Evaluation of interaction among indigenous rhizobacteria and Vigna unguiculata on remediation of metal-containing abandoned magnesite mine tailing

Abandoned magnesite mine heap causing pollution to nearby farmland and water reservoir. Thus the intention of this research was to screening metal mobilizing and absorbing bacteria from the rhizosphere section of V. unguiculata from farmland nearby to magnesite mine. Further, studied their stimulus effect on growth, biomass, and phytoextraction prospective of V unguiculata in mine tailing. The results of the physicochemical properties of mine tailing shows that four metals (Pb, Mn, Cd, and Zn) were crossing the permissible limit. Out of 27 isolates, 2 isolates (MMS15 and MMS17) were identified with maximum metal tolerance for up to 700 mg L^-1 (MIC) and metal mobilization (Pb 5.5 and 5.87, Mn 6.6 and 4.88, Cd 1.99 and 2.59, and Zn 6.55 and 6.94 mg kg^-1) and biosorption efficiency as Pb 3.74 and 3.74, Mn 4.9 and 4.7, Cd 2.41 and 3.96, and Zn 4.3 and 4.9 mg g^-1. These two strains were identified as members of B. cereus and Kosakonia sp. using 16S rRNA technique and labelled strains NDRMN001 and MGR1, respectively. The Kosakonia sp. MGR1 effectively fixes the nitrogen in the rate of 81.94% and B. cereus NDRMN001 solubilizes 69.98 ± 2.31 mg L^-1 of soluble phosphate. The experimental group's study results show that the group C (Kosakonia sp. MGR1 and B. cereus NDRMN001) has effectively stimulate the growth, biomass, and phytoextraction potential of V. unguiculata. The results conclude that the optimistic interaction between these two bacteria could be more significant to minimize the metal pollution in magnesite mine tailing.

Effect assessment of chelators on bioaccessible and total chromium extraction in soils polluted by chromite processing wastes

Solid wastes from chromium-processing facilities, when used as fill material, have generated chromium point source contamination of soils and groundwaters, that remains after decades in many urban and peri urban areas all over the world, causing environmental impacts that need to be addressed in a sustainable economic, social and environmental way. Representative surface soil samples, from a polluted area affected by chromite wastes burials, were used to carry on a feasibility study on Phytoextraction applicability, and chelating agents' selection to reduce environmental risks, considering chromium bioaccessible forms reduction as an objective. Tests for natural (only vegetation), and induced phytoextraction (plants + chelating agents) applicability were performed at greenhouse facilities under controlled conditions at two rounds. Natural phytoextraction tests, using first wheat and then corn plants, allowed to observe a low but significant 4,8% reduction in soil chromium. At induced phytoextraction trials, when comparing the action of the different chelating agents versus a blank on final soil chromium concentration, the results were not so conclusive globally (0,5% less soil chromium in trials in which the first crop was wheat followed by corn, and 2% in trials in which the first and the second crop was corn). In each group, the most "effective" chelating agent differed: EDDS for the first set, MGDA for the second one.The addition of chelating compounds in the soil could result in an increasing of the Cr oxidizable fraction mainly composed by Cr species associated to the organ mineral complexes.

Chemometric characterization of heavy metals in soils and shoots of the two pioneer species sampled near the polluted water bodies in the close vicinity of the copper mining and metallurgical complex in Bor (Serbia): Phytoextraction and biomonitoring contexts

In terms of investigating the authentic plant biomonitoring and phytoextraction potentials, the samples of soils and shoots of the sun spurge (SS) and common nettle (CN), were collected near several polluted water bodies in the close vicinity of the copper mining/metallurgical complex in Bor (Serbia) and characterized with regard to the content of heavy metal(oid)s: As, Cd, Pb, Cu, and Zn. The methods applied in this work such as inductively coupled plasma-mass spectrometry, one-way analysis of variance, Pearson's correlation study, hierarchical cluster analysis, and the calculation of bioaccumulation rates (expressed through the so called mobility ratios, MRs), provided very informative data on the potentials of both investigated pioneer species. The most important findings were: 1) In most cases, SS was more effective in metal extraction/translocation/bioaccumulation than CN, and especially with regard to Cu; in this particular case, extremely high concentrations were recorded and also, some significant MRs were calculated, which may be a signal of its promising potential for Cu-phytoremediation, practically, Cu-phytoextraction; however, generally, the values of most calculated MRs were very low (<1, for both plants); 2) The shoots of both plants reflected soundly the current status of metal presence in the studied environment and they can be recommended for seasonal screenings of a general level of metal pollution in the areas of interest; however, specifically, they cannot reflect quite correctly the level of soil pollution; 3) Soil Cu, and As were detected in alarming concentrations.

Effect of planting density of the macrophyte consortium of Typha domingensis and Eleocharis acutangula on phytoremediation of barium from a flooded contaminated soil

Barite (BaSO₄) is a component of drilling fluids used in the oil and gas industry and may cause barium (Ba) contamination if it is spilled onto flooded soils. Under anoxic soil conditions and low redox potential, sulfate can be reduced to a more soluble form (sulfide), and Ba can be made available. To design a solution for such environmental issues, a field study was conducted in a Ba-contaminated flooded area in Brazil, in which we induced Ba phytoextraction from the management of the planting density of two intercropped macrophytes. Typha domingensis and Eleocharis acutangula were grown in four initial planting densities: "Ld" (low density: 4 and 32 plants m^-2); "Md" (medium density: 8 and 64 plants m^-2); "Hd" (high density: 12 and 128 plants m^-2); "Vhd" (very high density: 16 and 256 plants m^-2). Vhd produced the largest number of plants after 300 days. However, the treatments did not differ in terms of the amount of biomass. The increments in the initial planting density did not increase the Ba concentration in the aerial part. The greatest Ba phytoextraction (aerial part + root) was achieved by Ld treatment, which removed approximately 3 kg of Ba ha^-1. Md and Vhd treatments had the highest Ba translocation factors. Because more plants per area did not result in greater Ba phytoextraction, a lower planting density was recommended for the intercropping of T. domingensis and E. acutangula to promote the phytoextraction of barium, due to possible lower implementation costs in contaminated flooded environments.

Willow and poplar for the phyto-treatment of landfill leachate in Mediterranean climate

Phytotechnological approaches using living plants are currently being proposed to address a wide range of environmental purposes including the treatment of landfill leachate (LL). Despite their popularity, few studies have investigated this possibility under actual Mediterranean conditions using fast-growing trees. This research reports the results of a two-year project where poplar and willow grown in mesocosm were tested for their ability to withstand and remove specific pollutants from different [Low: 7% (1st year) and 15% (2nd year); High: 15% (1st year) and 30% (2nd year)] amounts of LL. Results indicate that both species were able to treat 340 (Low) and 680 (High) m³ ha^-1 in the establishment year (70 days) and 2470 (Low) and 4950 (High) m³ ha^-1 in the second year (150 days). Both species yielded the same aboveground biomass, but under high LL treatment, poplar performed better than willow. Poplar showed on average significantly higher extraction rates for Cd, Cu, P, and N than willow. Moreover, under high LL treatment, poplar also seemed more efficient than willow in decreasing the concentration of specific pollutants (BOD₅, COD and As) in output effluent. However, with low LL loads both species were able to significantly reduce other compounds (i.e. NH₄-N, Cu and Ni). By contrast, Cl, surfactants, and NO₃-N, had a tendency to accumulate over time in the effluent and could still represent an actual constraint to large-scale application of the technique. The fate of such pollutants should be investigated with further research to better inform strategies used to manage low amounts of high-concentrated effluent.

Extracting cadmium in the presence of salt: a study on three poplar clones under controlled conditions

This study aimed at determining the cadmium phytoextraction potential of three Populus alba L. clones cultivated in the presence of increasing sodium chloride concentrations. Plantlets of a commercial and two autochthonous poplar clones were grown in perlite with nutrient solution enriched in CdSO₄ (50 and 100 μM) and NaCl (25 and 50 mM), administered either alone or in combination. The three clones showed significant variation not only in cadmium and salt tolerance, accumulation and content, but also in the effect of the interaction between the two elements on these parameters. The toxic effect of Cd and salt excess on plants was mutually exacerbated by the presence of both. Even though the outcome of the joint treatment was always a decrease in shoot Cd or Na accumulation, the three clones showed variation in the extent of such reduction. Evaluating the total element content per plant shoot, the fast-growing commercial clone displayed the highest phytoextraction potential for Cd and Na, either alone or in mixture. Our results demonstrated for the first time that the Cd response in presence of salt can vary in the different clones.

Individual and combined application of Cu-tolerant Bacillus spp. enhance the Cu phytoextraction efficiency of perennial ryegrass

Forage grasses have recently received a remarkable amount of attention as promising candidates for decontaminating metal-polluted soils, but this strategy is time-consuming and inefficient. The present study aimed to address the beneficial effects of screened plant growth-promoting rhizobacteria (PGPR) strains Bacillus sp. EhS5 and EhS7 on perennial ryegrass and tall fescue. Single or combined inoculation considerably increased the biomass yield and Cu content of inoculated ryegrass compared with uninoculated plants, thereby enhancing the extraction efficiency at different Cu contamination levels. Bioaugmentation did not show a positive impact on the improvement of fescue's phytoextraction efficiency. Principal component analysis (PCA) and Pearson correlation coefficient results identified root development and photosynthesis as the key variables influencing ryegrass biomass. Antioxidant activities and Cu bioavailability are the key variables influencing Cu accumulation. The inoculated ryegrass showed improved photosynthetic status as the photosystem II system efficiency parameters increased and energy dissipation in the form of heat (DI_o/RC) decreased with the help of PGPR. The root length, diameter, surface area, and forks of inoculated ryegrass increased remarkably. The levels of scavengers of reactive oxygen species were enhanced in these plants. Moreover, PGPR significantly increased soil Cu bioavailability by secreting siderophores and organic acid and by increasing soil organic carbon content. Dual inoculation showed better results than individual inoculation in improving ryegrass growth and Cu translocation under high Cu contamination level according to PCA. This study systematically explored the effects and mechanisms of the Bacillus-ryegrass combined remediation and provided a novel method for cleaning Cu-contaminated sites.

