Phytostabilization potential of Jatropha curcas L. in polymetallic acid mine tailings

Sustainable use of composted sewage sludge: Metal(loid) leaching behaviour and material suitability for application on degraded soils

Composted sewage sludge was investigated as a promising material for the reclamation or remediation of degraded sites. Using sewage sludge as soil amendment provides environmental benefits and risks while supporting circularity and waste minimisation. This study aims to comprehensively assess the suitability of locally available low-cost sludge treatment for sustainable and environmentally safe topsoil disposal in a brownfield area affected by coal mining. A nine-month composting was conducted before field application to the soil environment. The objectives were to assess: (i) composting time-dependent and pH-dependent metal(loid) leachability from composted sludges, (ii) the effect of sludges on metal(loid) leachability from soil over the first six months, and (iii) metal(loid) plant uptake during the first vegetation season as well as the bioaccumulation and translocation factors. The set of standardised leaching experiments confirmed the positive effect of compost maturity, i.e. despite some fluctuations over time, metal(loid) availability from the final composts was very low. Some metals showed unusual pH-dependent behaviour with the highest leachability at pH 8 due to excessive release of dissolved organic matter from the not-yet-stabilised matrix. Ecotoxicity testing confirmed the safety of the final composts for further soil application. The sludge-amended plots displayed similar metal(loid) leaching and pH evolution in time compared to the control biomass-amended plot. However, plant species (Artemisia vulgaris L.) that formed the natural vegetation cover of the experimental plots showed cumulative metal(loid) uptake. Cadmium and zinc were identified as the critical metals possibly related to the applied sludges, yielding high bioaccumulation and translocation factors. Yet, the quality of the compost feedstock, heterogeneity, and background values of the brownfield site need to be considered. Nevertheless, soil respiration indicated no adverse effects on soil health six months after sludge application. Overall, the composted material demonstrated potential suitability for remediation application in the studied area.

Native desert plants have the potential for phytoremediation of phytotoxic metals in urban cities: implications for cities sustainability in arid environments

Arid regions can benefit from using native desert plants, which require minimal freshwater and can aid in remediating soil phytotoxic metals (PTMs) from traffic emissions. In this study, we assessed the ability of three native desert plants-Pennisetum divisum, Tetraena qatarensis, and Brassica tournefortii-to accumulate phytotoxic metals (PTMs) in their different plant organs, including leaves, stems, and roots/rhizomes. The PTMs were analyzed in soil and plant samples collected from Dubai, United Arab Emirates (UAE). The results indicated significantly higher levels of PTMs on the soil surface than the subsurface layer. Brassica exhibited the highest concentrations of Fe and Zn, measuring 566.7 and 262.8 mg kg-1, respectively, while Tetraena accumulated the highest concentration of Sr (1676.9 mg kg-1) in their stems. In contrast, Pennisetum recorded the lowest concentration of Sr (21.0 mg kg-1), while Tetraena exhibited the lowest concentrations of Fe and Zn (22.5 and 30.1 mg kg-1) in their leaves. The roots of Pennisetum, Brassica, and Tetraena demonstrated the potential to accumulate Zn from the soil, with concentration factors (CF) of 1.75, 1.09, and 1.09, respectively. Moreover, Brassica exhibited the highest CF for Sr, measuring 2.34. Pennisetum, however, could not translocate PTMs from its rhizomes to other plant organs, as indicated by a translocation factor (TF) of 1. In contrast, Brassica effectively translocated the studied PTMs from its roots to the stem and leaves (except for Sr in the leaves). Furthermore, Pennisetum exclusively absorbed Zn from the soil into its leaves and stems, with an enrichment factor (EF) greater than 1. Brassica showed the ability to uptake the studied PTMs in its stem and leaves (except for Fe), while Tetraena primarily absorbed Sr and Zn into its stems. Based on the CF and TF results, Pennisetum appears to be a suitable species for phytostabilization of both Fe and Zn, while Brassica is well-suited for Sr and Zn polluted soils. Tetraena shows potential for Zn phytoremediation. These findings suggest that these plants are suitable for PTMs phytoextraction. Furthermore, based on the EF results, these plants can efficiently sequester PTMs.

Conceptualization of the comprehensive phyto-radiotoxicity incurred by radiocesium and strategies to expunge the metal using biotechnological and phytoremediative approaches

Agricultural pollution with 137Cs is an ecological threat due to its sustained half-life and radioactivity. Release of radiocesium isotopes after major nuclear power plant accidents like the Fukushima Dai-ichi and the Chernobyl nuclear power plant disasters have severely affected the surrounding growth of agricultural crops and vegetables cultivated across extensive areas. Even years after the nuclear accidents, biosafety in these agricultural fields is still questionable. Due to similarity in charge and ionic radius between radiocesium and K+, the radionuclides are promiscuously uptaken via K+ channels expressed in plants. Bioaccumulation of radiocesium reportedly promotes physiological and anatomical anomalies in crops due to radiation and also affects the rhizospheric architecture. Due to radiation hazard, the ecological balance and quality are compromised and ingestion of such contaminated food results in irreversible health hazards. Recently, strategies like exogenous supplementation of K+ or genetic engineering of K+ channels were able to reduce radiocesium bioaccumulation in plants taking the advantage of competition between radiocesium and K+ translocation. Furthermore, bioremediation strategies like phycoremediation, mycoremediation, phytoremediation and rhizofiltration have also showed promising results for removing radiocesium from polluted sites. It has been proposed that these eco-friendly ways can be adopted to de-pollute the contaminated sites prior to subsequent cultivation of crops and vegetables. Hence it is essential to: 1) understand the basic radiotoxic effects of radiocesium on agricultural crops and surrounding vegetation and, 2) design sustainable ameliorative strategies to promote radiocesium tolerance for ensuring food and social security of the affected population.

Phytoremediation of toxic heavy metals in polluted soils and water of Dargai District Malakand Khyber Pakhtunkhwa, Pakistan

Abstract The contamination of natural resources with heavy metals released from steel mills is the primary cause of soil and water pollution in the Dargai Malakand, located on the northern side of Pakistan. Therefore, the present study was aimed to determine the level of heavy metals in soil and water samples of this area. The wild plant growing (nine native plants: Pteris vittata, Populus nigra, Eucalyptus camaldulensis, Persicaria maculosa, Arundo donax, Xanthium strumarium, Verbascum thapsus, Ricinus communis and Parthenium hysterophorus) there were then tested for their phytoremediation capabilities which is an environmentally friendly, generally utilized, and low-cost approach to eliminate heavy metals from polluted soils and water. Soil, water, and effluent samples were taken from the contaminated sites of seven steel mills in Dargai District Malakand and subjected to heavy metals analysis. Based on bioconcentration factor (BCF) and translocation factor (TF) calculated, The highest BCF for zinc was recorded for Pteris vittata roots (3.93), while the lowest value was observed for Verbascum thapsus leaves (0.306). Pteris vittata root showed the highest BCF for iron (1.618), while Ricinus communis leaves showed the lowest (0.023). The highest BCF value for chromium was highest for Populus nigra roots (0.717), while the lowest value was recorded for Persicaria maculosa leaves (0.031). For the selected metals; Fe, Zn and Cr the highest TF were recorded for Pteris vittata (0.988), Verbascum thapsus (0.944) and Xanthium strumairum (0.968) respectively. Therefore, it is recommended that these plants should be grown near to steel mills to reclaim heavy metals from industrial effluent, polluted soil as well as from polluted water.

Compost, plants and endophytes versus metal contamination: choice of a restoration strategy steers the microbiome in polymetallic mine waste

Finding solutions for the remediation and restoration of abandoned mining areas is of great environmental importance as they pose a risk to ecosystem health. In this study, our aim was to determine how remediation strategies with (i) compost amendment, (ii) planting a metal-tolerant grass Bouteloua curtipendula, and (iii) its inoculation with beneficial endophytes influenced the microbiome of metal-contaminated tailings originating from the abandoned Blue Nose Mine, SE Arizona, near Patagonia (USA). We conducted an indoor microcosm experiment followed by a metataxonomic analysis of the mine tailings, compost, and root samples. Our results showed that each remediation strategy promoted a distinct pattern of microbial community structure in the mine tailings, which correlated with changes in their chemical properties. The combination of compost amendment and endophyte inoculation led to the highest prokaryotic diversity and total nitrogen and organic carbon, but also induced shifts in microbial community structure that significantly correlated with an enhanced potential for mobilization of Cu and Sb. Our findings show that soil health metrics (total nitrogen, organic carbon and pH) improved, and microbial community changed, due to organic matter input and endophyte inoculation, which enhanced metal leaching from the mine waste and potentially increased environmental risks posed by Cu and Sb. We further emphasize that because the initial choice of remediation strategy can significantly impact trace element mobility via modulation of both soil chemistry and microbial communities, site specific, bench-scale preliminary tests, as reported here, can help determine the potential risk of a chosen strategy.

