Selection of appropriate organic additives for enhancing Zn and Cd phytoextraction by hyperaccumulators

Chelant-enhanced phytoextraction is one of the most promising technologies to remove heavy metals from soil. The key of the technology is to choose suitable additives in combination with a suitable plant. In the present study, laboratory batch experiment of metal solubilization, cress seeds germination were undertaken to investigate the metal-mobilizing capability and the phytotoxicity of organic additives, including ethylene diamine triacetic acid （EDTA）, citric acid, acetic acid, oxalic acid, glutamine and monosodium glutamate waste liquid （MGWL） from food industry. Experiments in pots were carried out to study the effects of the additives on Zn and Cd phytoextraction. Furthermore, a leaching experiment with lysimeter was performed to evaluate the environmental risks of additive-induced leaching to underground water. The results showed that EDTA had a strong mobilizing ability for Zn and Cd, followed by mixed reagent （MR） and MGWL. MGWL and acetic acid at 5 mmol equivalent per liter resulted in seed germination index less than 2%. Experiments in pots verified the phytotoxicity of acetic acid and MGWL. Addition of the mixed reagent at 6--10 mmol/kg significantly increased Zn phytoextraction by Thlaspi caerulescens. The same for EDTA and the mixed reagent at 10 mmol/kg by Sedum dfredii. But only mixed reagents could significantly increase Cd phytoextraction by the studied hyperaccumulators. This suggested that the strong chelant was not always the good agent to enhance phytoextraction. S. alfredii combined with 2--10 mmol/kg soil MR was preferred for phytoremediation of Cd/Zn contaminated soils in southern China, this could result in high phytoextraction of Cd/Zn and reduce the leaching risk to underground water than EDTA assisted phytoextration.

Phytoextraction:A Cost-effective Approach to Metal-contaminated Soils

This paper will review the topic of phytoextraction,a major approach of phytoremediation,by clarifying the roles of hyperaccumulators,bio-mechanisms involved,issues regarding contaminant uptake,artificial chelation,genetic selection,and cultivation.The paper will also address the practical issues and the regulatory context of this emerging technology and briefly discuss avenues for future research.

Comparison on the phytoextraction efficiency of Bidens pilosa at heavy metal contaminated site in natural and electrokinetic conditions

The plant samples of Bidens pilosa were collected from a coal gangue vacant site and its surrounding area,located in central China,to study the remediation effect of the plant species on heavy metal(HM)contamination in both natural and electrokinetic(EK)conditions.The analytical results showed that the effect of phytoextraction and bioconcentration on the heavy metals in the sample of the EK group is more significant than those in the other control group.Compared with the results of natural condition,under the EK condition the concentrations of cadmium(Cd),lead(Pb),copper(Cu)and zinc(Zn)in the stems and leaves of the Bidens pilosa increased to 0.40 mg/kg,4.23 mg/kg,7.27 mg/kg,830.24 mg/kg,respectively,with their increments of 292%,1731%,141%,2076%.For root samples,the Cd,Pb,Cu and Zn concentrations increased to 0.52 mg/kg,4.36 mg/kg,10.87 mg/kg,and 98.12 mg/kg and the increase rates were 1034%,140%,29%,and 181%,respectively.The phytoextraction efficiency of the Bidens pilosa was significantly higher than that of control group.The removal efficiency of Cd,Pb,Cu and Zn in soil increased to 26%,72%,27%,and 79%with the EK applied.In addition,the mechanism of HM migration,extraction and enrichment in Bidens pilosa under the EK condition was discussed.

Isolation of Mucor circinelloides Z4 and Mucor racemosus Z8 from heavy metal-contaminated soil and their potential in promoting phytoextraction with Guizhou oilseed rap

Fungi Z4 and Z8, isolated from the heavy metal polluted soil, have strong resistance to Cd and Pb. The strains were identified on the base of their morphology and internal transcribed spacers(ITS) region. Pot experiments were conducted to study the effect of two strains(Z4 and Z8) on the growth and accumulation of Cd and Pb of Guizhou oilseed rape. The results show that strains Z4 and Z8 belong to Mucor circinelloides and Mucor racemosus, respectively. The heights of Guizhou oilseed rape inoculated with strain Z8 increase by 47.90% than the control. The highest fresh mass is found in the plant with Z4/Z8, which is enhanced by160.81%. Pot experiments show that Z4/Z8 inoculums can accelerate accumulation of heavy metals in the plant. The contents of Cd and Pb are increased by 117.60% and 63.48%, respectively. Meanwhile, the heavy metal concentrations in potting soil with the two strains are found to be lower than those of the control, and the concentrations of Cd and Pb are decreased by 60.57% and 27.12%,respectively.