Exogenous plant growth regulator alleviate the adverse effects of U and Cd stress in sunflower (Helianthus annuus L.) and improve the efficacy of U and Cd remediation

Plant growth regulators (PGRs) are widely used in agricultural activities and have the potential to improve plant growth and plant tolerance against metal stress. PGR-assisted phytoextraction is now an effective and inexpensive method for enhancing the plant removal of toxic metals from soil. In this study, we conducted experiments to determine the effects of PGR treatments on soil uranium (U) and cadmium (Cd) removal by sunflowers as well as their stress response to U and Cd contamination. We found that the plant growth was inhibited by combined U and Cd stress in sunflowers compared with that of the control; however, the application of exogenous PGR had reduced the combined U and Cd stress by stimulating photosynthesis, decreasing the levels of active oxygen and lipid peroxidation, and enhancing the activity of the antioxidant defence systems. Exogenous PGR also increased the uptake of U and Cd by sunflowers and therefore, improved their U and Cd remediation efficiency. Moreover, indoleacetic acid (IAA) was the most effective PGR at removing U and Cd in the soil; the U and Cd removal efficiency was 484.21% and 238.85% higher in the 500 mg L^-1 IAA application compared with that of the control without PGR application, respectively. Furthermore, none of the PGR treatments significantly influenced the available U and Cd contents in soil. Our results, therefore, may provide some detailed understanding on the technologies for the sustainable remediation of U and Cd contaminated soil by the combination of PGR treatments and phytoextraction.

Endophytic inoculation coupled with soil amendment and foliar inhibitor ensure phytoremediation and argo-production in cadmium contaminated soil under oilseed rape-rice rotation system

Phytoremediation coupled with agro-production is a sustainable strategy for remediation of toxic metal contaminated farmlands without interrupting crop production. In this study, high accumulating oilseed rape was rotated with low accumulating rice to evaluate the effects of crop rotation on growth performance and uptake of cadmium (Cd) in plants. In this system, oilseed rape was inoculated with plant growth promoting endophyte (PGPE) consortium, and rice was applied with soil composite amendment and foliar inhibitor. The results showed, compared with rice monoculture, crop rotation coupled with superposition measure has potential to enhance yield, biomass and nutritional quality of both crops, as well as to increase Cd uptake in non-edible tissues of oilseed rape and to reduce Cd concentration in individual parts of rice, thus accelerating phytoextraction and ensuring food safety. These comprehensive management practices removed 7.03 and 7.91% total Cd from two experiment fields, respectively, in three years phytoremediation. These results demonstrated a feasible technical mode for phytoremediation coupled with argo-production in slightly Cd contaminated field, and also provided useful information for further investigation of interaction mechanisms between the rotated crops and biofortification measures.

Phosphorus and sulfur in a tropical soil and their effects on growth and selenium accumulation in Leucaena leucocephala (Lam.) de Wit

Selenium (Se) is an essential metalloid element for mammals. Nonetheless, both deficiency and excess of Se in the environment are associated with several diseases in animals and humans. Here, we investigated the interaction of Se, supplied as selenate (Se⁺⁶) and selenite (Se⁺⁴), with phosphorus (P) and sulfur (S) in a weathered tropical soil and their effects on growth and Se accumulation in Leucaena leucocephala (Lam.) de Wit. The P-Se interaction effects on L. leucocephala growth differed between the Se forms (selenate and selenite) supplied in the soil. Selenate was prejudicial to plants grown in the soil with low P dose, while selenite was harmful to plants grown in soil with high P dose. The decreasing soil S dose increased the toxic effect of Se in L. leucocephala plants. Se tissue concentration and total Se accumulation in L. leucocephala shoot were higher with selenate supply in the soil when compared with selenite. Therefore, selenite proved to be less phytoavailable in the weathered tropical soil and, at the same time, more toxic to L. leucocephala plants than selenate. Thus, it is expected that L. leucocephala plants are more efficient to phytoextract and accumulate Se as selenate than Se as selenite from weathered tropical soils, for either strategy of phytoremediation (decontamination of Se-polluted soils) or purposes of biofortification for animal feed (fertilization of Se-poor soils).

Phytoremediation of toxic metals present in soil and water environment: a critical review

Heavy metals are one of the most hazardous inorganic contaminants of both water and soil environment composition. Normally, heavy metals are non-biodegradable in nature because of their long persistence in the environment. Trace amounts of heavy metal contamination may pose severe health problems in human beings after prolonged consumption. Many instrumental techniques such as atomic absorption spectrophotometry, inductively coupled plasma-mass spectrometry, X-ray fluorescence, neutron activation analysis, etc. have been developed to determine their concentration in water as well as in the soil up to ppm, ppb, or ppt levels. Recent advances in these techniques along with their respective advantages and limitations are being discussed in the present paper. Moreover, some possible remedial phytoremediation approaches (phytostimulation, phytoextraction, phyotovolatilization, rhizofiltration, phytostabilization) have been presented for the removal of the heavy metal contamination from the water and soil environments.

Saponaria officinalis L. and Achillea millefolium L. as possible indicators of trace elements pollution caused by mining and metallurgical activities in Bor, Serbia

This study evaluates bioaccumulation and translocation potentials of trace elements (TEs) by Saponaria officinalis L. (soapwort) and Achillea millefolium L. (yarrow) in order to select and optimize phytoremediation methods for the polluted environment of the city of Bor, Serbia. According to the enrichment factor for soil (i.e., 57.9-128.8 for Cd and As), pollution index (i.e., 6.6-84.7 for Cu), pollution load index (2.9-98.8), individual potential risk factors (11.5-5163), and potential ecological risk index values (260-6379), urban and rural soils from the city of Bor were classified as very contaminated with the investigated TEs. The results from all the indices and statistical analysis showed significant ecological risks of Cu, As, and Cd at the investigated sites and urge the need for remediation. The enrichment factor of the plants for As (566.3) and Cd (306.2) indicated a high enrichment level of the herb organs at all the sites. Since there are small differences in metal accumulation index values between the herbs and their parts (root, shoot), soapwort and yarrow can be considered as potential bioindicators. Based on the biological concentration and translocation factors, soapwort can be recommended as a suitable herb for phytoextraction purposes of Pb, As, and Cd polluted areas. Yarrow shows good characteristics for phytoextraction of Cu, Pb, and As from the contaminated soil. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) results indicate their similar origin from atmospheric deposition. Therefore, these herbs can be utilized as a bioindicator and phytoremediator in polluted areas influenced by metallurgical activities to detect possible levels of TEs.

Three-year field experiment on the risk reduction, environmental merit, and cost assessment of four in situ remediation technologies for metal(loid)-contaminated agricultural soil

The traditional assessment of agricultural soil remediation technologies pay limited attention to sustainability and only considers the decrease in contaminant concentrations and cost, even though the sustainability of these technologies has been prioritized. This 3-year field study comprehensively assessed the sustainability of four commonly used agricultural soil remediation technologies in terms of metal(loid) removal efficiency, environmental merit, and cost. The farmland was contaminated by previous sewage irrigation with excessive amounts of As, Cd, and Pb. The four selected remediation technologies used were phytoextraction, intercropping of hyperaccumulators and cash crops, chemical immobilization, and turnover and attenuation (T&A). A risk reduction-environmental merit-cost model was utilized to compare these four technologies. Results showed that T&A reduced the health risks posed by excess metal(loid)s by ∼47% and yielded the highest risk reduction and lowest cost. Phytoextraction achieved the highest environmental merit because it produced the least interruption to the environment. A simplified assessment frame for soil remediation technology was established from a retrospective aspect using data from a real soil remediation project. Environmental merit is a less considered factor and more difficult to quantify than risk reduction or cost, thus requiring increased attention.

Effects of low molecular weight organic acids on Cu accumulation by castor bean and soil enzyme activities

Chelating agents have been considered as an important phytoremediation strategy to enhance heavy metal extraction from contaminated soil. A pot experiment was conducted to explore the effects of low molecular weight organic acids (LMWOAs) on the phytoremediation efficiency of copper (Cu) by castor bean, and soil enzyme activities. Results indicated that the addition of all the three kinds of LMWOAs (citric, tartaric, oxalic acids) did not decrease the biomass of castor bean, despite the fact they reduced the concentration of chlorophyll-a in leaves compared to the control. The Cu concentrations in the roots and shoots significantly increased by 6-106% and 5-148%, respectively, in the LMWOAs treatments so that the total accumulation of Cu by whole plants in all the LMWOAs treatments increased by 21-189% in comparison with the control. The values of the translocation factor (TF) and bio-concentration factor (BCF) of Cu in castor bean also rose following the addition of LMWOAs, indicating that the LMWOAs enhanced the uptake and transportation of Cu. Moreover, the application of LMWOAs did not significantly change the soil pH but significantly increased the activity of soil enzymes (urease, catalase, and alkaline phosphatase). The addition of exogenous LMWOAs increased the available Cu significantly in the soil, thus promoted the phytoextraction efficiency of Cu by castor bean. These results will provide some new insights into the practical use of LMWOAs for the phytoremediation of heavy-metal-contaminated soil employing castor bean.

