Phytostabilization of heavy metals by the emergent macrophyte Vossia cuspidata (Roxb.) Griff.: A phytoremediation approach

The present study was conducted to investigate the potential of Vossia cuspidata as a phytoremediator to accumulate heavy metals from polluted water bodies. Thirty-two quadrats, distributed equally in eight sites (six polluted sites along the Ismailia canal and two unpolluted sites along the Nile River) were selected seasonally for plant, water, and sediment investigations. Winter plants recorded the highest values of shoot height, diameter, and leaf width, but the lowest shoot density. Plants collected in autumn had the lowest values of leaf length, width, and area, while those collected in spring had the highest shoot density, with the lowest shoot height. Summer populations had the highest fresh and dry plant biomass, while winter plants had the lowest. Fresh production and dry biomass of V. cuspidata in the unpolluted Nile were significantly higher than those in polluted canals. Chlorophyll a and carotenoid concentrations were reduced under pollution stress. Spring plants accumulated the highest concentrations of Cr, Cu, and Pb in their root, and the lowest concentrations of Al, Cd, Cr, and Zn in their shoot. The bioaccumulation factor for most investigated metals, except Al, Cr, and Fe was greater than 1, while the translocation factor of all metals was less than 1, therefore this plant is considered to be a potential for these metals phytostabilization.     

金属型植物的研究进展

金属型植物是治理和修复土壤重金属污染的理想材料.综述了金属型植物的耐性机理、生殖生物学及进化生态学方面的研究进展,并对目前研究中存在的问题进行了分析和展望.     

Phytostabilization of iron ore tailings through Calophyllum inophyllum L

The phytostabilization of waste material generated during mining and processing of iron ore through Calophyllum inophyllum L. have been investigated. Iron ore tailings and its varying composition with garden soil were taken to study plant growth, chlorophyll content and metal uptake pattern of Calophyllum inophyllum L. These studies indicate that 100% survival of plant species was noted in all the treatments without any toxicity symptoms. The increase in growth parameters and chlorophyll content along with the high metal accumulation in plant tissues suggests that Calophyllum inophyllum L. may be a potential tool for phytoremediation. The accumulation of Pb (1662 microgm/gm) and Fe (2313 microgm/gm) was observed to be maximum in the plant tissues followed by Cu, Zn, Cr, and Ni. The TF values for most of the heavy metals was observed to be > 1 which indicates that the plant can efficiently translocate these toxic metals to its above ground parts. Removal of more than 30% of the most of the heavy metal like Fe, Pb, and Cu & Zn has been observed in all the treatments during one year of observation. The overall study clearly suggests that the plant can be used as an efficient tool for restoration of mining wastes and other similarly contaminated sites.     

Effect of Organic Manures on the Growth of Cymbopogon citratus and Chrysopogon zizanioides for the Phytoremediation of Chromite-Asbestos Mine Waste: A Pot Scale Experiment

The abandoned chromite-asbestos mines are located in the Roro hills, West Singhbhum, Jharkhand, India, where mining operation ceased in 1983, and since then these mines are causing environmental pollution. The present study was planned to phytoremediate these metalloid and metal contaminated mine waste by using two aromatic grasses, Cymbopogon citratus and Chrysopogon zizanioides by applying different proportions of amendments (chicken manure, farmyard manure and garden soil). Mine waste has neutral pH, low electrical conductivity and organic carbon with higher concentration of total metals (Cr and Ni) as compared to soil. Application of manures resulted significant improvements of mine waste characteristics and plant growth, reduction in the availability of total extractable toxic metals (Cr, Ni) and increase in Mn, Zn and Cu concentration in the substrate. The maximum growth and biomass production for C. citratus and C. zizanioides were found in T-IV combination comprising of mine waste (90%), chicken manure (2.5%), farmyard manure (2.5%) and garden soil (5%). Addition of T-IV combination also resulted in low Cr and Ni accumulation in roots and reduction in translocation to shoots. Study indicates that C. citratus and C. zizanioides can be used for phytostabilization of abandoned chromite-asbestos mine waste with amendments.     

