was applied to the As-contaminated soil, was planted in the soil. The As leaching behavior of the treated soil and As accumulation in were evaluated. The results showed that FC immobilized As more effectively than Fe(0) and zeolite in soils with high As concentrations. When the FC dosage was 0.5 % (w/w), As concentration of root (the main medicinal part) decreased by 56%, and root biomass increased by 55%. Results indicated FC could reduce the non-specifically adsorbed As fraction (F1) and specifically adsorbed As fraction (F2) by 22 to 31% and 5 to 17%, respectively, thus reducing the toxicity characteristic leaching procedure leachable As concentration by 41 to 67%. The finding of an iron plaque coating on the plant root and its function as a barrier to As uptake by is reported here for the first time. The occurrence of iron plaque led to a reduction in As concentration in the phellem and xylem-phloem by 66 to 80% and 43 to 70%, respectively. Our findings will help in developing As contamination control in areas where is planted and set a foundation for a FC-based As immobilization technology.

Combining phytoremediation with soil flushing for arsenic removal from contaminated soil.

Arsenic (As) contamination poses a high risk to public health in China. Remediation of soil As contamination is an urgent need. Development of more effective remediation technologies is crucial in order to achieve remediation goals. In this study, pot experiments were carried out to study the As removal effectiveness of planting Pteris vittata L. (P.v.) and Lolium multiflorum L. (L.m.) in combination with in situ soil flushing using monopotassium phosphate (KH2PO4) solutions. Results showed that planting P.v. and L.m. in combination with 8 days of KH2PO4 solution soil flushing achieved 35.20% and 52.93%. As removal efficiency in the rhizosphere soil, respectively, which was significantly higher than 9.14% removal from soil flushing alone. Results also indicated that planting P.v. and L.m. changed the speciation of As to labile form, facilitating As removal from soil. Growing P.v. with in situ KH2PO4 flushing was more effective in remediating As-contaminated agricultural soil; L.m. could not be used in place of P.v to achieve the same remediation efficiency. This research provides an important guidance on plant screening for phytoremediation in combination with in situ flushing to remediate As-contaminated soil.

A combined process coupling phytoremediation and in situ flushing for removal of arsenic in contaminated soil.

Phytoremediation and soil washing are both potentially useful for remediating arsenic (As)-contaminated soils. We evaluated the effectiveness of a combined process coupling phytoremediation and in situ soil flushing for removal of As in contaminated soil through a pilot study. The results showed that growing Pteris vittata L. (P.v.) accompanied by soil flushing of phosphate (P.v./Flushing treatment) could significantly decrease the total As concentration of soil over a 37day flushing period compared with the single flushing (Flushing treatment). The P.v./Flushing treatment removed 54.04% of soil As from contaminated soil compared to 47.16% in Flushing treatment, suggesting that the growth of P. vittata was beneficial for promoting the removal efficiency. We analyzed the As fractionation in soil and As concentration in soil solution to reveal the mechanism behind this combined process. Results showed that comparing with the control treatment, the percent of labile arsenate fraction significantly increased by 17% under P.v./Flushing treatment. As concentration in soil solution remained a high lever during the middle and later periods (51.26-56.22mg/L), which was significantly higher than the Flushing treatment. Although soil flushing of phosphate for more than a month, P. vittata still had good accumulation and transfer capacity of As of the soil. The results of the research revealed that combination of phytoremediation and in situ soil flushing is available to remediate As-contaminated soils.

Removal of heavy metals and arsenic from a co-contaminated soil by sieving combined with washing process.

Batch experiments were conducted with a heavy metals and arsenic co-contaminated soil from an abandoned mine to evaluate the feasibility of a remediation technology that combines sieving with soil washing. Leaching of the arsenic and heavy metals from the different particle size fractions was found to decrease in the order: <0.1, 2-0.1, and >2mm. With increased contact time, the concentration of heavy metals in the leachate was significantly decreased for small particles, probably because of adsorption by the clay soil component. For the different particle sizes, the removal efficiencies for Pb and Cd were 75%-87%, and 61%-77% for Zn and Cu, although the extent of removal was decreased for As and Cr at <45%. The highest efficiency by washing for Pb, Cd, Zn, and As was from the soil particles >2mm, although good metal removal efficiencies were also achieved in the small particle size fractions. Through SEM-EDS observations and correlation analysis, the leaching regularity of the heavy metals and arsenic was found to be closely related to Fe, Mn, and Ca contents of the soil fractions. The remediation of heavy metal-contaminated soil by sieving combined with soil washing was proven to be efficient, and practical remediation parameters were also recommended.

Distribution pattern of polycyclic aromatic hydrocarbons in particle-size fractions of coking plant soils from different depth.

