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To solve the problem of excessive heavy metals in farmland soil, there is a pressing need for research effort to screen for the soil passivator materials. The effects of combined passivators on cadmium (Cd) availability in soils and uptake by pakchoi have been investigated based on the passivator screening and pot experiment. The results indicated that sepiolite, calcined lime and polyacrylamide (PAM) could significantly decrease the available Cd content in soils among eight kinds of inorganic and organic passivators, which were declined by 28.64%, 40.06% and 74.55%, respectively. Therefore, sepiolite, calcined lime and PAM were identified as the components of the combined passivators to grow pakchoi. The pakchoi planting experiment results of combined passivators showed that the combination of "calcined lime+PAM+sepiolite" was the most effective in decreasing the available Cd content in soils, which can reduce it by 39.83% (P<0.05). Meanwhile, the increases in ratio of weak organic bound or iron and manganese oxidation fractions in soils were responsible for the transformation of soil available Cd to the more stabilized fraction after applying of combined passivators. The positive passivation responses of "calcined lime+PAM+sepiolite" for Cd transfer to the aboveground of pakchoi and "calcined lime+PAM" for Cd absorption by pakchoi root demonstrated that these combined passivators could reduce Cd uptake by pakchoi. Thus, application of combined passivator of "calcined lime+PAM+sepiolite" can effectively reduce the Cd availability and Cd uptake by pakchoi in this study. Based on the results of the present research would provide a useful reference to remediate Cd contaminated soils. [ABSTRACT FROM AUTHOR]

Soil cadmium (Cd) pollution endangers the human health through the food chain and has become a serious concern in China. The study was to investigate the effects of amendments on Cd availability and uptake by crop in contaminated soils after calcined lime (C), hydroxyapatite (H) and pig manure (P) were applied alone and combination to the purple and black soils under com-wheat rotation. Results showed that crop biomass, Cd concentration, soil pH, DTPA extractable Cd and Cd fractions were significantly changed when applying amendments into both soils. Calcined lime and hydroxyapatite could significantly decline Cd availability in both soils regardless of crop type, and application of hydroxyapatite and pig manure increased the crop biomass. More obviously Cd fractions changes were observed in com growing period, especially applied with calcined lime and hydroxyapatite. Calcined lime increased carbonate-bound (Carb-Cd) Cd fractions resulted from 17.17% to 29.23% and from 17.26% to 35.38%, and hydroxyapatite increased Fe- and Mn oxide-bound (Ox-Cd) Cd fractions from 29.54% to 42.91% and from 19.32% to 36.54% in the purple and black soils. However, the exchangeable (Ex-Cd) and organic matter-bound (Org-Cd) Cd fractions were slightly increased after applying pig manure into both soils. Moreover, combined amendments prepared from alkaline materials and organic fertilizers could decrease grain Cd concentrations and increase crop biomass simultaneously. The immobilization effects of combined amendments were more remarkable in the black soil, such as hydroxyapatite + pig manure (HP) and calcined lime + hydroxyapatite + pig manure (CHP). This research demonstrated that Cd availability in soil and Cd uptake by crop root were the main factors to affect Cd immobilization, while the translocation in crop could hardly influence the Cd immobilization. [ABSTRACT FROM AUTHOR]

Soil cadmium (Cd) pollution has become a serious environmental focus of attention of the worldwide. Cd availability in soils and uptake by rape (Brassia campestris L.) grown in Cd-contaminated soils after supplied the mixture of wheat or com straw and chicken manure as organic amendments (labeled as WC and CC) into soils were studied. Results showed that WC amendments application generally promoted the dry matter of rape tissues at the first 50 days and significantly improved antioxidant enzymes activity of rape leaves regardless of planting period. Application with WC amendment might be more advantageous in decreasing Cd uptake by rape than CC amendment. It was worth mentioning that Cd contents in roots, stems and leaves reduced by 50.84% and 63.14% at the second 50 days when supplied WC amendment of 12.0g kg"1 of TOC into soils. Application with WC amendment could effectively decline the Cd availability on account of the Cd form redistribution from exchangeable Cd to unavailable Cd. Additionally, significantly negative correlations (P<0.01) between the soil pH, SOM content and exchangeable Cd were observed. After supplied with WC amendment into soil, the increases of soil pH and SOM content were also contributed to the reduction of Cd availability in soils and rape uptake. Accordingly, the mixture of wheat straw and chicken manure can be used as an organic amendment to reduce soil Cd availability and plant uptake in heavy metal contaminated soils. [ABSTRACT FROM AUTHOR]

