Assessment of heavy metal uptake and translocation in Dyera costulata for phytoremediation of cadmium contaminated soil

Abstract

Heavy metal pollution is a widespread global problem causing serious environmental concern. Cadmium, one of the heavy metals, is water soluble and can be transferred from soil to plants and enter into the food chain. It is detrimental to human health because it accumulates in the body and can cause renal tubular dysfunction, pulmonary emphysema and osteoporosis. This heavy metal needs to be cleaned up for a clean and safe environment. An experiment was conducted to evaluate the potential of Dyera costulata as a phytoremediator to absorb cadmium from contaminated soils. Dyera costulata seedlings were planted on six different growth media (soil + different levels of cadmium): Control, 25 ppm Cd, 50 ppm Cd, 75 ppm Cd, 100 ppm Cd and 150 ppm Cd. The highest growth performance mainly height, basal diameter and number of leaves were in the control, 50 ppm Cd and 25 ppm Cd treatments, respectively. The highest accumulation of cadmium (52.9 ppm) was in the 75 ppm Cd treatment. Among the plant parts, leaves showed the highest concentration of cadmium. Dyera costulata showed high translocation factor and low bioconcentration factor values in soil at high cadmium concentrations and was also able to tolerate and accumulate high concentrations of cadmium. The roots of Dyera costulata were found to be suitable for the absorption of cadmium in contaminated soils. This species can be an efficient phytoremediator for soils contaminated with cadmium.     

重金属污染土壤的螯合剂诱导植物修复研究进展

植物修复作为一种生态友好型原位绿色修复技术成为重金属污染土壤修复研究的热点。然而,目前最具有推广价值的超积累植物因生物量低、生长缓慢、对重金属的积累具有专一性等缺点,大大限制了植物修复技术在重金属污染尤其是复合重金属污染土壤治理方面的推广应用。利用生长速度快、生物量大的普通植物借助其它技术辅助的联合植物修复便成了有效可行的替代途径和研究焦点。近年来,金属螯合剂诱导的化学-植物联合修复技术备受关注。本文综述了螯合剂诱导植物修复技术的研究进展、修复机理和目前存在的问题,并对该项技术的未来研究方向给予了展望。     

Amaranthus Tricolor Has the Potential for Phytoremediation of Cadmium‐Contaminated Soils

Phytoremediation is a developing technology that uses plants to clean up pollutants in soils. To adopt this technology to cadmium (Cd)–contaminated soils efficiently, a Cd hyperaccumulator with fast growth rate and large biomass is required. In the present study, we selected Caryophyllales as a potential clade that might include Cd hyperaccumulators because this clade had a high mean concentration of zinc (Zn), which is in the same element group as Cd. Three species in Caryophyllales and three species in different clades were grown with Cd. Among them, Amaranthus tricolor showed high accumulating ability for Cd under both water‐culture and soil‐culture conditions, whereas Brassica juncea, a known Cd hyperaccumulator, accumulated high concentrations of Cd in shoots only under water‐culture conditions. This result suggests that A. tricolor has Cd‐solubilizing ability in rhizosphere. Because A. tricolor has large biomass and high growth rate, this species could be useful for phytoremediation of Cd‐contaminated fields.     

香薷属植物在重金属修复中的应用进展

香薷属植物应用于重金属修复经历了矿区植物资源调查和比较、室内模拟研究、田间规模修复以及修复后处置研究,已经初步形成一个植物修复技术的完整体系。在现有技术条件下,把生态修复模式、品种驯化及诱导剂"配方"应用到香薷属植物修复土壤重金属污染对提高修复效率具有重要意义。     

Using profitable chrysanthemums for phytoremediation of Cd- and Zn-contaminated soils in the suburb of Shanghai

Purpose

We studied the profitable phytoremediation method with commercial chrysanthemum (Chrysanthemum indicum L.) in order to remediate the soils contaminated with heavy metals and generate economy income from the contaminated sites.

