Remediation Of Cd Research Articles

Remediation of Pb and Cd contaminated sediments by wheat straw biochar and microbial community analysis

Wheat straw biochar (BC) or modified wheat straw biochar (MBC) could affect the aggregate structure of soil, effectively adsorb heavy metal and reduce the bioavailability of heavy metals in soil. TGA, BET, FTIR and SEM were used to characterize the surface morphology and structure of BC and MBC. The adsorption properties of BC and MBC on Pb(‌II) and Cd(‌II) in solution systems were investigated by batch experiments, and the remediation performance of Pb and Cd contaminated sediment by BC or MBC were studied by pot experiments. The results showed that MBC had a larger specific surface area of 46.04 m2/g and total pore volume 0.0555 cm3/g; the adsorption isotherms of Pb(II) and Cd(II) for BC and MBC were more suitable for Langmuir model (R2 over 0.91), and the maximum adsorption capacities of Pb(II) and Cd(II) by MBC could reach 71.14 and 115.64 mg/g, respectively. BC or MBC promoted the transformation of Pb and Cd from the extractable acid fraction to the oxidizable and residual fraction, reduced the migration of heavy metals and enhanced the stability of aggregates. Therefore, the results provided a perspective for the dredged contaminated sediments used as planting soil. In addition, BC or MBC, as soil amendments, could improve the abundance of microbial community. At the phylum level, the main dominant bacteria were Proteobacteria and Bacteroidetes.

Optimizing Oxalic Acid Application Regime to Maximize Sunflower Remediation Efficacy in Cd-Contaminated Soils

The exogenous application of oxalic acid is a potential approach to amplifying phytoremediation performance on Cd-contaminated soils. However, few studies explore the optimal oxalic acid application regime from a perspective of coupling different concentrations and timings to maximize Cd removal rate. Given this, a pot experiment was conducted using oil sunflower (Helianthus annuus L.) as the test plant. Oxalic acid was added to the pots at concentrations of 1, 2, 3, 4, 5, and 6 mmol/kg at 20, 30, 40, and 50 days after emergence. A control (CK) without exogenous oxalic acid was also included. We examined the discrepancies in various soil Cd forms, sunflower height, plant non-protein thiol (NPT) levels, and soil Cd remediation efficiency under different oxalic acid application regimes. The results showed that applying oxalic acid at a concentration of 4 mmol/kg reduced the proportion of Fe-Mn oxide Cd and organic Cd compared to the control (CK), while increased the proportion of available Cd. The optimal application time is 30 or 40 days after emergence. The addition of exogenous oxalic acid promoted the growth of sunflowers, with the greatest increase in plant height observed when 4 mmol/kg oxalic acid was applied at 30 days after emergence. Exogenous oxalic acid enhanced the absorption of Cd by sunflower roots, with the total Cd accumulation in roots, stems, and leaves being higher than in the control (CK). When 4 mmol/kg oxalic acid was applied at 30 days after emergence, the total Cd accumulation in roots, stems, and leaves was highest. Under different application times and concentration levels of oxalic acid, Cd accumulation was highest in roots, followed by leaves, with stems showing the lowest accumulation. The NPT content in each part is as follows: root > stem > leaf. Applying 5 mmol/kg oxalic acid after 30 days of sunflower emergence resulted in relatively higher total NPT content in roots, stems, and leaves compared to the control (CK). The TOPSIS model was used for comprehensive evaluation, which showed that 4 mmol/kg oxalic acid application at 30 days after emergence could be used as the optimal oxalic acid application regime for phytoremediation. These findings indicate that the addition of oxalic acid effectively promoted the absorption of Cd by sunflower and increased the efficiency of Cd removal from the rhizosphere soil, with the optimal removal of soil Cd achieved by applying oxalic acid at a concentration of 4 mmol/kg 30 days after the emergence of oilseed sunflower seedlings.

