Phytoremediation Strategies for Heavy Metal Contamination: A Review on Sustainable Approach for Environmental Restoration

Current globalization trends and important breakthroughs globally need a complete study of heavy metal contamination, its causes, its impacts on human and environmental health, and different remediation strategies. Heavy metal pollution is mostly produced by urbanization and industry, which threatens ecosystems and human health. Herein, we discuss a sustainable environmental restoration strategy employing phytoremediation for heavy metal pollution, the carcinogenic, mutagenic, and cytotoxic effects of heavy metals such as cadmium, copper, mercury, selenium, zinc, arsenic, chromium, lead, nickel, and silver, which may be fatal. Phytoremediation, which was prioritized, uses plants to remove, accumulate, and depollute pollutants. This eco-friendly method may safely collect, accumulate, and detoxify toxins using plants, making it popular. This study covers phytostabilization, phytodegradation, rhizodegradation, phytoextraction, phytovolatilization, and rhizofiltration. A phytoremediation process’s efficiency in varied environmental circumstances depends on these components’ complex interplay. This paper also introduces developing phytoremediation approaches including microbe-assisted, chemical-assisted, and organic or bio-char use. These advancements attempt to overcome conventional phytoremediation’s limitations, such as limited suitable plant species, location problems, and sluggish remediation. Current research includes machine learning techniques and computer modeling, biostimulation, genetic engineering, bioaugmentation, and hybrid remediation. These front-line solutions show that phytoremediation research is developing towards transdisciplinary efficiency enhancement. We acknowledge phytoremediation’s promise but also its drawbacks, such as site-specific variables, biomass buildup, and sluggish remediation, as well as ongoing research to address them. In conclusion, heavy metal pollution threatens the ecology and public health and must be reduced. Phytoremediation treats heavy metal pollution in different ways. Over time, phytoremediation systems have developed unique ways that improve efficiency. Despite difficulties like site-specificity, sluggish remediation, and biomass buildup potential, phytoremediation is still a vital tool for environmental sustainability.

Physico-Chemical Properties of Soils from Diguel and Koudalwa Tchad,and Phytoremediation Potentials of Acasia and Kinkeliba Plants in Removing Cr and Cu from These Soils

The aim of this study to investigate the physico-chemical properties of soils from Diguel and Koudalwa Tchad,and phytoremediation potentials of acasia and kinkeliba plants in removing Cr and Cu from these soils.Soil was sampled from the tannery plant in Diguel and agricultural land around crude oil activities in Koudalwa.Soils were characterized by the following properties:pH,(Electrical Conductivity),TDS(Total Dissolved Solids),salinity,bulk density,OM(Organic Matter),nitrate,phosphate,clay,silt,sand,and textural class.The acasia and kinkeliba plants were used to decontaminate Cu and Cr from sample soils for 30 days period.The bulk density of all the soil samples from Kouldawa was higher compared to Diguil,ranging from 1.421 to 1.64 g/cm^(3)compared to 1.21 to 1.51 g/cm^(3)for Diguel.Most of the soils in Kouldawa are mineral soils,while those of Diguel are mostly mineral soil with some organics.Diguel soils are richer in nitrate(577.9 to 2,687.32 mg/kg in Diguel and 33.64 to 197.64 mg/kg in Kouldawa)and phosphate than soils from Kouldawa.Soils from the studied areas are not saline except for a subsurface soil in Diguel(salinity,4.21;EC,4.280 dS/m;TDS,3,040 mg/L).The highest amount of Cr and Cu removed by acasia is 78%and 53.12%compared to 73.8%and 52.21%by kinkeliba.Diguel soil can be very suitable for agriculture and Kouldawa soils for construction.Acasia and kinkeliba can be effectively used to decontaminate the studied soils from heavy metal pollution.

