Immobilization Of Cd In Soil Research Articles

Effect of biochar on cadmium bioavailability and uptake in wheat (Triticum aestivum L.) grown in a soil with aged contamination

Cadmium (Cd) is a well-known and widespread toxic heavy metal while the effects of biochar (BC) on Cd bioavailability and toxicity in wheat, especially in soils with aged contamination are largely unknown. In the present study, the effect of rice straw BC on Cd immobilization in soil and uptake by wheat in an agricultural contaminated-soil was investigated. Different levels of rice straw BC (0%, 1.5%, 3.0% and 5% w/w) were incorporated into the soil and incubated for two weeks. After this, wheat plants were grown in the amended soil until maturity. The results show that the BC treatments increased the soil and soil solution pH and silicon contents in the plant tissues and in the soil solution while decreased the bioavailable Cd in soil. The BC application increased the plant-height, spike-length, shoot and root dry mass and grain yield in a dose additive manner when compared with control treatment. As compared to control, BC application increased the photosynthetic pigments and gas exchange parameters in leaves. Biochar treatments decreased the oxidative stress while increased the activities of antioxidant enzymes in shoots compared to the control. The BC treatments decreased the Cd and Ni while increased Zn and Mn concentrations in shoots, roots, and grains of wheat compared to the control. As compared to the control, Cd concentration in wheat grains decreased by 26%, 42%, and 57% after the application of 1.5%, 3.0%, and 5.0% BC respectively. Overall, the application of rice straw BC might be effective in immobilization of metal in the soil and reducing its uptake and translocation to grains.

Immobilization and bioavailability of heavy metals in greenhouse soils amended with rice straw-derived biochar

Pollution of greenhouse soils and crops by heavy metals as a result of annual application of large amounts of pesticides and fertilizers is of great concerns. We investigated the effect of biochar (BC) as a potential immobilizing medium for cadmium (Cd) by assessing Cd bioavailability, fractions, and uptake of metals by lettuce plants in metal-contaminated greenhouse soils. Experiments were conducted in two typical vegetable greenhouses displaying different levels of heavy metal pollution (GH1, lightly heavy-metal-polluted greenhouse; GH2, heavily heavy-metal-polluted greenhouse), in Wuhan City suburbs, Hubei Province, China. For each greenhouse site three replicates of each of three levels of BC (B0, 0tha−1; B10, 10tha−1; B20, 20tha−1) were arranged in a randomized complete block design. The application of BC increased soil pH and soil organic matter and changed Cd fractions in the soil. The exchangeable Cd fraction decreased and there was an increase in the oxide- and organic-bound and residual fractions with the application of BC, implying that BC application could immobilize the Cd in greenhouse soil. The rates of Cd immobilization in soil increased with the amount of BC applied. The exchangeable Cd fractions in soils amended with B10 decreased by 45–62% and in soils amended with B20 by 66–89% compared to the control. The addition of BC reduced the concentration of Cd in lettuce shoots in the lightly heavy-metal-polluted soils, but in the heavily heavy-metal-contaminated soils it had either no effect, or promoted Cd absorption by lettuce shoots. Total Cd measured in lettuce tissues did not decrease with the addition of BC when compared to the control, as there was increased accumulations of lettuce biomass with biochar application.

Effect of inorganic amendments for in situ stabilization of cadmium in contaminated soils and its phyto-availability to wheat and rice under rotation.

Cadmium (Cd) toxicity is a widespread problem in crops grown on contaminated soils, and little information is available on the role of inorganic amendments in Cd immobilization, uptake, and tolerance in crops especially under filed conditions. The effect of three amendments, monoammonium phosphate (MAP), gypsum, and elemental sulfur (S), on Cd immobilization in soil and uptake in wheat and rice plants, under rotation, were investigated under field conditions receiving raw city effluent since >20 years and contaminated with Cd. Three levels of each treatment, 0.2, 0.4, and 0.8% by weight, were applied at the start of the experiment, and wheat was sown in the field. After wheat harvesting, rice was sown in the same field without application of amendments. Both crops were harvested at physiological maturity, and data regarding grain yield, straw biomass, Cd concentrations, and uptake in grain and straw, and bioavailable Cd in soil and soil pH were recorded. Both MAP and gypsum application increased grain yield and biomass of wheat and rice, while S application did not increase the yield of both crops. MAP and gypsum amendments decreased gain and straw Cd concentrations and uptake in both crops, while S application increased Cd concentrations in these parts which were correlated with soil bioavailable Cd. We conclude that MAP and gypsum amendments could be used to decrease Cd uptake by plants receiving raw city effluents, and gypsum might be a better amendment for in situ immobilization of Cd due to its low cost and frequent availability.

