Shoot Pb Concentrations Research Articles

Earthworm activities weaken the immobilizing effect of biochar as amendment for metal polluted soils

The effect of earthworms on the immobilization of heavy metals by biochar was investigated using 4-week soil pot experiments. Our results showed that both sludge and rice husk biochars applied to Cd, Pb and Zn contaminated soils significantly reduced the bioavailability of those heavy metals in soils, and their concentrations in soil pore water. The Cd and Pb concentrations in pakchoi shoots were decreased by 10.8%–11.7% and 21.5%–26.5%, respectively, in biochar treatments alone. Biochar and earthworm treatments, alone or in combination, can significantly increase pakchoi growth. However, compared with biochar-treated alone, applying earthworms into pots with biochar treatments significantly reduced soil pH by 0.1–0.19 units, increased the Cd, Pb and Zn concentrations in soil pore water, their bioavailability and total uptake in shoots. Additionally, earthworms weaken the immobilization effect of biochar on heavy metals. The results of principal component analysis and correlation analysis showed that earthworm treatment was the main cause of soil pH reduction, and soil pH was significantly negatively correlated with the bioavailable Cd, Pb and Zn concentrations in the soil. Furthermore, the effect of the earthworm digestive system (casts) on bioavailable Cd, Pb and Zn concentrations could not explain their changes in the soil. In addition, the application of biochar had no significant effect on the survival and heavy metal enrichment of earthworm. Therefore, the effect of earthworms must be considered in the process of Cd, Pb and Zn contaminated farmland soil remediation using biochar.

Lead Phytostabilization and Cationic Micronutrient Uptake by Maize as Influenced by Pb Levels and Application of Low Molecular Weight Organic Acids

ABSTRACTPhytoremediation is a promising technique to clean up toxic heavy metals including lead (Pb). A greenhouse trial was conducted to evaluate the effectiveness of citric, succinic, malonic and oxalic acids on micronutrient uptake and phytoremediation of Pb contaminated soil by maize under different Pb levels. Mean root and shoot dry weights of maize decreased with increasing Pb levels. At the lowest Pb level, application of citric and oxalic acids caused increase effects on root and shoot dry weight, respectively, as compared to the absence of organic acid. As Pb levels increased, micronutrient uptake in maize shoot decreased. Among the studied organic acids, only the application of oxalic acid increased uptake of all micronutrients in maize shoot as compared to control at the lowest Pb level. Mean root and shoot Pb concentration and uptake and also uptake index noticeably increased at the highest Pb level. All tested acids increased Pb concentration and uptake in maize root. At the highest Pb level, organic acids, except for citric acid, significantly increased shoot Pb uptake and uptake index as compared to the absence of organic acid. Translocation factors less than 1, demonstrated that most of Pb taken up by maize accumulated in root as compared to shoot. According to results reported herein, application of malonic, succinic and oxalic acids is a good strategy to enhance phytostabilization potential of Pb by maize in pb-polluted soils.

Effect of eggshell and lime on growth and mineral nutrition of kalmi (Ipomoea aquatica: Convolvulaceae) grown on lead contaminated soil

A pot experiment was conducted to evaluate the effect of Eggshell and Lime in ameliorating lead uptake to alleviate toxicity of lead in Kalmi (Ipomoea aquatica).The lengths, fresh and dry weights of shoot was decreased significantly in 200 mg Pb kg-1soil as compared to the control. The similar significant decreasing trend in macro nutrient concentration in shoot and root was also observed. The percentage of N, P, K, S, Mg and Ca concentrations in edible parts (shoots) decreased by 7.73, 54.55, 12.50, 35.29, 17.65 and 19.61, respectively in 200 mg Pb kg-1 treated pots compared to the control. On the other hand, Pb concentration in shoot and root was the highest at 200 mg Pb kg-1 treated pots (36.14 and 111.14 mg Pb kg-1) and the lowest was in the control treatment (3.48 and 14.48 mg Pb kg-1 pot-1). Treatments of lime and eggshell had positive effects on the productivity of Kalmi and remediating the effect of lead uptake by the plants. Between the two amendments eggshell showed better efficiency in ameliorating the toxic effects of lead and increasing the macro nutrients uptake by plants. Lime and eggshell ameliorated Pb uptake of kalmi in shoot (edible parts) by 32.26 and 61.79% compared with the control and reduced root to shoot transfer (TrF) of Pb by15.15 and 30.30% in shoots and roots of kalmi compared to the untreated pots.
 J. Biodivers. Conserv. Bioresour. Manag. 2019, 5(1): 85-92