As a new type of adsorption material, biochar has become a hotspot in the environmental field such as soil remediation and enhancement of carbon storage. However, little attention has been given to relationship between the deceased heavy metal bioavailability and the changes in soil humus composition with biochar addition. In this experiment, a pot experiment was conducted to apply different proportions of biochar (0%, 0.5%, 1%, 2% and 5%) to cadmium (Cd) -contaminated soil, and the soil physical and chemical properties, humic components, available Cd and Cd concentration in wheat were determined. Results showed that soil pH and soil organic matter (SOM) was significantly increased and the DGT-Cd was significantly decreased under all biochar treatments, with 5% biochar addition had the greatest impact. The content of fulvic acid (FA) and humin (HM) in soil increased with the increase of biochar addition, while the content of humic acid (HA) showed a decrease trend with the application of biochar. The Cd concentration in wheat roots, stems and grains was significantly negatively correlated with soil pH, HM, SOM and FA content, but positively with soil available cadmium (DGT-Cd) and HA. The results demonstrated that biochar can effectively immobilize heavy metals, thereby increasing soil pH, changing the humus component, and reducing heavy metal bioavailability in contaminated soils. [ABSTRACT FROM AUTHOR]

Inoculation of Bacillus may mediate plant growth and decrease uptake of heavy metals, but the combined effects and the mechanisms of Bacillus sp. and biochar on the cadmium availability and plant uptake are far less investigated. The effects of a plant growth-promoting B. amyloliquefaciens NS16, biochar, and their combination on the plant biomass and Cd accumulation in pakchoi and the mechanisms involved were characterized. Results showed that the biochar addition and NS16 inoculation, in combination or alone, significantly promoted plant biomass and decreased Cd uptake by plants with increased organic matter contents (by 13.2-44.5%) and increased microbial biomass carbon and nitrogen (by 6.91-56.3%), and populations of bacteria and fungi (by 11.2-103%), and the decreased available Cd concentrations measured by DGT (by 13.2-44.5%), in the rhizosphere soils. Compared with the initial pH, the inoculation of NS16 did not affect the pH values significantly, while the treatments of biochar and biochar + NS16 increased that of the rhizosphere soil significantly. Results suggested that the alkalinized rhizosphere, promoted organic matter contents, enhanced microbial biomass and community, and decreased Cd availability may have contributed to the decreased Cd accumulation in plants under effects of biochar addition and NS16 inoculation. [ABSTRACT FROM AUTHOR]

In this study, a graphene/biochar composite (BG composite) were synthesized by mixing the graphene (Gr) onto com cob biomass followed by slow pyrolysis, and tested for the sorption characteristics of cadmium (Cd) from aqueous solutions. The structure and morphology analysis of the adsorbents showed that graphene was coated on the surface of biochar, resulting in a larger surface area, more functional groups, greater thermal stability, and higher removal efficiency of Cd compared to original biochar. The optimum pH values were 5.0-9.0 and the optimal dosages of BC, BG 1 and BG5 were 0.5-2, 1-3 or 2-4 g/L for 10 mg/L Cd removal, respectively. The Cd adsorption kinetics and isotherm for BG composites can be described using the pseudo second-order model and Freundlich model. The biochar's characteristics and adsorption experiments demonstrated that electrostatic attraction, precipitation, complexation and ion exchange are the possible Cd removal mechanisms. Results suggested that the BG composite is an efficient, economic, and environmentally friendly multifunctional adsorbent for environmental remediation. [ABSTRACT FROM AUTHOR]

Biochar performs well in the remediation of heavy metals or pesticides-polluted soil and thereby reduces agricultural diffuse pollution, which is rarely applied to organic and inorganic combined pollution. The study selected thiourea-modified pig manure biochar to remedy soil and simultaneously to reduce cadmium and glyphosate diffuse loss based on sorption process. The results showed that the Freundlich and Langmuir model well fit the adsorption of cadmium and glyphosate. Compared with pig manure biochar, the pH value and the ash content of thiourea-modified pig manure biochar decreased by 0.82 and 5.02%, respectively. The adsorption capacity and binding ability of biochar to cadmium and glyphosate increased. The thiourea-modified pig manure biochar-amended soil responded differently to different initial Cd and glyphosate concentrations in the single- and binary-system. This study provides an economic and environmental technical means to solve the problem of composite pollution in the actual environment. [ABSTRACT FROM AUTHOR]

In this study, biochar (BC) was produced from sycamore wood through a typical slow pyrolysis process and modified with sodium hydroxide (SBC), phosphoric acid (PBC), urea (UBC), and thiourea (TBC) at various concentrations. The BCs were characterized with scanning electron microscopy, surface area analysis, and elements analysis. The efficiency and mechanism of cadmium adsorption by SBC, PBC, UBC, and TBC from aqueous solution was investigated through a series of adsorption experiments. Results showed that the adsorption efficiencies of SBC and UBC were greater than those of TBC and PBC. They are also reasonable in terms of treatment costs and are ideal adsorbents. We can infer that chemical modification of BC changed their surface groups and structures and thus enhanced or reduced their adsorption properties. [ABSTRACT FROM AUTHOR]