Bioavailability Of Cd Research Articles

Combined Application of Biochar and Calcium Superphosphate Can Effectively Immobilize Cadmium and Reduce Its Uptake by Cabbage

Biochar and phosphate fertilizer are commonly employed for the mitigation of soil cadmium (Cd) contamination. Nevertheless, there is a dearth of research regarding the mechanism behind their joint implementation. In this study, a combination of corn straw biochar (0 (C0), 5 (C5), and 10 (C10) g kg−1) and calcium superphosphate (0 (P0), 0.1 (P1), 0.2 (P2), 0.5 (P5), and 1.0 (P10) g kg−1) was applied in pot experiments, and the effects of the combined application on Cd bioavailability and its uptake by cabbage were investigated in Cd-contaminated soils. The results demonstrated that the combined treatment of applying biochar and Ca(H2PO2)2 yielded a significant decrease in the uptake of Cd by cabbage in alkaline soil, in contrast to the individual treatments of biochar or Ca(H2PO2)2. Compared to the CK treatment (C0P0), the Cd content in the shoots decreased by 46.26% and in the roots decreased by 24.81%, while the biomass of the cabbage demonstrated a noteworthy increase in C5P10 treatment. Compared to the CK treatment, the content of available phosphate (AP) in the soil increased by 17.57 mg kg−1, residual Cd increased by 22.02%, the exchangeable Cd decreased by 45.86%, and carbonate-bound Cd decreased by 20.55% in the C5P10 treatment. Therefore, it is advisable to use a combination of 5 g kg−1 biochar and 1 g kg−1 Ca(H2PO2)2 for the restoration of soil contaminated with Cd.

Differential effects of pH on cadmium accumulation in Artemisia argyi growing in low and moderately cadmium-contaminated paddy soils

BackgroundPhytoremediation is affected by physical and chemical properties of the soil such as soil pH, moisture, and nutrient content. Soil pH is a key element influencing Cd bioavailability and can be easily adjusted in agricultural practices. The soil pH level may relate to the effectiveness of phytoremediation; however, this has not been extensively investigated. In the current study, we evaluated the effect of Cd contamination level (0.56 and 0.92 mg/kg) and soil pH (5, 6, and 7) on Cd accumulation and allocation in Artemisia argyi, a fast-growing perennial crop.ResultsOur results indicated that higher soil Cd concentrations reduce A. argyi biomass, and the loss of the root mass was particularly significant. Higher soil pH decreased Cd content in stems and roots of A. argyi cultivated in moderately Cd-polluted soil, and increased Cd content in stems and roots of the plant grown in low Cd-polluted soil. Higher soil pH decreased the percentage of Cd distributed in the soluble fraction and cell walls and increased the percentage of Cd in the organelles of leaf cells for moderate soil Cd levels. The bioconcentration and translocation factor exceeded 4.0 and 1.0, respectively, across all tested treatments, indicating that A. argyi is a promising candidate for phytoremediation. Notably, the effects of soil pH on Cd accumulation and subcellular distribution in A. argyi differed between low and moderately Cd-contaminated soils.ConclusionAdjustments to soil pH based on the degree of Cd contamination can enhance Cd extraction by A. argyi, thereby reducing the overall remediation cycle of cadmium-polluted paddy fields of South China.Graphical

Bioaccumulation and health risks of chromium and cadmium in <em>Basella alba</em> with emphasis on Urea, muriate of potash and triple super phosphate mixtures

Basella alba is a commonly consumed green leafy vegetable in South Asian countries and it is considered as an economical source of essential vitamins and dietary fibers. Urea, muriate of potash (MOP) and triple super phosphate (TSP) mixture is the most commonly used inexpensive fertilizer mixture in the commercial cultivation of B. alba. This study was conducted to assess the effect of using a mixture of Urea-MOP-TSP on the bioaccumulation potential of cadmium (Cd) and chromium (Cr) by the leaves of B. alba. Pots treated with the Urea-MOP-TSP mixture and compost were maintained in a greenhouse with controlled light and temperature settings. The concentrations of Cd and Cr in the root zone soil, roots and leaves of B. alba were analyzed using an Atomic Absorption Spectrophotometer after acid digestion. The health risk of consuming B. alba was evaluated using the daily intake of metals, health risk index and cancer risk index. The results showed that Cd and Cr can bioaccumulate in the leaves of B. alba. The bioaccumulation potential of Cr was higher than that of Cd. Although the daily intake of Cd and Cr from B. alba were below the maximum values stipulated by the WHO, the cancer risk index indicated potential cancer risks based on Cd intake due to consumption of B. alba cultivated using the Urea-MOP-TSP mixture. Furthermore, the health risks associated with the hyper-accumulation of Cd and Cr in the edible parts of B. alba cultivated using compost were significantly less compared to that of the plants treated with the Urea-MOP-TSP mixture. Therefore, if B. alba is cultivated using chemical fertilizer, it is recommended to regularly monitor the concentrations of Cd and Cr in the cultivation soil, chemical fertilizer and in the edible parts of B. alba to prevent the excessive buildup of Cd and Cr along the food chain. In addition, it is recommended to identify the potential microbial assemblages that can be inoculated to the cultivation soil to reduce the bioavailability of Cd and Cr.