The concentrations of 16 priority polycyclic aromatic hydrocarbons (PAHs) in four size fractions (<2, 2-20, 20-200, >200 µm) in soils at different depth from a heavily contaminated crude benzol production facility of a coking plant were determined using GC-MS. Vertically, elevated total PAHs concentrations were observed in the soils at 3.0-4.5 m (layer B) and 6.0-7.5 m (layer C), relatively lower at 1.5-3.0 m (layer A) and 10.5-12.0 m (layer D). At all sampling sites, the silt (2-20 µm) contained the highest PAHs concentration (ranged from 726 to 2,711 mg/kg). Despite the substantial change in PAHs concentrations in soils with different particle sizes and lithologies, PAHs composition was similarly dominated by 2-3 ring species (86.5-98.3 %), including acenaphthene, fluorene, and phenanthrene. For the contribution of PAHs mass in each fraction to the bulk soil, the 20-200 µm size fraction had the greatest accumulation of PAHs in loamy sand layers at 1.0-7.5 m, increasing with depth; while in deeper sand layer at 10.5-12.0 m, the >200 µm size fraction showed highest percentages and contributed 81 % of total PAHs mass. For individual PAH distribution, the 2-3 ring PAHs were highly concentrated in the small size fraction (<2 and 2-20 µm); the 4-6 ring PAHs showed the highest concentrations in the 2-20 µm size fraction, increasing with depth. The distribution of PAHs was primarily determined by the sorption on soil organic matter and the characteristics of PAHs. This research should have significant contribution to PAH migration study and remediation design for PAHs-contaminated sites.

Cleaner production of Chinese cabbage by intercropping from Cd contaminated soil: Effects of hyperaccumulator variety and planting strip width.

The utilization of Cd-contaminated soil in vegetable crop production can lighten the food crisis and improve the soil environmental resilience. Intercropping is a reliable technology in safety production from contaminated soil. A field-scale experiment was carried out to unravel how plant species and pattern affect the growth and Cd uptake of Chinese cabbage from Cd contaminated land. Among all the intercropping systems designed in this study, one row of Chinese cabbage intercropping with one row of Solanum nigrum L. is the best planting mode (high yields (2.78 kg/m2) and low Cd accumulation (0.02 mg/kg) of Chinese cabbage). Combined with the in-depth joint analysis of diverse soil physicochemical features (soil nutrient characteristics and microbial community structure), biomass yield and quality, and soil microbiological properties, we elaborated that two measures (screening hyperaccumulation types and controlling planting strip width) were the major factors in determining the growth of the aboveground and underground parts of Chinese cabbage respectively, thus directly regulating the application effectiveness of intercropping technology. The intertwined mechanisms (interspecific and intraspecific relationship) of different intercropping systems are summarized, which include better utilization of space, light and other resources in the aboveground part, bioavailability of nutrient, drive of soil bacteria and alleviated soil Cd stress in the underground part, etc. Our research outputs indicate the effectiveness and feasibility of intercropping can be improved by optimizing the streamline configuration and plant mode, which provide theory of reference and practical evidence for warranting the food safety and agricultural soil remediation simultaneously.

Environmental risk presented by arsenic contamination of building and facility surfaces in a coking plant.

Arsenic contamination on the surface of buildings and facilities at a coking plant and associated health risk were studied. A total of 94 wipe samples from 56 buildings and facilities were collected, and As concentrations were found to range from 0.01 to 23.90 µg/100 cm(2). 20.2% of the samples exceeded the As level calculated to present health risk: 4.02 µg/100 cm(2). Arsenic mean concentration was found to be highest on the surface of bricks, and coking zone showing the highest As risk. The findings of this study may provide clues to As pollution control and risk evaluation in coking plants.

Enhanced delivery of engineered Fe-Mn binary oxides in heterogeneous porous media for efficient arsenic stabilization.

Heterogeneity in sediment and aquifer is universal, resulting in preferential flows of injected materials in the high permeability regions and forming flow by-passed zones in the low permeability regions during in-situ subsurface remediation. This adverse effect can considerably delay the completion of remedial operations and significantly increase the cost. Column experiments were designed and conducted to study the transport of starch- and starch-xanthan gum modified Fe-Mn binary oxide particles (SFM and SXFM) in saturated heterogeneous porous media and to reveal the particles' arsenic (As) stabilization performance. Fine-in-Coarse (FIC) and Coarse-in-Fine (CIF) patterns of heterogeneous packings were set up in the columns. Testing results demonstrated that starch-xanthan gum dual treatment on Fe-Mn binary oxides successfully improved the particles' migration capability in heterogeneous porous media and their distribution uniformity attributed to the profound shear thinning behavior of xanthan gum solution. The addition of xanthan gum to the system increased the viscosity and shear thinning property of the SXFM suspension, making it a better candidate for delivery. Both SFM and SXFM stabilized As in heterogeneously packed sediment collected from a contaminated site, with SXFM showing better stabilization performance than SFM. The stabilization effects of SXFM were 90.7-97.0%, compared to 82.0-95.2% of SFM.

Potential hot spots contaminated with exogenous, rare earth elements originating from e-waste dismantling and recycling.

