Cd Species Research Articles

Simultaneous enhancement of soil properties along with water-holding and restriction of Pb–Cd mobility in a soil-plant system by the addition of a phosphorus-modified biochar to the soil

Soil quality deterioration and heavy metal contamination have greatly limited soil productivity in mining areas. As soil is a complex system with various properties and interactions, it is imperative to conduct a comprehensive investigation to understand the amendment's mechanisms at work in the soil in mining areas as well as effective ways to address its deteriorating quality. In this study, a potassium dihydrogen phosphate-modified maize straw-cow dung biochar (PBC) was applied as a soil amendment. Various physicochemical properties of the soil including organic matter, total nitrogen, available phosphorus, and pore characteristics were analyzed. This study also assessed soil-saturated water content and soil moisture characteristic curve. Lettuce biomass was measured and changes in various speciation of Pb and Cd in the soil, and the accumulation of Pb and Cd in lettuce were examined. Results showed that the addition of PBC increased soil organic matter, total nitrogen, and available phosphorus while reducing soil bulk density, it also increased soil porosity, saturated water content, and capillary water capacity. Soil structure analysis using CT scanning revealed that 3% PBC increased the macrospores volume fraction while 5% PBC made the pores more uniform. Lettuce biomass increased by 53.3%. 5% PBC resulted in a 56.79% and 38.30% reduction in Pb and a 44.56% and 16.60% reduction in Cd in roots and shoots of lettuce respectively. PBC facilitated the transformation of Pb and Cd from unstable fractions to stable fractions through complexation and precipitation. Overall, the addition of PBC effectively improved soil nutrients, porosity, and water-holding capacity, promoted plant growth, immobilized Pb and Cd, as well as reduced the bioavailability in contaminated-soil from mining areas. This study provides an effective strategy and a new perspective for the remediation of Pb–Cd-contaminated soils.

Cadmium speciation in cacao beans changes during a fermentation-like incubation

Cadmium (Cd) concentrations in cacao often exceed food limits. Recently, it was shown that cacao bean fermentation enhances Cd solubility, opening potential for Cd mitigation in cacao products. This study was set-up to identify changes in Cd speciation during fermentation. X-Ray absorption spectroscopy (XAS) complemented with speciation calculations, were used on samples collected from high and low Cd farms, that were subjected to a fermentation-like incubation that reached high temperatures (>45 °C) and acidic pH (<5). Incubation decreased nib Cd concentration up to a factor 1.5 and changed Cd complexation in high Cd beans from sulphur to oxygen ligands, likely due to pH changes. In beans with lower Cd concentrations, Cd was complexed before and after incubation with oxygen-ligands. A combination of pH changes and/or phytate breakdown may explain the migration of Cd outward from the nib. XAS and speciation calculations proved complimentary techniques and indicated similar speciation changes during fermentation.

Biochar improves the yield and quality of Erigeron breviscapus in heavily cadmium-polluted soil

Simultaneously utilizing and remediating soil contaminated with cadmium (Cd) is propitious and economically beneficial. In this study, Erigeron breviscapus, a raw medicinal material used to extract scutellarin, was utilized to conduct a pot experiment including five treatments. Under a control without Cd and biochar addition (CK), soil exogenously added with high concentration of Cd (0.01%) were used to investigate the effects of different biochar doses (0%, 5%, 10%, and 15%, denoted as CdB0, CdB5, CdB10, and CdB15, respectively) on the yield (shoot biomass) and quality (represented by scutellarin content) of E. breviscapus as well as soil remediation. The results showed that soil with addition of high Cd decreased the shoot biomass and scutellarin content of E. breviscapus by 33.6% and 70.8%, respectively. Compared with CdB0, the shoot biomass and scutellarin content of CdB15 increased by 24.7% and 312.0%, respectively. Biochar application (CdB5, CdB10, and CdB15) changed the soil Cd speciation and reduced the soil available Cd and plant Cd concentrations by 17.4%–121.8% and 26.4%–42.6%, respectively, compared with CdB0. However, the chlorophyll content, catalase activity, and acquisition of N, Fe, and Cu of E. breviscapus were increased in CdB5, CdB10, and CdB15 compared with CdB0. In addition, the Cd toxicity mitigation effect enhanced with increasing biochar application, and the application of 15% biochar resulted in the highest shoot biomass and scutellarin content of E. breviscapus. The results of this study highlight the importance of biochar for improving the Cd adaptability of E. breviscapus and provide a reference for the simultaneous utilization and remediation of heavily Cd-contaminated soil.

