The potential of the flora from different regions of Pakistan in phytoremediation: a review

Assessment of herbaceous community structure for identifying metal-tolerant species at different land uses in and around Varanasi city

Plant community structure under different land uses provides an important understanding of vegetation dynamics to safeguard future restoration programmes and balance ecosystem services. Therefore, this study was carried out to estimate the alterations in soil properties and contamination by potentially toxic metals at different land uses (industrial, brick kiln, highway, and residential areas) compared to the reference (botanical garden area) site coupled with their subsequent influence on herbaceous community structure, bioconcentration, translocation, and extraction amount of metals in different plant species. Most of the total and phytoavailable metals (Co, Cr, Cd, Cu, Ni, Pb, Mn, and Zn) were higher at the contaminated sites compared to the reference site. The number of herbaceous species was highest at the reference site and minimum at the industrial site. Dominant and tolerant species were Cyanodon dactylon, Croton bonaplandianus, Achyranthus aspera, Malvestrum coromendelianum, Dicanthium annulatum, Nicotiana hindostana, Sporobolus virginicus, and Parthenium hysterophorus, found at the industrial, brick kiln, and highway sites. Based on transfer coefficients, C. bonaplandianus, D. annulatum, and Eleusine indica were recognized as potential accumulators, whereas C. dactylon, Commelina benghalensis, A. aspera, Amaranthus sessilis, and M. coromendelianum were found as excluder species for different metals. The identified tolerant herbaceous species could be used for future phytoremediation strategies and the prevention of hazardous risks to living components of contaminated sites.

Potential application of enhanced phytoremediation for heavy metals treatment in Nepal

Heavy metals contamination in soil and water resources is a great threat to developing countries because of the lack of waste treatment facilities. A majority of wastewater treatment methods are known to be expensive and out of reach for municipalities and small pollution treatment enterprises. Phytotechnology is a promising, sustainable, environment-friendly, and cost-effective technique for domestic and industrial wastewater treatment in places where land is available. However, interest in conventional remediation methods and the lack of information on recent advances in a significant portion of the society in developing countries have restrained the applications of phytoremediation. This review discusses the concept of phytoremediation, mechanisms of heavy metals removal by plants, and the potential application of enhanced phytoremediation technologies in developing countries like Nepal. The authors also review the commercially viable hyperaccumulator species with their native distribution, heavy metals intake capacity, and their availability in Nepal. Those native plants can be utilized locally or introduced strategically in other parts/countries as well. Thus, for a flora-rich country like Nepal, this study holds great potential and presents enhanced phytoremediation as an effective and sustainable strategy for the future.

The role of NADPH oxidases in regulating leaf gas exchange and ion homeostasis in Arabidopsis plants under cadmium stress

NADPH oxidase, an enzyme associated with the plasma membrane, constitutes one of the main sources of reactive oxygen species (ROS) which regulate different developmental and adaptive responses in plants. In this work, the involvement of NADPH oxidases in the regulation of photosynthesis and cell ionic homeostasis in response to short cadmium exposure was compared between wild type (WT) and three RBOHs (Respiratory Burst Oxidase Homologues) Arabidopsis mutants (AtrbohC, AtrbohD, and AtrbohF). Plants were grown under hydroponic conditions and supplemented with 50 µM CdCl₂ for 24 h. Cadmium treatment differentially affected photosynthesis, stomatal conductance, transpiration, and antioxidative responses in WT and Atrbohs mutants. The loss of function of RBOH isoforms resulted in higher Cd²⁺ influx, mainly in the elongation zone of roots, which was more evident in AtrbohD and AtrbohF mutants. In the mature zone, the highest Cd²⁺ influx was observed in rbohC mutant. The lack of functional RBOH isoforms also resulted in altered patterns of net K⁺ transport across cellular membranes, both in the root epidermis and leaf mesophyll. The analysis of expression of metal transporters by qPCR demonstrated that a loss of functional RBOH isoforms has altered transcript levels for metal NRAMP3, NRAMP6 and IRT1 and the K⁺ transporters outward-rectifying K⁺ efflux GORK channel, while RBOHD specifically regulated transcripts for high-affinity K⁺ transporters KUP8 and HAK5, and IRT1 and RBOHD and F regulated the transcription factors TGA3 and TGA10. It is concluded that RBOH-dependent H₂O₂ regulation of ion homeostasis and Cd is a highly complex process involving multilevel regulation from transpirational water flow to transcriptional and posttranslational modifications of K/metals transporters.

