Phytoextraction of Risk Elements by Willow and Poplar Trees

To characterize the phytoextraction efficiency of two clones of willow trees (Salix x smithiana Willd., Salix rubens) and two clones of poplar trees (Populus nigra x maximowiczii, Populus nigra Wolterson) were planted in contaminated soil (0.4–2.0 mg Cd.kg^?1, 78–313 mg Zn.kg^?1, 21.3–118 mg Cu.kg^?1). Field experiment was carried out in Czech Republic. The study investigated their ability to accumulate heavy metals (Cd, Zn, and Cu) in harvestable plant parts. The poplars produced higher amount of biomass than willows. Both Salix clones accumulated higher amount of Cd, Zn and Cu in their biomass (maximum 6.8 mg Cd.kg^?1, 909 mg Zn.kg^?1, and 17.7 mg Cu.kg^?1) compared to Populus clones (maximum 2.06 mg Cd.kg^?1, 463 mg Zn.kg^?1, and 11.8 mg Cu.kg^?1). There were no significant differences between clones of individual species. BCs for Cd and Zn were greater than 1 (the highest in willow leaves). BCs values of Cu were very low. These results indicate that Salix is more suitable plant for phytoextraction of Cd and Zn than Populus. The Cu phytoextraction potential of Salix and Populus trees was not confirmed in this experiment due to low soil availability of this element.     

Phytoextraction of Heavy Metals from Highly Contaminated Soils Using Sauropus androgynus

It has been found that Sauropusandrogynus has a strong adaptive capacity in multiple heavy-metal-contaminated soils. Field trials in highly heavy-metal-contaminated soils were conducted to investigate the extraction efficiency of Cd, Cu, Pb, and Zn by S. androgynus. The yield of S. androgynus could reach 10.01 t ha^?1, and the amount of Cd, Cu, Pb, and Zn extracted by the plant was 57.36, 218.57, 2078.11, and 19.64 g ha^?1, respectively. S. androgynus removed 0.35%, 0.01%, 0.03%, and 1.37% of the total soil Cd, Cu, Pb, and Zn in one growing season, respectively. By comparing the extracting capability and yield with some hyperaccumulators reported in the literature, S. androgynus was considered to be a highly effective plant to extract heavy metals (Cd, Cu, Pb, and Zn). The plant should be useful for phytoextraction of soils contaminated by the heavy metals.     

Efficiency of Repeated Phytoextraction of Cadmium and Zinc from an Agricultural Soil Contaminated with Sewage Sludge

Long-term application of sewage sludge resulted in soil cadmium (Cd) and zinc (Zn) contamination in a pot experiment conducted to phytoextract Cd/Zn repeatedly using Sedum plumbizincicola and Apium graceolens in monoculture or intercropping mode eight times. Shoot yields and soil physicochemical properties changed markedly with increasing number of remediation crops when the two plant species were intercropped compared with the unplanted control soil and the two monoculture treatments. Changes in soil microbial indices such as average well colour development, soil enzyme activity and soil microbial counts were also significantly affected by the growth of the remediation plants, especially intercropping with S. plumbizincicola and A. graveolens. The higher yields and amounts of Cd taken up indicated that intercropping of the hyperaccumulator and the vegetable species may be suitable for simultaneous agricultural production and soil remediation, with larger crop yields and higher phytoremediation efficiencies than under monoculture conditions.     

新疆杨叶肉原生质体游离和纯化的研究

以新疆杨(Populus albaL.var.pyramidalis)无菌苗叶片为材料,就其原生质体游离、纯化方法及影响因素等进行了研究。结果表明,cellulase R-10、hemicellulase和pectolase Y-23对原生质体产量有极显著影响。适宜新疆杨叶片原生质体游离的条件为CPW KM8P 3.0?llulase R-10 0.5%~1.5%macerozyme R-10 0.5%hemicellulase 0.1%~0.5%pectolase Y-23 0.6 mol/L甘露醇,酶解温度27℃,酶解时间8 h。在此条件下,原生质体产量达1.57×107个/gFW,活力79.41%,而且蔗糖等密度离心法中的上浮法纯化原生质体效果最佳,最适蔗糖浓度为30%。     

