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Soil organic matter plays an important role in cadmium adsorption and immobilization. Since different organic matter components affect cadmium adsorption processes differently, selecting the right organic substrate and knowing how to apply it could improve cadmium remediation. This study compares the effects of two contrasting organic molecules; chitosan and citric acid, on cadmium adsorption and speciation in acidic Ultisol. The adsorption of chitosan to Ultisol significantly increased the soil positive charge while adsorption of citric acid increased the soil negative charge. At pH 5.0, the maximum amount of cadmium adsorbed in excess chitosan was 341% greater than that in excess citric acid. About 73-89% and 60-62% of adsorbed cadmium were bound to Fe/Mn oxides and organic matter/sulfide at pH 4.0 while this fraction was 77-100% and 57-58% for citric acid and chitosan at pH 5.0, respectively. This decrease in the complexing ability of chitosan was related to the destabilizing effect of high pH on chitosan's structure. Also, the sequence through which chitosan, citric acid, and cadmium were added into the adsorption system influenced the adsorption profile and this was different along a pH gradient. Specifically, adding chitosan and cadmium together increased adsorption compared to when chitosan was pre-adsorbed within pH 3.0-6.5. However, for citric acid, the addition sequence had no significant effect on cadmium adsorption between pH 3.0-4.0 compared to pH 6.5 and 7.5, with excess citric acid generally inhibiting adsorption. Given that the action of citric acid is short-lived in soil, chitosan could be a good soil amendment material for immobilizing cadmium.

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Metabolic cross-feeding is a pervasive interaction between bacteria to acquire novel phenotypes. However, our current understanding of the survival mechanism for cross-feeding in cocultured bacterial biofilms under heavy-metal conditions remains limited. Herein, we found that Comamonas sp. A23 produces L-phenylalanine to activate the L-phenylalanine degradation pathway in Enterobacter sp. A11, enhancing biofilm formation and cadmium [Cd(II)] immobilization in A11. The genes responsible for L-phenylalanine-degradation (paaK) and cell attachment and aggregation (csgAD) are essential for biofilm formation and Cd(II) immobilization in A11 induced by L-phenylalanine. The augmentation of A11 biofilms, in turn, protects A23 under Cd(II) and H2O2 stresses. The plant-based experiments demonstrate that the induction of two rice Cd(II) transporters, OsCOPT4 and OsBCP1, by A11 and A23 enhances rice resistance against Cd(II) and H2O2 stresses. Overall, our findings unveil the mutual dependence between bacteria and rice on L-phenylalanine cross-feeding for survival under abiotic stress.

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Soil cadmium (Cd) is immobilized by the progressing biomineralization process as microbial induced phosphate precipitation (MIPP), which is regulated by phosphate (P) solubilizing microorganisms and P sources. However, little attention has been paid to the implications of Cd biosorption during MIPP. In this study, the newly isolated Penicillium oxalicum could immobilize 5.4-12.6 % of Cd2+, while the presence of hydroxyapatite (HAP) considerably enhanced Cd2+ immobilization in P. oxalicum and reached over 99 % Cd2+ immobilization efficiency within 7 days. Compared to P. oxalicum mono inoculation, MIPP dramatically boosted Cd biosorption and biomineralization efficiency by 71 % and 16 % after 96 h cultivation, respectively. P. oxalicum preferred to absorbing Cd2+ and reaching maximum Cd2+ biosorption efficiency of 87.8 % in the presence of HAP. More surface groups in P. oxalicum and HAP mineral involved adsorption which resulted in the formation of Cd-apatite [Ca8Cd2(PO4)6(OH)2] via ion exchange. Intracellular S2-, secreted organic acids and soluble P via HAP solubilization complexed with Cd2+, progressively mineralized into Cd5(PO4)3OH, Cd(H2PO4)2, C4H6CdO4 and CdS. These results suggested that Cd2+ immobilization was enhanced simultaneously by the accelerated biosorption and biomineralization during P. oxalicum induced P precipitation. Our findings revealed new mechanisms of Cd immobilization in MIPP process and offered clues for remediation practices at metal contaminated sites.

