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Lithium, as an emerging contaminant, lacks sufficient information regarding its environmental and ecotoxicological implications within soil-plant systems. Employing maize, wheat, pea, and water spinach, we conducted a thorough investigation utilizing a multispecies, multiparameter, and multitechnique approach to assess the pollution characteristics and ecotoxicological effects of lithium. The findings suggested that lithium might persist in an amorphous state, altering surface functional groups and chemical bonds, although semiquantitative analysis was unattainable. Notably, lithium demonstrated high mobility, with a mild acid-soluble fraction accounting for 29.66-97.02% of the total, while a minor quantity of exogenous lithium tended to be a residual fraction. Plant analysis revealed that in 10-80 mg Li/kg soils lithium significantly enhanced certain growth parameters of maize and pea, and the calculated LC50 values for aerial part length across the four plant species varied from 173.58 to 315.63 mg Li/kg. Lithium accumulation in the leaves was up to 1127.61-4719.22 mg/kg, with its inorganic form accounting for 18.60-94.59%, and the cytoplasm fraction (38.24-89.70%) predominantly harbored lithium. Furthermore, the model displayed that growth stimulation might be attributed to the influence of lithium on phytohormone levels. Water spinach exhibited superior accumulation capacity and tolerance to lithium stress and was a promising candidate for phytoremediation strategies. Our findings contribute to a more comprehensive understanding of lithium's environmental behavior within soil-plant systems, particularly within the context of global initiatives toward carbon neutrality.

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Soil washing technology plays an important role in the removal of heavy metals, and the efficacy of this process depends on the washing agent used. Due to the difficulty in treating soils contaminated by multiple heavy metals, there is still a need for further exploration of efficient washing agents with low environmental impact. Although single washing agents, such as chelators, can also effectively remove heavy metals from soil, combining efficient washing agents and determining their optimal washing conditions can effectively improve their removal efficiency for multiple heavy metals in soil simultaneously. Based on the previous research, the present study was carried out to combine different types of washing agents to remediate contaminated soils at a commonly e-waste recycling site. The objectives were to investigate their efficient washing conditions and assess the impact of the washing process on the speciation distribution and pollution level associated with heavy metals in soil. The results showed that the combination of HEDP (1-hydroxyethylidene-1,1-diphosphonic acid) and FeCl3 at a ratio of 6:4 exhibited the most effective removal of Cd, Cu and Ni from the contaminated soil at an e-waste recycling site. Under optimal washing conditions, with a soil-to-liquid ratio of 1:20 and a washing time of 48 h, the removal rates of Cd, Cu and Ni were 96.72%, 69.91% and 76.08%, respectively. It needed to be emphasized that the combination washing agents were able to remove most of the acid-soluble, reducible and oxidizable fractions of heavy metals, and even the removal rates of the stable residual fraction (e.g., of Cd) was at a relatively high level. In addition, the washing process significantly reduced the pollution level associated with heavy metals in soil. This study aid in the development of combined efficient washing agents and explores optimal washing strategies for the remediation of Cd, Cu, and Ni-contaminated soil at e-waste recycling sites. The findings may play a role in enhancing the remediation capabilities for soils contaminated with multiple heavy metals, due to its characteristics of and high-efficiency and environmental friendliness.

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High concentrations of arsenic and antimony contamination in soil are a potential risk to the ecological environment and human health. Soil washing can effectively and permanently reduce the soil contamination. This study used Aspergillus niger fermentation broth as a washing agent to remove As and Sb from contaminated soil. Characterization of organic acids in the fermentation broth by high-performance liquid chromatographic (HPLC) and chemically simulated leaching experiments revealed that oxalic acid played a significant role in removing As and Sb from the soil. The effect of washing conditions on the metal removal rate of Aspergillus niger fermentation broth was investigated by batch experiments, and the optimal conditions were determined: no dilution, pH 1, L/S ratio 15:1, and leaching at 25 °C for 3 h. The soils were washed three times under optimal conditions, with 73.78%, 80.84%, and 85.83% removal of arsenic and 65.11%, 76.39%, and 82.06% removal of antimony, respectively. The results of metal speciation distribution in the soil showed that the fermentation broth could effectively remove As and Sb on amorphous Fe/Al hydrous oxides in soil. The analysis of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) of soils before and after washing showed that the washing of Aspergillus niger fermentation broth had a minor effect on the structural changes of soils. After washing, soil organic matter and soil enzyme activity were increased. Thus, Aspergillus niger fermentation broth shows excellent potential as a washing agent for removing As and Sb from soils.