新疆杨愈伤组织原生质体的游离与纯化

目的:以愈伤组织为材料,研究新疆杨原生质体的游离、纯化。方法:以新疆杨愈伤组织为材料,采用简单试验设计和方差分析方法,对新疆杨原生质体游离的影响因素进行研究,并利用二乙酸荧光素染色法观察原生质体活力。结果:适宜新疆杨愈伤组织原生质体游离的较适宜条件是:CPW+2.0%纤维素酶R-10+1.0%离析酶R-10+1.0%果胶酶Y-23+0.6 mol/L甘露醇,酶解温度27℃,酶解时间8 h。在此条件下,原生质体产量达8.5×106个/(g.FW),活力达83.6%。原生质体纯化可采用蔗糖等密度离心法,较适蔗糖浓度为30%。结论:研究筛选出的酶解因素组合与等密度离心条件较适宜新疆杨愈伤组织原生质体的游离和纯化。     

Protection from Paraquat-Mediated Photo-Oxidative Stress by Glutathione in Poplar (Populus tremula×P. alba) Plants

Abstract: The sensitivity of hybrid poplar (Populus tremula × P. alba) to oxidative stress mediated by paraquat exposure was analysed with leaf discs from wild-type plants and plants expressing the bacterial cDNA of the enzymes of glutathione synthesis, namely gshI, encoding γ-glutamylcysteine synthetase (ECS), or gshII, encoding glutathione synthetase (GS), both in the cytosol. It was expected that leaf discs containing more than 2-fold elevated glutathione concentrations due to over-expression of ECS are less susceptible to paraquat exposure than wild-type plants and transformants over-expressing GS. However, neither over-expression of GS nor of ECS improved paraquat tolerance of the leaves. This result was surprising, because in wild-type plants reduced paraquat sensitivity of young compared with mature leaves coincided with ca. 30 % higher glutathione contents of the young leaves. Apparently, developmental changes in paraquat sensitivity of poplar leaves are controlled by factors different from glutathione contents. Feeding experiments with glutathione and its metabolic precursor γ-glutamylcysteine (EC) plus gly showed that glutathione can provide protection from paraquat-mediated photo-oxidative stress; but at least ca. 5-fold elevated glutathione levels are required for this effect in poplar leaves. Currently, such high glutathione levels have not been achieved by the application of plant molecular biology techniques. The significance of glutathione for the compensation of photo-oxidative stress is discussed.     

Removal of Cadmium from Contaminated Soils by Multiple Washing with Iron (III) Chloride

In the present study, three concentrations of FeCl₃ were applied to the Cd-contaminated soils at two solid-to-solution ratios, and 1–3 washes were applied. The Cd removal percentages increased with the number of washes. An optimal treatment for removing Cd from the soil was a solid-to-solution ratio of 1/2 using 45 mM FeCl₃ and three washes. However, the application of FeCl₃ decreased the soil pH values, increased the soil electrical conductivity, and also changed the exchangeable concentrations of cations. These changes negatively influenced the germination percentage of pak choi (Brassica campestris L. ssp. chinensis) compared with control soils.     

Phytoextraction of soil cadmium and zinc by microbes-inoculated Indian mustard (Brassica juncea)

Abstract

A pot experiment was carried out to evaluate the effect of Pseudomonas fluorescens and Trichoderma harzianum inoculation on the uptake of zinc (Zn) and cadmium (Cd) by Indian mustard (Brassica juncea) from the soil having three different concentrations of Zn (300, 600, 900 mg/kg) and Cd (5, 10, 15 mg/kg) separately. Microbial inoculation resulted in significantly better plant growth, available metal content and their uptake than control (without microbes). Available Zn was enhanced, ca.1.6- and 1.4-fold and Cd ca. 2.5- and 1.8-fold, by P. fluorescens and T. harzianum, respectively. P. fluorescens resulted in an increase in Zn uptake by 113.9, 51.9 and 58.4% and T. harzianum by 42.6, 32.1 and 33.9% over control from soils having 300, 600 and 900 mg Zn, respectively, while of the corresponding results for Cd were 110.2, 48.9 and 58.1% with P. fluorescens and 42.6, 30.9 and 33.4% with T. harzianum from soil having 5, 10 and 15 mg Cd, respectively, after 90 days of treatment. In general the rate of metal uptake was higher during the initial 30 days and declined later.     