Materials and methods

A field experiment was carried out to remediate the contaminated soil through growing the commercial chrysanthemum plants in a farmland polluted with heavy metals of Cd and Zn due to application of creek sediments in the western suburb of Shanghai, Southeast China, since June 2013.

Results and discussion

After the consecutive 3 years of phytoremediation, Cd and Zn contents in the soil were reduced by 78.1% and 28.4%, respectively. We also found that the rice grain growing on the 3-year phytoremediated soil met the requirements of dietary safety, so did the vegetable growing on the 5-year phytoremediated soil.

Conclusions

Growing chrysanthemum plants as a method of phytoremediation can not only remove a large amount of toxic heavy metals from the contaminated soil but also be highly profitable from the sales of chrysanthemum flowers.

     

The effect of sewage‐sludge on the heavy metal content of soils and plant tissue

Abstract

Domestic sewage sludge applied to farm fields at a rate of 44.9 kg/ha in a mixture with lime and sawdust was found to increase the soil levels of cadmium, chromium, copper, lead, mercury, nickel and zinc. The average levels in sludge treated soil were: 0.11, 0.56, 3.59, 2.72, 0.068, 1.49 and 2.57 ppm, respectively. The increases were small and the overall loading factors were well below recommended maximums. The uptake of these heavy metals by grass and legume plants was variable with cadmium, copper and zinc levels being higher in those plants growing in the sludge treated soils but only copper was significantly higher. The heavy metal contents found were all within the levels normally found in grass and legume plants. The higher mean concentration in plants growing on the sludge treated soils were cadmium 0.495; chromium 1.22; copper 12.3; lead 1.54; mercury 0.022; nickel 4.08 and zinc 28.4 ppm.     

The Effect of Temperature on the Accumulation of Cadmium, Copper, Zinc, and Lead by Scirpus acutus and Typha latifolia: A Comparative Analysis

Wetland plants have a capacity for metal sequestration and have been used to remediate such environmental contaminants. How this capacity will be affected by a warming environment is not well-known. Our objective was to identify the effect of small environmentally realistic increases in temperature on metal (cadmium, zinc, lead, and copper) accumulation in Typha latifolia as compared with Scirpus acutus. These common wetland plant species were grown in metal-contaminated sediments at 13??C, 16??C, and 18??C for 3?months to determine the effect of environmentally realistic temperatures on metal accumulation. Cd¹⁰⁹ was used as a radiotracer to study the effect of temperature on uptake kinetics. Growth of the two wetland plants differed markedly; S. acutus displayed linear growth reaching a maximum height of ca. 100?cm; by contrast, T. latifolia grew to ca. 40?cm by day?60 with no further growth occurring over the remainder of the 105-day growth period. S. acutus accumulated more cadmium, lead, and zinc from contaminated sediments than T. latifolia, but only within roots and rhizomes. Although not significant, uptake of cadmium, lead, and zinc by both plants was enhanced under warmer conditions and was most pronounced in S. acutus. This was supported by the radiotracer studies which indicated that under the higher temperatures, there was increased rates of Cd¹⁰⁹ uptake by shoots of S. acutus. By contrast, temperature did not affect Cd¹⁰⁹ uptake rate constants in T. latifolia. S. acutus appears to be more effective at sequestering metals from contaminated sediments; this species as compared to T. latifolia may also be more affected by a warming climate. In the design of wetlands for metal remediation, differences in how these two plants sequester metals from their environment should be considered.     