A phytoextraction trial strengthened by Streptomyces pactum and plant nutrients: In view of plant bioindicators and phytoextraction indices

The present work was done to explore the joint effect of Streptomyces pactum (Act12) and plant nutrients on phytoremediation of smelter-contaminated soils. The physiological indicators and phytoextraction indices of potherb mustard (Brassica juncea, Coss) grown in Act12 inoculated soil with or without Hoagland's solution (H), humic acid (HA) and peat (PS) were evaluated. The results indicated that H, HA and PS acted synergistically with Act12, notably increasing chlorophyll and soluble protein contents and thereby promoting plant growth. Soil nutrient treatments reduced the antioxidant activities (PPO, CAT and POD) by 28.2-41.4%, 22.3-90.1% and 15.2-59.4% compared to control, respectively. Act12 and H treatments markedly facilitated plant to accumulate more cadmium (Cd) and zinc (Zn), but it was observed decreases when applied with HA and PS. Metal uptake (MU) values further indicated the differences in phytoextraction efficiency, i.e., H > PS > Control > HA. Taken together, Act12 combined with plant nutrients contributed to alleviating metal toxicity symptoms of plant. Hoagland's solution and peat were highlighted in the present phytoextraction trial, and recommended as soil additives.

Preliminary study on Cd accumulation characteristics in Sansevieria trifasciata Prain

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

Evaluating the efficacy of Atriplex spp. in the phytoextraction of road salt (NaCl) from contaminated soil

Soil and freshwater salinization are growing issues worldwide. Road salt, primarily sodium chloride (NaCl), is a significant contributor to this issue in North America. In this study, the ability of three native Canadian halophytes (Atriplex patula, Atriplex hortensis, and Atriplex canescans) to remove Na⁺ and Cl^- from contaminated soil was investigated. Field and greenhouse studies determined plant survivability in roadside areas, as well as Na⁺ and Cl^- extraction levels. The Atriplex spp. accumulated 18-55 mg Na⁺ g^-1 dry weight (DW) and 41-64 mg Cl^- g^-1 DW when grown for a two-month period in soil spiked with NaCl to simulate a very highly contaminated roadside. Using A. patula, it would theoretically take 6 growing seasons to remove all salt from an area contaminated with 1540 μg Cl^- g^-1, while A. hortensis and A. canescens would take 19 and 9 years, respectively. Salt content in shoot components (seeds, stem, leaves) was determined to provide further insight on phytoextraction processes. In all three Atriplex species, the leaves had the highest Cl^- concentration, followed by the seeds (bracteoles included), with the lowest concentrations found in the stem. These novel findings provide important information for road salt remediation and indicate that using Atriplex spp. may be a viable way in which to reduce the environmental impact of road salting.

Potential use of king grass (Pennisetum purpureum Schumach. × Pennisetum glaucum (L.) R.Br.) for phytoextraction of cadmium from fields

Using king grass (Pennisetum purpureum Schumach. × Pennisetum glaucum (L.) R.Br.) for phytoextraction is a promising technology for producing large amounts of biomass fuel while remediating contaminated soil. To assess the practical phytoextraction capacity of king grass, we conducted a field experiment with three different soil types (loam, sandy loam, clay loam) and cadmium (Cd) concentrations (0, 0.25, 0.5, 1, 2, 4, 8, and 16 mg kg^-1, aged stably for 6 years). King grass were harvested at two different periods (elongation and maturity) to identify the optimal harvest time for extraction efficiency. The results showed that all treatments had bioconcentration factor (BCF) > 1 and translocation factor (TF) < 1; Cd is mainly stored in the roots. However, due to a high shoot biomass, the highest quantity of Cd extracted from shoots was 2.75 mg plant^-1, from the experimental group with 16 mg kg^-1 Cd added in sandy loam. A significant positive relationship (P < 0.05) was observed between the amount of Cd extracted from king grass stems, leaves, and roots from soil with the diethylene triamine pentacetate acid (DTPA) extractable Cd concentration. The Cd concentration in shoots at the maturity stage is lower than at the elongation stage, mainly due to the effect of biological dilution. Meanwhile, there is significantly more biomass (P < 0.05) at the maturity stage than at the elongation stage. At the latter, the extraction efficiency of the three soils was loam > sandy loam > clay loam, while at maturity it was sandy loam > clay loam > loam. This change in extraction efficiency can be attributed mainly to differences in soil DTPA-extractable Cd concentration and growth rate caused by differences in soil physical and chemical properties. According to calculations from multiple harvests using three types of soil, remediating contaminated soil with 0-16 mg kg^-1 Cd would take 13.9-224.5 and 19.5-250.6 years, extracting 7.21-265.23 and 4.96-330.52 g ha^-1 Cd while producing 33.62-66.50 and 73.8-110.5 t ha^-1 dry biomass at the elongation (90 days) and maturity (120 days) stages, respectively. In summary, king grass has major potential for remediating Cd-contaminated soil while producing large volumes of biofuel.

Fava bean intercropping with Sedum alfredii inoculated with endophytes enhances phytoremediation of cadmium and lead co-contaminated field

Phytoremediation coupled with agro-production is considered a sustainable strategy for remediation of trace element contaminated fields without interrupting crop production. In this study hyperaccumulator Sedum alfredii was intercropped with a leguminous plant fava bean (Vicia fava) in cadmium (Cd) and lead (Pb) co-contaminated field to evaluate the effects of intercropping on growth performance and accumulations of trace elements in plants with plant growth promoting endophyte (PGPE) consortium application. The results showed, compared with monoculture, intercropping coupled with inoculation application promoted biomass as well as Cd and Pb concentrations in individual parts of both plants, thus increasing the removal efficiencies of trace elements (4.49-folds for Cd and 5.41-folds for Pb). Meanwhile, this superposition biofortification measure maintained normal yield and nutrient content, and limited the concentration of Cd and Pb within the permissible limit (<0.2 mg kg^-1 FW) in fava bean during the grain production. These results demonstrated a feasible technical system for phytoremediation coupled with agro-production in slightly or moderately Cd and Pb co-contaminated field, and also provided useful information for further investigation of interaction mechanisms between intercropping and PGPEs inoculation.

Arbuscular mycorrhiza and Aspergillus terreus inoculation along with compost amendment enhance the phytoremediation of Cr-rich technosol by Solanum lycopersicum under field conditions

Chromium (Cr) contamination is a potential threat to the agricultural soil. Arbuscular mycorrhizal (AM) fungi have potential to remediate the heavy metal polluted soils. It was hypothesized that Cr phytoremediation potentiality of AM fungi could be enhanced in combination with saprophytic filamentous fungi and soil amendment. Tomato plants were raised in Cr polluted technosol amended with compost, inoculated with mixed-culture of AM fungi and Aspergillus terreus. It was found that, triple treatment (soil amendment with compost along with AM fungi and A. terreus inoculation) enhanced biomass production (up to 315%), fruit setting (up to 49%), photosynthetic pigments (up to 214%) and carbohydrate content (up to 400%) whereas reduced the proline (up to 76.5%), catalase (up to 34.2%), peroxidase (up to 58.9%) and root membrane permeability (up to 74.2%). The effect of AM fungi with compost amendment was additive, while it was synergistic with A. terreus. AM fungi enhanced the extraction of Cr from the substrate, but retained in the mycorrhizal root, thereby reduced the translocation into shoot and in fruit, Cr translocation was undetectable. At the end of experiment Cr content in the substrate was significantly decreased (up to 37.9%). Soil amendment with compost along with AM fungi and A. terreus inoculation can be used for reclamation of Cr polluted soils at field scale.

Urea application enhances cadmium uptake and accumulation in Italian ryegrass

Italian ryegrass (Lolium multifolorum Lam.) has a potential phytoextraction capacity for cadmium (Cd), which is considered as the most toxic heavy metal (HM) pollutant in the farmland. The promotion effect of urea application on Italian ryegrass growth has been clarified, while it is not clear whether and how urea application affects Cd accumulation in Italian ryegrass under Cd stress. A 2-year pot experiment was conducted to investigate the effect of urea application on Cd accumulation and related mechanisms by uptake inhibition and kinetics experiments. The results showed that both shoot biomass and Cd concentration under Cd stress were increased by up to 213.37% and 84.74% in 2016 and 38.15% and 47.11% in 2017 after urea application, respectively. The shoot Cd accumulation reached maximum value (910.23 and 630.09 μg pot-1 in 2016 and 2017, respectively) at the level of 300 kg ha-1 urea. Superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities were significantly increased by urea application. Compared with control group, urea application significantly improved inhibition ratio of 2, 4-dinitrophenol (DNP) rather than LaCl3 and Ca2+. Cadmium uptake kinetics experiment showed that urea application significantly decreased the Km value and improved the α value (P < 0.01), but no significant effect on the Vmax value (P > 0.05). In conclusion, we proposed that the higher affinity to Cd2+ of the membrane transporter after urea application promoted the active uptake of Cd, which contributed to the effective Cd accumulation capacity in Italian ryegrass.