Phytoextraction of Trace Metals (Cd, Ni and Pb) by Panicum maximum Grown on Natural Soil

This study aims to assess the effective capacity of Panicum maximum to accumulate cadmium (Cd), nickel (Ni) and lead (Pb). P. maximum observed in a greenhouse was subjected to 2 ppm of Cd, 50 ppm of Ni, 100 ppm of Pb contaminated soil and uncontaminated soil, for 120 days. Plant growth and biomass produced concentration of trace metals in soil and plant, bioaccumulation and transfer factors, location of potentially toxic elements in tissues and cells of plant have been determined. Stem length and biomass produced by P. maximum were higher on the uncontaminated soil followed respectively by those of soil-contaminated by Pb, Cd and Ni. Bioaccumulation factors of trace metals were 8.93 (Pb), 8.47 (Ni) and 3.37 (Cd). Ni was more accumulated in shoot biomass (FT > 1), while Pb and Cd were concentrated in root biomass (FT < 1). Pb is accumulated preferentially in endodermis (roots) and epidermis (leaves). As for Ni and Cd, they are concentrated in central cylinder of roots and in conductive bundles of leaves. At cellular level, Ni and Cd are mainly concentrated in intracellular compartments of leaves and roots, while Pb is strongly detected at cell walls.

Tissue culture tools for selenium hyperaccumulator Neptunia amplexicaulis for development in phytoextraction

Neptunia amplexicaulis is an herbaceous legume endemic to the Richmond area in central Queensland,Australia and is one of the strongest known Selenium hyperaccumulators on earth,showing significant potential to be utilised in Se phytoextraction applications.Here a protocol was established for in vitro micropropagation of Se hyperaccumula-tor N.amplexicaulis using nodal segments from in vitro-germinated seedlings.Shoot multiplication was achieved on Murashige and Skoog(MS)basal media supplemented with various concentrations of 6-Benzylaminopurine(BA)(1.0,2.0,3.0 mg L^(−1))alone or in combination with low levels of Naphthaleneacetic acid(NAA)(0.1,0.2,0.3 mg L^(−1)),with 2.0 mg L^(−1) BA+0.2 mg L^(−1) NAA found to be most effective.Elongated shoots were rooted in vitro using NAA,with highest root induction rate of 30%observed at 0.2 mg L^(−1) NAA.About 95%of the in vitro rooted shoots survived acclimatization.Clonally propagated plantlets were dosed with selenate/selenite solution and assessed for Se tissue concentrations using Inductively Coupled Plasma Atomic Emission Spectroscopy(ICP-AES)and found to retain their ability to hyperaccumulate.The protocol developed for this study has potential to be optimised for generating clonal plants of N.amplexicaulis for use in research and phytoextraction industry applications.

Phytoextraction of Metal Contaminants by Typha Angustifolia: Interaction of Lead and Cadmium in Soil-Water Microcosms

A greenhouse study was conducted on phytoextraction and accumulation of lead (Pb) and cadmium (Cd) from contaminated soil – water microcosms by the narrow-leaved cattail, Typha angustifolia. The plants were grown in sandy loam soil containing 1,666 and 38.5 mg/L of Pb(NO3)2 and Cd(NO3)2 respectively. The trends of lead and cadmium by T. angustifolia for all soil – water microcosms suggested interaction effects as decreased soil lead concentrations and increased water cadmium concentrations over time. T. angustifolia expressed trends as increased biomass in all contaminated shoots and roots examined. Cadmium uptake in shoot and root biomass slightly decreased when lead was initially added to the soil but cadmium uptake in root biomass increased after 30 days. Data suggested an interaction between lead and cadmium and possible that lead uptake was inhibited when cadmium was present.