Soil Nitrogen Fertilization Effects on Phytoextraction of Cadmium and Lead by Tobacco (Nicotiana tabacum L.)

A greenhouse experiment using 24 plastic pots filled with 6 kg of Pb- and Cd-contaminated soil was carried out. In all 24 pots, soils were heavy metal–contaminated with 10 mg Cd kg^?1 soil and 500 mg of Pb kg^?1 soil by using CdCl and PbNO₃. Two-month-old tobacco (Nicotiana tabacum L.) plants were used to extract these heavy metals. Results showed that tobacco is able to remove Cd and Pb from contaminated soils and concentrate them in its harvestable part, that is, it could be very useful in phytoextraction of these heavy metals. Increasing additions of ammonium nitrate to soil (50, 100, and 150 mg N kg^?1 soil) significantly (p ≤ .05) increased aboveground Cd and Pb accumulation during a 50-day experimental period, whereas increasing additions of urea to soil (50 and 100 mg N kg^?1 soil) did not show these effects at the same significance levels. Increasing additions of ammonium nitrate to soil shows as dry matter increases, both accumulated Cd and accumulated Pb also increase when tobacco plants are growing under Pb- and Cd-contaminated soil conditions. Higher Pb concentrations depress Cd/Pb ratios for concentrations and accumulations, suggesting that Pb negatively affects Cd concentration and/or accumulation.     

Multiple shoot regeneration from root organ cultures of Populus alba x P. grandidentata

Excised roots of various ages from Crandon and Hansen clones of Populus alba x P. grandidentata were tested for their regeneration capacity. Sixty-day-old excised roots that contained root tips were found to be most suitable. The highest number of shoots (an average of 111 shoots/root segment with Crandon and 98 with Hansen) was obtained by adding 22M and 14M zeatin to the medium, respectively. The two clones of hybrid poplar responded similarly to growth regulator treatments; however, the number of shoots produced was greater from the root organs derived from Crandon clones. Regenerated shoots were rooted in basal Woody Plant Medium without any growth regulators. Successful transplantation into soil and growth was achieved with all plants.     

Phytoextraction and Accumulation of Boron and Selenium by Poplar (Populus) Hybrid Clones

There has been much interest recently in central California for reusing drainage water to grow trees. A sand-culture study was conducted to investigate the accumulation of boron (B) and selenium (Se) in eight hybrid poplar (Populus) clones irrigated with synthetic agricultural effluent containing increasing levels of chloride salt, B, and Se. Electrical conductivity (EC) ranged from 1.5 to 15 dS m^-1, B levels from 1 to 5 mg L^-1, and Se levels from 100 to 500 μg L^-1. Compared with all tree organs, the leaves accumulated the greatest concentrations of B and Se at the time of harvest. The results show that pooled leaf B concentrations were positively correlated with EC levels (r = 0.78, P < 0.001) and negatively correlated (r = -0.53, P < 0.001) with leaf dry matter for all clones at all tested B levels. Combined leaf and stem Se data show, respectively, a significant decrease (P < 0.05 level) in tissue accumulation of Se with increased salinity. Toxicity symptoms (e.g., burning leaf margins, shoot die back) occurred in most clones grown at 12 and 15 dS m^-1 treatments leading to leaf abscission. Based on the data, clone 49177 (Populus trichocarpa × P. deltoidus) best tolerated the tested parameters among the clones and accumulated the greatest amount of B and Se. The moderate ability of the Populus species to remove and accumulate B and Se from saline effluent is most effective at salinity levels less than 7 dS m^-1.     

