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Ethylenediamine disuccinic acid enhanced phytoextraction of nickel from contaminated soils using Coronopus didymus (L.) Sm
... Heavy metals in soils originate from natural and anthropogenic sources (Sidhu et al., 2018(Sidhu et al., , 2020. Natural sources correspond to lithogenesis, weathering, erosion, and other geological processes (Kabata-Pendias, 2011), while anthropic sources include industrial activities (Antoniadis et al., 2019;Kasemodel et al., 2019), recycling of electronic waste (Jiang et al., 2019), disposal and incineration of solid urban waste (Figueiredo et al., 2019), vehicular emissions (Silva et al., 2017b), and agricultural activities, mainly the use of pesticides and chemical fertilizers (Silva et al., 2016). ...
... Food production in locations close to industrial areas occurs in several regions of the world and is directly related to urbanization, rapid population growth, and high demand for food in large cities Saljnikov et al., 2019). Agriculture in areas that received industrial wastes can promote the transfer of heavy metals from the soil to edible parts of the crops (Sidhu et al., 2018). The consumption of contaminated food represents the main nonoccupational pathways of exposure to heavy metals (Antoniadis et al., 2019;Hu et al., 2018;Sharma & Nagpal, 2019). ...
... The accumulation of metals in crops varies with the metal availability in the soil and mobility in the plant (Bi et al., 2009;Pan et al., 2016). Zhuang et al. (2009) found that the consumption of vegetables was the most significant route of metal exposure for humans, with Cd posing the highest risk to human health due to the high transfer from the soil to the crops (Sidhu et al., 2018). Indeed, Cd was the metal with the greatest translocation from the soil to the edible tissues of 78 food crops grown in contaminated soils in China, with leafy and tuberous root species showing the highest Cd bioaccumulated (Zheng et al., 2020). ...
Food production in areas contaminated by industrial wastes poses a serious risk to farmers and consumers. Here, we evaluate Cd, Cr, Ni, and Pb concentrations in the soils and the edible parts of lettuce, chives, tomatoes, pepper, and cassava plants grown by small farmers in areas contaminated by slag from an abandoned steel plant in Havana, Cuba. The total, environmentally available, and bioavailable concentrations of metals in the soils and the metals bioconcentration factor in the plants were determined. The risks to human health from food and soil ingestion were estimated. The total and environmentally available concentrations of Cd, Cr, and Pb were above values considered safe by international standards, with likely adverse effect on human health. Cadmium was the most bioavailable metal, reflected in the highest accumulation in the crops' edible parts. Even with negligible DTPA-available Cr concentrations in soils, the Cr concentrations in edible parts of the crops exceeded regulatory levels, suggesting that rhizosphere mechanisms may increase Cr availability. The consumption of vegetables represented 70% of the daily intake dose for Cr, Cd, and Ni, while accidental ingestion of contaminated soil is the predominant human exposure route for Pb. Our results demonstrated the health risks associated with cultivating and consuming vegetables grown on metal contaminated soils in Havana and can assist public policies capable of guaranteeing the sustainability of urban agriculture and food security.
... The major producers of flax are Canada, Russia, China, Kazakhstan, the United States of America, and India as shown in Figure 2 [47]. For accumulation and phytoextraction of toxic heavy metals such as lead, arsenic, etc., previous investigations have been conducted [48][49][50][51][52][53][54]. Flax shows a resistance against heavy metals so is an excellent candidate for phytoremediation when grown on metal contaminated soil. ...
... The fruit is a round and dry capsule containing many glossy brown seeds composed of five carpels. The For accumulation and phytoextraction of toxic heavy metals such as lead, arsenic, etc., previous investigations have been conducted [48][49][50][51][52][53][54]. Flax shows a resistance against heavy metals so is an excellent candidate for phytoremediation when grown on metal contaminated soil. ...
... Hosman et al. [53] conducted a pot experiment using flax plants as a phytoremediator for metal contaminated soil which was artificially spiked with Cd (0 (control), 10, 20, and 40 mg kg −1 soil), Pb (0 (control), 150, 500, and 700 mg kg −1 soil), and Zn (0 (control), 400, 800, and 1000 mg kg −1 soil). Compared to the control, a significant reduction in germination percentage was observed in flax seedlings. ...
Flax (Linum usitatissimum L.) is an important oil seed crop that is mostly cultivated in temperate climates. In addition to many commercial applications, flax is also used as a fibrous species
or for livestock feed (animal fodder). For the last 40 years, flax has been used as a phytoremediation tool for the remediation of different heavy metals, particularly for phytoextraction when cultivated on
metal contaminated soils. Among different fibrous crops (hemp, jute, ramie, and kenaf), flax represents the most economically important species and the majority of studies on metal contaminated soil for
the phytoextraction of heavy metals have been conducted using flax. Therefore, a comprehensive review is needed for a better understanding of the phytoremediation potential of flax when grown in
metal contaminated soil. This review describes the existing studies related to the phytoremediation potential of flax in different mediums such as soil and water. After phytoremediation, flax has the
potential to be used for additional purposes such as linseed oil, fiber, and important livestock feed. This review also describes the phytoremediation potential of flax when grown in metal contaminated
soil. Furthermore, techniques and methods to increase plant growth and biomass are also discussed in this work. However, future research is needed for a better understanding of the physiology, biochemistry, anatomy, and molecular biology of flax for increasing its pollutant removal efficiency.
... Nevertheless, chelating agents also have adverse effects on plant growth and development as they can cause etiolation, withering and even death when present in excess amounts (Hasan et al., 2019). Sidhu et al. (2018) previously reported that 2 mmol/kg EDDS significantly decreased shoot and root biomass of the tested plant (Coronopus didymus (L.) Sm.), with significant increases in the H 2 O 2 and malondialdehyde (MDA) contents of the plant leaves. ...
... The maximum MDA and H 2 O 2 concentrations in sunflowers under U and Cd treatments was observed in the set-up with 7.5 mmol/kg EDDS addition. EDDS addition induced more oxidative damage to sunflowers under U and Cd combined stress, which can be attributed to ROS overproduction, promotion of lipid peroxidation, and loss of cell membrane integrity (Sidhu et al., 2018). This might be due to the increased U and Cd accumulation in sunflower tissues when treated with EDDS. ...
... Similar phenomena were observed in our studies. Sidhu et al. (2018) also demonstrated that MDA and H 2 O 2 concentrations were significantly increased when 2 mmol/kg EDDS is added to nickel-stressed Coronopus didymus (L.) Sm. Another possible reason for this is that EDDS is also toxic to plant growth, and it can induce plant oxidative stress in uncontaminated soils (Li et al., 2018). ...
Applying biodegradable chelating agents to assist in phytoremediation is a promising method to increase the remove efficiency of metal pollutants from contaminated soils. The effects of biodegradable chelating agents on improving the phytoremediation capacity in uranium (U) and cadmium (Cd) contaminated soil was investigated using sunflowers, which were grown in pots containing soil with U and Cd added at 15 mg/kg. After 2 months of growth, citric acid (CA), oxalic acid (OA) and ethylenediamine disuccinate (EDDS) at various concentrations (0, 2.5, 5.0 and 7.5 mmol/kg) were applied. The results showed that plant biomass decreased by 12.12% for shoot and 15.74% for root under U and Cd combined stress. Meanwhile, chelating agent treatments, especially with EDDS, enhanced U and Cd stress in plants by decreasing biomass, inhibiting photosynthesis, and increasing malondialdehyde and H2O2 levels. The U uptake of plants after CA addition was significantly greater than that after OA and EDDS addition. Nevertheless, EDDS addition has better effects on Cd uptake than CA and OA addition. U and Cd remove efficiencies reached the maximum following the application of 5.0 mmol/kg CA and 5.0 mmol/kg EDDS, which were 177.48% and 181.51% higher than that of the control, respectively. Furthermore, the bioavailable U content in soils treated with CA were higher than that in soils treated with EDDS, whereas bioavailable Cd content significantly increased due to EDDS addition. These results suggest that biodegradable chelating agents have significant effects on improving the U and Cd phytoremediation potential of sunflowers.
... Co-and chelating agent-related impacts on plant growth may be associated with competition between Co and other vital micronutrients, such as Mg, Fe, and Zn, due to the promotion of bioavailable Co content in the soil by chelating agents (Ferraz et al. 2012;Zhang et al. 2013;Chen et al. 2019). Another possible reason is the impairment of pigment generation with increased chelant-Co contents, thus leading to the inhibition of plant growth (Amari et al. 2014;Sidhu et al. 2018). Under Co exposure, chelating agent-induced reductions in the dry mass of shoots and roots have been reported in Brassica napus L. (Adiloglu 2016). ...
... In the 40-or 60-mg kg −1 Co soil, a high concentration of the chelating agents also significantly (p < 0.05) increased the MDA and H 2 O 2 contents, and EDDS and NTA showed a more obvious response to stress than CA and OA. Chelating agent application, especially that of EDDS and NTA, induced serious oxidative damage to the test plants under Co stress, which was correlated with the generation and accumulation of H 2 O 2 , which degrades lipids and promotes lipid peroxidation and damages the integrity of the plant cell membrane (Bauddh and Singh 2015;Sidhu et al. 2018). This may be associated with the enhanced Co accumulation in the tissues of sweet alyssum when treated with Co and chelating agents, and a high concentration of chelant complexes with Co in the test plants may cause enhanced stress to the plant cells (Wa Lwalaba et al. 2017;Chen et al. 2019). ...
