四川甘洛铅锌矿区优势植物的重金属含量

通过野外调查采样,分析了四川凉山州甘洛县铅锌矿区土壤的重金属含量,以及矿区生长的13种优势植物对Pb、Zn、Cd、Cr、Cu的吸收与富集能力及其富集特性.结果表明,矿区土壤受Pb、Zn、Cd 3种重金属污染严重,13种植物体内的Pb含量均高于普通植物10倍以上,具有修复矿区土壤铅污染的潜力,其中植物1的转运系数和富集系数都大于1,满足Pb超富集植物的基本特征.Zn在凤尾蕨、细风轮菜、大火草、蔗茅、小飞蓬和牛茄子中含量较高.小飞蓬和紫茎泽兰的Cd含量较一般植物高出17～61倍,其中,紫茎泽兰的转运系数与富集系数均大于1,其对Cd的吸收特性值得进一步研究.     

Functional expression of a bacterial heavy metal transporter in Arabidopsis enhances resistance to and decreases uptake of heavy metals

Large parts of agricultural soil are contaminated with lead (Pb) and cadmium (Cd). Although most environments are not heavily contaminated, the low levels observed nonetheless pose a high risk of heavy metal accumulation in the food chain. Therefore, approaches to develop plants with reduced heavy metal uptake are important. Recently, many transgenic plants with increased heavy metal resistance and uptake of heavy metals were developed for the purpose of phytoremediation. However, to reduce heavy metal in the food chain, plants that transfer less heavy metals to the shoot are required. We tested whether an Escherichia coli gene, ZntA, which encodes a Pb(II)/Cd(II)/Zn(II) pump, could be useful for developing plants with reduced heavy metal content. Yeast cells transformed with this gene had improved resistance to Pb(II) and Cd(II). In Arabidopsis plants transformed with ZntA, ZntA was localized at the plasma membrane and improved the resistance of the plants to Pb(II) and Cd(II). The shoots of the transgenic plants had decreased Pb and Cd content. Moreover, the transgenic protoplasts showed lower accumulation of Cd and faster release of preloaded Cd than wild-type protoplasts. These results show that a bacterial transporter gene, ZntA, can be functionally expressed in plant cells, and that that it may be useful for the development of crop plants that are safe from heavy metal contamination.     

Evaluation of Transgenic Poplars Over-Expressing Enzymes of Glutathione Synthesis for Phytoremediation of Cadmium

Abstract: Recently, phytoremediation of soils polluted with heavy metals has received a lot of attention. Since glutathione (GSH) and its derivatives (e.g., phytochelatins) play a major role in plant defence against environmental pollutants, we tested the effects of over-expression of bacterial genes for GSH synthesis in poplar on cadmium accumulation. A pilot experiment with CdCl₂ in hydroponics revealed that poplars over-expressing γ-glutamylcysteine synthetase (γ-ECS) accumulated significantly more Cd in root tissue than wild type or glutathione synthetase over-expressing poplars. To test the partitioning of Cd in different organs, poplar lines over-expressing γ-ECS in the cytosol and in chloroplasts were treated with 0.2 mM CdCl₂ in hydroponics. Significant amounts of Cd were translocated to leaves, but significant differences in Cd accumulation were not observed between transgenic and wild type plants. To evaluate these lines for large-scale phytoremediation of cadmium, plants were treated with 2 mM Cd in soil. Over a four-week period, the poplar plants were able to accumulate up to 5.3 mg Cd. Most remarkably, in young leaves of both transgenic lines, Cd was accumulated to concentrations 2.5 - 3 times higher than in the wild type. The increased allocation of cadmium to the young leaves represents a potentional advantage for the phytoremediation process using the same plants over several vegetation periods. The use of transgenic poplar lines with enhanced glutathione production capacity seems to be of particular advantage in highly polluted soils.     