New Miscanthus hybrids cultivated at a Polish metal-contaminated site demonstrate high stomatal regulation and reduced shoot Pb and Cd concentrations

The increased bioeconomy targets for the biomass share of renewable energy production across Europe should be met using land unsuitable for food production. Miscanthus breeding programs targeted the production of plants with a diverse range of traits allowing a wider utilization of land resources for biofuel production without competing with arable crops. These traits include increasing tolerances to drought, chilling, and to metal(loid)s excess. Two novel Miscanthus hybrids, GNT41 and GNT34, were compared against Miscanthus x giganteus (Mxg) on metal-contaminated arable land in Poland. This study aimed at evaluating their yield, biomass quality and quantifying seasonal differences in photosynthetic and transpiration parameters. A secondary objective was to identify key physiological mechanisms underlying differences in metal accumulation between the investigated plants. The new hybrids produced a similar yield to Mxg (13–15 t ha−1 yr−1), had shorter shoots, higher Leaf Area Index and stem number. Based on gas exchange measurements, GNT34 exhibited isohydric (water-conserving) behavior. The stomatal response to light of the new hybrids was at least twice as fast as that of Mxg, a trait that is often associated with increased seasonal water use efficiency. This contributed to the almost 40% reduction in shoot Pb and Cd concentrations for the new hybrids as compared to Mxg. This suggested that promoting stomatal regulation in conjunction with improved water conservation may be a target for improving plants for wider use on metals contaminated land.

Amelioration of lead (Pb) from contaminated soil using organic amendments

Pot experiments were conducted at the department of Soil, Water and Environment, University of Dhaka to evaluate the effect of used tea leaves and poultry litter in ameliorating lead uptake and to alleviate toxicity of lead in Red amaranth (Amaranthus tricolor L.). The length, fresh weight and dry weight of shoot was decreased significantly by 34.83, 34.69 and 36.48%, respectively, in 200 mg kg-1 Pb treated pots compared to the control. The similar significant decreasing trend in case of macro nutrient concentration in shoot and root samples were also observed. %N, P, K, S, Mg and Ca concentration in edible parts (shoots) decreased by 66.3, 5.27, 52.17, 30.32, 61.54 and 62.87% in 200 mg kg1 lead (Pb) treated pots compared to the control. On the other hand Pb concentration in shoot and root was the highest at 200 mg kg-1Pb treated pots (55 and 189 mg kg-1 pot-1) and the lowest was in the control treatment (0.45 and 20 mg kg-1 pot-1). Biomass production were positively influenced by the application of organic amendments as well as lead uptake was significantly ameliorated into Red amaranth shoot and root due to application of used tea leaves and poultry litter which reduced soil to plant transfer (TrF) of Pb by 47.39, 56.34 and 16.67, 22.22% in shoots and roots of red amaranth, respectively, compared to the untreated pots.
 Bangladesh J. Sci. Ind. Res.54(2), 177-186, 2019

Intermittent lead-induced stress on antioxidant enzyme activity and subcellular distribution of Pb in Pogonatherum crinitum seedlings.

