Reduction of Cd accumulation in pak choi (Brassica chinensis L.) in consecutive growing seasons using mercapto-grafted palygorskite

Removal of Cd from solution and in-situ remediation of Cd-contaminated soil by a mercapto-modified cellulose/bentonite intercalated nanocomposite

A novel intercalated nanocomposite of mercapto-modified cellulose/bentonite (LCS-BE-SH) was synthesized by high-speed shearing method in one step at room temperature, and was applied to remove Cd from solution and remediate Cd-contaminated soil. Results revealed that cellulose long-chain molecules have intercalated into bentonite nanolayers and interlayer spacing was increased to 1.411 nm, and grafting -SH groups improved adsorption selectivity, which enabled LCS-BE-SH to have distinct capability of Cd adsorption (qmax = 147.21 mg/g). Kinetic and thermodynamics showed that Cd adsorption onto LCS-BE-SH was well fitted by pseudo-second-order and Langmuir adsorption isotherm. Characterizations of the adsorbents revealed that synergistic effect of complexation (e.g., CdS, CdO) and precipitation (e.g., Cd(OH)2, CdCO3) mechanism played a major role in Cd removal. In soil remediation, application of LCS-BE-SH was most effective (67.31 %) in Cd immobilization compared to the control (8.85 %), which reduced exchangeable Cd from 37.03 % to 11.44 %. Meanwhile, soil pH, soil organic matter, available phosphorus, and enzyme activities (catalase, urease, and dehydrogenase) were improved LCS-BE-SH treatment. The main immobilization mechanism in soil included complexation (e.g., CdS, CdO) and precipitation (e.g., Cd(OH)2, Cd-Fe-hydroxide). Overall, this work applied a promising approach for Cd removal in aqueous and Cd remediation in soil by using an effective eco-friendly LCS-BE-SH nanocomposites.

Transcriptome and ultrastructural analysis revealed the mechanism of Mercapto-palygorskite on reducing Cd content in wheat

Large areas of crop yields in northern China have faced with cadmium (Cd) contamination problems. Mercapto-modified palygorskite (MP), as a highly efficient immobilization material, could reduce Cd absorption in wheat and alleviate its biotoxicity. However, the molecular mechanism underlying MP-mediated Cd reduction and detoxification processes in wheat is not well understood. This aim of this study was to investigate the biochemical and molecular mechanisms underlying the reduction in Cd accumulation in wheat (Triticum aestivum L.). The results showed that MP application decreased the Cd concentration by 68.91-74.32% (root) and 70.68-77.2% (shoot), and significantly increased the glutathione (GSH) and phytochelatins (PCs) contents in root and shoot. In addition, with the application of MP, the percentage of Cd in the cell walls and organelles of wheat decreased, while that of Cd in soluble components was increased. The content of Cd in all components was significantly reduced. Ultrastructural analysis revealed that MP thickened the cell wall, promoted vesicle formation in the membrane and protected the integrity of intracellular organelles in wheat. Transcriptome analysis further confirmed the above results. MP upregulated the expression of several genes (CCR, CAD COMT and SUS) involved in cell wall component biosynthesis and promoted vesicle formation on cell membranes by upregulating the expression of PLC and IPMK genes. In addition, genes related to antioxidant synthesis (PGD, glnA and GSS) and photosynthesis (Lhca, Lhcb) were altered by MP to alleviate Cd toxicity in wheat. This present work will help to more thoroughly elucidate the molecular mechanism by which wheat defends against Cd contamination under MP application and provide and important research basis for the application of this material in the future.

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.