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As a passivation material for heavy metals in-situ remediation, biochar (BC) has often been expected to maintain long-term adsorption performance for target pollutants. There is still lack of consensus about the impact of aging processes on biochar properties, particularly with respect to its long-term sorption performance. In this study, the changes to immobilization mechanisms as well as the speciation distribution of Cd(II) triggered by combined aging simulation (dry-wet, freeze-thaw cycle and oxidation treatment) on BC prepared under three levels of pyrolysis temperatures (300, 500 and 700 °C) were investigated. The results showed significant inhibition of aging on adsorption performance with the adsorptive capacity of BC300, BC500 and BC700 for Cd(II) decreased by 31.12 %, 50.63 % and 14.94 %, respectively. However, sequential extraction results indicated little influence of the aging process on the relative fractionation of Cd(II) speciation. The distribution of readily bioavailable, potentially bioavailable and non-bioavailable fractions of Cd(II) on BC showed only minimal changes post-aging. Overall, there was less Cd(II) sorption following aging, but the fractional availability (in relative terms) remained the same. Compared with 300 and 700 °C, the biochar prepared under 500 °C accounted the highest fraction of non-bioavailable Cd(II) (67.23 % of BC500, 59.17 % of Aged-500), and thus showed most promising for Cd(II) immobilization. This study has important practical significance for the long-term application of biochar in real environment.

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Enhancing the uptake and enrichment of heavy metals in plants is one of the important means to strengthen phytoremediation. In the present study, citric acid (CA), tartaric acid (TA), and malic acid (MA) were applied to enhance phytoremediation by Bidens pilosa L. in Cd-contaminated soil. The results showed that by the addition of appropriate concentrations of CA, TA, and MA, the values of the bioconcentration factor increased by 77.98%, 78.33%, and 64.49%, respectively, the translocation factor values increased by 16.45%, 12.61%, and 5.73%, respectively, and the values of the phytoextraction rates increased by 169.21%, 71.28%, and 63.11%, respectively. The minimum fluorescence values of leaves decreased by 31.62%, 0.28%, and 17.95%, while the potential efficiency of the PSII values of leaves increased 117.87%, 2.25%, and 13.18%, respectively, when CA, TA, and MA with suitable concentration were added. Redundancy analysis showed that CA and MA in plants were significantly positively correlated with plant growth, photosynthesis, and other indicators, whereas TA showed a negative correlation with most indicators. Moreover, CA addition could significantly increase the abundances of Azotobacter, Pseudomonas, and other growth-promoting bacteria, and the abundance values of Actinophytocola and Ensifer were improved in TA treatments. Therefore, our results demonstrated that low-molecular-weight organic acids could enhance phytoremediation, and exogenous CA could significantly improve the phytoremediation of Cd-contaminated soil by Bidens pilosa L.

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While sewage irrigation relieves water shortages in Northern China, its excessive application triggers a series of environmental problems, such as heavy-metal pollution. Soil profile and river sediment profile samples from the sewage irrigation area (SIA) were collected by selecting the farmlands in which sewage irrigation activity has been reported since the 1960s, around Huiji River (HJR) and Huafei River (HFR) in Kaifeng, Henan Province, China, as research areas. In this study, the total amount of heavy metals (Cr, Cd, Pb, Mn, Zn, and Ni) and the heavy-metal speciation analysis using the modified BCR sequential extraction method were used to evaluate the impacts of wastewater on agricultural soils and the potential risk. Furthermore, the least contaminated Cr (VI) was selected for the study of adsorption characteristics to determine the environmental capacity of soils for heavy metals when the composition of wastewater changes under long-term effluent irrigation conditions. The results show that: (1) the concentrations of heavy metals in soil continuously decreased with depth, while the opposite was observed in sediment, reflecting the continuous improvement in water quality over the historical period; (2) In the topsoil, the mean concentrations (mg·kg−1) in rank order are as follows: Mn (588.68) > Zn (284.21) > Pb (99.76) > Cr (76.84) > Ni (34.71) > Cd (3.25), where Cd exceeded the control value by 3.15 times around HFR, and sediment samples also showed higher heavy metal concentrations in HFR than in HJR; (3) Speciation distribution and risk assessment code (RAC) indicate that Mn and Cd were at medium risk and that Cd warrants attention due to its being a non-essential toxic element in humans; (4) The adsorption rates of soil in various layers in different profiles within SIAs for Cr (VI) gradually increased with the increasing initial content of Cr (VI). Among the three isothermal adsorption models, the fit result obtained by the Langmuir equation was superior to those obtained by the Freundlich equation and the linear equation.