Remediation of a Sandy Soil Contaminated with Cadmium,Nickel, and Zinc using an Insoluble Polyacrylate Polymer

Abstract

This study was carried out to investigate whether an insoluble polyacrylate polymer could be used to remediate a sandy soil contaminated with cadmium (Cd) (30 and 60 mg Cd kg^?1 of soil), nickel (Ni) (50 and 100 mg Ni kg^?1 of soil), zinc (Zn) (250 and 400 mg Zn kg^?1 of soil), or the three elements together (30 mg Cd, 50 mg Ni, and 250 mg Zn kg^?1 of soil). Growth of perennial ryegrass was stimulated in the polymer‐amended soil contaminated with the greatest amounts of Ni or Zn, and when the three metals were present, compared with the unamended soil with the same levels of contamination. Shoots of plants cultivated in the amended soil had concentrations of the metals that were 24–67% of those in plants from the unamended contaminated soil. After ryegrass had been growing for 87 days, the amounts of water‐extractable metals present in the amended soil varied from 8 to 53% of those in the unamended soil. The results are consistent with soil remediation being achieved through removal of the metals from soil solution.     

Field-Scale Assessment of Phytotreatment of Soil Contaminated with Weathered Hydrocarbons and Heavy Metals (9 pp)

Background, Aim and Scope   Phytoremediation is a remediation method which uses plants to remove, contain or detoxify environmental contaminants. Phytoremediation has successfully been applied for the removal of fresh hydrocarbon contamination, but removal of aged hydrocarbons has proven more difficult. Biodegradation of hydrocarbons in the subsurface can be enhanced by the presence of plant roots, i.e. the rhizosphere effect. Phytostabilization reduces heavy metal availability via immobilization in the rhizosphere. Soils contaminated by both hydrocarbons and heavy metals are abundant and may be difficult to treat. Heavy metal toxicity can inhibit the activity of hydrocarbon-degrading microorganisms and decrease the metabolic diversity of soil bacteria. In this experiment, weathered hydrocarbon- and heavy metal- contaminated soil was treated using phytoremediation in a 39- month field study in attempts to achieve both hydrocarbon removal and heavy metal stabilization. Materials and Methods: A combination of hydrocarbon degradation and heavy metal stabilization was evaluated in a field-scale phytoremediation study of weathered contaminants. Soil had been contaminated over several years with hydrocarbons (11400±4300 mg kg dry soil)-1 and heavy metals from bus maintenance activities and was geologically characterized as till. Concentrations of soil copper, lead and zinc were 170±50 mgkg-1, 1100±1500 mg kg-1 and 390±340 mg kg-1, respectively. The effect of contaminants, plant species and soil amendment (NPK fertilizer or biowaste compost) on metabolic activity of soil microbiota was determined. Phytostabilization performance was investigated by analyses of metal concentrations in plants, soil and site leachate as well as acute toxicity to Vibrio fischeri and Enchtraeus albidus. Results: Over 39 months hydrocarbon concentrations did not decrease significantly (P=0.05) in non-amended soil, although 30% of initial hydrocarbon concentrations were removed by the last four months of study. In soil amended with NPK fertilizer and municipal biowaste compost, 65 % and 60 % of hydrocarbons were removed, respectively. The soil contained metabolically diverse bacteria, measured as carbon source utilization and extracellular enzymatic activities. Compost addition resulted in a slight increase in enzymatic activities. Diesel fuel utilization potential in Biolog MT2 plates inoculated with a soil suspension was enhanced by both compost and NPK compared to non-amended soil. Soil toxicity to V. fischeri and E. albidus was low. The leachate was not toxic to V. fischeri. Pine (Pinus sylvestris), poplar (Populus deltoides x Wettsteinii), grasses and clover (Trifolium repens) survived to varying degrees in the contaminated soil. All plants suffered from phytotoxicity symptoms and some trees died during the study period. Plants formed a dense cover over the compost-amended soil, whereas non-amended soil had areas devoid of vegetation throughout the study. Vegetation coverage in the NPK-amended quarter was about 50 % after the first four months of study, but increased gradually to 100 %. Heavy metals did not accumulate in plant tissue. Discussion: Removal of hydrocarbons from weathered unfertilized hydrocarbon-contaminated soil was not statistically significant despite the presence of a viable hydrocarbon-degrading microbial community. This effect is attributed to soil heterogeneity and low bioavailability of hydrocarbons. Hydrocarbon concentrations were not reduced to the desired level, i.e., 1500 mg hydrocarbons (kg of dry soil)-1, in any treatment. . The presence of clay minerals and organic matter within the compost may have limited heavy metal transfer to leachate and plant tissue. Conclusions: Weathered hydrocarbons were partly decomposed in soil fertilized with NPK fertilizer or biowaste compost, but not from unfertilized soil. The active hydrocarbon-degrading microbiota and low toxicity of soil to V. fischeri and E. albidus indicates low availability of contaminants to microorganisms. Despite high heavy metal concentrations, the soil contained metabolically diverse bacteria, measured as carbon source utilization and extracellular enzymatic activities. Heavy metals did not accumulate in test plants. Pine and poplar suffered from phytotoxicity symptoms in the soil and could not enhance hydrocarbon removal in compost-amended soil. Compost addition combined with a grass and legume crop is suggested for stabilization of combined hydrocarbon- and metal-contaminated soil. Recommendations and Perspectives: Both compost and NPK fertilizers can be used to enhance phytoremediation of soil contaminated with weathered hydrocarbons in the presence of heavy metals; however, compost addition is recommended since it enables greater vegetative coverage. This in turn may decrease heavy metal mobility. Phytoremediation can be used for remediation of soil contaminated with weathered hydrocarbons in the presence of heavy metals. However, phytoremediation of weathered contaminants requires extended periods of time; thus, other remediation methods should be considered in the event of soil contamination posing an immediate public health and/or environmental threat.     