Local Plants Potentially Suitable for Phytoremediation of Soils Polluted by Heavy Metals: The Case of Landfill Sites

Landfills are contaminated sites that need to be cleaned up to prevent human and environmental exposure to pollutants. This article aims to identify local plants capable of restoring soil polluted by heavy metals. To this end, plant species at the Bonoua landfill were inventoried. X-ray fluorescence spectrometry was used to determine the heavy metal content of soil and plants from the landfill. The bioconcentration factor (BCF) of metals in plants was evaluated. The Bonoua landfill is covered with 62 plant species, comprising 28 botanical families and 50 genera. The BCF varied from 0.08 (titanium) to 2.27 (strontium) for Phyllanthus amarus;from 0.06 (titanium) to 1.83 (copper) for Alternanthera sessilis and from 0.03 (arsenic) to 2.10 (strontium) for Amaranthus spinosus. Phyllanthus amarus, Alternanthera sessilis, and Amaranthus spinosus are strontium-accumulating species (BCF > 1). Similarly, copper BCF values were above 1 for Phyllanthus amarus, and Alternanthera sessilis. These two plant species are therefore copper accumulators. In short, Phyllanthus amarus, Alternanthera sessilis, and Amaranthus spinosus are candidate species for phytoremediation of heavy metal-polluted soils, given their BCF > 1.

Phytoremediation of Mine Acid Water Using Aquatic Plants

One of the impacts resulting from mining process is the occurrence of AMD(Acid Mine Drainage),which is rainwater or groundwater mixed with rock.AMD contains specific sulfides in coal,leading to highly acidic water with elevated concentrations of iron and manganese.Furthermore,phytoremediation offers a method to enhance specific contaminant levels in various environmental mediums,including soil,sediment,dirt or sludge,groundwater,and surface water.This waste treatment approach employs readily applicable,efficient,and effective plant species,such as burhead or Amazon sword,Melati air(Echinodorus palaefolius),Water hyacinth or eceng gondok(Eichhornia crassipes),and globe fimbry or Mendong(Fimbritylis globulosa)which are aquatic plants in South Sumatra with the capacity to absorb heavy metals.Therefore,this study aims to measure the growth response of each aquatic plant(Echinodorus palaefolius,Eichhornia crassipes,and Fimbritylis globulosa)in each treatment.It also analyzes the amount of heavy metal uptake in the form of Fe and Mn by each aquatic plant(Eichhornia crassipes,Echinodorus palaefolius,and Fimbritylis globulosa)used.Additionally,it investigates the ability of these plants to facilitate the phytoremediation of AMD using compost derived from OPEFB(Oil Palm Empty Fruit Bunches)to reduce the presence of Fe and Mn elements.The study employs a bioreactor and encompasses two treatment factors,namely the type of aquatic plants(Echinodorus palaefolius,Eichhornia crassipes,and Fimbritylis globulosa)and the composition comparison between OPEFB compost and limestone.The result shows that the combination of treatments in terms of plant types and media composition yields the highest growth,with a weight of 286.25 g in T2K1 treatment.This involves Eceng gondok and a media composition of compost to limestone in a ratio of 50%to 50%.Moreover,Mendong exhibits the highest absorption of Fe metal,with a value of 0.82 g,followed by Eceng gondok with 0.55 g,while Melati displays the lowest at 0.38 g.Regarding the absorption of Mn,Eceng gondok demonstrates the highest uptake,measuring 0.36 g,followed by Melati and Mendong at 0.11 g and 0.06 g,respectively.

Assessment of Sunflower (Helianthus annuus L.) for Phytoremediation of Heavy Metal Polluted Mine Tailings—A Case Study of Nampundwe Mine Tailings Dam, Zambia