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Grate furnace and fluidized bed are the most widely used technologies for municipal solid waste incineration (MSWI), which play significant roles in characteristics of MSWI fly ash. A comparative study of the physicochemical characteristics, microstructure morphology and leaching toxicity of fluidized bed and grate furnace MSWI fly ash was conducted in this work, and some resource utilization and disposal treatments were proposed. Results showed that calcium salt and chlorine salt formed the dominant components of MSWI fly ash. CaO-SiO2-Al2O3 ternary system indicated that MSWI fly ash had potential pozzolanic activity, similar to coal fly ash and blast furnace slag. The total Pb, Cd and Zn contents in fluidized bed MSWI fly ash was only 1/2, 1/3 and 2/3 of grate furnace MSWI fly ash, respectively. Leachability of Pb in MSWI fly ash collected from Dalian, Shanghai, Zhuji and Hangzhou was 4.25 mg/L, 3.83 mg/L, 3.84 mg/L and 3.68 mg/L, 28.3, 25.5, 25.6 and 24.5 times as much as the national standard limitation (GB16889-2008), respectively. However, grate furnace MSWI fly ash with high chloride and unstable chemical speciation distribution of heavy metals would pose more environmental risk toits immobilization and disposal. Fluidized bed fly ash is a promising candidate for preparing the Portland cement clinker, microcrystalline glass and ceramics due to its high Si and Al content. Grate furnace MSWI fly ash is more appropriate for Alinite cement preparation because of high chloride content.

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In this study, the long-term leaching behaviors of Cd, Cr, Cu, Ni, Pb, and Zn in municipal solid waste incineration (MSWI) fly ash samples from grate-type (GT) and circulating fluidized bed (CFB) incinerators were investigated and compared under the simulated landfill leachate corrosion scenario, which was determined to be more severe than the acid rain corrosion scenario. The total heavy metal contents showed increasing hierarchies of Ni

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Cynara cardunculus L. is a multipurpose crop, characterized by high production of biomass suitable for energy purposes and green chemistry. Taking advantage of its already demonstrated ability to grow in polluted environments that characterize many world marginal lands, the aim of this work was to investigate the response of different cardoon genotypes to exposure to cadmium (Cd) and arsenic (As) pollution, in order to use this crop for rehabilitation of contaminated sites and its biomass for energy production. In this study, seeds of two wild cardoon accessions harvested in rural and industrial Sicilian areas and of a selected line of domestic cardoon were used, and the grown plants were spiked with As and Cd, alone or in combination, at two different concentrations (500 and 2000 µM) and monitored for 45 days. The growth parameters showed that all the plants survived until the end of experiment, with growth stimulation in the presence of low concentrations of As and Cd, relative to metal-free controls. Biomass production was mostly allocated in the roots in As treatment and in the shoots in Cd treatment. Cd EXAFS analysis showed that tolerance to high concentrations of both metals was likely linked to complexation of Cd with oxygen-containing ligands, possibly organic acids, in both root and leaf biomass with differences in behaviour among genotypes. Under As+Cd contamination, the ability of the plants to translocate As to aboveground system increased also showing that, for both metal(loid)s, there were significant differences between genotypes studied. Moreover, the results showed that Cynara cardunculus var. sylvestris collected in an industrial area is the genotype that, among those studied, had the best phytoextraction capability for each metal(loid).