Preventative effect of crop straw-derived biochar on plant growth in an arsenic polluted acidic ultisol

In different regions of the world, arsenic (As) contaminated soils poses a serious threat to plant growth and its physiological processes. Organic amendments are a cost-effective and environmentally friendly way to improve plant growth under stress conditions in contaminated soils. In As polluted acidic ultisol, a greenhouse trial was conducted to investigate the protective effects of peanut straw biochar (PSB) and canola straw biochar (CSB) on soybean mineral nutrition, antioxidant enzymes, and physiological growth parameters. The current study used eighteen treatments with different levels of As ((1) 0 mg kg^-1, (2) 30 mg kg^-1, (3) 60 mg kg^-1) and biochar (PSB and CSB) (0%, 1%, and 2%). The result suggests that biochar addition under As stress in highly weathered acidic ultisol soil increased soybean growth attributes and defense mechanisms. The PSB was more effective than the CSB in a dose-dependent manner. The application of 2% PSB in polluted soil resulted in significant increases in soybean height (58%), biomass production (root (44%) and shoot length (52%)), chlorophyll contents (92%), soybean functional leaves (62%), total soluble sugars (TSS) (71%) and base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺). However, biochar application decreased proline, MDA, H₂O₂, and O₂^- by 64%, 82%, 49%, and 45% respectively. Furthermore, biochar application increased (Phosphate) P and As uptake in soybean, with PSB application exhibiting a greater increase than CSB application. As a result, crop straw-derived biochar can reduce As-induced soybean plant damage and insert a protective effect in As-contaminated acidic ultisol soils.

Heavy metals uptake and translocation of typical wetland plants and their ecological effects on the coastal soil of a contaminated bay in Northeast China

Heavy metal pollution in coastal zone is a global environment problem concerning the international society. As an eco-friendly and economical method, phytoremediation is a promising strategy for improving heavy metal pollution in coastal soil. In order to alleviate the ecological risk of heavy metal pollution in Jinzhou Bay, a typical and important heavy industrial area in China, three local wetland plants (Scirpus validus, Typha orientalis and Phragmites australis) were selected and planted in the field. The plants showed strong tolerance of high concentrations of heavy metals. Stressed by the heavy metals, the root weight of S. validus and P. australis increased 114.74% and 49.91%, respectively. The concentrations of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn, As, Hg) accumulated in the plant roots were 4-60 times higher than that in plant shoots. The SEM analysis found that abundant heavy metals were adhered to the root surface closely. Bioconcentration factor of heavy metals on the plant roots were 0.08-0.89 (except Cr, Ni), while the translocation factor from roots to above ground of plants were 0.02-0.27. Furthermore, the wetland plants improved the regional ecological environment quality. The concentrations of heavy metals in the rhizosphere soil decreased significantly. Compared with the bulk soil, the potential ecological risk index in the rhizosphere soil reduced 26.51%-69.14%. Moreover, the microbial diversity in rhizosphere soil increased significantly, and the abundances of Proteobacteria and Bacteroidetes also increased in rhizosphere soil. Pearson correlations indicated that Hg, As, Ni and Cr were negatively correlated with Proteobacteria (p < 0.05), and Cu was significantly negative correlated with Bacteroidetes (p < 0.05). The results support that using suitable local plants is a promising approach for repairing heavy metal contaminated costal soil, not only because it can improve the regional ecological environment quality, but also because it can enhance the landscape value of coastal zone.

Comprehensive and critical appraisal of plant-based defluoridation from environmental matrices

Fluoride is recognized as one of the global environmental threats because of its non-biodegradable nature and long-term persistence in the environment. This has created the dire need to explore various defluoridation techniques (membrane process, adsorption, precipitation, reverse osmosis, ion exchange, and electrocoagulation). Owing to their cost ineffectiveness and high operational costs, these technologies failed to find any practical utility in fluoride remediation. Comparatively, defluoridation techniques involving the use of low-cost plant-derived adsorbents and fluoride phytoremediators are considered better alternatives. Through this review, an attempt has been made to critically synthesize information about various plant-based bioadsorbents and hyperaccumulators from existing literature. Moreover, mechanisms underlying the fluoride adsorption and accumulation by plants have been thoroughly discussed that will invigorate the researchers to develop novel ideas about process/product modifications to further enhance the removal potential of the adsorbents and plants. Literature survey unravels that various low-cost plant-derived adsorbents have shown their efficacy in defluoridation, yet there is an urgent need to explore their pragmatic application on a commercial scale.

Biological approaches of fluoride remediation: potential for environmental clean-up

Fluoride (F), anion of fluorine which is naturally present in soil and water, behaves as toxic inorganic pollutant even at lower concentration and needs immediate attention. Its interaction with flora, fauna and other forms of life, such as microbes, adversely affect various physiochemical parameters by interfering with several metabolic pathways. Conventional methods of F remediation are time-consuming, laborious and cost intensive, which renders them uneconomical for sustainable agriculture. The solution lies in cracking down this environmental contaminant by adopting economic, eco-friendly, cost-effective and modern technologies. Biological processes, viz. bioremediation involving the use of bacteria, fungi, algae and higher plants that holds promising alternative to manage F pollution, recover contaminated soil and improve vegetation. The efficiency of indigenous natural agents may be enhanced, improved and selected over the hazardous chemicals in sustainable agriculture. This review article emphasizes on various biological approaches for the remediation of F-contaminated environment, and exploring their potential applications in environmental clean-up. It further focuses on thorough systemic study of modern biotechnological approaches such as gene editing and gene manipulation techniques for enhancing the plant-microbe interactions for F degradation, drawing attention towards latest progresses in the field of microbial assisted treatment of F-contaminated ecosystems. Future research and understanding of the molecular mechanisms of F bioremediation would add on to the possibilities of the application of more competent strains showing striking results under diverse ecological conditions.