Calcium oxide nanoparticles ameliorate cadmium toxicity in alfalfa seedlings by depriving its bioaccumulation, enhancing photosystem II functionality and antioxidant gene expression

Cadmium (Cd) is a highly toxic and carcinogenic pollutant that poses significant risks to living organisms and the environment, as it is absorbed by the plant roots and accumulates in different parts of crop during its production. A promising sustainable strategy to counteract these threats to use calcium oxide nanoparticles (CaO-NPs) as soil supplements in fodder crops. This approach has shown notable morpho-physiological and biochemical improvements under metal toxicity conditions. However, the specific mechanisms driving Cd tolerance, particularly at physio-biochemical level and antioxidant related genes expression in fodder crops including alfalfa remain unexplored. CaO-NPs supplementation can trigger various signaling pathways that lead to enhance the photosynthetic pigments formation, stomatal conductance, CO2 assimilation rate and quantum yield of photosystem II. In this study, we evaluated various doses of CaO-NPs (0, 25, 50, and 100 mg kg−1) for their efficacy in reducing Cd bioavailability and toxicity in alfalfa plants. Our results demonstrated that Ca2+ and Cd2+, which share the same ionic radius, compete for ion transport through channels. The small size and high availability of CaO-NPs facilitate their rapid translocation within plant tissues, reducing metal uptake by 61 % in shoots and 30 % in roots. Notably, application of CaO-NPs at 100 mg kg−1 significantly increased shoot length (44 %) and root lengths (35 %) as compared to Cd-treated control plants. The highest dose of CaO-NPs also improved photosynthetic efficiency and gas exchange attributes including (gs, Tr, Pn and Ci) by 66 %, 27 %, 33 % and Ci 21 %, respectively, compared with the Cd treated control. Moreover, CaO-NPs (at 100 mg kg−1) alleviated metal-induced oxidative stress by boosting antioxidant enzyme activity like SOD (25 %) POD (42 %), CAT (72 %) and APX (87 %) and diminishing reactive oxygen species (ROS) production when compared with sole Cd treatment. Scanning and transmission electron microscopy revealed that CaO-NPs positively impacted stomatal conductance and mitigated Cd toxicity in leaf ultrastructure. Additionally, the highest dose of CaO-NPs markedly upregulated the expression of antioxidant-related genes, MsCu/Zn SOD, MtPOD, MtCAT, and MtAPX in roots and shoots by 0.67 and 1.03 fold-change (FC), 0.61 and 0.53 FC, 0.54 and 0.88 FC, and 0.46 and 0.66 FC, respectively. In conclusion, CaO-NPs demonstrate significant potential for environmentally friendly mitigation of Cd stress in alfalfa by reducing its uptake, thereby supporting sustainable agriculture.

Cadmium immobilization by mercapto-palygorskite in alkaline soil: Impacts on soil microbial communities and wheat rhizosphere metabolism

Weakly alkaline cadmium (Cd) contaminated soil in China has aroused great concern regarding its impact on food security and human health. Mercapto-modified palygorskite (MP) has exhibited good potential to minimize Cd accumulation in wheat, it is imperative to understand the underlying mechanisms within the soil-wheat-microbial system for sustainable development of agrochemicals. This study evaluated the effects of various MP dosages on soil Cd bioavailability, rhizosphere metabolomics, microbial community structure and wheat growth. The results indicated that MP (0.05–0.2 %) application significantly reduced Cd accumulation in wheat grains by 59.0–83.2 % (p < 0.05) and inhibited Cd translocation from root to grain. MP also promoted Mn oxide formation and redistributed the exchangeable Cd to Fe–Mn oxide-bound forms (44.2–109.6 %), thus lowering soil Cd bioavailability by 17.9–32.5 %. Additionally, MP reduced wheat rhizosphere organic acid levels, altered rhizosphere carbon and nitrogen pools, and stimulated the growth of Cd-tolerant Alternaria and Cladosporium, while inhibiting the growth of Fusarium. These findings highlight the potential of MP to modulate soil rhizosphere metabolism and microbial communities, offering a novel perspective on its environmental implications and supporting agrochemical sustainability.