High potential of symbiotic interactions between native mycorrhizal fungi and the exotic tree Eucalyptus camaldulensis for phytostabilization of metal-contaminated arid soils

Waste dumps generated by mining activities contain heavy metals that are dispersed into areas leading to significant environmental contamination. The objectives of this study were (i) to survey native plants and their associated AM fungal communities from waste soils in a Moroccan mine site and (ii) to follow Eucalyptus growth in soil collected from the waste-mine. AM spores from native plant species were collected from the mining site and the surrounding uncontaminated areas were multiplied and inoculated onto Eucalyptus camaldulensis. The results showed that (i) the native plant species recorded in the waste did not show an active metal uptake, (ii) the selected native plant species are associated with AM mycorrhizal fungi and (iii) the use of AM fungi adapted to these drastic conditions can improve the growth of the fast-growing tree, E. camaldulensis and its tolerance to high soil Cu content. In conclusion, it is suggested that in order to define efficient low-cost phytostabilization processes, the use of native resources (i.e., mixtures of native mycorrhizal fungi) in combination with fast-growing tree species such as Eucalyptus, could be used to optimize the establishment of a permanent cover plant in contaminated areas.     

Evaluation of Mycorrhizal Influence on the Development and Phytoremediation Potential of Canavalia Gladiata in Pb-Contaminated Soils

Soil contamination by heavy metals is a serious problem to humans due to its high level of toxicity. The heavy metal lead (Pb) is commonly used in industries and if the disposal of residues that contain this element is not done properly may result in tragic consequences to the organisms. In this experiment we assessed the potential of a forrage leguminous, Canavalia gladiata, to phytoremediate lead-contaminated soil under mycorrhizal influence. The experimental design was composed of 4 Pb doses (0, 250, 500, and 1000 mg kg^?1 of soil) and the plants were inoculated or uninoculated with arbuscular mycorrhizal fungi (AMF). We observed that the nodulation was severely affected by the presence of Pb independently of the mycorrhizal status; most of the elements analyzed were affected independently of the mycorrhizal status with exception of P. The mycorrhizal colonization was able to restrict the entrance of Pb in plants under high concentrations of Pb but promoted it's accumulation in both organs under intermediate concentrations of this element. Besides the mycorrhization did not promote plant growth under Pb stress, the use of this plant may be considered to be used for phytostabilization purposes.     

Plant Communities in Multi-Metal Contaminated Soils: A Case Study in the National Park of Alta Murgia (Apulia Region - Southern Italy)

A phytosociological study was conducted in the National Park of Alta Murgia in the Apulia region (Southern Italy) to determine the adverse effects of metal contamination of soils on the distribution of plant communities. The phytosociological analyses have shown a remarkable biodiversity of vegetation on non-contaminated soils, while biodiversity appeared strongly reduced on metal-contaminated soils. The area is naturally covered by a wide steppic grassland dominated by Stipa austroitalica Martinovský subsp. austroitalica. Brassicaceae such as Sinapis arvensis L. are the dominating species on moderated contaminated soils, whereas spiny species of Asteraceae such as Silybum marianum (L.) Gaertn. and Carduus pycnocephalus L. subsp. pycnocephalus are the dominating vegetation on heavily metal-contaminated soils. The presence of these spontaneous species on contaminated soils suggest their potential for restoration of degraded lands by phytostabilization strategy.     

Phytoremediation Potential of Plants Growing on the Pb-Contaminated Soil at the Song Tho Pb Mine,Thailand

The contamination of lead (Pb) is one of the main environmental problems on a global scale. This study assessed the potential of native metallophytes growing on the Song Tho Pb mine in Kanchanaburi province, Thailand, by a field survey. Plants and the associated soil samples were collected. Total Pb concentrations were analyzed by a flame atomic absorption spectrophotometer after a microwave-assisted acid digestion. While total Pb concentrations of top soils varied from 4881 to 16,720 mg/kg, those in soil around the roots ranged from 421 to 48,883 mg/kg. A total of 12 species belonging to eight families accumulated Pb concentrations in roots (47–32,633 mg/kg) which were higher than those in shoots (non-detected values – 1489 mg/kg). Bidens pilosa, with Pb accumulation in shoots > 1000 mg/kg and translocation factor (TF) > 1, could be useful in phytoextraction as a hyperaccumulator. Thysanolaena latifolia and Mimosa pudica with bioconcentration factor > 1 and TF < 1 could be useful in phytostabilization as excluders. So far, not many Pb hyperaccumulators are reported. The results from this study proposed a new candidate, B. pilosa, for Pb extraction. The potential use of these three phytoremediators should be further investigated using hydroponic and pot experiments.     