Mitigation strategies for excessive cadmium in rice.

Cadmium (Cd)-contaminated rice is a human food safety problem that lacks a clear solution. A large amount of rice having an excessive Cd content is processed yearly, but it cannot be discarded and placed in landfills because it will cause secondary pollution. How do we best cope with this toxic rice? From the perspectives of food safety, food waste prevention, and human hunger eradication, the use of contemporary physical, chemical, and biological techniques to lower the Cd content in postharvest Cd-contaminated rice so that it can be used safely is the best course of action. In this review, the contamination, chemical speciation, and distribution of Cd in rice are analyzed and discussed, as are the methods of Cd removal from rice, including a comparison of the advantages and disadvantages of various techniques. Owing to the limitations of current technology, research and technological development recommendations for removing Cd from rice grain are presented. The chemical and biological methods produce higher Cd-removal rates than physical methods. However, they are limited to small-scale laboratory applications and cannot be applied on a large industrial scale. For the efficient safe removal of Cd from food, mixed fermentation with lactic acid bacteria and yeast has good application prospects. However, limited strains having high Cd-removal rates have been screened. In addition, modern biotechnology has rarely been applied to reduce rice Cd levels. Therefore, applying genetic engineering techniques to rapidly obtain microorganisms with high Cd-removal rates in rice should be the focus of future research.

Geochemical factors controlling the mobilization of geogenic cadmium in soils developed on carbonate bedrocks in Southwest China

Soils developed on carbonate bedrocks commonly contain high contents of geogenic cadmium (Cd). The bioavailability of Cd greatly varies among such soils and tends to be elevated in paddy soils compared to upland soils. However, the factors controlling the mobilization of geogenic Cd in paddy soils remain unclear. Therefore, this study aimed to reveal the processes and influencing factors of Cd mobilization in soils, by collecting upland soils and paddy soils from a carbonate region in Southwest China and analyzing the integrated soil properties and content, speciation and bioavailability of Cd. The results showed that the in-situ weathering of Cd-rich limestone (average of 0.66 mg/kg) resulted in the enrichment of Cd in overlying soils (4.75 to 13.2 mg/kg). Based on sequential extraction, ∼43%, 18% and 17% of Cd in paddy soils was retained by Mn oxides, Fe oxides and the residual fraction, respectively. Hence, the transformation of Mn oxides drove the redistribution of Cd. In the upper layers, Cd released from Mn oxides was sequestered by soil organic matter and carbonate. Based on extraction using diethylene triamine pentaacetic acid (DTPA), paddy soils presented a higher Cd bioavailability (27%) than upland soils (18%). Furthermore, both the bioavailability and mobility of Cd gradually increased toward the surface in the profiles. The bioavailability of Cd was significantly correlated with the content of soil organic matter in these soils, indicating that soil organic matter was another crucial factor controlling Cd mobilization in paddy soils. The outcomes of this study provided new evidence for understanding the mobilization of Cd in soils and are helpful for developing pollution-control strategies to combat geogenic Cd in paddy soils in carbonate regions.

More Effective Mobilization of Hg2+ from Human Serum Albumin Compared to Cd2+ by L-Cysteine at Near-Physiological Conditions.