Mining activities have led to a generation of large quantities of heavy metals laden wastes which are released into the environment in an unsustainable way causing the contamination of the ecosystems and posing a risk to human health. Most mining companies have not employed any rehabilitation or remediation program of the heavy metal laden waste. The aim of this study was to assess the potential of sunflower for phytoremediation of heavy metal polluted mine tailings. Phytoremediation is an emerging technology in the remediation of mine tailings that uses tolerant plant species to clean up contaminated sites. It uses plants with high biomass and sunflower has been identified as such. These plants can extract, transfer, sequester and stabilize a variety of metals through mechanisms such as phytoextraction, phytostabilization, phytoaccumulation and phytovolatilization. Pot experiments were conducted by growing sunflower (Helianthus annuus L.) in pyrite mine tailings and in agricultural soil as a control. The study showed that the concentration of Cu reduced from 40.76 mg/kg to 36.59 mg/kg, Zn reduced from 3.58 mg/kg to 3.49 mg/kg and Fe reduced from 23.70 mg/kg to 10 mg/kg respectively in the mine tailings after 6 weeks. Analysis of harvested sunflower (roots, stems, leaves) showed that sunflower could remove heavy metals from the tailings and the highest removal efficiency was 53.7% and the highest translocation factor was 0.25. It was concluded that sunflower has the potential to remediate contaminated mine tailings and that phytoremediation is a viable and efficient technology to treat soils contaminated with heavy metals.

Research Progress of Phytoremediation Technology on Soils Polluted by Heavy Metals in Mining Areas

Phytoremediation is an efficient and economic ecological technology. It includes phytostabilization, phytovolatilization, and plant absorption. In the research, status quo and progress of Phytostabilization and plant absorption in soils polluted with heavy metals in metal mines were summarized, including the characteristics and status quo of phytoremediation and selection method of hyperaccumulator. In addition, further research was proposed as well.

Research on Phytoremediation of Heavy Metal Pollution in River Sediment by Medicago sativa L.

[Objective] The aim was to study the phytoremediation of heavy metal pollution in river sediment by Medicago sativa L.,so as to provide reliable references for the phytoremediation of heavy metal pollution in river sediment.[Method] The air-dried,screened and mixed sediment was put in rectangular PVC box（0.6 m×0.5 m×0.4 m） with seepage vent at the bottom,and the water holding capacity（WHC） of sediment was kept at 30%-60% by deionized water.The seeds of Medicago sativa L.were sown in April 2010,and seedlings were thinned after 7 d.Samples were collected from rhizosphere soil every 30 d,and were used to determine the content of heavy metals,bacteria quantity and enzyme activity in sediment.In addition,the accumulation of heavy metals in the roots,stems and leaves of plant was measured after harvest in October.[Result] Different parts of Medicago sativa L.varied in accumulation capacity to different heavy metals.The accumulation amount of Zn in Medicago sativa L.was the highest,especially in roots.Meanwhile,the accumulation amount of heavy metals like Ni,Cr,Cu and Pb in roots was higher than that of stems and leaves.In contrast,Mn was mainly accumulated in leaves and its amount accounted for 42.47% of the total amount in plant.Besides,the accumulation amount of all heavy metals was the lowest in stems.Ni,Cr,Cu and Pb could be degraded more effectively than Mn,and increasing the planting time and sowing times of crop was beneficial to the degradation of heavy metals.After planted Medicago sativa L.,the quantity of microorganisms in sediment went up obviously,and dehydrogenase activity also showed an increaseing trend.[Conclusion] Medicago sativa L.has certain restoring effect on Zn,Ni,Cr,Cu and Pb,and could be used to restore heavy metal pollution in river sediment.

Phytoremediation of Contaminated Chemical Plant Sites

[Objective] The aim was to research phytoremediation effects on soils with combined pollution. [Method] With simulation experiment, the test selected plants suitable for phytoremediation in soils polluted with Pb-Cd, PAHs, and Pb-Cd-PAHs,respectively and ryegrass was grown to explore phytoremediation on contaminated sites by adjusting bio-availability. [Result] After 70 d growing of ryegrass, the content of available Pb in contaminated soils was 375.26 mg/kg, the content of Cd was 4.9mg/kg after 90 d, and the content of B [a]P was 0.60 mg/kg after 100 d, which were all lower compared with soil limits. [Conclusion] Ryegrass is a suitable plant for phytoremediation.