The role of the cell wall in the mechanism of lead and zinc tolerance in Anthoxanthum odoratum L

The respiration rate and viability of cultured cells and protoplasts isolated from two clones of Anthoxanthum odoratum tolerant to both zinc and lead were unaffected by the presence of zinc. Although intact cells were largely unaffected by the presence of lead, protoplasts isolated from cultured cells were susceptible, showing a reduced respiration rate and a high mortality. In contrast cultured cells and protoplasts of non-tolerant clones of A. odoratum were susceptible to both zinc and lead. The results provide direct evidence that in A. odoratum the cell wall is part of the mechanism of tolerance to lead, but not to zinc.     

Identification and characterization of Cr-, Cd-, and Ni-tolerant bacteria isolated from mine tailings

Eleven bacterial strains were isolated from soil samples collected from mine tailings. Bacterial strains were checked for tolerance against heavy metals (Cr, Cd, Ni), using the agar dilution method. All the strains showed multiple tolerances against heavy metals, but the most promising results appeared in strains BCr3, BCd33, and BNi11: they were tolerant to 15 mM of Cr⁶⁺, 7.5 mM of Cd²⁺, and 10 mM of Ni²⁺, respectively. The effect of heavy metals on bacterial growth was tested together with their ability to grow in different pH, NaCl, and temperature values. Bacterial isolates grew well between pH 7.5 and 8.5. The optimum temperature for maximum growth was between 35 and 37°C, and no significant change in bacterial growth was observed in the presence of 2% NaCl. In addition, the bioaccumulation potential of bacterial strains was investigated. Bacterial strains BCr3, BCd33, and BNi11 showed high bioaccumulation ability of Cr (68.7%), Cd (72.4%), and Ni (69.8%), respectively. All bacterial isolates were identified by 16S rRNA gene sequencing. Analysis of plasmid content revealed that all bacterial isolates contained a single plasmid. Further, polymerase chain reaction together with DNA sequence analysis was used to screen all bacterial strains for the presence metal tolerance genes (czcD, chrA, chrB, czcB, czcC, nccA, and cadA) on both plasmid and chromosomal genomes.     

Use of Cordia Africana in the Phytostabilization of Substrates from Excavations of the Ore Courtyard at the Port of Itaguai,Brazil

The objective of this study was to evaluate the phytostabilization of two substrates contaminated with heavy metals from excavations of the ore courtyard at the port of Itaguai, Brazil. Initially, an inventory of tree species located near the study area was performed to select species for phytostabilization. The species Cordia africana exhibited deeper roots, a larger diameter at chest height (DCH) and crown diameter, as well as higher concentrations of Zn, Cd, and Pb in the trunk, bark, and roots compared to the other investigated species. The tolerance of the selected species to the metals Zn, Cd, and Pb was subsequently assessed through a greenhouse test. The substrates used in the experiment also obtained from excavations at the ore courtyard and showed different levels of heavy metals, indicating either low contamination (Substrate 1) or high contamination (Substrate 2). Alkaline industrial waste steel slag (SS) was used as an amendment to reduce the solubility of heavy metals. Application of the amendment agent to the substrates reduced the bioavailability of heavy metals, favoring the growth of C. africana. This species presents potential for use in phytostabilization programs due to its tolerance for heavy metals and the observed higher accumulation of these metals in the roots and especially the trunk of this species compared to other vegetal parts.     