Although chronic low-level exposure to Hg2+ and Cd2+ causes human nephrotoxicity, the bioinorganic processes that deliver them to their target organs are poorly understood. Since the plasma protein human serum albumin (HSA) has distinct binding sites for these metal ions, we wanted to gain insight into these translocation processes and have employed size-exclusion chromatography coupled on-line to an inductively coupled plasma atomic emission spectrometer using phosphate-buffered saline mobile phases. When HSA 'labeled' with Hg2+ and Cd2+ (1:0.1:0.1) using 300 μM of L-methionine was analyzed, the co-elution of a single C, S, Cd, and Hg peak was observed, which implied the intact bis-metalated HSA complex. Since human plasma contains small molecular weight thiols and sulfur-containing metabolites, we analyzed the bis-metalated HSA complex with mobile phases containing 50-200 µM of L-cysteine (Cys), D,L-homocysteine (hCys), or glutathione (GSH), which provided insight into the comparative mobilization of each metal from their respective binding sites on HSA. Interestingly, 50 µM Cys, hCys, or GSH mobilized Hg2+ from its HSA binding site but only partially mobilized Cd2+ from its binding site. Since these findings were obtained at conditions simulating near-physiological conditions of plasma, they provide a feasible explanation for the higher 'mobility' of Hg2+ and its concomitant interaction with mammalian target organs compared to Cd2+. Furthermore, 50 µM Cys resulted in the co-elution of similar-sized Hg and Cd species, which provides a biomolecular explanation for the nephrotoxicity of Hg2+ and Cd2+.

Influence of Modified Biochar on Soil Fluoride and Cadmium Speciation and Their Bioavailability to Tea Seedling (Camellia Sinensis L.)

ABSTRACT Biochar is widely used as a good soil amendment, while knowledge of modified biochar application in tea garden soils contaminated by fluoride (F) and cadmium (Cd) is insufficient. The tea seedling (Camellia sinensis L.) growth assay was performed to evaluate interaction of soil Cd and F and the improving effect of aluminum trichloride-modified corn stalk biochar (Al-BC) on their speciation, phytoaccumulation and phytotoxicity. Results showed that soil F speciation ratio sequence was as follows: residual > exchangeable > organic-bound > water-soluble > Fe/Mn oxide-bound. Soil exchangeable Cd was the largest Cd speciation (>35.6%), probably due to the low pH values in the acid tea gardens. Root F contents showed a strong significant relationship with soluble F contents (r = 0.92, P < .01) and similarly root Cd highly connected with exchangeable Cd (r = 0.86, P < .01). Seedling height, fresh and dry weight, root surface area, length, and photosynthetic pigment showed different sensitivities to F or Cd oxidative stress and toxicity effects, and only root F contents significantly inversely correlated with them (r = 0.74–0.80, P < .01). The interaction of Cd and F, could influence their speciation distribution and antagonized each other in root accumulation. Meanwhile, joint simulation models showed that antagonistic effects were observed in the F and Cd mixture soils for most cases at Enshi. Biochar application reduced bioavailable F and Cd contents, and thus decreased F and Cd accumulation in tea roots and obviously alleviated toxicity effects. For instance, biochar application significantly reduced root F contents, which had 33.2% to 62.2% declines at Enshi and 39.7% to 77.2% declines at Huanggang. Meanwhile, the soil properties were improved as biochar added, with an increase in soil pH, EC, CEC and organic matter. Overall, Al-modified biochar was beneficial environmental materials for reducing both F and Cd bioavailability.