The Combination of Biochar and Phosphorus-Containing Materials Can Effectively Enhance the Remediation Capacity of Amaranth on Cadmium-Contaminated Soil and Improve the Structure of Microbial Communities

Cadmium (Cd) pollution in soil has become a huge problem for agricultural production in China and even the world. Passivation and phytoremediation are two important remediation technologies for Cd pollution. In this study, the cadmium-contaminated and phosphorus-poor farmland soil around a mining area in Huainan was taken as the research object, and the remediation effect of biochar and phosphorus-containing materials on soil cadmium pollution was discussed. The results showed that the combined application of biochar and phosphorus-containing materials significantly reduced the pH of non-rhizosphere soil and rhizosphere soil, and increased the content of soil dissolved organic carbon (DOC). The combined application of biochar and phosphorus-containing materials significantly reduced soil pore water Cd and soil available Cd. In addition, both a single application of biochar and synergistic application of biochar and phosphorus-containing materials significantly increased the biomass of aboveground and underground parts of amaranth and soil urease and catalase activities. Phosphorus application reduced the bioavailability of Cd in soil. With the increase in phosphorus application, the content of available Cd in soil decreased significantly, and there was a certain negative correlation between Cd content and phosphorus content in plants. The abundance of beneficial microorganisms such as Ochrobactrum, Anaerolinea, Achromobacter, and Cellvibrio in soil was significantly increased after the synergistic application of biochar and phosphorus-containing materials.

Reclamation of co-pyrolyzed dredging sediment as soil cadmium and arsenic immobilization material: Immobilization efficiency, application safety, and underlying mechanisms

The safe management of toxic metal-polluted dredging sediment (DS) is imperative owing to its potential secondary hazards. Herein, the co-pyrolysis product (DS@BC) of polluted DS was creatively applied to immobilize soil Cd and As to achieve DS resource utilization, and the efficiency, safety, and mechanism were investigated. The results revealed that the DS@BC was more effective at reducing soil Cd bioavailability than the DS was (58.9–73.2% vs. 21.8–27.4%), except for the dilution effect, whereas the opposite phenomenon occurred for soil As (25.5–35.7% vs. 35.7–42.8%). The DS@BC immobilization efficiency was dose-dependent for both Cd and As. Soil labile Cd and As were transformed to more stable fractions after DS@BC immobilization. DS@BC immobilization inhibited the transfer of soil Cd and As to Brassica chinensis L. and did not cause excessive accumulation of other toxic metals in the plants. The appropriate addition of the DS@BC (8%) sufficiently alleviated the oxidative stress response of the plants and enhanced their growth. These findings indicate that the DS@BC was safe and effective for soil Cd and As immobilization. DS@BC immobilization decreased the diversity and richness of the rhizosphere soil bacterial community because of the dilution effect. The DS@BC immobilized soil Cd and As via direct adsorption, and indirect increasing soil pH, and regulating the abundance of specific beneficial bacteria (e.g., Bacillus). Therefore, the use of co-pyrolyzed DS as a soil Cd and As immobilization material is a promising resource utilization method for DS. Notably, to verify the long-term effects and safety of DS@BC immobilization, field trials should be conducted to explore the effectiveness and risk of harmful metal release from DS@BC immobilization under real-world conditions.

The effect of biochar amendment on Cd accumulation in Bidens pilosa L: Changing Cd subcellular distribution, cell wall polysaccharide Cd-binding capacity and composition

Biochar can reduce Cd uptake by plants, thereby reducing its biotoxicity, but the mechanisms involved at the subcellular level have not been thoroughly elucidated. In this work, we explored the effect of maize straw biochar on Cd accumulation by Bidens pilosa L. and its mechanism at subcellular levels. After 90 days of potting experiment, the subcellular fractions were extracted by differential centrifugation, and the polysaccharide fractions of root cell walls were extracted by leaching centrifugation, and then the Cd content of each fraction was determined. Results showed that Cd was preferentially distributed in cell walls of three organs. Additionally, biochar addition resulted in a greater distribution of Cd from cell wall to soluble fractions and organelles in stems. These results suggested that cell wall immobilization and intracellular compartmentalization were critical detoxification mechanisms tackling Cd stress with biochar addition of Bidens pilosa L. Pectin was the main sink where Cd was stored. And galacturonic acid content in pectin occupied the highest ratio among the three polysaccharide fractions. After biochar addition, in hemicellulose the change of Cd content was consistent with the change of galacturonic acid content. These results suggested that the galacturonic acid in hemicellulose played an important role in Cd binding. Biochar addition reduced the bioavailability of soil Cd and improved the growth environment, thus inducing Bidens pilosa L. to change the composition of root cell wall in response to Cd stress.

