An overview of phytoremediation as a potentially promising technology for environmental pollution control

Phytoremediation is the use of plants for the removal of pollutants from contaminated soil or water. Phytoremediation is an environmentally friendly and cost-effective alternative to current remediation technologies. This review article outlines general aspects of phytoremediation, along with discussions about its advantages and limitations. It further reviews various phytoremediation processes in detail: phytoextraction, rhizofiltration, phytostabilization, phytodegradation, and phytovolatilization. Unlike previous review articles available in various journals, this paper presents a more comprehensive view of this issue, and deals with a much wider range of its applications to environmental pollution control. These include the treatment of wastewaters, removal of heavy metals and metalloids (e.g. lead and arsenic), phytoremediation of organic pollutants, such as 2,4,6-trinitrotoluene (TNT) and polychlorinated biphenyls (PCBs), and cleanup of soil and water contaminated with radionuclides, such as cesium (¹³⁷Cs) and strontium (⁹⁰Sr). This paper also describes recent developments of transgenic plants for improving phytoremediation. Along the way, the present status of phytoremediation research in Korea is briefly introduced. Finally, the article concludes with suggestions for future research.     

Expression of an Arabidopsis Ca/H antiporter CAX1 variant in petunia enhances cadmium tolerance and accumulation

Phytoremediation is a cost-effective and minimally invasive technology to cleanse soils contaminated with heavy metals. However, few plant species are suitable for phytoremediation of metals such as cadmium (Cd). Genetic engineering offers a powerful tool to generate plants that can hyperaccumulate Cd. An Arabidopsis CAX1 mutant (CAXcd), which confers enhanced Cd transport in yeast, was ectopically expressed in petunia to evaluate whether the CAXcd expression would enhance Cd tolerance and accumulation in planta. The CAXcd-expressing petunia plants showed significantly greater Cd tolerance and accumulation than the controls. After being treated with either 50 or 100 μM CdCl₂ for 6 weeks, the CAXcd-expressing plants showed more vigorous growth compared with controls, and the transgenic plants accumulated significantly more Cd (up to 2.5-fold) than controls. Moreover, the accumulation of Cd did not affect the development and morphology of the CAXcd-expressing petunia plants until the flowering and ultimately the maturing of seeds. Therefore, petunia has the potential to serve as a model species for developing herbaceous, ornamental plants for phytoremediation.     

Effect of combined herbal feed additives on methane,total gas production and rumen fermentation

The present study was to evaluate effect of herbal feed additives on methane and total gas production during the rumen fermentation for environment and animal health concern. Different parts of the five medicinal plants were selected such as leaf and small stems of Ocimum sanctum (Tulsi), roots of Curcuma longa (Haldi), fruits of Emblica officinalis (Amla), leaves of Azadirachta indica (Neem) and leaves and small stem of Clerodendrum phlomidis (Arni) for our study. Addition of different herbal additive combinations did not influence IVDMD and total gas production however methane production (mg/g of substrate DM) was significantly (P<0.05) reduced in Amla: Neem and Neem: Arni combinations. Total nitrogen significantly (P<0.01) increased in the combinations of Tulsi: Haldi and Amla: Neem. TCA–ppt-N is significantly (P<0.01) increased in Tulsi: Haldi, Haldi: Amla, Amla: Neem and Neem: Arni however NH₃-N (mg/dl) significantly decreased in all treatments. We conclude that the screening of plant combinations, Amla: Neem and Neem: Arni have potential to decrease methane production and our herbal feed supplements have no side-effects on the ruminant in small amount.     