Biosorption of Toxic Metals by Water Lettuce (<Emphasis Type="Italic">Pistia stratiotes</Emphasis>) Biomass

Adsorption isotherms were constructed to evaluate the potential use of water lettuce (Pistia stratiotes) dry biomass for the biosorption of zinc and cadmium. One gram of dry biomass of this plant was treated with five increasing doses of zinc (1.8, 18, 50, 79, and 105 mg L^?1) and four doses of cadmium (0.01, 0.1, 1, and 10 mg L^?1), for nine collection times (1, 3, 6, 12, 24, 36, 48, 60, and 72 h). The levels of these metals were determined by atomic absorption spectrophotometry. To evaluate changes in the surface morphology of the dry biomass, scanning electron microscopy (SEM) images were taken of the samples subjected to the greatest contamination, and these were compared with the images of the samples without zinc and cadmium (control). The ISOFIT software was used to select the isotherm model that best fit the biosorption of metals by water lettuce dry biomass. The linear model was determined to be the best-fitting isotherm model, because it had the lowest corrected Akaike information criterion (AICc) value and a Akaike weight (AICw) value closest to one, which indicates the high affinity of the biosorbent for the adsorbates evaluated. The results for both metals demonstrated greater than 70% reductions in the concentrations of the metals in the contaminated solutions. The SEM images indicated changes in the morphology of the contaminated biomass, thus demonstrating the biosorption mechanisms and confirming the potential of the dry biomass of this plant for use in the remediation of solutions contaminated with zinc and cadmium.     

Improvement of phytoremediation effects with help of different fertilizer

Abstract

Phytoremediation is increasingly used to remediate metal contaminated soils. However, in order to provide technically efficient phytoremediation of contaminated sites the plant yield and metal uptake have to be enhanced dramatically. The aim of the study was to find appropriate combination of plant species and fertilizers capable of improving yields of the plants and stimulate a transfer of metals to more available to the plants forms. Wheat Triticum vulgare was used for the phytoremediation research. To increase yield of crops and enhance mobility of metals in the rhizosphere the soils were amended with three fertilizers (urea, horse manure, and “ispolin”). Short-term (36 d) vegetation test showed that concentrations of heavy metals in the plants grown in contaminated soil (from site 2) were significantly higher than those in the plants grown in clean soil (from site 1). Growth of wheat resulted in a decrease of Cd content in the soil. Amendment of the contaminated soil with urea enhanced the effect and the decrease of Cd concentration in the soil was more significant. The best effect was demonstrated after application of ispolin: concentrations of Cd, Cu, Pb, and Zn in the rhizosphere decreased 1.2–1.4 times as compared with those in the initial contaminated soil (the decrease was statistically significant).     