A biochar-based amendment improved cadmium (Cd) immobilization, reduced its bioaccumulation, and increased rice yield

Cadmium (Cd) contamination of soil threatens human health, food security, and ecosystem sustainability. The in situ stabilization of Cd has been recognized as a potentially economical technology for the remediation of Cd-contaminated soil. Recently, biochar (BC) and activated carbon (AC) have received widespread attention as eco-friendly soil amendments that are more beneficial for plant growth, soil health, and remediation of contaminated soil. An experiment was performed in a paddy field to investigate the effects of two different types of BC (maize straw biochar and bamboo biochar) and AC (coconut shell activated carbon) in combination with rape organic fertilizer (R), calcium magnesium phosphate fertilizer (P), and fulvic acid (F), respectively, on soil Cd immobilization, Cd accumulation in rice, and yield. The results indicated that the BC/AC-based amendments reduced soil bioavailable Cd (DTPA-Cd) and brown rice Cd by 9.58%–27.06% and 19.30%–71.77%, respectively. The transformation of exchangeable Cd (Ex-Cd) to carbonate-bound Cd (Ca-Cd), Fe-Mn oxide bond (Ox-Cd), and residual (Re-Cd) in soil accounted for the mitigation of Cd uptake and enrichment by rice. Additionally, BC-/AC-based amendments altered soil physicochemical properties, which significantly increased the soil pH and cation exchange capacity (CEC), total nitrogen (TN), total phosphorus (TP), soil organic carbon (SOC), and dissolved organic carbon (DOC), directly promoting soil health. All BC-/AC-based amendments significantly increased FeIMP and MnIMP concentrations by 47.31%–160.34% and 25.72%–73.09% in the Fe/Mn plaque (IMP), respectively. Maize straw and bamboo biochar-based amendments significantly increased rice yield by 10.46%–20.41% and 9.94%–16.17%, respectively, while coconut shell-activated carbon severely reduced rice yield by 65.06%–77.14%. The correlation analysis revealed that leaf Cd and IMP primarily controlled Cd uptake by rice, and soil pH, Eh, CEC, SOC, IMP, and TP influenced DTPA-Cd in soil. This field study demonstrated that maize straw and bamboo biochar-based amendments not only reduced soil DTPA-Cd in paddy fields but also decreased the accumulation of Cd in brown rice, as well as improved rice yield, which has potential application in Cd-contaminated agriculture fields. Coconut shell-activated carbon severely decreased rice yields, which is not appropriate for rice production.

Synergistic Release of Cd(II) and As(V) from Ternary Sorption Systems Containing Ferrihydrite Nanoparticles: The Role of Binary and Ternary Surface Complexes

Cadmium (Cd) and arsenic (As) generally exhibit mutually beneficial co-sorption behavior on iron oxyhydroxides through multiple mechanisms, including surface precipitation, ternary surface complexes, and electrostatic interactions. However, the numerous factors that control the immobilization of Cd and As in turn complicated the processes and mechanisms involved in their co-desorption from iron minerals, which hindered the full understanding of their geochemical behaviors. Here, the simultaneous release of Cd(II) and As(V) from newly precipitated ferrihydrite nanoparticles by either Ca or P was investigated through kinetics and isothermal desorption experiments. We showed that the Cd(II) and As(V) present two-phase desorption processes (rapid desorption and slow desorption) in both binary (Fe-Cd or Fe-As alone) and ternary systems (Fe-Cd-As co-presence). Compared to their binary counterparts, Cd(II) and As(V) in the ternary systems are more prone to detachment from ferrihydrite. Further desorption of Cd(II) and As(V) at different co-presence scenarios (different initial concentrations) demonstrated mutual promotion behaviour towards their counterparts; the co-presence of Cd(II) facilitates the desorption of As(V), while the co-presence of As(V) also promotes the desorption of Cd(II). XPS and FTIR results demonstrated that either Ca or P showed minor effects on the binding environment of Cd and As. Further results from the in-situ ATR-FTIR experiment and second derivative peak fitting analysis indicate that the enhanced detachment of Cd(II) and As(V) from the ternary system may be due to the synergistic desorption of the ternary surface complexes and other surface complex species. Our results provide new insights into the prediction of the environmental behaviour of the coexistence of Cd(II) and As(V) in iron-rich geological settings. The potential environmental risks of iron-based remediation methods should be considered due to the enhanced bioavailability of Cd(II) and As(V) in co-presence circumstances.