Phytomanagement of iron mine soil by Ricinus communis L. and garden soil

Soil pollution and heavy metals (HMs) contamination caused by the improper management of mine soil is a major concern for the environment and the associated living beings. The present study was carried out for 90 days with iron mine soil (MS) amendment with different ratios of garden soil (GS) (0, 25, 50, 75 and 100%). The study investigates the growth performance, metal tolerance, metal accumulation (Fe, Pb, Cu and Ni) ability of R. communis L. and the improvement in soil health after harvesting the plants. The MS had a high level of Fe, Pb, Cu and Ni (2017.17, 65.34, 34.02 and 69.15 mg kg^-1 respectively) with significantly low pH, water holding capacity (WHC), organic carbon (OC), organic matter (OM) and nutrients along with microbial biomass carbon and nitrogen (Cmic and Nmic). The study found that there are higher growth rates and biomass for plants grown in all GS treatments compared to 100% MS. The relative water content (%), tolerance index and carotenoid content exhibit upwards trends with the increasing growing period. The HMs accumulation in shoot and root was found highest for Fe (1354.44 and 3989.61 mg kg^-1) and Pb (31.88 and 34.83 mg kg^-1). The metal extraction ratio for all studied metals was found maximum in 50 and 75% GS treatment plants. Further, the HMs removal percentage was recorded between 14.82 and 54.86%. The soil physicochemical and biological properties like electrical conductivity, total nitrogen, Cmic and Nmic increased up to 50% and the OC and OM improved manyfold in 100% MS. Based on the findings, it is concluded that R. communis L. has the potential to easily cultivate in mine abandoned soil and tolerate high concentrations of HMs.

Carbon nanoparticles improve the effect of compost and arbuscular mycorrhizal fungi in drought-stressed corn cultivation

Drought is an important threat worldwide, therefore, it is vital to create workable solutions to mitigate the negative effects of drought stress. To this end, we investigated the interactive effect of compost (Comp), arbuscular mycorrhizal fungi (AMF) and carbon nanoparticles (CNPs) on maize plant crops under drought stress. The combined treatments were more effective at increasing soil fertility and promoting the growth of maize plants under both control and drought stress conditions by 20.1% and 39.4%, respectively. The interactions between treatments, especially the effects of Comp-AMF-CNPs mixture, reduce the activity of photorespiration induced H₂O₂ production that consequently reduces drought-related oxidative damages (lipid peroxidation and protein oxidation). Plants treated with Comp-AMF or Comp-AMF-CNPs showed an increase in their antioxidant defense system. Comp-AMF-CNPs increased enzyme activities by 50.3%, 30.1%, and 71% for ascorbate peroxidase (APX), dehydro-ASC reductase (DHAR), and monodehydro-ASC reductase (MDHAR), respectively. Comp-AMF-CNPs also induced the highest increase in anthocyanins (69.5%) compared to the control treatment. This increase was explained by increased anthocyanin percussor, by 37% and 13% under control and drought, respectively. While the increases in biosynthetic key enzymes, phenylalanine aminolayse (PAL) and chalcone synthase (CHS) were 77% and 5% under control and 69% and 89% under drought, respectively. This work advanced our understanding on how Comp-AMF-CNPs improve growth, physiology, and biochemistry of maize plants under drought stress conditions. Overall, this study suggests the effectiveness of Comp-AMF-CNPs as a promising approach to enhance the growth of maize plants in dry areas.

Visible Light-Driven Advanced Oxidation Processes to Remove Emerging Contaminants from Water and Wastewater: a Review

The scientific data review shows that advanced oxidation processes based on the hydroxyl or sulfate radicals are of great interest among the currently conventional water and wastewater treatment methods. Different advanced treatment processes such as photocatalysis, Fenton's reagent, ozonation, and persulfate-based processes were investigated to degrade contaminants of emerging concern (CECs) such as pesticides, personal care products, pharmaceuticals, disinfectants, dyes, and estrogenic substances. This article presents a general overview of visible light-driven advanced oxidation processes for the removal of chlorfenvinphos (organophosphorus insecticide), methylene blue (azo dye), and diclofenac (non-steroidal anti-inflammatory drug). The following visible light-driven treatment methods were reviewed: photocatalysis, sulfate radical oxidation, and photoelectrocatalysis. Visible light, among other sources of energy, is a renewable energy source and an excellent substitute for ultraviolet radiation used in advanced oxidation processes. It creates a high application potential for solar-assisted advanced oxidation processes in water and wastewater technology. Despite numerous publications of advanced oxidation processes (AOPs), more extensive research is needed to investigate the mechanisms of contaminant degradation in the presence of visible light. Therefore, this paper provides an important source of information on the degradation mechanism of emerging contaminants. An important aspect in the work is the analysis of process parameters affecting the degradation process. The initial concentration of CECs, pH, reaction time, and catalyst dosage are discussed and analyzed. Based on a comprehensive survey of previous studies, opportunities for applications of AOPs are presented, highlighting the need for further efforts to address dominant barriers to knowledge acquisition.

Alleviation of Cadmium and Nickel Toxicity and Phyto-Stimulation of Tomato Plant L. by Endophytic Micrococcus luteus and Enterobacter cloacae

Cadmium (Cd) and nickel (Ni) are two of the most toxic metals, wreaking havoc on human health and agricultural output. Furthermore, high levels of Cd and Ni in the soil environment, particularly in the root zone, may slow plant development, resulting in lower plant biomass. On the other hand, endophytic bacteria offer great promise for reducing Cd and Ni. Moreover, they boost plants’ resistance to heavy metal stress. Different bacterium strains were isolated from tomato roots. These isolates were identified as Micrococcus luteus and Enterobacter cloacae using 16SrDNA and were utilized to investigate their involvement in mitigating the detrimental effects of heavy metal stress. The two bacterial strains can solubilize phosphorus and create phytohormones as well as siderophores. Therefore, the objective of this study was to see how endophytic bacteria (Micrococcus luteus and Enterobactercloacae) affected the mitigation of stress from Cd and Ni in tomato plants grown in 50 μM Cd or Ni-contaminated soil. According to the findings, Cd and Ni considerably lowered growth, biomass, chlorophyll (Chl) content, and photosynthetic properties. Furthermore, the content of proline, phenol, malondialdehyde (MDA), H₂O₂, OH, O₂, the antioxidant defense system, and heavy metal (HM) contents were significantly raised under HM-stress conditions. However, endophytic bacteria greatly improved the resistance of tomato plants to HM stress by boosting enzymatic antioxidant defenses (i.e., catalase, peroxidase, superoxide dismutase, glutathione reductase, ascorbate peroxidase, lipoxygenase activity, and nitrate reductase), antioxidant, non-enzymatic defenses, and osmolyte substances such as proline, mineral content, and specific regulatory defense genes. Moreover, the plants treated had a higher value for bioconcentration factor (BCF) and translocation factor (TF) due to more extensive loss of Cd and Ni content from the soil. To summarize, the promotion of endophytic bacterium-induced HM resistance in tomato plants is essentially dependent on the influence of endophytic bacteria on antioxidant capacity and osmoregulation.

Effect of the Co-Application of Eucalyptus Wood Biochar and Chemical Fertilizer for the Remediation of Multimetal (Cr, Zn, Ni, and Co) Contaminated Soil

Contamination of soil with heavy metals is a worldwide problem, which causes heavy metals to release into the environment. Remediation of such contaminated soil is essential to protect the environment. The aims of this study are: first, to compare the effect of biochar and the joint application of biochar with fertilizer for the phytoremediation of heavy metals-contaminated soil using Acacia auriculiformis; second, to study the effect of the application rate of biochar in improving the physicochemical properties of the soil. The soil samples were collected from an active coal mine dump and assessed for their physicochemical properties and heavy metals toxicity. Initial results indicated that the soil has poor physicochemical properties and was contaminated with the presence of heavy metals such as Zn, Ni, Cu, Cr, and Co. Later, the heavy metals-contaminated soil was mixed with the 400 and 600 °C biochar, as well as the respective biochar–fertilizer combination in varying mixing ratios from 0.5 to 5% (w/w) and subjected to a pot-culture study. The results showed that the application of both varieties of biochar in combination with fertilizer substantially improved the physicochemical properties and reduced the heavy metals toxicity in the soil. The biochar and fertilizer joint application also substantially improved the soil physiochemical properties by increasing the application rate of both varieties of biochar from 0.5 to 5%. The soil fertility index (SFI) of the biochar and biochar–fertilizer amended soil increased by 49.46 and 52.22%, respectively. The plant’s physiological analysis results indicated a substantial increase in the plant’s shoot and root biomass through the application of biochar and biochar–fertilizer compared to the control. On the other hand, it significantly reduced the heavy metals accumulation and, hence, the secretion of proline and glutathione hormones in the plant cells. Therefore, it can be concluded that the joint application of biochar with the application rate varying between 2.5 to 5% (w/w) with the fertilizer significantly improved the physicochemical properties of the soil and reduced the heavy metals toxicity compared to the controlled study.