Pogonatherum crinitum is a promising lead (Pb) hyperaccumulator due to its high Pb tolerance and accumulation ability. However, the mechanisms that support Pb accumulation and tolerance in P. crinitum are not yet clearly understood. An indoor hydroponic experiment was conducted by cultivating P. crinitum seedlings exposed to intermittent Pb stress for 60days, divided into four stages (T1, T2, T3 and T4), with a 15-day duration per stage. The following concentrations of Pb were used: 0, 500, 0, 500mg·l-1 and 0, 1000, 0, 1000mg·l-1 ). Antioxidant enzyme activity, Pb concentration and subcellular distribution of Pb were measured at each of the above stages. The results showed that superoxide dismutase (SOD) activity in shoots, and SOD, peroxidase (POD) and malondialdehyde (MDA) activity in shoots and roots significantly increased from T1 (no Pb stress) to T2 (Pb stress) in both 500mg·l-1 and 1000mg·l-1 treatments; however, no significant difference was noted between stages T3 (no Pb stress) and T4 (Pb stress). There was no obvious effect of Pb stress on catalase (CAT) activity in shoots and roots among different stages. The Pb concentration in shoots was up to 5090.90mg·kg-1 and 7573.57mg·kg-1 , and the bioconcentration factor (BFC) was 10.18 and 7.57 for the 500mg·l-1 and 1000mg·l-1 treatments, respectively, which confirmed the Pb hyperaccumulator characteristics of P. crinitum. For plants under Pb stress, most of the Pb was fixed in the cell walls, with a smaller amount in leaves and root vacuoles. Both SOD and POD scavenging of reactive oxygen radicals and fixing and compartmentalisation of Pb in the cell wall might play important roles in detoxification of P. crinitum seedlings in response to Pb stress. There was no phased response of P. crinitum to intermittent Pb stress and the physiological response to Pb stress may be contiguous.

The potential of an energy crop “Conocarpus erectus” for lead phytoextraction and phytostabilization of chromium, nickel, and cadmium: An excellent option for the management of multi-metal contaminated soils

Past studies have thoroughly explored the phytoextraction/phytostabilization potentials of different plant species for particular metals. However, none of the plants was able to tackle the problem of multi-metal in contaminated soils. We report herewith the potential of Conocarpus erectus to extract lead (Pb) while having the capability to stabilize chromium (Cr), nickel (Ni) and cadmium (Cd) in polluted soil. The C. erectus was subjected to grow for 120 days in a soil spiked with four different levels of each metal i.e. Pb (0, 600, 1200 and 2400 mg kg−1), Ni (0, 50, 100 and 200 mg kg−1), Cr (0, 150, 300 and 600 mg kg−1) and Cd (0, 20, 40 and 80 mg kg−1). Data related to plant growth, physiology, biochemistry and antioxidants activities revealed that forenamed parameters were significantly reduced with increasing spiking levels. Contrarily, metal speciation in plant parts (metal concentrations in shoots and roots, and metal contents in these corresponding plant parts), metal removal per pot, and DTPA-extractable metals from the soil were significantly increased with increasing spiking level upon the termination of the experiment. Curiously, each spiking level demonstrated elevated Pb concentrations in shoots than roots, while the concentrations of other metals (Cr, Ni, and Cd) were found higher in roots than in the shoots. Likewise, at each spiking level, C. erectus showed both bioconcentration factor (BCF) and translocation factor (TF) values greater than 1 for Pb, while these values were ever lower than 1 for Cr, Ni, and Cd. Moreover, the percentages of Pb removal were ever higher than other metals at each spiking level. Outcomes of our experiment suggest that C. erectus has immense potential for the phytoextraction of Pb and phytostabilization of Cr, Ni, and Cd in polluted soil. It is suggested that this plant can be used to tackle the problem of multi-metal pollution in soils.

Biochar induced Pb and Cu immobilization, phytoavailability attenuation in Chinese cabbage, and improved biochemical properties in naturally co-contaminated soil