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Bacteria have evolved a variety of strategies to defend themselves against cadmium toxicity, however, the specific mechanisms involved in the enhancement of bacterial cadmium resistance by sulfur sources are unclear. In this study, a novel cadmium (Cd)-tolerant bacterium, Stenotrophomonas geniculata G303, was isolated from activated sludge. The growth of strain G303 under diverse Cd concentrations was investigated, and the minimum inhibitory concentration of Cd was found to be 1 mM. Strain G303 effectively remove 94.7 % of Cd after 96 h of culture. Extracellular CdS was detected using multiple methods, with the CdS formed being aggregated in the biofilm. The addition of cysteine and thiosulfate to the medium significantly enhanced the Cd resistance and removal capacity of strain G303. Integrated genomic and proteomic analyses revealed that heavy metal transporters cooperate to resist Cd stress. Cysteine and thiosulfate improved Cd tolerance in strain G303 by upregulating nitrogen and energy metabolism. Proteins associated with nitrate reduction likely played a pivotal role in cysteine and thiosulfate metabolism. Notably, cysteine synthase and the SUF system played crucial roles in CdS formation. This study systematically explored the impact of cysteine and thiosulfate on the Cd resistance of strain G303, deepening our understanding of the microbial response mechanism to heavy metals.

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Selenium (Se) is a trace element that is essential for human health. Daily dietary Se intake is governed by the food chain through soil-plant systems. However, the cadmium (Cd) content tends to be excessive in seleniferous soil, in which Se and Cd have complex interactions. Therefore, it is a great challenge to grow crops containing appreciable amounts of Se but low amounts of Cd. We compared the effects of five Se-transforming bacteria on Se and Cd uptake by Brassica rapa L. in a native seleniferous Cd-polluted soil. The results showed that three Se-oxidizing bacteria (LX-1, LX-100, and T3F4) increased the Se content of the aboveground part of the plant by 330.8%, 309.5%, and 724.3%, respectively, compared to the control (p < 0.05). The three bacteria also reduced the aboveground Cd content by 15.1%, 40.4%, and 16.4%, respectively (p < 0.05). In contrast, the Se(IV)-reducing bacterium ES2-45 and weakly Se-transforming bacterium LX-4 had no effect on plant Se uptake, although they did decrease the aboveground Cd content. In addition, the three Se-oxidizing bacteria increased the Se available in the soil by 38.4%, 20.4%, and 24.0%, respectively, compared to the control (p < 0.05). The study results confirm the feasibility of using Se-oxidizing bacteria to simultaneously enhance plant Se content and reduce plant Cd content in seleniferous Cd-polluted soil.

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Interactions between silicate bacteria and silicates are very common in nature and hold great potential in altering their mutual physicochemical properties. But their interactions in regulating contaminants remediation involving performance and mechanisms are often overlooked. Here, we focused on the interactions between silicate bacteria (Paenibacillus polymyxa, PP; Bacillus circulans, BC) and a soil silicate montmorillonite (Mt), and their impact on Cd(II) immobilization. The obtained results showed that Mt greatly promoted the growth of the bacteria, resulting in a maximum 10.31 times increase in biomass production. In return, the bacteria strongly enhanced the Cd(II) adsorption on Mt, with adsorption capacities increased by 80.61%-104.45% in comparison to the raw Mt. Additionally, the bacteria-Mt interaction changed Cd(II) to a more stabilized state with a maximum reduction of 38.90%/g Mt in bioavailability. The enhancement of Cd(II) adsorption and immobilization on the bacterial modified Mt was caused by the following aspects: (1) the bacteria activities altered the aggregation state of Mt and made it better dispersed, thus more active sites were exposed; (2) the microbial activities brought about more rough and crumpled surface, as well as smaller Mt fragments; (3) a variety of microbial-derived functional groups were introduced onto the Mt surface, increasing its affinity for heavy metals; (4) the main Cd(II) immobilization mechanism was changed from ion exchange to the combination of ion exchange and functional groups induced adsorption. This work elucidates the potential ecological and evolutionary processes of silicate bacteria-soil clay mineral interactions, and bears direct implications for the clay-mediated bioremediation of heavy metals in natural environments.