... This may be associated with the enhanced Co accumulation in the tissues of sweet alyssum when treated with Co and chelating agents, and a high concentration of chelant complexes with Co in the test plants may cause enhanced stress to the plant cells (Wa Lwalaba et al. 2017;Chen et al. 2019). Our findings are in agreement with Sidhu et al. (2018), who found enhanced MDA and H 2 O 2 contents under the application of EDDS in nickel-stressed Coronopus didymus (L.) Sm. Similarly, Liang et al. (2019) reported that EDDS increased the phytotoxicity in Pteris vittata L. exposed to As-, Cd-, and Pb-contaminated soil. ...
Purpose
Combining biodegradable chelating agents with phytoextraction is an efficient technique to amend metal-contaminated soils, but most studies have addressed remediation efficiency rather than a comprehensive understanding of the interactions among plant stress, metal accumulation, and metal bioavailability. This study aimed to investigate the effects of biodegradable chelating agents on improving the efficiency of phytoextraction for cobalt (Co)-contaminated soil by sweet alyssum (Lobularia maritima (L.)) and to explore the interrelationships among plant stress, Co accumulation, and Co bioavailability.
Materials and methods
Sweet alyssum (three plants per pot) was grown in pots containing soil with Co added at 0, 40, and 60 mg kg⁻¹, respectively. After 70 days of growth, we added four biodegradable chelating agents (EDDS, NTA, CA, and OA) at various concentrations (0, 2.5, 5.0, and 7.5 mmol kg⁻¹). The plants were harvested after 7 days, and the biomass, reactive oxygen species (ROS) parameters, Co concentrations of the shoot and root, and available Co content in the soil were analyzed.
Results and discussion
The results demonstrate that chelating agents significantly (p < 0.05) improved the phytoextraction capability of sweet alyssum and influenced plant growth and stress. The capability of EDDS to activate Co was higher than that of other chelating agents at identical concentrations in Co-contaminated soils. Furthermore, we observed that a moderate concentration (40 mg kg⁻¹) of Co could promote plant growth and that high concentrations of Co (60 mg kg⁻¹) and EDDS (7.5 mmol kg⁻¹) cause enhanced stress to plant growth, even resulting in lower shoot Co accumulation than that in the moderate EDDS treatment (5.0 mmol kg⁻¹).
Conclusions
The present study demonstrates that the application of EDDS may be a better choice for Co phytoextraction than NTA, CA, and OA; nevertheless, a high concentration of EDDS may enhance the negative effects on plant growth, physiological traits, and Co accumulation.
... The application of EDDS has been shown to decrease the biomass of plants grown in Pb-contaminated soils and the decrease is more pronounced at a high chelate dose (10 mmol kg À1 soil) (Zhao et al., 2016). EDDS can also increase the accumulation of metals in plant tissue, which subsequently induces oxidative damage by increasing the level of reactive oxygen species (ROS) and lipid peroxidation (Cestone et al., 2012;Sidhu et al., 2018). As the main source of ROS, hydrogen peroxide (H 2 O 2 ) and superoxide radicals (O 2 À ) can damage DNA, proteins, lipids, and other cellular components in plant tissues (Woodson et al., 2015). ...
... The application of EDDS increased the Cu-induced accumulation of MDA, O 2 À , and H 2 O 2 in plant organs (Fig. 1), resulting in severe oxidative damage and limitation of plant growth. Increases in MDA and ROS levels in plant organs exposed to metal stress, caused by EDDS application (Sidhu et al., 2018), are owing to the alteration of the lipoxygenase pathway by the accumulated chelant and metalechelate complexes (Yin et al., 2015). The application of EDDS resulted in a negative impact on the antioxidant enzyme system (SOD, CAT, APX, and POD) of alfalfa, confirming that EDDS application increases oxidative damage to the test plant by reducing its ability to scavenge ROS. ...
Chelants application can increase the bioavailability of metals, subsequently limiting plant growth and
reducing the efficiency of phytoremediation. Plant growth-promoting rhizobacteria (PGPRs) and rhizobium
have substantial potential to improve plant growth and plant tolerance to metal stress. We evaluated
the effects of co-inoculation with a PGPR strain (Paenibacillus mucilaginosus) and a Cu-resistant
rhizobium strain (Sinorhizobium meliloti) on the efficiency of biodegradable chelant (S,S-ethylenediaminedisuccinic
acid; EDDS) assisted phytoremediation of a Cu contaminated soil using alfalfa. The
highest total Cu extraction by alfalfa was observed in the EDDS-treated soil upon co-inoculation with the
PGPR and rhizobium strains, which was 1.2 times higher than that without co-inoculation. Partial least
squares path modeling identified plant oxidative damage and soil microbial biomass as the key variables
influencing Cu uptake by alfalfa roots. Co-inoculation significantly reduced the oxidative damage to alfalfa
by mitigating the accumulation of malondialdehyde and reactive oxygen species, and improving the
antioxidation capacity of the plant in the presence of EDDS. EDDS application decreased microbial diversity
in the rhizosphere, whereas co-inoculation increased microbial biomass carbon and nitrogen, and
microbial community diversity. Increased relative abundances of Actinobacteria and Bacillus and the
presence of Firmicutes taxa as potential biomarkers demonstrated that co-inoculation increased soilnutrient content, and improved plant growth. Co-inoculation with PGPR and rhizobium can be useful for
altering plantesoil biochemical responses during EDDS-enhanced phytoremediation to alleviate
phytotoxicity of heavy metals and improve soil biochemical activities. This study provides an effective
strategy for improving phytoremediation efficiency and soil quality during chelant assisted phytoremediation
of metal-contaminated soils.
... These include physical, chemical and biological techniques. Phytoremediation has become a promising, inexpensive, in situ clean-up and environmentally friendly technology for soil remediation as compared with other techniques, which exploits the natural ability of a green plant to stabilize or remove pollutants from soils (Sarwar et al. 2017;Sidhu et al. 2017bSidhu et al. , 2018a. The key to the success of the remediation system is to find plant species that can accumulate or hyperaccumulate heavy metals (Liu et al. 2015b). ...
... To further appreciate the Cd accumulation efficiency in Y. japonica plants, the BCF value was used, which is more vital than the Cd concentrations in plant tissues when judging the feasibility of phytoextraction for a given plant (Zhao et al. 2003;Sidhu et al. 2018aSidhu et al. , 2020. According to Baker (1981), the BCF values ˃ 1 indicates the potential of green plants for remediation of heavy metals polluted soils. ...
Cadmium (Cd) is one of the most toxic contaminants, causing a lot of harm to environment and the human health. An outdoor pot experiment for 60 days was conducted to study the Cd(II) effects on growth, biomass, physiological properties, Cd uptake, and accumulation in Youngia japonica plants but also to evaluate the effect of Y. japonica growth on enzyme activity of Cd-contamination soils. Generally, the application of Cd(II) less than 120 mg kg⁻¹ stimulated the growth of the plants, whereas at 160 mg kg⁻¹ or higher levels, a significant reduction was observed. For all treatments > 10 mg kg⁻¹ Cd(II) in soil, values of Cd in roots and aboveground parts were more than the critical value of 100 mg kg⁻¹ and reached highest values of 252.51 and 314.29 mg kg⁻¹, respectively. The bioconcentration factors (BCF) and translation factors (TF) for all Cd treatments were more than 1.0, with the former ranging from 1.03 to 5.46 and the later from 1.04 to 1.33. The activities of peroxidase (POD) and superoxide dismutase (SOD), as well as the levels of glutathione (GSH) and proline in Y. japonica plants after exposure to 10–200 mg kg⁻¹ Cd(II) were stimulated, implying that they were defensive guards to the oxidative stress produced by Cd. The urease, dehydrogenase, and alkaline phosphatase activities under low Cd concentrations can be enhanced by planting Y. japonica species but inhibited under high Cd concentrations. Our data provide comprehensive evidence that Y. japonica has the typical properties of a Cd hyperaccumulator and thus may be practically employed to alleviate Cd from contaminated soils.
... Shoot metal uptake (Pb, Cd) and translocation factor (TF) were determined by following formulas (Sidhu et al. 2018b(Sidhu et al. , 2020 ...
... Lou et al. (2017) also noted a substantial decrement in chlorophyll (up to 39%) and carotenoid contents (up to 45%) with increasing Cd (50 and 150 mg L −1 ) and Pb (1000 mg L −1 ) contamination as compared to control in Festuca arundinacea Schreb. Pb and Cd stress-induced oxidative stress by increasing the ROS production in plant body such as superoxide radicals (O · 2 − ) (Sidhu et al. 2018b(Sidhu et al. , 2017b. Plants tackle this problem through the production of antioxidants such as SOD which may scavenge these highly toxic superoxide radicals (O · 2 − ) into less toxic form under metal (Cd) stress (Sidhu et al. 2017b). ...
