镉耐性固定细菌的筛选及其对不同品种小麦镉吸收的阻控效应

为筛选重金属耐性固定细菌并探索其阻控小麦对重金属的积累效应,从根际土壤筛选镉耐性固定细菌,研究细菌吸附特性以及细菌对两种小麦Cd含量、富集系数和转移系数的影响。结果表明:筛选到一株镉耐性固定细菌菌株YM4,经16S rDNA序列分析鉴定为假单胞菌(Pseudomonas sp.)。YM4能耐受225 mg·L-1高浓度Cd2+,在含50 mg·L-1Cd2+培养基中对Cd的去除率达到58.9%。YM4对Cd的去除以胞外吸附为主。红外光谱分析发现,细胞壁上参与吸附或结合Cd的官能基团主要有─OH、─NH、羧基和磷酸基团等。小麦盆栽试验中,YM4显著降低小麦地上部(茎叶、麦壳)Cd积累量(11.31%~46.05%和10.12%~42.22%),使籽粒Cd积累量明显下降(26.79%~62.24%,红麦;25.27%~28.99%,白麦)。YM4能显著降低两种小麦茎叶、籽粒和麦壳的Cd富集系数以及籽粒的Cd转移系数。研究表明,镉耐性固定细菌Pseudomonas sp. YM4能降低小麦籽粒Cd含量,阻控小麦对Cd的吸收积累,对中轻度Cd污染土壤的粮食安全生产具有潜在应用价值。

镉吸附细菌的分离及其对土壤镉的固定

【目的】探究镉吸附细菌是否能够高效固定土壤有效镉(Cd),为土壤有效Cd的微生物固定提供理论依据。【方法】利用含Cd2+牛肉膏蛋白胨液体培养基对细菌进行Cd的耐受性测试筛选出镉抗性强的菌株;通过16S rRNA基因相似性及系统进化分析鉴定耐镉细菌,将菌细胞加入含CdCl2溶液中进行Cd^2+吸附效率测定;通过土培模拟实验,测定土壤pH、碱解氮、有效磷、速效钾、有机质、CEC、有效Cd及微生物数量来分析镉吸附细菌对镉污染土壤的影响。【结果】从德阳鱼腥草根际土壤中分离获得的57株细菌对Cd^2+表现出不同程度的抗性,并从中筛选出3株耐Cd优势细菌普罗威登斯菌属(Providencia)DY8、芽孢杆菌属(Bacillus)DY3和芽孢杆菌属(Bacillus)DY1-4。其对溶液中的Cd2+表现出较好的吸附作用,吸附效率随着Cd^2+浓度升高而降低。DY8、DY3、DY1-4能使镉污染土壤中有效Cd含量分别降低72.11%、68.55%、62.32%,同时显著提高镉污染土壤中碱解氮、有效磷的含量。【结论】Cd污染农田土壤中含有丰富的耐Cd微生物资源,Cd吸附细菌能降低土壤中有效Cd的含量,且能有效改善土壤养分条件。

Synthesis of phosphate-embedded calcium alginate beads for Pb(Ⅱ) and Cd(Ⅱ) sorption and immobilization in aqueous solutions

The phosphate-embedded calcium alginate beads were successfully synthesized based on sodium alginate, calcium dihydrogen phosphate and sodium hydrogen carbonate. Scanning electron microscopy, Fourier transformed infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were conducted to characterize the morphology and structure of the phosphate-embedded calcium alginate beads. The effects of pH and the initial concentration of the metal ions on Pb(II) and Cd(II) sorption by the beads were investigated. The optimal pH values for Pb(II) and Cd(II) sorption are 4.0 and 5.5, respectively. The optimal initial concentrations of Pb(II) and Cd(II) are 200 mg/L and 25 mg/L, correspondingly, and the removal efficiencies are 94.2% and 80%,respectively. The sorption mechanism is that the heavy metal ions accessed the beads firstly due to the large surface area, combinedwith OH?, and then precipitated with phosphate radical, which was proven by FTIR and XRD. The sorption of Pb(II) and Cd(II) isfitted to Langmuir isotherm model with R2 values of 0.9957 and 0.988, respectively. The sorption capacities of Pb(II) and Cd(II) are263.16 mg/g and 82.64 mg/g, respectively. The results indicate that the phosphate-embedded calcium alginate beads could be appliedto treating Pb(II)/Cd(II)-containing wastewater and it could be implied that the synthesized beads also could be used as a kind of soil ameliorant for remediation of the heavy metal contaminated paddy soil.