Contamination of agricultural soils with potential toxic elements (PTEs) has caused serious health and environmental concern all over the world. Therefore, eco-friendly solutions for Pb and Cu immobilization were required to minimize their mobility through various types of biochar amendments in contaminated soil. A greenhouse pot study was conducted to evaluate the comparative effect of rapeseed residue (RP), and rice straw (RS)-derived biochars, produced at different temperatures on Pb and Cu mobility and their accumulation in a high metal accumulating crop such as Chinese cabbage (Brassica chinensis L.). Sequential extraction, leaching toxicity, and phytoavailability techniques were used to assess Pb and Cu mobility. The impacts of various types of biochars on soil surface electronegative charge and soil enzymatic activity were also investigated in contaminated soil. The sequential extraction results revealed that the application of 5% of high-temperature rice straw biochar (RS550) and rapeseed residue biochar (RP550) significantly reduced the acid-soluble fractions (active fractions) of Pb and Cu by 53.50 and 50.35% respectively. Following the addition of 5% RS550, the residual fraction (stable fractions) of Pb and Cu were increased by 36.14 and 50.94% respectively. A remarkable decrease in Pb and Cu phytoavailability and solubility was observed after the soil was treated with 5% of both RS550 and RP550 biochars. In all biochar treatments, the maximum reduction of Pb concentration in roots and shoots of the cabbage was 37.81 and 26.54%, respectively, while the concentration of Cu decreased by 50.41 and 46.25%, respectively. Incorporation of biochar into contaminated soils also improved soil urease, catalase, and acid phosphatase activities as compared to the control soil. Biochar application greatly enhanced the Pb and Cu immobilization, reduced phytoavailability to Chinese cabbage, and improved soil enzymes activity. The significant increment in soil surface electronegative charges and soil pH after biochar incorporation was considered one of the Pb and Cu immobilization mechanisms. Overall, application of rice straw biochar produced at 550 °C could potentially be a safe, efficient, and sustainable approach to stabilize Pb and Cu and restore soil functions in contaminated soil.

A multivariate analysis of physiological and antioxidant responses and health hazards of wheat under cadmium and lead stress.

Soil contamination with heavy metals is a global issue confronting the environmental pollution and human/animal health. Much work has been done on physiological and antioxidant responses of wheat in hydroponic experiments and health risks from individual heavy metal contamination to human, but limited information is available on their combined application in soil. Therefore, this pot study delineates the uptake of lead and cadmium, as well as physiological responses of wheat and associated health risks under different levels of alone and combined Cd and Pb treatments. Metal uptake increased with their increasing applied levels. The highest Cd (4.24, 1.38, and 0.92mgkg-1) and Pb (763.33, 39.63, and 16.35mgkg-1) concentrations in root, shoot, and grain, respectively, were observed at highest applied levels (0.4mM Cd and 10mM Pb). Furthermore, all the treatments increased lipid peroxidation and activities of superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase, while decreased total chlorophyll contents and membrane stability index. Under combined application of Cd and Pb, the toxicity and detoxification responses of wheat increased compared to alone treatments. Multivariate analysis further confirmed the toxicity and accumulation pattern of metals under alone and combined treatments. Target hazard quotient values of Cd and Pb were < 1 under alone and combined treatments. The health hazard index values of Pb (97.07 and 87.89%) were higher than those of Cd (2.93 and 12.10%) in combined application for human and buffalo, respectively. This study highlights that the multi-metal contamination (Cd and Pb) is detrimental for wheat growth and human/animal health.

Strategies for lead distribution in organs of Phragmites australis (Cav.) Trin. ex Steud. (Common reed) subjected to Pb pollution in flood and drought environments

Heavy metal allocation in clonal organs, stems, leaves, and roots has not been systematically studied for rhizomatous perennial plants. Here, pot experiments have been designed to investigate lead (Pb) distribution in different organs of Phragmites australis (Cav.) Trin. ex Steud. Common reed subjected to 0–4500 mg Pb kg−1 under both flood and drought conditions. In either water treatment, Pb concentrations in offspring shoots were lower than in parent shoots; however, the opposite response was observed for biomass allocation for which parent shoots protected offspring shoots. Lower allocation of Pb to leaves rather than stems in offspring shoots could be a protective strategy of leaves under flood conditions. Lower Pb allocation to rhizomes is better for rhizome growth. This further provides energy for the growth of buds and offspring shoots, because the rhizome biomass and the number of buds and offspring shoots were not significantly inhibited by Pb levels of ≤ 3000 mg kg−1 in the flooded environment. These Pb allocation strategies could enhance the resistance capacity of reeds to Pb contamination by stabilizing population propagation and productivity, especially at Pb levels of ≤ 3000 mg kg−1 under flood conditions.