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The detoxification of cadmium (Cd) or chromium (Cr) by microorganisms plays a vital role in bacterial survival and restoration of the polluted environment, but how microorganisms detoxify Cd and Cr simultaneously is largely unknown. Here, we isolated a bacterium, Cupriavidus sp. MP-37, which immobilized Cd(II) and reduced Cr(VI) simultaneously. Notably, strain MP-37 exhibited variable Cd(II) immobilization phenotypes, namely, cell adsorption and extracellular immobilization in the co-presence of Cd(II) and Cr(VI), while cell adsorption in the presence of Cd(II) alone. To unravel Cr(VI)-induced extracellular Cd(II) immobilization, proteomic analysis was performed, and methylglyoxal-scavenging protein (glyoxalase I, GlyI) and a regulator (YafY) showed the highest upregulation in the co-presence of Cd(II) and Cr(VI). GlyI overexpression reduced the intracellular methylglyoxal content and increased the immobilized Cd(II) content in extracellular secreta. The addition of lactate produced by GlyI protein with methylglyoxal as substrate increased the Cd(II) content in extracellular secreta. Reporter gene assay, electrophoretic mobility shift assay, and fluorescence quenching assay demonstrated that glyI expression was induced by Cr(VI) but not by Cd(II), and that YafY positively regulated glyI expression by binding Cr(VI). In the pot experiment, inoculation with the MP-37 strain reduced the Cd content of Oryza sativa L., and their secreted lactate reduced the Cr accumulation in Oryza sativa L. This study reveals that Cr(VI)-induced detoxification system drives methylglyoxal scavenging and Cd(II) extracellular detoxification in Cd(II) and Cr(VI) co-existence environment.

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Secondary mineralization is a promising method for remediating cadmium (Cd) pollution in sediments, but the poor stability of Cd-containing secondary minerals is a bottleneck that limits the development of this approach. The existence of phosphate can enhance the formation of stable secondary minerals and points a new direction for Cd immobilization. In this research, a novel syntrophic system composed of phosphate solubilizing bacteria (PSB) and dissimilatory iron reducing bacteria (DIRB) was established and the effect and mechanism of Cd immobilization in the system were also explored. The results showed that under the conditions of DIRB:PSB (V:V)= 3:1, syntrophic bacteria dosage of 5% and glucose dosage of 5 g/L, Cd incorporated in the secondary minerals could account for about 60% of the total Cd. In the pH range of 5-9, alkaline environment was conducive to the immobilization of Cd and the percentage of combined Cd was up to 58%, while the combined Cd in secondary minerals decreased from 62% to 56% with the increase of initial Cd concentration from 0.1 to 0.3 mmol/L. In addition, XRD, XPS, Mössbauer and other characterization results showed that secondary minerals, such as Cd exchange hydroxyapatite (Cd-HAP) and kryzhanovskite (Fe3(PO4)2(OH)3) were formed in this new system. The established syntrophic system of PSB and DIRB is thus a prospective bioremediation technology for Cd immobilization in sediments and can avoid the potential risk might be caused by the addition of phosphorus-containing materials.

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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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Improper application of phosphorus (P) fertilizer during soil cadmium (Cd) immobilization reduces the efficiency of fertilizer and Cd remediation. In this study, we synthesized three types of nano-hydroxyapatite (NHAP) with different surface charges as slow-release P fertilizers during Cd immobilization. We also evaluated the effects of wollastonite application with or without NHAP addition, in comparison with triple superphosphate (TSP) or bulk hydroxyapatite, on Cd accumulation in Amaranthus tricolor L. The results showed that adding wollastonite significantly reduced P availability (23.5%) in the soil, but it did not inhibit plant P uptake. In wollastonite-amended soil, the application of negatively/positively charged NHAP significantly increased plant biomass by 643-865% and decreased Cd uptake by 74.8-75.1% compared to the unamended soil as well as showed greater efficiency than those with TSP. This was ascribed to the increased soil pH (from 3.94 to 6.52-6.63) and increased abundance of organic acids (including citric acid, malic acid, lactic acid, and acetic acid) secreted by plants. In addition, the P-preferring bacterial class Bacteroidia was specific to soils amended with both wollastonite and NHAP-. These results suggest that NHAP- may be an appropriate P fertilizer for soil Cd immobilization using wollastonite.