Phytoremediation potential of chromium-containing tannery effluent-contaminated soil by native Indian timber-yielding tree species

Twenty-six native Indian tree species that are used for the enhanced tree cover program of the forest department (Government of Tamilnadu, India) were screened for phytoremediation of tannery effluent-contaminated soil containing high chromium content. Out of 26 tree species tested, 10 timber-yielding tree species were selected for further phytoremediation monitoring. After a series of treatments with tannery effluent sludge, the chromium content was measured in the plant parts. The saplings of Acacia auriculiformis, Azadirachta indica, Albizzia lebbeck, Dalbergia sisso, and Thespesia populnea were identified as efficient bioaccumulators of chromium from Cr-contaminated soil. Acacia auriculiformis accumulates higher amounts of Cr in both the root and stem. Dalbergia sisso and T. populnea were found to accumulate higher quantity of Cr in the roots, whereas A. indica, A. richardiana, and A. lebbeck accumulate Cr in their stem. The stress response of the plant species was assessed by quantifying the antioxidative enzymes such as catalase, superoxide dismutase, glutathione reductase, and DHAR. Activity of all the enzymes was observed to gradually increase following treatment with tannery effluent sludge.     

Phytoremediation of toxic trace elements in soil and water

Toxic heavy metals and metalloids, such as cadmium, lead, mercury, arsenic, and selenium, are constantly released into the environment. There is an urgent need to develop low-cost, effective, and sustainable methods for their removal or detoxification. Plant-based approaches, such as phytoremediation, are relatively inexpensive since they are performed in situ and are solar-driven. In this review, we discuss specific advances in plant-based approaches for the remediation of contaminated water and soil. Dilute concentrations of trace element contaminants can be removed from large volumes of wastewater by constructed wetlands. We discuss the potential of constructed wetlands for use in remediating agricultural drainage water and industrial effluent, as well as concerns over their potential ecotoxicity. In upland ecosystems, plants may be used to accumulate metals/metalloids in their harvestable biomass (phytoextraction). Plants can also convert and release certain metals/metalloids in a volatile form (phytovolatilization). We discuss how genetic engineering has been used to develop plants with enhanced efficiencies for phytoextraction and phytovolatilization. For example, metal-hyperaccumulating plants and microbes with unique abilities to tolerate, accumulate, and detoxify metals and metalloids represent an important reservoir of unique genes that could be transferred to fast-growing plant species for enhanced phytoremediation. There is also a need to develop new strategies to improve the acceptability of using genetically engineered plants for phytoremediation.

     

Effect of Cyclic Phytoremediation with Different Wetland Plants on Municipal Wastewater

Phytoremediation is a promising cleanup technology for contaminated soils, groundwater, and wastewater that is both low-tech and low-cost. The objective of this study was to investigate the ameliorative effect of phytoremediation on municipal wastewater (MWW). For this purpose, a phytoremediation garden was established using different aquatic plants species [Pistia stratiotes, Eichhornia crassipess, Hydrocotyle umbellatta, Lemna minor, Tyhpa latifolia, and Scirpus acutus ] in seven earthen pond systems (P1-P7) for the cyclic treatment of MWW. The physico-chemical analysis of MWW was carried out before and after the cyclic phytoremediation. Results showed that pH, EC and turbidity of MWW were reduced by 5.5%, 33.7%, and 93.1%, respectively after treatment (from P1 to P7). Treatment system also reduced total dissolved solids (TDS) by 35.2%, Cl by 61%, HCO₃ by 29.2%, hardness by 45.7%, Ca by 32.3% and Mg by 55.9%. Nitrate concentration was reduced by 77.6% but SO₄ was enhanced slightly. An ameliorative combined effect of wetland plants namely L. minor, T. latifolia, and S. acutus on MWW was noticed. Sequential phytoremediation with a mixture of plants was more effective than that relying only on a single plant species.     