A Comparison of the Solubilizing Potential of Some Aminopolycarboxylic Acids, Hortrilon^(█)and Fetrilon^(█)for Use in Phytoextraction

Phytoextraction has been introduced as a new technology to clean up soils contaminated with heavy metals as the use of conventional methods to clean up the soil is very expensive and destructive to the ecosystem. However, using plants to clean up contaminated soils takes a considerable period before the contaminants are removed from the soil by the plants. This has necessitated the use of amendments to enhance phytoextraction in order to shorten the period of contaminants removal by plants. In view of this, a pot experiment was conducted to study the effect of various aminopolycarboxylic acids (EDTA, EDDS, NTA dry and NTA liquid) and two commercial fertilizers which are Hortrilon? and Fetrilon? on their ability to solubilize Cd and Zn in contaminated soils. It was observed that the inducing effect of EDTA on the solubility of Cd and Zn persisted throughout the experimental period. Initially, EDDS enhanced the solubility Cd and Zn, however, its effect dissipated with time. The application of both NTA dry (powder) and NTA liquid had a significant effect on the solubility of Zn as a result of the formation of Zn-NTA soluble complexes. Hortrilon? and Fetrilon? solubilized significant concentrations of both Cd and Zn with Hortrilon? having the greatest inducing effect on the solubility of Cd and Zn.

Phytoextraction Capacity of <i>Chrysopogon nigritanus</i>Grown on Arsenic Contaminated Soil

This study aims to investigate the capacity of Chrysopogon nigritanus to accumulate As from contaminated soils. The experiment was conducted in a greenhouse. C. nigritanus was subjected to uncontaminated soil and As contaminated soil (50 mg/kg, 100 mg/kg and 150 mg/kg of As), for 180 days. Plant growth and biomass produced, concentration of As in soil and plant, bioaccumulation and transfer factors, as the location of As in tissues and cells of the plant have been determined. Plant growth decreased significantly with increasing of soil As concentration. C. nigritanus accumulated more As in roots biomass. The highest bioaccumulation factor values were found in contaminated soil at 50 mg As/kg (As 50), then contaminated soil at 100 mg As/kg (As 100) and contaminated soil at 150 mg As/kg (As 150). As was essentially fixed to the intracellular compartment of the roots, stems and leaves. In roots tissues, As was mainly retained in the rhizodermis and the pericycle. While in stems tissues, As was preferentially accumulated in the conductive bundles. In the leaves, the final destination of As was epidermis tissues.

Plant coexistence can enhance phytoextraction of cadmium by tobacco (Nicotiana tabacum L.) in contaminated soil

A mesocosm experiment was conducted to investigate whether plant coexistence affects cadmium （Cd） uptake by plant in contaminated soil. Tobacco （Nicotiana tabacum L. var. K326） and Japanese clover （Kummerowia striata （Thunb.） Schindl.） were used. Cadmium was applied as 3CdSO4.SH2O in solution at three levels （0, 1, and 3 mg/kg soil） to simulate an unpolluted soil and soils that were slightly and moderately polluted with Cd. Tobacco （crop）, Japanese clover （non-crop）, and their combination were grown under each Cd treatment. Compared to monoculture and under all Cd treatments, co-planting with Japanese clover did not affect tobacco biomass but significantly increased Cd concentration in all tobacco tissues and enhanced Cd accumulation in tobacco shoots and roots. Compared to monoculture, co-planting reduced soil pH and increased Cd bioavailability. For tobacco, co-planting with Japanese clover increased the Cd bioconcentration factor （BCF） in Cd contaminated soil. Japanese clover also accumulated substantial quantities of Cd in shoots and roots. Thus, total Cd uptake by the plants was much greater with co-planting than with monoculture. The results suggested that phytoextraction can be effectively increased through tobacco co-planting with Japanese clover in mildly Cd-contaminated soil.