Micro- and Macroelements Content of Plants Used for Landfill Leachate Treatment Based on Phragmites australis and Ceratophyllum demersum

One of the key problems associated with the functioning of landfills is the generation of leachate. In order to reduce their negative impact on the environment, various treatment technologies are applied. Among them, solutions based on the use of phytotechnology deserve special attention. The aim of this study was to evaluate the impact of landfill leachate on the content of micro- and macroelements in plant material. The research was carried out in four municipal waste landfills located in Poland. Emergent macrophytes (P. australis) and submergent macrophytes (C. demersum) were used in this research. The migration and distribution of pollutants reaching the roots and shoots of P. australis from water solutions were also studied. The concentrations of heavy metals in the studied plants were low in all analysed cases. Higher metal contents could often be observed in roots rather than in shoots, but these differences were insignificant. The chemical composition of the studied plant samples was primarily related to the source of origin of the treated leachate (landfill), as clearly demonstrated by cluster analysis. In the conducted studies, no important differences were noted in the accumulation of the studied components between submergent plants (C. demersum) and emergent macrophytes (P. australis).

Stabilization of metals in sludge-amended soil using red mud and its effects on yield and oil quality of Brassica juncea cultivar Kranti

Prolonged application of sewage-sludge may cause excessive accumulation of metal(oid)s in soil, leading to phytotoxic effects. Spread of contaminants in soil can probably be hindered by using an effective metal(oid) stabilizer. Pot experiment in open field conditions was conducted for five months to evaluate the metal(oid) (Al, Cu, Zn, Cd and Cr) stabilization potential of red mud (RM) in sludge-amended soil and its effects on growth, yield, oil quality parameters and metal(oid) accumulations in Brassica juncea cultivar Kranti. The test plant was grown at different RM concentrations (0, 5, 10 and 15% w/w) in sludge-amended soil (soil/sludge: 2:1 w/w). As the total and phytoavailable metal(oid) concentrations in sludge were high, its application increased their concentrations in soil compared to the control (no RM and sludge). Increasing RM concentrations in sludge-amended soil effectively stabilized Cd followed by Cr, Cu, Zn and Al, leading to their reduced contents in plants coupled with enhanced growth performance and yield. Maximum plant (root and shoot) biomass (14.9%) and seed yield (40.4%) were found in 10% RM treatment, whereas oil content showed substantial increase with increasing RM treatments in sludge-amended soil. Mustard oil showed low rancidification, high long-chain fatty acids, saturated and polyunsaturated (ω-3 and ω-6) fatty acids within FAO ranges for edible oils under varying RM treatments compared to sludge-amended soil. Furthermore, high oleic and low erucic acid contents in mustard oil indicated a better oil quality under different RM treatments. Metal(oid) contents in seeds under different red mud treatments were within FAO/WHO limits for consumption. Thus, RM applications preferably 5 and 10% (w/w) in sludge-amended soil might be effective in stabilization of metal(oid)s using B. juncea cultivar Kranti coupled with better yield, improved oil quality and metal(oid)s within limits for human consumption.

Growth, biochemical, and antioxidant response of pot marigold (Calendula officinalis L.) grown in fly ash amended soil

The present study was carried out to determine the impact of FA application on growth performance, biochemical parameters, and antioxidant defense activity of Calendula officinalis. The results revealed that under a low dose of FA (40%) amended soil, the plant growth performance and metal tolerance index (MTI) were increased compared to control plants and further decreased with increased FA application (60%, 80%, and 100% FA). In addition, the incorporation of 40% FA in soil not only improved the physicochemical properties of soil but also increased the biochemical parameters in the Calendula plant, however, these parameters declined under high FA applications. It was also observed that antioxidant enzyme activity (SOD, CAT, POD, and APX) in leaves of Calendula officinalis increased at high FA application (100% FA) to combat heavy metal stress from FA. The overall study suggests that 40% FA amended soil is the best suitable dose for growing Calendula officinalis and can be considered as metal tolerant species for phytoremediation of 40% FA amended soil.Novelty statement: Fly ash (FA) management is a major problem nowadays. The present study was carried out for FA utilization and to determine the impact of FA amended soil on growth performance, antioxidant properties, and biochemical attributes of Calendula officinalis. This is a sustainable approach in which waste (FA) utilization was done simultaneously with the enhancement in response of the medicinally potent Calendula species. The novelty of this study also suggests that Calendula has phytoremediation potential for remediation of heavy metal polluted soil. Further, the relationship between the growth, biochemical parameters, and antioxidant defense mechanism of Calendula grown on FA amended soil was studied which has not been studied so far. It was found that Calendula is a hyperaccumulator that can adapt to heavy metal stress from FA due to its ability to mitigate oxidative damage. Statistical analysis (ANOVA, Duncan's multiple range test, and PCA) was done for the results obtained using SPSS (11.5) and Origin 8 Pro software.

Transfer of Potentially Toxic Elements in the Soil-Plant System in Magnesite Mining and Processing Areas

Mining activities, ore concentrations, and transport processes generate large amounts of pollutants, including hazardous elements, which are released into the environment. This work presents the results of experimental research aimed at evaluating the environmental risks of soil and plant contamination in two magnesite mining and processing areas in the Slovak Republic, and assesses the phytoremediation potential of dominant plant species. Eleven potentially toxic elements in the soil were investigated using X-ray fluorescence spectrometry (Cd, Pb, Cr, Zn, Cu, As, Ni, Mn, Mg, Fe) and atomic absorption spectrometry (Hg). In plants, potentially toxic elements were investigated using inductively coupled plasma mass spectrometry (Cu, As, Cd, Pb) and inductively coupled plasma atomic emission spectrometry (Cr, Zn, Mn, Mg). Selected soil parameters (pH, redox potential, and soil organic matter) were also investigated. Soil contamination was evaluated using environmental indices (geoaccumulation index—Igeo, enrichment factor—EF, contamination factor—Cf, degree of contamination—Cd). The phytoremediation potential of plants was evaluated using the bioconcentration factor (BCF) and the translocation factor (TF). The soil reaction in the studied areas indicated a strong alkalization of the soil. The soils in Jelšava-Lubeník were significantly contaminated with Cr, As, Mn, and Mg. The most significant enrichment based on the average values of EF was found to be in the order of Cd > Mg > Zn > Cu > As > Cr > Ni > Pb > Fe > Hg > Mn. The observed values of Cf and Cd indicated a high degree of soil contamination. In Košice, the soils were found to be significantly contaminated with Cr, Mn, Mg, and Ni. The most significant enrichment was found in the order of Cd > Mn > Ni > Pb > Zn > Mg > Cu > As > Fe > Cr > Hg. Very high Cf was found for Pb and Cr. The results of correlation and hierarchical cluster analyses suggest a similar origin of pollutants caused by significant anthropogenic interventions due to magnesite mining and processing. The investigated dominant plant species, Phragmites australis, Agrostis stolonifera, Elytrigia repens, and Taraxacum officinale are able to accumulate high concentrations of the monitored potentially toxic elements without more serious load or damage. The results of BCF and TF confirmed that P. australis and T. officinale appeared to be suitable accumulators in the phytoextraction process. In the case of E. repens and A. stolonifera it was confirmed that they accumulate and immobilize high concentrations of potentially toxic elements, especially in the roots, establishing the suitability of their use in phytostabilization processes.