Trace element accumulation in Salvinia natans from areas of various land use types

Salvinia natans meets many criteria for accumulative bioindicators and phytoremediation agents. However, the majority of studies on its bioaccumulation capacity were performed under controlled culture conditions. In the present study, Salvinia natans was investigated in a field study. Plant and water samples were collected from aquatic reservoirs located in areas with various dominant land uses (forested, agricultural, residential and industrial). Contents of 10 trace elements (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) and phytomass were measured to estimate the bioindication and phytoremediation potential of the species. Results showed that contents of trace elements in S. natans were high compared with other aquatic ferns (Azolla japonica, A. pinata) as well as free-floating vascular plants (e.g. Pistia stratiotes, Hydrocharis morsus-ranae, Lemna sp., Eichhornia crassipes). High bioaccumulation factors for Cu, Fe, Mn, Ni, Pb and Zn confirm accumulative abilities of the plant. Application of neural networks (SOFMs) confirmed that the species may be used in bioindication: the land use type determined the composition of substances carried into water reservoirs with runoff and trace elements accumulated in Salvinia tissues. Ferns in industrial areas had the highest content of Cd, Cu and Zn, while in residential areas plants showed the highest content of As, Co, Fe, Mn, Ni and Pb. Element contents in S. natans in forested areas were the lowest. High standing stocks of Cd, Mn and Ni indicated an important role of S. natans in the cycling of elements and potential use in their removal from aquatic ecosystems.

Effect of different phosphorus sources on soybean growth and arsenic uptake under arsenic stress conditions in an acidic ultisol

Soil arsenic (As) contamination is a serious concern because of its mark negative impacts on plant growth and physiological processes. In plant-soil system, As competes against phosphorus (P) which depends on charge component of different soil types. The main objective of this study was to investigate the influence of ((NH4)3PO4 (PO43-) and Ca5(PO4)3(OH) (phosphorite)) in ameliorating As stress on plant physiological process against As toxicity and their role in As accumulation. We performed eighteen treatments with different levels of As (0, 35, and 70 mg/kg) and P (0, 100, and 200 mg/kg) against two P sources of PO43- and phosphorite. Overall, more improvement in plant growth was observed by addition of PO43- than phosphorite. Significant increases in plant height (51%), dry biomass (root (49%) and shoot (40%)), chlorophyll contents (88%), total soluble sugars (58%) and plant functional leaves (51%) were observed by PO43- application as compared to their corresponding un-fertilized treatment under As stress conditions. However, proline and MDA contents were decreased by 49% and 71% with PO43- applied, respectively, under As stress. The As and P uptake by soybean were remarkably enhanced by the application of PO43- than phosphorite. Therefore, highly soluble P supplementation has great potential to minimize As-induced damage to plant growth in acidic soils and improve As uptake by plants. The findings obtained in present study will be used as an important tool for amelioration of As polluted acidic soils.

Mechanisms of Cr(VI) resistance by endophytic Sphingomonas sp. LK11 and its Cr(VI) phytotoxic mitigating effects in soybean (Glycine max L.)

Chromium Cr(VI) is highly toxic and leads to impaired phenotypic plasticity of economically important crops. The current study assessed an endophytic-bacteria assisted metal bio-remediation strategy to understand stress-alleviating mechanisms in Glycine max L (soybean) plants inoculated with Sphingomonas sp. LK11 under severe Cr(VI) toxicity. The screening analysis showed that high Cr concentrations (5.0 mM) slightly suppressed LK11 growth and metal uptake by LK11 cells, while significantly enhancing indole-3-acetic acid (IAA) production. Endophytic LK11 significantly upregulated its antioxidant system compared to control by enhancing reduced glutathione (GSH), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities to counteract Cr-induced oxidative stress. Cr toxicity induced cell morphological alteration, as shown by SEM-EDX analysis and triggered significant lipid peroxidation. The interaction between LK11 and soybean in Cr-contaminated soil significantly increased plant growth attributes and down-regulated the synthesis of endogenous defense-related phytohormones, salicylic acid and abscisic acid, by 20% and 37%, respectively, and reduced Cr translocation to the roots, shoot, and leaves. Additionally, Cr-induced oxidative stress was significantly reduced in LK11-inoculated soybean, regulating metal responsive reduced GSH and enzymatic antioxidant CAT. Current findings indicate that LK11 may be a suitable candidate for the bioremediation of Cr-contaminated soil and stimulation of host physiological homeostasis.