Integrating rhizosphere bacterial structure and metabolites with soil Cd availability in different parent paddy soils

Soil bacterial community structure and rhizosphere metabolites are important pathways for rice to respond to external Cd stress. The specific correlations between these microorganisms, metabolites and inherent soil properties, as well as the mechanisms they utilize to regulate Cd availability across different parent soils remain underexplored, emphasizing the need for deeper understanding to inform effective soil management strategies. In this study, five typical parent soils with large differences in properties (quaternary red clay soil (hereby defined as Q), granite soil (G), river sandy mud (R), yellow mud soil (Y), stucco field (S)) in Chinese paddy soils were collected, and extra Cd were added (CK: 0 mg·kg−1, Cd: 2.4 mg·kg−1).The result indicated that the toxicity impact of Cd in rice grains in G was the weakest, and the highest Cd bioavailability in S. The abundance of Proteobacteria, Bacteroidota and Firmicutes showed an increasing trend in G, while they decreased significantly in S. The contents of Cis-9-palmitoleic acid and phosphoethanolamine increased by 170.02 % and 154.03 % in G, decreased by 218.62 % and 181.58 % in S. MBNT15 and Desulfobacterota showed a significant negative correlation with humic acid molecular weight (MW) extracted from parent soils and Clay (montmorillonite, illite, kaolinite) contents, while they exhibited a positive correlation with soil organic matter (OM) content (P < 0.01). The MW played a crucial role in shaping rhizosphere metabolites with R2 value of 0.8498. These results elucidate how soil bacterial communities, rhizosphere metabolites, and inherent soil properties interact to regulate Cd availability across different parent soils.

Screening nitrogen-fixing cyanobacteria that can alleviate cadmium toxicity to rice and reduce cadmium accumulation in brown rice

Among food crops, rice is the most serious food crop contaminated with cadmium (Cd). It is critical to reduce Cd bioavailability in the soil and prevent its accumulation in brown rice. The use of microorganisms to lessen Cd toxicity in rice has been the subject of numerous studies carried out in recent years. The nitrogen-fixing cyanobacterium (NFC) is a potent biofertilizer and heavy metal biosorbent. However, there is a dearth of research on the impact of NFC supplementation on rice's susceptibility to Cd poisoning. This study screened for Cd-tolerant NFCs and assessed how well they might promote growth and lower the amount of Cd in rice. Four NFCs with tolerance to 1 mg L−1 Cd were selected from ten NFCs. The results of seedling experiment showed that SCAU-10 treatment increased plant height and biomass while reducing Cd levels in seedlings by 62.0 %. The pot experiment also demonstrated that SCAU-10 was effective in lowering Cd content in brown rice by 85.3 %. Reducing the bioavailability of soil Cd, shielding rice roots, preventing Cd transfer from below to above ground, generating phytohormones, and enhancing the photochemical electron quantum yield of rice leaves are a few possible action mechanisms of the NFC. It indicates that Trichormus sp. SCAU-10 has a great deal of promise for use as a biofertilizer in the safe management of Cd-contaminated rice fields. This is the first report on using Trichormus sp. biofertilizer for relieving the toxicity of Cd to rice and reducing Cd accumulation in brown rice.