Chelate Agents Enhanced Electrokinetic Remediation for Removal Cadmium and Zinc by Conditioning Catholyte pH

The feasibility of using chelate agents to enhance the electrokinetic remediation of heavy metal contaminated soils has been investigated in this study. Chelate agents were used as washing solutions as well as purging solutions at the electrode compartments. The pH value of the soil significantly affects the removal of heavy metal ions. Due to electrolysis reaction pH increases near the cathode. Without conditioning of the pH value metals precipitate as hydroxides. This problem is solved by the addition of an acid in the cathode compartment. The heavy metals that are dissolved will move to either the cathode or the anode, depending on their charges. This paper presents the results of electrokinetic extraction of cadmium using acetic acid, citric acid and pyridine-2,6-dicarboxylic acid (PDA) as washing and purging solutions, and the removal of zinc using ethylenediamine tetraacetic acid (EDTA) and sodium metabisulfite (Na²S²O⁵) as washing and purging solutions, respectively. The results showed that the increased experimental time induced a higher removal efficiency of cadmium and zinc.     

Heavy-Metal Bioavailability and Chelate Mobilization Efficiency in an Assisted Phytoextraction Process by Sesbania sesban (L.) Merr

Chelate-induced phytoextraction is an innovative technique for cleaning metal- contaminated soil. The present study evaluates the degree of metal mobilization in soil and enhancement of phytoextraction of cadmium (Cd), lead (Pb), and zinc (Zn) by Sesbania sesban (L.) Merr. from artificially contaminated soil by application of ethylenediaminetetraacetic acid (EDTA). After 30 days of plant growth, the pots were divided into three sets (0.0, 2.5, and 5.0 mmol EDTA per kg soil). Experimental results indicated that levels of diethylenetriaminepentaacetic acid (DTPA)–extractable metals and metals in the leachate decreased as the EDTA dose increased. Plant growth parameters and total chlorophyll contents in the plants with EDTA applied were less than those of control. However, EDTA application significantly reduced metal accumulation in root and increased metal accumulation in the shoot of plants; similar results were obtained for the bioconcentration factor and translocation factor. The application of 5 mmol EDTA kg^?1 to metal-spiked soil may be an efficient alternative for the chemically enhanced phytoextraction by S. sesban.     

植物对镉毒害的形态和生理响应研究进展

Cadmium (Cd) contamination has posed an increasing challenge to environmental quality and food security.In recent years,phytoremediation has been particularly scrutinized because it is cost-effective and environmentally friendly,especially the use of metal-hyperaccumulating plants to extract or mine heavy metals from polluted soils.Under Cd stress,responses of hyperaccumulator and non-hyperaccumulator plants differ in morphological responses and physiological processes such as photosynthesis and respiration,uptake,transport,and assimilation of minerals and nitrogen,and water uptake and transport,which contribute to their ability to accumulate and detoxify Cd.This review aims to provide a brief overview of the recent progresses in the differential responses of hyperaccumulator and non-accumulator plants to Cd toxicity in terms of growth and physiological processes.Such information might be useful in developing phytoremediation technology for contaminated soils.     