Investigating the potential of different jute varieties for phytoremediation of copper-contaminated soil

Copper (Cu), with many documented cases of Cu toxicity in agriculture lands, is becoming an increasingly common issue in and elsewhere in China. However, fibrous crop such as jute is being used as phytoremediation candidate in Cu-contaminated soils due to its huge biomass. A pot experiment was conducted using four different varieties (HT, C-3, GC, and SH) of jute grown in highly Cu-contaminated soil (2221 mg kg^-1), collected from Hubei Province, China. Results from this study showed that C-3 and HT were more resistant to Cu stress, while GC and SH had a serious effect due to high concentration of Cu and a significant decrease in growth and biomass. Furthermore, Cu in roots, leaves, stem core, and bast were higher in C-3 and HT compared with GC and SH. Likewise, at post-harvesting stage, maximum Cu concentration from Cu-contaminated soil was extracted by C-3 and HT while small amount was accumulated by GC and SH. The high content of malondialdehyde (MDA) in the leaves of GC and SH indicated that Cu induced oxidative damage while the antioxidative enzyme activities of superoxidase dismutase (SOD) and peroxidase (POD) were increased to scavenge reactive oxygen species (ROS) formed during oxidative stress in the plants. Conclusively, it can be identified that when grown in Cu-contaminated soil, C-3 and HT have greater ability to grow in polluted soils and possible phytoremediation materials to revoke a large amount of Cu.

The influence of light combination on the physicochemical characteristics and enzymatic activity of soil with multi-metal pollution in phytoremediation

Light irradiation with suitable quality and intensity could influence the success of phytoremediation by improving the biomass yield of plants. However, mechanisms involved in this influence on the contaminant accumulation and translocation ability of plants have rarely been studied. Five light combinations with different red (R) and blue (B) ratios (0, 10, 50, 75 and 100 % blue) at the same intensity (220 μmol m^-2 s^-1) were used to assist phytoremediation using Noccaea caerulescens, and the change in physicochemical characteristics and enzymatic activities of soils after phytoremediation were evaluated. Compared with the control, the light combinations and monochromic blue light significantly increased the activities of soil ureases, invertases, and phosphatases, whereas monochromic red light strongly inhibited the activities of these enzymes, because different light irradiations altered the formation and excretion of carbohydrates from plants for soil microorganism consumption. Plants under B₅₀R₅₀ treatment accumulated the highest concentrations of metals, but their chlorophyll concentrations and lipid peroxidation were similar to those other species with lower metal concentrations. Hence, light with a proper blue/red ratio can simultaneously improve the physicochemical characteristics and enzymatic activities of soils, increase the metal uptake capacity and oxidation resistance of plants, and reduce the leaching risk during phytoremediation processes.

Lead Tolerance and Enrichment Characteristics of Several Ornamentals Under Hydroponic Culture

The growth response, tolerance, and enrichment characteristics of six ornamental species, Chlorophytum comosum, Calendula officinalis, Iris lacteal, Belamcanda chinensis, Saponaria officinalis, and Polygonum lapathifolium were studied under hydroponic culture with lead (Pb) concentrations ranging from 0 to 1000 mg/L. The results showed that the growth of the tested ornamental species under Pb stress was inhibited. Belamcanda chinensis presented the largest tolerance index (0.75), and Calendula officinalis had the highest toxicity threshold (500 mg/L) under Pb stress. The highest Pb contents in the shoots were detected in Iris lacteal and Belamcanda chinensis. The enrichment coefficients in the shoots of Iris lacteal and Belamcanda chinensis were significantly higher than those in the other ornamental species. In conclusion, Iris lacteal and Belamcanda chinensis are the most tolerant and have the greatest Pb enrichment and translocation abilities under Pb stress, and thus, they have a strong potential to restore Pb-contaminated water bodies and soils.

Transfer and bioaccumulation of mercury from soil in cowpea in gold mining sites

In this study, we evaluated the phytoremediation ability of three different genotypes of cowpea (Vigna unguiculata L. Walp) grown on mercury-contaminated soils from gold mining areas. In particular we compared a native genotype with two commercial lines L-019 and L-042. The plants were cultivated in soils amended at different concentrations of Hg (i.e. 0.2, 1, 2, 5 and 8 mg kg^-1). After three months exposure, we determined plant growth, seed production, and Hg accumulation in different plant tissues (root, leaf, seed and stem). Indices of soil-plant metal transfer such as translocation, bioconcentration and bioaccumulation factors were calculated. Results showed that the native variety presented the highest seed production (3.8 g), however the highest plant biomass (7.9 g) was observed in line L-019, both on Hg-contaminated soil of 1 mg kg^-1. The different plant tissues differed in terms of Hg concentration (root > leaf > stem). In the highest treated soil, the line L-042 accumulates higher Hg in both roots and leaves, while line L-019 accumulates more metal in stems. In line L-019, Hg concentrations in the fruit showed significant differences being higher in the valves than in the seeds. The transfer factors were generally lower than 1 and indicates the low accumulation of Hg by cowpeas. The estimated daily Hg intake through cowpea consumption showed values far below the threshold of 0.57 μg kg^-1 dw day^-1 recommended by the World Health Organization. Our results show cowpea V. unguiculata as a good protein-rich food substitute of Hg-contaminated fish for populations living near gold mining sites.

Effects of EDDS on the Cd uptake and growth of Tagetes patula L. and Phytolacca americana L. in Cd-contaminated alkaline soil in northern China

Phytoextraction has been considered an effective and environment-friendly method for removing heavy metals from contaminated soil. However, the efficiency, mechanism, and adaptability of phytoextraction by hyperaccumulators in Cd-polluted weakly alkaline soil have not been investigated in detail. In this study, pot experiments were conducted to evaluate the enhanced effects of S,S-ethylenediamine disuccinic acid (EDDS) on phytoextraction in alkaline soil by measuring the degradation kinetic characteristics of EDDS and Cd absorption dynamics of Tagetes patula L. (T. patula) and Phytolacca americana L. (P. americana) for a period of 55 days. Results showed that the half-life of EDDS varied from 4.20-7.07 days and 3.35-4.36 days for T. patula and P. americana, respectively. EDDS-activated Cd reached saturation at a low dosage (1 mM) and a single application of EDDS was found to be better than double applications. The activation of EDDS on Cd applied before 45 days of harvest was better than that before 15 days of harvest, and disappeared after a 35-day application. Correspondingly, the Cd concentration in P. americana and T. patula leaves increased significantly after 3 days of the EDDS application. However, T. patula had a biomass 2.57 times and Cd absorption capacity 10.06 times higher than P. americana. EDDS showed almost no influence on the stem and leaf biomass of T. patula; however, the root weight decreased by 9.44-71.77%. The Cd concentration in T. patula leaves of all the treatments was 1.00-1.81 times that of the control group. In comparison with other treatments, the EDDS application (3 mM) before 15 days of harvest extracted the highest amount of Cd (601.45 μg/pot) in T. patula shoots, reaching 1.40 times that in the control group. Therefore, T. patula might be a more suitable phytoremediator for Cd-polluted alkaline soil than P. americana; the most effective method was the EDDS application (3 mM) before 15 days of harvest.

Responses of soil bacterial community and Cd phytoextraction to a Sedum alfredii-oilseed rape (Brassica napus L. and Brassica juncea L.) intercropping system

Soil pollution with heavy metals has become a common problem in agricultural ecosystems and poses a threat to food safety and human health. Intercropping is now considered a promising alternative to address this issue. However, our understandings about the influences of intercropping systems on rhizosphere microbiota composition and their association with plant performance are still limited. In this study, rhizobox microcosm experiments were conducted to investigate the influence of cropping regimes (i.e. monoculture and intercropping) on the rhizosphere bacterial microbiota and their linkages with the phytoextraction of cadmium (Cd) by Zhongyouza 19 (Brassica napus L.), Xikou Huazi (Brassica juncea L.) and Sedum alfredii using 16S rRNA gene sequencing. Cadmium accumulation in shoots of B. napus and B. juncea grown under intercropping were enhanced by 370% and 27.8% respectively, as compared to monoculture. Soil compartmentation as a major determinant explained 57.6% of the rhizosphere bacterial microbiota variation, whereas plant species and cropping regime accounted for 26.4% of the variation. The overall abundance of the taxa was Proteobacteria, Acidobacteria, Bacteroidetes, Chloroflexi, Verrucomicrobia, and Actinobacteria. Intercropping significantly enriched amplicon sequence variants (ASVs) abundance belonging to Actinobacteria, Bacilli, Deltaproteobacteria while depleting that of Acidobacteria in rhizosphere. Intercropping with S. alfredii influenced more on microbial composition of B. napus rhizosphere. The change in rhizosphere bacterial communities was related to metal availability, soil properties, and plant parameters. The enriched families of Pedosphaeraceae, Ruminococcaceae, Chitinophagaceae, Gemmatimonadaceae, Nitrosomonadaceae, and Parachlamydiaceae were positively correlated with metal concentration in plants. These results indicate that S. alfredii and oilseed rape intercropping could be a promising approach for enhancing the remediation of Cd contaminated soil. Understanding the complex plant-microbe-metal interactions of intercropping system could facilitate the development of remediation strategy for phytoremediation of contaminated soils and sustainable agricultural production.