Nickel; whether toxic or essential for plants and environment - A review

Nickel (Ni) is becoming a toxic pollutant in agricultural environments. Due to its diverse uses from a range of common household items to industrial applications, it is essential to examine Ni bioavailability in soil and plants. Ni occurs in the environment (soil, water and air) in very small concentrations and eventually taken up by plants through roots once it becomes available in soil. It is an essential nutrient for normal plant growth and development and required for the activation of several enzymes such as urease, and glyoxalase-I. Ni plays important roles in a wide range of physiological processes including seed germination, vegetative and reproductive growth, photosynthesis as well as in nitrogen metabolism. Therefore, plants cannot endure their life cycle without adequate Ni supply. However, excessive Ni concentration can lead to induce ROS production affecting numerous physiological and biochemical processes such as photosynthesis, transpiration, as well as mineral nutrition and causes phytotoxicity in plants. ROS production intensifies the disintegration of plasma membranes and deactivates functioning of vital enzymes through lipid peroxidation. This review article explores the essential roles of Ni in the life cycle of plant as well as its toxic effects in details. In conclusion, we have proposed different viable approaches for remediation of Ni-contaminated soils.

Assessment of Cadmium Scavenging Potential of Canna indica L

The aquatic plant, Canna indica L. (Indian shoot) of Cannaceae family was investigated to assess cadmium scavenging potential at 5, 10, 25, 50, 100 and 150 mg Cd L^-1 exposers. The results showed that Canna has considerable potential of cadmium accumulation, which was up to 58.69 and 10.13 mg Cd kg^-1 dry weight in root and shoot of Canna, respectively. The effects of different cadmium levels on biomass production of plant tissues were significantly (p = 0.05) showed negative relation due to cadmium toxicity. The root concentration factor was higher than the bioconcentration factor which indicated the lower translocation factor of Canna. Considering the high root concentration factor, average bioconcentration factor, rapid growth and optimum adaptive properties up to 100 mg Cd L^-1 level, the Canna could be employed as an eco-friendly and efficient aquatic plant for cadmium scavenging. This study plays a potential role in remediation of cadmium contaminated wastewater.

Role of Burkholderia cepacia CS8 in Cd-stress alleviation and phytoremediation by Catharanthus roseus

The current study was performed to assess the effect of Burkholderia cepacia CS8 on the phytoremediation of cadmium (Cd) by Catharanthus roseus grown in Cd-contaminated soil. The plants cultivated in Cd amended soil showed reduced growth, dry mass, gas-exchange capacity, and chlorophyll contents. Furthermore, the plants exhibited elevated levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) under Cd stress. The bacterized plants showed higher shoot length, root length; fresh and dry weight. The improved stress tolerance in inoculated plants was attributed to the reduced quantity of MDA and H₂O₂, enhanced synthesis of protein, proline, phenols, flavonoids, and improved activity of antioxidant enzymes including peroxidase, superoxide dismutase, ascorbate peroxidase, and catalase. Similarly, the 1-aminocyclopropane-1-carboxylate deaminase activity, phosphate solubilization, auxin, and siderophore production capability of B. cepacia CS8 improved growth and stress alleviation in treated plants. The bacterial inoculation enhanced the amount of water extractable Cd from soil. Furthermore, the inoculated plants showed higher bioconcentration factor and translocation factor. The current study exhibits that B. cepacia CS8 improves stress alleviation and phytoextraction potential of C. roseus plants growing under Cd stress.

Combined application of compost and Bacillus sp. CIK-512 ameliorated the lead toxicity in radish by regulating the homeostasis of antioxidants and lead

Lead (Pb) contamination is ubiquitous and usually causes toxicity to plants. Nevertheless, application of compost and plant growth promoting rhizobacteria synergistically may ameliorate the Pb toxicity in radish. The present study assessed the effects of compost and Bacillus sp. CIK-512 on growth, physiology, antioxidants and uptake of Pb in contaminated soil and explored the possible mechanism for Pb phytotoxicity amelioration. Treatments comprised of un-inoculated control, compost, CIK-512, and compost + CIK-512; plants were grown in soil contaminated with Pb (500mgkg^-1) and without Pb in pot culture. Lead caused reduction in shoot dry biomass, photosynthetic rate, stomatal conductance, relative water contents, whereas enhanced root dry biomass, ascorbate peroxidase, catalase, malondialdehyde and electrolyte leakage in comparison with non-contaminated control. Plants inoculated with strain CIK-512 and compost produced significantly higher dry biomass, photosynthetic rate and stomatal conductance in normal and contaminated soils. Bacterial strain CIK-512 and compost synergy improved growth and physiology of radish in contaminated soil possibly through homeostasis of antioxidant activities, reduced membrane leakage and Pb accumulation in shoot. Possibly, Pb-induced production of reactive oxygen species resulted in increased electrolyte leakage and malondialdehyde contents (r = 0.88-0.92), which led to reduction in growth (r = -0.97) and physiology (r = -0.38 to -0.80), however, such negative effects were ameliorated by the regulation of antioxidants (r = 0.78-0.87). The decreased activity of antioxidants coupled with Pb accumulation in aerial part of the radish indicates the Pb-phytotoxicity amelioration through synergistic application of compost and Bacillus sp. CIK-512.