Possibility of using industrial by-product combinations to remediate cadmium and arsenic contaminated soil

It is inevitable to produce by-products in industrial and mining production, and how to deal with these by-products has become a major environmental issue. Meanwhile, many studies have shown that applying soil amendments is a feasible measure for effectively controlling soil pollution. Finding low-cost and efficient soil passivators is an effective way to safely utilize polluted soil. This article provides a method of “treating contamination with waste”. Through spinach pot experiments, different proportions and doses of granite powder (A, quarry waste), market purchased conditioner (B), “granite powder+iron sulfate mineral (titanium powder industrial waste)” (C), and “granite powder+iron sulfate mineral+market purchased conditioner” (CB) were used to treat soil co-contaminated with cadmium (Cd) and arsenic (As). The results indicate that amendments affect the available Cd and As in soil by changing soil pH and cation exchange capacity. The amendment of A, B, C, and CB all has remarkable reduction rates of soil available Cd at 65.48 %, 57.02 %, 61.37 %, and 43.15 %, respectively, compared to the control. Both A and B increase the available As content in the soil and the As content in spinach. However, both C and CB reduced the available As content in the soil by 60.32 % and 12.48 %. CB treatment could simultaneously reduce the accumulation of Cd and As in spinach, increase chlorophyll content, and promote spinach growth. It was worth noting that the 3 % CB treatment has the best effect, with Cd and As content in spinach stems and leaves decreasing by 51.13 % - 69.62 % and 35.46 % - 59.53 %, respectively, and the repair cost being as low as 76.5 $ ton−1. Therefore, the combined application of granite powder, market purchased conditioner, and iron sulfate minerals for the remediation of Cd and As co-polluted soil was a cost-effective and environmentally friendly technology. However, applying these soil composite amendments also requires attention to adjusting with the soil type and with pollution type, which we are currently studying.

Remediation of cadmium contaminated soil using electrokinetic-phytoremediation system with rotary switching electrodes.

Considering both electrokinetic remediation and phytoremediation have limitations, an electrokinetic phytoremediation (EP) system was constructed to obtain efficient and environmentally friendly remediation results. This study indicates that the electric field can promote the absorption of Cd by ryegrass with little impact on soil physicochemical properties under the condition of rotary switching electrodes, and the accumulation of Cd in the aboveground and underground parts of ryegrass increased by 145.2% and 93.7%, respectively. The DC electric field combined with ryegrass under rotary switching electrode mode proved to be the optimal condition for the remediation of Cd contaminated soil with a remediation efficiency of 66.7%. Moreover, the rotary switching of the electrodes alleviated the suppression of the growth of ryegrass by the DC electric field. During the EP remediation process, the electric field promoted the transformation of the residue state of Cd to the other forms, which accelerated the desorption rate of Cd from the soil and facilitated the migration of Cd into plants. In conclusion, EP is a green and efficient remediation technology for heavy metal contaminated soil with good application prospects.

Effects and mechanisms of microbial ecology and diversity on phytoremediation of cadmium-contaminated soil under the influence of biodegradable organic acids

In recent years, heavy metal pollution has become a global environmental problem and poses a great threat to the health of people and ecosystems. Therefore, strategies for the effective remediation of Cd from contaminated soil are urgently needed. In this study, ryegrass was utilized as a remediation plant, and its remediation potential was enhanced through the application of Citric Acid (CA) in conjunction with Bacillus megaterium (B. megaterium). The P3 treatment (CA + Bacillus megaterium) exhibited a significantly higher efficiency in promoting cadmium extraction by ryegrass, resulting in a 1.79-fold increase in shoot cadmium accumulation compared to the control group (CK) with no Bacillus megaterium or CA. Moreover, the P3 treatment led to an increased abundance of Actinobacteriota, Acidobacteriota, and Patescibacteria in the rhizosphere. The concentration of amino derivatives (such as betaine, sulfolithocholylglycine, N-alpha-acetyl-lysine, glycocholic acid, arginyl-threonine) showed significant upregulation following the P3 treatment. In summary, this study proposes a viable approach for phytoremediation of soil contaminated with cadmium by harnessing the mobilizing abilities of soil bacteria.