Leguminous plants nodulated by selected strains of Cupriavidus necator grow in heavy metal contaminated soils amended with calcium silicate

Increasing concern regarding mining area environmental contamination with heavy metals has resulted in an emphasis of current research on phytoremediation. The aim of the present study was to assess the efficiency of symbiotic Cupriavidus necator strains on different leguminous plants in soil contaminated with heavy metals following the application of inorganic materials. The application of limestone and calcium silicate induced a significant increase in soil pH, with reductions in zinc and cadmium availability of 99 and 94 %, respectively. In addition, improved nodulation of Mimosa caesalpiniaefolia, Leucaena leucocephala and Mimosa pudica in soil with different levels of contamination was observed. Significant increases in the nitrogen content of the aerial parts of the plant were observed upon nodulation of the root system of Leucaena leucocephala and Mimosa pudica by strain UFLA01-659 (36 and 40 g kg^?1) and by strain UFLA02-71 in Mimosa caesalpiniaefolia (39 g kg^?1). The alleviating effect of calcium silicate resulted in higher production of dry matter from the aerial part of the plant, an increase in nodule number and an increase in the nitrogen fixation rate. The results of the present study demonstrate that the combination of rhizobia, leguminous plants and calcium silicate may represent a key factor in the remediation of areas contaminated by heavy metals.     

Phytoremediation of heavy metal contaminated soil potential by woody plants on Tonglushan ancient copper spoil heap in China

Fast-growing metal-accumulating woody plants are considered potential candidates for phytoremediation of metals. Tonglushan mining, one of the biggest Cu production bases in China, presents an important source of the pollution of environment. The sample was collected at Tonglushan ancient copper spoil heap. The aims were to measure the content of heavy metal in the soil and woody plants and to elucidate the phytoremediation potential of the plants. The result showed that soil Cu, Cd and Pb were the main contamination, the mean contents of which were 3166.73 mg/kg, 3.66 mg/kg and 137.06 mg/kg respectively, which belonged to severe contamination. Fourteen species from 14 genera of 13 families were collected and investigated; except for Ligutrum lucidum, the other 13 woody plants species were newly recorded in this area. In addition, to assess the ability of metal accumulation of these trees, we proposed accumulation index. Data suggested that Platanus × acerilolia, Broussonetia papyrifera, Ligutrum lucidum, Viburnum awabuki, Firmiana simplex, Robina pseudoacacia, Melia azedarach and Osmanthus fragrans exhibited high accumulated capacity and strong tolerance to heavy metals. Therefore, Platanus × acerilolia and Broussonetia papyrifera can be planted in Pb contaminated areas; Viburnum awabuki, Firmiana simplex, Robina pseudoacacia and Melia azedarach are the suitable trees for Cd contaminated areas; Viburnum awabuki, Melia azedarach, Ligutrum lucidum, Firmiana simplex, Osmanthus fragrans and Robina pseudoacacia are appropriate to Cu, Pb and Cd multi-metal contaminated areas.     

Suitability of aromatic plants for phytoremediation of heavy metal contaminated areas: a review

Abstract

This review briefly elucidates the research undertaken and benefits of using aromatic plants for remediation of heavy metal polluted sites. A sustainable approach to mitigate heavy metal contamination of environment is need of the hour. Phytoremediation has emerged to be one of the most preferable choices for combating the metal pollution problem. Aromatic plants can be used for remediation of contaminated sites as they are non-food crops thus minimizing the risk of food chain contamination. Most promising aromatic plants for phytoremediation of heavy metal contaminated sites have been identified from families – Poaceae, Lamiaceae, Asteraceae, and Geraniaceae. They act as potential phytostabilisers, hyper accumulators, bio-monitors, and facultative metallophytes. Being high value economic crops, monetary benefits can be obtained by growing them in tainted areas instead of food crops. It has been observed that heavy metal stress enhances the essential oil percentage of certain aromatic crops. Research conducted on some major aromatic plants in this context has been highlighted in the present review which suggests that aromatic plants hold a great potential for phytoremediation. It has been reported that essential oil from aromatic crops is not contaminated by heavy metals significantly. Thus, aromatic plants are emerging as an ideal candidate for phytoremediation.

Highlights

? Aromatic plants hold a great potential for phytoremediation of heavy metal contaminated sites.

? Being high value economic crops, monetary benefits can be obtained by growing them in contaminated areas instead of food crops.

? Research done on some major aromatic plants in this context has been highlighted in the present review.     