This work aims to assess growth, physiology, and metal uptake response of Brachiaria mutica and Leptochloa fusca under different contamination levels of Cd (10 and 50 mg kg⁻¹) and Pb (50 and 250 mg kg⁻¹) stress. Results of pot trial showed increasing metal concentration affected B. mutica more as compared to L. fusca. In B. mutica metal stress substantially reduced shoot dry biomass, root dry biomass, total chlorophylls, and carotenoids contents by 89%, 85%, 65%, and 61%, respectively, while enhanced the SOD activity up to 62 U min⁻¹ g⁻¹ FW. L. fusca showed better growth, chlorophylls and carotenoid contents, SOD activity (up to 79 U min⁻¹ g⁻¹ FW), shoot metal uptake potential (Cd 110 µg pot⁻¹, Pb 91.57 µg pot⁻¹), and root metal concentration (Cd 126 mg kg⁻¹ dm, Pb 117 mg kg⁻¹ dm) compared to B. mutica under Pb and Cd stress. While both grass species showed metal translocation factor less than unity under all levels of metal stress. Keeping in view the above results, it is concluded that L. fusca having better growth and physiology with TF < 1 could be used for phytostabilization of Pb and Cd to reclaim the soil having moderate to lower levels of contamination.
... The application of EDDS has been shown to decrease the biomass of plants grown in Pb-contaminated soils and the decrease is more pronounced at a high chelate dose (10 mmol kg À1 soil) (Zhao et al., 2016). EDDS can also increase the accumulation of metals in plant tissue, which subsequently induces oxidative damage by increasing the level of reactive oxygen species (ROS) and lipid peroxidation (Cestone et al., 2012;Sidhu et al., 2018). As the main source of ROS, hydrogen peroxide (H 2 O 2 ) and superoxide radicals (O 2 À ) can damage DNA, proteins, lipids, and other cellular components in plant tissues (Woodson et al., 2015). ...
... The application of EDDS increased the Cu-induced accumulation of MDA, O 2 À , and H 2 O 2 in plant organs (Fig. 1), resulting in severe oxidative damage and limitation of plant growth. Increases in MDA and ROS levels in plant organs exposed to metal stress, caused by EDDS application (Sidhu et al., 2018), are owing to the alteration of the lipoxygenase pathway by the accumulated chelant and metalechelate complexes (Yin et al., 2015). The application of EDDS resulted in a negative impact on the antioxidant enzyme system (SOD, CAT, APX, and POD) of alfalfa, confirming that EDDS application increases oxidative damage to the test plant by reducing its ability to scavenge ROS. ...
... The most common type of phytoremediation is phytoextraction in which green plants are cultivated in metalcontaminated soil and accumulate large amounts of metals in their above ground parts; these are hyperaccumulator species [31,48,49]. Previously, many plant species have been used as hyperaccumulators for a range of heavy metals in the soil [23,[50][51][52][53][54][55]. A report presented by Muszynska and Hanus-Fajerska [31] mentioned that around 500 different plant species are known as hyperaccumulators and can accumulate a large amount of toxic pollutants in their aboveground parts without any toxic effects. ...
... In contrast, some plant species have the potential to generate organic acids in their rhizosphere, which may also act as a chelate, creating a complex known as an organic acid complex with metal interactions, and can take up a large amount of metal from the soil [52,96]. [53,97]. Moreover, chelates aid efficient metal phytoextraction but not their elimination, e.g. an increase in low molecular weight organic acids concentration in the rhizosphere provides carbon sources for soil microorganisms that facilitate metal mobilization from the soil to the plant by (a) replacing adsorbed metals at the surface of soil particles through ligand-exchange reactions, and (b) developing metal-organic complexes [97]. ...
Jute (Corchorus capsularis) is a widely cultivated fibrous species with important physiological characteristics including biomass, a deep rooting system, and tolerance to metal stress. Furthermore, Corchorus species are indigenous leafy vegetables and show phytoremediation potential for different heavy metals. This species has been used for the phytoremediation of different toxic pollutants such as copper (Cu), cadmium (Cd), zinc (Zn), mercury (Hg) and lead (Pb). The current literature highlights the physiological and morphological characteristics of jute that are useful to achieve successful phytoremediation of different pollutants. The accumulation of these toxic heavy metals in agricultural regions initiates concerns regarding food safety and reductions in plant productivity and crop yield. We discuss some innovative approaches to increase jute phytoremediation using different chelating agents. There is a need to remediate soils contaminated with toxic substances, and phytoremediation is a cheap, effective, and in situ alternative, and jute can be used for this purpose.
... The most common type of phytoremediation is phytoextraction in which green plants are cultivated in metalcontaminated soil and accumulate large amounts of metals in their above ground parts; these are hyperaccumulator species [31,48,49]. Previously, many plant species have been used as hyperaccumulators for a range of heavy metals in the soil [23,[50][51][52][53][54][55]. A report presented by Muszynska and Hanus-Fajerska [31] mentioned that around 500 different plant species are known as hyperaccumulators and can accumulate a large amount of toxic pollutants in their aboveground parts without any toxic effects. ...
... In contrast, some plant species have the potential to generate organic acids in their rhizosphere, which may also act as a chelate, creating a complex known as an organic acid complex with metal interactions, and can take up a large amount of metal from the soil [52,96]. [53,97]. Moreover, chelates aid efficient metal phytoextraction but not their elimination, e.g. an increase in low molecular weight organic acids concentration in the rhizosphere provides carbon sources for soil microorganisms that facilitate metal mobilization from the soil to the plant by (a) replacing adsorbed metals at the surface of soil particles through ligand-exchange reactions, and (b) developing metal-organic complexes [97]. ...
Abstract: Jute (Corchorus capsularis) is a widely cultivated fibrous species with important
physiological characteristics including biomass, a deep rooting system, and tolerance to metal stress.
Furthermore, Corchorus species are indigenous leafy vegetables and show phytoremediation
potential for different heavy metals. This species has been used for the phytoremediation of different
toxic pollutants such as copper (Cu), cadmium (Cd), zinc (Zn), mercury (Hg) and lead (Pb). The
current literature highlights the physiological and morphological characteristics of jute that are
useful to achieve successful phytoremediation of different pollutants. The accumulation of these
toxic heavy metals in agricultural regions initiates concerns regarding food safety and reductions in
plant productivity and crop yield. We discuss some innovative approaches to increase jute
phytoremediation using different chelating agents. There is a need to remediate soils contaminated
with toxic substances, and phytoremediation is a cheap, effective, and in situ alternative, and jute
can be used for this purpose.
Keywords: fibrous crop; phytoextraction; environmental pollutants; morphological traits; soil
remediation; chelating agents
... Wang et al. (2019) and Yang et al. (2021a) suggested that the addition of GLDA could enhance Cd and As's bioavailability effectively. EDDS was found to improve the phytoextraction of Ni by Coronopus Didymus L. from polluted soils (Sidhu et al., 2018). In addition, Hussain et al. (2019) utilised citric acid for phytoextraction of metals from multi-metal contaminated soil by soybean plant aided by Kocuria rhizophila (Glycine max L.). ...
Phytoremediation is a biological remediation technique known for low-cost technology and environmentally friendly approach, which employs plants to extract, stabilise, and transform various compounds, such as potentially toxic elements (PTEs), in the soil or water. Recent developments in utilising chelating agents soil remediation have led to a renewed interest in chelate-induced phytoremediation. This review article summarises the roles of various chelating agents and the mechanisms of chelate-induced phytoremediation. This paper also discusses the recent findings on the impacts of chelating agents on PTEs uptake and plant growth and development in phytoremediation. It was found that the chelating agents have increased the rate of metal absorption and translocation up to 45% from roots to the aboveground plant parts during PTEs phytoremediation. Besides, it was also explored that the plants may experience some phytotoxicity after adding chelating agents to the soil. However, due to the leaching potential of synthetic chelating agents, the use of organic chelants have been explored to be used in PTEs phytoremediation. Finally, this paper also presents comprehensive insights on the significance of using chelating agents through SWOT analysis to discuss the advantages and limitations of chelate-induced phytoremediation.
... The following are some examples of how plants interact with pollutants. Phytoextraction: This method includes the contaminant being removed from the soil and accumulating in a plant portion (e.g., the root, stem, or leaf) (Sidhu et al., 2018). Phytotransformation or Phytodegradation: The pollutant is converted into a less hazardous form when it is absorbed by the plant. ...
We are pleased to present this book entitled “Recent Advances in Agricultural Science and Technology for Sustainable India”. Ratnesh Kumar Rao, Secretary, Mahima Research Foundation and Social Welfare are not new to Agriculture students. With his vast experience in Academic activities, he has dealt this complex subject and edited, with practical approach and simple language, to meet the requirement of the students and teachers of Agriculture.
The large gap between potential and current crop yields makes increased food production attainable. India’s low agricultural productivity has many causes, including scarce and scant knowledge of improved practices, low use of improved seed, low fertilizer use, inadequate irrigation, conflict, absence of strong institutions, ineffective policies, lack of incentives and prevalence of diseases. Climate change could substantially reduce yields from rainfed agriculture in some countries. With scarcity of land, water, energy, and other natural resources, meeting the demands for food and fiber will require increases in productivity.