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Treating and utilizing heavy metal enriched plants have become growing problems. In this work, a series of composite foams were made from the powder of Cadmium-rich plant, polyacrylonitrile (PAN) and polyurethane (PU). Test results indicated that the addition of plant powder can not only increase the specific surface area, but also improve the apparent density and thermal stability of the foams. Besides, compared with the foam without plant powder, the powder-added foams exhibited a decreasing trend for thermal conductivity, and the minimum was 0.048 w/(m·k), which indicated that the addition of plant powder can help to enhance the thermal insulation of composite foam. More importantly, the results of leaching experiment showed that the leaching rate of heavy metal cadmium in the composite foam with 50% plant powder content was as low as 0.14% after being immersed in the acidic (pH = 3) solution for 5 days, which implies that the foam materials are very safe. This study provides a new way to realize high value-added resource utilization of heavy metal-enriched plants.

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In-situ soil cadmium (Cd) immobilization helps to reduce Cd accumulation in rice grain, while its effects on bioaccessibility of Cd in rice during digestion and the associated health risk from rice consumption remain unclear. Here, we combined in-situ soil Cd immobilization and bioaccessibility-corrected health risk assessment (HRA) to minimize both the risk and uncertainty of Cd exposure from rice consumption. Wollastonite with or without four different phosphates (P) were applied to immobilize soil Cd at paddy fields, and their influences on Cd, essential elements, and amino acids in rice grain were analyzed. Moreover, a bioaccessibility-corrected HRA was conducted to accurately reflect the Cd exposure risk from ingesting these rices. The results showed the co-application of wollastonite and four different P reduced Cd concentrations in rice grain equally, while their impacts on bioaccessibility of Cd in rice during simulated human digestion were inconsistent (53-71%). The HRA based on bioaccessibility of Cd in rice revealed that Cd exposure risk from rice consumption was lowest with the application of wollastonite, followed by the co-application of wollastonite and sodium hexametaphosphate. This work highlights the value of bioaccessibility-corrected HRA for screening the optimal Cd immobilization strategy to achieve safer rice consumption.

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Nowadays, remediation of soil contaminated with potentially toxic metal is a great international concern. In this study, a novel modified gangue material (MGE) is synthesized from coal gangue (GE) through a low-temperature assisted with alkali roasting method, and is applied to the immobilization of cadmium (Cd2+) in contaminated soil. The various instruments (SEM-EDS, FTIR, XRD, TGA, and XPS) are employed to investigate the changes of microstructure and function of GE before and after the modification. The results showed that a large number of active groups (Si-O, Al-O, Fe-O, -OH, -CO, and -COOH) are observed on the surface of MGE, which is conducive to the removal of Cd2+. Besides, the adsorption kinetics, and isotherm models are introduced to analyze the potential adsorption mechanism, which suggesting that the adsorption behavior can be well fitted by pseudo-second-order and Langmuir models. The potential mechanisms of MGE include the ion exchange, complexation, electronic attraction, and precipitation. According to the pot experiment, the application of MGE can significantly improve the growth of pakchoi, and increase the pH of soils. Meanwhile, the content of available Cd2+ is reduced in the treatment with MGE, by a factor of 14.2%-29.8%. Correspondingly, the content of Cd2+ in different parts of pakchoi is also decreased. The study shows that the MGE can be strongly recommended as an efficient and safe amendment to stabilize Cd2+ in contaminated soil.

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Nanomaterials have great application potential for the remediation of heavy metal contaminated sediments, but their environmental impacts are still limited. Herein, graphene oxide-supported nanoscale zero-valent iron (GNZVI) was synthesized to explore its role in mediating the immobilization of cadmium (Cd) from contaminated river sediments, with the consideration of the potential impacts on sediment enzyme activities and bacterial community. Compared to NZVI and GO, GNZVI could more effectively promote the transformation of mobile Cd into stable speciation with a maximum residual percentage increasing by 64.82% after 56 days of treatment. The activities of urease, catalase and sucrase were gradually increased and stabilized with the prolongation of treatment time, indicating that the metabolic function of sediments was recovered. 16 S rRNA gene sequencing results confirmed that the application of GNZVI increased the abundance of some Fe(III)-reducing bacteria, further stimulating the bioavailability of organic matter. Additionally, the properties of GO were gradually changed via microbial reduction and finally showed similar properties to rGO. The critical role of rGO as an electrical conductor was to promote the electron transfer process of microbial Fe(III) mineral reduction, which redistributes part of the Fe(III) mineral-associated Cd to more stable secondary iron minerals, thereby further improving the stabilization efficiency of r-GNZVI for Cd.

