Phytoremediation Potential of Heavy Metals by Cyperus rotundus
2023 年 11 巻 p. 20-35
詳細
2023 年 11 巻 p. 20-35
Growing industrialization and urbanization are seriously polluting the environment with hazardous heavy metals. Heavy metal pollution has caused major consequences on human health and the environment on a global level. Economically effective and environmentally friendly methodologies and technologies are utilized globally to remediate heavy metal-contaminated soils and wastewater. Phytoremediation is one of the potential technologies for the in-site treatment of heavy metal-contaminated soil and water. Over 163 plant species with the ability of metal concentration and tolerance have been discovered in the world as possible phytoremediators. Among the plant species used for phytoremediation, Cyprus rotundus is a safe and inexpensive phytoremediation agent that has a high capacity to accumulate heavy metals in its plant parts. This review provides a general overview of the phytoremediation potential of Cyperus rotundus through reviewing relevant originally published research articles. For the study, a literature survey was conducted by using articles from top academic research databases including ScienceDirect, JSTOR, Google Scholar, and PubMed. A total number of 71 originally published articles related to phytoremediation and heavy metal phytoremediation of Cyperus rotundus were selected for the review. According to previous studies, Cyperus rotundus is capable of extracting and accumulating As, Cd, Pb, Rb, Sn, and Zn in its roots and shoots when the soil is highly polluted with the aforementioned heavy metals. Moreover, Cypreus rotundus indicate a considerable value of bioconcentration factors and translocation factors to different heavy metals, whereas it emphasizes the possible remediation of heavy metals through this plant species. Consequently, Cyperus rotundus could be identified as a possible hyperaccumulator and Phytostabilizer for most heavy metals for upcoming phytoremediation studies.
It is indeed a serious concern that the environment is becoming alarmingly more polluted with hazardous heavy metals as a result of growing industrialization and urbanization [1]. The leading causes of such a transformation often include both anthropogenic and natural sources [2]. Due to anthropogenic activities such as fertilizer application, waste disposal and mining, the rate of environmental pollution and releasing significant amounts of potentially harmful compounds has increased alarmingly [3]. Concerning safe food production, the entry of heavy metals into the food chain is a significant problem as it can lead to poisoning and diseases in humans and animals [4]. Several approaches are being utilized to deal with this issue of heavy metal contamination, but most of these are expensive and often would not even produce better results [2]. As a result, global-scale interest has been gained in developing economically efficient and ecologically friendly approaches and technologies to deal with heavy metal contamination [5]. Physicochemical technologies such as chemical precipitation, membrane filtration, adsorption, coagulation flocculation, photocatalytic degradation, ion exchange, and oxidation with ozone and hydrogen peroxide are typically used to decontaminate polluted sites [6]. These technologies are expensive and difficult to integrate into a single process to meet emissions regulations [6, 7]. Therefore, phytoremediation has been identified as one of the most promising techniques for the in-site remediation of heavy metal-contaminated soil and water, for both inorganic and organic pollutants [8].
Phytoremediation is the process of using plants to remove hazardous chemicals from soils and groundwater in contaminated sites [9]. Some plant species can store exceptionally high quantities of heavy metals within plant tissues without impairing their growth [3]. However, mine reclamation and biogeochemical exploration solely depend on proper plant selection. According to previous studies, 163 plant species from 45 families have been discovered to be metal-tolerant and suitable for flourishing in the presence of harmful metals at elevated concentrations [9, 10]. Plant species with high resistance to heavy metals, and long and fast-growing root systems, are often chosen as remediates [11]. Phytoremediation can be seen as a long-term remediation strategy since many cropping cycles persist over several years, which is required to decrease metals to acceptable levels [10].
According to Nafea et al. [12], Cyperus rotundus is a safe and affordable bioremediation agent that has a massive ability to load high amounts of heavy metals in their root and shoot systems. Moreover, it gives an immense contribution to the restoration and rehabilitation of natural aquatic and terrestrial systems. Thus, the objectives of this review are to summarize the current literature on phytoremediation, the type of heavy metals which could remediate by C. rotundus and the processes and techniques of phytoremediation by C. rotundus.
The aromatic sedge Cyperus rotundus L belongs to the family Cyperaceae. In damp or dry soil, it thrives as a perennial plant next to water sources [12]. Cyperus rotundus is among the world’s most aggressively invasive weeds and is prevalent throughout India [13]. It is often known as java grass, nut grass, purple nut sedge, mastha, red nut sedge, tiger nut, rhizoma cyperi, motha and nagarmotha. C. rotundus can be found in a wide range of agro-climatic zone and is common in temperate, tropical, and subtropical parts of the globe, such as South, South East and Central Asia, Africa, South and North America, and Australia [13].