Application of Bacillus megaterium MCR-8 improved phytoextraction and stress alleviation of nickel in Vinca rosea

The current research was performed to evaluate the effect of Bacillus megaterium MCR-8 on mitigation of nickel (Ni) stress in Vinca rosea grown on Ni-contaminated soil (50, 100, and 200 mg Ni kg^-1 soil). The treated plants exhibited reduced growth, biomass, gas exchange capacity, and chlorophyll (Chl) content under Ni stress. The inoculated plants growing in Ni-contaminated media exhibited relatively higher growth, total soluble protein, and proline contents. Similarly, bacterial inoculation improved the activity of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) under Ni stress. The Ni stress alleviation in inoculated plants was attributed to the reduced level of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), enhanced synthesis of protein, proline, phenols, and flavonides in conjunction with improved activity of antioxidant enzymes. The growth-promoting characteristics of microbe such as 1-aminocyclopropane-1-carboxylate deaminase (ACCD) and phosphate solubilization activity, siderophore, and auxin production capability also improved the growth and stress mitigation in inoculated plants. Furthermore, the inoculated plants exhibited higher value for bioconcentration factor (BCF), translocation factor (TF), and resulted in higher loss of Ni content from soil. The current results exhibited the beneficial role of B. megaterium MCR-8 regarding stress alleviation and Ni phytoextraction by V. rosea.

Enhanced bioremediation of lead-contaminated soil by Solanum nigrum L. with Mucor circinelloides

Strain selected from mine tailings in Anshan for Pb bioremediation was characterized at the genetic level by internal transcribed spacer (ITS) sequencing. Results revealed that the strain belongs to Mucor circinelloides. Bioremediation of lead-contaminated soil was conducted using Solanum nigrum L. combined with M. circinelloides. The removal efficacy was in the order microbial/phytoremediation > phytoremediation > microbial remediation > control. The bioremediation rates were 58.6, 47.2, and 40.2% in microbial/phytoremediation, microbial remediation, and phytoremediation groups, respectively. Inoculating soil with M. circinelloides enhanced Pb removal and S. nigrum L. growth. The bioaccumulation factor (BF, 1.43), enrichment factor (EF, 1.56), and translocation factor (TF, 1.35) were higher than unit, suggesting an efficient ability of S. nigrum L. in Pb bioremediation. Soil fertility was increased after bioremediation according to change in enzyme activities. The results indicated that inoculating S. nigrum L. with M. circinelloides enhanced its efficiency for phytoremediation of soil contaminated with Pb.

Effect of lead (Pb) on antioxidation system and accumulation ability of Moso bamboo (Phyllostachys pubescens)

The antioxidation system and accumulation ability of Moso bamboo (Phyllostachys pubescens), which is a valuable remediation material with large biomass and rapid growth rate were studied in hydroponics and pot experiments. In hydroponics experiment, TBARS concentrations and SOD activities decreased with increase of Pb treatments. The activities of POD boost up with elevated Pb treatments, and reached peak level with application of 400μM Pb. Proline concentrations reduced with application of 20μM Pb and then enhanced consistently with application of 100 and 400μM Pb. The biomass of Moso bamboo improved with increase of Pb treatments upto 400mgkg^-1, and then decreased with application of each additional increment of Pb in pot experiment. Application of 800mgkg^-1 Pb showed significant increase of photosynthetic pigments, however, non significant variation was observed for other treatments. The Pb concentration in roots, stems and leaves attained 523mgkg^-1, 303mgkg^-1 and 222mgkg^-1 respectively with application of 1600mgkg^-1 Pb compared with control. Analysis of TEM-EDX revealed that Pb in cell was mostly concentrated in cytoplasm then in cell wall and followed by vacuole. It is concluded that Moso bamboo may be potential remediation species for phytoremediation in low Pb contaminated soils.

A comparison of trace metal bioaccumulation and distribution in Typha latifolia and Phragmites australis: implication for phytoremediation

The aims of the present investigation were to reveal various trace metal accumulation abilities of two common helophytes Typha latifolia and Phragmites australis and to investigate their potential use in the phytoremediation of environmental metal pollution. The concentrations of Fe, Mn, Zn, Cu, Cd, Pb and Ni were determined in roots, rhizomes, stems and leaves of both species studied as well as in corresponding water and bottom sediments from 19 sites selected within seven lakes in western Poland (Leszczyńskie Lakeland). The principal component and classification analysis showed that P. australis leaves were correlated with the highest Mn, Fe and Cd concentrations, but T. latifolia leaves with the highest Pb, Zn and Cu concentrations. However, roots of the P. australis were correlated with the highest Mn, Fe and Cu concentrations, while T. latifolia roots had the highest Pb, Zn and Cd concentrations. Despite the differences in trace metal accumulation ability between the species studied, Fe, Cu, Zn, Pb and Ni concentrations in the P. australis and T. latifolia exhibited the following accumulation scheme: roots > rhizomes > leaves > stems, while Mn decreased in the following order: root > leaf > rhizome > stem. The high values of bioaccumulation factors and low values of translocation factors for Zn, Mn, Pb and Cu indicated the potential application of T. latifolia and P. australis in the phytostabilisation of contaminated aquatic ecosystems. Due to high biomass of aboveground organs of both species, the amount of trace metals stored in these organs during the vegetation period was considerably high, despite of the small trace metals transport.