Phytostabilization of arsenic and associated physio-anatomical changes in Acanthus ilicifolius L

The carcinogenic attribute of arsenic (As) has turned the world to focus more on the decontamination and declining the present level of As from the environment especially from the soil and water bodies. Phytoremediation has achieved a status of sustainable and eco-friendly approach of decontaminating pollutants, and in the present study, an attempt has been made to reveal the potential of As remediation by a halophyte plant, Acanthus ilicifolius L. Special attention has given to analyse the morphological, physiological and anatomical modulations in A. ilicifolius, developed in response to altering concentrations of Na₂AsO₄.7H₂O (0, 70, 80 and 90 μM). Growth of A. ilicifolius under As treatments were diminished as assessed from the reduction in leaf area, root length, dry matter accumulation, and tissue water status. However, the plants exhibited a comparatively higher tolerance index (44%) even when grown in the higher concentrations of As (90 μM). Arsenic treatment induced reduction in the photochemical activities as revealed by the pigment content, chlorophyll stability index (CSI) and Chlorophyll a fluorescence parameter. Interestingly, the thickness and diameter of the xylem walls in the leaf as well as root tissues of As treated samples increased upon increasing the As concentration. The adaptive strategies exhibited by A. ilicifolius towards varying concentrations of As is the result of coordinated responses of morpho-physiological and anatomical attributes, which make the plant a promising candidate for As remediation, especially in wetlands.

A critical review of phytoremediation for acid mine drainage-impacted environments

Acid mine drainage (AMD), a waste product of mining activities containing sulfates, iron and heavy metals, causes severe environmental degradation and pose risks to human health and sustainable development. Areas impacted by AMD are lacking remediation techniques that holistically address the ecologic, social, and economic needs of affected communities, for which phytoremediation is a promising solution. This review article introduces AMD and AMD-impacted environments and critically discusses phytomanagement, phytoprotection, and phytorestoration approaches towards AMD-impacted environments. Continued research and application of such approaches will help optimize resource and revenue-generating potentials, address biodiversity loss and carbon storage concerns of climate change, and promote sustainable agricultural management. With a focus on energy crops, phytomining critical elements, carbon storage, co-cropping, allelopathy, and ecosystem restoration, this review examines phytoremediation research that addresses positive economic and environmental opportunities for AMD-impacted environments.

Gamma radiation-induced synthesis of a novel chitosan/silver/Mn-Mg ferrite nanocomposite and its impact on cadmium accumulation and translocation in brassica plant growth

Herein, a novel chitosan/silver/Mn_0.5Mg_0.5Fe₂O₄ (Cs/Ag/MnMgFe₂O₄) nanocomposite was synthesized with gamma irradiation assistant. The prepared Cs/Ag/MnMgFe₂O₄ nanocomposite was characterized via EDX, XRD, SEM, UV-vis spectroscopy. To evaluate the effects of soak low and high-dose nanocomposite on physiological parameters, photosynthetic pigments, antioxidant and non-antioxidant enzymes of cabbage under Cd stress, a factorial experiment was conducted based on CRD with five replications. The Cd stress decreased the morphological characteristics and photosynthetic pigments while increasing cabbage's antioxidant and non-antioxidant enzymes. The application of low and high-dose of nanocomposite decreased Cd content in leaves by about 42.86%, 60.48%, and the root by approximately 18.72%, 28.72%, respectively, and translocation factors and tolerance index, H₂O₂, O₂, and malondialdehyde. In contrast, the application of high of the nanocomposite increased the values of SPAD chlorophyll about 27.50%, stomatal conductance about 87.18%, net photosynthetic rate about 44.90%, intercellular CO₂ concentration about 32.00%, and transpiration rate about 85.20%, as compared to Cd stress. Furthermore, the application of low and high-dose Cs/Ag/MnMgFe₂O₄ nanocomposite enhances the antioxidant and non-antioxidant enzymes of the cabbage plant compared to Cd stress. Generally, it was conducted that Cs/Ag/MnMgFe₂O₄ nanocomposite can be used as a proper tool for increasing cabbage plants under Cd stress.

Phytoremediation as an effective tool to handle emerging contaminants

Phytoremediation is a process which effectively uses plants as a tool to remove, detoxify or immobilize contaminants. It has been an eco-friendly and cost-effective technique to clean contaminated environments. The contaminants from various sources have caused an irreversible damage to all the biotic factors in the biosphere. Bioremediation has become an indispensable strategy in reclaiming or rehabilitating the environment that was damaged by the contaminants. The process of bioremediation has been extensively used for the past few decades to neutralize toxic contaminants, but the results have not been satisfactory due to the lack of cost-effectiveness, production of byproducts that are toxic and requirement of large landscape. Phytoremediation helps in treating chemical pollutants on two broad categories namely, emerging organic pollutants (EOPs) and emerging inorganic pollutants (EIOPs) under in situ conditions. The EOPs are produced from pharmaceutical, chemical and synthetic polymer industries, which have potential to pollute water and soil environments. Similarly, EIOPs are generated during mining operations, transportations and industries involved in urban development. Among the EIOPs, it has been noticed that there is pollution due to heavy metals, radioactive waste production and electronic waste in urban centers. Moreover, in recent times phytoremediation has been recognized as a feasible method to treat biological contaminants. Since remediation of soil and water is very important to preserve natural habitats and ecosystems, it is necessary to devise new strategies in using plants as a tool for remediation. In this review, we focus on recent advancements in phytoremediation strategies that could be utilized to mitigate the adverse effects of emerging contaminants without affecting the environment.

Response of Prosopis farcta to gradually increased soil copper and cadmium levels based on an integrated investigation

The impact of gradually increased soil levels of copper (Cu) and cadmium (Cd) on the medicinal plant, Prosopis farcta, irrigated with metal-enriched water was determined. Plants were treated with 2.54, 5.08, 10.16, and 20.32 µg mL^-1 for Cu²⁺ and 6.13, 12.26, 24.52, and 49 µg mL^-1 for Cd²⁺. The rate of phytoremediation was measured by bioconcentration factor (BCF) and the relative bioconcentration factor (RBCF). The movement of metal ions from roots to shoots was calculated as the Translocation Factor (TF). The exposure of plants to Cd or Cu decreased plant growth and increased Cd and Cu concentration in their shoots and roots. The weight of both shoots and roots decreased linearly with the increase of Cu and Cd contents in roots and shoots. Cd was more toxic than Cu as expected. The water content of shoots and roots decreased linearly as heavy metal levels increased. Prosopis farcta can take up Cu and Cd in both Cu- and Cd-contaminated soils but was more capable for transporting Cd from roots to shoots rather than Cu although more Cu is taken up by roots. Prosopis farcta is a natural accumulator of Cu and Cd and can be used in phytoremediation.CONCISE NOVEL ASPECTS OF THIS STUDYThis is the first report to show that the medicinal plant Prosopis farcta is an accumulator for Cu and Cd.This was determined by gradual addition of the metals to the soil via irrigation by heavy metal-polluted water which can provide an opportunity for the plant to develop a metal-resistance mechanism.Choosing suitable plant species for heavy metal accumulation is a critical step for successful phytoremediation of heavy metal pollutants.CORE IDEASProsopis farcta is of interest as a medicinal plant.P. farcta can take up Cu and Cd in both Cu- and Cd-contaminated soils.P. farcta transports more Cd from roots to shoots but more Cu is taken up.

Phytoremediation of Toxic Metals: A Sustainable Green Solution for Clean Environment

Contamination of aquatic ecosystems by various sources has become a major worry all over the world. Pollutants can enter the human body through the food chain from aquatic and soil habitats. These pollutants can cause various chronic diseases in humans and mortality if they collect in the body over an extended period. Although the phytoremediation technique cannot completely remove harmful materials, it is an environmentally benign, cost-effective, and natural process that has no negative effects on the environment. The main types of phytoremediation, their mechanisms, and strategies to raise the remediation rate and the use of genetically altered plants, phytoremediation plant prospects, economics, and usable plants are reviewed in this review. Several factors influence the phytoremediation process, including types of contaminants, pollutant characteristics, and plant species selection, climate considerations, flooding and aging, the effect of salt, soil parameters, and redox potential. Phytoremediation’s environmental and economic efficiency, use, and relevance are depicted in our work. Multiple recent breakthroughs in phytoremediation technologies are also mentioned in this review.

A comparative appraisal of three important oil yielding plants for their biodiesel potential

In the present scenario, alternative energy sources are required to achieve the future economic prosperity where shortage of fossil fuels will be a limiting factor and hamper the global economic growth. Therefore, interest in biofuel is increasing continuously. The best way of sustainable development is fossil fuel supplementation with biodiesel to reduce the fossil fuel demand. Biodiesel is a clean burning, ester-based, oxygenated fuel derived from natural and renewable sources. Till now, majority of the people have worked on the biodiesel derived from edible oil. Instead of using edible oil, non-edible oil needs to be explored as feedstock for biofuel because half of the world's population is unable to afford the food oil as feedstock for fuel production. Looking at the significance of biodiesel and the resources of biofuel, in this paper, a comparative exhaustive study has been reported with for three important plants, namely Jatropha curcas, Pongemia pinnata and Balanites aegyptiaca. These plants were selected based on their biodiesel potential, availability, cultivation practices and general information available. The present study involves scientometric publications, comparison of fatty acid composition and biodiesel parameters. We have also compared climatic conditions for the growth of the plants, economic feasibility of biodiesel production and other ecological services. The study paves a way for sustainable solution to policy makers and foresters looking for selection of plant species as bioenergy resource.