Evaluation of phytoremediation potential of five Cd (hyper)accumulators in two Cd contaminated soils

A phytoextraction experiment with five Cd hyperaccumulators (Amaranthus hypochondriacus, Celosia argentea, Solanum nigrum, Phytolacca acinosa and Sedum plumbizincicola) was conducted in two soils with different soil pH (5.93 and 7.43, respectively). Most accumulator plants grew better in the acidic soil, with 19.59-39.63% higher biomass than in the alkaline soil, except for S. plumbizincicola. The potential for a metal-contaminated soil to be cleaned up using phytoremediation is determined by the metal uptake capacity of hyperaccumulator, soil properties, and mutual fitness of plant-soil relationships. In the acidic soil, C. argentea and A. hypochondriacus extracted the highest amount of Cd (1.03 mg pot^-1 and 0.92 mg pot^-1, respectively). In the alkaline soil, S. plumbizincicola performed best, mainly as a result of high Cd accumulation in plant tissue (541.36 mg kg^-1). Most plants achieved leaf Cd bioconcentration factor (BCF) of >10 in the acidic soil, compared to <4 in the alkaline soil. Soil Cd availability was chiefly responsible for such contrasting metal extraction capacity, with 5.02% fraction and 48.50% fraction of total Cd being available in the alkaline and acidic soil, respectively. In the alkaline soil, plants tended to increase rhizosphere soil available Cd mainly through excreting more low molecular weight organic acids, not through changing the soil pH. In the acidic soil, plants slightly decreased soil available Cd. Those species which have high Ca, Zn, Fe uptake capacity extract more Cd from soil, and a positive correlation was found between the concentrations of Cd and Ca, Zn, Fe in leaves. Soil available Ca²⁺, Mg²⁺, SO₄^2-, Cl^- did not play a key role in Cd uptake by plants. In summary, acidic soil was of higher potential to recover from Cd contamination by phytoextraction, while in the alkaline soil, S. plumbizincicola showed potential for Cd phytoextraction.

Indigenous soil bacteria and the hyperaccumulator Pteris vittata mediate phytoremediation of soil contaminated with arsenic species

Arsenic (As) is a pollutant of major concern worldwide, posing as a threat to both human health and the environment. Phytoremediation has been proposed as a viable mechanism to remediate As-contaminated soil environments. Pot experiments were performed to evaluate the phytoextraction efficiency of As by Pteris vittata, a known As hyperaccumulating fern, from soil amended with different concentrations of arsenate [As(V)] and arsenite [As(III)], the more common, inorganic As forms in soil. The greatest accumulation of As (13.3 ± 0.36 g/kg Dwt) was found in fronds of plants grown in soil spiked with 1.0 g As(V)/kg. The maximum As-bioaccumulation factor (27.3 ± 1.9) was achieved by plants grown in soil amended with 0.05 g As(V)/kg. A total of 864 bacterial cultures were isolated and examined for their ability to enhance phytoremediation of As-contaminated soils. Traits examined included tolerance to As (III and V), production of siderophores, and/or ability to solubilize calcium phosphate and indole acetic acid (IAA) production. A culture-based survey shows greater numbers of viable and As-resistant bacteria were found in the rhizosphere of As-grown plants compared to bulk and unplanted soils. The percentage of bacteria resistant to As(V) was greater (P < 0.0001) than those resistant to As(III) in culture medium containing 0.5, 1, 1.5, and 2 g As/L. Higher (P < 0.0001) percentages of siderophore producing (77%) and phosphate solubilizing (61%) bacteria were observed among cultures isolated from unplanted soil. About 5% (44 of 864) of the isolates were highly resistant to both As (III) and As (V) (2 g/L), and were examined for their As-transformation ability and IAA production. A great proportion of the isolates produced IAA (82%) and promoted As (V)-reduction (95%) or As(III)-oxidation (73%), and 71% exhibited dual capacity for both As(V) reduction and As(III) oxidation. Phylogenetic analysis indicated that 67, 23, and 10% of these isolates belonged to Proteobacteria, Actinobacteria, and Firmicutes, respectively. Analysis of the 16S rRNA gene sequences confirmed that these isolates were closely related to 12 genera and 25 species of bacteria and were dominated by members of the genus Pseudomonas (39%). These results show that these isolates could potentially be developed as inocula for enhancing plant uptake during large scale phytoremediation of As-impacted soils.

Localization of mercury and gold in cassava (Manihot esculenta Crantz)

The potential of cassava (Manihot esculenta Crantz.) for simultaneous Hg and Au phytoextraction was explored by investigating Hg and Au localization in cassava roots through Micro-Proton Induced X-Ray Emission, High-Resolution Transmission Electron Microscopy (HR-TEM) and X-Ray Diffractometry (XRD). The effect of Hg and Au in the cyanogenic glucoside linamarin distribution was also investigated using Matrix Assisted Laser Desorption Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (MALDI-FT-ICR-MS) imaging. Hg was located mainly in the root vascular bundle of plants grown in 50 or 100 μmol L^-1 Hg solutions. Au was localized in the epidermis and cortex or in the epidermis and endodermis for 50 and 100 μmol L^-1 Au solutions, respectively. For 50 μmol L^-1 solutions of both Hg and Au, the two metals were co-localized in the epidermis. When the Hg concentrations were increased to 100 μmol L^-1, Au was still localized to a considerable extent in the epidermis while Hg was located in all root parts. HR-TEM and XRD revealed that Au nanoparticles were formed in cassava roots. MALDI-FT-ICR-MS imaging showed linamarin distribution in the roots of control and plants and metal-exposed plants thus suggesting that linamarin might be involved in Hg and Au uptake and distribution.

Response of rhizospheric and endophytic bacterial communities of white mustard (Sinapis alba) to bioaugmentation of soil with the Pseudomonas sp. H15 strain

A factor that may significantly increase the efficacy of phytoextraction is soil bioaugmentation with specific bacteria, which can alter the composition of rhizospheric and endophytic bacterial communities. The aim of this study was to compare the effect of soil treatment with living (bioaugmentation) and dead (control) cells of the plant growth-promoting metal-resistant endophytic strain Pseudomonas sp. H15 on the bacterial community composition in the rhizo- and endo-sphere of white mustard during enhanced phytoextraction. The bacterial communities in the rhizosphere were dominated (51.7-68.2%) by Proteobacteria, regardless of the soil treatment or sampling point. A temporary increase in the number of sequences belonging to Gammaproteobacteria (up to 37.3%) was only observed 24 h after the soil treatment with living Pseudomonas sp. H15 cells, whereas for the remaining samples, the relative abundance of this class did not exceed 7.1%. The relative abundance of Proteobacteria in the endosphere of the roots, stems, and leaves of white mustard was higher in the control than in bioaugmented plants. The most pronounced dominance of the Gammaproteobacteria sequences was observed in the stems and leaves of the control plants at the first sampling point, which strongly indicates the ability of the plants to rapidly uptake DNA from soil and translocate it to the aboveground parts of the plants. Additionally, the bioaugmentation of the soil caused a diverse shift in the bacterial communities in the rhizo- and endo-sphere of white mustard compared to control. The most distinct differences, which were dependent on the treatment, were observed in the endosphere of plants at the beginning of the experiment and decreased over time. These results indicate that the rhizo- and endo-biome of white mustard reacts to soil bioaugmentation and may influence the efficiency of bacterial-assisted phytoextraction.

Leaching Behaviour and Enhanced Phytoextraction of Additives for Cadmium-Contaminated Soil by Pennisetum sp

The leaching behavior of five additives, including citric acid (CA), wood vinegar (WV), 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), polyaspartic acid (PASP) and FeCl₃, was investigated to evaluate the possibility of enhanced phytoextraction of Pennisetum sp. from cadmium-contaminated soil. FeCl₃ and CA have the highest leaching potential due to the ability that could convert large amounts of mobile fractions of Cd. The pot experiment showed that HEDP, WV, and PASP treatments could not only significantly increase the biomass of Pennisetum sp., but also maintain high uptake capacity of Cd by activating the stable fractions. HEDP has the highest Cd extraction efficiency and metal extraction ratio (MER) value. The phytoremediation efficiency could be improved mainly by increasing the biomass of the tolerant shoots, and Pennisetum sp. seems to have the maximum potential of phytoextraction to Cd with HEDP which could achieve a higher phytoextraction effect than Cd-hyperaccumulator.

Simultaneous biosurfactant-assisted remediation and corn cultivation on cadmium-contaminated soil

Phytoremediation using economic crops is an alternative treatment option for contaminated areas that are being utilized by people. In this study, phytoextraction with a local economic crop (corn) that allows simultaneous Cd contamination reduction and corn biomass utilization is proposed. Biosurfactants, rhamnolipid (RL) and saponin (SP), were introduced to enhance Cd phytoextraction. The optimum RL and SP dose was 4 mmol kg^-1. Cd uptake and corn biomass were higher with biosurfactant addition than in the control (without biosurfactants addition), by 2.7 and 2.3-fold, respectively, on the 30th day of corn plantation. The optimum biosurfactant doses were applied to phytoextraction experiments with corn at different corn growth stages (7th, 45th, and 80th day). The highest Cd uptake levels were recorded on day 45, and the maximum uptake was achieved with RL addition (39.06 mg Cd kg^-1). These results were confirmed by bioaccumulation factors, which indicated that RL enhanced soil Cd uptake by corn plants to the highest extent. However, Cd concentration in corn kernels from RL-assisted phytoextraction exceeded the standards for animal feed. On the other hand, although Cd uptake by corn plants in the presence of SP was lower, Cd content in the resulting corn kernels were within the allowable standard limit for animal feedstock. Moreover, compared to RL and control treatments, SP treatment resulted in higher Cd levels in the shoot than in the root, as confirmed by translocation factors. Meanwhile, SP could significantly promote soil Cd removal efficiency; Cd removal efficiencies on day 80 were in the order of SP (18.80%) > RL (11.33%) > control (4.59%). In addition, Cd leaching after addition of RL and SP was investigated. The two surfactants caused much lower Cd leaching from soil than ethylenediaminetetraacetic acid (EDTA). The results of this study indicate that SP-assisted Cd phytoextraction using corn is applicable for the remediation of Cd-contaminated areas in Mae Sot District.