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Studying the characteristics and health risks of heavy metals in atmospheric fine particulate matter (PM2.5) is a crucial component of understanding atmospheric pollution in China. Integrated 24 h PM2.5 samples were collected in winter and summer 2016 in Xi'an, China. The pollution levels, speciation, and health risks of seven PM2.5-bound metal elements (Al, As, Cd, Cr, Ni, Pb, and Zn) were investigated in this study. The average concentration of PM2.5 was 50.1 ± 30.4 µg m-3 and was higher in winter than in summer. Significant seasonal variations in the elements were also observed. The average concentration ratios of Al, As, Cd, Cr, and Pb decreased in summer by 17.5%, 6.4%, 42.5%, 34.1%, and 61.4% compared with their concentrations in winter, respectively, whereas Ni and Zn increased by 37.7% and 7.6% in summer. The soluble and exchangeable fraction (F1) accounted for large proportions of Cd and Pb concentrations, indicating their greater hazard to the environment and human health. Al, As, and Cr mainly existed in the residual state (F4), which had relatively high stability in particulate matter. Ni was consistently distributed in different forms (F1-F4). The bioavailability evaluation indicated that Pb, Cd, Ni, and Zn were potential bioavailable element which exhibited strong biological toxicity. Although the concentration of Pb was very low, its BI value was the highest. The carcinogenic and non-carcinogenic risks of Cr and As were relatively high, and thus require attention from the government and environmental management departments.

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The effects of calcium sulfate (CaSO4) dosage (mass ratio of CaSO4 to sludge), pyrolysis temperature and holding time on speciation distribution of Cr, Pb, Cu, Ni and Zn in biochar derived from co-pyrolysis of sewage sludge and CaSO4 were investigated. The appropriate CaSO4 dosages for better immobilization of different heavy metals were 0.075 (Cr), 0.025 (Pb), 0.025 (Cu), 0.025 (Ni), and 0.01(Zn), respectively. The corresponding proportions of heavy metals in stable state (oxidizable and residue fractions) were 96.99%, 89.23%, 99.55%, 87.43%, and 54.33%. The high pyrolysis temperature (750 °C) was conducive to immobilization of Cr, Pb and Zn, while the percentages of Cu and Ni in stable state were higher at low pyrolysis temperature (350 °C). The suitable holding time was 60 min (Cr, Cu) and 15 min (Pb, Ni and Zn), respectively. The characterization of samples showed that suitable pyrolysis temperature and holding time could promote the formation of crystals and spherical or ellipsoidal particles in biochar, and pyrolysis of aliphatic to form more mesopores and macropores, resulting in immobilization of more heavy metals. During co-pyrolysis process, CaSO4 was easily decomposed and generated CaS, CaO, CaCO3 and Ca(OH)2, which were beneficial to the immobilization of heavy metals.

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A novel heavy metal chelating agent, dithiocarboxylate-functionalized polyaminoamide dendrimer (PAMAM-0G-DTC), was evaluated for the stabilization of heavy metals from municipal solids waste incineration (MSWI) fly ash. PAMAM-0G-DTC achieved overall stabilization performance at a lower dosage (3% w/w) and a wider pH range (2-13) compared to conventional chelating agents such as sodium dimethyl dithiocarbamate (SDD) and dithiocarboxylate-functionalized tetraethylenepentamine (TEPA-DTC). The leaching toxicity of Pb and Cd in the MSWI fly ash by PAMAM-0G-DTC stabilization met the landfill requirements but could not be achieved by SDD and TEPA-DTC even at a 10 wt% concentration. Sequential chemical extraction of fly ash before and after stabilization shows that PAMAM-0G-DTC can be combined with active heavy metals in water-soluble, interchangeable, and carbonate states to form more stable heavy metals in organic and residual states. Mechanistic studies show that multiple PAMAM-0G-DTC molecules can combine with multiple heavy metals to form three-dimensional network-like super-molecular compounds with an infinite extension of space size. This makes the heavy metals more stable and embedded in the network-like super-molecular structure, thus minimizing the potential risk of leaching. Overall, by forming more geochemically stable phases, the treatment of fly ash with PAMAM-0G-DTC has a strong ability to reduce the toxic leaching of heavy metals at a lower dosage and suppress the risk of secondary pollution in a landfill at a wide range of pH values (2-13).