An in-situ investigation on the speciation and relationship of Zn and Cd in contaminated sediments: Bulk EXAFS, and micro synchrotron X-ray fluorescence

The determination of the speciation and binding types of metals is critical to assessing mobility and bioavailability in soils and sediments. The current study determined the speciation of Zn and Cd in contaminated sediments in the Baiyin district using X-ray absorption fine structure (XAFS) and micro-X-ray fluorescence (μ-XRF). The results revealed that the speciation of Zn in sediments was quite complicated and related to the mineralogical composition and physiochemistry in different locations, with speciation including Zn2+, Zn–Al layered double hydroxide (LDH), Zn primary minerals (sphalerite and franklinite), Zn-Calcite, and Zn-Ferrihydrite. In comparison to Zn, the speciation of Cd in sediments was found to be simpler and less influenced by the geochemical properties of the samples. The μ-XRF analysis indicated a strong correlation between the distribution of Cd and hot spots of Ca and Zn. The XAFS analysis confirmed that the dominant form of Cd was adsorbed on calcite and illite, suggesting a high level of bioavailability, mobility, and potential environmental risk. The results also showed that Zn and Cd coexisted and had a synergistic effect in the calcite and clay minerals of contaminated sediments. This study is the first report on the in-situ speciation of heavy metals in alkaline and calcareous sediment of north China, and the use of spectroscopy techniques allowed for the reliable identification of the speciation of Zn and Cd.

Enhanced the Efficiency of Electrocatalytic CO2 -to-CO Conversion by Cd Species Anchored into Metal-Organic Framework.

Metal-organic frameworks (MOFs) as a promising platform for electrocatalytic CO2 conversion are still restricted by the low efficiency or unsatisfied selectivity for desired products. Herein, zirconium-based porphyrinic MOF hollow nanotubes with Cd sites (Cd-PCN-222HTs) are reported for electrocatalytic CO2 -to-CO conversion. The dispersed Cd species are anchored in PCN-222HTs and coordinated by N atoms of porphyrin structures. It is discovered that Cd-PCN-222HTs have glorious electrocatalytic activity for selective CO production in ionic liquid-water (H2 O)-acetonitrile (MeCN) electrolyte. The CO Faradaic efficiency (FECO ) of >80% could be maintained in a wide potential range from -2.0 to -2.4V versus Ag/Ag+ , and the maximum current density could reach 68.0mA cm-2 at -2.4V versus Ag/Ag+ with a satisfied turnover frequency of 26220 h-1 . The enhanced efficiency of electrocatalytic CO2 conversion of Cd-PCN-222HTs is closely related to its hollow structure, anchored Cd species, and good synergistic effect with electrolyte. The density functional theory calculations indicate that the dispersed Cd sites anchored in PCN-222HTs not only favor the formation of *COOH intermediate but also hinder the hydrogen evolution reaction, resulting in high activity of electrocatalytic CO2 -to-CO conversion.

Co-adsorption mechanisms of Cd(II) and As(III) by an Fe-Mn binary oxide biochar in aqueous solution

Biochar can remove oppositely charged ionic species of Cd(II) and As(III)/As(V) from water but the co-adsorption mechanisms of the metal(loid)s are poorly understood. This study aims to unravel the co-absorption mechanisms of Cd(II) and As(III) by a Pennisetum sp. straw biochar (BC) modified with Fe-Mn oxide (FMBC). The maximum adsorption capacity of Cd(II) and As(III) by FMBC was 141.1 and 31.8 mg/g, respectively, which was 2.71 and 3.89 times higher than that of BC. The adsorption of Cd(II) by FMBC demonstrated a homogeneous monolayer chemical process, while the As(III) adsorption presented a heterogeneous multilayer process. In the dual-adsorbate system, Cd(II) increased the adsorption of As(III) on FMBC by 5.1–123.9%, while As(III) reduced the adsorption of Cd(II) by 0.7–24.8%, indicating respective synergism and competition effect. Systematic co-adsorption experiments and adsorbent characterization results suggested that the synergistic mechanism occurred via electrostatic attraction and ternary surface complexation, whereas the competitive effect emerged due to complexing reaction with oxygen-containing functional groups of FMBC. The FMBC could be a potential adsorbent to adsorb Cd(II) and As(III) simultaneously.