The Salicornia europaea potential for phytoremediation of heavy metals in the soils under different times of wastewater irrigation in northwestern Iran

The use of wastewater for irrigation usually leads to the buildup of potentially toxic elements (PTEs) in soils. The objective of this study was to assess the capacity of Salicornia europaea L. to uptake heavy metal when irrigated with wastewater at the vegetative, flowering, and reproductive stages of S. europaea for 2 and 4 days (in each stage) in the coastal saline area of Lake Urmia. The concentrations of heavy metals were detected in irrigated water, soil, and plant samples, while transfer factor (TF), bioconcentration factor (BCF), and bioaccumulation factor (BAF) were calculated. The results revealed that metal concentrations in the wastewater were above the permissible limits. The wastewater irrigation caused higher shoot biomass despite the high uptake of PTEs. Levels of Fe and Cu in plants were higher when irrigated with wastewater at the reproductive stage as compared to flowering and vegetative stages. The TF of wastewater-irrigated plants was higher at the flowering stage. TF of different metals at the flowering stage were in order of Zn > Pb > Ni > Cd > Cu, while the BCF increased in the order Cd > Cu > Zn > Ni > Pb. The BAF of the investigated PTEs at the flowering stage increased in the order Cd > Pb > Ni > Zn > Cu. In conclusion, higher Pb and Zn in the shoot indicated that the plant exhibited the phytoextraction mechanism, while Salicornia used a phytostabilization mechanism for roots-Cu, Ni, and Cd.

Effect of organosilicone and mineral silicon fertilizers on chemical forms of cadmium and lead in soil and their accumulation in rice

Cadmium (Cd) and lead (Pb) pollution in soil and their accumulation in edible parts possess a worldwide eco-environmental and health risk, especially in developing countries. Recently, organosilicone fertilizer (OSiF) has been reported to reduce uptake of heavy metals, but the effectiveness has not been verified and its associated mechanisms are not fully understood. This work investigated whether and how OSiF and mineral silicon fertilizer (MSiF) affect mitigation of Cd and Pb stress in rice (Oryza sativa). Both soil incubation and pot experiments were conducted to assess the effect of OSiF and MSiF on bioavailability of Cd and Pb in soil and their accumulation in rice. Additionally, a hydroponic experiment was conducted to study whether Si in rice can alleviate Cd stress. We found that both Si fertilizers could increase soil pH, induce the transformation of the acid soluble and reducible fractions of Cd and Pb to the oxidizable and residual fractions in soil, decreasing their bioavailability and the uptake of Cd and Pb in rice. However, Si in OSiF was not phyto-available, but Si in MSiF was available since available Si in soil and Si in plant increased in MSiF treatments but not in OSiF treatments. Meanwhile, rice grain yields significantly increased and the Cd and Pb content of brown rice reduced in MSiF treatments but not in OSiF treatments. In addition, Si was found to be able to alleviate Cd stress by improving the antioxidant capacity of rice. These results suggested that the decreased Cd and Pb accumulation in OSiF-treated rice was due to Cd and Pb immobilization in soil simply with pH increase, but in MSiF-treated rice Cd and Pb immobilization in soil (ex planta effect) and Si-conferred inhibitory effect of root-to-shoot Cd and Pb transport (in planta effect) contribute to the lower accumulation in rice.

Abandoned Mine Lands Reclamation by Plant Remediation Technologies

Abandoned mine lands (AMLs), which are considered some of the most dangerous anthropogenic activities in the world, are a source of hazards relating to potentially toxic elements (PTEs). Traditional reclamation techniques, which are expensive, time-consuming and not well accepted by the general public, cannot be used on a large scale. However, plant-based techniques have gained acceptance as an environmentally friendly alternative over the last 20 years. Plants can be used in AMLs for PTE phytoextraction, phytostabilization, and phytovolatilization. We reviewed these phytoremediation techniques, paying particular attention to the selection of appropriate plants in each case. In order to assess the suitability of plants for phytoremediation purposes, the accumulation capacity and tolerance mechanisms of PTEs was described. We also compiled a collection of interesting actual examples of AML phytoremediation. On-site studies have shown positive results in terms of soil quality improvement, reduced PTE bioavailability, and increased biodiversity. However, phytoremediation strategies need to better characterize potential plant candidates in order to improve PTE extraction and to reduce the negative impact on AMLs.

Cadmium, Chromium, and Lead Uptake Associated Health Risk Assessment of Alternanthera sessilis: A Commonly Consumed Green Leafy Vegetable

Green leafy vegetables are becoming increasingly popular in the developing countries due to their high nutritious value, common availability, and low cost. However, no studies have assessed the health risks associated with consumption of fresh green leafy vegetables. The present study assessed Cd, Cr, and Pb associated health risks in a commonly consumed green leafy vegetable in developing countries, Alternanthera sessilis. The Cd, Cr, and Pb concentrations in roots, leaves, and root zone soil of Alternanthera sessilis harvested from organic and non-organic cultivations were measured. The results indicated that Cd, Cr, and Pb concentrations in roots and leaves of Alternanthera sessilis exceeded the WHO/FAO safe limits for human consumption. Further, bioconcentration factor, soil to root, and root to leaf translocation factors indicated a potential of hyperaccumulating Cd in roots and leaves of Alternanthera sessilis. However, the target hazard quotients for Cd, Cr, and Pb were less than 1 indicating negligible health hazard associated with long time consumption of Alternanthera sessilis.

Phytostabilization of Phosphate Mine Wastes Used as a Store-and-Release Cover to Control Acid Mine Drainage in a Semiarid Climate

The abandoned Kettara pyrrhotite mine, located near Marrakech, Morocco, is an acid mine drainage (AMD) producer site. A store-and-release cover system made of phosphate wastes was built to prevent water infiltration and the formation of AMD. This cover system should be vegetated with appropriate plants to ensure its long-term sustainability and allow its reintegration in the surrounding ecosystem. Several indigenous plant species were studied. The choice of plant species was based mainly on their tolerance to trace elements contained in the phosphate wastes, and their low capacity to translocate these metals to their aboveground parts in order to limit the risk of pollutants transfer along the food chain. The main metals and metalloids (As, Cd, Co, Cu, Pb, Zn, Ni, Cr) are determined in 13 dominant plants naturally colonizing the store-and-release cover and their rhizospheric soils. The results showed that the phosphate cover contained high concentrations of Cr (138.04 mg/kg), Cu (119.86 mg/kg) and Cd (10.67 mg/kg) exceeding the regulatory thresholds values (Cr > 100 mg/kg, Cu > 100 mg/kg, Cd > 3 mg/kg). The studied plants revealed no hyper-accumulation of metals and metalloids, and lower concentrations in shoots than in roots. Six species (Plantago afra, Festuca ovina, Aizoon hispanicum, Herniaria cinerea, Echium plantagineum and Asphodelus tenuifolius) have bioconcentration factors greater than 1, and weak translocation factors, identifying them as appropriate candidates for phytostabilization of the phosphate cover.

Invasive Weed Asystasia gangetica as a Potential Biomonitor and a Phytoremediator of Potentially Toxic Metals: A Case Study in Peninsular Malaysia

The invasive weed Asystasia gangetica was investigated for its potential as a biomonitor and as a phytoremediator of potentially toxic metals (PTMs) (Cd, Cu, Ni, Pb, and Zn) in Peninsular Malaysia owing to its ecological resistance towards unfavourable environments. The biomonitoring potential of PTMs was determined based on the correlation analysis of the metals in the different parts of the plant (leaves, stems, and roots) and its habitat topsoils. In the roots, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 2.18, 9.22 to 139, 0.63 to 5.47, 2.43 to 10.5, and 50.7 to 300, respectively. In the leaves, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 1.16, 7.94 to 20.2, 0.03 to 6.13, 2.10 to 21.8, and 18.8 to 160, respectively. In the stems, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 1.25, 5.57 to 11.8, 0.23 to 3.69, 0.01 to 7.79, and 26.4 to 246, respectively. On the other hand, the phytoremediation potential of the five metals was estimated based on the bioconcentration factor (BCF) and the translocation factor (TF) values. Correlation analysis revealed that the roots and stems could be used as biomonitors of Cu, the stems as biomonitors of Ni, the roots and leaves as biomonitors of Pb, and all three parts of the plant as biomonitors of Zn. According to the BCF values, in the topsoil, the “easily, freely, leachable, or exchangeable” geochemical fractions of the five metals could be more easily transferred to the roots, leaves, and stems when compared with total concentrations. Based on the TF values of Cd, Ni, and Pb, the metal transfer to the stems (or leaves) from the roots was efficient (>1.0) at most sampling sites. The results of BCF and TF showed that A. gangetica was a good phytoextractor for Cd and Ni, and a good phytostabilizer for Cu, Pb, and Zn. Therefore, A. gangetica is a good candidate as a biomonitor and a phytoremediator of Ni, Pb, and Zn for sustainable contaminant remediation subject to suitable field management strategies.