The word Cyperus has been derived from the Greek term ‘kuperos’, which means ‘round’, while rotundus is Latin for ‘round’. Its tubers, which look like nuts but are botanically unrelated to nuts, have earned it the labels ”nut grass” and ”nut sedge” [9]. Cyperus rotundus is an erect, glabrous, perennial sedge that reaches a height of 7–40 cm and produces rhizomes and tubers prevalently. It produces an enormous network of subterranean rhizomes with a bulb base from one single tuber, which is 1–3 cm in length. The basal bulb is an enlargement of the rhizomes from which buds emerge to generate new plants [14, 15]. Its leaflets are dark green, linear, grooved on top, and devoid of ligules and auricles [15, 16]. The inflorescences of C. rotundus typically have 2–4 petals, which are comprised of tiny, dark reddish-brown to purplish-brown flowers containing three stamens and three stigmas linked to an unbranched, dark green, and glabrous culm [15, 17]. Typically, C. rotundus produces flowers in the summer and fruits in the winter. The tubers are triangular in shape, oblong-ovate, 12 mm thick, 10–35 mm long, yellow in color, and become black at maturation [15].
In many regions of the world, purple nutsedge (Cyperus rotundus L.) is one of the most problematic weeds. It often reproduces through tubers. This invasive plant is a problem for agriculture because of its quick growth, fierce competition for soil resources, herbicide resistance, and great adaptation, all of which result in substantial yield losses [15]. Compared to C3 weeds, it is a challenging C4 weed with a high photosynthetic capacity [18]. Rhizomes, which may expand upward, downward, or horizontally, are responsible for the plant’s short-term spread. Cyperus rotundus is a major weed of cotton (Gossypium hirsutum L.), maize (Zea mays L.), rice (Oryza sativa L.), sugarcane (Saccharum officinarum L.) and numerous crops [15, 19].
In some countries such as China, India, Iran and Japan, the rhizomes and tubers of Cyperus rotundus have long been used as a home medicine for the treatment of various medical conditions [20]. In traditional medicine, the tubers of this plant are used to treat inflammation, pain, fever, ulcers, burns and blisters, stomach and intestinal diseases, cure cramps, diarrhea, and period abnormalities [13]. In addition, the leaves, tubers, rhizomes, and seeds of C. rotundus demonstrate broad-spectrum action and are gaining prominence in perfumery, spices, culinary flavoring agents, pickles, curries, and numerous bakery goods throughout the world [13]. C. rotundus is widely utilized in the traditional systems of medicine of many Asian nations to alleviate a wide range of clinical conditions. Volatile and nonvolatile bioactive metabolites with essential pharmacological and therapeutic activities are primarily found in the subterranean rhizomes and tubers. The roots, tubers, and rhizomes of C. rotundus contain essential oil, which is the primary source of biologically active volatile metabolites. Its primary constituents are monoterpene aldehydes, monoterpene esters and hydrocarbons, monoterpene ketones and oxygenated monoterpene derivatives. The pharmacological and biological potential of C. rotundus is extensive. Antiallergic activity, Antianrdogenic property, Antiarthritic property, Anticarcinogenic property, Antidiarrhoeal activity, antimicrobial property and Antiinflammatory activity are all examples of C. rotundus’ wide spectrum of pharmacological and biological potential [13].
Since Cyperus spp. have a high capacity to withstand harsh climatic conditions [4], it grows very quickly and generates a substantial amount of aerial and subsurface biomass. Consequently, Cyperus rotundus shows a significant concentration and accumulation potential of heavy metals. Aside from all this, Cyperus rotundus may give a large root surface area, which is advantageous for the phytoremediation of oil-containing heavy metal-contaminated soils [8].
The term “heavy metal” can refer to any hazardous metal, regardless of its atomic mass or density [21]. An unclear set of elements that have metallic characteristics includes heavy metals. These include lanthanides, actinides, certain metalloids, and transition metals [22]. Any metal (or metalloid) may be regarded as a “contaminant” if it appears in an unintended location or in a form or intensity that has a negative impact on people or the environment. Lead (Pb), cadmium (Cd), mercury (Hg), Arsenic (As), chromium (Cr), copper (Cu), selenium (Se), Nickel (Ni), silver (Ag), and zinc are among the metals and metalloids (Zn). Aluminum (Al), Cesium (Cs), cobalt (Co), manganese (Mn), molybdenum (Mo), strontium (Sr), and uranium (U) are other less frequent metallic pollutants [21]. Environmental sources of metals include both natural geological processes and human actions. The displacement of specific pollutants from groundwater or subsurface soil layers, atmospheric depositing from volcanic activity, migration of continental specks of dust and, excessive weathering of mineral and metal ions from rocks are examples of natural sources [23]. According to Singh et al. [21] and Ghori et al. [24], disposal of industrial solid and liquid waste, wastewater sludge application, military activities, mining operations, utilization of agricultural chemicals, automobile emission, and energy production are frequent anthropogenic sources of heavy metals. Elevated concentrations of heavy metals can cause soil quality deterioration, crop yield losses, and poor agricultural productivity, causing significant risks to humans, animals, and ecosystem health [25, 26]. Many heavy metals are persistent in the environment and dietary meals. These are necessary in smaller doses for proper health, but in big quantities, they can indeed be toxic or hazardous [27]. Excess metal concentrations in farmed soils alter food quality and safety. In addition, high heavy metal concentrations increase the danger of kidney dysfunction, liver dysfunction, sterility, malignancies, neurological disorder, lymphoma, mental sickness and other toxicity issues [28]. Table 1 illustrates the types of heavy metals, their sources and their effects on human health. Arsenic (As) has a semi-metallic characteristic, which is noticeably poisonous and carcinogenic [27]. Arsenic (As) could be encountered by humans in a variety of ways, including natural and artificial sources [27]. Millions of individuals are chronically exposed to the As in many areas where groundwater is heavily contaminated [29]. There are various possible sources of As contamination in drinking water, such as the use of As-containing pesticides, the presence of As in naturally occurring mineral formations and the improper disposal of As-containing substances [27]. Individuals who work in industries that involve in pottery, glass production, smelting and refining of metals, production and usage of pesticides, preservation of wood materials and semiconductor production are more inclined to be exposed to the As [29]. Hyperglycemia, neurological issues, liver and renal failures are brought along with low to moderate amounts of the As exposure. Women are more susceptible than males to As-induced skin dermatitis. The As exposure is characterized by skin conditions such as keratosis, melanosis and pigmentation [30]. The toxicity of cadmium (Cd) in the environment is a major concern. Humans can be exposed to higher levels of Cd in a variety of ways where cigarette smoking is one of the major methods. Emissions from industrial processes such as mining, smelting, production of batteries, pigments, stabilizers and alloys are other contributors to Cd levels in the environment [29]. Cadmium (Cd) has been shown to have devastating effects even after minimal exposure. Cadmium (Cd) fumes may cause significant harm to the respiratory system if inhaled, including difficulty breathing, mucous membrane disruption and lung edema [31]. Furthermore, Cd can cause injury to developing brains and other organs of the fetus. The kidneys are especially vulnerable to cadmium toxicity because it tends to build up in the proximal tubular cells. Cadmium (Cd) can induce bone mineralization by either bone injury or renal failure [27, 31]. Lead (Pb) is a bluish-gray metal, naturally found in trace amounts in the crust of the earth. Despite the fact that Pb is a naturally occurring metal, human activities like the combustion of fossil fuels, mining and industries cause significant amounts to be released into the environment [29, 32]. Pb mostly gets into the body through gastrointestinal and respiratory pathways. Ingested Pb carries through the blood and builds up in the bones as insoluble phosphate. Moreover, this metal harm fundamental physiological functions, genetic expressions, anatomical systems and organs, including kidney, liver, reproductive, neurological, and immunological systems [28]. Chromium (Cr) has been identified as the seventh most prevalent element on Earth [33]. Chromium (Cr) is released into the environment from a diverse range of human and natural sources, particularly, industrial enterprises becoming the main source of release. Metal processing, chromate manufacturing, stainless steel welding, and the manufacture of ferrochrome and chrome pigments are the industries that contribute to the Cr release [29, 34]. Both Human and animal allergenicity and carcinogenicity are induced by Cr. In addition to triggering dermatitis allergies and nasal septum perforations, Cr is also clearly accountable for certain incidences of lung cancer. Some genetic changes occur as a result of Cr exposure, which leads to genetic defects [27, 34]. Mercury (Hg) serves as the most hazardous non-essential metal to humans [35]. Many human activities, including pharmaceutical, paper and pulp preservation, agriculture, chlorine and caustic soda manufacture sectors contribute to the environmental contamination of Hg. Mercury is a pervasive environmental contaminant and toxicant that causes extensive mutations and a variety of significant health consequences. Mercury could react with other elements to produce harmful organic and inorganic Hg-containing compounds [27, 36]. Long-term exposure to Hg results in impaired focus, hazy eyesight, and unstable walking. High levels of Hg exposure induce brain impairment and fatality. The Hg has harmful effects on the fetus that induce damage to the brain, blindness and neurodevelopmental delays [37]. Nickel (Ni) is regarded as a crucial component for many essential biological functions of humans. However, prolonged exposure to Ni might cause harmful effects on the human body [31]. The primary cause of the rise in Ni contaminants and the health hazards from Ni is the expansion of industrialization. Increased use of Ni metal refinement and fossil fuel burning, both contribute to a higher level of Ni-containing residues in the atmosphere and cause deterioration of air quality [28, 38]. Therefore, Chronic bronchitis, respiratory illnesses and lung cancer are caused by a high level of Ni contamination. Furthermore, Ni exposure has the greatest impact on the kidneys and causes kidney failures [28, 30]. Copper (Cu), a metallic element found naturally in all living things, is required in trace amounts for the survival of living begins. However, blooming industrialization has increased Cu pollution in the environment. Mining, refining and manufacturing of copper-based commodities such as wires, pipes, and sheet metals, as well as the burning of fossil fuels are the primary contributors of environmental Cu pollution [39]. Severe Cu poisoning causes gastrointestinal discomfort with symptoms like nausea, vomiting, and abdominal pain. Liver damage might occur at high dosages which is enough to cause mortality. Copper destroys red blood cells in which can lead to anemia. The liver and kidneys are particularly vulnerable to Cu toxicity and discrepancies in metabolic pathways [34, 39]. Zinc (Zn) is a very important mineral for human health, since it plays a key role in the production and control of a wide variety of proteins and enzymes. However, Zn in excess can be hazardous, leading to acute toxicity in living organisms [40]. The primary sectors contributing to the global Zn contamination are oil refining, plumbing and brass production. Exposure to Zn-contaminated food and drink can cause an acute gastrointestinal disease indicated by abdominal cramping, diarrhea and vomiting. Exposure to industrial operations such as galvanization often results in the inhalation of fumes containing Zn, resulting in serious respiratory problems [34, 40].