Removal of cadmium in contaminated soils by self-sustaining smoldering

Soil contamination by Cd presents a significant challenge for global eco-environment, while pyrolysis is an effectively method to removal of Cd in the soil, the further application of the technology has obstacle by the high device cost, large energy consumption and soil degradation. This study explored the application of self-sustaining smoldering as an energy-efficient technique for remediating of Cd-contaminated soils. The results shown that Cd could be desirable evacuated from soil by manipulate the key experiment parameter, especially the Cd-contaminated soil-to-PNs ratio. In this process, the content of Poly(vinyl) chloride (PVC) significantly influences the efficiency of Cd removal. Only 18.53 % of Cd was removed without PVC compared to that of 74.30 % after 3 % PVC was added into the soils. Chlorination of Cd(II) is the main reason for the removal of Cd during smoldering with PVC, which contrast to the volatilization of Cd is governed by reduction without PVC. Importantly, smoldering could effectively decline Cd species in the acid-soluble fraction and lower the bioavailability of Cd in treated soils with the DPTA-Cd decreased by 4.90–17.23 times compared with the untreated soils. Furthermore, due to the formed solid products, smoldering operation significantly increased soil total phosphorus and available phosphorus in the remediated soils, which is benefit for the reclamation goals. Overall, this study shows a great potential for remediation of Cd-contaminated soils by self-sustaining smoldering in the remediation industry.

Anatomical functional traits and hydraulic vulnerability of trees in different water conditions in southern Amazonia.

Understanding tree species' responses to drought is critical for predicting the future of tropical forests, especially in regions where the climate is changing rapidly. We compared anatomical and functional traits of the dominant tree species of two tropical forests in southern Amazonia, one on deep, well-drained soils (cerradão [CD]) and one in a riparian environment (gallery forest [GF]), to examine potential anatomical indicators of resistance or vulnerability to drought. Leaves of CD species generally had a thicker cuticle, upper epidermis, and mesophyll than those of GF species, traits that are indicative of adaptation to water deficit. In the GF, the theoretical hydraulic conductivity of the stems was significantly higher, indicating lower investment in drought resistance. The anatomical functional traits of CD species indicate a greater potential for surviving water restriction compared to the GF. Even so, it is possible that CD species could also be affected by extreme climate changes due to the more water-limited environment. In addition to the marked anatomical and functional differences between these phytophysiognomies, tree diversity within each is associated with a large range of hydraulic morphofunctional niches. Our results suggest the strong potential for floristic and functional compositional shifts under continued climate change, especially in the GF.

Significant difference in the efficacies of silicon application regimes on cadmium species and environmental risks in rice rhizosphere

Silicon (Si) is commonly applied as base-fertilizer or foliar-topdressing to palliate the uptake-translocation-accumulation of cadmium (Cd) in rice through Si–Cd antagonism. However, little is known about the fate of Cd in rice rhizosphere soil and its eco-environmental effects under different Si treatments. Here, systematic works had been carried out to elucidate the Cd species, soil properties, and environmental risks in rice rhizosphere driven by different Si soil-fertilization regimes including CK (without Si-addition), TSi (added before transplanting stage), JSi (added at jointing stage), and TJSi (split into two equal parts, added half before transplanting and another half at jointing stage). Results showed that TJSi outperformed the rest of fertilization regimes. The solid-phase-Cd concentrations treated with TSi, TJSi and JSi were increased by 4.18%, 5.73% and 3.41%, respectively, when compared to CK. The labile Cd (F1+F2) proportion of TJSi was reduced by 16.30%, 9.30% and 6.78%, respectively, when compared to CK, TSi, and JSi. Simultaneously, the liquid-phase-Cd concentration was appreciably suppressed by TJSi throughout the rice lifecycle, while TSi mainly abated Cd dissociation during the vegetative period, and JSi attenuated it during the grain-filling stage. The mobility factor of Cd treated with TJSi was the lowest, which was significantly lower than that of TSi (9.30%) and JSi (6.78%), respectively. Similarly, the oral exposure risk of TJSi was reduced by 4.43% and 32.53%; and the food-chain exposure risk of TJSi was decreased by 13.03% and 42.78%. Additionally, TJSi was the most effective in promoting enzyme activities and nutrient content in rhizosphere soil. Overall, TJSi is more positive and sustainable than TSi and JSi in reconstructing Cd-contaminated rhizosphere environments and abating the environmental risks of Cd. Agronomic practices in Cd-contaminated paddy soils can be informed by applying Si-fertilizer separately before transplanting and at jointing stage to achieve soil welfare and food security.

