Soil potentially toxic element pollution at different urbanization intensities: Quantitative source apportionment and source-oriented health risk assessment.

Potentially toxic element (PTE) pollution of urban soils has become the focus of social concern, but the differences of the sources, pollution levels and source-oriented human health risks (HHR) of PTE in urban soils among different urban intensity areas is rarely known. This study explored a comprehensive scheme that combined positive matrix factorization model and source-oriented assessment to quantitatively assess the priority pollution sources and HHR in urban soils from areas with different urbanization intensities. All the average values for PTE concentrations, except for Cr, were higher than their corresponding background values. The contributions made by the four sources (atmospheric deposition, agricultural activities, traffic activities, and natural sources) were relatively similar (22.29-29.89%) in the low urbanization intensity (LUI) area, whereas traffic activities and atmospheric deposition made the greatest contributions in the medium urbanization intensity (MUI) (29.12%) and the high urbanization intensity (HUI) (38.97%) areas, respectively. The geo-accumulation index results revealed that Cd was the most polluting element and the HUI area had the highest pollution levels. The content-oriented assessment of HHR demonstrated that the non-carcinogenic risks were acceptable, but the carcinogenic risks were unacceptable. According to the source-oriented HHR assessment, among the anthropogenic activities, atmospheric deposition contributed the most to carcinogenic risk of children in all areas, and atmospheric deposition, traffic activities and agricultural activities contributed the most to the carcinogenic risk of adults in HUI, MUI and LUI, respectively. This suggest that control measures need to be tailored to the appropriate urbanization intensity to effectively curb PTE pollution caused by anthropogenic activities.

Green remediation of Ni, Zn, and Cu in an electroplating contaminated site by wood vinegar with optimization and risk assessment.

Wood vinegar (WV) is a renewable organic compound, possessing characteristics such as high oxygenated compound content and low negative impact on soil. Based on its weak acid properties and complexing ability to potentially toxic elements (PTEs), WV was used to leach Ni, Zn, and Cu contaminated soil in electroplating sites. In addition, the response surface methodology (RSM) based on the Box-Behnken design (BBD) was established to clarify the interaction between each single factor, and finally completed the risk assessment of the soil. The amounts of PTEs leached from the soil climbed with the increase of WV concentration, liquid-solid ratio, and leaching time, while they surged with the decrease of pH. Under optimal leaching circumstances (the concentration of WV= 100 %; washing time= 919 min; pH= 1.00), the removal rates of Ni, Zn, and Cu could reach 91.7 %, 57.8 %, and 65.0 %, respectively, and the WV-extracted PTEs were mainly from the Fe-Mn oxides fraction. After leaching, the Nemerow integrated pollution index (NIPI) decreased from an initial value of 7.08 (indicating severe pollution) to 0.450 (indicating no pollution). The potential ecological risk index (RI) dropped from 274 (medium level) to 39.1 (low level). Additionally, the potential carcinogenic risk (CR) values reduced by 93.9 % for both adults and children. The results revealed that the washing process significantly reduced the pollution level, potential ecological risk, and health risk. Coupled with FTIR and SEM-EDS analysis, the mechanism of WV removal of PTEs could be explained from three aspects: acid activation, H+ ion exchange, and functional group complexation. In summary, WV is an eco-friendly and high-efficiency leaching material for the remediation of PTEs polluted sites, which will maintain soil function and protect human health.

Rape Straw Supported FeS Nanoparticles with Encapsulated Structure as Peroxymonosulfate and Hydrogen Peroxide Activators for Enhanced Oxytetracycline Degradation.