The effects of lead on photosynthetic performance of waxberry seedlings (Myrica rubra)

The photosynthesis was investigated 30 d after Pb treatment in Myrica rubra seedlings. The Pb treatment resulted in significantly increased Pb concentrations in shoots. Low Pb concentration exposure (≤2 mM) reduced the net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) without affecting the intercellular CO2 concentration (Ci), chlorophyll (Chl) content, and Chl fluorescence parameters. At 10 d after severe Pb treatment (≥4 mM), PN was inhibited and accompanied by Chl damage, while at 30 d, the inhibition of PN was followed by an increase of Ci and a decrease of gs, E, Chl content, and Chl fluorescence parameters. M. rubra showed a promising prospect for use in the soil phytoremediation, when Pb concentration is low, but the remediation efficiency of M. rubra is limited if Pb exceeds 2 mM.

Heavy metal (Pb) accumulation in metallophytes as influenced by the variations in rhizospheric and non-rhizospheric soils physico-chemical characteristics

ABSTRACTActivities at root-soil interface determine the solubility and uptake of metals by plants. Metal accumulation in plant species (Imperata cylindrical, Cynodon dactylon, Eleucine indica, Gomphrena celosoides, Sporobolus pyramidalis, Chromolaena odorata and Rhynchospora corymbosa) growing on Pb contaminated site as influenced by variations in physico-chemical characteristics, dissolved organic matter (DOM), Pb fractionation and different functional groups (using Fourier Transmittance Infra-red) of rhizospheric and non-rhizospheric soils was assessed. The electrical conductivity (2660–5520 µs) and Pb concentrations (51390.0–64080.0 mg/kg) were more in non-rhizospheric than rhizospheric soils having 276 µs to 3160 µs EC and 3289.0 to 44850.0 mg/kg Pb. More nutrients, DOM and carbohydrates functional groups (C-O; 1100 -1000 and O-H; 3700–3600) were found in rhizospheric compared to non-rhizospheric soils. The pH was slightly acidic (5.0–5.54) and E. indica with the lowest pH (5.0) accumulated highest Pb concentrations in shoot (8030 mg/kg) and root (16380 mg/kg) while C. odorata with highest values of pH, P, Ca and Mg in rhizospheric soil accumulated the least (root; 331.6 and shoot: 209.0 mg/kg). Pb was more in organic and residual fractions of rhizospheric and non-rhizospheric soils respectively. Reduction in pH, EC coupled with nutrients and DOM availability increased Pb uptake by plants.

Pb-induced phytotoxicity in para grass (Brachiaria mutica) and Castorbean (Ricinus communis L.): Antioxidant and ultrastructural studies

Hydroponics experiment was conducted to investigate the effects of different levels of Pb on Para Grass (Brachiaria mutica) and Castorbean (Ricinus communis L). Generally, Para Grass exhibited higher tolerance to excessive concentrations of Pb in nutrient solution, whereas a consistent decline was observed in growth of Castorbean plants exposed to similar Pb levels. Malondialdehyde (MDA) and H2O2 contents exhibited contrasting results with a general decrease in Para Grass and a linear increase in case of Castorbean. In both species a decrease was noticed in the activities of superoxide dismutase (SOD) and guaiacol peroxidase (G-POD) while catalase (CAT) activity was significantly increased. Ultrastructural studies revealed increased starch grains and adversely affected thylakoid membranes in chloroplasts of leaf cells of plants treated with 500 μM Pb. Photosynthetic parameters such as CO2 assimilation rate, stomatal conductance (gs) and transpiration rate (E) decreased in both plant species under different levels of Pb. Maximum concentrations of Pb in shoots of Para Grass and Castorbean were 1.29 and 0.352 g kg−1, respectively while in roots maximum values were 8.88 and 49.86 g kg−1, respectively. The high concentrations of Pb (about 5%) in the roots of Castorbean plants suggest its possible role in the phytoremediation/rhizofiltration of Pb contaminated water.