Though this book is mainly deals with the agriculture research and education, it will also be very handy for those who desire to start Agricultural Research in Science and Technology. We are sure this will be accepted very much by the students, teachers, scientists and Stakeholders of Agriculture all over the India. We solicit your encouragement in this endeavour.
... Application of agrochemicals like pesticides induce a significant amount of abiotic stress resulting in the production of ROS that leads to the disruption of cellular activities. Antioxidant enzymes mainly superoxide dismutase enzyme (SOD) and catalase (CAT) play a major role in protecting the cell from oxidative damage by scavenging the ROS and optimizing cell function by regulating cellular redox state and modifying gene expression (Sidhu et al. 2018;Singh et al. 2021). Superoxide dismutase enzyme converts superoxide anion-free radical (O 2 ) to H 2 O 2 . ...
The present study was designed to screen the Mesorhizobium strains (50) for tolerance with four recommended pesticides in chickpea. In-vitro, robust pesticide tolerant strains were developed in pesticides amended media over several generations. Further, verification of the multifunctional traits of pesticide tolerant mesorhizobia under pesticide stress was conducted in-vitro. Among different pesticides, significantly high tolerance in Mesorhizobium strains was observed with recommended doses of pendimethalin (37%) and ready-mix (36%) followed by chlorpyrifos (31%) and carbendazim (30%), on an overall basis. Based on multifunctional traits, Mesorhizobium strains viz. MR2, MR17 and recommended MR33 were the most promising. Ecological performance of the potential Mesorhizobium strains alone and in dual-inoculation with recommended PGP rhizobacterium strain RB-1 (Pseudomonas argenttinensis JX239745.1) was subsequently analyzed in field following standard pesticide application in PBG-7 and GPF-2 chickpea varieties for two consecutive rabi seasons (2015 and 2016). Dual-inoculant treatments; recommended RB-1 + MR33 (4.1%) and RB-1 + MR2 (3.8%) significantly increased the grain yield over Mesorhizobium alone treatments viz MR33 and MR2, respectively. Grain yield in PBG7 variety was significantly affected (7.3%) by the microbial inoculant treatments over GPF2 variety. Therefore, the potential pesticide tolerant strains MR2 and MR33 can be further explored as compatible dual-inoculants with recommended RB-1 for chickpea under environmentally stressed conditions (pesticide application) at multiple locations. Our approach using robust multifunctional pesticide tolerant Mesorhizobium for bio-augmentation of chickpea might be helpful in the formulation of effective bio-inoculants consortia in establishing successful chickpea–Mesorhizobium symbiosis.
... Furthermore, enhanced Ni phytoextraction studies have confirmed that EDDS stimulated significant Ni mobilization with the enhanced Ni translocation. (Sidhu et al., 2018). Thus, Ni competition should not be underestimated in the EDDS-enhanced phytoremediation studies. ...
In chelator-enhanced Zn phytoremediation studies, it is crucial to understand how the degradable chelators and the competition from other ions influence the concentration of Zn in the soil solution. This study investigated the biodegradability of two chelators (EDDS: Ethylenediamine-N,N′-disuccinic acid, and NTA: Nitrilotriacetic acid) and their effects on the Zn concentration in the soil solution during the growth of alfalfa (Medicago Sativa L.). The chelators were added at four doses (0, 0.5, 2 and 5 mmol kg⁻¹) in soils with varying Zn levels (189, 265 and 1496 mg kg⁻¹). The results showed that the lag phase before EDDS and NTA biodegradation varied from 0 to 7 days in the three soils. EDDS and NTA were completely decomposed within the assessed 57 days regardless of the applied dosage, with a half-life of 1.3–3.0 days in highly Zn-contaminated soil and 4.2–10.8 days in the two other soils. In soil solutions, the change in solubilized Zn was in line with EDDS and NTA degradation kinetics. Cu, Al, Fe and Mn were the main metal ions that competed against Zn for chelation. Besides, Ni competed with Zn in the whole process. Ca did not compete effectively in the three soils, while Mg was a competitor only at the initial stage. Our results show the importance of considering both the biodegradation rate and the competition between the target cation and other elements present in the soil when using chelators to enhance phytoremediation. A 30-day explorative incubation experiment is recommended to evaluate the appropriate application time of chelators and the target Zn exposure time for plants during phytoremediation.
... According to UNEP (2016), approximately >400 plants have extreme affinity for metal absorption and some of these plants have been reported in recent studies for remediating heavy metals. They include Jatropha curcas (Marrugo-Negrete et al., 2015), Stanleya pinnata (Bañuelos et al., 2015), Brassica juncea (Kathal et al., 2016), Pisum sativum (Tariq and Ashraf, 2016), Puccinellia frigida (Rámila et al., 2016), Brassica napus (Dhiman et al., 2016), Helianthus annuus (Farid et al., 2017), Salix viminalis (Mleczek et al., 2018), Coronopus didymus (Sidhu et al., 2018), Melilotus officinalis and Amaranthus retroflexus ...
Contamination of the environment by heavy metals is one of the major environmental issues which has drawn the attention of researchers globally owing to its grave threat to life especially as it concerns agriculture and water resources. Various human health risks are connected to heavy metals owing to their interrelationship with the food chain. To control this menace, different techniques including chemical, physical, and biological, have been exploited for effective heavy metals and metalloids removal from soils. Among these techniques, phytoremediation is an efficient and cost-effective green technology for heavy metals harvesting from both soil and water environments. This chapter, therefore, discusses phytoremediation as an effective multifaceted process that incorporates the significant effects and activities of both plants and some relevant microorganisms to decontaminate heavy metal polluted soil and water environments. Various mechanisms, recent advances, associated factors and challenges, innovative approaches, and possible future trends for the optimization of phytoremediation of heavy metals are equally discussed.
... Although EDTA has poor biodegradability, it also promotes toxic metal leaching, resulting in groundwater pollution [247]. In this way, microorganism-produced ethylene diamine disuccinate (EDDS) is a naturally occurring boosting material that is particularly successful at increasing toxic metal intake while reducing the risk of water pollution [248]. In contrast to EDTA, which is less bioavailable to Pb and Cd, EDDS improves the solubilizing and mobilization of Cu, Ni, and Zn [249,250]. ...
Contamination of aquatic ecosystems by various sources has become a major worry all over the world. Pollutants can enter the human body through the food chain from aquatic and soil habitats. These pollutants can cause various chronic diseases in humans and mortality if they collect in the body over an extended period. Although the phytoremediation technique cannot completely remove harmful materials, it is an environmentally benign, cost-effective, and natural process that has no negative effects on the environment. The main types of phytoremediation, their mechanisms, and strategies to raise the remediation rate and the use of genetically altered plants, phytoremediation plant prospects, economics, and usable plants are reviewed in this review. Several factors influence the phytoremediation process, including types of contaminants, pollutant characteristics, and plant species selection, climate considerations, flooding and aging, the effect of salt, soil parameters, and redox potential. Phytoremediation's environmental and economic efficiency, use, and relevance are depicted in our work. Multiple recent breakthroughs in phytoremediation technologies are also mentioned in this review.
... For example, the use of EDTA and citric acid (CA) increased the potential of plant extraction of PTEs from the soil by Indian mustard (Guo et al. 2019). In recent years, greater attention has been given to biodegradable and environmentfriendly chelating agents such as EDDS and NTA for extraction of PTEs from soil and sediments (Hartley et al. 2014;Naghipour et al. 2017;Sidhu et al. 2017aSidhu et al. , 2018a. The removal of Cd from marine sediments with EDTA, EDDS, NTA, and CA showed that the removal of Cd with NTA was higher than with EDDS (Song et al. 2016). ...
Phytoremediation has been proposed as a cost-effective method for removing potentially toxic elements (PTEs) from the soil. In this regard, biodegradable chelating agents can be used without harming the environment to increase the efficiency of phytoremediation. In the present work, a greenhouse experiment was conducted to investigate the effect of nitrilotriacetic acid (NTA; 0, 15, and 30 mmol L−1 per pot) on the uptake, chemical forms, and subcellular distribution of Cd in maize (Zea mays L.) grown in Cd-spiked soils (0, 25, and 50 mg Cd kg−1 soil) under leaching conditions. NTA application decreased biomass production (18–33%) yet enhanced Cd concentrations in shoots and roots of maize by more than 50%. Subcellular fractionation of NTA-applied Cd-containing leaves indicated that 41–53% of the Cd was localized in cell walls (FCW), 33–39% in soluble fraction (FS), and 13–19% in cellular organelles (FO). Moreover, NTA enhanced inorganic (FE), water-soluble (FW), and pectates and proteins-integrated Cd (FNaCl) forms, but reduced the insoluble forms (FHAc and FHCl). The increase of FNaCl may possibly help the plant to adapt to Cd stress. Also, NTA decreased soil DTPA-extractable Cd significantly, due to the increase in Cd leached and Cd absorbed by plants. The use of NTA can significantly increase the phytoremediation potential of maize, but it may also increase Cd toxicity in plants exposed to high amounts of Cd. Therefore, it is important to determine the optimal amount of chelator for enhancing phytoremediation.