Metal toxins can be contained as insoluble deposits, preventing them from interfering with important cellular level cytoplasmic metabolic activities [41]. Due to the fact that metals are non-biodegradable, they cannot be decomposed by natural processes. Heavy metals persist in the soil and sediment environment for a long time before being discharged to outside of the environment. They can also build and decay to become more poisonous when they react with other materials in the soil or sediment. Inorganic mercury and bacterial activity soil can transform into lethal methyl mercury, which people can subsequently ingest [42]. Due to the advent of heavy metals into the food chain, the ecosystem is deteriorating. In addition, heavy metals lessen the biodegradability of organic contaminants and create a multiplicative impact on environmental pollution. Excessive metals present in the soil pose a threat to the entire biosphere and are taken up by plants and animals through direct absorption and ingestion, posing a threat to the food chains. Also, the presence of these metals in soil alters the soil’s physical and chemical properties and natural chemistry, thereby reducing the quality of the soil and polluting the water [41]. Pollutants can exist in various states of surface waters, solutions, and suspensions. They may be carried over great distances by water, which allows particles to sink to the bottom. Droplets of liquid can either sink into the sediment or float to the surface. When a contaminant is transferred into the sea and oceans, the wind and currents convey it further. Then through marine life, persistent heavy metals can infiltrate the food chain [41]. Since the heavy metal contamination challenges safe access to quality water, food security and environmental and health concerns, it directly links with considerable economical damage in a nation. Therefore, efforts to reduce heavy metal concentrations in the environment in a cost-effective and safest way have become a major concern.
| Metal | Main sources | Harmful effect on humans | References |
|---|---|---|---|
| Arsenic | Fertilizers, pesticides, semiconductors, dyes | Cancer, death, nausea and vomiting | [27, 28] |
| Cadmium | Coal, mineral fertilizers, pesticides, batteries | Lung damage, kidney diseases, reproductive defects, defects in the growing fetus | [27, 30] |
| Lead | Paint production, mining, coal burning, pesticide, gasoline | Damage to the brain and renal system, neurological, hematological defects | [32, 70] |
| Chromium | Stainless steel, electroplating, paints, cement, mining | Asthma, cancer, renal damage, skin irritation, liver damage | [34] |
| Mercury | Batteries, pesticides, light bulbs | Nerve damage, defects in a growing fetus, kidney failure, lung damage | [36, 71] |
| Nickel | Steel industry, coal, gasoline, mining, electroplating | Brain and liver damage, kidney failure, lung cancers, allergies | [28] |
| Zinc | Brass industries, metal plating, plumbing operations, oil industry | Renal defects, anemia, skin defects, respiratory problems | [28, 34] |
| Copper | Mining, pesticides, fungicides, metal industry | Kidney dysfunction, liver damage, bone diseases, gastrointestinal discomfort | [39] |
The working process of phytoremediation is mainly influenced by the root rhizosphere by absorbing heavy metals through an extended root system, either depositing metals in the root biomass or transferring them to the stems and leaves [9]. Until the plant is harvested, it could continue to absorb toxins. After harvest, a lesser concentration of contamination will persist in the soil [9, 43]. Moreover, the plant species had different acceptable concentrations and accumulation potentials. The majority of metals absorbed by plants are either bonded to the cell wall or accumulated between the cell wall and the cell membrane [44]. Root cell vacuoles have a very high ability to absorb and retain metal ions. Certain substances, including metallothionein, inhibit toxicity by forming complexes with heavy metal ions such as copper [4, 45]. Some plant species have defensive mechanisms that increase the ability for heavy metal absorption, aggregation, and concentration in the root tissues and prohibit the ions from moving from the root to the shoot, particularly to its most sensitive organelles, the chloroplasts and photosystems [24]. Large regions polluted with low to moderate concentrations of heavy metals are amenable to phytoremediation techniques that emphasize the soil. Extremely polluted sites cannot be treated with phytoremediation because the extreme circumstances do not permit plant development. The maximum depth of soil that may be cleaned or stabilized is limited to the root zone of the plants. This depth might range from a few inches to many meters, depending on the plant [10]. Different plant species have specific mechanisms for the remediation of heavy metals (Figure 1) in their own surroundings including phytoextraction, rhizofiltration, phytostabilization, phytovolatilization, phytostimulation and phytotransformation.