Re-investigation of cadmium accumulation in Mirabilis jalapa L.: evidences from field and laboratory

Mirabilis jalapa L. was identified as a cadmium (Cd) hyperaccumulator, but data were mainly from laboratory conditions. The main aim of the present study was to confirm whether M. jalapa is a Cd hyperaccumulator by field survey and laboratory experiment. The field survey was conducted at 3 sites and 66 samples were collected, and the results showed that although M. jalapa did not exhibit any visible damage when growing on soil containing 139 mg Cd kg^-1, a low concentration of Cd (11.85 ± 3.45 mg kg^-1) in its leaves was observed. Although the translocation factor (TF) was up to 3.24 ± 0.42, the bioconcentration factor (BCF) was only 0.13 ± 0.07. The Cd accumulation in leaves of Lanping (LP, contaminated site) and Kunming (KM, clean site) populations reached 93.88 and 81.76 mg kg^-1 when artificially spiked soil Cd was 175 mg kg^-1, respectively. The BCFs of LP and KM populations were 0.55 and 0.48, and the TFs of the two populations were 3.98 and 4.15, respectively. Under hydroponic condition, the Cd concentration in young leaves of LP and KM populations was 78.5 ± 0.8 and 46.3 ± 1.2 mg kg^-1 at 5 mg L^-1 Cd treatment, respectively. Furthermore, a significantly positive correlation between tissue Cd concentration and total Cd, CaCl₂-extractable Cd, and TCLP-Cd (toxicity characteristic leaching procedure) in soil was established. Therefore, M. jalapa had constitutional characteristics for Cd tolerance and accumulation, but it was not a Cd hyperaccumulator.

Combined use of companion planting and PGPR for the assisted phytoextraction of trace metals (Zn, Pb, Cd)

Biomass production and metal accumulation in plant tissue (bioconcentration) are two critical factors limiting the phytoextraction rate. Metal translocation to aboveground organs should be accounted for as the third most important factor, as harvesting of the plant roots is usually economically disadvantageous. These three parameters could be potentially increased with the use of companion planting, a well-known agricultural technique, and inoculation with plant growth-promoting bacteria (PGPB). The aim of the study was to determine whether intercropping and inoculation with endophytic PGPB (Burkholderia phytofirmans PsJN^T) can increase the efficiency of phytoextraction of Zn, Pb, and Cd. The study was conducted on Brassica juncea (L.) Czern. "Małopolska" grown in a monoculture or co-planted with Zea mays L. "Codimon" and Medicago sativa L. "Sanditi." Results show that companion planting and inoculation with rhizobacteria can increase the efficiency of metal phytoextraction, mainly by increasing the yield of dry biomass and the survival rate of plants grown on contaminated soil. We have shown that the simultaneous planting of B. juncea with M. sativa and inoculation with PGPB were the most efficient variants of assisted phytoextraction reaching a recovery of 95% Zn, 90% Cd, and on average about 160% Pb compared with control B. juncea plants grown in monoculture.

Ochrobactrum intermedium and saponin assisted phytoremediation of Cd and B[a]P co-contaminated soil by Cd-hyperaccumulator Sedum alfredii

Pot-culture experiments were conducted to investigate the potential of microorganism-saponin assisted phytoremediation of cadmium (Cd) and benzo(a)pyrene (B[a]P) co-contaminated soil using Cd-hyperaccumulator Sedum alfredii. Results showed that B[a]P-degrading bacterium (Ochrobactrum intermedium B[a]P-16) inoculation significantly increased root (by 22.1-24.1%) and shoot (by 20.5-23.4%) biomass of S. alfredii, whereas the application of saponin had no effect on the growth of S. alfredii. The saponin solution at 2 g L^-1 extracted more Cd and B[a]P than water, saponin enhanced Cd and B[a]P bioavailability in soil and thus promoted their uptake and accumulation in S. alfredii. The activity of B[a]P-16, dehydrogenase and polyphenol oxidase in co-contaminated soil was promoted by growing S. alfredii, and the application of B[a]P-16 and saponins caused a significant (P < 0.05) increase in both enzyme activities. The maximum B[a]P removal rate (82.0%) and Cd phytoextraction rate (19.5%) were obtained by co-application of S. alfredii with B[a]P-16 and saponin. The B[a]P-16 and plant promoted biodegradation were the predominant contributors towards removal of B[a]P from soil. A significant (P < 0.05) synergistic effect of B[a]P-16 and saponin on B[a]P and Cd removal efficiency was observed in this study. It is suggested that planting S. alfredii with application of B[a]P-16 and saponin would be an effective method for phytoremediation of soil co-contaminated with Cd and PAHs.

EDTA-enhanced phytoremediation of heavy metals from sludge soil by Italian ryegrass (Lolium perenne L.)

Landscaping of sludge is a kind of recycling disposal, but the potential heavy metal risks limit its application. In this paper, the sludge soil was remediated by ryegrass, and the effect of ethylene diamine tetraacetic acid (EDTA) was studied through pot experiments. Italian ryegrass was planted in the sludge soil treated with six gradients concentrations of 0, 1, 2, 3, 4, 5 mmol kg^-1 of EDTA, and the planting conditions were kept the same. After 45 days of planting, compared with the control group (without EDTA treated), the application of 1-5 mmol kg^-1 EDTA decreased ryegrass biomass by 2-43%, reduced soil pH value by 0.21-0.34 unit, and reduced 4.1-9.7% capacity of exchange cation, but increased 1.4-8.6% soil organic matter. After growing ryegrass, the contents of heavy metals decreased by 10% for Cu, 15% for Zn, 6% for Ni, 14% for Cd and 44% for Pb; and after spraying EDTA decreased again by 33% for Cu, 31% for Zn, 56% for Ni, 24% for Cd, and 68% for Pb. In ryegrass, the uptake heavy metals were enhanced, and bio-concentration factor of Cu, Zn, Ni, Cd, and Pb of EDTA treated groups were 1.9, 1.6, 4.1, 2.7, and 4.8 times of the control group, respectively. However, EDTA only significantly increased transfer factor values of Cu and Zn, and made bio-extraction factor value of Cu greater than 1. The remediation factor values were used to comprehensive assess accumulation capacity of heavy metals by ryegrass under EDTA treating, and they ordered in Zn > Cu > Ni > Cd > Pb, and the best dose was 2 mmol kg^-1 EDTA. Prediction models for bio-concentration factor were established by using stepwise multiple linear regression, explaining 94.9-99.3% of the corresponding elements with soil organic matter, EDTA dosage, and/or pH value (p < 0.005). This paper provided effective heavy metals remediation data for municipal sludge landscape and the prediction models.

Insight into the mechanisms of plant growth promoting strain SNB6 on enhancing the phytoextraction in cadmium contaminated soil

Plant growth-promoting rhizobacteria (PGPR) assisted accumulator has been proposed as a phytoextraction method to clean cadmium (Cd) in contaminated soil, while the mechanisms were few studied regrading PGPR-soil-accumulator as an assemble. In this study, we revealed the possible mechanisms of the plant growth-promotion strain SNB6 on enhancing the Cd phytoextration of vetiver grass by the analysis of the whole genome of SNB6, soil biochemical properties and plant growth response. Results showed that SNB6 encoded numerous genes needed for Cd tolerance, Cd mobilization and plant growth promotion. SNB6 increased HOAc-extractable Cd that showed a positive correlation with Cd uptake in accumulator. In addition, SNB6 improved the biochemical activities (bioavailability of nutritional substances, bacterial count, soil respiration and enzyme activity) in rhizosphere soil. Moreover, the antioxidative enzymes activities of accumulator were significantly enhanced by SNB6. Consequently, SNB6 promoted Cd uptake and biomass of accumulator, thus enhancing the Cd phytoextraction. The maximum Cd extractions in root, stem and leaf reached to 289.47 mg/kg, 88.33 mg/kg and 59.38 mg/kg, respectively. Meanwhile, the total biomass of accumulator was increased by 9.68-45.99% in SNB6 treatment. These findings could be conducive to the understanding the mechanisms of PGPR on enhancing the Cd phytoextraction of accumulator.