油葵和苦荬菜根际土壤中镉和锌的活化机制及修复潜力比较

  目的  研究油葵和苦荬菜根际土壤固、液相对镉（Cd）和锌（Zn）的活化机制,比较两种植物在轻、中度复合污染农田的修复潜力。  方法  通过大田试验种油葵和苦荬菜,测定成熟期土壤的pH值、有机酸、重金属总量及其生物有效性;测定土壤溶液中的溶解性有机质（DOM）、主要离子、水溶态重金属及其形态分布;测定植物各部位中重金属的浓度及形态,通过计算重金属在植物中的富集系数（BCF）和转运系数（TF）,比较两种植物对土壤重金属污染的修复潜力。  结果  油葵和苦荬菜根系分泌的低分子有机酸均使根际土壤pH值下降明显,显著低于非根际土壤（P < 0.05）;苦荬菜根际土中低分子有机酸及DOM的浓度显著高于油葵根际土（P < 0.05）。两种植物根际土壤溶液中的Cd以离子态和DOM结合态为主,Zn以离子态为主;两种植物根际土壤中有效态的Cd差异不显著,油葵根际有效态Zn显著高于苦荬菜;两种植物根际土壤的Zn和Cd有效态与土壤溶液中Cd-DOM和Zn-DOM呈显著相关。苦荬菜根对重金属的富集能力较强,但油葵地上部分能吸收转运更多的Cd和Zn,并在叶中以毒性较低的不溶性磷酸盐结合态和草酸结合态富集。  结论  两种植物根际分泌的有机酸可以增加根际土壤中的Cd-DOM和Zn-DOM的浓度,提高土壤中的Cd和Zn的有效性,苦荬菜根际对重金属有较强的活化能力,但油葵地上部分对Cd和Zn的吸收转运能力更强。两种植物都具有较强的土壤重金属修复潜力,但从经济角度出发,油葵更适合现阶段我国农田重金属污染的修复。     

采用根滤去污工艺的污水净化植物补救系统决策支持软件

为了开发利用植物去除因吸收污染水而产生的重金属的商业化根滤系统和植物去污补救工艺,研究开发了微型计算机软件,以便为该系统的设计与运行提供参考。建立了一个基于Michaelis-Menton方程的工艺模型,可以定量确定在根滤系统中的植物积累和去除毒素物质的能力。采用一系列的算法处理信息并编入一个根滤设施的系统模型内。该系统模型将植物补救系统的物理元件——植物苗圃、根过滤系统、水的前处理与后处理、植物生物质的产后处理等与系统设计的工程方面包括工艺、运行、设施和系统集成结合起来。该软件内含的工程经济分析工具可用于分析主要设计变量对系统效率的影响     

Community structure of arbuscular mycorrhizal fungi associated with Robinia pseudoacacia in uncontaminated and heavy metal contaminated soils

The significance of arbuscular mycorrhizal fungi (AMF) in soil remediation has been widely recognized because of their ability to promote plant growth and increase phytoremediation efficiency in heavy metal (HM) polluted soils by improving plant nutrient absorption and by influencing the fate of the metals in the plant and soil. However, the symbiotic functions of AMF in remediation of polluted soils depend on plant–fungus–soil combinations and are greatly influenced by environmental conditions. To better understand the adaptation of plants and the related mycorrhizae to extreme environmental conditions, AMF colonization, spore density and community structure were analyzed in roots or rhizosphere soils of Robinia pseudoacacia. Mycorrhization was compared between uncontaminated soil and heavy metal contaminated soil from a lead–zinc mining region of northwest China. Samples were analyzed by restriction fragment length polymorphism (RFLP) screening with AMF-specific primers (NS31 and AM1), and sequencing of rRNA small subunit (SSU). The phylogenetic analysis revealed 28 AMF group types, including six AMF families: Glomeraceae, Claroideoglomeraceae, Diversisporaceae, Acaulosporaceae, Pacisporaceae, and Gigasporaceae. Of all AMF group types, six (21%) were detected based on spore samples alone, four (14%) based on root samples alone, and five (18%) based on samples from root, soil and spore. Glo9 (Rhizophagus intraradices), Glo17 (Funneliformis mosseae) and Acau3 (Acaulospora sp.) were the three most abundant AMF group types in the current study. Soil Pb and Zn concentrations, pH, organic matter content, and phosphorus levels all showed significant correlations with the AMF species compositions in root and soil samples. Overall, the uncontaminated sites had higher species diversity than sites with heavy metal contamination. The study highlights the effects of different soil chemical parameters on AMF colonization, spore density and community structure in contaminated and uncontaminated sites. The tolerant AMF species isolated and identified from this study have potential for application in phytoremediation of heavy metal contaminated areas.     