Structural Characterization of Toxicologically Relevant Cd2+-L-Cysteine Complexes.

The exposure of humans to Cd exerts adverse human health effects at low chronic exposure doses, but the underlying biomolecular mechanisms are incompletely understood. To gain insight into the toxicologically relevant chemistry of Cd2+ in the bloodstream, we employed an anion-exchange HPLC coupled to a flame atomic absorption spectrometer (FAAS) using a mobile phase of 100 mM NaCl with 5 mM Tris-buffer (pH 7.4) to resemble protein-free blood plasma. The injection of Cd2+ onto this HPLC-FAAS system was associated with the elution of a Cd peak that corresponded to [CdCl3]-/[CdCl4]2- complexes. The addition of 0.1-10 mM L-cysteine (Cys) to the mobile phase significantly affected the retention behavior of Cd2+, which was rationalized by the on-column formation of mixed CdCysxCly complexes. From a toxicological point of view, the results obtained with 0.1 and 0.2 mM Cys were the most relevant because they resembled plasma concentrations. The corresponding Cd-containing (~30 μM) fractions were analyzed by X-ray absorption spectroscopy and revealed an increased sulfur coordination to Cd2+ when the Cys concentration was increased from 0.1 to 0.2 mM. The putative formation of these toxicologically relevant Cd species in blood plasma was implicated in the Cd uptake into target organs and underscores the notion that a better understanding of the metabolism of Cd in the bloodstream is critical to causally link human exposure with organ-based toxicological effects.

Application potential of Vaccinium ashei R. for cadmium migration retention in the mining area soil

Despite numerous reports on phytoremediation of heavy metals contaminated soil, there are few reports on plant retention of heavy metals in the mining area slope. This study was the first of its kind to explore the cadmium (Cd) retention capacity of the blueberry (Vaccinium ashei Reade). Firstly, we investigated the stress response of blueberry to different soil Cd concentrations (1, 5, 10, 15, 20 mg/kg) to assess its potential for phytoremediation by pot experiments. The results showed that the blueberry biomass exposed to 10 and 15 mg/kg Cd was significantly increased compared with the control (1 mg/kg Cd); the blueberry crown increased by 0.40% and 0.34% in 10 and 15 mg/kg Cd-contaminated soil, respectively, compared with control; the blueberry heigh did not even change significantly in each treatment group; the total chlorophyll content, peroxidase and catalase activity of blueberry were enhanced in 5–20 mg/kg Cd treatments. Furthermore, the Cd contents of blueberry in the root, stem and leaf increased significantly as the Cd concentration of soil increased. We found that more Cd accumulated in blueberry root: the bioaccumulation concentration factor was root > stem > leaf for all groups; the residual-Cd (Cd speciation) in soil increased by 3.83%–411.11% in blueberry-planted versus unplanted groups; blueberry improved the Cd-contaminated soil micro-ecological environment including soil organic matter, available K and P, as well as microbial communities. Then, to investigate the effect of blueberry cultivation on Cd migration, we developed a bioretention model and revealed that soil Cd transport along the model slope was significantly weakened by blueberry cultivation, especially at the bottom of the model. In a word, this research suggests a promising method for the phytoremediation of Cd-contaminated soil and the reduction of Cd migration in mining areas.