Cadmium Removal Potential from Contaminated Soil by Tagetes erecta L. and Panicum maximum: Influence of Soil pH

The potential for cadmium (Cd) removal from contaminated soil by two species—marigold (Tagetes erecta L.) and Guinea grass (Panicum maximum)—was investigated in pot culture experiments in a greenhouse in triplicate. The concentration of Cd was varied from 50 to 200 mg kg^?1 and the pH was varied from 5.0 to 7.5 to investigate the effect of pH on Cd uptake. The results showed that total biomass of Guinea grass was around nine and seven times higher than that of marigold for Cd treatments of 50 and 100 mg kg^?1 at pH 5.0, respectively. Total cadmium uptake at Cd treatments of 50 and 100 mg kg^?1 at pH 5.0 by Guinea grass was 19.28 ± 3.14 and 36.06 ± 4.28 mg kg^?1, respectively, and for marigold was 15.66 ± 4.17 and 20.38 ± 3.24 mg kg^?1, respectively. The total Cd uptake by Guinea grass was 1.23 and 1.77 higher than that of marigold at Cd treatments of 50 and 100 mg kg^?1, respectively, at pH 5.0 due to higher biomass. The maximum Cd uptake by marigold and Guinea grass occurred at pH 5.0 at Cd treatment of 100 mg kg^?1. The results clearly show that the two species behave very differently for Cd uptake. Guinea grass is easy to grow, drought tolerant and, due to its higher biomass, it can be used for remediation of Cd-contaminated soil.     

Pulsed Electrokinetic Removal of Chromium,Mercury and Cadmium from Contaminated Mixed Clay Soils

Electrokinetic remediation (EKR) processes are energy intense systems as they are mainly run under continuous constant current supply mode. In this study, pulsed electrokinetic remediation (PEKR) technique was employed for the removal of Cd, Hg and Cr from mixed contaminated natural clay and bentonite soils. The effects of voltage gradient, pulse duty cycle and bentonite/clay ratio on the simultaneous removal efficiencies of the heavy metals and specific energy consumption were investigated. Fifteen (15) PEKR experiments were conducted according to Box–Behnken design (BBD) with each experiment allowed to continuously run for 21 days. Increase in the proportion of the bentonite significantly decreased the removal efficiency of the heavy metals while having insignificant effect on the energy consumption. Conversely, increase in both voltage gradient and pulse duty cycle increased the heavy metals removal efficiencies, though at the expense of increase in energy consumption due to combine effects of increase in the soil electrical conductivity, amount of current needed to sustain the applied voltage gradient as well as the raise in the soil pH. The maximum achievable removal efficiencies for Cd, Hg and Cr were 21.87, 78.06 and 89.64% respectively. The specific energy consumption significantly increased from the range of 91.67–154.17 kwh/m³ to 1700–2441.67 kwh/m³ as a result of combined effect of increasing voltage gradient and pulse duty cycle. This demonstrated that effective PEKR could be achieved with significance reduction in the energy consumption via appropriate selection of pulse duty and voltage gradient for clay soils of different proportion of montmorillonite.     

Phytoremediation of lead (Pb) and Arsenic (As) by Melastoma malabathricum L. from Contaminated Soil in Separate Exposure

This study was conducted to investigate the uptake of lead (Pb) and arsenic (As) from contaminated soil using Melastoma malabathricum L. species. The cultivated plants were exposed to As and Pb in separate soils for an observation period of 70 days. From the results of the analysis, M. malabathricum accumulated relatively high range of As concentration in its roots, up to a maximum of 2800 mg/kg. The highest accumulation of As in stems and leaves was 570 mg/kg of plant. For Pb treatment, the highest concentration (13,800 mg/kg) was accumulated in the roots of plants. The maximum accumulation in stems was 880 mg/kg while maximum accumulation in leaves was 2,200 mg/kg. Only small amounts of Pb were translocated from roots to above ground plant parts (TF < 1). However, a wider range of TF values (0.01–23) for As treated plants proved that the translocation of As from root to above ground parts was greater. However, the high capacity of roots to take up Pb and As (BF > 1) is indicative this plants is a good bioaccumulator for these metals. Therefore, phytostabilisation is the mechanism at work in M. malabathricum's uptake of Pb, while phytoextraction is the dominant mechanism with As.     