Effects of mercapto-palygorskite application on cadmium accumulation of soil aggregates at different depths in Cd-contaminated alkaline farmland

Mercapto-palygorskite (MP) is a novel immobilization material for cadmium (Cd) pollution, but the immobilization mechanism on alkaline Cd contaminated soil is not completely clear. In this paper, field experiment was carried out to study the effect of MP on the transfer of Cd in aggregates at different depth, the contribution of soil aggregates to the reduction of Cd in bulk soil and the immobilization mechanism of MP. The results showed that MP had no significant influence on the total Cd content, soil aggregates distribution, pH value, CEC value and enzyme activities no matter at any depth. At the depth of 0-20 cm, MP significantly reduced the DTPA-Cd in bulk soil by 60.7%, and increased the GWD and R_0.25 value. Similarly, the content of DTPA-Cd in the soil aggregates was deceased by 40.2-63.6%, the OM, DOC, available Fe, Mn and S in soil aggregates were significantly increased by 15.0-19.1%, 19.2-41.7%, 24.7-41.2% and 12.5-35.1% respectively. The Cd fraction of aggregates, especially exchangeable Cd (EXE-Cd) and bound to Fe/Mn oxide Cd (OX-Cd), was reduced by 5.4-28.1% and increased by 22.3-50.4%. In addition, MP had different effects on the GSF value of soil aggregates, but there was a downward trend for AF_X value at 0-20 cm soil depth. MP almost had no significant influence on the above indexes at the depth of 20-40 cm and 40-60 cm, but except the Cd fraction, the GSF and AF_X value in individual aggregates. Small aggregates (<1 mm) and large aggregates (>1 mm) contributed 59.1% and 22% to the reduction of Cd in bulk soil. Partial Least Structural Equation Model (PL-SEM) revealed that S promoted the production of available Fe, Mn, OM and DOC, while the content of DOC inhibited the formation of EXE-Cd and the available Fe and Mn boosted the production of OX-Cd.

Amine- and thiol-bifunctionalized mesoporous silica material for immobilization of Pb and Cd: Characterization, efficiency, and mechanism

In this study, a two-step functionalizing strategy by combining co-condensation with grafting procedures was employed to synthesize well-ordered Amino- and Thiol-Bifunctionalized SBA-15 (ATBS) mesoporous silica. Its physicochemical properties, performance, and mechanisms in immobilization of toxic metals Pb and Cd in water and soil were investigated. After bi-functionalization, X-ray diffractometer, transmission electron microscope, and N₂ adsorption-desorption measurements confirmed that the ATBS maintained a highly-ordered mesoporous structure, large surface area and pore volume. The elemental analysis, Fourier transform infrared spectroscopy and X-ray Photoelectron Spectroscopy (XPS) evidenced the successful incorporation of amine and thiol groups into ATBS. These structure and functional characteristics of ATBS benefited Pb and Cd sorption. Sorption isotherms of Pb and Cd were better fit with Sips and Redlich-Peterson models. Sorption kinetics suggested that Pb sorption was mainly regulated by chemical reactions, whereas both diffusion process and chemical reactions were rate-regulating steps in Cd sorption. ATBS showed the maximum sorption capacities for Pb and Cd at 120 and 38 mg g^-1, respectively. The sorption mechanisms revealed by XPS measurements suggested that Cd sorption was mainly attributed to thiol groups while Pb was efficiently bond to both thiol and amino groups. High and stable sorption efficiencies were attained in the pH range of 4-6, with a higher affinity towards Pb than Cd. Furthermore, its ability to immobilize Pb and Cd in soils was examined with an incubation experiment, which showed that ATBS reduced 30-56% of MgCl₂-extractable Pb and Cd in a contaminated soil. The synthesized sorbent via the two-step functionalizing strategy shows high sorption efficiency towards Pb and Cd, and thus it has potential application in remediating Pb and Cd contaminated water and soils.