... In addition, the promoted oxidative stress leads to lipids peroxidation which is harmful to plant growth. Malondialdehyde (MDA) is the final product of lipids peroxidation, whose level in plants can act as an excellent indicator of plant damage (Sidhu et al., 2018). To alleviate the oxidative stress and tolerate adverse effects caused by PTEs, plants have stimulated antioxidant systems comprise several ROS-removing enzymes, comprising of superoxide dismutase (SOD), peroxidase (POD), catalases (CAT), and ascorbate peroxidase (APX). ...
S,S)-ethylenediaminedisuccinic acid (EDDS) has a strong capacity to mobilize potentially toxic elements (PTEs) in phytoextraction. It can release NH 4 þ-N via biodegradation, which can enhance N supply to soil thereafter promote plant growth and plant resistance to PTEs. However, the advanced feature of released N in the EDDS-enhanced phytoextraction remains unclear. In the current study, the effects of N supply released from EDDS on ryegrass phytoextraction and plant resistance to PTEs were investigated in detail by a comparison with urea. Our results supported that the addition of both EDDS and urea increased N concentration in soil solution, yet EDDS needed more time to release available N for plant uptake and transported more N from root to shoot. Additionally, EDDS significantly increased the concentration of all targeted PTEs, i.e. Cu, Zn, Cd, and Pb, in the soil solution, which results in higher levels of their occurrence in plant biomass compared with urea. By contrast, the supply of N slightly enhanced the ryegrass uptake of micro-nutrients, i.e. Cu and Zn, yet it caused negligible effects on nonessential elements, i.e. Cd and Pb. The mobilized PTEs by EDDS lead to elevated oxidative stress because higher levels of malondialdehyde and O 2 À were observed. The supply of N attenuated oxidative stress caused by O 2 À and H 2 O 2 , which was associated with enhanced activities of superoxide dismutase and peroxidase. Our results advanced the understanding of the exogenous N supply and metal resistance mechanisms in the EDDS-enhanced phytoextraction. This study also highlighted that EDDS can serve as a N source to ease N-deficient problems in PTEs-contaminated soils.
... High concentrations of Cd may also inhibit the synthesis of DNA, increase the activity of proteolytic enzymes, and reduce protein content (Yang et al. 2018a). H 2 O 2 as one of the reactive oxygen species is a by-product of oxidative biochemical reactions in plants (Sidhu et al. 2016(Sidhu et al. , 2018a. High concentrations of Cd stress can produce excessive ROS, interfering with the balance between ROS production and elimination in plants, which is the main toxic reaction of plants to Cd (Kaur et al. 2017;Sidhu et al. 2016 Table 1 Environ Sci Pollut Res 2019). ...
In this study, cadmium (Cd) solution spraying and Cd-contaminated soil pot experiments were conducted to investigate the influence of Cd from atmospheric deposition and soil on the growth, cumulative distribution, chemical morphology, physiological, and biochemical responses of Amaranthus tricolor L. The results indicated that Cd in plants mainly came from soil (92–98%) and was stored in the roots in large quantities while the portion from atmospheric deposition could also effectively increase Cd content in stems and leaves (2–3%). Cd was mainly stored in plant cell walls and would transfer to the soluble part under high-concentration soil stress Cd from atmospheric deposition alone promoted the growth of plants, but high Cd concentrations from soil had the negative influence. The contents of H2O2 and MDA in plants increased under soil and atmospheric Cd stress, indicating that the plant cells were damaged by oxidative stress. The content of antioxidant enzymes such as POD, CAT, SOD, and antioxidants like AsA and GSH increased under low-concentration Cd stress but decreased under elevated stress, suggesting that high Cd-contaminated soil poses severe toxicity on the antioxidant system of the plants. Hence, the accumulation and physiological response of plants under multi-source Cd contamination were mainly affected by high soil Cd concentrations. Though the effect of atmospheric deposition is relatively less, it cannot be ignored.
... Phytoextraction: This mechanism involves removal of the contaminant from the soil and its accumulation in some part of the plant (e.g., root, stem or leaf) [65]. • Phytotransformation or Phytodegradation: After the absorption of the contaminant by the plant, it is transformed into a less toxic form. ...
Petroleum hydrocarbons, heavy metals and agricultural pesticides have mutagenic, carcinogenic, immunotoxic and teratogenic effects and cause drastic changes in soil physicochemical and microbiological characteristics, thereby representing a serious danger to health and environment. Therefore, soil pollution urgently requires the application of a series of physicochemical and biological techniques and treatments to minimize the extent of damage. Among them, bioremediation has been shown to be an alternative that can offer an economically viable way to restore polluted areas. Due to the difficulty in choosing the best bioremediation technique for each type of pollutant and the paucity of literature on soil bioremediation enhanced by the use of specific additives, we reviewed the main in situ and ex situ methods, their current properties and applications. The first section discusses the characteristics of each class of pollutants in detail, while the second section presents current bioremediation technologies and their main uses, followed by a comparative analysis showing their respective advantages and disadvantages. Finally, we address the application of surfactants and biosurfactants as well as the main trends in the bioremediation of contaminated soils.
... In addition, the promoted oxidative stress leads to lipids peroxidation which is harmful to plant growth. Malondialdehyde (MDA) is the final product of lipids peroxidation, whose level in plants can act as an excellent indicator of plant damage (Sidhu et al., 2018). To alleviate the oxidative stress and tolerate adverse effects caused by PTEs, plants have stimulated antioxidant systems comprise several ROS-removing enzymes, comprising of superoxide dismutase (SOD), peroxidase (POD), catalases (CAT), and ascorbate peroxidase (APX). ...
S,S)-ethylenediaminedisuccinic acid (EDDS) has a strong capacity to mobilize potentially toxic elements (PTEs) in phytoextraction. It can release NH 4 þ-N via biodegradation, which can enhance N supply to soil thereafter promote plant growth and plant resistance to PTEs. However, the advanced feature of released N in the EDDS-enhanced phytoextraction remains unclear. In the current study, the effects of N supply released from EDDS on ryegrass phytoextraction and plant resistance to PTEs were investigated in detail by a comparison with urea. Our results supported that the addition of both EDDS and urea increased N concentration in soil solution, yet EDDS needed more time to release available N for plant uptake and transported more N from root to shoot. Additionally, EDDS significantly increased the concentration of all targeted PTEs, i.e. Cu, Zn, Cd, and Pb, in the soil solution, which results in higher levels of their occurrence in plant biomass compared with urea. By contrast, the supply of N slightly enhanced the ryegrass uptake of micro-nutrients, i.e. Cu and Zn, yet it caused negligible effects on nonessential elements, i.e. Cd and Pb. The mobilized PTEs by EDDS lead to elevated oxidative stress because higher levels of malondialdehyde and O 2 À were observed. The supply of N attenuated oxidative stress caused by O 2 À and H 2 O 2 , which was associated with enhanced activities of superoxide dismutase and peroxidase. Our results advanced the understanding of the exogenous N supply and metal resistance mechanisms in the EDDS-enhanced phytoextraction. This study also highlighted that EDDS can serve as a N source to ease N-deficient problems in PTEs-contaminated soils.
... On the contrary, non-conventional techniques are proving a boon to mitigate Cd-contaminated ecosystems. Phytoremediation is a one such clean and green approach that employs plants in conformity with the soil microbes for the alleviation of heavy metal contaminants from the soil systems Muthusaravanan et al. 2018;Sidhu et al. 2018Sidhu et al. , 2020. ...
In the past few decades, cadmium (Cd) as soil contaminant is a major problem for the mankind. Cd contamination of soil and food crops is a critical environmental concern as it deteriorates the soil quality and creates threat to the food safety and human health. High Cd concentration in soils pose negative effects on the plants at physiological, structural and molecular levels. Secretion of certain secondary metabolites in the rhizosphere is a survival mechanism adopted by plants to tolerate and encounter Cd toxicity. Under metal-stressed conditions, secretion of root exudates in soil increases the external detoxification strategies of the plants. The secreted phytochemicals are gaseous compounds, inorganic and especially organic in composition. In plants, the role of these metabolites to confront Cd toxicity and induce tolerance under Cd distress is underrated. The review paper focuses on Cd sources, factors that affect its bioavailability, uptake and toxicity in the plants. Furthermore, it also highlights the contemporary progression in our understanding on the mechanisms of root exudation in plants and the effect of Cd toxicity on the root exudation. Finally, the review provides important information on the role of different root exudates to subsist Cd stress in plants naturally, particularly by reducing the dependence on synthetic amendments to enhance Cd-tolerance and its aquisition in plants.
Plants are always subjected to a variety of environmental stresses, which will
ultimately reduce the yield, and also affect the plant in certain other ways. Plants being exposed to heavy metal stress are also very common nowadays, out of which nickel (Ni) has gained considerable concentration because of its vigorously growing level in the atmosphere. Common household substances contain an adequate amount of Ni, and as a result, the concentration is being increased in water, air, and soil. On the immediate fixation of Ni in the soil, it is accumulated in plant body by their roots. Though, Ni is one of the most important micronutrients which is necessary for normal plant growth and development at a trace amount, but at high concentration it can cause toxic effect to the plant. At an excessive level, it may induce reactive oxygen species (ROS), which in turn can degenerate plasma membrane, can hamper certain physiological activates like photosynthesis, transpiration, and can deactivate certain metalloenzymes. But in contrast, it is a proven fact that Ni plays an essential role in antioxidant metabolism in plant. Ni is
the constituent element of several phyto-enzymes like Urease and glyoxalase I (Gly I). During stressed condition methylglyoxal (MG) is produced in the plant body, which is eliminated by glyoxalase enzyme, which confirms the indirect utility of Ni in stress management. In this chapter, we will discuss about the functionality of nickel in tolerance against a wide range of environmental stresses in detail.