Phytoremediation of heavy metals by Alternanthera bettzickiana: Growth and physiological response

The present study was aimed to evaluate the morphological, physiological and biochemical responses of Alternanthera Bettzickiana (Regel) G. Nicholson plant subjected to different levels of cadmium (Cd) and lead (Pb) (0, 0.5, 1.0 and 2.0 mM) stress. A. bettzickiana was able to accumulate Cd and Pb in different plant parts and total uptake of both metals was higher in shoots than roots. Plant growth, biomass and photosynthetic pigments increased with increasing metal concentrations, up to 1.0 mM, in soil and then decreased with higher metal levels. The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) increased under lower metal levels (0.5 and 1.0 mM) while decreased at higher metal levels (2.0 mM). Leaf and root electrolyte leakage (EL), malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents decreased at lower metal levels (≤1.0 mM) while increased at higher levels. The present study clearly signifies the potential of A. bettzickiana plant towards Cd and Pb tolerance and accumulation especially at lower metal levels.

Bioaccumulation of nickel by E. sativa and role of plant growth promoting rhizobacteria (PGPRs) under nickel stress

Phytoremediation potential of plants can be enhanced in association with microbes. Further, many plant growth-promoting rhizobacteria can improve growth under stress. The present study was conducted to investigate the effect of Pseudomonas putida (P. putida) on nickel (Ni) uptake and on growth of Eruca sativa (E. sativa). Three different levels of Ni (low; 150 ug/g, medium; 250 ug/g and high; 500 ug/g) were applied to the soil containing E. sativa seedlings, with or without P. putida. Ni-toxicity was measured by metamorphic parameters including shoot length, root length, biomass, chlorophyll and proline and Ni contents. Inoculation with P. putida increased 34% and 41% in root and shoot length and 38% and 24% in fresh, dry weight respectively, as compared to non-inoculated plants. Similarly, Ni uptake increased by up to 46% following P. putida inoculation as compared to non-inoculated plants. Indole acetic acid, siderophore and 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity in the growing media enhanced growth and Ni uptake in E. sativa. The present results offer insight on Plant Growth Promoting Rhizobacteria (PGPR), such as P. putida, for the potential to enhance the plant growth by inhibiting the adverse effects of Ni in E. sativa.

Cadmium Accumulation Characteristics in Turnip Landraces from China and Assessment of Their Phytoremediation Potential for Contaminated Soils

Heavy metal (HM) pollution is a global environmental problem that threatens ecosystem and human health. Cadmium (Cd) pollution is the most prominent HM pollution type because of its high toxicity, strong migration, and the large polluted area globally. Phytoremediation of contaminated soil is frequently practiced because of its cost-effectiveness and operability and because it has no associated secondary pollution. High-accumulation plants, including those identified as hyperaccumulators, play an important role in phytoremediation. Therefore, screening of plants to identify hyperaccumulators is important for continued phytoremediation. In the present study, we investigated the Cd tolerance and accumulation capabilities of 18 turnip landraces from China under a soil experiment with known Cd level. The results indicated that turnip has a high capacity for Cd accumulation. Furthermore, significant differences in Cd tolerance and accumulation characteristics were found among different landraces when they grew at 50 mg kg^-1 (dry weight) Cd concentration. Among the studied landraces, five turnip landraces met the requirements of Cd hyperaccumulators and three landraces were identified as potential candidates. However, the total Cd content accumulated by individual plant of different turnip landraces was dependent on both the Cd accumulation capacity and plant biomass. Compared with some reported Cd hyperaccumulators, turnip not only shows a high Cd-accumulation capacity but also has rapid growth and a wide distribution area. These advantages indicate that turnip may have considerable potential for phytoremediation of Cd-contaminated soil. Furthermore, the study also indicates that it is not advisable to consume turnip cultivated in an environment that exceeds safe Cd levels.

Phytoremediation potential of some agricultural plants on heavy metal contaminated mine waste soils, salem district, tamilnadu

The Pot culture experiment performed for phytoextraction potential of selected agricultural plants [millet (Eleusine coracana), mustard (Brassica juncea), jowar (Sorghum bicolor), black gram (Vigna mungo), pumpkin (Telfairia occidentalis)] grown in metal contaminated soils around the Salem region, Tamilnadu, India. Physiochemical characterization of soils, reported as low to medium level of N, P, K was found in test soils. The Cr content higher in mine soils than control and the values are 0.176 mg/L in Dalmia soil and 0.049 mg/L in Burn & Co soil. The germination rate low in mine soil than control soils (25 to 85%). The content of chlorophyll, carotenoid, carbohydrate and protein decreased in mine soils than control. The morphological parameters and biomass values decreased in experimental plants due to metal accumulation. Proline content increased in test plants and ranged from 0.113 mg g(-1) to 0.858 mg g(-1) which indicate the stress condition due to toxicity of metals. Sorghum and black gram plants reported as metal tolerant capacity. Among the plants, Sorghum produced good results (both biomass and biochemical parameters) which equal to control plant and suggests Sorghum plant is an ideal for remediation of metal contaminated soils.