Use of seed priming to improve Cd accumulation and tolerance in Silene sendtneri, novel Cd hyper-accumulator

Changes in the environment as a result of industrialisation and urbanisation impact negatively on plant growth and crop production. Cadmium (Cd) is one of the most dangerous metals that enters the food chain, with toxic effects on plants and human health. This study evaluated the potential of Silene sendtneri as a novel hyperaccumulator and the role of seed priming in tolerance and accumulation rate of Cd. The effect of different priming agents on germination performance, root growth, seedling development, metal uptake and accumulation, antioxidant defences including enzymatic and non-enzymatic antioxidants has been assessed. Seed priming using silicic acid, proline alone or in combination with salicylic acid- enhanced germination, seedling development, and root growth under Cd stress. The same priming treatments induced an increase of water content in shoots and roots when plants were exposed to Cd. The enzymatic antioxidant response was specific for the priming agent used. An increase in ferulic acid and rutin in shoots was related to the increase of Cd concentration in the medium. The concentration of malic and oxalic acid increased significantly in shoots of plants grown on high Cd concentrations compared to low Cd concentrations. Silene sendtneri can accumulate significant levels of Cd with enhanced accumulation rate and tolerance when seeds are primed. The best results are obtained by seed priming using 1% silicic acid, proline and salicylic acid.

Phytostabilization of coal mine overburden waste, exploiting the phytoremedial efficacy of lemongrass under varying level of cow dung manure

A pot study was performed to assess the phytoremedial potential of Cymbopogon citratus (D.C.) Staf. for reclamation of coal mine overburden dump wastes, emphasizing the outcome of amendment practices using cow dung manure (CM) and garden soil mixtures on the revegetation of over-burden wastes (OB). Wastes amendment with cow dung manure and garden soil resulted in a significant increase in soil health and nutrient status along with an increment in the phytoavailability of Zn and Cu which are usually considered as micronutrients, essential for plant growth. A significant increment in the total biomass of lemongrass by 38.6% under CM20 (OB: CM 80:20) was observed along with improved growth parameters under amended treatments as compared to OB (100% waste). Furthermore, the proportionate increases in the assimilative rate, water use efficiency, and chlorophyll fluorescence have been observed with the manure application rates. Lemongrass emerged out to be an efficient metal-tolerant herb species owing to its high metal-tolerance index (>100%). Additionally, lemongrass efficiently phytostablized Pb and Ni in the roots. Based on the strong plant performances, the present study highly encourages the cultivation of lemongrass in coal mining dumpsites for phytostabilization coupled with cow-dung manure application (20% w/w).

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.

Assessment of Cu, Pb and Zn content in selected species of grasses and in the soil of the roadside embankment

It was assumed in the study that heavy metals occurring in soils and the air accumulate in grasses constituting the main species used in the turfing of soil in road verges and embankments along traffic routes and in other parts of urbanized areas. The aim of the present study was to assess the bioaccumulation of Cu, Pb, and Zn in three selected lawn cultivars of five grass species and in the soil of the roadside green belt in terms of soil properties and heavy metal uptake by plants in the aspect of determining their usefulness in protecting the soils from contamination caused by motor vehicle traffic. Samples of the plant material and soil were collected for chemical analysis in the autumn of 2018 (October) on the embankment along National Road No. 17 between Piaski and Łopiennik (Poland), where 15 lawn cultivars of five grass species had been sown 2 years earlier. During the study, Cu, Pb, and Zn levels were determined in the aboveground biomass of the grasses under study and in the soil beneath these grasses (the 0-20 cm layer). All the grass species under study can thus be regarded as accumulators of Cu and Zn because the levels of these elements in the aboveground biomass of the grasses were higher than in the soil beneath these grasses. The present study demonstrates that the grasses can accumulate a large amount of Cu and Zn from soils and transfer it to the aboveground biomass. Tested species of grasses are not a higher bioaccumulators for Pb. The best grass species for the sowing of roadsides embankment, with the highest BCF values for the studied metals, is Lolium perenne (Taya variety).

Physiological response of metal tolerance and detoxification in castor (Ricinus communis L.) under fly ash-amended soil

Castor (Ricinus communis L.) is a metal tolerant plants and its ability to survive in highly polluted sites as well as its capacity for metal accumulation. There are very few reports on their physiological mechanism of metal tolerance and detoxification under fly ash. Therefore, an in-situ experiment was designed to study its biomass accumulation, photosynthetic response and antioxidative metabolism under different levels of fly ash amendments. Significant (P < 0.05) increase in plant biomass and metal tolerance index was observed in R. communis under 50 % fly ash in soil amendments in comparison to the control plants. In addition, photosynthetic activity was not significantly altered under fly ash amended soil in comparison to the garden soil, but these responses/activities were remarkable lowered under bare fly ash. The induction of antioxidant enzymes was also observed in different tissue over control under fly ash treatments. The bioconcentration factor (BCF) of Al, Fe, Zn, Mn, Cu and Cr in R. communis were recorded greater than one under fly ash (50%) with soil amendments. Therefore, it concluded that it can be used for phytoremediation of fly ash and fly ash (50%) with soil amendments enhanced phytoremediation ability.

Phytoremediation—From Environment Cleaning to Energy Generation—Current Status and Future Perspectives

Phytoremediation is a technology based on the use of green plants to remove, relocate, deactivate, or destroy harmful environmental pollutants such as heavy metals, radionuclides, hydrocarbons, and pharmaceuticals. Under the general term of phytoremediation, several processes with distinctively different mechanisms of action are hidden. In this paper, the most popular modes of phytoremediation are described and discussed. A broad but concise review of available literature research with respect to the dominant process mechanism is provided. Moreover, methods of plant biomass utilization after harvesting, with particular regard to possibilities of “bio-ore” processing for metal recovery, or using energy crops as a valuable source for bio-energy production (bio-gas, bio-ethanol, bio-oil) are analyzed. Additionally, obstacles hindering the commercialization of phytoremediation are presented and discussed together with an indication of future research trends.

Phytoremediation potential of naturally growing weed plants grown on fly ash-amended soil for restoration of fly ash deposit

Sida acuta Burm. f. and Cassia tora (L.) Roxb were identified as dominant plant species in fly ash deposit of NALCO, Koraput, India in our earlier study. However, little information is available on their physiological response to metal stress under fly ash amended soil. A pot experiment was designed with fly ash amended soil to assess its growth, photosynthesis, antioxidant defense along with metal accumulation. Addition of fly ash (50%) in soil amendments not only improved the soil physico-chemical characteristics but also increased the plant biomass. The studied plants were found to be a potential metal tolerant as metal tolerance index was more than 100% under fly ash amended soil. Leaf photosynthetic rate, chlorophyll content and photosystem II activity were not significantly changed under low level of fly ash amended soil (50%) compared to the garden soil. The induction of some antioxidative enzymes such as superoxide dismutase, ascorbate peroxidase, Guaiacol peroxidase and catalase in studied plants under elevated fly ash indicates metal tolerance ability of this plant to oxidative stress. Based on the bioaccumulation factor (BCF) and transfer factor (TF), these plants can be used for the remediation of Mn, Cu, Zn, Fe and Cr from fly ash.