Remediation of heavy metal-polluted alkaline vegetable soil using mercapto-grafted palygorskite: effects of field-scale application and soil environmental quality

Remediation materials are the most critical factors for in situ immobilization of soil contaminated by heavy metals. In this study, in order to improve the performance of palygorskite (Pal), a new remediation material, mercapto-grafted palygorskite (MPal) was synthesized by grafting mercapto groups onto the surface of Pal. The results of field application in northern China showed that at a dosage of 0.12-0.23 kg m^-2, MPal significantly reduced the available concentrations of Cd, Pb, and Cr in the soil by 52.2%, 29.9%, and 46.2%, respectively. Concurrently, Cd, Pb, and Cr concentrations in the shoots of head lettuce also decreased significantly, with the highest reduction being 44.0%, 61.5%, and 50.0%, respectively. At the same dosage, MPal had a better immobilization effect than Pal. There was no significant change in the pH of the vegetable soil, while the zeta potential decreased significantly, indicating that the MPal did not immobilize the heavy metals by increasing the pH, making it suitable for alkaline farmland soil. In addition, soil environmental quality was improved overall. MPal increased the activities of urease, β-glucosidase, cellulase, and catalase by 15.4%, 56.5%, 7.8%, and 14.9%, respectively. It increased the number of fungi and actinomycetes by 4.5% and 23.1%, respectively. MPal, as a new remediation material for soil contaminated by heavy metals, could achieve efficient remediation effects when applied in small doses. Compared with Pal, it is environmentally friendly, is low cost, and is more suitable for the treatment of heavy metal pollution in large areas of farmland.

Cd immobilization and soil quality under Fe-modified biochar in weakly alkaline soil

Cost-effective and environment-friendly implementation techniques are critical to the success of remediation in large-scale cadmium (Cd) contaminated agricultural soil. Field experiments were conducted to investigate the effect of Fe-modified biochar on Cd bioavailability in soils and uptake by maize (Zea mays L.), soil aggregate distribution and stability, and microbial community composition in weakly alkaline Cd-contaminated soil. Results showed that Fe-modified biochar optimized the structure and stability of soil aggregates. Moreover, the content of soil organic carbon increased by 6.59%-20.36% when compared with the control groups. However, DTPA-Cd concentration under the treatment of Fe-modified biochar was suffered by 37.74%-41.65% reduction in contrast with CK, and the significant decrease (P < 0.05) was obtained at 0.5% Fe-modified biochar. Moreover, sequential extraction procedures showed that the acid soluble and reducible states of Cd was converted into oxidizable and residual form. The addition of Fe-modified biochar inhibited Cd accumulation in maize, being 41.31%-76.64% (Zhengdan 958), 38.19%-70.95% (Liyu 86) and 52.30%-59.95% (Sanbei 218) reduction, respectively, in contrast with CK. The activity of catalase, urease and alkaline phosphatase in soil increased gradually with the addition of Fe-modified biochar. The enhancement in the number of soil bacterial OTUs and the values of Shannon, Chao1, ACE index indicated that Fe-modified biochar promoted the richness and diversity of bacterial communities. Therefore, the improvements of soil environment and biological quality indicated that Fe-modified biochar should be an alternative agent on remediation of Cd-contaminated soils.

Comparative effects of Tagetes patula L. extraction, mercapto-palygorskite immobilisation, and the combination thereof on Cd accumulation by wheat in Cd-contaminated soil

Phytoextraction and in situ immobilisation are two of the most commonly used remediation techniques for Cd-contaminated farmland. In theory, phytoextraction followed by immobilisation can reduce the total Cd and available Cd contents of the soil, making it suitable for the remediation of heavily Cd-contaminated alkaline soil. However, the real remediation efficiency is uncertain, and it is also unknown whether phytoextraction affects subsequent wheat Cd accumulation. In this study, two seasonal pot experiments were conducted to determine the effects of S,S-ethylenediamine disuccinic acid (EDDS)-assisted Tagetes patula L. (T. patula) extraction, mercapto-palygorskite (MPAL) immobilisation, and the combination thereof on subsequent Cd accumulation in wheat. EDDS application significantly increased the Cd content in the subsequent-soil solution, but the EDDS-activated Cd could not be absorbed by wheat roots. T. patula extraction decreased the subsequent soil pH value by 0.1-0.2 pH units, increased the available Cd content by 0.19 mg/kg, but had no effect on subsequent wheat Cd accumulation. The Cd absorption capacity of wheat roots and the Cd translocation capacity of wheat stems to grains of high-Cd wheat were higher than that of low-Cd wheat cultivar. The application of MPAL had no effect on soil pH value, but significantly decreased soil available Cd and exchangeable Cd contents by 17.78-36.76% and 21.13-52.63%; it also increased the Fe/Mn oxide-bound Cd fraction by 14.02-64.00%. MPAL application decreased the wheat grain Cd concentrations from 0.51 to 0.13 mg/kg (high-Cd wheat) and 0.35 to 0.05 mg/kg (low-Cd wheat), but had no negative effect on Fe, Mn, Cu, and Zn elements. Compared with the single MPAL application treatments, the combination treatments had no inhibition effect on Cd accumulation in wheat. MPAL is an efficient amendment, and considering the remediation efficiency, stability, and time of these methods, the combination of MPAL application with a low-Cd accumulation wheat cultivar represents a suitable proposal to ensure the safe production of wheat in Cd-contaminated alkaline soil.