Iron-based catalysts with high load content of iron sulfide (FeS) were commonly peroxymonosulfate (PMS) and hydrogen peroxide (H2O2) activators to degrade organic pollutants but limited catalytic efficiency and increased risk of ferrous ion leaching restricted their use. Meanwhile, various biomass materials such as straw, peel, and branch have been extensively prepared into biochar for mechanical support for iron-based catalysts; however, the preparation process of biochar was energy-intensive. In this study, FeS nanoparticles modified rape straw composites (RS-FeS) encapsulated with ethylenediaminetetraacetic acid (RS-EDTA-FeS) were successfully presented by in-situ synthesis method for efficiently activating PMS and H2O2 to degrade oxytetracycline (OTC), which was economical and environmentally friendly. The results showed that the modified rape straw can remove OTC efficiently, and the addition of EDTA also significantly enhanced the stability and the reusability of the catalyst. In addition, EDTA also promoted the activation of H2O2 at neutral pH. The OTC degradation efficiency of the two catalysts by PMS was faster than that of H2O2, but H2O2 had a stronger ability to remove OTC than PMS. The highest OTC removal efficiency of RS-FeS and RS-EDTA-FeS were 87.51 and 81.15%. O2•- and 1O2 were the major reactive oxidative species (ROS) in the PMS system. Furthermore, compared with RS-FeS, the addition of EDTA inhabited the generation of O2•- in the PMS system. Instead, O2•- and •OH were the major ROS in the H2O2 system, but 1O2 was also identified in RS-FeS/H2O2 system. RS-EDTA-FeS showed a trend of rising first and then decreasing in recycle test. Instead, the removal rate of OTC by RS-FeS decreased significantly with the increase in reuse times. In the actual wastewater test, the TOC removal of two catalysts active by H2O2 was better than PMS, which was consistent with the test results of OTC, indicating that the two catalysts have application value in the removal of organic pollutants in actual wastewater. This study directly used plant materials as catalysts and omits the preparation process of biochar, greatly reduces the preparation cost and secondary pollution of catalysts, and provides theoretical support for the deepening of advanced oxidation technology.

Response of microbiomes with different abundances to removal of metal fractions by soil washing.

Toxic metal contamination causes a great threat to soil ecosystem and human health. Soil washing is a fast practice for removing metals, but its influences on microbial diversity and the stability of soil ecosystem remain unknown. In this study, ethylenediaminetetraacetic acid (EDTA), citric acid (CA), and fermented pineapple peel residue (FPP) were used as representatives of chelates, low molecular organic acids and biological materials to wash Pb-polluted soils, and their impacts on microbial community were investigated. Washing with these agents effectively removed Pb, but altered microbial community structure. After washing with EDTA, CA, and FPP, 3-8 bacterial phyla and 1 fungal phylum greatly increased, while 7-20 bacterial and 0-6 fungal phyla severely decreased or even disappeared. The alterations of different microbiomes were closely related to soil metal fractions. The labile metal fraction had negative effects on most bacteria and fungi, but also showed positive influences on Actinobacteria, Patescibacteria, and Fusobacteria. The moderately stable and stable fractions were nontoxic to the most microbes, but still harmful to Patescibacteria and Deinococcus-Thermus. These findings provide new insights for the effects of soil washing remediation and toxicity of metal fractions on the microbiomes with different abundance.

Remediation of heavy metal contaminated soil by biodegradable chelator-induced washing: Efficiencies and mechanisms.

Biodegradable chelators (BCs) are promising substitutes for conventional washing agents in the remediation of heavy metal contaminated soil with strong complexing ability and less cost. However, great challenges for the applications of BC-assisted washing still exist, such as the assessment of the factor affecting the efficiency of metal removal and the unclear of the metal removal mechanism. Batch washing was therefore explored to evaluate the potential for four BCs for removing Cd, Pb, and Zn from polluted soils. The soil spectroscopic characteristics before and after washing were also investigated. The results demonstrated that iminodisuccinic acid (ISA) and glutamate-N, N-diacetic acid (GLDA) were an appealing alternative to commonly used non-biodegradable ethylenediaminetetraacetic acid, but glucomonocarbonic acid (GCA) and polyaspartic acid (PASP) were less efficient. Optimal parameters of BCs were determined to be a concentration of 50 mmol L-1, a pH of 5.0, a contact time of 120 min, and a solid/liquid ratio of 1:5, considering metal removal efficiencies and the suitable cost. A single removal washing could be up to 52.39% of Cd, 71.79% of Pb, and 34.13% of Zn from mine soil, and 98.28% of Cd, 91.10% of Pb, and 90.91% of Zn from polluted farmland soil. After washing, the intensity of heavy metal binding to soil colloids increased while the metal mobility reduced because of weakly bound fractions removed by BCs. The BCs-induced soil washing revealed that the possible mechanisms of metal removal included the acid dissolution, ion exchange, and surface complexation. Our findings highlight the potential application of especially ISA and GLDA as efficient washing agents to remove potentially toxic elements from contaminated soils.

Removal of lead, zinc and cadmium from contaminated soils with two plant extracts: Mechanism and potential risks.