Emerging contaminants: Evaluation of degradable chelators towards enhancing cadmium phytoextraction efficiency of bioenergy crop grown on polluted soil

Exogenous application of chelators towards enhancing heavy metals extraction efficiency of bioenergy crop has received considerable attention in recent time.However,little is known about optimal application rate,comparative evaluation of degradable versus non-degradable chelators and their impact on cadmium(Cd)speciation and uptake,physiological and biochemical activity of sweet sorghum grown under Cd stress.Four chelators namely,Nitrilotriacetic acid(NTA),tetrasodium N,N-diacetate(TDA),Ethylenediamine tetraacetic acid(EDTA),iminodisuccinic acid(IDA)and control(CK)were applied and compared at rates of 2,5,and 10 mmol kg^(-1) towards augmenting phytoextraction efficiency of sweet sorghum for Cd remediation in a screen house study.Results showed that sweet sorghum augmented with TDA significantly(P<0.05)increased biomass,enhanced Cd uptake and accumulation when compared to EDTA at application rate of 2-5 mmol kg1.TDA influenced Cd speciation via increasing acid-soluble,reducible,oxidizable,and residual fractions of Cd,thus increasing Cd bioavailability.NTA and TDA increased proline concentrations,antioxidant enzymes and net photosynthetic activity rate(Pn)comparably to EDTA in sweet sorghum,thus enhancing stress tolerance and stabilizing photosynthetic activities.Overall,exogenous application of degradable TDA at 2-5 mmol kg^(-1) could be recommended as replacement for non-degradable EDTA in a chelate assisted approach towards augmenting bioenergy crop for phytoremediation of Cd polluted soil.

Rhizobacteria helps to explain the enhanced efficiency of phytoextraction strengthened by Streptomyces pactum

The ultimate purpose of phytoextraction is not only to remove heavy metals from soil but also to improve soil quality.Here, we evaluated how the joint effect of Streptomyces pactum(strain Act12) and inorganic(Hoagland’s solution) and organic(humic acid and peat) nutrients affected the phytoextraction practice of cadmium(Cd) and zinc(Zn) by potherb mustard, and the microbial community composition within rhizosphere was also investigated.The results indicated that the nutrients exerted synergistically with Act12, all increasing the plant biomass and Cd/Zn uptakes.The inoculation of Act12 alone significantly increased dehydrogenase activity of rhizosphere soil(P<0.05), while urease and alkaline phosphatase activities varied in different dosage of Act12.Combined application of microbial strain with nutrients increased enzymatic activities with the elevated dosage of Act12.16S ribosomal RNA high-throughput sequencing analysis revealed that Act12 inoculation reduced the diversity of rhizosphere bacteria.The Act12 and nutrients did not change dominant phyla i.e.,Proteobacteria, Bacteroidetes, Gemmatimonadetes, Actinobacteria and Acidobacteria, but their relative abundance differed among the treatments with: Peat>Act12>Humic acid >Hoagland’s solution.Comparatively, Sphingomonas replaced Thiobacillus as dominant genus after Act12 application.The increase in the Sphingomonas and Flavisolibacter abundances under Act12 and nutrients treatments gave rise to growth-promoting effect on plant.Our results revealed the important role for rhizosphere microbiota in mediating soil biochemical traits and plant growth, and our approach charted a path toward the development of Act12 combined with soil nutrients to enhance soil quality and phytoextraction efficiency in Cd/Zn-contaminated soils.

Compounded chelating agent derived from fruit residue extracts effectively enhances Cd phytoextraction by Sedum alfredii

Chelating agent is known as the enhancer for metal phytoextraction;however,there is still a lack of efficient and environmentally sustainable chelators.Here,lemon residue extraction(LRE),prepared from 11 kinds of fruit wastes,was combined with N,N-bis(carboxymethyl)glutamic acid(GLDA),and tea saponin(T.S.)for the compounded plant-derived chelator(CPC),and their influences on Cd phytoextraction by the hyperaccumulator Sedum alfredii was evaluated.Among these fruits,the lemon residue extracted the most significant amount of Cd from the soil.The most effective CPC was at the volume ratio of three agents being 15:4:1(LRE:GLDA:T.S.).Compared with the deionized water,the solubility of three Cd minerals was increased by 85–256 times,and Cd speciation was substantially altered after CPC application.In the pot experiment,CPC addition caused evident increases in plant shoot biomass,Cd phytoextraction efficiency,and organic matter content compared with EDTA and nitrilotriacetic acid(NTA)application.CPC induced fewer changes in bacterial community composition compared with EDTA and had no pronounced influence on microbial biomass carbon and bacterialα-diversity,suggesting CPC had a subtle impact on the microbiological environments.Our study provides a theoretical base for the reutilization of fruit wastes and the development of environmental-friendly chelator that assists Cd phytoextraction.