Removal of cadmium from aqueous solution by immobilized Microcystis aeruginosa:Isotherms,kinetics and thermodynamics

The Microcystis aeruginosa(MA) was immobilized on sodium alginate and used as biosorbent for removal of Cd(Ⅱ) ions from aqueous solution.The biosorption process is pH dependent,and the optimum biosorption was observed at pH 6.0 with the biosorption capacity of 98.38 mg/g.Among Langmuir,Freundlich and Temkin isotherm models,the Freundlich and the Temkin isotherm fit well with the experimental data.Cd(Ⅱ) ions biosorption follows the pseudo-second-order kinetic model.The rate controlling mechanism study reveals that film diffusion is the rate-limiting step and intraparticle diffusion is also involved in biosorption.Thermodynamic parameters,such as Gibbs free energy(ΔG°),the enthalpy(ΔH°) and entropy(ΔS°) were calculated,and revealed that the biosorption process is spontaneous,exothermic and random.Furthermore,the immobilized MA can be regenerated using 0.1 mol/L HCl solutions.

Immobilization of Cd and Pb in soils by polymeric hydroxyl ferric phosphate

A polymeric hydroxyl ferric phosphate(PHFP)was prepared by using a byproduct of titanium dioxide containing ferrous sulfate and phosphates under alkaline condition.The PHFP was used to immobilize lead(Pb)and cadmium(Cd)in soils.Fourier transform infrared spectra,X-ray diffraction were applied to revealing the characteristics of PHFP,and the modified Tessier sequential extraction and column leaching experiment with simulated acid rain were used to assess the effectiveness of immobilization of Cd and Pb in soils by PHFP.The results showed that PHFP was indeed a polymer with complicated OH-Fe-P structure and consisted of Fe6(OH)5(H2O)4(PO4)4(H2O)2and Fe25(PO4)14(OH)24.Moreover,the removal rates of DTPA-extractable Cd and Pb in soils reached up to33%and45%,and the water-soluble Cd and Pb decreased by56%and58%,respectively,when PHFP was added in soils at4%dosage.In addition,the immobilization of Cd and Pb contributed to transforming water soluble,exchangeable and carbonate-bonded fractions to Fe and Mn oxides-bonded,organic-bonded and residual fractions.Under leaching with simulated acid rain,Cd and Pb release amount in PHFP amended soil declined by53%and52%,respectively,as compared with non-treated soil.The result implied that PHFP had a potential application for the remediation of Cd-and Pb-contaminated soils.

Immobilization of Lead and Cadmium in Contaminated Soil Using Amendments: A Review

Since the inception of industrial revolution, metal refining plants using pyrometallurgical processes have generated the prodigious emissions of lead(Pb) and cadmium(Cd). As the core target of such pollutants, a large number of soils are nowadays contaminated over widespread areas, posing a great threat to public health worldwide. Unlike organic pollutants, Pb and Cd do not undergo chemical or microbial breakdown and stay likely in site for longer duration after their release. Immobilization is an in-situ remediation technique that uses cost-effective soil amendments to reduce Pb and Cd availability in the contaminated soils. The Pb and Cd contamination in the soil environment is reviewed with focus on source enrichment, speciation and associated health risks, and immobilization options using various soil amendments. Commonly applied and emerging cost-effective soil amendments for Pb and Cd immobilization include phosphate compounds, liming, animal manure, biosolids, metal oxides, and biochar. These immobilizing agents could reduce the transfer of metal pollutants or residues to food web(plant uptake and leaching to subsurface water) and their long-term sustainability in heavy metal fixation needs further assessment.

Cadmium and Zinc Accumulation in Maize Grain as Affected by Cultivars and Chemical Fixation Amendments

A field experiment was conducted to investigate the effects of soil amendments(lime,nano-Si foliar solution and used diatomite) on the growth and metal uptake of three maize(Zea mays L.) cultivars grown in a Cd and Zn-contaminated acidic soil.The addition of lime significantly increased the maize grain yields and decreased the concentrations of Zn and Cd in the grains and shoots of maize when compared with the control.Among the three maize cultivars,Yunshi-5 accumulated the lowest amounts of Cd and Zn in the grain.The concentrations of Zn and Cd in the grain of Yunshi-5 conformed to the Chinese feed standards.These data revealed that a combination of low metal-accumulating maize and chemical fixation could effectively provide a barrier to prevent metals from entering the human food chain.