In-situ induced formation of Fe-OM association in soil: Theory and practice of remediation of cadmium contaminated paddy fields in high cadmium geological background areas

Cadmium (Cd) pollution in rice paddies, attributable to high geological Cd backgrounds, has emerged as a global concern. This study leverages the passivation mechanism of bioavailable Cd by iron-organic matter associations (Fe-OM) to explore a novel strategy for Cd immobilization. We examined the adsorptive capacity and removal efficiency of Cd by laccase-mediated Fe-OM association and assessed their natural stability using 57Fe isotopic tracing. Additionally, we conducted in-situ remediation trials in a Cd-enriched paddy soil. Our results indicate that the theoretical maximum adsorption capacity for Cd by the laccase-mediated Fe-OM is 100.0 mg/g, which is a 15% improvement over the common Fe-OM and a 150% enhancement over inorganic iron oxides (ferrihydrite). The 57Fe isotope tracing test showed that the affinity of laccase-modified organic matter for iron increased by 55.6%, and it exhibited better stability than common Fe-OM under anaerobic conditions. The field-scale remediation, predicated on the in situ synthesis of Fe-OM association, effectively reduced the bioavailable Cd concentration in the soil from 0.91 mg/kg to 0.40 mg/kg. Concurrently, the Cd concentration in rice grains was lowered from 0.63 mg/kg to 0.15 mg/kg, thus falling beneath the national safety threshold. This study represents a significant advancement in the safe reclamation and utilization of agricultural soils with elevated geological Cd burdens.

Combined toxicity of multiwall carbon nanotubes and cadmium on rice (Oryza sativa L.) growth in soil

The comprehensive effects of nanoparticles and coexisting heavy metals on plant growth are still unclear, especially in soil medium. The single and combined effects of multiwall carbon nanotubes (MWCNTs) and cadmium (Cd) on rice (Oryza sativa L.) growth were examined in this study through a 4 months pot experiment in 2022. Rice plants were exposed to different concentrations of MWCNTs (100 and 500 mg kg−1) in the presence of 5.0 mg kg−1 Cd stress. At the tillering stage, the 500 mg kg−1 MWCNTs addition reduced plant height by 8.0% and increased soluble protein content in the leaves by 13.7%, demonstrating that a single MWCNTs had a slight negative impact on rice growth. When exposed to Cd stress, the inclusion of 500 mg kg−1 MWCNTs led to a 6.7%–9.0% decrease in bioavailable Cd level in soil, resulting in considerable reductions in Cd content in roots (23.4%–29.9%), shoots (24.5%–28.3%) and grains (28.3%–66.2%). Compared to the single Cd treatment, the O. sativa L. leaves treated with Cd and MWCNTs (500 mg kg−1) had considerably reduced levels of malondialdehyde (MDA), soluble protein, and activities of antioxidant enzymes (POD, CAT, and SOD). The findings of this study indicated that appropriate concentrations of MWCNTs application in soil could alleviate Cd-induced toxicity on rice growth.

Bioassessment of Cd and Pb at Multiple Growth Stages of Wheat Grown in Texturally Different Soils Using Diffusive Gradients in Thin Films and Traditional Extractants: A Comparative Study.

The bioavailability of heavy metals in soil is a crucial factor in determining their potential uptake by plants and their subsequent entry into the food chain. Various methods, including traditional chemical extractants and the diffusive gradients in thin films (DGT) technique, are employed to assess this bioavailability. The bioavailability of heavy metals, particularly cadmium (Cd) and lead (Pb), is also influenced by soil texture and their concentrations in the soil solution. The primary objectives of this experiment were to compare and correlate the assessment of the Cd and Pb bioavailability using the DGT technique and traditional extractants across two soil textural classes: sandy clay loam (SCL) and clay loam (CL) at two contamination levels: aged contaminated (NC) and artificially contaminated (AC). The specific objectives included assessing the bioavailability of Cd and Pb at different growth stages of the wheat plant and correlating the DGT-based bioassessments of Cd and Pb with their concentrations in various plant parts at different growth stages. This study also compared the effectiveness of the DGT method and traditional extraction techniques in assessing the bioavailable fractions of Cd and Pb in soil. The regression analysis demonstrated strong positive correlations between the DGT method and various extraction methods. The results showed that the wheat plants grown in the AC soils exhibited lower root, shoot, and grain weights compared to those grown in the NC soils, indicating that metal contamination negatively impacts plant performance. The concentrations of Cd and Pb in the wheat tissues varied across different growth stages, with the highest levels observed during the grain filling (S3) and maturity (S4) stages. It is concluded that the in situ assessment of Cd and Pb though DGT was strongly and positively correlated with the Cd and Pb concentration in wheat plant parts at the maturity stage. A correlation and regression analysis of the DGT assessment and traditional extractants showed that the DGT method provides a reliable tool for assessing the bioavailability of Cd and Pb in soils and helped in developing sustainable soil management strategies to ensure the safety of agricultural products for human consumption.