Evaluation of phytoextracting cadmium and lead by sunflower,ricinus,alfalfa and mustard in hydroponic culture

Soil contaminated with heavy metals cadmium （Cd） and lead （Pb） is hard to be remediated. Phytoremediation may be a feasible method to remove toxic metals from soil, but there are few suitable plants which can hyperaccumulate metals. In this study, Cd and Pb accumulation by four plants including sunflower （Helianthus annuus L.）, mustard （Brassicajuncea L.）, alfalfa （Medicago sativa L.）, ricinus （Ricinus communis L.） in hydroponic cultures was compared. Results showed that these plants could phytoextract heavy metals, the ability of accumulation differed with species, concentrations and categories of heavy metals. Values of BCF （bioconcentration factor） and TF （translocation factor） indicated that four species had dissimilar abilities of phytoextraction and transportation of heavy metals. Changes on the biomass of plants, pH and Eh at different treatments revealed that these four plants had distinct responses to Cd and Pb in cultures. Measurements should be taken to improve the phytoremediation of sites contaminated with heavy metals, such as pH and Eh regulations, and so forth.

Removal of metals by sorghum plants from contaminated land

The growth of high biomass crops facilitated by optimal of agronomic practices has been considered as an alternative to phytoremediation of soils contaminated by heavy metals. A field trial was carded out to evaluate the phytoextraction efficiency of heavy metals by three varieties of sweet sorghum （Sorghum biocolor L.）, a high biomass energy plant. Ethylene diamine tetraacetate （EDTA）, ammonium nitrate （NH4NO3） and ammonium sulphate （（NH4）2SO4） were tested for their abilities to enhance the removal of heavy metals Pb, Cd, Zn, and Cu by sweet sorghum from a contaminated agricultural soil. Sorghum plants always achieved the greatest removal of Pb by leaves and the greatest removal of Cd, Zn and Cu by stems. There was no significant difference among the Keller, Rio and Mray varieties of sweet sorghums in accumulating heavy metals. EDTA treatment was more efficient than ammonium nitrate and ammonium sulphate in promoting Pb accumulation in sweet sorghum from the contaminated agricultural soil. The application of ammonium nitrate and ammonium sulphate increased the accumulation of both Zn and Cd in roots of sorghum plants. Results from this study suggest that cropping of sorghum plants facilitated by agronomic practices may be a sustainable technique for partial decontamination of heavy metal contaminated soils.

Variations in Uptake and Translocation of Copper, Chromium and Nickel Among Nineteen Wetland Plant Species

An experiment was carried out to investigate the variations in metal uptake and translocation among 19 wetland plant species in small-scale plots of constructed wetland using artificial wastewater containing 2.0 mg L^-1 copper （Cu）, 1.0 mg L^-1 chromium （Cr）, and 2.0 mg L^-1 nickel （Ni）. More than 97% of Cu, Cr, and Ni were removed from the wastewater by the wetland plant species. There were more than ]00-fold differences in the metal accumulation and more than ten-fold differences in the metal concentrations among the 19 plant species. These plants accumulated as high as 8.8% of Cu, 20.5% of Cr, and 14.4% of Ni when they were grown in the wetland soaked with the wastewater. Several plant species were found to be highly capable of accumulating one, two or all the three metals. The results indicated considerable variations in the metal removal abilities through phytoextraction among the 19 wetland plant species. It can be concluded that the selection of appropriate plant species in constructed wetland can be crucial for the improvement of metal removal efficiency of the wetland system.

Effect of Cadmium and Zinc on Growing Barley

The accumulation of metals, in particular of metals known as heavy in the plants poses problem. However, so with the state of traces, these metals are essential to the life, they can with stronger concentrations appear toxic. So to limit the risks, we have to study the effects of these pollutants on the living organisms. Among the techniques of phytorehabilitation, we find the phytoextraction. So, we are interested in the phytoextraction in the barley (Hordium vulgare) of a soil contaminated artificially by zinc and cadmium and the influence of these metals presence on the barley growth. The results show that the barley is tolerant in the zinc and the cadmium;it presents no sign of stress after 4 weeks of culture in soil contaminated by these metals. The accumulated zinc arrests at the level of roots and it is not transferred towards the air parts. On the other hand, the barley accumulates more cadmium compared to zinc.