Poisoning mechanism of different Cd precursors on Fe-Ce/TiO2 catalyst for selective catalytic reduction of NOx with NH3

As one of the most harmful heavy metals, Cd can present in many chemical forms in real flue gas and may deactivate the SCR catalysts, but the poisoning mechanism of different Cd species over the Fe-Ce/TiO2 catalysts remains unclear. Therefore, in our work, Fe-Ce/TiO2 catalyst is prepared and doped with Cd(NO3)2, CdCl2, and CdSO4, respectively, aiming to investigate the effect of different Cd precursors on the catalytic performance, physicochemical properties, and poisoning mechanisms of Fe-Ce/TiO2 catalyst. The results demonstrate that different Cd precursors exert different influences on the catalytic activity of the catalyst and the deactivation sequence is CdSO4 <Cd(NO3)2 <CdCl2. The doping of Cd decreases the specific surface area, promotes the grain growth of active species, and results in the aggregation of surface active species to varying degrees. Although the total H2 consumption of Cd poisoned catalysts is enhanced, they are not originated from more amounts of surface active species and thus it does not contribute to the redox cycles and catalytic activity of catalysts. The doping of Cd(NO3)2 decreases the surface acidity of catalysts, while CdCl2 and CdSO4 promote surface acidity, but the adsorbed NH3 over CdCl2 poisoned catalyst is unreactive. In addition, both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms are involved in the SCR reaction over the Fe-Ce/TiO2 catalyst and different Cd poisoning makes no change to the reaction mechanism.

Effect of flue gas components on the removal of cadmium pollutants by transition metal-modified activated carbon: Density functional theory and thermodynamic study

Removal of cadmium (Cd) pollutants from waste incineration (MSW) flue gas by modified activated carbon (AC) is of great potential, yet the influence of flue gas composition on their interaction mechanism is still unclear. Thus, density functional theory and thermodynamic analyses were combined to explore the effects of typical flue gas compositions (O2, HCl, NO, SO2, CO2, and H2O) on Cd species capture over the Fe/AC and Mn/AC surfaces. All flue gas compositions inhibit the adsorption of Cd species, wherein their inhibitory effects are mainly divided into two categories, i.e., one with moderate inhibition (HCl, CO2, and H2O), and the other with significant inhibition (O2, NO, and SO2). For the first category, HCl forms new active sites after adsorption on the surface, while CO2 and H2O have weak competitiveness with Cd species, resulting in mild inhibitory effects. Nevertheless, O atoms of O2/SO2 and N atoms of NO are highly effortless to bond with Fe/Mn atoms, and strongly exclude the Cd adsorption on the active sites, greatly weakening their binding strength. According to thermodynamic analysis, the fixation of Cd species by Fe/AC and Mn/AC spontaneously proceeds with the interference of flue gas components, while the selectivity to Cd species decreases with the increased temperature. In summary, it is instrumental to adjust the operating parameters and AC injection location to attenuate the negative effects of O2, SO2, NO, and high temperature on Cd capture by Fe/AC and Mn/AC.

Immobilization of Cd by mercapto-palygorskite in typical calcareous and acidic soil aggregates: Performance and differences

The microscale spatial heterogeneity and complexity of soil aggregates affect the properties and distribution of heavy metals (HMs). It has been confirmed that amendments can alter the distribution of Cd in soil aggregates. However, whether the Cd immobilization effect of amendments varies across soil aggregate levels remains unknown. In this study, soil classification and culture experiments were combined to explore the effects of mercapto-palygorskite (MEP) on Cd immobilization in soil aggregates of different particle sizes. The results showed that a 0.05–0.2% MEP application decreased soil available Cd by 53.8–71.62% and 23.49–36.71% in calcareous and acidic soils, respectively. The Cd immobilization efficiency of MEP in calcareous soil aggregates was in the following order: micro-aggregates (66.42–80.19%) > bulk soil (53.78–71.62%) > macro-aggregates (44.00–67.51%), while the efficiency in acidic soil aggregates was inconsistent. In MEP-treated calcareous soil, the percentage change in Cd speciation in micro-aggregates were higher than that in macro-aggregates, whereas there was no significant difference in Cd speciation between the four acidic soil aggregates. Mercapto-palygorskite addition in micro-aggregates of calcareous soil increased the available Fe and Mn concentrations by 20.98–47.10% and 17.98–32.66%, respectively. Mercapto-palygorskite had no effect on soil pH, EC, CEC, and DOC values, while the difference in soil properties between the four particle sizes was the main influencing factor of MEP treatments on Cd in calcareous soil. The effects of MEP on HMs varied across soil aggregates and soil types, but had strong specificity and selectivity for Cd immobilization. This study illustrates the influence of soil aggregates on Cd immobilization using MEP, which can be used to guide the remediation of Cd-contaminated calcareous and acidic soils.