Screening appropriate washing agents to remediate soils contaminated with heavy metals is crucial for decreasing metal hazards posing to environment and human health. In this study, two plant washing agents-water-extracted from Fagopyrum esculentum and Fordiophyton faberi, were applied to remove soil Pb, Zn, and Cd by washing. Results indicated that metal removals augmented with increase of washing solution concentrations, decreased with increasing pH values of the solution and followed the pseudo-second-order model depending on contact duration. At concentration of 50 g/L, pH 3 and contact duration of 120 min, F. esculentum had higher removals of Pb (5.98-6.83%), Zn (21.82-27.94%), and Cd (39.90-40.74%) than those of F. faberi. And metal ions could be removed by binding with carboxyl, hydroxyl, amide, amine and aromatic groups in washing solutions. The potential risks of residual metals declined by 51.35-52.12% for mine soil and 48.51-49.96% for farmland soil with exchangeable and carbonate-bound fractions obviously extracted after a single washing (P < 0.05). And soil organic carbon and nutrients increased to some extent except for total phosphorus and available potassium. Moreover, soil phytotoxicity lowered except that some adverse effects on seed germination existed. Therefore, the water extract from F. esculentum is a promising washing agent for heavy metal removal.

Feasibility of nanoscale zero-valent iron to enhance the removal efficiencies of heavy metals from polluted soils by organic acids.

Soil washing with natural chelators to remediate metal-contaminated soils has been gained attention by researchers. However, the abilities of the chelators to remediate the multiple metal polluted soils are less effective. This study employed zero-valent iron nanoparticle (nZVI) to enhance the removal efficiencies of citric (CA), tartaric (TA) and oxalic acids (OA), and evaluate their feasibility. Results showed that metal removal efficiencies increased with the increasing concentration of nZVI and soil-liquid ratio, decreased with the increasing solution pH. The kinetic simulation indicated that pseudo-first-order and pseudo-second-order models could be used for describing the washing processes. Additionally, metal removals were significantly improved by addition of nZVI (p < 0.05). The highest enhancements of soil Cd, Pb and Zn removals under solution pH of 4.0, soil-liquid ratio of 1:20 and washing time of 120 min reached 12.83% (OA- nZVI), 24.92% (CA-nZVI) and 11.64% (OA- nZVI) for mine soil, and 19.24% (TA- nZVI), 18.16% (CA-nZVI) and 8.93% (OA- nZVI) for farmland soil, respectively. After soil washing, the exchangeable forms and the environmental risks of residual metals were markedly diminished in soils. Therefore, the combinations of the organic acids and nZVI are the feasible practices to repair the soils contaminated by heavy metals.

Feasibility of four wastes to remove heavy metals from contaminated soils.

Soil washing is one of the permanent techniques to remove heavy metals, and washing agent is a key influence factor for this technique, but there is still lack of high-efficiency, eco-friendly, and inexpensive agents. In this study, four wastes including pineapple peel (PP), soybean straw (SS), broad bean straw (BBS) and tea residue (TR) were employed to remove cadmium (Cd), lead (Pb) and zinc (Zn) in contaminated soils. The Fourier transform infrared spectroscopy (FTIR) analysis indicated that hydroxyl, carboxyl, amine, carbonyl and amide groups were involved in the interaction with metal ions by complexation or ion exchange. We then investigated the influences of various conditions including washing solution concentration, pH, and washing time. The metal removal efficiencies with these agents increased as the concentration augmented from 5 to 80 g L-1, decreased or presented an asymmetric V-shaped curve with increasing pH from 2.5 to 7.5, and fit intraparticle diffusion or Elovich model with washing time increasing. PP has the highest removals for Cd (90.1%), Pb (18.6%), and Zn (15.2%) in soil A, and 85.8, 24.8, and 69.4% in soil B, respectively. The relatively high metal removal was mainly attributed to effective removal of the exchangeable and acid soluble fractions. Moreover, single washing not only lowered the potential ecological risk of the heavy metals, but moderated the effects on soil chemical properties. Therefore, PP was a feasible washing agent to remediate soils contaminated by heavy metals.

Enhanced simultaneous removal of phosphate and ammonium from swine wastewater using magnetic magnesium-loaded Chinese herbal medicine residues: Performance, mechanism, and resource utilization.