Overexpression of phytochelatin synthase (<Emphasis Type="Italic">AtPCS</Emphasis>) in rice for tolerance to cadmium stress

Phytoremediation is an important strategy adapted by plants to sequester and/or detoxify pollutants. Phytochelatins, a family of cysteine-rich thiol-reactive peptides, bind to various heavy metals and metalloids making them good candidates for phytoremediation. Phytochelatin synthase catalyses the final step in the biosynthesis of phytochelatins and can be used as a strategy to improve tolerance against heavy metals. In the present study, an AtPCS gene was overexpressed in rice following the in planta transformation approach. Stringent screening strategies were standardized to select putative transformants under a Cd stress of 125 μM at both seedling and plant levels. Molecular analysis by PCR in 18 tolerant plants confirmed the transgene integration and absence of Agrobacterium. Genomic Southern analysis further confirmed the integration of the T-DNA as a single copy. The stability of the T-DNA in the progeny of 5 selected T₁ generation plants was confirmed by tolerance assay, molecular characterization and biochemical analysis for the reduced glutathione, phytochelatin content and lipid peroxidation. This strategy is discussed as a potential mechanism to enhance the tolerance of rice plants to Cd stress.     

Phytoremediation in the Tropics—The Effect of Crude Oil on the Growth of Tropical Plants

Phytoremediation is a nondestructive, cost-effective in-situ technology to clean up contaminated soils. In the case of contamination with petroleum hydrocarbons, plants enhance microbial degradation of the contaminant in the rhizosphere. The potential of this technology for the tropics should be high due to prevailing climatic conditions favoring plant growth and stimulating microbial activity. Investigations of the potential of tropical plants for phytoremediation, however, are scarce. The present work studied two grasses and six legumes from the eastern savannah of Venezuela on their reaction to crude oil contamination in soil. Results shall help to identify plants with a potential for phytoremediation and subsequent studies. Seedling emergence and biomass production were determined for plants growing in soil contaminated with 0%, 3%, and 5% heavy crude oil. Contamination had, in general, a tendential but not significant negative influence on seedling emergence. Dry matter production was reduced by only a few percent to up to 85%. Furthermore, in some legumes inhibition of nodulation was observed. The grass Brachiaria brizantha and the legumes Centrosema brasilianum and Calopogonium mucunoides are promising for phytoremediation because in contaminated soil they combined high seedling emergence with least affected biomass production. Since they are cultivated forage/soil cover species also in other regions of the tropics, their potential for phytoremediation of petroleum contaminated soils extends beyond Venezuela.     

Endophyte-assisted phytoremediation: mechanisms and current application strategies for soil mixed pollutants

Abstract

Phytoremediation uses plants and associated microbes to remove pollutants from the environment and is considered a promising bioremediation method. Compared with well-described single contaminant treatments, the number of studies reporting phytoremediation of soil mixed pollutants has increased recently. Endophytes, including bacteria and fungi, exhibit beneficial traits for the promotion of plant growth, stress alleviation, and biodegradation. Moreover, endophytes either directly or indirectly assist host plants to survive high concentrations of organic and inorganic pollutants in the soil. Endophytic microorganisms can also regulate the plant metabolism in different ways, exhibiting a variety of physiological characteristics. This review summarizes the taxa and physiological properties of endophytic microorganisms that may participate in the detoxification of contaminant mixtures. Furthermore, potential biomolecules that may enhance endophyte mediated phytoremediation are discussed. The practical applications of pollutant-degrading endophytes and current strategies for applying this valuable bio-resource to soil phytoremediation are summarized.     