Evaluation of heavy metal availability prior to an <Emphasis Type="Italic">in situ</Emphasis> soil phytoremediation program

Metal mobility and the fractionation of elements and thus the biological uptake of Zn, Pb and Cd by plants were investigated using a simplified analytical procedure for soluble and bioavailable metals using a four-step sequential extraction procedure. Results showed that there was a low proportion of immediately soluble metals, as well as a high proportion of metals that could be released and would so be available for plant uptake. In the sequential extraction procedure, considering the total partition, there was a large proportion of Pb, Cd and Zn extracted in a readily mobile form. In acidic soils the content of metals in ready mobile form (exchangeable-bound to carbonates as well as to Fe and Mn oxides) and bound to organic matter constitutes an important source of potentially available elements. The same pattern was observed in alkaline soils, where almost 80% of the metals could be remobilized and be potentially available to plants. Knowing the metal partitioning and mobility of heavy metals it is very important for evaluating the phytoremediation efficiency.     

Modeling of phytoextraction efficiency of microbially stimulated Salix dasyclados L. in the soils with different speciation of heavy metals

Bioaugmentation of soils with selected microorganisms during phytoextraction can be the key solution for successful bioremediation and should be accurately calculated for different physicochemical soil properties and heavy metal availability to guarantee the universality of this method. Equally important is the development of an accurate prediction tool to manage phytoremediation process. The main objective of this study was to evaluate the role of three metallotolerant siderophore-producing Streptomyces sp. B1–B3 strains in the phytoremediation of heavy metals with the use of S. dasyclados L. growing in four metalliferrous soils as well as modeling the efficiency of this process based on physicochemical and microbiological properties of the soils using artificial neural network (ANN) analysis. The bacterial inoculation of plants significantly stimulated plant biomass and reduced oxidative stress. Moreover, the bacteria affected the speciation of heavy metals and finally their mobility, thereby enhancing the uptake and bioaccumulation of Zn, Cd, and Pb in the biomass. The best capacity for phytoextraction was noted for strain B1, which had the highest siderophore secretion ability. Finally, ANN model permitted to predict efficiency of phytoextraction based on both the physicochemical properties of the soils and the activity of the soil microbiota with high precision.     

Phytoavailability of Heavy Metals and Metalloids in Soils Irrigated with Wastewater,Akaki, Ethiopia: A Greenhouse Study

Irrigation with untreated wastewater from several industrial, commercial, and domestic discharges for decades caused accumulation of various heavy metals and metalloids in soils along the Akaki River in Ethiopia. Assessment of environmental threats and the potential phytoremediation of the soils require understanding of the toxic elements’ uptake and distribution in plant parts. Hence, a greenhouse study was performed to examine the phytoavailability and distribution of Cr, Ni, Co, Cu, Zn, Cd, Pb, Hg, Se, V, and As in forage grasses: Oat (Avena sativa), Rhodes grass (Chloris gayana), Setaria (Setaria sphacelata), and the legumes Alfalfa (Medicago sativa) and Desmodium (Desmodium unicinatum). The average contents of Cr, Ni, Co, Cu, Zn, Pb, Hg, Se, and V in the plants were generally higher than the background levels for forage grasses/legumes, and some of these elements were in the phytotoxic range. Root bioconcentration factor (BCF = root to soil concentration ratio) > 1 was observed for Cu (Oat, Rhodes, Desmodium, and Setaria: Fluvisol), Zn (Setaria: Fluvisol), Cd (Rhodes: Fluvisol; Setaria from both soils) and Hg (Oat and Alfalfa: Fluvisol). Alfalfa and Desmodium displayed translocation factor > 1 (TF = shoot to root concentration ratio) for most heavy metals. Most heavy metals/metalloids may pose a health threat to humans and stock via introduction to the food chain. The plant factors (species and plant part), soil factors (soil type, soil fractions, pH, and CEC), and their interactions significantly (p < 0.05) influenced plant heavy metal and metalloid levels. However, the role of plant part and species emerged as the most important on heavy metal uptake, translocation, sequestration, and ultimately transfer to the food chain. Accordingly, the uptake and distribution of heavy metals/metalloids in the plants reflect the potential environmental and health hazards attributable to the use of fodder grasses, legumes, and cultivation of vegetables in soils with polymetallic and metalloid contamination.     