Figure 1: Various mechanisms of phytoremediation
Phytovolatilization; Removing pollutants as volatiles. Phytoextraction; Pollutants accumulated in plant parts. Phytodegradation; Degradation of pollutants into an inactive form. Phytostabilization; Process of immobilizing pollutants. Phytostimulation; Stimulating microbial activity and breaking down pollutants.
Plants absorb metals from the soil and transport them to harvestable plant parts, and they accumulate inside the plant organs [43]. Plants could phytoextract both essential (Cu, Mg, Mo, K, Fe, Mn, Ni, P, and Zn) and non-essential (Se, B, Cd, Co, Cr, Ag, and Hg) metals required for plant growth [46]. To be successful, phytoextraction relies on several plant properties, including its ability to quickly build biomass and its capability to store substantial quantities of elements in the shoot tissue [47].
6.2 RhizofiltrationThe mechanism of purifying water via a dense network of roots eliminates toxic heavy metals. Toxins are absorbed or adsorbed by the roots [9]. Plant suitability for rhizofiltration is determined by the root system; it should have a more comprehensive, hairy root system with a large surface area. Plants use the rhizofiltration process to remove heavy metals and radioactive elements such as Cd, Cu, Ni, Pb, Cr, Cs, As, U, and Sr [46]. The phytoremediation technique rhizofiltration is a potential option for this typical way of remediation of metal from aquatic habitats. The process entails hydroponically cultivating plants and replanting them into metal-contaminated waterways. Then, their roots absorb and accumulate the metals. Metals can precipitate on root surfaces as a result of root exudates and pH variations in the rhizosphere. Roots or whole plants are collected and disposed, as plants become saturated with metals [48]. The use of this strategy for remediation may involve more difficult and prone to failure than alternative approaches of comparable cost. The maintenance of effective hydroponic systems and hydroponic transplants will contribute to the success of the project [10].
6.3 Phytostabilization /PhytorestorationThe process by which pollutants are removed from soil or water and transforming heavy metals into a less toxic state and immobilizing the pollutants [9]. Plants immobilize the heavy metals in soils by root adsorption, complexation and precipitation into nontoxic forms [46]. This method is a specialized version of the in-situ inactivation method, whereby the functionality of plants is subordinate to the function of soil amendments. Phytostabilization, unlike other phytoremediation procedures, does not aim to eliminate metal pollutants from a site but also to stable them and lessen the danger to animals, plants and the environment [47]. As a result, metals are less likely to enter the food chains and move into the environment [49]. The polluted soil can be amended with organic or inorganic materials to increase the effectiveness of phytostabilization. By altering the soil pH and redox potential of the soil, these soil amendments can change metal speciation, decrease heavy metal dissolution and bioavailability [5].
6.4 PhytovolatilizationThe process of removing pollutants by converting them to less hazardous volatile compounds utilizing plants, in conjunction with the process of plant transpiration [46]. Metal pollutants including As, Hg, and Se may exist as vapor compounds in the environment. Phytovolotalization is done through naturally occurring or genetically engineered plants that can collect heavy metals from the soil, physiologically transform them into gasses within the plant, and release them into the atmosphere. Once toxins have been eliminated by volatilization, there is no way to stop them from migrating to other places compared with other remediation methods [47]. However, according to Yan et al. [5], pollutants are not entirely eliminated by phytovolatilization; some remain in the environment. Contaminants just move from the soil to the atmosphere, whereupon they pollute the surrounding air with potentially hazardous volatile chemicals. Furthermore, rainfall could re-deposit chemicals in the soil.
6.5 PhytostimulationThe process of stimulating soil microbial activity in order to break down pollutants, often by symbiotic associated relationships of microbes with plant roots [9]. Large numbers of various microbial populations thrive in this soil. Thus, plant roots emit plant exudates that supply carbon and energy for microbial growth and development. This combination of plants and microorganisms is utilized to boost the biodegradation of heavy metals and pollutants [43]. Phytostimulation alters the properties of the rhizosphere and allows for rhizodeposition [50].
6.6 Phytotransformation / PhytodegradationThe mechanism of chemical alteration of pollutants by using plant metabolism into the inactive, degraded or immobilized form [9].
To remediate metal from polluted soils, phytoextraction and phytostabilization have been proposed and focused more than the other methods [4]. When designing a phytoremediation approach for a contaminated location, ecological concerns must also be considered. Particularly, one must evaluate the potential effects of phytoremediation on local ecological connections, especially those affecting other crops. Since phytoremediation plants would be cultivated in polluted soil and water, where other crops may not survive due to contaminant toxicity, the problem of crop competition is unlikely to develop [47]. Lum et al. [3] study has revealed that Cyperus rotundus has the capacity to extract Cr and Rb from polluted soils containing up to 20 ml/kg of engine oil levels. According to Subashini et al. [9], C. rotundus grass species is recommended for the remediation of cadmium and chromium-contaminated soils since it acts as an efficient accumulator of cadmium and chromium. Nafea et al. [12] identified that C. rotundus could absorb and accumulate As, Cd, Pb, and Zn in their roots and shoot systems when the soil is heavily contaminated with heavy metals.