Due to its low cost and rarity of secondary pollutants, phytoremediation has long ago emerged as a crucial clean-up technology for the remediation of heavy metal-polluted soil. Brassica juncea was a popular plant employed for the purpose of phytoextraction due to its high tolerance for metallic constituents and extreme soil conditions; however, the extraction efficiency was low. In an approach to boost the efficacy of phytoextraction, numerous studies have been conducted. The current study used ethylenediaminetetraacetic acid as a chelating agent to enhance the phytoextraction of Lead in contaminated soil using Brassica juncea. The effect of Pb concentration on remediation efficiency was investigated with and without ethylenediaminetetraacetic acid addition, and some valuable findings were reported. The results show that adding ethylenediaminetetraacetic acid in the treatment can significantly increase the phytoextraction potential of Brassica juncea by 37.35% extraction efficiency. Additionally, a substantial amount of lead up to 12,893 mg/kg was accumulated in the roots, and about 7,493.33 mg/kg was transported to the leaves of the experimental plants. The findings also confirm that Brassica juncea could endure Lead stress even at a higher level of 1000 mg/kg without manifesting phytotoxic symptoms.
Heavy metals are nonbiodegradable and accumulate in the environment. Persistent pollutants such as heavy metals can enter the food chain via marine life, affecting predators such as larger fish, birds, and mammals, including humans, who transmit the pollutants to various environments. Much investigation has been carried out to mitigate the heavy metal pollution in the environment. Until now, heavy metal decontamination has relied on ethylenediaminetetraacetic acid (EDTA), a highly effective chelating agent. Although EDTA is particularly effective at mobilizing metals, its limited biodegradability means it can persist in the environment for a long time. As a result, biodegradable chelating agents were introduced to replace nonbiodegradable chelating agents due to their environmental friendliness. The chemical and physical properties of biodegradable aminopolycarboxylates such as iminodisuccinic acid, methylglycinediacetic acid, ethylenediamine-N, N′-disuccinic acid, nitrilotriacetic acid, and tetrasodium glutamate diacetate, as well as organic acids such as citric acid, will be studied and evaluated to see if they can perform similarly to standard chelant EDTA in terms of heavy metal pollution mitigation. Even though the chelating agents used are biodegradable, there is no guarantee that metal extraction effectiveness will be improved over traditional chelating agents, and it also depends on the type of heavy metal to be chelated. In short, many factors that contribute to metal extraction efficiencies, such as pH and chelating agent concentration, should be investigated in this chapter. Most importantly, although biodegradable chelants will decay in the environment, heavy metals will be left behind and will last longer in the ecosystem. In a nutshell, it is worth checking whether heavy metal pollution still exists after using a biodegradable chelant.
Contamination of land and aquatic ecosystems with heavy metals (HMs) is a global issue having the persistent potential to damage the quality of food and water. In the present study, Tagetes erecta L. plants were used to assess their potential to uptake HMs from wastewater. Plants were grown in soil for 20 days and then transplanted in hydroponic system containing Hoagland nutrient solution. After more than 15 days of growth, plants were then subjected to wastewater from tannery and surgical industries in different concentrations ranging from 25 to 100% in combination of citric acid (5 and 10 mM). After 6 weeks of treatment, plants were collected and segmented into roots, stem, and leaves for characterizing the morphological properties including plant height, roots length, fresh and dry mass of roots, stem, and leaves. For evaluation of the effect of wastewater on the plants, photosynthetic pigments; soluble proteins; reactive oxygen species (ROS); antioxidant enzymes SOD, POD, CAT, and APX; and metal accumulation were analyzed. Application of industrial wastewater revealed a significant effect on plant morphology under wastewater treatments. Overall growth and physiological attributes of plant decreased, and metal accumulation enhanced with increasing concentration of wastewater. Similarly, the production of ROS and antioxidant enzymes were also increased. Chlorophyll, protein content, and enzyme production enhanced with CA (5 and 10 mM) mediation; however, ROS production and EL were reduced. Metals analysis showed that the maximum accumulation of Pb was in roots, while Cr and Ni in the stem which further increased under CA mediation. Overall, the metal accumulation ability was in the order of Pb > Ni > Cr under CA.
Graphical Abstract
Vegetation has successfully been used for cleaning up metal(loid) polluted water body and lands through extracting and accumulating these contaminants in their aboveground biomass (phytoextraction). As this remedial technique is approaching extensive demonstration scale application and potential commercialisation, research efforts have been investigating new ways to achieve the valorisation of its by‐products, the heavy‐metal‐enriched biomass (HMEB). Biomass pyrolysis as an energy conversion technique represents a key step to numerous valorisation options of HMEB. During the pyrolysis of HMEB, understanding the thermal decomposition pathways and the migration and transformation of metal(loid)s are critical for the production of clean, safe and value‐added end‐products. This work performs a state‐of‐the‐art review of the studies conducted on phytoextraction and biomass pyrolysis of HMEB with emphasis on the properties of pyrolysis products as well as the behaviour of heavy metal(loid)s during pyrolysis in relation with HMEB feedstock properties and the variables of the process. This article is protected by copyright. All rights reserved.
Nickel (Ni) is an indispensable component of the urease enzyme that plays a key role in urea/nitrogen metabolism in plants. Therefore, it has been designated as an essential micronutrient, the latest one included in the list of elements required in trace amount. Plants rarely face the deficiency of this micronutrient because the seed possesses a concentration that is sufficient for the entire life span of the plant. However, its absence or deficient concentration is manifested in characteristic disorders or deficiency diseases called leaf-burn disease, leaf-tip necrosis, and mouse-ear disease. Excess concentrations of Ni also inflict different physiological and metabolic alterations such as plant growth inhibition, disturbed uptake and translocation of water and mineral nutrients, and slowing of the attributes related to photosynthesis including stomatal functioning, and enzyme inhibition. Ni also generates oxidative stress and stimulates both the enzymatic and nonenzymatic antioxidant system. To cope with the stress generated by excess Ni, plants have evolved some peculiar strategies such as the prevention of influx or exclusion by the plasma membrane, chelation by phytochelatins, metalothionines, and nicotinamine. The complexed Ni is subsequently compartmentalized into the vacuole. These tolerance strategies help in the accumulation of large amount Ni by the process called hyperaccumulation and subsequently in the management of the Ni polluted soil. All these aspects are presented here comprehensively to discuss the effects of low and excess levels of Ni on the plant growth and development, and metabolism as well as the tolerance strategies in plants. In addition to this, the extent of extraction of Ni by the hyperaccumulators is also presented.
Various natural and uncontrolled human activities lead to the addition of pollutants like heavy metals into soil and water which pose deleterious effects on the health of living organisms. Some of the heavy metals (HMs) play a biological role at optimum concentrations above which they pose toxic effects. However, some of the HMs do not participate in any biological activity, therefore, act toxic even at minute concentrations. Since the plants cannot shift their position due to sessile habits, therefore they are readily exposed to the HMs in the soil. This affects the overall growth and productivity of the plants. Upon their entry into the plant body, HMs produce numerous effects at morphological, physiological, biochemical, and molecular levels. They lead to imbalances in the production and mitigation of free radicals that hinder various biochemical processes essential for the growth of plants. However, plants tend to scavenge the free radicals produced with the help of the antioxidants that maintain the balance of ROS. Several responses like reduced biomass, photosynthetic pigments, photosynthetic efficiency, water use efficiency, mineral nutrition imbalances, chromosomal aberrations, inhibition of cell divisions, chlorosis, and necrosis are some of the responses produced by the plants when grown under an HM toxic environment. However, some of the plants act as hyperaccumulators of the HMs and help in phytoremediation. This chapter summarizes the responses of plants produced against various HMs like Lead (Pb), Mercury (Hg), Copper (Cu), Chromium (Cr), Arsenic (As), Nickel (Ni), Iron (Fe), and Zinc (Zn).
Environmental adversities like heat, cold, drought, salinity, ultraviolet radiation and flooding induces abiotic distress in plants and are the pioneer limiting factors for plant growth, development and productivity. Anthropogenic activities have fuelled changes in global climatic conditions and these changes have incremented multiple abiotic stresses in crop plants. Researchers are making unprecedented efforts to intercept heavy crop losses and in turn to generate more food and feed to meet the demands of the ever-increasing human population. Highlighting the techniques involved to combat abiotic stresses, their role in regulating plant growth and development under unfavourable climatic factors holds substantial importance. This chapter reviews the role of osmoprotectants, polyamines, flavonoids and phytohormones in plant growth and development under abiotic stress conditions and their metabolic engineering for producing abiotic stress-tolerant transgenic plants. This strategy can prove a vital tool to minimise heavy crop losses and alleviate the problem of increasing food demand of human populations.