Mobility and Translocation of Heavy Metals from Mine Tailings in Three Plant Species after Amendment with Compost and Biosurfactant

An experiment was performed to determine the effects of mine tailings alone mixed with compost or with compost plus crude biosurfactant on the accumulation of heavy metals (Pb, Zn, Cu, Cr, Cd, and Ni) in Acacia retinodes, Nicotiana glauca, and Echinochloa polystachya. The plants were grown in soil, mine tailings, and mine tailings containing compost over a period of seven and five months for shrubs or grass, respectively. The plants Acacia retinodes and Nicotiana glauca grown in mine tailings containing compost showed increases in dry biomass (from 62 to 79%) compared with plants in only tailings. Heavy metals accumulated in the roots and leaves showed high translocation rates of Cr in N. glauca, Cd in A. retinodes, and Ni in E. polystachya. Concentrations of heavy metals in the three plants irrigated with crude biosurfactant were not significantly different from those irrigated with water. Zn and Cd fractions within mine tailings containing compost were bound to carbonate, Pb was bound to residues, and Cu was bound to Fe-oxides. Cd had the highest mobility factor followed in order by Zn, Pb, and Cu. The elevated concentrations of Pb in roots and the low translocation rate for N. glauca and A. retinodes indicate that they are suitable for phytostabilizing Pb and Zn.     

Phytoremediation potential of Eichornia crassipes in metal-contaminated coastal water

The potential of Eichornia crassipes to serve as a phytoremediation plant in the cleaning up of metals from contaminated coastal areas was evaluated in this study. Ten metals, As, Cd, Cu, Cr, Fe, Mn, Ni, Pb, V and Zn were assessed in water and the plant roots and shoots from the coastal area of Ondo State, Nigeria and the values were used to evaluate the enrichment factor (EF) and translocation factor (TF) in the plant. The critical concentrations of the metals were lower than those specified for hyperaccumulators thus classifying the plant as an accumulator but the EF and TF revealed that the plant accumulated toxic metals such as Cr, Cd, Pb and As both at the root and at the shoot in high degree, which indicates that the plant that forms a large biomass on the water surface and is not fed upon by animals can serve as a plant for both phytoextraction and rhizofiltration in phytoremediation technology.     

The potential of phytoremediation using hyperaccumulator plants: a case study at a lead-zinc mine site

Contamination with heavy metals is one of the most pressing threats to water and soil resources, as well as human health. Phytoremediation might potentially be used to remediate metal-contaminated sites. A major advance in the development of phytoremediation for heavy metal affected soils was the discovery of heavy metal hyperaccumulation in plants. This study applied several established criteria to identify hyperaccumulator plants. A case study was conducted at a mining area in the Hamedan province in the west central region of Iran. The results indicated that plant metal accumulation differed among species and plant parts. Plant species grown in substrata with elevated metal levels contained significantly higher metal levels. Using the most common criteria, Euphorbia macroclada and Centaurea virgata can be classified as hyperaccumulators of specific heavy metals measured in this study and they might potentially be used for the phytoremediation of contaminated soils.     

VETIVER GRASS,VETIVERIA ZIZANIOIDES: A CHOICE PLANT FOR PHYTOREMEDIATION OF HEAVY METALS AND ORGANIC WASTES

Glasshouse and field studies showed that Vetiver grass can produce high biomass (>100t/tha^?1 year^?1) and highly tolerate extreme climatic variation such as prolonged drought, flood, submergence and temperatures (?15°–55°C), soils high in acidity and alkalinity (pH 3.3–9.5), high levels of Al (85% saturation percentage), Mn (578 mg kg^?1), soil salinity (ECse 47.5 dS m^?1), sodicity (ESP 48%), and a wide range of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Se, and Zn). Vetiver can accumulate heavy metals, particularly lead (shoot 0.4% and root 1%) and zinc (shoot and root 1%). The majority of heavy metals are accumulated in roots thus suitable for phytostabilization, and for phytoextraction with addition of chelating agents. Vetiver can also absorb and promote biodegradation of organic wastes (2,4,6-trinitroluene, phenol, ethidium bromide, benzo[a]pyrene, atrazine). Although Vetiver is not as effective as some other species in heavy metal accumulation, very few plants in the literature have a wide range of tolerance to extremely adverse conditions of climate and growing medium (soil, sand, and tailings) combined into one plant as vetiver. All these special characteristics make vetiver a choice plant for phytoremediation of heavy metals and organic wastes.