Phytoremediation of heavy metal polluted soils and water:Progresses and perspectives

Environmental pollution affects the quality of pedosphere,hydrosphere,atmosphere,lithosphere and biosphere.Great efforts have been made in the last two decades to reduce pollution sources and remedy the polluted soil and water resources.Phytoremediation,being more cost-effective and fewer side effects than physical and chemical approaches,has gained increasing popularity in both academic and practical circles.More than 400 plant species have been identified to have potential for soil and water remediation.Among them,Thlaspi,Brassica,Sedum alfredii H.,and Arabidopsis species have been mostly studied.It is also expected that recent advances in biotechnology will play a promising role in the development of new hyperaccumulators by transferring metal hyperaccumulating genes from low biomass wild species to the higher biomass producing cultivated species in the times to come.This paper attempted to provide a brief review on recent progresses in research and practical applications of phytoremediation for soil and water resources.

Phytoremediation and its models for organic contaminated soils

Soil pollution has been attracting considerable public attentions over the last decades. Sorts of traditional physiochemical methods have been used to remove the organic pollutants from soils. However, the enormous costs and low efficiencies associated with these remediation technologies limit their availabilities. Phytoremediation is an emerging technology that uses plants to cleanup pollutants in soils. As overwhelmingly positive results have been shown, phytoremediation is a most economical and effective remediation technique for organic contaminated soils. In this paper phytoremediation and its models for organic contaminated soils are viewed. The mechanisms of phytoremediation mainly include the direct plant uptake of organic pollutants, degradation by plant-derived degradative enzymes, and stimulated biodegradation in plant rhizosphere. Phytoremediation efficiency is close related to physicochemical properties of organic pollutants, environmental characteristics, and plant types. It is no doubt that soil amendments such as surfactants improve the solubilities and availabilities of organic pollutants in soils. However, little information is available about effects of soil amendments on phytoremediation efficiencies. Phytoremediation models have been developed to simulate and predict the environmental behavior of organic pollutants, and progress of models is illustrated. In many ways phytoremediation is still in its initial stage, and recommendations for the future research on phytoremediation are presented.

Role of soil rhizobacteria in phytoremediation of heavy metal contaminated soils

Heavy metal pollution of soil is a significant environmental problem and has its negative impact on human health and agriculture. Rhizosphere, as an important interface of soil and plant, plays a significant role in phytoremediation of contaminated soil by heavy metals, in which, microbial populations are known to affect heavy metal mobility and availability to the plant through release of chelating agents, acidification, phosphate solubilization and redox changes, and therefore, have potential to enhance phytoremediation processes. Phytoremediation strategies with appropriate heavy metal-adapted rhizobacteria have re-ceived more and more attention. This article paper reviews some recent advances in effect and significance of rhizobacteria in phytoremediation of heavy metal contaminated soils. There is also a need to improve our understanding of the mechanisms in-volved in the transfer and mobilization of heavy metals by rhizobacteria and to conduct research on the selection of microbial isolates from rhizosphere of plants growing on heavy metal contaminated soils for specific restoration programmes.

Assessment of Pb uptake,translocation and immobilization in kenaf (Hibiscus cannabinus L.) for phytoremediation of sand tailings

The potential of kenaf (Hibiscus cannabinus L.) for phytoremediation of lead (Pb) on sand tailings was investigated.A pot experiment employing factorial design with two main effects of fertilizer and lead was conducted in a nursery using sand tailings from an ex-tin mine as the growing medium.Results showed that Pb was found in the root,stem,and seed capsule of kenaf but not in the leaf.Application of organic fertilizer promoted greater biomass yield as well as higher accumulation capacity of Pb.In Pb-spike...

“Co-culture Engineering”for Enhanced Phytoremediation of Metal Contaminated Soils

A co-culture of two plant materials, Astragalus sinicus L., a leguminous plant with concomitant nodules, and Elsholtzia splendens Naki-a Cu accumulator, along with treatments of a chelating agent (EDTA), root excretions (citric acid), and a control with E. splendens only were used to compare the mobility of heavy metals in chelating agents with a co-culture and to determine the potential for co-culture phytoremediation in heavy metal contaminated soils. The root uptake for Cu, Zn, and Pb in all treatments was significantly greater (P ＜ 0.05) than that of the control treatment. However with translocation in the shoots, only Cu, Zn, and Pb in plants grown with the EDTA treatment and Zn in plants cocropped with the A. sinicus treatment increased significantly (P ＜ 0.05). In addition, when a co-culture in soils with heavy and moderate contamination was compared, for roots in moderately contaminated soils only Zn concentration was significantly less (P ＜ 0.05) than that of heavily contaminated soils, however, Cu, Zn, and Pb concentrations of shoots were all significantly lower (P ＜ 0.05). Overall, this 'co-culture engineering' could be as effective as or even more effective than chelating agents, thereby preventing plant metal toxicity and metal leaching in soils as was usually observed in chelate-enhanced phytoremediation.