Immobilization of Cd in soil and changes of soil microbial community by bioaugmentation of UV-mutated Bacillus subtilis 38 assisted by biostimulation

To develop an efficient bio-immobilization technology for the remediation of heavy metals in soil, a mutant species of Bacillus subtilis (B38) was acquired by UV irradiation and selection under high concentration of cadmium (Cd) in a previous study. Immobilization of Cd in soil has been achieved and reported earlier by a technology of bioaugmentation of B38 assisted by biostimulation (BAB) using a bio-waste (NovoGro) from an enzyme company. In the present study, B38 was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FT-IR). The results proved that the cell morphology and functional groups on the cell surface of B. subtilis changed after the mutation and interaction with Cd. The applicability of BAB as a practicable bioremediation technology was evaluated by checking the inhibition on Cd bioaccumulation by carrots (Daucus carota), the enhancement on carrot biomass, and the change of Cd speciation in soil. The BAB technology reduced Cd contents in carrot shoots and roots by 16% and 55%, respectively. Simultaneously, the exchangeable fraction of Cd in soil under BAB treatment decreased significantly. Furthermore, a PCR-DGGE-based experiment was performed to evaluate the effect of BAB technology on soil microbial communities. The BAB technology could enhance the proliferation of both exotic B38 and native microbes.

Effects of Nano Particle Hydroxyapatite on Cadmium Bioaccumulation and Translocation in Pakchoi (<i>Brassia chinensis</i>) from Cadmium Polluted Soil

A pot experiment was conducted to investigate the effect of nano particle hydroxyapatite (nHAP) on Cadmium(Cd) contaminated soil. The Cd uptake of pakchoi in Cd polluted soil treated with various concentration of nHAP were studied. In addition, the effect of nHAP on chemical fraction distribution in Cd contaminated soil was evaluated. Results indicated that by adding the nHAP, the Cd level in pakchoi shoots and roots decreased significantly compared to the control. The mechanism of this treatment involved bioavailability reduction and immobilization of Cd in soil, resulting in the transformation of available fractions to unavailable fractions. In conclusion, with the addition of nHAP, the resistance to Cd of pakchoi in contaminated soil could be significantly enhanced and the quality of the plants improved.

Biochars immobilize soil cadmium, but do not improve growth of emergent wetland species Juncus subsecundus in cadmium-contaminated soil

Purpose An addition of biochar mixed into the substrate of constructed wetlands may alleviate toxicity of metals such as cadmium (Cd) to emergent wetland plants, leading to a better performance in terms of pollutant removal from wastewater. The objective of this study was to investigate the impact of biochars on soil Cd immobilization and phytoavailability, growth of plants, and Cd concentration, accumulation, and translocation in plant tissues in Cd-contaminated soils under waterlogged conditions. Materials and methods A glasshouse experiment was conducted to investigate the effect of biochars derived from different organic sources (pyrolysis of oil mallee plants or wheat chaff at 550 °C) with varied application amounts (0, 0.5, and 5 % w/w) on mitigating Cd (0, 10, and 50 mg kg −1 ) toxicity to Juncus subsecundus under waterlogged soil condition. Soil pH and CaCl2/EDTA-extractable soil Cd were determined before and after plant growth. Plant shoot number and height were monitored during the experiment. The total root length and dry weight of aboveground and belowground tissues were recorded. The concentration of Cd in plant tissues was determined. Results and discussion After 3 weeks of soil incubation, pH increased and CaCl2-extractable Cd decreased significantly with biochar additions. After 9 weeks of plant growth, biochar additions significantly increased soil pH and electrical conductivity and reduced CaCl2-extractable Cd. EDTAextractable soil Cd significantly decreased with biochar additions (except for oil mallee biochar at the low application rate) in the high-Cd treatment, but not in the low-Cd treatment. Growth and biomass significantly decreased with Cd additions, and biochar additions did not significantly improve plant growth regardless of biochar type or application rate. The concentration, accumulation, and translocation of Cd in plants were significantly influenced by the interaction of Cd and biochar treatments. The addition of biochars reduced Cd accumulation, but less so Cd translocation in plants, at least in the low-Cd-contaminated soils. Conclusions Biochars immobilized soil Cd, but did not improve growth of the emergent wetland plant species at the early growth stage, probably due to the interaction between biochars and waterlogged environment. Further study is needed to elucidate the underlying mechanisms.