Risk Assessment of the Abandoned Jukjeon Metal Mine in South Korea Following the Korean Guidelines

Toxic metal contamination in the vicinity of Korean abandoned metal mines has been reported. A risk assessment for these metals was performed for the inhabitants in the area of the abandoned Jukjeon metal mine. Soil, groundwater, and crop samples were collected around the mine. After pretreatment of these samples, metal concentrations were measured and then a risk assessment was performed using the Korean soil-contamination risk assessment guidelines. Phytoaccumulation of metals in crops was observed in soybeans (As and Zn), red peppers (Zn), sweet potatoes (As and Zn), and cabbage (Cu), which had higher metal concentrations than soils in the area. The metal intake rate was highest for inhalation of soil. Cancer risk was highest from ingestion of As-contaminated crops. The sum of carcinogenic risks was 6.29 × 10^–3. The non-carcinogenic risk was highest for ingestion of As-contaminated crops (8.17). Most of the risks were attributable to As, Pb, and Hg contamination, therefore these three metals must be considered as the principal metals toxic to human health in the sampled area. In particular, the inhalation of metal-contaminated soil should be considered for risk assessment along with ingestion of water and crops in abandoned mine areas.     

Correlation between NaCl Sensitivity of Rhizobium Bacteria and Ineffective Nodulation of Leguminous Plants

A sodium chloride (NaCl)-sensitive mutant of Rhizobium fredii USDA191, which contained a single copy of Tn5-Mob transposed into chromosomal DNA, was obtained by Tn5-Mob random insertion. The growth rate of this mutant was lower than that of the wild type in the presence of 0.2 M NaCl and it seemed to lack the inductive ATP production in response to the addition of NaCl. This mutant induced the formation of small and whitish nodules on lateral roots of soybeans, which were negative for acetylene reduction activity, indicating that the nodules were ineffective for nitrogen fixation. The mutant also reduced the weight of above-ground portions and roots to 64 and 55%, respectively, compared with the weight of the plants inoculated with the wild-type cells. These results suggest that NaCl sensitivity of Rhizobium bacteria is one of the important factors for nodule formation and nitrogen fixation.     

Cadmium Sorption Characteristics of Soil Amendments and its Relationship with the Cadmium Uptake by Hyperaccumulator and Normal Plants in Amended Soils

In order to select appropriate amendments for cropping hyperaccumulator or normal plants on contaminated soils and establish the relationship between Cd sorption characteristics of soil amendments and their capacity to reduce Cd uptake by plants, batch sorption experiments with 11 different clay minerals and organic materials and a pot experiment with the same amendments were carried out. The pot experiment was conducted with Sedum alfredii and maize (Zea mays) in a co-cropping system. The results showed that the highest sorption amount was by montmorillonite at 40.82 mg/g, while mica was the lowest at only 1.83 mg/g. There was a significant negative correlation between the n value of Freundlich equation and Cd uptake by plants, and between the logarithm of the stability constant K of the Langmuir equation and plant uptake. Humic acids (HAs) and mushroom manure increased Cd uptake by S. alfredii, but not maize, thus they are suitable as soil amendments for the co-cropping S. alfredii and maize. The stability constant K in these cases was 0.14–0.16 L/mg and n values were 1.51–2.19. The alkaline zeolite and mica had the best fixation abilities and significantly decreased Cd uptake by the both plants, with K ≥ 1.49 L/mg and n ≥ 3.59.     

Broad environmental tolerance of native root-nodule bacteria of Biserrula pelecinus indicate potential for soil fertility restoration

Background: Biserrula pelecinus is an annual legume native to the Mediterranean basin, found in pastureland, alone or in association with other legumes (Leguminosae) and grasses (Poaceae). It has been used in revegetation programmes of mining wastes showing phytoremediation potentials and thus becoming potentially highly attractive for plant ecology and restoration management of natural ecosystems.

Aims: To characterise native root-nodule bacteria isolated from B. pelecinus from the Iberian Peninsula, and to select suitable N fixers for field-application and soil rehabilitation.

Methods: Strains were isolated and molecularly identified by 16S rRNA amplification and sequencing. Strains were phenotypically characterised in different abiotic conditions (acidity, salinity and heavy metals) and tested for their ability to fix atmospheric N₂. The most suitable N fixers were applied in greenhouse experiments with B. pelecinus under different fertilization levels to assess their tolerance to fertilized and polluted soils, commonly encountered in restoration projects.