Phytoremediation of petroleum polluted soil

An experimental study of the rhizosphere effect on phytoremediation of petroleum polluted soil was carried out with three species of grasses, namely Pannicum, Eleusine indica （L.） Gaerth, and Tall Fescue. After a period of 150 days, this pot experiment showed that the rhizosphere of these three species accelerated the degradation of petroleum hydrocarbons to different extents. The results showed that the number of microorganisms in the rhizosphere increased by three orders of magnitude. The induction of the plant rhizosphere and the coercion influence of petroleum changed the species and activity of microorganisms. The degradation of petroleum hydrocarbons in the rhizosphere was 3-4 times that in unplanted soil. The dehydrogenase activity in the rhizosphere was 1.61-2.20 times that in unplanted soil, but the catalase activity was 0.90-0.93 times that in unplanted soil, and soil moisture content increased by 5% compared with the unplanted soil.

Phytoremediation for phenanthrene and pyrene contaminated soils

Phytoremediation of soil contaminated with phenanthrene and pyrene was investigated using twelve plant species. Plant uptake and accumulation of these chemicals were evaluated. At the end of the experiment(45 d), the remaining respective concentrations of soil phenanthrene and pyrene in spiked vegetated soils, with initial phenanthrene of 133 3 mg/kg and pyrene of 171 5 mg/kg, were 8 71—16 4 and 44 9—65 0 mg/kg, generally 4 7%—49 4% and 7 1%—35 9% lower than their concentrations in the non vegetated soils. The loss of phenanthrene and pyrene in vegetated spiked soils were 88 2%—93 0% and 62 3%—73 8% of the added amounts of these contaminants, respectively. Although plant uptake and accumulation of these compounds were evident, and root concentrations and RCFs(root concentration factors; defined as the ratio of PAH concentrations in roots and in the soils on a dry weight basis) of these compounds significantly positively correlated to root lipid contents, plant uptake and accumulation only accounted for less than 0 01% and 0 23% of the enhanced loss of these chemicals in vegetated versus non vegetated soils. In contrast, plant promoted microbial biodegradation was the dominant mechanism of the phytoremediation for soil phenanthrene and pyrene contamination. Results from this study suggested a feasibility of the establishment of phytoremediation for soil PAH contamination.

Potential of Pteris vittata L. for phytoremediation of sites co-contaminated with cadmium and arsenic: The tolerance and accumulation

Field investigation and greenhouse experiments were conducted to study the tolerance of Pteris vittata L. （Chinese brake） to cadmium （Cd） and its feasibility for remediating sites co-contaminated with Cd and arsenic （As）. The results showed that P. vittata could survive in pot soils spiked with 80 mg/kg of Cd and tolerated as great as 301 mg/kg of total Cd and 26.8 mg/kg of diethyltriaminepenta acetic acid （DTPA）-extractable Cd under field conditions. The highest concentration of Cd in fronds was 186 mg/kg under a total soil concentration of 920 mg As/kg and 98.6 mg Cd/kg in the field, whereas just 2.6 mg/kg under greenhouse conditions. Ecotypes of P. vittata were differentiated in tolerance and accumulation of Cd, and some of them could not only tolerate high concentrations of soil Cd, but also accumulated high concentrations of Cd in their fronds. Arsenic uptake and transportation by P. vittata was not inhibited at lower levels （〈20 mg/kg） of Cd addition. Compared to the treatment without addition of Cd, the frond As concentration was increased by 103.8% at 20 mg Cd/kg, with the highest level of 6434 mg/kg. The results suggested that the Cd-tolerant ecotype of P. vittata extracted effectively As and Cd from the site co-contaminated with Cd and As, and might be used to remediate and revegetate this type of site.