Dismantling and recycling e-waste has been recognized as a potential emission source of rare earth elements (REEs). However, the presence of REEs in typical regional soils has yet to be studied. Given the potential health implications of such soil contamination, it is vital to study the characteristics, spatial distribution, and pollution level of REEs caused by e-waste dismantling as well as determine the influencing mechanism. This study focused on Guiyu Town as an example site, which is a typical e-waste dismantling base. From the site, 39 topsoil samples of different types were collected according to grid distribution points. Soil profiles were also collected in the dismantling and non-dismantling areas. The REE characteristic parameters showed that the REE distribution was abnormal and was affected by multiple factors. The results of the integrated pollution index showed that approximately 61.5% of soil samples were considered to be lightly polluted. Spatial distribution and correlation analysis showed that hot spots of REE-polluted soil coincided with known, main pollution sources. Moreover, there was a significant negative correlation (p ≤0.05) between the REE concentration and the distance from the pollution source. E-waste disassembly and recycling greatly affect the physical and chemical properties of the surrounding soil as well as downward migration areas. In the disassembly area, REE accumulated more easily in the surface layer (0-20 cm). Geographical detector results showed that distance factor was the main contribution factor for both light rare earth elements (LREE) and heavy rare earth element (HREE) (q = 34.59% and 53.33%, respectively). REE distribution in soil was nonlinear enhanced by different factors. Taken together, these results showed that e-waste disassembling and recycling not only directly affected the spatial distribution of REEs, but that their distribution was also affected by land use type and soil properties.

Ball-milled magnetite for efficient arsenic decontamination: Insights into oxidation-adsorption mechanism.

Conventional adsorbents for decontaminating arsenic exhibit low efficacy for the removal of arsenite (As(III)). This study aims to develop a robust As adsorbent from natural magnetite (M0) via a facile ball milling process, and evaluate their performance for decontaminating As(III) and As(V) in water and soil systems. The ball milling process decreased the particle size and crystallinity of M0, resulting in pronounced As removal by the ball-milled magnetite (Mm). Ball milling under air facilitated the formation of Fe-OH and Fe-COOH functional groups on Mm interface, contributing to effective elimination of As(III) and As(V) via hydrogen bonding and complexation mechanisms. Synergistic oxidation effects of hydroxyl and carboxyl groups, and reactive oxygen species (O2·-, and ·OH) on the transformation of As(III) to As(V) during the adsorption were proposed to explain the enhanced As(III) removal by Mm. A short-term soil incubation experiment indicated that the addition of Mm (10 wt%) induced a decrease in the concentration of exchangeable As by 30.25%, and facilitated the transformation of water-soluble As into residual fraction. Ball milling thus is considered as an eco-friendly (chemical-free) and inexpensive (scalable, one-stage process) method for upgrading the performance of natural magnetite towards remediating As, particularly for tackling the highly mobile As(III).

Novel insights into the adsorption of organic contaminants by biochar: A review.

With rising concerns in the practical application of biochar for the remediation of environment influenced by various organic contaminants, a critical review to facilitate insights the crucial role that biochar has played in wastewater and polluted soil decontamination is urgently needed. This research therefore aimed to describe different intriguing dimensions of biochar interactions with organic contaminants, which including: (i) an introduction of biochar preparation and the related physicochemical properties, (ii) an overview of mechanisms and factors controlling the adsorption of organic contaminants onto biochar, and (iii) a summary of the challenges and an outlook of the further research needs in this issue. In the light of the survey consequences, the appearance of biochar indicates the potential in substituting the existing costly adsorbents, and it has been proved that biochar is one promising adsorbent for organic pollutants adsorption removal from water and soil. However, some research gaps, such as dynamic adsorption, potential environmental risks, interactions between biochar and soil microbes, novel modification techniques, need to be further investigated to facilitate its practical application. This research will be conductive to better understanding the adsorption removal of organic contaminants by biochar.

Cosorption of Zn(II) and chlortetracycline onto montmorillonite: pH effects and molecular investigations.

Ionic antibiotics and metals generally coexist, and their interaction can affect their sorption behaviors onto soil minerals, therefore determining their environmental hazards. This study investigated the sorption and cosorption of Zn(II) and chlortetracycline (CTC) onto montmorillonite at different solution pH (3-10) using batch experiments and extended X-ray absorption fine structure (EXAFS) analysis. The Langmuir model could reproduce well the sorption isotherms of Zn(II) and CTC. The presence of CTC/Zn(II) could promote the maximum sorption capacity (Qm) of Zn(II)/CTC, based on site energy distribution (SED) theory. Generally, Zn(II) sorption increased with pH increasing. Comparatively, CTC sorption decreased as pH increased till approximately pH 5.0, then increased continuously with pH increasing. Both CTC and Zn(II) co-existence enhanced their individual sorption in both acidic and neutral environments. The processes behind CTC and Zn(II) sorption mainly included cation exchange and surface complexation. The EXAFS data evidenced that the presence of CTC could alter the species of Zn(II) on montmorillonite via surface complexation at pH 4.5 and 7.5, with Zn-CTC complexes being the predominant species on montmorillonite at pH 7.5. At pH 9.5, Zn(II) may exist onto montmorillonite in precipitated form similar to Zn-Al hydrotalcite-like compound (HTlc) regardless of CTC presence.