Magnetic magnesium (Mg)-loaded Chinese herbal medicine residues (MM-TCMRs) were fabricated to simultaneously remove and recover phosphate and ammonium from wastewater. The MM-TCMRs exhibited larger specific surfaces and rougher structures with massive spherical particles than those of original residues. They could be separated by adjusting the magnetic field. The phosphate and ammonium adsorption by MM-TCMRs were matched with the pseudo-second-order model, while the Langmuir model yielded the maximum adsorption capacities of 635.35 and 615.57 mg g-1, respectively. Struvite precipitation on the MM-TCMRs surface was the primary removal mechanism with electrostatic attraction, ligand exchange, intra-particle diffusion, and ion exchange also involved. The recyclability of MM-TCMRs confirmed their good structural stability. More importantly, the nutrient-loaded MM-TCMRs enhanced alfalfa growth and improved soil fertility in planting experiments. Collectively, the MM-TCMRs are promising candidates for nutrient removal and recovery from wastewater.

Nonflammable superhydrophobic passive cooling Cellulose-CaCO3 film.

Energy consumption from air cooling systems in summer, water scarcity in hot regions, and the functional reusability of waste paper are emerging environmental problems. Finding solutions to these problems simultaneously remains a significant challenge. Herein, a superhydrophobic passive cooling Cellulose-CaCO3 film with hierarchical nano-sheets was fabricated to realize daytime radiative cooling with a temperature drop of 15-20 °C in summer and water harvesting with harvesting efficiency of 387 mg cm-2h-1 bd utilization of recycled waste paper. The superhydrophobic Cellulose-CaCO3 film demonstrates its self-cleaning properties against inorganic and organic pollutants. Furthermore, the superhydrophobicity of the film was maintained after base/acid corrosions, dynamic water flushing, and thermal treatment at 100 °C for 7 h, exhibiting good durability of the superhydrophobicity. Moreover, the superhydrophobic Cellulose-CaCO3 film is nonflammable after exposure to fire combustion for 1 min. In addition to waste paper, waste maize straws, and pasteboards were also collected to produce superhydrophobic passive cooling films. Results indicate that the above three cellulose-based raw materials can be well used to prepare durable superhydrophobic passive cooling materials. Environmental toxicology assessments confirm the safety of the material. This study not only provides a protocol for preparing superhydrophobic materials; but also demonstrates their potential for passive cooling and water harvesting.

Inhibition of high sulfur on functional microorganisms and genes in slightly contaminated soil by cadmium and chromium.

It is generally accepted that sulfur can passivate the bioavailability of heavy metals in soil, but it is not clear whether high sulfur in cadmium (Cd) and chromium (Cr) contaminated soil has negative effect on soil microbial community and ecological function. In this study, total sulfur (TS) inhibited the Chao 1, Shannon, Phylogenetic diversity (Pd) of bacterial and Pd of fungi in slightly contaminated soil by Cd and Cr around pyrite. TS, total potassium, pH, total chromium, total cadmium, total nitrogen, soil organic matter were the predominant factors for soil microbial community; the contribution of TS in shaping bacterial and fungal communities ranked at first and fifth, respectively. Compared with the low sulfur group, the abundance of sulfur sensitive microorganisms Gemmatimonas, Pseudolabrys, MND1, and Schizothecium were decreased by 68.79-97.22% (p < 0.01) at high sulfur one; the carbon fixation, nitrogen cycling, phosphorus cycling and resistance genes abundance were significantly lower (p < 0.01) at the latter. Such variations were strongly and closely correlated to the suppression of energy metabolism (M00009, M00011, M00086) and carbon fixation (M00173, M00376) functional module genes abundance in the high sulfur group. Collectively, high sulfur significantly suppressed the abundances of functional microorganisms and functional genes in slightly contaminated soil with Cd and Cr, possibly through inhibition of energy metabolism and carbon fixation of functional microorganisms. This study provided new insights into the environmental behavior of sulfur in slightly contaminated soil with Cd and Cr.

Effects of climate and geochemical properties on the chemical forms of soil Cd, Pb and Cr along a more than 4000 km transect.

Soil heavy metal speciation has received much attention for their different ecological and environmental effects. However, the effects of climate and soil geochemical properties on them in uncontaminated soils at macroscale were still unclear. Therefore, a transect more than 4000 km was chosen to study the effects of these factors on soil Cd, Pb and Cr forms. The results revealed that mean annual temperature and precipitation showed significant positive relations with the exchangeable and Fe-Mn oxide bound states of Cd, Pb and Cr, and residual Cr. And humidity and drought indexes were significantly positively correlated with their organic and carbonate bound forms, respectively. As for soil geochemical properties, pH displayed significant negative relationships with exchangeable, Fe-Mn oxide and organic bound Pb and Cr, and exchangeable Cd. Fe2O3 was significantly positively with the exchangeable and Fe-Mn oxide bound Cd, Pb and Cr, and residual Cr. And soil organic matter showed positive relations with organic bound Pb and Cr, and residual Cd and Cr, displayed negative relationships with carbonated bound Pb and Cr. Overall, climate and soil geochemical properties together affect the transformation and transport of heavy metals between different forms in uncontaminated soils.