Biochar is an organomineral tool for mitigation of Cd toxicity in rice embedded soil and plant

Cadmium (Cd) contamination poses a significant threat to plants and human, as it can easily accumulate in plant tissues, leading to biochemical and physiological disorders. There is a growing interest in using biochar to mitigate the absorption of heavy metals by rice plants. This study tested peach biochar (PB) and its various levels of applications to evaluate the promising level for Cd remediation in contaminated soil. The application of PB3 had a significant impact on Cd mitigation, with extractable Cd (AB-DTPA) in soil decreasing from 66 mg kg−1 to 18 mg kg−1. Cd content in shoots decreased from 2.5 mg kg−1 to 0.9 mg kg−1, and in grains decreased from 1.1 mg kg−1 to 0.5 mg kg−1. Moreover, the PB treatment led to increased rice yield, from 4.9 to 10 g pot−1, and biological yield, from 4 to 20 g pot−1. The soil also showed improved organic matter content, increasing from 0.4% to 0.7%, and enhanced levels of nitrogen (N), phosphorus (P), and potassium (K), by increases from 2.1 g pot−1 to 5 g pot−1, 58 mg kg−1 to 83 mg kg−1, and 40 mg kg−1 to 63 mg kg−1, respectively. These findings demonstrate the potential of PB in mitigating Cd contamination in soil and reducing its uptake by rice plants.

Excellent adsorption of toxic Cd (II) ions from water with effective antibacterial activity by novel GO-ZnO-curcumin composite.

A significant health risk arises from the bioaccumulation of harmful Cd (II) in drinking water. Here, we report the unique Cd (II) remediation from drinkingwater by using novel GO-ZnO-curcumin composite. The composites were tailored by varying the ratio of GO-ZnO and curcumin. The composites followed Langmuir adsorption isotherm and pseudo-second-order kinetics. ZnO nano-rods were more effective in Cd (II) than ZnO nano-disks. A maximum adsorption capacity of 4580 ± 40mg/gm was achieved for 21G-B with a removal efficiency of 87.5% at neutral pH under optimized conditions. The removal process was governed by ion exchange and electrostatic attraction, followed bycation exchange capacity (CEC). The lattice parameter increase was detected after adsorption of Cd (II) ions. The regeneration and reusability of the composite was studied. Also, the effect of presence of dyes such as methylene blue on Cd (II) adsorption was noted. The latter had negligible effect on Cd (II) removal efficiency from water. The composite showed high antibacterial activity against B. subtilis and P. aeruginosa with minimum inhibitory concentration (MIC) of 10 ± 0.75µg/ml and 5 ± 1µg/ml respectively due to the presence of zinc. Composite stability was confirmed through leaching and thermal gravimetric analysis (TGA) analysis. The study establishes the nanocomposite as a potential material for remediation of hazardous Cd (II) ions from real water samples under neutral conditions.

A New Model for Effective Remediation and Comprehensive Utilization of Cd–Pb Composite Contaminated Farmland by Ornamental Plants

A New Model for Effective Remediation and Comprehensive Utilization of Cd–Pb Composite Contaminated Farmland by Ornamental Plants

Unlocking Cd(II) biosorption potential of Candida tropicalis XTA 1874 for sustainable wastewater treatment

Cd(II) is a potentially toxic heavy metal having carcinogenic activity. It is becoming widespread in the soil and groundwater by various natural and anthropological activities. This is inviting its immediate removal. The present study is aimed at developing a Cd(II) resistant strain isolated from contaminated water body and testing its potency in biological remediation of Cd(II) from aqueous environment. The developed resistant strain was characterized by SEM, FESEM, TEM, EDAX, FT-IR, Raman Spectral, XRD and XPS analysis. The results depict considerable morphological changes had taken place on the cell surface and interaction of Cd(II) with the surface exposed functional groups along with intracellular accumulation. Molecular contribution of critical cell wall component has been evaluated. The developed resistant strain had undergone Cd(II) biosorption study by employing adsorption isotherms and kinetic modeling. Langmuir model best fitted the Cd(II) biosorption data compared to the Freundlich one. Cd(II) biosorption by the strain followed a pseudo second order kinetics. The physical parameters affecting biosorption were also optimized by employing response surface methodology using central composite design. The results depict remarkable removal capacity 75.682 ± 0.002% of Cd(II) by the developed resistant strain from contaminated aqueous medium using 500 ppm of Cd(II). Quantitatively, biosorption for Cd(II) by the newly developed resistant strain has been increased significantly (p < 0.0001) from 4.36 ppm (non-resistant strain) to 378.41 ppm (resistant strain). It has also shown quite effective desorption capacity 87.527 ± 0.023% at the first desorption cycle and can be reused effectively as a successful Cd(II) desorbent up to five cycles. The results suggest that the strain has considerable withstanding capacity of Cd(II) stress and can be employed effectively in the Cd(II) bioremediation from wastewater.