Thiol-functionalized nano-silica for in-situ remediation of Pb, Cd, Cu contaminated soils and improving soil environment

Heavy metal contamination has been threatening the health of human beings. To decrease the bio-toxicity of heavy metals, a thiol-functionalized nano-silica (SiO₂-SH) was adopted to remediate the soil contaminated by lead (Pb), cadmium (Cd) and copper (Cu). The remediation effect of SiO₂-SH on contaminated soils was investigated by the uptake of the heavy metals into lettuce and pakchoi in pot experiment. The bio-toxicity of the SiO₂-SH was evaluated, and its immobilization mechanisms were proposed by the fraction distribution of Cd, Pb and Cu. It was found that the SiO₂-SH can significantly reduce the uptake of Cd, Pb, Cu into pakchoi by 92.02%, 68.03%, 76.34% and into lettuce by 89.81%, 43.41%, 5.76%, respectively. The chemical species analyses of Cd, Pb, Cu indicate SiO₂-SH can transform the heavy metal in acid soluble states into reducible fraction and oxidizable fraction, thereby inhibiting the extraction of heavy metals into soil solution. The concentrations of microbial biomass carbon, organic matter, and cation exchange capacity of the soil increased while the soil bulk density decreased after remediation. Those changes demonstrate that SiO₂-SH not only has no bio-toxic impact on the soil environment but also improves the soil environment, which proves the prepared SiO₂-SH is environmental-friendly. The SiO₂-SH could be a promising amendment for heavy metal contaminated soils.

Effects of mercapto-palygorskite on Cd distribution in soil aggregates and Cd accumulation by wheat in Cd contaminated alkaline soil

Cadmium (Cd) contamination in alkaline soils is a serious issue in China. As the basic structural units of soil, soil aggregates play an important role in the migration and transformation of heavy metal. However, there are few studies on the effects of adding amendments on Cd distribution in soil aggregates in alkaline soils. In this study, pot experiments were conducted to assess the effects of mercapto-palygorskite (MPAL) on soil aggregates and Cd accumulation in wheat. The results showed that MPAL application had no effect on wheat yield but significantly reduced the Cd uptake by the roots and the Cd transport to the adjacent internode. Application of 0.1% MPAL reduced the Cd concentration in two wheat grains (0.57 and 0.44 mg/kg, control) to 0.10 and 0.09 mg/kg in moderately Cd-contaminated soil, which are below the China national standard limit of 0.1 mg/kg (GB 2762-2017). MPAL application had no effect on soil pH, cation exchange capacity, mass proportion and mean weight diameter of soil aggregates, but increased soil organic matter content. Importantly, MPAL application promoted the migration of Cd from large particles (>0.25 mm) to small particles (<0.048 mm), reduced the unstable Cd fractions in >0.25 mm soil particles of clay soil and in >0.075 mm soil particles of sandy soil, and increased the stable Cd fractions in bulk soils and soil aggregates. The effects of MPAL addition on soil aggregates (grain size fraction metals loading and accumulation factor) of sandy soil were more prominent than on those of clay soil. Under MPAL treatments, wheat grains Cd concentration was significantly positively correlated with the available Cd in >0.075 mm soil particles and the total Cd in >0.25 mm soil particles. These results indicated that MPAL application in alkaline soils promoted the migration of Cd to micro-aggregates and inhibited the uptake and transport of Cd by wheat roots, thus reducing the Cd concentration in wheat grains.