Cadmium and lead accumulations and agronomic quality of a newly bred pollution-safe cultivar (PSC) of water spinach.

Breeding for pollution-safe cultivars (PSCs) can reduce pollutant accumulation in crops. However, the PSC breeding would face the risk of nutritional quality reduction, which is usually ignored in conventional breeding programs targeting to increase crop yield or nutritional quality. Thus, the doubt whether the risk would exist has to be clarified for supporting the PSC breeding. In the present study, a newly bred Cd/Pb-PSC of water spinach (Ipomoea aquatic Forsk.) and its parents (QLQ with low-Cd/Pb accumulation ability and T308 with high yield) of water spinach were employed to clarify the above-mentioned issue. Yields, and concentrations of Cd, Pb, nitrite, and organic and inorganic nutrients in shoots of the three experimental lines were determined. There were no significant differences in Cd/Pb concentration between the new PSC and QLQ, in nitrite content between the new PSC and its two parents and in yield between the new PSC and T308. It is decisively significant that shoot concentrations of organic and inorganic nutrients in the Cd/Pb-PSC were as high as those in one of its parents. It is affirmed that the breeding operations (crossing and consequently continuous selfing) for lowering Cd/Pb accumulation capacity of water spinach would not lower the nutritional values of the obtained Cd/Pb-PSCs from the breeding, which should be a pillar that supports the feasibility to minimize Cd/Pb pollution in vegetables using PSC-breeding method.

Microbial‐Enhanced Phytoremediation of Lead Contaminated Calcareous Soil by Centaurea cyanus L

Microbe‐assisted phytoremediation is a promising technology for remediation of potentially toxic element contaminated soils. A greenhouse study was conducted to assess the effect of Pseudomonas spp. and Glomus spp. on phytoremediation of a Pb‐contaminated calcareous soil by Centaurea cyanus L. The study was carried out as a factorial experiment arranged in a randomized complete block design with three replications. Factors are microbial inoculation in three levels (mix inoculation with Glomus spp. or Pseudomonas spp. and non‐inoculated) and four Pb concentrations (0, 250, 500, and 1000 mg kg−1) in soil. The results revealed that microbial inoculation significantly increased the shoot dry weight and Pb accumulation in C. cyanus compared to non‐inoculated plants. Comparison of microbial treatments indicated that higher shoot Pb concentration, shoot modified bioconcentration factor (shoot mBCF, 5.33–5.63) and translocation factor (TF, 1.09–1.2) are obtained for Pseudomonas spp. inoculation, while higher plant biomass, plant Pb accumulation, root Pb concentration, root mBCF (5.91–6.46) and lower TF (0.77–0.99) are recorded for Glomus spp. inoculation. These results show that Pseudomonas spp. and Glomus spp. are more effective in phyotoextraction and phytostabilization of Pb by C. cyanus, respectively. It could be concluded that Pseudomonas spp. and Glomus spp. would be a promising strategy in bioremediation of Pb‐contaminated soils, especially at medium levels of soil Pb contamination (250 and 500 mg kg−1).

Cistus monspeliensis L. as a potential species for rehabilitation of soils with multielemental contamination under Mediterranean conditions