The ultimate goal of heavy metal contaminated soil remediation is to increase crop yields on the premise of ensuring food production safety. Soil contaminated by heavy metals threatens the quality of agricultural products and human health. Hence, it is necessary to choose appropriate economic and effective remediation techniques to control the deterioration and revive the land quality. Among the methods available, biochar application for adsorption and remediation of heavy metal contaminated soil is emerging to be a sustainable approach. Biochar introduction to the soil provides organic matter and essential macro and micronutrients like C, N, P, K, Ca, Mg, etc., which enhances soil enzyme and microbial activities. Additionally, the plant root environment, soil water retention, and saturated hydraulic conductivity can be improved in the presence of biochar. This chapter is intended to present an overview of the production techniques of biochar, its properties, and characteristics required for effective heavy metal removal and the corresponding process conditions, mechanisms involved in the interaction of biochar with heavy metals, and the benefits as well as bottlenecks of biochar application in soil.
Contamination of different environmental matrices (air, soil, and water) by toxic heavy metals is a widespread problem that disturbs the environment as an outcome of many anthropocentric practices. Heavy metals exceeding the permissible limits exert deleterious impacts on human beings, causing life-threatening health manifestations and detrimental effects on the environment. This has alarmed the dire need to explore various modern remediation techniques that can be utilized to lower excessive concentrations. Owing to their high-cost effectiveness, unsatisfactory output, environmentally unfriendly, complicated procedure, and high operational costs, these technologies failed to find any practical utility in remediation. On the other hand, plants and associated microorganisms are receiving more consideration as a means of remediating or degrading environmental pollutants. This chapter provides us insights into the various environmental friendly techniques that will improve our environment’s quality. Among which, phytoremediation is considered an effective technique which is known for its esthetic benefits and endless applicability. Furthermore, metal-resistant bacteria (plant growth-promoting rhizobacteria) are also reported to play a pivotal role in the phytoremediation and solubilization of minerals. Thus, this chapter critically reviews the phytoremediation technology and the efficient exploitation of microbes to alleviate the environmental burden of toxic heavy metals.
Ethylenediamine-N,N'-disuccinic acid [(S,S)-EDDS] is a biodegradable strong chelating agent that can currently be produced by biological methods, including fermentation and enzymatic synthesis. The fermentation of (S,S)-EDDS is mainly performed in Amycolatopsis japonicum MG417-CF17, and the highest fermentation level reported is 20 g/L. (S,S)-EDDS biosynthesis is inhibited by low-micromolar zinc concentrations. The gene cluster aesA-H is involved in the synthesis of (S,S)-EDDS, and (S)-N-(2-aminoethyl) aspartic acid (AEAA) is most likely to be a key intermediate coupling the biosynthesis and biodegradation of (S,S)-EDDS in microorganisms. The highest reported level of enzymatic synthesis of (S,S)-EDDS is 209 g/L. Most of the existing enzymatic synthetic routes use ethylenediamine and fumaric acid as substrates. When using aspartate ammonia lyase as a catalyst, the product is (R,S)-configured, while (S,S)-EDDS can be obtained with EDDS lyase. After purification and then immobilization, EDDS lyase was used in 11 batch reactions (864.5 h); the yield reached 94%, and the maximum space-time yield was 1.55 g/(L·h). Enzymatic methods have a clearer mechanism than fermentation and are more economical and environmentally friendly. By further optimizing the reaction conditions, this method is expected to replace chemical synthesis in manufacturing (S,S)-EDDS.
Industrialization has dramatically accelerated in recent decades, owing primarily to satisfy the needs of the existing population. In the early 19th century, after the discovery of oil as an alternative fuel, its production and refining in the subsequent years, chemical leaks have become the likely events that occur most often during the shipping and refining of oil having the potential to pollute marine, soil, sediments, and other ecosystems. Various physical and chemical remediation approaches have been used to treat emerging toxins over time; however, due to their high cost and inefficiency, emphasis has shifted toward the idea of bioremediation, in the search for better solutions. Being successfully used to treat the Exxon Valdez oil spill on March 24, 1989, bioremediation has proven to be a promising method for treating oil spills. In contrast to physicochemical approaches, bioremediation is a greener solution that is cost-effective and has a lower environmental impact. This approach involves applying natural or genetically modified microorganisms to a contaminated site and/or enriching the polluted habitat with nutrients, which is referred to as bioaugmentation and bio stimulation, respectively. Plants, microorganisms (bacteria, fungi, cyanobacteria, microalgae), and enzymes are examples of biologically supported processes. Future oil spill bioremediation science should concentrate on these novel facets of the technique, paving the way for bioremediation to be used in the real world to achieve promising contaminants degradation outcomes.
Although Solanum nigrum L. is a phytoremediator for different metals, its growth and physiology are still influenced by toxic levels of cadmium (Cd). Thus, the development of eco-friendly strategies to enhance its tolerance, maintaining remediation potential is of special interest. The present work aimed to evaluate the effects of exogenous application of melatonin (MT) in the physiological and biochemical responses of S. nigrum and remediation potential exposed to Cd. After 30 days of exposure, the results revealed that Cd-mediated inhibitory effects on biomass and photosynthetic pigment synthesis were efficiently mitigated upon application of melatonin, without affecting Cd accumulation. Higher levels of Cd were found in roots, regardless of the pretreatment with the melatonin. Foliar application of melatonin, however, induced distinctive effects, lowering malondialdehyde (MDA), relative electrical conductivity (REL), and proline levels in shoots. These changes contributed to improvements in the water status, photosynthetic pigment synthesis, and biomass production of S. nigrum under Cd stresses. Overall, our results indicate a protective effect of melatonin on S. nigrum response to excess Cd, contributing to a better tolerance and growth rate, without disturbing its phytoremediation potential.
Novelty statement
Although Solanum nigrum L. is a phytoremediator for different metals, its growth and physiology are still influenced by toxic levels of cadmium. This study evaluated the potential of melatonin to boost S. nigrum defence against Cd toward a better growth rate and remediation potential.
Soil pollution caused by toxic and hazardous chemical contaminants is in high enough concentrations to be of risk to plants, wildlife, humans and certainly for soil to itself. Pot experiments were conducted to investigate the phytoextraction capacity of an ornamental plant Sansevieria roxburghiana cultivated in soil artificially contaminated with 200, 400, and 600 mg kg⁻¹ of zinc (Zn) treatments including control for 6 weeks. The soil was amended with garlic and cilantro extracts as the natural irrigation solutions (metal chelants). Garlic application significantly enhanced the Zn accumulation and was found to be the most efficient chelating amendment, increasing concentrations of Zn in roots from 65 mg kg⁻¹ to 423 mg kg⁻¹ dry weight (DW) soil. The phytochemical screening of acetone and ether extracts of S. roxburghiana plant samples revealed the presence of biologically active phytochemicals. Thin layer chromatography (TLC) of plant extracts revealed antibacterial efficacy against pathogenic bacterial strain. The plant samples were also characterized by thermogravimetric analysis and differential scanning calorimetric technique. The use of ornamental plant and varied irrigation solutions in our present study revealed positive effects on growth and phytoextraction together with an improvement of the soil quality.
Heavy metal contamination represents a health risk due to occupational and environmental exposure, and their introduction into the food chain. Green technology and affordable to remediate sites contaminated with heavy metals is the phytoremediation. However, although phytoremediation represents a cheap and sustainable technology, it is very important to evaluate the interaction of the compounds associated with an increase or decrease in the ability to remove and phytoaccumulate heavy metals. This chapter presents general information obtained, from scientific sources, on the use of citric acid, ethylene diamine tetra acetic acid, glutathione, sulfur, nitrous oxide as chemical amendments to improve the processes of heavy metal phytoremediation. The information described here will be useful to carry studies about the improvement and potential of plants in the phytoremediation.
Heavy metals pollution represents a serious issue for cultivable lands and ultimately threatens the worldwide food security. Lead (Pb) is a menacing metal which induces toxicity in plants and humans. Lead toxicity reduces the photosynthesis in plants, resulting in the reduction of plant growth and biomass. The excessive concentration of Pb in soil accumulates in plants body and enters into food chain, resulting in health hazards in humans. The phytoremediation is eco-friendly and cost-efficient technique to clean up the polluted soils. However, to the best of our Knowledge, there are very few reports addressing the enhancement of the phytoremediation potential of castor bean plants. Therefore, the present study aimed to investigate the potential role of glutathione (GSH), as a promising plant growth regulator, in enhancing the lead stress tolerance and phytoremediation potential of castor bean plants grown under lead stress conditions. The results indicated that Pb stress reduced the growth, biomass, chlorophyll pigments and gas exchange attributes of castor bean plants, causing oxidative damage in plants. Pb stress induced the oxidative stress markers and activities of antioxidant enzymes. On the other hand, the application of GSH reduced oxidative stress markers, but enhanced the growth, biomass, photosynthetic pigments, gas exchange attributes, Pb accumulation and antioxidant enzymes activities of lead-stressed castor bean plants. Both Pb uptake and Pb accumulation were increased by increasing concentrations of Pb in a dose-additive manner. However, at high dose of exogenous GSH (25 mg L-1) further enhancements were recorded in the Pb uptake in shoot by 48% and in root by 46%; Pb accumulation was further enhanced in shoot by 98% and in root by 101% in comparison with the respective control where no GSH was applied. Taken together, the findings revealed the promising role of GSH in enhancing the lead stress tolerance and phytoremediation potential of castor bean (Ricinus communis) plants cultivated in Pb-polluted soils through regulating leaf gas exchange, antioxidants machinery, and metal uptake.