用突变点检测方法预测木生境下污染土壤中的可提性镉、铅和锌

Accumulation of heavy metals in soils poses a potential risk to plant production, which is related to availability of the metals in soil. The phytoavailability of metals is usually evaluated using extracting solutions such as salts, acids or chelates. The purpose of this study was to identify the most significant soil parameters that can be used to predict the concentrations of acetic and citric acid-extractable cadmium (Cd), lead (Pb) and zinc (Zn) in contaminated woody habitat topsoils. Multiple linear regression models were established using two analysis strategies and three sets of variables based on a dataset of 260 soil samples. The performance of these models was evaluated using statistical parameters. Cation exchange capacity, CaCO3, organic matter, assimilated P, free Al oxide, sand and the total metal concentrations appeared to be the main soil parameters governing the solubility of Cd, Pb and Zn in acetic and citric acid solutions. The results strongly suggest that the metal solubility in extracting solutions is extractable concentration-dependent since models were overall improved by incorporating a change point. This change point detection method was a powerful tool for predicting extractable Cd, Pb and Zn. Suitable predictions of extractable Cd, Pb and Zn concentrations were obtained, with correlation coefficient (adjusted r) ranging from 0.80 to 0.99, given the high complexity of the woody habitat soils studied. Therefore, the predictive models can constitute a decision-making support tool for managing phytoremediation of contaminated soils, making recommendations to control the potential bioavailability of metals. The relationships between acetic and/or citric acid-extractable concentrations and the concentrations of metals into the aboveground parts of plants need to be predicted, in order to make their temporal monitoring easier.     

Effects of cadmium stress on seedlings of various rangeland plant species (Avena fatua L., Lathyrus sativus L., and Lolium temulentum L.): Growth,physiological traits,and cadmium accumulation

A pot culture experiment was performed to study the effect of cadmium stress (Cd stress) on seedling growth, physiological traits, and remediation potency of Avena fatua, Lathyrus sativus, and Lolium temulentum. The seedlings of these native rangeland plant species were treated with 0, 2, 4, and 6 mM cadmium nitrate concentrations. Based on the results of analysis of variance (p < 0.05), the shoot height, shoot dry weight, root length, root dry weight, root: shoot ratio, total chlorophyll content, soluble sugars, and protein contentof A. fatua, L. sativus, and L. temulentum significantly decreased with increased cadmium concentrations. Generally, translocation factor (TF) and tolerance index (TI) decreased significantly as the concentration of cadmium increased. The maximum TF and TI of studied plants in various concentrations of Cd were observed in L. temulentum followed by L. sativus and A. fatua. The root concentration factor (RCF) values of all studied plants were higher than 1 under different cadmium concentrations. Our results indicate that Lolium temulentum could be labeled as an accumulator of Cd asthe values of TF and RCF are greater than 1. A. fatua and L. sativus showed a potential to be used in the phytoremediation of Cd-contaminated soils.     

Heavy metal accumulation in plants on Mn Mine tailings

The profile distribution of β-gulcosidase activity in twelve typical paddy soil profiles with high productivity in the Taihu Lake region of China were investigated. Activities of β-gulcosidase in the plow layers were in the range of 52.68- 137.02μg PNP g^-1 soil h^-1 with a mean of 89.22μg PNP g^-1 soil h^-1. However, most plow layers ranged from 70 to 110 μg PNP g^-1 soil h^-1. The profile distribution of β-gulcosidase activity in the 12 soil profiles decreased rapidly with soil depth, with activity at the 60 cm depth only about 10% of that in the surface layers （0-15 cm or 0-20 cm）. In these soil profiles, β-gulcosidase activity was significantly positively correlated with soll organic carbon and arylsulphatase activity. Meanwhile, a significantly negative correlation was shown between β-gulcosidase activity and soil pH.