For most plants, high heavy metal concentrations in soil, water, and sediments are prevalent stress factors. But specific plant species are capable of changing their environments in order for them to survive [51]. Plant species that thrive in heavy metal-contaminated environments may be divided into three major classes based on their adaption techniques and heavy metals content: metal excluders, indicators and hyperaccumulators [52]. When it comes to phytoremediation, hyperaccumulator plants are a common option [53]. In contrast to the vast majority of plants which are hyperaccumulators store a wide range of metals and metalloids in their tissues at concentrations hundreds or thousands of times higher than the average plants [54, 55]. Metal excluders are plants that may avoid heavy metals from migrating from their roots to their aboveground tissues. In comparison to the increased metal content in their roots, some species could retain relatively low metal content in their shoots. Indicator plants are plants that may collect metals in aboveground tissues; therefore, the metal concentrations in the tissues represent the metal concentrations in the soil. However, as long as heavy metals are accumulated, this sort of plant will eventually perish [53]. According to Ashraf et al. [56], C. rotundus L was considered to be a potential hyperaccumulator plant for use in upcoming phytoremediation experiments. It is a challenge to identify species that possess all of the required characteristics to meet the hyperaccumulation criterion. Phytoextraction is a convoluted process since metal availability varies geographically within a region and impacts a plant’s ability to absorb it. Therefore, Ashraf et al. [57] identified Cyperus rotundus is the only species that meets the requirements as a hyperaccumulator. Then time to time, the use of Cyperus for phytoremediation has indeed been discussed in a variety of ways.
The study of Sultana et al. [2] tested the extent which Cyperus rotundus might tolerate Nickel with a hydroponic solution test. Knop’s hydroponic solution was used in pots, and the plants were cultivated there and the intake was calculated for a period of 7 days. According to the results, it was shown that Cyperus rotundus could withstand nickel concentrations as high as 16mg/l for at least five days. Cyperus rotundus was reported with strong phytoremediation capability at a nickel content of 14mg/l. Nafea et al. [12] examined the efficacy of C. rotundus as a biocompatible material for removing heavy metals including As, Cd, Pb, and Zn from contaminated soils. From that study, it was revealed that Cyperus rotundus has a strong capability for removing heavy metals from the soil and accumulating them in its tissues. Roots of C. rotundus plants were observed to absorb and accumulate heavy metals from the polluted soil at a far higher rate than shoots of the other plant species studied. According to Nafea et al. [12], Arsenic is the highest absorbed metal among other metals, recorded with 109 mg/g dry weight in roots and 75 mg/g dry weight. And with the increasing concentrations of As, Cd, Pb, and Zn heavy metals in the irrigation water, the accumulation of heavy residues has increased in every treatment. Moreover, this was proven by the finding of Garba et al. [53] that Cyperus rotundus has an immense ability to remediate Zn, Cd, Ni and Pb metals, respectively. According to Garba et al. [53], Cyperus rotundus could be utilized effectively as a phytostabilizer for Zn, Pb, and Ni. This method lowers metal movement and leaching into groundwater, as well as the bioavailability of metals for entrance into the food chain. In comparison to phytoextraction, there is no need to dispose of the metal-absorbed plant material using this method. Additionally, the grass could act as a Cd metal indicator. These plants are capable of accumulating metals in their roots and concurrently translocating them to their shoots; hence, the metal levels in the shoots reflect the metal content in the soil. Jahan et al. [4] study revealed that C. rotundus possesses the key characteristics of a copper-tolerant plant species. C. rotundus can tolerate copper stress up to 300 mg per kilogram of soil and assist copper accumulation in the roots, tubers, and shoots without affecting the dry matter of the subterranean organs. Moreover, it revealed that C. rotundus does not show any stress-related signs, including leaf discoloration, leaf withering, decreased leaf chlorophyll quantity, bowed shoots or weak roots, which proves the copper-resilient ability of the plant. With the increased concentration of Cu, contamination created a severe rise in the copper content in the shoot tissues. Ashraf et al. [56] conducted a Sn accumulation experiment on three Cyperus species in pots with varying concentrations of Sn. High potentials for aboveground Sn accumulation were confirmed for the Cyperus species evaluated. In all of the species studied, Sn was taken up by the aboveground parts of the plants rather than being stored in the roots. Leaves accumulated considerably more heavily than branches did. The study showed that Cyperus has a strong accumulation capacity which makes them a good candidate for Sn phytoremediation.