Model optimization of cadmium and accumulation in switchgrass (Panicum virgatum L.): potential use for ecological phytoremediation in Cd-contaminated soils

Soil pollution with heavy metals is an increasingly serious threat to the environment, food security, and human health. Therefore, it is urgent to develop economic and highly efficient soil restoration technology for environmental improvement; phytoremediation is an option that is safe, has low cost, and is environmentally friendly. However, in selecting hyperaccumulators or tolerant plants, theories and operation technologies for optimal restoration should be satisfied. In this study, the switchgrass growth response and performance of phytoextraction under the coupling effect of Cd and pH were investigated by evaluating seed germination, seedling growth, and the Cd content in the plant to evaluate the potential use of switchgrass as a phytoremediation plant in cadmium contaminated soil. This study conducted three sets of independent experiments with five levels of Cd concentrations, including two orthogonal matrix designs of combining Cd with pH values. The results showed that switchgrass was germinated well under all treatments (Cd concentration of 0-500 μM), but the seedling growth was significantly affected by Cd and pH, as shown by multivariate regression analyses. Hormesis was found during the growth of switchgrass plants exposed to low Cd concentrations under hydroponic conditions, and switchgrass plants were capable of developing with a Cd concentration of 100-175 μM and pH of 4.1-5.9. Mild acidic conditions can enhance the ability of Cd to accumulate in switchgrass. Switchgrass was moderately tolerant to Cd and may be used as a phytoremediation plant for Cd-contaminated soils in the future. Our results also suggest that hormetic effects should be taken into consideration in the phytoremediation of Cd-contaminated soils. We discuss the physiological and biochemical mechanisms contributing to the effective application of the plant for the phytoremediation of Cd-contaminated soils.

Effect of plant growth-promoting rhizobacteria inoculation on cadmium (Cd) uptake by Eruca sativa

Microbe-assisted phyto-remediation approach is widely applied and appropriate choice to reduce the environmental risk of heavy metals originated from contaminated soils. The present study was designed to screen out the nested belongings of Eruca sativa plants and Pseudomonas putida (ATCC 39213) at varying cadmium (Cd) levels and their potential to deal with Cd uptake from soils. We carried out pot trial experiment by examining the soil containing E. sativa seedlings either treated with P. putida and/or untreated plants subjected to three different levels (ppm) of Cd (i.e., 150, 250, and 500). In all studied cases, we observed an increase in Cd uptake for E. sativa plants inoculated with P. putida than those of un-inoculated plants. Cd toxicity was assessed by recording different parameters including stunted shoot growth, poor rooting, and Cd residual levels in the plants that were not inoculated with P. putida. Significant difference (p < 0.05) of different growth parameters for inoculated vs non-inoculated plants was observed at all given treatments. However, among the different treatments, E. sativa exhibited increased values for different growth parameters (except proline contents) at lower Cd levels than those of their corresponding higher levels, shoot length (up to 27 %), root length (up to 32 %), whole fresh plant (up to 40 %), dry weight (up to 22 %), and chlorophyll contents (up to 26 %). Despite the hyperaccumulation of Cd in whole plant of E. sativa, P. putida improved the plant growth at varying levels of Cd supply than those of associated non-inoculated plants. Present results indicated that inoculation with P. putida enhanced the Cd uptake potential of E. sativa and favors the healthy growth under Cd stress.

Differential effects of cadmium and chromium on growth, photosynthetic activity, and metal uptake of Linum usitatissimum in association with Glomus intraradices

The current study was aimed at analyzing the differential effects of heavy metals (cadmium and chromium) and mycorrhizal fungus; Glomus intraradices on growth, chlorophyll content, proline production, and metal accumulation in flax plant (Linum usitatissimum L.). Heavy metal accumulation rate in flax varied from 90 to 95 % for Cd and 61-84 % for Cr at a concentration range of 250 to 500 ppm for both metals in 24 days of experiment. Growth and photosynthetic activity of flax reduced to an average of 21 and 45 %, respectively. However, inoculation of G. intraradices significantly increased the plant biomass even under metal stressed conditions. Additionally, mycorrhizal association also assists the Cd and Cr increased uptake by 23 and 33 %, respectively. Due to metal stress, chlorophyll contents were decreased by 27 and 45 %, while 84 and 71 % increased proline content was observed under Cd and Cr stress, respectively. The present results clearly signify the differential response and potential of flax plant towards heavy metal tolerance and accumulation that can further increase with mycorrhizal fungus.