Ecological and human health hazards of soil heavy metals after wildfire: A case study of Liangshan Yi autonomous prefecture, China.

Soil samples were collected in at different depths from the conflagration area in Liangshan Yi Autonomous Region, China, to investigate the distribution characteristics and ecological and human health risks of heavy metals after a wildfire. The samples collected comprise wildfire ash (WA) above the soil surface, ash soil (AS) 0-5 cm, and plain soil (PS) 5-15 cm below the soil surface. Additionally, reference soil (RS) was collected from a nearby unburned area at the same latitude as the conflagration area. The results showed that the concentrations of zinc (Zn), copper (Cu), lead (Pb), and cadmium (Cd) in the WA and AS were significantly higher than in reference soil (RS) (p < 0.05). Concentrations of Pb in the PS were 2.52 times higher than that in RS (17.9 mg kg-1) (p < 0.05). The AS and WA had the highest Index of potential ecological risks (RI > 600). In addition, The Cd in AS and WA contributed the most to the highest Improved nemerow index (INI) and RI with a contribution of more than 80%. The concentration of heavy metals was used to establish non-carcinogenic effects and cancer risks in humans via three exposure pathways: accident ingestion of soil, dermal contact with soil, and inhalation of soil particles. Hazard index (HI) values of each sample were all less than 1, indicating the non-carcinogenic risk was within the acceptable range and would not adversely affect the local population's health. The Cancer risk (CR) values of Cr, As, Cd, and Ni were all below 1 × 10-6, indicating that heavy metal pollution from this wildfire did not pose a cancer risk to residents.

A novel bio-washing eluent obtained from fermentation of fruit wastes for removal of soil Pb: efficiency, mechanism, and risk assessment.

Agricultural wastes are inexpensive materials for soil remediation. However, the direct water extracts from these wastes showed low efficiency for Pb removal, thus limiting their application. In this study, citrus pericarp (CP) and pineapple peel (PP), as the common agricultural wastes, were inoculated with lactic acid bacteria to produce fermentation liquors (FCP and FPP) for improving Pb removal efficiency. Results showed that the Pb removal rates by FCP and FPP reached 37.3 and 43.6%, and increased by almost 50.0% than those by CP and PP. The ecological risk of Pb reduced by 83.0-88.2% after five times continuous washing with FCP and FPP, and the Pb concentrations conformed to soil remediation standard of China. Moreover, soil organic carbon 1.5 times increased in the washed soils, while total potassium improved by 40.7-68.0%. The mechanisms of Pb removal by these wastes involved in adsorption-desorption of Pb2+, complexation with organic ligands, and co-precipitation of Pb complexes. The increase of low molecular organic acids during the fermentation promoted dissolution of Pb and provided more hydroxyl, carboxyl, and amine groups to interact with Pb2+, thus improving its removal rate. Therefore, fermentation liquid from fruit wastes is a novel, effective, and ecofriendly bio-washing eluent for Pb removal from contaminated soils.

Cadmium-resistant phosphate-solubilizing bacteria immobilized on phosphoric acid-ball milling modified biochar enhances soil cadmium passivation and phosphorus bioavailability.

Cadmium (Cd) can accumulate in agriculture soil from the regular application of phosphorus (P) fertilizer. Microbiological method is considered as a potentially effective strategy that can not only remediate the Cd-contaminated soil but also provide the phosphorus needed for crop growth. However, the toxicity of Cd may affect the activity of microorganisms. To solve this problem, Klebsiella variicola with excellent phosphate solubilization ability (155.30 mg L-1 at 48 h) and Cd adsorption rate (90.84 % with 10 mg L-1 Cd initial concentration) was firstly isolated and identified in this study. Then, a phosphoric acid and ball milling co-modified biochar (PBC) was selected as the carrier to promote the activities of K. variicola under Cd pollution. Surface characterization revealed that the promotion of K. variicola by PBC was mainly attributed to the large specific surface area and diverse functional groups. Compared to contaminated soil, microbial PBC (MPBC) significantly increased the pakchoi biomass and phosphorus (P) content, while the Cd content in leave and root of pakchoi (Brassica chinensis L.) decreased by 25.90-43.46 % (P < 0.05). The combined application also favored the transformation of the resistant P fractions to bioavailable P, and facilitated the immobilization of 20.12 % exchangeable Cd to reducible, oxidizable, and residual Cd in the treated soil. High-throughput sequencing revealed that the response of the soil microbial community to the MPBC was more beneficial than K. variicola or PBC alone. Therefore, the application of MPBC has the potential to act as an efficient, stable, and environmentally friendly sustainable product for Cd remediation and enhanced P bioavailability in agricultural production.