Effect of sterilization on cadmium immobilization and bacterial community in alkaline soil remediated by mercapto-palygorskite

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

Effects of metal stabilizers on soil hydraulic characteristics and mobility of cadmium

This study investigated the effect of typical stabilizers on hydraulic properties, immobilization, and leachate characteristics based on the diffusive gradient thin-films technique (DGT) and a leaching experiment. Three types of stabilizers were classified based on various characteristics of soil field capacity (θf), and their immobilization effects were as follows: (i) θf increased and the immobilization of Cd was achieved with nanohydroxyapatite, increasing θf by 19.36% and decreasing the bioavailable Cd by 78.84%; (ii) the increasing θf conversely inhibited cadmium stabilization. Straw biochar averagely promoted θf by 17.39%, while the stabilization was suppressed; (iii) other stabilizers (zeolite, montmorillonite, and sepiolite) had no significant effect on θf and immobilization. It is suggested that stabilization depends on chemical mechanisms and is probably also affected by hydraulic mechanisms. The first types of stabilizers formed precipitates with poor solubility, and the strong affinity of heavy metals to soil particles can account for that the increasing θf had a negligible influence on the dissolution equilibrium of the heavy metals. Attapulgite also belongs to this type. The second and third types of stabilizers primarily adsorbed cadmium through ion exchange, resulting in the relatively easy heavy metal release. Increasing θf facilitated the desorption of heavy metals in the case of the second stabilizer type. However, the inconspicuous change in θf caused by the third stabilizer type had no impact on stabilization. Moreover, Cd leaching was positively correlated with bioavailable Cd and soil permeability. Heavy metal migration induced by colloids less than 90 nm in coarse biochar treatments deserves further research.

Remediation of cadmium and lead polluted soil using thiol-modified biochar

Thiol-modified rice straw biochar (RS) was prepared by an esterification reaction with β-mercaptoethanol and used for the remediation of Cd and Pb polluted soils. Modified biochar was characterized through elemental analysis, BET analysis, FE-SEM, FT-IR and XPS. These analytical results revealed that thiol groups were successfully grafted onto the surface of the biochar and were involved in metal ion complexation. Batch sorption experiments indicated that Cd²⁺ and Pb²⁺ sorption onto RS described well by a pseudo second order kinetic model and a Langmuir isotherm. The maximum adsorption capacities for Cd²⁺ and Pb²⁺, in the single-metal systems, were 45.1 and 61.4 mg g^-1, respectively. In the binary-metal systems, RS selectively adsorbed Cd²⁺ over Pb²⁺. Cd²⁺ and Pb²⁺ were removed mainly through surface complexation. In the soil incubation experiments (28 days), RS reduced the available Cd by 34.8-39.2 %; while, RS reduced the available Pb by 8.6 %-11.1 %. This research demonstrates RS as a potentially effective amendment for the remediation of heavy metal polluted soils.

Leaching behavior and efficiency of cadmium in alkaline soil by adding two novel immobilization materials