Utilizing heavy metal-laden water hyacinth biomass in vermicomposting

We studied the efficiency of water treatment by water hyacinth (Eichhornia crassipes) from heavy metals (Zn, Cd, Pb, Cu), as well as a possibility of using water hyacinth biomass obtained during treatment for vermicomposting by Eisenia fetida and the vermicompost quality in a model experiment. The results showed that the concentration of heavy metals in the trials with water hyacinth decreased within 35 days. We introduced water hyacinth biomass to the organic substrate for vermicomposting, which promoted a significant weight gain of earthworms and growth in their number, as well as a 1.5- to 3-fold increase in coprolite production. In the trial with 40 % of Eichhornia biomass in the mixture, we observed a 26-fold increase in the number and a 16-fold weight gain of big mature individuals with clitellum; an increase in the number of small individuals 40 times and in the number of cocoons 140 times, as compared to the initial substrate. The utilization of water hyacinth biomass containing heavy metals in the mixture led to a 10-fold increase in the number of adult individuals and cocoons, which was higher than in control. We found out that adding 10 % of Eichhornia biomass to the initial mixture affected slightly the number of microorganisms and their species diversity in the vermicompost. Adding Eichhornia biomass with heavy metals reduced the total number of microorganisms and sharply diminished their species diversity. In all trials, adding water hyacinth in the mixture for vermicomposting had a positive impact on wheat biometric parameters in a 14-day laboratory experiment, even in the trial with heavy metals.

Mining in New Caledonia: environmental stakes and restoration opportunities

New Caledonia is a widely recognised marine and terrestrial biodiversity hot spot. However, this unique environment is under increasing anthropogenic pressure. Major threats are related to land cover change and include fire, urban sprawling and mining. Resulting habitat loss and fragmentation end up in serious erosion of the local biodiversity. Mining is of particular concern due to its economic significance for the island. Open cast mines were exploited there since 1873, and scraping out soil to access ores wipes out flora. Resulting perturbations on water flows and dramatic soil erosion lead to metal-rich sediment transport downstream into rivers and the lagoon. Conflicting environmental and economic aspects of mining are discussed in this paper. However, mining practices are also improving, and where impacts are inescapable ecological restoration is now considered. Past and ongoing experiences in the restoration of New Caledonian terrestrial ecosystems are presented and discussed here. Economic use of the local floristic diversity could also promote conservation and restoration, while providing alternative incomes. In this regard, Ecocatalysis, an innovative approach to make use of metal hyperaccumulating plants, is of particular interest.

Diazotrophs-assisted phytoremediation of heavy metals: a novel approach

Heavy metals, which have severe toxic effects on plants, animals, and human health, are serious pollutants of the modern world. Remediation of heavy metal pollution is utmost necessary. Among different approaches used for such remediation, phytoremediation is an emerging technology. Research is in progress to enhance the efficiency of this plant-based technology. In this regard, the role of rhizospheric and symbiotic microorganisms is important. It was assessed by enumeration of data from the current studies that efficiency of phytoremediation can be enhanced by assisting with diazotrophs. These bacteria are very beneficial because they bring metals to more bioavailable form by the processes of methylation, chelation, leaching, and redox reactions and the production of siderophores. Diazotrophs also posses growth-promoting traits including nitrogen fixation, phosphorous solubilization, phytohormones synthesis, siderophore production, and synthesis of ACC-deaminase which may facilitate plant growth and increase plant biomass, in turn facilitating phytoremediation technology. Thus, the aim of this review is to highlight the potential of diazotrophs in assisting phytoremediation of heavy metals in contaminated soils. The novel current assessment of literature suggests the winning combination of diazotroph with phytoremediation technology.

Cadmium phytoremediation by Arundo donax L. from contaminated soil and water

The potential of Arundo donax L. for phytoextraction of cadmium (Cd) from contaminated soil and water was probed. The plants were grown under greenhouse conditions in pots containing a nutrient solution or soil with increasing doses of Cd (0, 50, 100, 250, 500, 750, and 1000 μg L(-1)) for 21 days. The growth and physiology of plants were evaluated at the end of the experiment. The maximum Cd content in root was 300 μg g(-1) during hydroponics experiments over 230 μg g(-1) in soil experiment. Cd concentration in stem was 262 μg g(-1) at 750 μg L(-1) supplied Cd in hydroponics over 191.2 μg g(-1) at 1000 in soil experiment. The maximum Cd concentration in leaves from hydroponics was 187 μg g(-1). Relatively low Cd uptake occurred during soil experiment with low translocation factor (TF) values. Both Bioaccumulation Factor (BF) and TF values for hydroponics were greater than 1. The IC50 values of ABTS and DPPH showed that both time and increasing Cd concentrations affected the production of antioxidants with lower half maximal inhibitory concentration (IC50) value on the 21st days. A. donax showed better potential for Cd remediation of aquatic environments.