Remediation of Pb, Cd, and Cu contaminated soil with Mg‐Fe‐Al layered double hydroxides (LDHs) synthesized from waste red mud

AbstractSoils contaminated with multiple heavy metals pose a significant threat to human health and ecosystem functionality. Following a “treat pollution with waste” strategy, we synthesized Mg‐Fe‐Al ternary layered double hydroxides (LDHs) from waste Bayer red mud for the remediation of heavy metal contaminated soils. Characterization using XRD, FTIR, SEM and EDS methods revealed a characteristic layered structure rich in functional groups, offering reaction sites for heavy metal passivation. Passivation experiments showed that the application of Mg‐Fe‐Al LDHs (2.5 wt.%) reduced the availability of Pb (29.7%), Cd (64.1%) and Cu (66.0%) in contaminated soil from a sulphide iron ore area in southern Sichuan Province. Simulated acid rain experiments showed leachate concentrations of Pb, Cd, and Cu reduced by 43.3%, 72.7% and 42.4%, respectively. This work provides a reference for the development of high‐performance and environmentally friendly adsorption‐stabilizing materials for green remediation.

Montmorillonite Clay as an Adsorbent for the Remediation of Cd (II) Ions in Aqueous Solutions: A Comparison With Pb (II) Ions

ABSTRACTHeavy metal ions are hazardous to both human health and the environment. Montmorillonite (MMT) clay has recently piqued interest for its adsorption capacity of heavy metals and its use in controlling contaminants, in particular in surface and waste waters. This research sheds light on the possibility of the application of natural Albanian MMT clay from the Prrenjas Region of Albania as an adsorbent of Cd (II) ions in aqueous solutions, making a comparison with the capacity of such clay for the adsorption of Pb (II) ions. The set of variables studied included concentrations of metal ions, amount of clay pH, time, and temperature of interaction and adsorption process (all of them following batch technique), and optimal conditions have been determined. The adsorption capacity of natural clay for Cd (II) ions was 6.735 mg/g, as compared to 17.9 mg/g for Pb (II) ions. Langmuir and Freundlich isotherms were applied to evaluate the mode of adsorption with results showing that all isotherms are linear and the Langmuir model fitted better with the experimental data. It is determined that the adsorption of Cd (II), similar to that of Pb (II), is well‐fitted by the second‐order reaction kinetic following the Lagergen model. The results demonstrate good potentiality for Prrenjas MMT as a low‐cost adsorbent to remove Cd (II) from aqueous systems, in particular, for wastewater treatment.

Optimal biochar selection for cadmium pollution remediation in Chinese agricultural soils via optimized machine learning

Biochar is effective in mitigating heavy metal pollution, and cadmium (Cd) is the primary pollutant in agricultural fields. However, traditional trial-and-error methods for determining the optimal biochar remediation efficiency are time-consuming and inefficient because of the varied soil, biochar, and Cd pollution conditions. This study employed the machine learning method to predict the Cd immobilization efficiency of biochar in soil. The predictive accuracy of the random forest (RF) model was superior to that of the other common linear and nonlinear models. Furthermore, to improve the reliability and accuracy of the RF model, it was optimized by employing a root-mean-squared-error-based trial-and-error approach. With the aid of the optimized model, the empirical categories for soil Cd immobilization efficiency were biochar properties (60.96 %) > experimental conditions (19.6 %) ≈ soil properties (19.44 %). Finally, this study identified the optimal biochar properties for enhancing agricultural soil Cd remediation in different regions of China, which was beneficial for decision-making regarding nationwide agricultural soil remediation using biochar. The immobilization effect of alkaline biochar was pronounced in acidic soils with relatively high organic matter. This study provides insights into the immobilization mechanism and an approach for biochar selection for Cd immobilization in agricultural soil.