The study of EDTA enhanced Cd accumulation and formation in Napier grass using synchrotron μX-ray fluorescence imaging and X-ray absorption spectroscopy

In this study, Pennisetum purpureum, a fast growing and highly tolerant plant, was used as a Cadmium (Cd) hyperaccumulator associated with Ethylenediaminetetraacetic acid (EDTA). It was found that P. purpureum's shoots and roots grown in the presence of EDTA accumulated significantly higher Cd than those grown in the absence of EDTA. Synchrotron μX-ray fluorescence imaging demonstrated the significant Cd accumulation in the internal tissues of root: endodermis, xylem and phloem, while at stem, it was found at the external tissues: epidermis and phloem. Synchrotron X-ray Absorption Spectroscopy was used to characterize the Cd speciation in plant cells. P. purpureum was discovered to accumulate Cd (II) form. In order to determine the possibilities of Cd bonding in chemical compounds, linear combination fitting of Cd K-edge XANES spectra was carried out. The EDTA-free condition as a control revealed mainly Cd–N/O bonding ligand, while the EDTA-treated condition mostly showed Cd–N/O and Cd–S bonding. The overall results suggested that EDTA is a potential substance to enhance the efficiency of Cd absorption in P. purpureum.

Endophytic Bacteria in Ricinus communis L.: Diversity of Bacterial Community, Plant−Growth Promoting Traits of the Isolates and Its Effect on Cu and Cd Speciation in Soil

Ricinus communis L. shows certain tolerance to and good accumulation ability with heavy metals. Endophytic bacteria−enhanced phytoremediation is an effective method to improve heavy metal extraction efficiency. Here, for better application of castor in phytoremediation, the Illumina high−throughput sequencing was carried out to reveal the endophytic bacterial community in the tissues of castor grown in two locations, and traditional microbial cultivation was used to isolate endophytic bacteria from castor. The dominant bacterial phyla were Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes and Acidobacteria, and Proteobacteria was absolutely dominate in all castor tissues. There were significant differences in the composition of endophytic bacterial communities between castor grown in two sites, with obvious variation in the relative abundance of the dominant phylum. The samples from two sites also had their own unique dominant bacterial genera. The analysis of alpha diversity illustrated that the diversity and species richness of endophytic bacteria community in different parts of castor sampled in Tonglushan mining area were lower than those in Gangxia village, Yangxin county. In total, there were 44 endophytic bacteria strains isolated from the tissues of castor, of which 42 strains possessed three or more growth−promoting properties. Most of these isolates were tolerant to Cu or Cd to varying degrees. Eight isolates were selected for further Cu mobilization and soil incubation experiments. Strains TR8, TR18, TR21, YL1, YS3 and YS5 could well solubilize Cu2(OH)2CO3 in medium. Strain YS3 had the best effect on increasing soil DTPA−Cu and DTPA−Cd contents by 8.4% and 6.9%, respectively. Inoculated endophytic isolates were conducive to the conversion of heavy metal forms from insoluble to relatively unstable, and could increase available phosphate content in soil (10.8–29.2%). Therefore, the plant growth−promoting endophytes screened from castor have great application prospects and can provide important support for the microbial−assisted phytoremediation of heavy metal−contaminated soil.