How accompanying ions affect soil heavy metal removal by polyepoxysuccinic acid during washing?

Soil washing with green eluent is an efficient technique to remediate heavy metal contaminated farmland. In addition to eluent, less is known about the roles of accompanying ions on heavy metal removal. We investigated the effects of accompanying ions including Fe3+, Mn2+, Ca2+, Mg2+, Al3+, Si4+ and PO43- on the desorption of Pb2+ and Cd2+ in paddy and arid soils using ethylenediaminetetraacetic acid and polyepoxysuccinic acid as eluents. The release rates of target and accompanying ions showed significant fast and slow reaction stages based on corresponding analysis and kinetic models. In fast reaction stage, Pb2+ and Cd2+ performed geochemical analogy with Ca2+, Mg2+ and PO43-. The release curves of these ions were fitted well with Elovich model, indicating that they released from oxysalt surface into solution via ion exchange, and dissolution of Fe/Mn/Al/Si (hydr)oxides through H+- and ligand-promoted dissolution. In slow reaction stage, Pb2+ and Cd2+ were related to Fe3+, Mn2+, Al3+ and Si4+, which were controlled by intraparticle diffusion process. H+ slowly diffused into interlayer of phyllosilicates to displace target and accompanying ions by ion exchange. Therefore, this research filled the gap of accompanying ions driving the release behavior of heavy metal ions during leaching.

Soil quality and ecological benefits assessment of alpine desertified grassland following different ecological restoration measures.

Introduction: Soil quality plays an irreplaceable role in plant growth for restored grassland. However, few studies investigate the comprehensive effects considering soil and vegetation properties during the restoration of desertified grassland, which restrict the virtuous circle of restored grassland ecosystem. Methods: By setting three restoration patterns of enclosure plus grass (EG), enclosure intercropping shrub-grass (ESG), and enclosure plus sand-barrier and shrub-grass (ESSG) with three different restoration years (≤5, 7-9, and ≥15 years), we selected 28 physicochemical and microbial indicators, and constructed a minimum data set (MDS) to analyze the influences of restoration measurements on soil quality and ecological benefits in alpine desertified grassland. Results: The results showed that the MDS comprised seven soil quality indicators: silt, total nitrogen (TN), carbon-nitrogen ratio (C/N), total potassium (TK), microbial biomass carbon (MBC), microbial biomass phosphorus (MBP), and fungi. Soil quality index (SQI) and ecological restoration effect index (EREI) in restored grasslands significantly increased by 144.83-561.24% and 87.21-422.12%, respectively, compared with unrestored grassland, and their positive effects increased with extending restoration years. The increasing effects of SQI and EREI were the highest in ESSG, followed by EG and ESG. The increasing rate of SQI began to decrease after 5 years in EG and ESG, while it decreased after 7-9 years in ESSG, and that of EREI in EG was lower than ESSG in each restoration year. Our work revealed that ESSG was the optimum restoration pattern for desertified grassland, and anthropogenic monitoring and management measurements such as applying organic fertilization and mowing return reasonably should be carried out at the beginning of 5 years in EG and ESG as well as 7 years in ESSG to maintain sustainable ecological benefits. Discussion: The study highlights that soil quality, including microbial properties, is a key factor to evaluate the restoration effects of desertified grassland.

Characterization of ionic liquids removing heavy metals from electroplating sludge: Influencing factors, optimisation strategies and reaction mechanisms.