Crystal phase conversion of amorphous Fe−Mn binary oxides promote the sequestration and redistribution of arsenic, cadmium, and lead in the soil: Comparison with crystalline form

Iron and manganese oxides participate in nearly all geochemical processes in soils. The crystal phase conversion of the Fe−Mn oxides is a crucial process that controls the transport and the fate of metal(loid)s (such as Pb, Cd, and As). However, this conversion and its contribution in immobilization are seldom reported. In this study, the phase transition process of amorphous Fe−Mn oxides has been investigated using TEM, HE−XRD and PDF analyses. The role of heavy metal atoms in the Fe−Mn oxides lattice has been revealed through atomic−scale structural characterization, including bond lengths and coordination numbers. In detail, Mn oxides and Fe oxides exhibit synergistic effects. Mn oxides oxidize As(III) to As(V). Meanwhile, the adsorbed As, Cd, and Pb irons were redistributed and incorporated into the lattice of the Fe−Mn oxides during the crystal phase conversion of the Fe oxides. During this process, the proportion of residual fraction of As, Cd, and Pb increased by 30 %, 25 %, and 9 %, respectively, after 28 d. 100 %, 41.8 %, and 60.7 % of decarbonate−extractable As, DTPA−extractable Cd and Pb could be immobilized, respectively. This study provides insight into the contribution of Fe−Mn oxides in controlling the cycling of metals and offers an advanced strategy in remediation of As, Cd, and Pb in contaminated soil.

Thermodynamic, kinetic, and equilibrium studies of Cu(II), Cd(II), Ni(II), and Pb(II) ion biosorption onto treated Ageratum conyzoid biomass

The issue of environmental contamination, particularly caused by the existence of heavy metal particles, is a major and widely recognized subject that receives substantial global attention. The remediation of Cu(II), Cd(II), Ni(II), and Pb(II) ionic metal particles from synthetic wastewater using chemically treated plant leaves of Ageratum conyzoides (TAC) as a biosorbent was investigated. The biosorption process was implemented utilizing a batch system, wherein several operational parameters were considered, including temperature, pH, agitation time, biosorbent dosage, and initial concentration of the metal ion. Langmuir, Freundlich, Temkin, and D-R isotherm models were used to evaluate equilibrium data. The analyzed parameter exhibits characteristics that were best fitted with the Langmuir isotherm. The observed biosorption capacities (qm) of Cu(II), Pb(II), Ni(II), and Cd(II) ions on the TAC were measured as 51.573, 30.49, 33.53, and 35.91 mg/g, respectively, at a temperature of 22 °C. The affinity sequence of these metal ions follows the order Cu(II) > Pb(II) > Ni(II) > Cd(II). The measured values for the biosorption free energy change (ΔG) of Cu(II), Pb(II), Cd(II), and Ni(II) metal ions ranged from −1.017 to −4.723, −1.368 to −3.612, −2.785 to −5.21, and −1.047 to −5.135 kJ/mol, respectively. The enthalpy (ΔH) for Cu(II), Pb(II), Cd(II), and Ni(II) were determined to be +19.33, +6.82, +14.83, and +38.07 kJ/mol, respectively. Similarly, the corresponding entropy changes (ΔS) for the same series of metal ions were recorded as +0.075, +0.064, +0.063, and +0.135 kJ/mol.K. The pseudo-second-order kinetic models yielded superior outcomes in comparison to the pseudo-first-order kinetic models. The findings of the experiment indicated that the TAC demonstrates favorable efficacy in extracting all four metal ions. Hence, the utilization of biomass derived from Ageratum conyzoides leaves has proven to be a viable and economically feasible approach for biosorption of all four metals.