Assessment of phytoremediation potential of native plant species naturally growing in a heavy metal-polluted saline-sodic soil

Many areas throughout the world, mainly arid and semi-arid regions, are simultaneously affected by salinity stress and heavy metal (HM) pollution. Phytoremediation of such environments needs suitable plants surviving under those combined stresses. In the present study, native species naturally growing under an extreme condition, around Qaleh-Zari copper mine located in the eastern part of Iran, with HM-contaminated saline-sodic soil, were identified to find suitable plant species for phytoremediation. For this purpose, the accumulation of HMs (Cu, Zn, Cd, and Pb) in the root and shoot (stem and leaf) of the plants and their surrounding soils was determined to find their main phytoremediation strategies: phytoextraction or phytostabilization. Seven native species surviving in such extreme condition were found, including Launaea arborescens (Batt.) Murb, Artemisia santolina Schrenk, Pulicaria gnaphalodes (Vent.) Boiss, Zygophyllum eurypterum Boiss. & Buhse, Peganum harmala L., Pteropyrum olivieri Jaub. & Spach, and Aerva javanica (Burm. f.) Juss. ex Schult. Evaluation of phytoremediation potential of the identified species based on the calculated HM bioconcentration in roots, HM translocation from roots to shoots, and HM accumulation in the shoots revealed that all of the species were metal phytostabilizers rather than hyperaccumulators. Therefore, these native species can be used for phytostabilization in the HM-contaminated saline soils to prevent HMs entering the uncontaminated areas and groundwater. Compared with the biennial low-biomass hyperaccumulators, some native species such as Z. eurypterum and A. javanica may have more economic value for phytoremediation because of a significant accumulation of HMs in their relatively higher biomass.

Cupriavidus basilensis strain r507, a toxic arsenic phytoextraction facilitator, potentiates the arsenic accumulation by Pteris vittata

As a toxic and carcinogenic metalloid, arsenic has posed serious threat to human health. Phytoremediation has emerged as a promising approach to circumvent this problem. Arsenic uptake by Pteris vittata is largely determined by arsenic speciation and mainly occurs via roots; thus, rhizospheric microbial activities may play a key role in arsenic accumulation. The aim of this study was to investigate the potential of arsenic resistant rhizobacteria to enhance arsenic phytoextraction. A total of 49 cultivable rhizobacteria were isolated from the arsenic hyperaccumulating fern, Pteris vittata, and subjected to an initial analysis to identify potentially useful traits for arsenic phytoextraction, such as arsenic resistance and the presence of aioA(aroA)-like (arsenite oxidase-like) gene. Isolated strain r507, named as Cupriavidus basilensis strain r507, was a selected candidate for its outstanding arsenic tolerance, rapid arsenite oxidation ability, and strong colonization to P. vittata. Strain r507 was used in co-cultivation trials with P. vittata in the field for six months. Results showed that the inoculation with strain r507 potentiated As accumulation of P. vittata up to 171%. Molecular analysis confirmed that the inoculation increased the abundance of aioA-like genes in the rhizosphere, which might have facilitated arsenite oxidation and absorption. The findings of this study suggested the feasibility of co-cultivating hyperaccumulators with facilitator bacteria for practical arsenic phytoremediation.

Insight into nitrogen and phosphorus enrichment on cadmium phytoextraction of hydroponically grown Salix matsudana Koidz cuttings

Cadmium (Cd) has already caused worldwide concern because of its high biotoxicity to human and plants. This study investigated how nitrogen (N) and phosphorus (P) enrichment alter the toxic morpho-physiological impacts of and accumulation of Cd in hydroponically grown Salix matsudana Koidz cuttings. Our results showed that Cd significantly depressed growth and induced a physiological response on S. matsudana cuttings, exhibiting by reduced biomass, decreased photosynthetic pigment concentrations, and increased soluble protein and peroxidase activity of shoots and roots. N and P enrichment alleviated the Cd toxic effects by increasing production of proline which prevented cuttings from damage by Cd-induced ROS, displaying with decreased malondialdehyde concentration, and stimulated overall Cd accumulation. Enrichment of N and P significantly decreased the upward Cd transfer, combing with enhanced root uptake (stimulated root activity) and retranslocation from stem, resulted in extensive Cd sequestration in S. matsudana roots. In both root and xylem, concentration of Cd is positively correlated with N and P. The improved phytoextraction potential by N and P enrichment was mainly via elevating Cd concentration in roots, probably by increased production of phytochelatins (e.g., proline) which form Cd chelates and help preventing damage from Cd-induced ROS. This study provides support for the application of S. matsudana in Cd phytoextraction even in eutrophic aquatic environments.

Accumulation of heavy metals in a macrophyte Phragmites australis: implications to phytoremediation in the Arabian Peninsula wadis

Heavy metal-polluted wetlands could be remediated by harvesting metal accumulating plants, i.e., using phytoextraction. We studied a macrophyte Phragmites australis and assessed its potential to be utilized in the phytoremediation of heavy metal-polluted wetlands, specifically in wadis in the Arabian Peninsula. We sampled six polluted wadi sites and measured Mn, Fe, Ni, Cu, Zn, Cd, and Pb concentrations in the roots, rhizomes, stems, and leaves of P. australis, as well as in sediment and water. We analyzed the correlations between different plant organs, water, and sediment, and calculated the accumulation and translocation of the metals to the plant organs. We found indications for the accumulation of Cd, Zn, and Pb into P. australis and somewhat contradictory indications for the accumulation of Cu. We suggest that P. australis is a good candidate to be utilized in the phytoremediation of heavy metal-polluted wadis in the Arabian Peninsula where the few wadis offer many valuable ecosystem services for urban citizens.

Inoculation with abscisic acid (ABA)-catabolizing bacteria can improve phytoextraction of heavy metal in contaminated soil

Promotion of plant capacity for accumulation of heavy metals (HMs) is one of the key strategies in enhancing phytoremediation in contaminated soils. Here we report that, Rhodococcus qingshengii, an abscisic acid (ABA)-catabolizing bacteria, clearly boosts levels of Cd, Zn, and Ni in wild-type Arabidopsis by 47, 24, and 30%, respectively, but no increase in Cu was noted, when compared with non-inoculated Arabidopsis plants in contaminated growth substrate. Furthermore, when compared with wild-type plants, R.qingshengii-induced increases in Cd, Zn, and Ni concentrations were more pronounced in abi1/hab1/abi2 (ABA-sensitive mutant) strains of Arabidopsis, whereas little effect was observed in snrk2.2/2.3 (ABA insensitive mutant). This demonstrates that metabolizing ABA might be indispensable for R. qingshengii to improve metal accumulation in plants. Bacterial inoculation significantly elevated the expression of Cd, Zn, and Ni-related transporters; whereas the transcript levels of Cu transporters remained unchanged. This result may be a reasonable explanation for why the uptake of Cd, Zn, and Ni in plants was stimulated by bacterial inoculation, while no effect was observed on Cu levels. From our results, we clearly demonstrate that R. qingshengii can increase the accumulation of Cd, Zn, and Ni in plants via an ABA-mediated HM transporters-associated mechanism. Metabolizing ABA in the plants by ABA-catabolizing bacterial inoculation might be an alternative strategy to improve phytoremediation efficiency in HMs contaminated soil.

Morpho-physiological traits, gaseous exchange attributes, and phytoremediation potential of jute (Corchorus capsularis L.) grown in different concentrations of copper-contaminated soil

Jute (Corchorus capsularis L.) is the most commonly used natural fiber as reinforcement in green composites and, due to its huge biomass, deep rooting system, and metal tolerance in stressed environments, it is an excellent candidate for the phytoremediation of different heavy metals. Therefore, the present study was carried out to examine the growth, antioxidant capacity, gaseous exchange attributes, and phytoremediation potential of C. capsularis grown at different concentrations of Cu (0, 100, 200, 300, and 400 mg kg^-1) in a glass house environment. The results illustrate that C. capsularis can tolerate Cu concentrations of up to 300 mg kg^-1 without significant decreases in growth or biomass, but further increases in Cu concentration (i.e., 400 mg kg^-1) lead to significant reductions in plant growth and biomass. The photosynthetic pigments and gaseous exchange attributes in the leaves of C. capsularis decreased as the Cu concentration in the soil increased. Furthermore, high concentrations of Cu in the soil caused lipid peroxidation by increasing the malondialdehyde content in the leaves. This implies that elevated Cu levels cause oxidative damage in C. capsularis. Antioxidants, such as superoxidase dismutase and peroxidase, come into play to scavenge the reactive oxygen species which are generated as a result of oxidative stress. In the present study, the concentrations of Cu in different parts of the plant (the roots, leaves, stem core, and fibers) were also investigated at four different stages of the life cycle of C. capsularis, i.e., 30, 60, 90, and 120 days after sowing (DAS). The results of this investigation reveal that, in the earlier stages of the growth, Cu was highly accumulated in the belowground parts of the plant while little was transported to the aboveground parts. Contrastingly, at a fully mature stage of the growth (120 DAS), it was observed that the majority of Cu was transported to the aboveground parts of the plant and very little accumulated in the belowground parts. The results also show a progressive increase in Cu uptake in response to increasing Cu concentrations in the soil, suggesting that C. capsularis is a potential bio-resource for the phytoremediation of Cu in Cu-contaminated soil.

Mercury resistance and bioremediation mediated by endophytic fungi

The present study proposes the use of endophytic fungi for mercury bioremediation in in vitro and host-associated systems. We examined mercury resistance in 32 strains of endophytic fungi grown in culture medium supplemented with toxic metal concentrations. The residual mercury concentrations were quantified after mycelial growth. Aspergillus sp. A31, Curvularia geniculata P1, Lindgomycetaceae P87, and Westerdykella sp. P71 were selected and further tested for mercury bioremediation and bioaccumulation in vitro, as well as for growth promotion of Aeschynomene fluminensis and Zea mays in the presence or absence of the metal. Aspergillus sp. A31, C. geniculata P1, Lindgomycetaceae P87 and Westerdykella sp. P71 removed up to 100% of mercury from the culture medium in a species-dependent manner and they promoted A. fluminensis and Z. mays growth in substrates containing mercury or not (Dunnett's test, p < 0.05). Lindgomycetaceae P87 and C. geniculata P1 are dark septate endophytic fungi that endophytically colonize root cells of their host plants. The increase of host biomass correlated with the reduction of soil mercury concentration due to the metal bioaccumulation in host tissues and its possible volatilization. The soil mercury concentration was decreased by 7.69% and 57.14% in A. fluminensis plants inoculated with Lindgomycetaceae P87 + Aspergillus sp. A31 and Lindgomycetaceae P87, respectively (Dunnet's test, p < 0.05). The resistance mechanisms of mercury volatilization and bioaccumulation in plant tissues mediated by these endophytic fungi can contribute to bioremediation programs. The biochemical and genetic mechanisms involved in bioaccumulation and volatilization need to be elucidated in the future.