7.1 Bioconcentration factors (BCF) and Translocation factors (TF)Phytostabilization potentially benefits from plants’ tolerance and accumulation of toxic metals. So that the bioconcentration factor (BCF), which is defined as the ratio of the metal concentration in the roots to metal concentration in the soil, would be used to evaluate the capacity of a plant to accumulate metals from soils [58]. The capacity of a plant to move metals from its roots to its shoots is referred to as the translocation factor (TF) [59]. Moreover, the translocation factor (TF) is used to compare metal translocation levels in plants from the root zone to the respiratory organs [60]. However, the ability of a plant for phytoremediation may be estimated in two ways: by its bioconcentration factor (BCF) and by its translocation factor (TF) [58]. In most cases, the process of phytoextraction needs the movement of heavy metals to the parts of the plant that can be harvested with relative ease [61]. Heavy metals must be transported to the plant sections that can be extracted successfully during the phytoextraction process. The capacity of various plants to absorb metals from soils and translocate them to the shoots can be compared by measuring their BCF and TF, respectively. Although hyperaccumulators aggressively take up and translocate metals into the aboveground biomass, tolerant plants tend to limit soil-to-root and root-to-shoot transfers, resulting in significantly lower accumulation. Most probably, phytoextraction cannot be performed on plants with lower BCF and TF values [62]. Plants that possess both TF and BCF values more than one have the ability to be exploited for phytoextraction. If the BCF is higher than one and the TF is less than one, the plants have the ability for phytostabilization [62].
Subashini et al. [9] revealed that cadmium has a BCF value of 44.18 and 4.42 BCF value for chromium. These BCF values suggested that the C. rotundus species of sedge, is an efficient accumulator of Cd and Cr and hence, it can be used to advocate for use in the remediation of cadmium and chromium-contaminated soils. Soils polluted with old engine oil at concentrations of up to 20 ml/kg may be amenable to the extraction of Cr and Rb by Cyperus rotundus [3]. Cd concentrations of 20 ml/kg and Rb concentrations of 20 ml/kg are suggested for phytostabilization in oil-contaminated soil, respectively. Cyperus rotundus had reported substantial BCF values for Zn, Rb and Cd. It shows a maximum BCF value for Cd in the oil-free soil, and this value declined with increasing oil content [3]. Table 2 indicates different BCF and TF values of Cyperus rotundus. The Cyperus plants living in the mining areas have the capacity to extract the metals from the soil and deposit heavy metals in plant roots and shoots. According to Shingadgaon and Chavan [63], the bioconcentration factor (BCF) and translocation factor (TF) of Cyperus rotundus on different heavy metals could be indicated as follows: BCF: Fe>Co>Cr>Zn>Mn>Ni>Cu>Pb>Cd and TF: Cd>Cu>Fe>Ni>Mn>Pb>Co>Zn>Cr.
| Metal | Heavy metal accumulation (mg/kg) | BCF value | TF value | References |
|---|---|---|---|---|
| Zinc (Zn) | Root 384.90 Shoot 306.20 |
1.31 | 0.80 | [64] |
| Root 257 .00 Shoot 97.00 |
2.57 | 0.377 | [63] | |
| Root 435.006 Shoot 459.002 |
1.38 | 1.55 | [53] | |
| Lead (Pb) | Root 39.90 Shoot 34.10 |
1.71 | 0.85 | [64] |
| Root 335.006 Shoot 159.002 |
1.31 | 0.47 | [53] | |
| Root 163.00 Shoot 89.00 |
1.63 | 0.546 | [63] | |
| Cadmium (Cd) | Root 0.94 Shoot 0.65 |
2.35 | 0.69 | [64] |
| Root 68.00 Shoot 66.00 |
0.68 | 0.971 | [63] | |
| Root 291.008 Shoot 258.002 |
1.01 | 0.89 | [53] | |
| Nickel (Ni) | Root 8.00 Shoot 9.002 |
14.00 | 1.29 | [53] |
| Root 222.00 Shoot 127.00 |
2.22 | 0.572 | [63] | |
| Copper (Cu) | Root 26.62 Shoot 22.72 |
1.25 | 0.85 | [64] |
| Root 186.00 Shoot 121.00 |
1.86 | 0.651 | [63] | |
| Root 0.565 Shoot 0.272 |
0.409 | 0.481 | [65] | |
| Manganese (Mn) | Root 2.581 Shoot 1.432 |
1.942 | 0.554 | [65] |
| Root 244.00 Shoot 136.00 |
2.44 | 0.558 | [63] | |
| Root 689.12 Shoot 78.46 |
0.5623 | 0.432 | [57] | |
| Tin (Sn) | Root 194.80 Shoot 658.12 |
0.4022 | 10.215 | [57] |
Garba et al. [53] investigated the BCF and TF values at various concentrations of Zn, Cd, Ni, and Pb heavy metals. The study conducted by Garba et al. [53] has revealed that for Zn, Cyperus rotundus could be recommended for phytostabilization of Zn in the root since its BCF values are larger than one and its TF values are less than one. With a larger concentration of Zn in the root than in the shoot, C. rotundus can stabilize the soil. This finding completely agrees with Sabo and Ladan [64], where the BCF value is larger than the TF value of Zn. Lum and Chikoye [3] also recorded a higher BCF value of 1.1 for Zn, while Shingadgaon and Chavan [63] recorded a BCF value of 2.57 for Zn in C. rotundus, which is higher than one. The Pb is also showing such phytostabilization ability due to higher BCF values and its low TF values. In terms of metal uptake, Pb accumulation in root tissues is higher than the shoot tissues, due to the endodermis’s casparian strip obstruction [65]. Ashraf et al. [57] reported that the greatest quantities of Pb were found in five mining site plant species, including Cyperus rotundus. Moreover, Shingadgaon and Chavan [63] recorded BCF and TF values for Pb as 1.63 and 0.546, respectively, which shows greater BCF value and lower TF value. The majority of BCF and TF values for Cd (Table 2) are almost equal to one