Effects of EDTA, citric acid, and tartaric acid application on growth, phytoremediation potential, and antioxidant response of Calendula officinalis L. in a cadmium-spiked calcareous soil

The improved efficiency of cadmium (Cd) phytoextraction potential of Calendula officinalis L. was evaluated in Cd-spiked calcareous soil, using various chelating agents. In a greenhouse study, three chelating agents, including EDTA, citric acid (CA), and tartaric acid (TA), were applied to Cd-spiked soils (50 and 100 mg kg^-1) under C. officinalis L. cultivation. According to the results, C. officinalis grew normally without any toxicity signs at various Cd levels of the soil; however, with increasing the Cd levels, the plant dry weight biomass decreased, and activities of antioxidant enzymes (AOEs) increased. The application of CA and TA in Cd-spiked soils improved the physiologic traits of plants and mitigated the Cd stress since the activities of AOEs decreased. Oppositely, due to increasing the Cd excessive permeability to the root of the plant, EDTA application diminished the physiologic traits and increased the activities of AOEs. The results also showed that all the chelators, especially EDTA, markedly increased the Cd mobility factor (from 58.80% to 65.20-89.60%) in Cd-spiked soils. The bioconcentration factor (BCF = 1.3-2.90) and translocation factor (TF = 1.28-1.58) of Cd, which were >1 in all treated and untreated plant samples, as well as the accumulated Cd >100 mg kg^-1, demonstrated that C. officinalis is a Cd-hyperaccumulator plant which could remediate Cd by the phytoextraction process. Regarding the biodegradation of CA, as well as the increased TF efficiency of Cd and plant biomass of CA treatments (by decreasing oxidative stress), compared to EDTA and TA treatments, it is recommended that CA be used as a superior chelating agent to enhance the efficiency of Cd phytoremediation in C. officinalis.

Implications of spatial heterogeneity of tailing material and time scale of vegetation growth processes for the design of phytostabilisation

Phytostabilisation projects for tailing dams depend on processes occurring at spatial scales of 10⁶ m² and at decadal time scales. Most experiments supporting the design and monitoring of such projects have much smaller spatial and time scales. Usually, they are only designed for one single scale. Here, we report the results of three coupled experiments performed at pot, lysimeter and field plot scales using six sampling periodstimes from 3 to 20 months. The work explicitly accounts for the sampling times when evaluating the effects of amendments on the performance of plants grown in tailing substrates. Two treatments with potentially complementary roles were applied: zeolites to decrease availability of Cd, Cu, Pb and Zn and green fertilizer to increase the availability of nutrients. Zeolites have a positive influence on plant development, especially in the early stages. Analyses of the pooled datasets for all sampling times revealed the possibility of predicting plant physiological variables, such as protein concentrations, pigments and oxidative stress enzyme activities, as a function of the factors extracted by principal component analysis from the metal concentrations in plants, phosphorus concentrations in plants, and sampling times. Two potentially general methodological rules were extracted: account for the spatial geochemical variability of tailings, and cover the broadest possible range of time scales by experiments. The proposed experimental methodology can be of general use for the design of tailing dam remediation technologies with improvements involving the set of measured variables and sampling frequency and by carefully relating the costs to the institutional aspects of tailing dam management.

Phytoremediation: Environmentally sustainable way for reclamation of heavy metal polluted soils

Soil contamination with toxic metals is a widespread environmental issue resulting from global industrialization within the past few years. Therefore, decontamination of heavy metal contaminated soils is very important to reduce the associated risks and for maintenance of environmental health and ecological restoration. Conventional techniques for reclamation of such soils are expensive and environmental non-friendly. Phytoremediation is an emerging technology implementing green plants to clean up the environment from contaminants and has been considered as a cost-effective and non-invasive alternative to the conventional remediation approaches. There are different types of phytoremediation including, phytostabilization, phytostimulation, phytotransformation, phytofiltration and phytoextraction, the latter being most extensively acknowledged for remediation of soils contaminated with toxic heavy metals. Recent literature is gathered to critically review the sources, hazardous effects of toxic heavy metals and environmentally sustainable phytoremediation technique for heavy metal polluted soils to offer widespread applicability of this green technology. Different strategies to enhance the bioavailability of heavy metals in the soil are also discussed shortly. It can be concluded that phytoremediation of heavy metal contaminated soils is a reliable tool and necessary for making the land resource accessible for crop production.

Status, progress and challenges of phytoremediation - An African scenario

Environmental pollution occasioned by artisanal activities and technical failures at exploration sites has affected mostly oil producing and other mineral resources mining regions in developed and developing nations. As conventional techniques of remediation seem to be progressively unreliable and inefficient, contaminated land management experts have adopted a plant-based technology described as 'phytoremediation' for effective detoxification and removal of contaminants in substrate environmental media (soil and sediment). This technique, has gained public acceptance because of its aesthetic, eco-friendly, solar energy driven and low cost attributes. With complexity of environmental pollution in Africa, identification of appropriate remediation approach that deliver net environmental benefit and economic profit to the society is vital, while also focusing on the exploitation of plants genetic tools for more clarity on phyto tolerance, uptake and translocation of pollutants. In this article, we reviewed the status, progress and challenges of phytoremediation in selected African countries (South Africa, Nigeria, Tanzania, Zambia, Egypt and Ghana), the ecological impact of the pollutants, phytoremediation strategies and the possible plants of choice. Besides highlighting the support roles played by soil fauna and flora, the fate of harvested biomass/dieback and its future prospects are also discussed. We further explored the factors challenging phytoremediation progress in Africa, amidst its promising potentials and applicability for sustainable ecosystem management paradigm.

Growth and physiological response of lemongrass (Cymbopogon citratus (D.C.) Stapf.) under different levels of fly ash-amended soil

Revegetation with metal tolerant plants for management of fly ash deposits is an important environmental perspective nowadays. Growth performance, photosynthesis, and antioxidant defense of lemongrass (Cymbopogon citratus (D.C.) Stapf.) were evaluated under various combination of fly ash amended with garden soil in order to assess its fly ash tolerance potential. Under low level of fly ash (25%) amended soil, the plant growth parameters such as shoot, root, and total plant biomass as well as metal tolerance index were increased compared to the control plants grown on garden soil, followed by decline under higher concentration of fly ash (50%, 75% and 100%). In addition, leaf photosynthetic rate, stomatal conductance, and photosystem (PS) II activity were not significantly changed under low level of fly ash (25%) amended soil compared to the garden soil but these parameters were significantly decreased further with increase of fly ash concentrations. Furthermore, increase of activities of some antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and guaiacol peroxidase over control were noticed in lemongrass under all fly ash treatments. Taken together, the study suggests that lemongrass can be used for phytoremediation of fly ash at 25% amended soil.

Potential of Cassia alata L. Coupled with Biochar for Heavy Metal Stabilization in Multi-Metal Mine Tailings

To explore the effect of different biochars on Cassia alata L. growth and heavy metal immobilization in multi-metal mine tailings, a 100-day pot experiment was conducted. Three biochars derived from Hibiscus cannabinus core (HB), sewage sludge (SB) and chicken manure (MB), were added to mine tailings at rates of 0.4%, 1% and 3% (w/w). The results showed that the root biomass, shoot biomass, plant height and root length were 1.2-2.8, 1.7-3.2, 1-1.5 and 1.6-3.3 times of those in the control group, respectively. Pb, Zn, Cu, Cd and As contents in the shoot decreased by 63.9-89.5%, 46.9-66.0%, 32.7-62.4%, 40.4-76.4% and 54.9-77.5%, respectively. The biochar significantly increased the pH and decreased the mild acid-soluble Pb and Cu concentrations in the mine tailings. Specifically, SB immobilized Pb and Cu better than MB and HB did, although it did not immobilize As, Zn or Cd. Meanwhile, more attention should be paid to the potential As release as the biochar application rate increases. In conclusion, Cassia alata L. coupled with 3% of SB could be an effective measure for restoring multi-metal mine tailings. This study herein provided a promising ecological restoration technique for future practice of heavy metal stabilization in mine tailings.