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Humic acid can effectively bind several metals and is regarded as a promising soil washing agent. Previous studies indicate that carboxylic groups dominate metal binding to humic acid. In this study, a synthetic humic-like acid (SHLA) with high COOH content (5.03 mmol/g) was used as a washing agent to remove metals (Cu, Zn, Ni, Pb, As) from two contaminated agricultural soils (Soil 1 (pH: 6.17 ±â€¯0.11; organic carbon: 5.91 ±â€¯0.40%; Cu: 302.86 ±â€¯3.97 mg/kg; Zn: 700.45 ±â€¯14.30 mg/kg; Pb 323.56 ±â€¯4.84 mg/kg; Ni: 140.16 ±â€¯1.59 mg/kg) and Soil 2 (pH: 9.83 ±â€¯0.01; organic carbon: 2.52% ±â€¯0.25%; Cu: 242.81 ±â€¯10.66 mg/kg; Zn: 841.00 ±â€¯22.31 mg/kg, Pb 451.21 ±â€¯1,92 mg/kg, As: 242.23 ±â€¯5.24 mg/kg)). The effects of solution pH (4 to 11), liquid/solid ratio (L/S ratio, 5:1 (mL:g) to 80:1 (mL:g)), SHLA concentration (100 mg/L to 2000 mg/L), and contact time (0 to 1440 min) on % metal removal were investigated and optimum conditions identified: pH of 9, L/S ratio of 1:80, SHLA concentration of 1500 mg/L at 25 °C for 4 h. Under optimum conditions, a single washing removed 45.2% of Cu, 34.6% of Zn. 42.2% of Ni and 15.6% of Pb from Soil 1, and 30.6% of Cu, 28.1% of Zn. 14.6% of As and 18.1% of Pb from Soil 2. A modified BCR extraction of the two soils before and after washing indicated that the SHLA mainly removed metals in the exchangeable and acid soluble fraction and reducible fraction, which could effectively reduce bioavailability and environmental risk of metals. On a molar basis, SHLA was a more effective washing agent than commercial humic acid, Na2EDTA, citric acid and tartaric acid. Overall, SHLA shows great potential for use as a soil washing agent.

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Microbial dissimilatory iron reduction could remediate reducible pollutants in groundwater, such as nitrobenzene (NB). But the natural attenuation rate in aquifer is limited. To stimulate this process, emulsified vegetable oil (EVO) was injected as a remediation agent. The mechanism of this process was studied. Results showed that the addition of EVO made iron easier used by microorganisms and thus promoted dissimilatory iron reduction. The readily used Fe(III) served as electron acceptor and was reduced to Fe(II). Fe(II) supplied electrons to NB, with NB reduced to aniline. Sulphide in the aquifer media also donated electrons and oxidized to polysulfide, then forming precipitates with Fe(II) to the surface of aquifer media, and thus slowing down the electron supplying of EVO and forming permanent efficiency for NB remediation. The work helps to complete a systematic understanding of NB remediation process under stimulation of EVO.

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The combination of biochar and compost has been proven to be effective in heavy metals contaminated wetland soil restoration. However, the influence of different proportions between biochar and compost on immobilization of heavy metals in soil has been less studied up to date. Therefore, we investigated the effect of different ratios of biochar-compost mixtures on availability and speciation distribution of heavy metals (Cd, Zn and Cu) in wetland soil. The results showed that applying all amendment combinations into wetland soil increased gradually the total organic carbon (TOC) and water-extract organic carbon (WEOC) as the compost percentage rose in biochar-composts. The higher pH was obtained in a certain biochar addition (20% and 40%) in combinations due to efficient interaction of biochar with compost. All amendments could significantly decrease availability of Cd and Zn mainly from pH change, but increase available Cu concentration as the result of increased water-extract organic carbon and high total Cu content in compost. Moreover, amendments can decrease easily exchangeable fraction and increase reducible of Cd and Zn greatly with increase of compost content in combinations, while amendments containing compost promote transformation of Cu from Fe/Mn oxide and residual fractions to organic bindings. These results demonstrate that different ratios of biochar and compost have a significant effect on availability and speciation of heavy metals in multi-metal-contaminated wetland soil.

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