Lead Phytoremediation in Contaminated Soils Using Ornamental Landscape Plants

Lead (Pb) in the urban environment can have a negative effect on human health, especially children’s health. Reducing elevated Pb exposure in the home landscape is essential. The purpose of this study was to determine which ornamental groundcover landscape plants uptake Pb from contaminated soil. Plants for both shade and sun were selected. Plants for shade [Brake fern (Pteris vittata), Asian Jasmine (Trachelospermum asiaticum), “Big Blue” Liriope (Liriope muscari), and St. Augustinegrass (Stenotaphrum secundatum)] and sun [Variegated Liriope (Liriope muscari “Variegata”), Asian Jasmine (Trachelospermum asiaticum), Asparagus Fern (Asparagus setaceus), and Bermudagrass (Cynodon dactylon)] adapted landscape groundcover plants successfully assimilated Pb grown in soil containing 250 ppm and 500 ppm Pb concentrations. Additionally, soil movement at both 25 mph and 50 mph wind speed was significantly different, with increased soil movement at 50 mph. Therefore, it was determined that landscape plants adapted to both sun and shade can help remove Pb from contaminated soils and stabilize soil particles reducing the movement of soil and be aesthetically pleasing.

Phytoremediation of Soil Contaminated with Crude Oil Using Mucuna Bracteata

This study examines the ability of Mucuna bracteata DC. to remediate soil contaminated with increasing levels of crude oil up to 20%. It also investigates the effect of fertilizer application on crude oil degradation. Changes in crude oil concentrations, pH and moisture of the soil in eight experimental pots were tracked over a period of 9 weeks. The crude oil levels in soil were analysed as Total Petroleum Hydrocarbons (TPHs) using the UV-Vis spectrophotometer. The study revealed the capacity of Mucuna bracteata to phytoremediate soil contaminated with crude oil in all experimental pots though the plant died at 20% contamination towards the end of the experiment. The plant survived up to 15% contamination with that in the fertilized pot showing better physiological conditions. In all instances, fertilized pots showed higher rates of crude oil reduction. The amounts of crude oil degraded in fertilized pots were also higher except at 20% contamination. The soil pH varied over a narrow range throughout the experimental period. Moisture of soil contaminated with 15% and 20% crude oil was higher than that contaminated with 5% and 10% crude oil. Mucuna bracteata showed signs of phytoextraction which can be subject to further study. This study contributed a new candidate of phytoremediation for soil contaminated with high level of crude oil.

Preliminary study on Cd accumulation characteristics in Sansevieria trifasciata Prain

Phytoremediation techniques to clean heavy metal pollution soil depend on identifying plant species that can act as phytoremediators.One important approach to screening potential phytoremediators is to evaluate characteristics of heavy metal accumulation.In this study,we performed firsthand analysis of Cd tolerance and accumulation characteristics of three Sansevieria trifasciata cultivars by pot experiment.Plant growth results showed that all three S.trifasciata cultivars can tolerate 50 mg kg^-1 soil Cd concentration.After growth under 50 mg kg^-1 soil Cd concentration for 4 months,the Cd bioconcentration factors in the shoots of S.‘Trifasciata’,S.trifasciata‘Laurentii’,and S.trifasciata‘Silver Hahnii’were 1.26,1.30,and 1.19,while those in the roots were 12.53,11.43,and 5.45,respectively.This result reveals the considerably low translocation factors of 0.10,0.12,and 0.22 for S.‘Trifasciata’,S.trifasciata‘Laurentii’,and S.trifasciata‘Silver Hahnii’,respectively.These results suggest that all three S.trifasciata cultivars had high Cd absorption capacities but low Cd translocation capacities.In combination with total Cd accumulation distribution and plant growth characteristics,S.trifasciata can be designed as a phytostabilizer in Cd-contaminated soils in its cultivation regions.Meanwhile,the mechanism of high Cd tolerance and accumulation characteristics in the roots of S.trifasciata should be explored.This study provides new resources for dealing with Cd-contaminated soils and exploring Cd tolerance and accumulation mechanisms in plants.