Application of red mud in hydrothermal remediation of Cd- and petroleum-contaminated soil

Developing a technique to simultaneously remove the harmful effects of organic matter and heavy metals from composite-polluted soil is of great importance, as it could reduce the time required for land restoration. In this study, red mud was used as an additive to remediate Cd- and petroleum-contaminated soil (CPCS) using hydrothermal technology, and its effects on the total organic carbon (TOC), total Cd, and available Cd (CdA) in the soil were evaluated. During hydrothermal extractions, when the temperature increased from 150 °C to 350 °C, the TOC removal efficiency increased from 16.32 % to 61.29 %, while the ratio of CdA (RCdA) decreased from 32.28 % to 10.72 %, and after adding 2 g of red mud, the RCdA decreased from 46.54 % to 20.30 %. During hydrothermal oxidations, adding red mud increased the TOC removal efficiency from 78.44 % at 0 g to 84.62 % at 3 g when the amount of oxidant was 30 mL, and RCdA decreased from 31.62 % to 19.46 %. These results indicate that hydrothermal treatments could significantly affect the organic substances in soil, and red mud played the roles of a catalyst and passivator during hydrothermal oxidation. The passivation of Cd by red mud was promoted under high-temperature conditions and an appropriate increase in the oxidant concentration and reaction time could promote the removal of organic matter and the reduction of CdA. However, excessive oxidants and reaction time could cause further decomposition of organic matter, leading to a decreased ability to capture Cd.

Preparation of porous biochar from fusarium wilt-infected banana straw for remediation of cadmium pollution in water bodies

The problem of cadmium pollution and its control is becoming increasingly severe issue in the world. Banana straw is an abundant bio raw material, but its burning or discarding in field not only causes pollution but also spreads fusarium wilt. The objective of this paper is to utilize biochar derived from the wilt-infected banana straw for remediation of Cd(II) pollution while to eliminate the pathogen. The activity of wilt pathogen in biochar was determined by PDA petri dish test. The Cd(II) adsorption of the biochar was determined by batch adsorption experiments. The effects of KOH concentration (0.25, 0.5 and 0.75 M) on the physicochemical characteristics of the biochar were also observed by BET, SEM, FTIR, XRD and XPS. Results showed that pristine banana straw biochar (PBBC) did not harbor any pathogen. The specific surface area (SSA) and Cd(II) adsorption capacity of 0.75 M KOH modified banana straw biochar (MBBC0.75M) were increased by 247.2% and 46.1% compared to that of PBBC, respectively. Cd(II) adsorption by MBBC0.75M was suitable to be described by the pseudo-second-order kinetic model and Freundlich isotherm. After Cd(II) adsorption, the CdCO3 were confirmed by XRD and observed through SEM. The weakness and shift of oxygen-containing functional groups in MBBC0.75M after Cd(II) adsorption implied that those groups were complexed with Cd(II). The results showed that pyrolysis could not only eliminate banana fusarium wilt, but also prepare porous biochar with the wilt-infected banana straw. The porous biochar possessed the potential to adsorb Cd(II) pollutants.

How does the biochar-supported sulfidized nanoscale zero-valent iron affect the soil environment and microorganisms while remediating cadmium contaminated paddy soil?