The Iberian Pyrite Belt (IPB; SW of the Iberian Peninsula) is one of the most important volcanogenic massive sulphide ore deposits in the world. Cistus monspeliensis L. is a native woody shrub that grows spontaneously in non-contaminated soils as well as in soils with multielemental contamination from the IPB. In this study, different ecophysiological parameters of C. monspeliensis growing in soils with different levels of metal(loid)s were evaluated to assess the potential of this species for revegetation of degraded areas. Composite samples of plants and rhizosphere soils were sampled in São Domingos and Lousal mines and in a reference area without soil contamination (Pomarão, Portugal) (Portuguese sector of IPB). Classical characterisation of the soils and quantification of their total and available metal(loid) concentrations were done. Multielemental concentration was determined in plants (shoots and roots). Ecophysiological parameters were also determined in shoots: concentrations of pigments (chlorophylls, anthocyanins and carotenoids), antioxidants (glutathione and ascorbate) and hydrogen peroxide as well as activities of several antioxidative enzymes. Although mining soils present high total concentrations of potentially hazardous elements, their available fractions were low and similar among studied areas. Soil pH as well as concentrations of extractable P, total concentrations of As, Cd and Ni and concentrations of Cu, Cr, Ni, Pb and Sb in the soil available fraction differentiate the studied areas. Only concentrations of Cd, Pb and Sb in roots and shoots were explained by the concentrations of the same elements in the soil available fraction. Although the majority of elements were translocated from roots to shoots, the shoots concentrations were below the toxic values for domestic animals and only As, Mn and Zn reached phytotoxic concentrations. Ecophysiological parameters were similar independently of the studied area. Due to its adaptability, tolerance and standard plant features, C. monspeliensis is a good choice for rehabilitation of soils with multielemental contamination under similar climatic characteristics.

Capability of Secale montanum trusted for phytoremediation of lead and cadmium in soils amended with nano-silica and municipal solid waste compost.

The purpose of this study is to evaluate the capability of Secale montanum trusted for phytoremediation of contaminated soils with lead (Pb) and cadmium (Cd). To conduct this study, soil samples were taken from contaminated rangelands soils around National Lead & Zinc Factory, Zanjan, Iran. In this study, which was performed in a greenhouse, after preparing the pot and treating soils with nano-silica (NS) and municipal solid waste compost (MSWC) amendments, 20 Secale seeds were cultured in each pot. The translocation factor (TF), the bio-concentration factor (BCF), and remediation factor (RF) were calculated to determine the phytoremediation capability of Secale. Six months after establishment, plant organs were harvested and Pb and Cd concentrations were measured in shoot and roots of Secale. For statistical analysis and to compare the obtained means, ANOVA and Tukey's tests were performed, respectively. The pot experiment results showed that Pb uptake and accumulation by roots of S. montanum were highest in pots amended with NS500. In comparison, Pb concentration in shoots of Secale was highest in pots amended with MSWC 2%. In general, it seems that NS500 and MSWC 2% help phytoremediation capability of Secale in the Pb-contaminated soils.

Heavy metal phytoextraction-natural and EDTA-assisted remediation of contaminated calcareous soils by sorghum and oat.

The abilities of sorghum (Sorghum bicolor L.) and oat (Avena sativa L.) to take up heavy metals from soils amended with ethylenediaminetetraacetic acid (EDTA) were assessed under greenhouse conditions. Both plants were grown in two soils contaminated with heavy metals (Gujranwala-silty loam and Pacca-clay loam). The soils were treated with 0, 0.625, 1.25, and 2.5mMEDTAkg-1 soil applied at both 45 and 60days after sowing (DAS); the experiment was terminated at 75 DAS. Addition of EDTA significantly increased concentrations of Cd, Cr, and Pb in roots and shoots, and bio-concentration factors and phytoextraction rates were also increased. Post-harvest soil analysis showed that soluble fractions of metals were also increased significantly. The increase in Cd was ≈3-fold and Pb was ≈15-fold at the highest addition of EDTA in Gujranwala soil; in the Pacca soil, the increase was less. Similarly, other phytoremediation factors, such as metal translocation, bio-concentration factor, and phytoextraction, efficiency were also maximum when soils were treated with 2.5mMEDTAkg-1 soil. The study demonstrated that sorghum was better than oat for phytoremediation.