Milk vetch returning combined with lime materials alleviates soil cadmium contamination and improves rice quality in soil-rice system

Milk vetch (Astragalus sinicus L.) returning and lime materials is employed as an effective strategy for remediating cadmium (Cd)-contaminated paddy fields. However, the combined effects of them on alleviating Cd pollution and the underlying mechanisms remain poorly explored. Therefore, this study investigated the impact of these combined treatments on soil properties, iron oxides, iron plaque, mineral elements, and amino acids through a field experiment. The following treatments were employed: lime (LM), limestone (LS), milk vetch (MV), MV + LM (MVLM), and MV + LS (MVLS), and a control (CK) group with no materials. Results demonstrated that treatments significantly decreased soil available Cd by 19.40–32.55 %, 10.20–39.58 %, and 25.36–40.66 % at tillering, filling, and maturing stages compared to CK, respectively. Moreover, exchangeable Cd was transformed into more stable fractions. Compared with individual treatments, MVLM and MVLS treatments further decreased available Cd and exchangeable Cd. Overall, Cd in brown rice was reduced by 18.97–77.39 % compared with CK. And the Cd in iron plaque decreased by 14.12–31.14 %, 24.65–61.60 %, 2.6–38.28 % across three stages. Furthermore, soil pH, dissolved organic carbon, and cation exchange capacity increased, along with 0.22–62.09 % and 0.57–10.66 % increases in free and amorphous iron oxide contents at all stages, respectively. Compared with lime alone, the integration of MV returning facilitated increased formation of Fed, Feo and enhanced the antagonistic effect among grain Ca with Cd; Additionally, it increased AAs in brown rice, improving rice quality and potentially reducing Cd transport. Mantel tests and Partial least squares path modeling revealed a significant positive correlation between Cd in IP and rice Cd uptake and a significant negative correlation between available Cd, Fed and Feo. These findings provide valuable insights into the mechanisms involved in mitigating soil Cd bioavailability using integrated approaches with MV returning and lime materials.

Effects of freeze-thaw leaching on physicochemical properties and cadmium transformation in cadmium contaminated soil

This study aims to investigate the effect of the combined method of freeze–thaw and leaching on the removal of cadmium (Cd) in soil and to provide a theoretical basis for the remediation of farmland soil polluted by heavy metals. The removal process and mechanism of Cd were deduced through oscillatory leaching experiments and freeze–thaw leaching simulation experiments, and the influence of the freeze–thaw leaching technology on the soil environment was evaluated. The results of oscillatory leaching showed that a mixture consisting of 0.80 mol/L citric acid and 0.80 mol/L ferric chloride in a 1:19 vol ratio effectively remove 47.75 % of Cd, indicating that the composite leaching agent could effectively remove Cd from the soil. The results of the freeze–thaw leaching simulation experiment showed that although the freeze–thaw leaching treatment increased the total Cd content in the 0–5 cm soil layer, the total Cd content in the 5–10 cm, 10–15 cm, and 15–20 cm soil layers decreased by 5.08 %, 2.39 %, and 5.68 %, respectively. The freeze–thaw leaching increased the content of exchangeable Cd (p<0.05), carbonate bound Cd, but decreased organic bound Cd and residual Cd (p<0.05), thereby increasing the bioavailability of Cd. Freeze–thaw leaching not only increased the competitive adsorption of Cd2+ by decreasing soil pH, cation exchange capacity, and increasing the content of exchangeable calcium and exchangeable magnesium, thus reducing the adsorption of Cd in soil. And the results of XPS and FTIR similarly showed that the freeze–thaw leaching could promote the chelation between Cd2+ and hydroxyl, carboxyl and carbonyl functional groups. Although the freeze–thaw leaching destroyed the large particle structure (0.05–2 mm) and large pores in the soil, and increased the clay content (<0.002 mm) and the proportion of small pores in the soil, the XRD results showed that freeze–thaw leaching had no significant effect on the minerals in the soil. In summary, this study shows that freeze–thaw leaching has a significant effect on the removal of soil heavy metals, suggesting that the synergistic effect of freeze-thaw and leaching should be considered in the process of removing soil pollutants in seasonal freeze–thaw zones, and that this method provides a new insight into the remediation of contaminated soils.