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Cadmium pollution in alkaline soil in some areas of northern China seriously threatens agricultural production and human health, but there are few materials and methods to remediate cadmium pollution in alkaline soil. Therefore, it is necessary to further study the economic and adaptive remediation and regulation techniques of cadmium pollution in alkaline soil. In the study, a pot experiment was conducted to study the effects of MP and MnSO4 combined treatment on the immobilization effect of cadmium contaminated alkaline soils. The results showed that LM and HM treatments in different periods had little effect on the content of extractable Cd fraction in soil without MP treatment, but the EXC-Cd content in the soil with Mn(15) was lower than that in the soil with Mn(29). The EXC-Cd content under MP+ LM and MP + HM treatments reduced by 3%-7% and 7%-9%, respectively. The OX-Cd content increased by 13%-16% after MP + Mn treatment. The content of DTPA-Cd decreased by 17.9%-28.6% under MP + Mn treatment except for MP + HM(15). Under the treatment of MP, LM(29), HM, MP + LM and MP + HM, the content of Cd in shoots of pak choi were decreased by 27.2%, 13.1%, 19.8%-27.9%, 28.5%-54.2% and 34.2%-41.1%, respectively. Compared with CK, the TFCd values in HM(15), LM(29), HM(29), MP + LM(29) and MP + HM(29) treatments were reduced to 35.7%, 41.1%, 35.7%, 42.9% and 37.5%, respectively, while no statistical difference was observed in other treatments. There was no significant difference in BCFCd between MP(15) and LM(15), but the BCFCd was significantly decreased. For MP + MnSO4 treatment group, the content of Mn oxides in soil was negatively correlated with the content of EXC-Cd (P < 0.05) and positively correlated with the content of OX-Cd (P < 0.05).

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In this study, we isolated a highly cadmium (Cd)-resistant bacterium, Pseudomonas sp. B7, which immobilized 100% Cd(II) from medium. Culturing strain B7 with Cd(II) led to the change of functional groups, mediating extracellular Cd(II) adsorption. Proteomics showed that a carbonic anhydrase, CadW, was upregulated with Cd(II). CadW expression in Escherichia coli conferred resistance to Cd(II) and increased intracellular Cd(II) accumulation. Fluorescence assays demonstrated that CadW binds Cd(II) and the His123 residue affected Cd(II) binding activity, indicating that CadW participates in intracellular Cd(II) sequestration. Chinese cabbage pot experiments were performed using strain B7 and silicate [Si(IV)]. Compared with the control, Cd content in aboveground parts significantly decreased by 21.3%, 29.4% and 32.9%, and nonbioavailable Cd in soil significantly increased by 129.4%, 45.0% and 148.7% in B7, Si(IV) and B7 +Si(IV) treatments, respectively. The application of Si(IV) alone reduced chlorophyll content by 20.8% and arylsulfatase activity in soil by 33.9%, and increased malonaldehyde activity by 15.0%. The application of strain B7 alleviated the negative effect of Si(IV) on plant and soil enzymes. Overall, application of Si(IV) is most conducive to the decreased Cd accumulation in plant, and strain B7 is beneficial to maintaining soil and plant health.

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Microbially induced phosphate precipitation (MIPP) is an advanced bioremediation technology to immobilize heavy metals. An indigenous bacterium QY14 with the function of mineralization isolated from Cd contaminated farmland soil was identified as Burkholderia ambifaria. The minimum inhibitory concentration value for QY14 was 550 mg/L for soluble Cd concentration. This study found that the addition of 10 mM Ca2+ during MIPP process could significantly increase the removal ratio of Cd, and the maximum removal ratio of Cd with 10 mM Ca2+ and without Ca2+ in solution was 99.97% and 76.14%, respectively. The increase of acid phosphatase activity and the formation of precipitate containing calcium caused by 10 mM Ca2+ addition contributed the increase of Cd removal efficiency. The results of SEM-EDS, FTIR and XRD showed that Cd was removed by forming Cd containing hydroxyapatite (Cd-HAP). In addition, the dissolution experiment showed the Cd release ratio of Cd-HAP (0.01‰ at initial pH 3.0 of solution) was lower than Cd-absorbed HAP, indicating that Cd was more likely removed by the formation of Ca10-xCdx(PO4)6(OH)2 solid solution. Our findings revealed MIPP-based bioremediation supplied with 10 mM Ca2+ could increase the Cd removal and could potentially be applied for Cd remediation.