Optimization of NPK fertilization combined with phytoremediation of cadmium contaminated soil by orthogonal experiment

In the current experiment, influence of NPK composition on the Cd contaminated soil-plant (Solanum nigrum L.) system as well as the phytoremediation efficiency were comprehensively studied. The composition of NPK was optimized for a sustainable phytoremediation and simultaneous agronomic technique in Cd-contaminated soil by orthogonal (L₁₄) experiment, aimed to achieve plant productivity and maximum phytoremediation potential enhancement. Results showed that different treatments of NPK composition enhanced soil properties including saccharase, urease, catalase and acid phosphatase activities as compared to the control treatment, however, soil pH was slightly decreased by 3.64%~6.67% with different composition of NPK treatments. Plant biomass and Cd concentration in the aboveground part (stem and leaves) of S. nigrum were significantly (P < 0.05) enhanced by 14.19%~48.97% and 38.50%~127.15% as compared to control plants with the addition of NPK fertilizers having different composition. Meanwhile, with the application of NPK fertilizer root/shoot Cd ratio and translocation factor (TF) was significantly decreased, however, bioconcentration factor (BCF) was increased as compared to control. Additionally, different composition of NPK fertilizers significantly increased photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids) and soluble protein in comparison to control. The activities of antioxidant enzymes in S. nigrum including ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and glutathione reductase (GR) were increased, while malonaldehyde (MDA) and proline contents were decreased. Principal component analysis (PCA) showed that N₃P₂K₂ treatment had the highest comprehensive score amongst other studied treatments of NPK composition, owing to its optimal composition for the investigated soil-S. nigrum system. Moreover, it was found that optimal composition (N₃P₂K₂) of fertilizer resulted in increase of the plant resistance to Cd and the efficiency of phytoextraction. Therefore, it is suggested to all the small-holder famers and scientific community that precise composition of NPK fertilizer should be utilized according to soil properties, environmental conditions and plant requirements under Cd-stress condition in order to achieve maximum biomass, Cd uptake efficiency as well phytoremediation potential in moderately Cd contaminated soil.

Copper-induced oxidative stress, initiation of antioxidants and phytoremediation potential of flax (Linum usitatissimum L.) seedlings grown under the mixing of two different soils of China

Flax (Linum usitatissimum L.), one of the oldest cultivated crops, continues to be widely grown for oil, fiber and food. Furthermore, the plants show a metal tolerance dependent on species so is ideal for research. Present study was conducted to find out the influence of copper (Cu) toxicity on plant biomass, growth, chlorophyll content, malondialdehyde (MDA) contents, proline production, antioxidative enzymes and metal up taken by L. usitatissimum from the soil grown under mixing of Cu-contaminated soil with natural soil by 0:1 (control), 1:0, 1:1, 1:2 and 1:4. Results revealed that, high concentration of Cu in the soil affected plant growth and development by reducing plant height, plant diameter and plant fresh and dry biomass and chlorophyll contents in the leaves compared with the control. Furthermore, Cu in excess causes generation of reactive oxygen species (ROS) such as superoxide radical (O^-) and hydroxyl radicals (OH), which is manifested by high malondialdehyde (MDA) and proline contents also. The increasing activities of superoxidase dismutase (SOD) and peroxidase (POD) in the roots and leaves of L. usitatissimum are involved in the scavenging of ROS. Results also showed that L. usitatissimum also has capability to revoke large amount of Cu from the contaminated soil. As Cu concentration in the soil increases, the final uptake of Cu concentration by L. usitatissimum increases. Furthermore, the soil chemical parameters (pH, electrical conductivity and cation exchange capacity) were increasing to highest levels as the ratio of Cu concentration to the natural soil increases. Thus, Cu-contaminated soil is amended with the addition of natural soil significantly reduced plant growth and biomass, while L. usitatissimum is able to revoke large amount of Cu from the soil and could be grown as flaxseed and a potential candidate for phytoremediation of Cu.

Urban soil phytomanagement for Zn and Cd in situ removal, greening, and Zn-rich biomass production taking care of snail exposure

The phytoextraction potential of Arabidopsis halleri (L.) O'Kane & Al Shehbaz and Salix viminalis L. to partially remove Zn and Cd in soil was investigated. In an urban field site, a very short rotation coppice of willows was implemented, and growth parameters were monitored for 3 years. A. halleri was cultivated in the same site with or without fertilizer to improve biomass yield and/or Zn and Cd aerial part concentrations. Effects of harvest and co-cultivation on these two parameters were measured. To determine if willows and A. halleri leaves were risky in case of consumption by a herbivorous invertebrate like the landsnail Cantareus aspersus, metal concentrations of snails fed with Zn- and Cd-enriched and low enriched leaves were compared. Willows and A. halleri grew well on the metal-contaminated soil (1.7 and 616 mg kg^-1 Cd and Zn, respectively). The A. halleri Zn foliar concentration reached the Zn hyperaccumulation threshold (> 10,000 mg kg^-1 DW) in the presence of NPK fertilizer and although the soil was alkaline (pH > 8.2). Cd concentration increased with harvest and fertilizer. Cd and Zn foliar concentrations of willows were far above baseline values. Laboratory snails exposure revealed that willow leaves ingestion caused a moderate increase of Cd, Pb, and Zn bioaccumulation in snails compared to the one caused by A. halleri ingestion. The soil and plant metal concentrations were reflected by field snail biomonitoring. This study confirmed the interest of selecting A. halleri and willows to partially remove Zn and Cd in the soil and emphasized their potential usefulness in greening urban contaminated area and producing raw materials for green chemistry while paying attention to the environmental pollutant transfer.

Accumulation and distribution of cadmium and lead in 28 oilseed rape cultivars grown in a contaminated field

Heavy metal pollution in soils has become an important concern for human health. Therefore, it is vital to develop suitable remediation strategies for contaminated soils. Oilseed rape tolerates high concentrations of heavy metals and is a promising candidate for the phytoextraction of cadmium (Cd) and lead (Pb) from metal-contaminated soils. A field experiment was conducted to evaluate 28 oilseed rape cultivars including Brassica napus L. and Brassica juncea L. for their ability to accumulate Cd and Pb. These cultivars were grown in a field co-contaminated with Cd (0.78 mg kg^-1) and Pb (330 mg kg^-1). The results showed that concentrations in shoots ranged from 1.22 to 3.01 mg kg^-1 for Cd and from 10.8 to 29.5 mg kg^-1 for Pb. Cadmium and Pb accumulations in shoots could reach 83.4 and 799 μg plant^-1, respectively. The majority of translocation factors (TFs) for Cd (> 1.0) were higher than for Pb (≤ 1.0). However, concentrations of Cd and Pb in seeds were much lower, in the range of 0.04 to 0.21 mg kg^-1 and 0.04 to 0.51 mg kg^-1, respectively. The seed yields of oilseed rape varied from 1238 to 2904 kg ha^-1, with a mean value of 2289 kg ha^-1. Among the cultivars, three (OS-9, OS-12, and OS-15) were selected as Cd and Pb potential accumulators, with Cd accumulation in shoots being 2.74-3.70 times higher and Pb accumulation in shoots being 3.37-5.23 times higher as compared with the lowest accumulating cultivar. These selected cultivars (B. napus) have application potential for phytoextraction of Cd and Pb from polluted soils without stopping agricultural activities and accompanying food safety issues.

Phytoremediation of Heavy Metal-Contaminated Sites: Eco-environmental Concerns, Field Studies, Sustainability Issues, and Future Prospects

Environmental contamination due to heavy metals (HMs) is of serious ecotoxicological concern worldwide because of their increasing use at industries. Due to non-biodegradable and persistent nature, HMs cause serious soil/water pollution and severe health hazards in living beings upon exposure. HMs can be genotoxic, carcinogenic, mutagenic, and teratogenic in nature even at low concentration. They may also act as endocrine disruptors and induce developmental as well as neurological disorders, and thus, their removal from our natural environment is crucial for the rehabilitation of contaminated sites. To cope with HM pollution, phytoremediation has emerged as a low-cost and eco-sustainable solution to conventional physicochemical cleanup methods that require high capital investment and labor alter soil properties and disturb soil microflora. Phytoremediation is a green technology wherein plants and associated microbes are used to remediate HM-contaminated sites to safeguard the environment and protect public health. Hence, in view of the above, the present paper aims to examine the feasibility of phytoremediation as a sustainable remediation technology for the management of metal-contaminated sites. Therefore, this paper provides an in-depth review on both the conventional and novel phytoremediation approaches; evaluates their efficacy to remove toxic metals from our natural environment; explores current scientific progresses, field experiences, and sustainability issues; and revises world over trends in phytoremediation research for its wider recognition and public acceptance as a sustainable remediation technology for the management of contaminated sites in the twenty-first century.