Impact assessment of Zeolite, Ca-bentonite and Biochar amendments on Cd bioavailability and fractions in polluted calcareous soils

The refining of polluted soils by heavy elements is one of the most important environmental policies in industrialized and developing countries. Using adsorbents is a suitable procedure for the immobilization of heavy metals in polluted soils. This study aimed to assess the immobilization of Cadmium (Cd) in polluted calcareous soil affected by the application of organic and inorganic amendments including Biochar (from grape pruning residues) and natural Zeolite and their interaction under wheat cultivation. The treatments used in this study were two amendments of Zeolite and Biochar (from grape pruning wastes) at three levels (0, 1, and 4%) and three levels of Cd contamination (0, 75, and 150 mg/kg soil). A 16-week incubation period was considered for the homogenization of the amendments in soil and wheat was grown according to the standards procedure. At the end of incubation, different fractions of Cd including residual, exchangeable, bonded to organic matter, bonded to carbonate and bonded to iron and manganese. Also available Cd by DTPA and EDTA methods and 1000-grain weight of wheat were measured. The results showed that the highest amount of Cd bound to organic matter was obtained in 4% Biochar treatment to 15 mg/kg. The highest and lowest amounts of Cd extracted with DTPA were obtained in the control one (92 mg/kg) and the level of 4% Biochar (67 mg/kg), respectively. The results showed that increasing the amount of Biochar and Zeolite amendments increased the weight of 1000 grains of wheat in all treatments. According to the results of the study, the use of Biochar and Zeolite reduced the amount of Cd extracted by DTPA ( 82.436 mg/kg) and EDTA (115.605 mg/kg). Finally, the results showed that the use of Biochar and Zeolite has reduced active Cd and its mobility in the soil due to increasing organic and carbonate fractions. Combining biochar and zeolite in soil remediation efforts can enhance their effectiveness in reducing the concentration and mobility of active Cd. The biochar provides a stable carbon matrix for long-term immobilization of Cd, while the zeolite offers additional adsorption capacity and ion-exchange capabilities. This synergistic effect can lead to improved soil quality and reduced environmental risks associated with Cd contamination.

Spatial patterns and mechanism of the impact of soil salinity on potentially toxic elements in coastal areas

Soil salinization and heavy metal pollution in the Yellow River Delta region have elicited increasing concern. Therefore, revealing the underlying mechanism of the impact of soil salinity on potential toxic elements (PTEs) is crucial for environmental protection and the rational utilization of resources in this area. In this study, we employed CatBoost–SHAP and multiscale geographically weighted regression (MGWR) models to comprehensively investigate the spatial effects of soil electrical conductivity (EC1:5) on PTEs. Additionally, we employed a space–for–time substitution strategy with the aim of investigating how increasing soil salinity, represented by EC1:5, K+, Na+, Ca2+, and Mg2+, affects the bioavailability of PTEs over time. The primary findings are as follows: (1) for most PTEs, the influence of soil EC1:5 on the bioavailable forms of these elements surpassed its impact on their total concentrations. (2) The results of the MGWR model indicated that exchangeable Ca (aCa) in the soils of the eastern coastal areas markedly increased the bioavailable Cd (aCd), bioavailable Cu (aCu), and bioavailable Zn (aZn). (3) When the soil EC1:5 ranges between 2 and 6 dS/m, exchangeable Na (aNa) primarily competed for the adsorption sites of bioavailable Pb (aPb). However, as the soil EC1:5 increases to 6–10 dS/m, exchangeable Mg (aMg) and aCa became the primary competing ions, with aMg playing a more significant role than aCa. These findings provide valuable theoretical insights and practical guidance for saline-alkali soil improvement and PTEs pollution control in the Yellow River Delta region, thereby providing a foundation for sustainable environmental management and resource utilization.

Asynchronous Synergetic Remediation Strategy for Cd-Contaminated Soil via Passivation and Phytoremediation Technology

Cadmium (Cd) contamination in soil has emerged as a significant challenge for agricultural production. Phytoremediation and passivation are key techniques for remediating Cd-contaminated soil. However, few studies have focused on the synergistic effects of these two techniques. In this work, the effectiveness of synergetic remediation strategies, both synchronous and asynchronous, utilizing passivation and phytoremediation techniques, was explored. The results of pot experiments and field experiments indicated that optimal remediation effects were obtained by asynchronous synergetic remediation, removing over 80% of bioavailable Cd within 14 days. Mechanistic studies conducted using XPS analysis, soil property analysis, and microbial diversity analysis confirmed that the chelation effect of SDD and soil pH value are the primary factors contributing to the effectiveness of both remediation strategies. In contrast, the variations in microbial populations are identified as the crucial factors influencing the varying outcomes of the two sequential remediation approaches. This research demonstrates that asynchronous synergistic remediation is a promising strategy for mitigating Cd contamination in soil.