or less than one, indicating that for Cd, C. rotundus might be considered as a possible metal indicator. According to Lum et al. [3] with an increase in concentration of Cd, a growing trend in the translocation factor could be observed. Therefore, such plants may store metals in their roots and simultaneously transport them to their aboveground tissues. Considering BCF and TF values of Mn and Cu, BCF values are larger than one and its TF values are less than one. According to Shingadgaon and Chavan [63], Cu and Mn show TF values of 0.651 and 0.558 respectively, which are less than one. These values agree with the results of Ashraf et al. [57] which show TF value of Cu as 0.432. Due to that, C. rotundus could be possible phytostabilizer for Mn and Cu. In accordance with Ashraf et al. [57], Sn levels were found to be considerably greater in four plant species including Cyperus rotundus. The emergent macrophyte, Cyperus rotundus had the highest level of Sn at 1990.44 mg/kg. Therefore, this plant could be suggested as a potential Sn hyperaccumulator. According to the study, TF value of Cyperus rotundus for Sn has been indicated as 10.215, which is a greater TF value. Therefore, this value indicates that Cyperus rotundus can acquire more heavy metal in shoots than in root, acting as good accumulator for Sn, rather than a phytostabilizer. According to the table of the studies, Ni has greater BCF values than TF, which indicates that the root tissues collected a greater amount of trace elements than the shoot tissues. Therefore, C. rotundus may be best understood as a Ni stabilizer in the soil because it causes Ni to accumulate in plant roots. Hence, with considering the majority of heavy metal remediation by the sedge, the phytoremediation ability of Cyperus rotundus can be defined as a phytostabilizer for metals, rather than a phytoextractor.
In order to discover plant species and their potential of phytoremediation, significant efforts have been undertaken in many studies. With the help of various studies, Cyperus rotundus has been identified as a potential candidate for the phytoremediation of heavy metal. Though it has hyperaccumulation potential, the ability of up taking these heavy metals mainly influenced by their physiological adaptations rather than metal concentration in the soil [66]. Therefore, understanding these processes is challengeable from soil to root and shoots in one single pot experiment, and the actual field conditions may differ from the experimented conditions. Moreover, sites contaminated by intricate combinations of several pollutants may provide difficulties for phytoremediation using such plant species [67]. Apart from above challenges, there is a risk that metals might be transferred to humans through grazing animals [64]. Furthermore, there is a serious concern regarding how the contaminated plant biomass will really be stored, handled, and placed. Compression and composting of plant biomass reduce and diminishes overall volume, transportation costs but causing in an increment in the leakage of soluble metal-organic compounds. Therefore, proper disposal of harvested plant biomass, without environmental contamination is also a challenge [68]. The hyperaccumulator plants such as Cyperus rotundus, employed in heavy metal phytoremediation are short-lived with poor biomass synthesis and low growth rates, limiting the efficacy of phytoextraction [69]. On average, the remediation of toxic heavy metal polluted soils by phytoextraction takes a longer period, a minimum up to tens of years. Therefore, the relatively slow phase of phytoremediation is a major drawback [68]. The effectiveness of phytoremediation through plant species is frequently and strongly correlated with seasonal weather and climatic conditions. The hyperaccumulation capacity can be diminished by pest and disease attacks along with changing climate in the tropics and subtropics [68].
Due to their persistence and ability to build in soils, heavy metals cause a significant threat to environmental quality and make their way into the food chain which causes serious health issues. By entering food chains, heavy metals restrict access to clean water and threaten food security. Hence, it is crucial to remediate these heavy metals and use the most cost-effective and secure approaches. Phytoremediation, an environmentally friendly way of rehabilitating polluted soil and wastewater, can be a highly efficient and cost-effective method of reducing heavy metal toxicity. In-site phytoremediation of heavy metal-polluted soil and sediment is one of the most promising alternatives to minimize the metal toxicity. According to studies undertaken over the past few decades, C. rotundus is a possible phytoremediator that can be utilized primarily to remediate a variety of heavy metals that include As, Cd, Pb, Rb, Sn, and Zn. C. rotundus is a prevalent Phytostabilizer for most heavy metals rather than a phytoextractor and has a prominent ability to store trace elements inside the root system. Most of these studies reviewed here have been conducted under limited conditions in pot experiments. So that, many additional studies are required to examine the phytoremediation mechanisms of C. rotundus and the hyperaccumulating, phytostabilizing and phytoextracting ability of the plant. In addition, to upgrade the phytoremediation technology to a commercial scale, crop development research is needed with a combination of improved agronomic management and enhanced plant genetic approaches.