The disposal of electroplating sludge (ES) is a common concern of researchers. Currently, it is difficult to achieve effective fixation of heavy metals (HMs) using traditional ES treatment. As green and effective HMs removal agents, ionic liquids can be used for the disposal of ES. In this study, 1-butyl-3-methyl-imidazole hydrogen sulphate ([Bmim]HSO4) and 1-propyl sulphonic acid-3-methyl imidazole hydrogen sulphate ([PrSO3Hmim]HSO4) were used as washing solvents for the removal of Cr, Ni, and Cu from ES. In reaction with increased agent concentration, solid-liquid ratio, and duration, the amount of HMs eliminated from ES rises, whereas opposite patterns were shown in response to rising pH. The quadratic orthogonal regression optimisation analysis also revealed that the ideal washing specifications for [Bmim]HSO4 were 60 g L-1, 1:40, and 60 min, respectively, for agent concentration, solid-liquid ratio, and washing time, while those for [PrSO3Hmim]HSO4 were 60 g L-1, 1:35, and 60 min, respectively. Under the optimal experimental conditions, the Cr, Ni, and Cu removal efficiencies for [Bmim]HSO4 were 84.3, 78.6, and 89.7%, respectively, and those values for [PrSO3Hmim]HSO4 were 99.8, 90.1, and 91.3%, respectively. This was mainly attributed to that ionic liquids enhance metal desorption through acid solubilisation, chelation, and electrostatic attraction. Overall, ionic liquids are reliable washing reagents for ES contaminated by HMs.

A review on fabricating functional materials by electroplating sludge: process characteristics and outlook.

As the end product of the electroplating industry, electroplating sludge (ES) has a huge annual output and an abundant heavy metal (HM). The effective disposal of ES is attracting increasing attention. Currently, the widely used ES disposal methods (e.g. landfill and incineration) make it difficult to effectively control of HMs and synchronously utilise metal resources, leading to a waste of metal resources, HMs migration, and potential harm to the environment and human health. Therefore, techniques to limit HMs release into the environment and promote the efficient utilisation of metal resources contained within ES are of great interest. Based on these requirements, material reuse is a great potential means of ES management. This review presents an overview of the process flows, principles and feasibilities of the methods employed for the material reuse of ES. Several approaches have been investigated to date, including (1) additions in building materials, (2) application in pigment production, and (3) production of special functional materials. However, these three methods vary in their treatment scales, property requirements, ability to control HMs, and degree of utilisation of metal resources in ES. Currently, the safety of products and costs are not paid enough attention, and the large-scale disposal of HMs is not concordant with the effective management of HMs. Accordingly, this study proposes a holistic sustainable materialised reuse pattern of ES, which combines the scale and efficiency of sludge disposal and pays attention to the safety of products and the cost of transformation process for commercial application.

Activation and tolerance of Siegesbeckia Orientalis L. rhizosphere to Cd stress.

This experiment investigated the changes of rhizosphere soil microenvironment for hyperaccumulation-soil system under Cd stress in order to reveal the mechanism of hyperaccumulation and tolerance. Thus, Cd fractions, chemical compositions, and biochemical characteristics in rhizosphere soil of Siegesbeckia orientalis L. under Cd stress conditions of 0, 5, 10, 25, 50, 100, and 150 mg kg-1 were investigated through a root bag experiment, respectively. As a result, Cd induced the acidification of S. orientalis rhizosphere soil, and promoted the accumulation of dissolved organic carbon (DOC) and readily oxidizable organic carbon (ROC), which increased by 28.39% and 6.98% at the maximum compared with control. The percentage of labile Cd (acid-soluble and reducible Cd) in soil solution increased significantly (P < 0.05) from 31.87% to 64.60% and from 26.00% to 34.49%, respectively. In addition, rhizosphere microenvironment can alleviate the inhibition of Cd on soil microorganisms and enzymes compare with bulk soils. Under medium and low concentrations of Cd, the rhizosphere soil microbial biomass carbon (MBC), basal respiration, ammonification and nitrification were significantly increased (P < 0.05), and the activities of key enzymes were not significantly inhibited. This suggests that pH reduction and organic carbon (DOC and ROC) accumulation increase the bioavailability of Cd and may have contributed to Cd accumulation in S. orientalis. Moreover, microorganisms and enzymes in rhizosphere soils can enhance S. orientalis tolerance to Cd, alleviating the nutrient imbalance and toxicity caused by Cd pollution. This study revealed the changes of physicochemical and biochemical properties of rhizosphere soil under Cd stress. Rhizosphere soil acidification and organic carbon accumulation are key factors promoting Cd activation, and microorganisms and enzymes are the responses of Cd tolerance.