Lead, zinc, and cadmium uptake, accumulation, and phytoremediation by plants growing around Tang-e Douzan lead-zinc mine, Iran

In the current study, soils of Tang-e Douzan mine, located in Isfahan, Iran, were collected and analyzed for soluble, exchangeable, and total amounts of Pb, Zn, Cd, Ca, and Mg. The maximum Pb, Zn, Cd, Ca, and Mg concentrations in soils were 2500, 1100, 59, 43,800, and 1320 mg/kg for total metals, 86, 83, 6.3, 4650, and 48 mg/kg for their exchangeable fractions, and 59, 3.7, 0.53, 430, and 6.4 mg/kg for their soluble fractions, respectively. All specimens collected, including 69 plant species, were analyzed for Pb, Zn, and Cd. Moreover, their phytoremediation potential was investigated by calculating bioconcentration factors (BCF), translocation factors (TF), and extraction factors (EF) for each heavy metal. Analysis of the leaves for heavy metals showed no metal hyperaccumulation. The highest shoot concentrations of Pb (298 mg/kg) and Zn (740 mg/kg) were found in Roemeria hybrida subsp. dodecandra and Cd (43 mg/kg) in Chenopodium foliosum. Plants having BCFs and TFs > 1 are capable of phytoextraction. Among the analyzed species, four had both TFs and BCFs > 1 for Zn, 13 for Cd, and none for Pb. R. hybrida, Bromus squarrosus, Descurainia sophia, and Poa bulbosa seem to be the best choices for phytoextraction of Zn. Aegilops columnaris, Allium ampeloprasum subsp. iranicum, B. squarrosus, and Cousinia piptocephala are the best choices for phytoextraction of Cd. Plants with BCF > 1 and TF < 1, including Cerastium dichotomum and Muscari neglectum for Pb, Ceratocephala falcata, M. neglectum, Ornithogalum orthophyllum, and Ranunculus arvensis for Zn and C. falcata, M. neglectum, O. orthophyllum, and R. hybrida subsp. dodecandra for Cd, are proposed to be the most efficient species for metal phytostabilization.

Floristic surveys of hydrocarbon-polluted sites in some Cameroonian cities (Central Africa)

Soils pollution with hydrocarbons is on the increase, especially in developing countries like Cameroon. Identifying plant species capable of growing on hydrocarbon-polluted soils remains an essential step in phytoremediation, a low cost, solar energy driven clean up technique in which living green plants are used. Here, we report floristic surveys conducted in 4 cities of Cameroon to identify plants with phytoremediation capacities. A total of 13 hydrocarbon-polluted sites were surveyed in each city using the quadrat method. Unpolluted sites served as the control. 106 species belonging to 76 genera and 30 families were identified on hydrocarbon-polluted sites. Plant diversity was shown to be higher (166 species contained in 125 genera and 50 families) in the control sites. Poaceae, Cyperaceae, Asteraceae and Amaranthaceae families have a higher taxonomic richness on polluted sites (16, 15, 10 and 8 taxa respectively). Shannon diversity index of the hydrocarbon-polluted sites (1.6 to 2.7 bits/ind.) were significantly lower than the control sites (2.7 to 3.2 bit/ind.). Based on a relative frequency > 10% and abundance > 7%, our results show that more than 15 plant species could be tested in preliminary trials to determine their phytoremediation/cleaning-up capacities on hydrocarbon-polluted soils in the tropics.

Modeling of phytoextraction efficiency of microbially stimulated Salix dasyclados L. in the soils with different speciation of heavy metals

Bioaugmentation of soils with selected microorganisms during phytoextraction can be the key solution for successful bioremediation and should be accurately calculated for different physicochemical soil properties and heavy metal availability to guarantee the universality of this method. Equally important is the development of an accurate prediction tool to manage phytoremediation process. The main objective of this study was to evaluate the role of three metallotolerant siderophore-producing Streptomyces sp. B1-B3 strains in the phytoremediation of heavy metals with the use of S. dasyclados L. growing in four metalliferrous soils as well as modeling the efficiency of this process based on physicochemical and microbiological properties of the soils using artificial neural network (ANN) analysis. The bacterial inoculation of plants significantly stimulated plant biomass and reduced oxidative stress. Moreover, the bacteria affected the speciation of heavy metals and finally their mobility, thereby enhancing the uptake and bioaccumulation of Zn, Cd, and Pb in the biomass. The best capacity for phytoextraction was noted for strain B1, which had the highest siderophore secretion ability. Finally, ANN model permitted to predict efficiency of phytoextraction based on both the physicochemical properties of the soils and the activity of the soil microbiota with high precision.

Screening for Autochthonous Phytoextractors in a Heavy Metal Contaminated Coal Mining Area

In order to protect public health and crops from soil heavy metal (HM) contamination at a coal mining area in Henan, central China, HM pollution investigation and screening of autochthonous HM phytoextractors were conducted. The concentrations of cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn) in surface soils exceeded the corresponding local background values and the China National Standard (CNS). The maximum potential ecological risk (RI) was 627.30, indicating very high ecological risk. The monomial risk of Cd contributed the most to the RI, varying from 85.48% to 96.48%. The plant community structure in the study area was simple, and was composed of 24 families, 37 genera and 40 species. B. pilosa, A. roxburghiana, A. argyi, A. hispidus were found to be the most dominant species at considerable risk sites. Based on the comprehensive analysis of Cd concentration, bioconcentration factor, translocation factor and adaptability factor, B. pilosa and A. argyi had potential for phytoextraction at considerable risk sites. A. roxburghiana had potential for Cd phytoextraction at moderately risk sites and A. hispidus seemed suitable for phytostabilization. The results could contribute to the phytoremediation of the similar sites.

Phytoremediation of metals using lemongrass (Cymbopogon citratus (D.C.) Stapf.) grown under different levels of red mud in soil amended with biowastes

Due to hostile condition of red mud (RM), its utilization for vegetation is restricted. Therefore, RM with biowastes as soil amendment may offer suitable combination to support plant growth with reduced risk of metal toxicity. To evaluate the effects of RM on soil properties, plant growth performance, and metal accumulation in lemongrass, a study was conducted using different RM concentrations (0, 5, 10, and 15% w/w) in soil amended with biowastes [cow dung manure (CD) or sewage-sludge (SS)]. Application of RM in soil with biowastes improved organic matter and nutrient contents and caused reduction in phytoavailable metal contents. Total plant biomass was increased under all treatments, maximally at 5% RM in soil with SS (91.4%) and CD (51.7%) compared to that in control (no RM and biowastes). Lemongrass acted as a potential metal-tolerant plant as its metal tolerance index is >100%. Based on translocation and bioconcentration factors, lemongrass acted as a potential phytostabilizer of Fe, Mn, and Cu in roots and was found efficient in translocation of Al, Zn, Cd, Pb, Cr, As, and Ni from roots to shoot. The study suggests that 5% RM with biowastes preferably SS may be used to enhance phytoremediation potential of lemongrass.

Sediment washing by EDTA and its reclamation by sodium polyamidoamine-multi dithiocarbamate

Sodium polyamidoamine-multi dithiocarbamate (PAMAM-DTC) is a kind of heavy metals capturing agent, containing functional groups of dithiocarbamate that could strongly chelate heavy metals. In this paper, it was applied to precipitate heavy metal ions from meal-EDTA and reclaim EDTA during sediment washing process. The extracting performance of fresh EDTA was studied as a function of EDTA concentration, liquid/sediment (L/S), pH, and extraction time. Then the EDTA effluents were treated with PAMAM-DTC, Na2S and sodium diethyldithiocarbamate (DDTC) to compare their effectiveness on capturing metals from metal-EDTA complexes. Four divalent heavy metals were investigated (Pb, Cd, Cu, Zn). PAMAM-DTC shows much better performance. Pb, Cd and Cu could almost be precipitated completely by PAMAM-DTC under the dosage of 350 mg L^-1, while Zn could be only partly precipitated which may due to its failure in competition with the other three metal ions on chelation with PAMAM-DTC. The reclaimed EDTA was reused in three cycles of sediment washing, and the amount of heavy metals extracted just slightly decreased in each cycle.

Jatropha curcas and assisted phytoremediation of a mine tailing with biochar and a mycorrhizal fungus

Soil pollution is an important ecological problem worldwide. Phytoremediation is an environmental-friendly option for reducing metal pollution. A greenhouse experiment was conducted to determine the growth and physiological response, metal uptake, and the phytostabilization potential of a nontoxic Jatropha curcas L. genotype when grown in multimetal-polluted conditions. Plants were established on a mine residue (MR) amended or not amended with corn biochar (B) and inoculated or not inoculated with the mycorrhizal fungus Acaulospora sp. (arbuscular mycorrhizal fungus, AMF). J. curcas was highly capable of growing in an MR and showed no phytotoxic symptoms. After J. curcas growth (105 days), B produced high desorption of Cd and Pb from the MR; however, no increases in metal shoot concentrations were observed. Therefore, Jatropha may be useful for phytostabilization of metals in mine tailings. The use of B is recommended because improved MR chemical properties conduced to plant growth (cation-exchange capacity, organic matter content, essential nutrients, electrical conductivity, water-holding capacity) and plant growth development (higher biomass, nutritional and physiological performance). Inoculation with an AMF did not improve any plant growth or physiological plant characteristic. Only higher Zn shoot concentration was observed, but it was not phytotoxic. Future studies of B use and its long-term effect on MR remediation should be conducted under field conditions.