Nutrient resorption responses to water and nitrogen amendment in semi-arid grassland of Inner Mongolia, China

Litterfall and fine root production is a major pathway for carbon and nutrient cycling in forest ecosystems. We investigated leaf litterfall, fine-root mass, production and turnover rate in the upper soil (0–30 cm) under four major tree species (Leucaena leucocephala, Acacia nilotica, Azadirachta indica, Prosopis juliflora) of the semi-arid region of India. All the four tree species showed an unimodal peak of leaf litterfall with distinct seasonality. Leucaena leucocephala and Acacia nilotica had maximum leaf litterfall between September and December while Azadirachta indica and Prosopis juliflora shed most of their leaves between February and May. Annual leaf litterfall of the four species ranged from 3.3 Mg ha^?1 (Leucaena leucocephala) to 8.1 Mg ha^?1 (Prosopis juliflora). Marked seasonal variations in amount of fine root biomass were observed in all the four tree species. Fine root production was maximum in Prosopis juliflora (171 g m^?2 y^?1) followed by Azadirachta indica (169 g m^?2 y^?1), Acacia nilotica (106 g m^?2 y^?1) and Leucaena leucocephala (79 g m^?2 y^?1). Fine root biomass showed a seasonal peak after the rainy season but fell to its lowest value during the winter and dry summer season. Fine root turnover rate ranged from 0.56 to 0.97 y^?1 and followed the order Azadirachta indica > Leucaena leucocephala > Prosopis juliflora > Acacia nilotica. The results of this study demonstrated that Prosopis juliflora and Azadirachta indica had greater capability for maintaining site productivity as evidenced from greater leaf litterfall and fine root production.     

Carbon capture and sequestration by a treatment wetland

An understanding of detailed kinetic of CO₂ removal by plants can lead to an effective design of the phytoremediation process for anthropogenic CO₂ reduction. This study examines the CO₂ removal rates of five wetland plants (Cyperus alternifolius, Dracaena fragrans, Iris ensata, Iris setosa and Thalia dealbata) by using saturation reaction and first-order reaction kinetic equations. It was determined that the elevation of CO₂ levels stimulated the plant-CO₂ uptake rate. The maximum CO₂ removal rates (k) of plants were found to range between 0.76 and 1.21 g m^?2 h^?1. The magnitude of first-order kinetic coefficient of plants (k′) had a close relationship with CO₂ level at half-velocity (K). For consistency, the same kinetics were applied to the continuous flow experiment. A saturation kinetic approach was well suited to estimate the removal rate of CO₂ in continuous flow system, while a first-order kinetic approach was limited to inflow CO₂ levels below 500 ppm.     

Azadirachtin in the fruit of melia azedaiuch

Azadirachtin, a triterpenoid of Azadirachta indica with feeding and growth disruptive effects on certain insects, has been found in Melia azedarach.     

高生物量经济植物修复重金属污染土壤研究进展

植物修复是重金属污染土壤修复的重要方法之一。利用高生物量经济植物修复重金属污染土壤,能够兼顾生态和经济效益,具有很大的应用前景。本文系统分析了植物修复现状及存在的问题,提出利用高生物量经济植物修复重金属污染土壤的优势,总结了近年来利用高生物量经济植物吸收重金属的研究进展,探讨了改善高生物量经济植物修复重金属污染土壤效率的方法,以期为提高植物修复经济效益、促进植物修复广泛应用提供参考。     

重金属污染的转基因植物修复——原理与应用

污染环境的植物修复技术具有成本低、不造成二次污染等优点。从自然界中寻找用于污染环境修复的超富积植物不仅难度大 ,而且受生物量、生长周期以及地理环境等因素的限制。近几年迅速发展起来的通过转基因植物进行污染环境的修复技术显示了广阔的应用前景。外源基因在植物的高效表达可以提高植物吸收、运输、降解污染物的能力以及修复的效率 ,并可以作为研究不同污染物修复机理的实验系统。以转基因植物修复几种主要的重金属污染为例 ,介绍了转基因植物修复的原理、现状及存在问题 ,并探讨了提高转基因植物修复效率的一些方法 。     

Can CO2 Fertilization Enhance Phytoremediation of Organic Soil Contamination?