Recent research progress in geochemical properties and restoration of heavy metals in contaminated soil by phytoremediation

Heavy metals are widely distributed contaminants in natural environments and their potential threats to human health have attracted worldwide concerns due to the food chain. Therefore, great efforts have been made to reduce them to a safe level in soil. Compared with the traditional methods, the method using plants to remove them has been accepted as a feasible and efficient way. Herein, the geochemical behavior of heavy metals and the restoration methods with phytoremediation were reviewed. In addition, issues on heavy metal speciation as well as its influencing factors, phytoremediation mechanism, phytoremediation effect and vegetation selection principle used for phytoremediation were discussed.

Current Situation of Heavy Metal Pollution in Farmland Soil and Phytoremediation Application

Phytoremediation technology is a newly-developed way of soil heavy metal pollution repair with high efficiency and good ecological comprehensive benefit. This paper briefly introduces the soil heavy metal pollution status at home and abroad,and focuses on the analysis of harm,sources and current situation of soil heavy metal pollution at home and abroad as well as mechanism and application of phytoremediation.Finally it discusses the key problems in phytoremediation technology that need to resolve in the future.

EDTA-enhanced phytoremediation of lead contaminated soil by Bidens maximowicziana

Phytoremediation is a potential cleanup technology for the removal of heavy metals from contaminated soils. Bidens is a new Pb hyperaccumulator, which not only has remarkable tolerance to Pb but also extraordinary accumulation capacity for Pb. The maximum Pb concentration was 1509.3 mg/kg in roots and 2164.7 mg/kg in overground tissues. The Pb distribution order in the B. was： leaf 〉 stem 〉 root. The effect of amendments on phytoremediation was also studied. The mobility of soil Pb and the Pb concentrations in plants were both increased by EDTA application. Compared with CK （control check）, EDTA application promoted translocation of Pb to overground parts of the plant. The Pb concentrations in overground parts of plants was increased from 24.23-680.56 mg/kg to 29.07-1905.57 mg/kg. This research demonstrated that B. maximowicziana appeared to be suitable for phytoremediation of Pb contaminated soil, especially, combination with EDTA.

Use of Sorghum Crops for in Situ Phytoremediation of Polluted Soils

There has been carried out a comparative research, which allow us to determine the quantities and the central points of accumulation ofPb, Cu, Zn and Cd in the vegetative and reproductive organs of the four sorghum varieties （technical sorghtan, sugar sorghum, sudan grass and grain sorghnm）, as well as to ascertain the possibilities for their growth in soils contaminated with heavy metals and their application for phytoremediation purposes. The experimental plots were situated at different distances （0.1 and 15.0 kin） from the source of pollution-the Non-Ferrous Metal Works near Plovdiv, Bulgaria. On reaching commercial ripeness, the crops were gathered and the concentrations of Pb, Cu, Zn and Cd in their different parts-roots, stems, leaves and gains-were determined through dry mineralization. To determine the heavy metal content in the samples, ICP was used. A clearly distinguished trend exists which describes the accumulation of heavy metals within the vegetative and reproductive organs of the studied crops. Sudan grass and technical sorghum accumulated larger heavy metal quantities compared to sugar sorghum and grain sorghum, as the majority of the heavy metals was retained by the roots and a very small amount was translocated to epigeous parts. The depots for accumulation were in the following order： roots 〉 leaves 〉 stems 〉 grains. The studied crops can be related to metal-tolerant crops and can be cultivated on softs which are of low, medium or high contamination with lead, zinc and cadmium, as they do not exhibit a tendency of accumulating these elements in grains at levels above the maximum permissible concentrations for fodder. The selective accumulation of Pb, Cu, Zn and Cd in the roots and the possibility to remove the root-remains makes technical sorghum, sugar sorghum and Sudan grass extremely suitable for phytoremediation purposes. The possible use of grains for animal food guarantees the economic expedience upon the selection of these crops.