Results: B. pelecinus root-nodule isolates tolerated pH from 4.5 to 9.5 grew in saline conditions (2.5% of NaCl), and tolerated 50 µM of Al³⁺ and Mn²⁺. Three isolates efficient in N₂ fixation, relative to the reference Mesorhizobium strain, were considered excellent candidates for the amelioration of nutrient poor sites.

Conclusions: These results provide valuable information for the potential use in soil restoration of B. pelecinus in a wide-range of conditions, exploiting the natural variability of its root-nodule bacteria.     

Molecular biology of metal tolerances of plants

Abstract. The review discusses some of the important aspects of the molecular biology of metal tolerances in animals, fungi and plants. First, results of classical ecological and genetical studies are briefly outlined. The evidence for the occurrence and properties of metal-binding proteins (metallothioneins) and peptides (phytochelatins) in fungi and plants is described. It is concluded that at present there is no firm evidence to suggest that a protein homologous with the metallothioneins of animals and fungi occurs in plants. The discovery of phytochelatins, γ-glutarnyl peptides, containing only glutamic acid, cysteine and glycine, in plants is described and evidence for their role in heavy metal tolerance is assessed. The difference between sulphur metabolism in animals and plants and its relationship to heavy metal tolerances is discussed in terms of the occurrences of metallothioneins in animals and phytochelalins in plants. Future prospects for research in this area are outlined in terms of identification of plant genes coding for metallothioneins and for the enzymes involved in the synthesis of phytochelatins.     

Lygus hesperus （Heteroptera： Miridae） tolerates high concentrations of dietary nickel

Nickel hyperaccumulator plants contain unusually elevated levels of Ni （〉 1 000 μg Ni/g）. Some insect herbivores, including Lygus hesperus （Western tarnished plant bug）, have been observed feeding on the California Ni hyperaccumulator Streptanthus polygaloides. This bug may be able to utilize S. polygaloides as a host either through its feeding behavior or by physiological tolerance of Ni. This experiment determined the Ni tolerance of L hesperus by offering insects artificial diet amended with 0, 0.4, 1, 2, 4.5, 10, 20 and 40 mmol Ni/L and recording survival. Survival varied due to Ni concentration, with diets containing 10 mmol Ni/L and greater resulting in significantly lower survival compared to the control （0 mmol Ni/L） treatment. Insects tolerated diet containing as much as 4.5 mmol Ni/L, a relatively elevated Ni concentration. I conclude that L hesperus can feed on S. polygaloides because it is Ni-tolerant, probably due to physiological mechanisms that provide it with resistance to plant chemical defenses including elemental defenses such as hyperaccumulated Ni.     

超富集植物对重金属耐受和富集机制的研究进展

超富集植物对重金属耐受和富集机制的研究成为近年来植物逆境生理研究的热点,在简要总结细胞壁沉淀、重金属螯合效应、酶活性机制和细胞区室化作用的基础上,概述了超富集植物对重金属的耐受机制,讨论了重金属跨根细胞质膜运输,共质体内运输、木质部运输和跨叶细胞膜运输的富集过程。     

Leaching of Cd,Zn, Pb,and Cu in Packed and Undisturbed Columns of Soils Affected by the Spill from a Pyrite Mine in the South of Spain

A study has been made of the leaching of Cd, Zn, Pb, and Cu in three representative soils within the zone affected by the spill from a pyrite mine in Aznalcollar (Sevilla, Spain) employing packed soil columns. According to the breakthrough and cumulative leaching curves, the relative mobilities of the different toxic elements in the columns are as follows: Cd> Zn> Cu> Pb. The effect of leaching on the distribution of metals as a function of depth using intact soil cores was also studied. The results showed that the soils themselves have a good capacity for immobilizing the soluble fraction of the elements from the spilled mud. This capacity varied as follows: clayey soil with a high carbonate content > clayey soil with a moderate carbonate content > sandy-clay loam soil with a low carbonate content. However, sandy soils with a low carbonate content could pose a risk to groundwater if initial contamination was high. These results could be considered during the evaluation of remedial technologies for the immobilization of soil metals.