The seriousness and harmfulness of cadmium (Cd) pollution have been gradually attracting wide attention. Remediation materials currently play a critical role in the remediation of Cd-polluted soils. However, the amendments that can efficiently remediate Cd-polluted alkaline soils are relatively few. In this study, a column leaching experiment was conducted to determine the effects of mercapto-palygorskite (MPAL) and mercapto-sepiolite (MSEP) on the leaching behavior and chemical fraction distribution of heavy metals, and to explore the remediation efficiency of two novel materials in alkaline soils through aging experiments. The results showed that, under DTPA-assisted leaching, the maximum concentration of leachate Cd in MPAL and MSEP was below 1/30 (0.1 mg·kg^-1) of the total Cd concentration among leaching and significantly lower than that in CK, palygorskite (PAL), and sepiolite (SEP) treatments. Meanwhile, MPAL and MSEP decreased the leaching efficiency of Cd stability, had negligible effects on the essential micronutrients Cu and Zn, and did not influence the pH and electrical conductivity (EC) values of leachate. After leaching, the Fe/Mn oxide-bound Cd increased in MPAL and MSEP, whereas the exchange fraction Cd and carbonate-bound Cd decreased. Aging results showed that MPAL and MSEP effectively reduced 62.39% and 44.89% of DTPA-Cd after 1 day of aging, while at same dosage (0.3%) PAL and SEP reduced 7.79% and 6.75% of DTPA-Cd after 30 days of aging and showed no obvious efficiency. It was thus concluded that MPAL and MSEP can be considered as two novel and efficient soil remediation materials for Cd-polluted alkaline soils.

Inhibition of Cd accumulation in winter wheat (Triticum aestivum L.) grown in alkaline soil using mercapto-modified attapulgite

Cd contamination in agricultural soils threatens the safety of agricultural products and poses human health risk via food chain. However, the remediation of Cd polluted alkaline soils has not drawn the public concern, and the corresponding efficient amendments that can reduce Cd accumulation in crop grains are relatively few. In current study, mercapto-modified attapulgite (MA in abbreviation) was selected as the amendment to conduct winter wheat (Triticum aestivum L.) cultivation pot experiment to investigate the effect of MA on Cd accumulation in winter wheat and Cd bioavailability in alkaline soil. MA had no adverse impact on the normal growth of winter wheat but could inhibit Cd accumulation in wheat grain of both cultivars grown in alkaline soil with a maximum reduction of 75%, while pH-regulating amendment sepiolite had no reduction effect. In the term of soil chemistry, MA could decrease the zeta potential of soil particles and enhance the sorption amount of Cd on soil particles, resulted in the increase of Fe-Mn-oxides bounded Cd fraction in alkaline soil. The enhanced sorption effect combined with complexation effect of MA itself, made the exchangeable and bioavailable Cd concentrations in the soil decrease. In the term of plant uptake, MA could inhibit the uptake of Cd via roots from the soil, and hinder Cd transfer from roots to grains. MA had environmental friendliness and capability in the aspect of soil pH, effective cation exchange capacity and available micronutrients in the soil. The high performance of MA in inhabitation of Cd in winter wheat revealed that it was an efficient immobilization agent with great application potential for Cd-polluted alkaline soil.

Effects of chicken manure application on cadmium and arsenic accumulation in rice grains under different water conditions

Widespread contamination of agricultural soil with Cd and As has resulted in substantial transfer and accumulation of these toxicants in rice grains. In the present study, we investigated the effects of chicken manure application on Cd and As concentrations and As speciation in the rice grains grown under different water conditions by pot experiment. Under aerobic condition, the application of chicken manure increased soil pH and soil Eh during most of the growth period of rice. Consequently, the application of chicken manure has little effect on total Cd, slightly decreased total As and inorganic As of rice grains when applied at rate of 2.0%. Under intermittent irrigation condition, the application of chicken manure increased soil pH and decreased soil Eh during most of the growth period of rice. Thus, chicken manure decreased total Cd, As, and inorganic As of rice grains. Besides, there was increased reduction of Cd and As with increase in the amount of chicken manure applied. Under flooded condition, the application of chicken manure increased soil pH before heading but decreased soil pH after heading. The application of chicken manure dramatically decreased total and inorganic As in rice grains, and slightly decreased Cd of rice grains. There was increased reduction of total As concentration with the increase in the amount of chicken manure applied. Meanwhile, the inorganic As concentration was the lowest when the concentration of chicken manure was 1.0%.