Effects of Arbuscular Mycorrhizal Fungi on the Growth and Uptake of La and Pb by Maize Grown in La and Pb-Contaminated Soil

A greenhouse pot experiment was conducted to investigate the effects of arbuscular mycorrhizal (AM) fungi Claroideoglomus etunicatum (CE) and Rhizophagus intraradices (RI) on AM colonization rate, biomass, nutrient uptake, C:N:P stoichiometry, and the uptake and transport of lanthanum (La) and lead (Pb) by maize (Zea mays L.) grown in La-and Pb-contaminated soils (combined La-Pb concentrations of 50, 200, and 800 mg·kg-1). The aim was to provide a scientific basis for the remediation of soils contaminated by rare earth elements and heavy metals. The results indicated that symbiotic associations were successfully established between the two isolates and maize, and the average AM colonization rate ranged from 26.7% to 95.8%. The increasing concentrations of La and Pb in soils significantly decreased the mycorrhizal colonization rate, biomass, and mineral nutrition concentrations of the maize, and significantly increased C:P and N:P ratios and the concentrations of La and Pb in shoots and roots of maize. The shoot and root dry weights of maize were significantly increased by 17.8%-158.9% with two AM fungi inoculations, while the P concentration of shoots and roots of the maize were significantly increased by 24.5%-153.8%. Inoculation with two AM fungi decreased the C:P and N:P ratios, consistent with the growth rate hypothesis. With AM fungi inoculation in three types of La-Pb co-contaminated soils, root Pb concentrations of the maize significantly increased by 51.3%-67.7%; shoot Pb concentrations of the maize significantly decreased by 16.0%-67.7%; and the transport rate of Pb from root to shoot of the maize decreased by 31.5%-54.7%. Meanwhile, inoculation with AM fungi significantly increased the shoot La concentrations in the maize grown in soils mildly contaminated with La-Pb, while it significantly decreased shoot La concentrations, increased root La concentrations of maize, and inhibited the transport of La from root to shoot of the maize grown in soils moderately contaminated with La-Pb, but had no significant effect in severely contaminated soils. The results showed that AM fungi had the potential to promote phytoremediation of soils contaminated with rare earth elements and heavy metals, with potential applications to revegetate such contaminated soil ecosystems.

Influences of king grass (Pennisetum sinese Roxb)-enhanced approaches for phytoextraction and microbial communities in multi-metal contaminated soil

Additions of fertilizers or chelators to soils has been suggested as a potentially effective means of improving phytoextraction of heavy metals from polluted soils by large-biomass plants. The study investigated the effects of applications of three ammonium fertilizers (NH4NO3, [NH4]2SO4, and NH4Cl) and two chelators (ethylene-diamine-tetraacetic acid, EDTA, and nitrilotriacetic acid, NTA) on soil microbial community structure, and the biomass and metal distribution in tissues of king grass (Pennisetum sinese Roxb), in soils contaminated with Cd, Pb, and Zn. Analysis of phospholipid fatty acids (PLFAs) revealed that the ammonium fertilizers (especially NH4Cl) increased soil bacteria and actinomycete activity but did not affect fungi, whereas EDTA was found to be more toxic to bacteria and the actinomycetes than NTA. Ammonium fertilization enhanced P. sinese total biomass to a significantly greater degree than EDTA or NTA (P<0.05), with shoots representing 91.8–94.8% of total biomass. Metal concentrations in the roots were 6.0–15.9 (Cd), 26.5–99.9 (Pb), and 3.4–8.4 (Zn) times higher than in the shoots. The highest shoot Cd and Zn concentrations occurred in plants treated with NH4Cl, whereas the highest shoot Pb concentrations occurred in plants treated with EDTA. The total accumulations of the metals in P. sinese were 0.71–1.60mgplant−1 for Cd, 0.97–1.83mgplant−1 for Pb, and 13.12–36.57mgplant−1 for Zn. The highest amounts of Cd and Zn were extracted in the shoots, whereas the 67.7–91.8% of total Pb extraction amounts were allocated to the roots. Treatment with ammonium chloride resulted in the highest total accumulation of both Cd and Zn, whereas EDTA was more efficient than the NTA and ammonium fertilizers in stimulating total Pb accumulation. The results indicated that P. sinese is incapable of removing multi-metals simultaneously, and that although NH4Cl fertilization enhances the removal of Cd and Zn from the soil, it has less of an effect on Pb-removal efficiency.