Stabilization of Oxidic Tailings and Contaminated Soils by Calcium Oxyphosphate Addition: The Case of Montevecchio (Sardinia,Italy)

The effectiveness of an in situ heavy metals fixation technique aimed at converting contaminants to low solubility and low bioavail-ability forms, eliminating the risk posed by oxidic tailings and contaminated soils, was investigated. Calcium oxyphosphate salt (Ca(H₂PO₄)₂·H₂O) was used as a stabilizing agent for oxidic tailings and contaminated soils originating from Montevecchio, Sardinia, Italy. Stabilization was effected by mixing the contaminated soil or oxidic tailing sample with calcium oxyphosphate salt at various doses. The effectiveness of stabilization was evaluated by USEPA TCLP standard toxicity testing. Complementary EDTA extraction tests and biological tests using beans Phaseolous vulgaris as plant indicator were carried out. The toxicity of Pb and Cd was reduced below TCLP regulatory limits at calcium oxyphosphate doses higher than 0.7 and 0.2% w/w for soils and tailings, respectively. Lead solubility according to the EDTA test decreased with phosphate dose for both materials tested. Lead uptake by plant leaves and roots from the soil sample decreased with the phosphate addition, while Cd uptake remained almost constant. An adverse effect on plant growth and Zn uptake was observed for calcium oxyphosphate dose up to 1.1% w/w. Based on the results, a remediation scheme for oxidic tailings and contaminated soils is proposed.     

Cryopreservation of white poplar (Populus alba L.) by vitrification of in vitro-grown shoot tips

 Shoot tips from in vitro-grown, cold-hardened stock plants of white poplar (Populus alba L.) were successfully cryopreserved at –196  °C by one-step vitrification. After preculturing at 5  °C for 2 days on hormone-free MS medium containing different sucrose concentrations, and loading for 20 min with 2 m glycerol and 0.4 m sucrose, shoot tips were treated with the PVS2 vitrification solution and plunged directly into liquid nitrogen. Best survival rate (90%) was obtained when shoot tips were precultured on 0.09 m sucrose, hormone-free MS medium, vitrified by exposure to PVS2 solution for 60 min at 0  °C and, following cryopreservation, rewarmed at 40  °C and washed in 1.2 m sucrose solution for 20 min. Regrowth was improved by plating shoot tips on a gelled MS medium containing 1.5 μm N⁶-benzyladenine plus 0.5 μm gibberellic acid, while shoot rooting was achieved on MS medium containing 3 μm indole-3-butyric acid. Following this procedure, almost 60% rooted shoots were obtained from cryopreserved shoot tips. Received: 1 February 1999 / Revision received: 3 May 1999 · Accepted: 21 May 1999     

Cadmium removal from contaminated soil by thermally responsive elastin (ELPEC20) biopolymers

Cadmium contamination of soil is a major concern in the biosphere. Beyond the suite of available physico-chemical treatment methods, green and more efficient technologies are desired to reduce cadmium and other heavy metal contaminants to acceptable levels. Elastin-like polypeptides (ELP) composed of a polyhistidine domain (ELPH12) can be used as an environmentally benign chelating agent for ex situ soil washing. However, ELPH12 is relatively non-selective. A biopolymer with metal-binding domains that have stronger affinity, capacity, and selectivity would have distinct advantages. The aim of this work is to investigate the use of a new generation of ELP biopolymer, ELPEC20, containing synthetic phytochelatin (EC) as the metal-binding domain for ex situ soil washing. ELPEC20 was shown to bind cadmium more effectively and selectively than ELPH12. The binding constant of ELPEC20 is an order of magnitude higher and the binding capacity is fivefold higher than ELPH12. In contrast to ELPH12, no decrease in cadmium binding was observed in the presence of other competing metal ions. The improved selectivity and binding capacity provided by ELPEC20 were directly reflected in the enhanced cadmium extraction efficiency from contaminated soil. In batch washing studies up to 62% of the bound cadmium was removed by ELPEC20 while less than 12% was removed by ELPH12. Cadmium was removed not only from the exchangeable fraction but also the oxidizable fraction. The high-affinity binding sites of ELPEC20 also results in very rapid extraction with complete removal achieved within 1 h, suggesting that ELPEC20 could be used as part of a rapid (short retention time) technology with minimum possibility for the biodegradation of biopolymers.     