Low efficiency is a key problem confronting the development and application of phytoremediation technology. Based on political pressure to reduce CO₂ emissions in China and the fact that CO₂ is necessary for plant photosynthesis, the effects of captured CO₂ fertilization on phytoremediation of soil di-(2-ethylhexyl) phthalate (DEHP) pollution by C₃ plant (mung bean, Vigna radiata L.) and C₄ plant (maize, Zea mays L.) were investigated. Results showed that DEHP pollution negatively affected the growth and rhizosphere environments of both plants. After CO₂ fertilization, both plants had more biomass (aboveground, belowground, and total dry weight), higher alkaline phosphatase activity, and more microbes with DEHP tolerance in their rhizospheres. Superoxide dismutase activity in leaves of both plants decreased significantly. Microbial community composition in both rhizospheres changed. CO₂ fertilization also increased plant uptake of DEHP, particularly in the roots, and decreased residual DEHP concentrations in the rhizospheres. These effects were more evident in the C₃ than in the C₄ plant. This study indicated that CO₂ fertilization can enhance the phytoremediation process of polluted soil through promoting plant growth, improving the rhizosphere environment, and increasing plant uptake of DEHP, particular in a C₃ plant. CO₂ fertilization could be considered as a measure to enhance phytoremediation.     

Phytoremediation—A Novel and Promising Approach for Environmental Clean-up

ABSTRACT

Phytoremediation is an eco friendly approach for remediation of contaminated soil and water using plants. Phytoremediation is comprised of two components, one by the root colonizing microbes and the other by plants themselves, which degrade the toxic compounds to further non-toxic metabolites. Various compounds, viz. organic compounds, xenobiotics, pesticides and heavy metals, are among the contaminants that can be effectively remediated by plants. Plant cell cultures, hairy roots and algae have been studied for their ability to degrade a number of contaminants. They exhibit various enzymatic activities for degradation of xenobiotics, viz. dehalogenation, denitrification leading to breakdown of complex compounds to simple and non-toxic products. Plants and algae also have the ability to hyper accumulate various heavy metals by the action of phytochelatins and metallothioneins forming complexes with heavy metals and translocate them into vacuoles. Molecular cloning and expression of heavy metal accumulator genes and xenobiotic degrading enzyme coding genes resulted in enhanced remediation rates, which will be helpful in making the process for large-scale application to remediate vast areas of contaminated soils. A few companies worldwide are also working on this aspect of bioremediation, mainly by transgenic plants to replace expensive physical or chemical remediation techniques. Selection and testing multiple hyperaccumulator plants, protein engineering of phytochelatin and membrane transporter genes and their expression would enhance the rate of phytoremediation, making this process a successful one for bioremediation of environmental contamination. Recent years have seen major investments in the R&D, which have also resulted in competition of filing patents by several companies for economic gains. The details of science & technology related to phytoremediation have been discussed with a focus on future trends and prospects of global relevance.     

Phytoremediation as a prospective method for rehabilitation of areas contaminated by long-term sewage sludge storage: A Ukrainian–Greek case study

Soil contamination by heavy metals could be caused by long-term storage of sewage sludge on the territory of most municipal wastewater treatment plants (WWTPs) worldwide. Different methods to deal with heavy metal pollution and rehabilitation can be applied, but they are costly. Phytoremediation is a method using plants in order to extract, sequester and/or detoxify pollutants such as heavy metals. Phytotechnologies are more advantageous economically, than other in situ and ex situ remedial approaches (they estimated to be at least 40% less costly) (ITRC, 2001).In this work the suitability of several plant species for phytoremediation under natural conditions was studied. Brassica napus, Medicago sativa, Zea mays, Triticum aestivum and Hordeum vulgare were grown in pots with sewage sludge from “Bezludivka” WWTP in Kharkiv, Ukraine and from Sindos WWTP in Thessaloniki, Greece.Plants in the experimental series were compared to those in the control samples (the same species grown in compost). In experimental series, shoot growth was less reduced in T. aestivum and H. vulgare than in the other plant species studied. M. sativa had the lowest germination rate. Generally B. napus and M. sativa, giving less biomass production than Z. mays and T. aestivum, were characterized by higher ability to accumulate heavy metals (Cd, Cu, Ni, Pb, Zn, Cr, As and Hg).