Lime and Phosphate Could Reduce Cadmium Uptake by Five Vegetables Commonly Grown in South China

A pot experiment was conducted in artificially Cd-contaminated (5 mg Cd kg −1) soils to investigate the feasibility of using lime (3 g kg −1) or phosphate (80 mg P kg −1) to mitigate uptake of Cd by vegetables. Five common vegetables in South China, including lettuce ( Lactuca sativa L. var. ramosa Hort.), Chinese cabbage [ Brassica rapa L. subsp. Chinensis (L.) var. parachinensis (L. H. Bailey) Hanect], Chinese broccoli ( Brassica oleracea L. var. albiflora Kuntze), white amaranth ( Amaranthus tricolor L.) and purslane ( Amaranthus viridis L.), were grown in the soils and harvested after 60 d. The results showed that liming significantly reduced Cd uptake by most vegetables by 40%-50% (or a maximum of 70%), mainly due to immobilization of soil Cd. Increased availability of Ca in the soil might also contribute to the Cd uptake reduction as a result of absorption competition between Ca and Cd. Liming caused biomass reduction in white amaranth and purslane, but did not influence growth of the other vegetables. Phosphate decreased Cd uptake by vegetables by 12%-23%. Compared with lime, phosphate decreased, to a smaller extent, the bioavailability of Cd in most cases. Phosphate markedly promoted growth of vegetables. Changes in soil chemistry by adding lime or phosphate did not markedly influence nutrient uptake of vegetables except that lime increased Ca content and phosphate increased P content in shoots of the vegetables. The results suggested that a proper application of lime could be effective in reducing Cd uptake of vegetables, and phosphate could promote growth of the vegetables as well as alleviate the toxicity of Cd.

Effects and mechanisms of amendments on remediation of cadmium contaminated acid paddy soils

A field experiment was conducted to study Cd immobilization in Cd contaminated soils. The study analyzed the remediation effects of lime (L), fused calcium magnesium phosphate (P), sepiolite (S), humic acid (H) and mixed lime amendments (LP, LS and LH) on Cd bioavailability in a Cd contaminated acid paddy soils. The results indicate that amendments significantly change the proportion of Cd forms in contaminated soils. Except for H, the other 3 amendments lower acid extractable fraction of Cd, while increasing oxidation fraction and residual Cd. The 4 amendments reduce the 0.1 mol·L-1 NaNO3 and 0.01 mol·L-1 CaCl2 extracted Cd by 26%～97%. The order of reduction is LS S LP P L LH H. The content of Cd in the aboveground parts of rice decreases by 6%～49% under amendment application. Amendment increasing soil pH is the main factor influencing soil Cd immobilization. In conclusion therefore, sepiolite could be a suitable amendment of Cd contaminated acid paddy soils. However, humic acid is not so suitable for remediating Cd contaminated acid paddy soils.

Immobilization and phytotoxicity of Cd in contaminated soil amended with chicken manure compost

The experiment was conducted to evaluate the effect of compost application on the immobilization and biotoxicity of Cd in winter wheat ( Triticum aestivum L.) potted soils. Soils treated with various levels of Cd (0–50 mg Cd kg −1 soil) were amended with 0, 30, 60 and 120 g compost kg −1 soil. The fractions of Cd in soil were evaluated by a sequential extraction procedure. Compost application resulted in more than 70% lower soluble/exchangeable Cd (KNO 3) but increased the concentration of organic-bound (NaOH) and inorganic precipitates (EDTA) Cd in soils. Addition of compost was effective in reducing the phytotoxicity of Cd by decreasing more than 50% Cd uptake by wheat tissue and improving wheat growth. Alleviation of Cd phytotoxicity by compost was attributed primarily to the increase of soil pH, complexation of Cd by the organic matter and coprecipitation with P content. Compost was effective in the immobilization of Cd in soils and can be used to remediate Cd-contaminated soils.