Seasonal Variation of Photoinhibition of Photosynthesis in Bark from Populus Tremula L.

In the bark of Populus tremula L. photochemical efficiency of photosystem 2 (PS2) determined as Fv/Fm decreased during winter. The strongest reduction was found after cold periods. The degree of reduction depended on irradiance since the lowest levels of Fv/Fm were found on the sun-exposed side of the stem and below thin phellem. Therefore, photoinhibition was partly responsible for the reduction in Fv/Fm. The photochemical efficiency of PS2 recovered in late April about a month before the trees got leaves. In the laboratory, Fv/Fm recovered within about a week under low irradiance at 20 °C. Rapid recovery of photochemical efficiency of PS2 in the bark may be important to reduce respiratory loss of CO2 from the stem before the trees get leaves.     

Enhanced Phytoremediation of Cadmium-Contaminated Soil by Parthenium hysterophorus Plant: Effect of Gibberellic Acid (GA3) and Synthetic Chelator,Alone and in Combinations

The roles of gibberellic acid (GA₃) and ethylenediaminetetraacetic acid (EDTA) in phytoremediation of cadmium (Cd)-contaminated soil by Parthenium hysterophorus plant was investigated. GA₃ (10^?9, 10^?7, and 10^?5M) was applied as a foliar spray. EDTA was added to soil in a single dose (160 mg/kg soil) and split doses (40 mg/kg soil, four split doses). GA₃ and EDTA were used separately and in various combinations. P. hysterophorus was selected due to its fast growth and unpalatable nature to herbivores to reduce the entrance of metal into the food chain. The Cd phytoextraction potential of the P. hysterophorus plant was evaluated for the first time. Cd significantly reduced plant growth and dry biomass (DBM). GA₃ alone increased the plant growth and biomass in Cd-contaminated soil, whereas EDTA reduced it. GA₃ in combination with EDTA significantly increased the growth and biomass. The highest significant DBM was found in treatment T3 (10^?5M GA₃). All treatments of GA₃ or EDTA significantly enhanced the plant Cd uptake and accumulation compared with control (C1). The highest significant root and stem Cd concentrations were found in the combination treatment T11 (GA₃ 10^?5M + EDTA split doses), whereas in leaves it was found in the EDTA treatments. Cd concentration in plant parts increased in the order of stem < leaves < roots. The combination treatment T9 (GA₃ 10^?7M + EDTA split doses) showed the significantly highest total Cd accumulation (8 times greater than control C1, i.e., only Cd used). The GA₃ treatments accumulated more than 50% of the total Cd in the roots, whereas the EDTA treatments showed more than 50% in the leaves. Root dry biomass showed a positive and significant correlation with Cd accumulation. GA₃ is environment friendly as compared with EDTA. Therefore, further investigation of GA₃ is recommended for phytoremediation research for the remediation of metal-contaminated soil.     

Heavy Metals in Agricultural Soils of the Mouriki-Thiva Area (Central Greece) and Environmental Impact Implications

The heavy metal content of 51 surface soil samples from the agricultural region of Mouriki-Thiva (central Greece) was investigated by a combination of mineralogical (X-ray diffraction and scanning electron microscopy) and geochemical (aqua regia and 0.5 M HCl extractions) methods in order to determine the levels of contamination, as well as the origin, distribution and mobility of selected metals. The geology of the area includes ultrabasic rocks, and consequently the soils have anomalous values in Ni (621-2639 mg/kg) and Cr (134-856 mg/kg). Whereas Cr is mainly hosted in the crystal structure of chromite, Ni is primarily mobilized from olivine and serpentine. Nickel, and to a lesser extent Cr, were also found to be absorbed in Fe oxides. The results of a single 0.5 HCl leach revealed significant differences in the mobility and potential bioavailability of Ni and Cr in representative soil samples; Nickel is substantially more labile, and as a result a potential amount of this metal is readily available to the plants. The whole area is heavily contaminated by Ni and Cr and consequently the monitoring of the agricultural products of the region for their heavy metal content is strongly recommended.