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In this study, a novel biochar-based compound fertilizer (BCF) was synthesized with maize straw biomass, diatomite, triple superphosphate and urea at different temperatures (300 °C, 450 °C, 600 °C) and mixture proportions (5:1:1:x and 10:1:1:x). An investigation was conducted into the effects of BCF at low application rates on the immobilization of available cadmium, soil fertility and maize growth. The lab incubation experiments showed that the low doses of BCF (B5PNx and B10PNx) contributed to a significant reduction of the Cd availability in soil, with the highest reduction rate of available Cd up to 44.13%. Field experiments demonstrated that the low doses ( < 0.1%) of BCF（especially for B5PN600）led to the improvement of soil fertility and maize growth (including maize yield) and the significant reduction of Cd contents in maize grains. The increase of pyrolysis temperature could enhance the biochar adsorption capacity for Cd2+ by increasing both specific surface areas and total pore volume. The modification of urea, diatomite and triple superphosphate played a vital role on cadmium immobilization, soil improvement and maize growth by forming porous adsorption, precipitates or complexation with the increase of functional groups, as well as supplementation of N, P, Si nutrients. This study suggested that the biochar-based compound fertilizer (BCF with a mixture ratio of 5:1:1:x) produced at 600 °C could be served as a promising and eco-friendly remediation agent for the arable soils polluted with Cd, with reduction of chemical fertilizers.

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Cadmium (Cd) pollution in alkaline soil in some areas of northern China has seriously threatened wheat production and human health. However, there are still few effective amendments for alkaline soil, and the mechanism of amendments with a good immobilization effect remains unclear. In this study, soil sterilization experiments were conducted to investigate the effects of soil microorganisms on the immobilization of a novel amendment-mercapto palygorskite (MPAL) in Cd-contaminated alkaline soils. The results showed that the mercapto on the MPAL surface was not affected by autoclaving. Compared with the control, the available Cd concentration in 0.025% MPAL treatments decreased by 18.80-29.23% after 1 d of aging and stabled after 10 d of aging. Importantly, the immobilization of MPAL on Cd in sterilized soil was significantly better than that in natural soil due to the changes in Cd fractions. Compared with MPAL-treated natural soil, exchangeable Cd fraction and carbonate-bound Cd fraction in MPAL-treated sterilized soil decreased by 20.79-27.09% and 20.05-26.45%, while Fe/Mn oxide-bound Cd fraction and organic matter-bound Cd fraction increased by 17.77-22.68% and 18.85-27.32%. Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analysis found that the potential functions of the microbial community in normal and sterilized soil were different significantly. Soil sterilization increased the soil pH and decreased the arylsulfatase activity, but did not change the soil zeta potential and available sulfur. The changes in Cd fractions in MPAL-treated sterilized soil may be related to the reduction in the bacterial community and the changes in function microbial, but not to the soil properties. In addition, MPAL application had little effects on the bacterial community, soil pH value, zeta potential, available sulfur, and arylsulfatase. These results showed that the immobilization of MPAL on Cd in alkaline soil was stable and effective, and was not affected by soil sterilization and soil microorganism reduction.

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Metals that contaminate soil are one of the major problems seriously affecting sustainable agriculture worldwide. Cadmium (Cd) toxicity to agricultural crops is a global problem. Mobility of Cd in contaminated soil can be minimized by the amendment of soil passivators which will ultimately reduce its movement from soil to plants. A pot study was performed to evaluate the impact of sepiolite from 1% to 5% on Cd solubility and its accumulation in spinach tissues. Soil pH, Cd fractionation, Cd accumulation in spinach tissue and Cd adsorption mechanism were determined. Results were recorded that soil pH was increased from 0.3 to 1.0 units with the increasing rate of sepiolite from 1% to 5%. Similarly, Cd contents in acid soluble phase was decreased by 42.8% and increased in residual phase by 35.8% at 5% rate, relative to control. Moreover, the significant reduction in Cd uptake by spinach shoots and roots was occurred by 26.2% and 30.6% at 5% rate, respectively. Furthermore, the maximum Cd adsorption capacity 37.35 mg g-1 was recorded at 5% rate relative to control. The analysis of FTIR, XRD and SEM also confirm the ability of sepiolite for Cd polluted soil restoration and thereby, reduces its phytoavailability in polluted soil to alleviate food security challenges.

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