In previous studies, iron-based nanomaterials, especially biochar (BC)-supported sulfidized nanoscale zero-valent iron (S-nZVI/BC), have been widely used for the remediation of soil contaminants. However, its potential risks to the soil ecological environment are still unknown. This study aims to explore the effects of 3% added S-nZVI/BC on soil environment and microorganisms during the remediation of Cd contaminated yellow-brown soil of paddy field. The results showed that after 49 d of incubation, S-nZVI/BC significantly reduced physiologically based extraction test (PBET) extractable Cd concentration (P < 0.05), and increased the immobilization efficiency of Cd by 16.51% and 17.43% compared with S-nZVI and nZVI/BC alone, respectively. Meanwhile, the application of S-nZVI/BC significantly increased soil urease and sucrase activities by 0.153 and 0.446 times, respectively (P < 0.05), improving the soil environmental quality and promoting the soil nitrogen cycle and carbon cycle. The results from the analysis of the 16S rRNA genes indicated that S-nZVI/BC treatment had a minimal effect on the bacterial community and did not appreciably alter the species of the original dominant bacterial phylum. Importantly, compared to other iron-based nanomaterials, incorporating S-nZVI/BC significantly increased the soil organic carbon (OC) content and decreased the excessive release of iron (P < 0.05). This study also found a significant negative correlation between OC content and Fe(II) content (P < 0.05). It might originate from the reducing effect of Fe-reducing bacteria, which consumed OC to promote the reduction of Fe(III). Accompanying this process, the redistribution of Cd and Fe mineral phases in the soil as well as the generation of secondary Fe(II) minerals facilitated Cd immobilization. Overall, S-nZVI/BC could effectively reduce the bioavailability of Cd, increase soil nutrients and enzyme activities, with less toxic impacts on the soil microorganisms.

Addition of microbes shifts the ability of soil carbon sequestration in the process of soil Cd remediation

Addition of microbes shifts the ability of soil carbon sequestration in the process of soil Cd remediation

High-efficiency remediation of Hg and Cd co-contaminated paddy soils by Fe–Mn oxide modified biochar and its microbial community responses

Fe–Mn oxide modified biochar (FMBC) was produced to explore its potential for remediation of Hg–Cd contaminated paddy soils. The results showed that the application of FMBC decreased the contents of bioavailable Hg and Cd by 41.49–81.85% and 19.47–33.02% in contrast to CK, while the amount of labile organic carbon (C) fractions and C-pool management index (CPMI) was increased under BC and FMBC treated soils, indicating the enhancement of soil C storage and nutrient cycling function. Dry weight of different parts of Oryza sativa L. was enhanced after the addition of BC and FMBC, and the contents of Fe and Mn in root iron–manganese plaques (IMP) were 1.46–2.06 and 6.72–19.35 times higher than those of the control groups. Hg and Cd contents in brown rice under the FMBC treatments were significantly reduced by 18.32–71.16% and 59.52–72.11% compared with the control. FMBC addition altered the composition and metabolism function of soil bacterial communities, especially increasing the abundance of keystone phyla, including Firmicutes, Proteobacteria and Actinobacteria. Partial least squares path modelling (PLSPM) revealed that the contents of Na2S2O3–Hg, DTPA–Cd and IMP were the key indicators affecting Hg and Cd accumulation in rice grains. These results demonstrate the simultaneous value of FMBC in remediation of Hg and Cd combined pollution and restoring soil fertility and biological productivity.Graphical

The defensin protein NtCAL1 functions as a positive factor in plant cadmium accumulation and resistance in tobacco

Cadmium (Cd) poses a threat to food safety and human health. Plant defensins are small peptides that involved in Cd metabolism. however, the function of tobacco phyto-defensin protein NtCAL1 in Cd metabolism remains poorly understood. Here we identified the effects of NtCAL1 from tobacco on Cd metabolism. We provide evidence that NtCAL1 is located in the cell wall and varied expressed in organs of developmental stages. The overexpression of NtCAL1 has been demonstrated to enhance the content of AsA and antioxidant enzyme (CAT and APX) activities, as well as to positively regulate the expression of NtRAMP3, NtHMAα and NtHMAβ. The NtCAL1 was identified as a positive regulator of cadmium (Cd) translocation from the root to the shoot. Furthermore, the accumulation of Cd was inhibited by Cd foliar inhibitors. In conclusion, we propose that NtCAL1 acts synergistically with other proteins involved in Cd uptake and transport, thereby enhancing Cd tolerance through the upregulation of antioxidant substances and the activation of antioxidant enzymes.The NtCAL1 provides a significant potential tool for the development of low-Cd tobacco, while remediation of Cd contaminated field soils.