Cadmium (Cd) is a prevalent, non-essential, carcinogenic, and hazardous heavy metal that reduces plant productivity and capacity of arable land area around the globe. In the present substrate-based pot study, seedlings of Brassica napus 180015 were grown equidistantly in the spiked-substrate medium for 60 days under increasing concentrations of Cd (0, 10, 20, 30, 40, 50 mg kg⁻¹). Following harvest, the morpho-physio-biochemical, antioxidative, and Cd-induced tolerance responses were evaluated in B. napus under an increasing Cd stress regime. Additionally, these parameters were also investigated to select the plant's threshold tolerance limit for Cd under the spiked-substrate system. B. napus showed dynamic behavior regarding morpho-physio-biochemical attributes, including agronomic features, biomass, photosynthetic pigments, relative water content under increased Cd toxicity. Cd stress-induced hydrogen peroxide (H2O2) production with high MDA contents and passive EL, followed by the orchestration of both enzymatic (SOD, POD, APX, CAT, and GR) and non-enzymatic antioxidants (flavonoids, TPC, TPA, proline, and total soluble protein) up to a certain limit. In addition, Cd-induced stress upregulated transcriptional levels of antioxidative enzyme SOD, POD, APX, GR, and MT encoded genes in B. napus. The increasing trend of Cd accumulation in different tissues at the highest Cd concentration was as follows: root > leaf > stem. In spiked substrate system, B. napus demonstrated improved metal extractability performance and a high potential for phyto-management of low to moderate Cd contamination, implying that this study could be used for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.
Novelty statement
This study provides an insight into Cd-coping mechanisms of oilseed rape involved in alleviating toxicity and simultaneous phyto-management of increasing Cd concentration under spiked substrate system. The current study is the first scientific evidence of using a Cd-spiked soilless substrate medium. The present study will further strengthen our understanding of Cd-instigated positive responses in B. napus. Furthermore, it will provide a useful basis for integrative breeding programs and decontaminating heavy metals in real contaminated scenarios.
Global climate change is identified as a major threat to survival of natural ecosystems. Climate change is a dynamic, multifaceted system of alterations in environmental conditions that affect abiotic and biotic components of the world. It results in alteration in environmental conditions such as heat waves, intensity of rainfall, CO2 concentration and temperature that lead to rise in new pests, weeds and pathogens. Climate change is one of the major constraints limiting plant growth and development worldwide. It impairs growth, disturbs photosynthesis, and reduces physiological responses in plants. The variations in global climate have gained the attention of researchers worldwide, as these changes negatively affect the agriculture by reducing crop productivity and food security. With this background, this review focuses on the effects of elevated atmospheric CO2 concentration, temperature, drought and salinity on the morphology, physiology and biochemistry of plants. Furthermore, this paper outlines an overview on the reactive oxygen species (ROS) production and their impact on the biochemical and molecular status of plants with increased climatic variations. Also additionally, different tolerance strategies adopted by plants to combat environmental adversities have been discussed.
Globally, environmental contamination by potentially noxious metalloids like arsenic is becoming a critical concern to the living organisms. Arsenic is a non-essential metalloid for plants and can be acclimatised in plants to toxic levels. Arsenic acquisition by plants poses serious health risks in human due to its entry in the food chain. High arsenic regimes disturb plant water relations, promote the generation of reactive oxygen species (ROS) and induce oxidative outburst in plants. This review evidences a conceivable tie-up among arsenic levels, speciation, its availability, uptake, acquisition, transport, phytotoxicity and arsenic detoxification in plants. The role of different antioxidant enzymes to confer plant tolerance towards the enhanced arsenic distress has also been summed up. Additionally, the mechanisms involved in the modulation of different genes coupled with arsenic tolerance have been thoroughly discussed.This review is intended to present an overview to rationalise the contemporary progressions on the recent advances in phytoremediation approaches to overcome ecosystem contamination by arsenic.
The bioavailability of heavy metal and growth of hyperaccumulator are key factors controlling the phytoextraction of heavy metal from soil. In this study, the efficacy and potential microbial mechanisms of digestate application in enhancing Cd extraction from soil by Pennisetum hybridum were investigated. The results showed that digestate application significantly promoted the height, tiller number, and biomass yield of Pennisetum hybridum. The application also increased the activities of urease, sucrase, dehydrogenase, available Cd contents of rhizosphere soils (from 2.21 to 2.46 mg kg⁻¹), and the transfer factors of Cd from root to shoot and leaf. Assuming three annual harvests, digestate application would substantially reduce time needed for Pennisetum hybridum to completely absorb Cd from soil—from 15-16 yr to 10 yr. Furthermore, the results of microbial community diversity analysis showed that digestate irrigation was more facilitated for the growth of the predominant bacteria, which were Actinobacteria and Chloroflexi at phylum level, and Sphingomonas and Nitrospiraat genus level, which mainly have the functions of promoted plant growth and metal resistance. The results suggested that the enhanced phytoextraction of Cd by Pennisetum hybridum with digestate application might mainly attributed to the increased Cd bio-availability and the enhanced plant growth, indicating that an approach combining digestate and Pennisetum hybridum could be a promising strategy for remediating Cd-contaminated soils.
The aim of this study was to assess the potential of the woody nickel hyperaccumulator species Blepharidium guatemalense (Standl.) Standl. for agromining in southeastern Mexico. Pot trials consisting of nickel dosing (0, 20, 50, 100 and 250 mg Ni kg-1), and synthetic and organic fertilization were conducted. Field trials were also undertaken with different harvesting regimes of B. guatemalense. Foliar nickel concentrations increased significantly with rising nickel additions, with a 300-fold increase at 250 mg Ni kg-1 treatment relative to the control. Synthetic fertilization strongly increased nickel uptake without any change in plant growth or biomass, whereas organic fertilization enhanced plant shoot biomass with a negligible effect on foliar nickel concentrations. A 5-year-old stand which was subsequently harvested twice per year produced the maximum nickel yield tree-1 yr-1, with an estimated total nickel yield of 142 kg ha-1 yr-1. Blepharidium guatemalense is a prime candidate for nickel agromining on account of its high foliar Ni concentrations, high bioconcentration (180) and translocation factors (3.3), fast growth rate and high shoot biomass production. Future studies are needed to test the outcomes of the pot trials in the field. Extensive geochemical studies are needed to identify potential viable agromining locations.
Keywords: agronomy, fertilization, hyperaccumulation, neotropics, Ni yield, phytomining.
Heavy metals as toxic pollutants emerging from industrial development areas are serious threat to the environment and life on earth. Notwithstanding research during the last few decades, soil contamination with heavy metals is still challenging due to lack of a single reliable technology for the restoration of affected soils. There are several approaches for eradicating heavy metals from the environment; but most of these techniques involve complex mechanics, unaffordable costs, longer time, secondary pollution, logistical issues, and soil degradation. Nevertheless, among them, phytoremediation by using metal-accumulating or tolerant plants seems an attractive technology for heavy metal remediation due to its advantages of being efficient, eco-friendly, and cost-effectiveness. This chapter describes the conventional as well as advanced approaches of phytoremediation, including the types of efficient plants, role of rhizomicrobes, and prospects of using genetic engineering and antioxidant systems to confiscate the heavy metals from soil.
Plants used in phytoremediation should accumulate and tolerate a specific pollutant. Here, we aimed at evaluating a possible arsenic (As) accumulation and mechanisms of tolerance against As-induced damage in Landoltia punctata to explore this species for phytoremediation. Plants were subjected to increasing As levels. As absorption was higher with increasing As levels. The activity of superoxide dismutase and glutathione reductase as well as anthocyanin levels increased with As levels. Catalase and peroxidase activities increased in plants subjected to As levels up to 1.0 mg L⁻¹ and decreased at higher levels. Due to the antioxidant system, higher levels of reactive oxygen species were restrained in plants under low levels of As. However, the levels of superoxide anion, hydrogen peroxide, and lipid peroxidation increased in response to the impaired antioxidant system induced by the highest As levels. Biomass decreased in plants exposed to As and scanning electron microscopy revealed root structural damage in the root cap of plants under 3.0 mg L−1 As. This work highlights that L. punctata can be considered a hyperaccumulator species and has potential for As phytoremediation when levels are lower than 1.0 mg L⁻¹—a concentration 100-fold higher than that recommended for drinking water.
Novelty Statement: Landoltia punctata can be considered a hyperaccumulator species and has the potential for arsenic phytoremediation when levels are lower than 1.0 mg L⁻¹.
Ethylenediamine-N,N'-disuccinic acid (EDDS) is a promising chelating agent for the remediation of heavy metal-contaminated soil. In general, EDDS is produced through a chemical method. In this study, we report an efficient biotechnological approach for EDDS production using an immobilized enzyme. We expressed the EDDS lyase in E. coli and obtained 19.8 g/L of EDDS through a reaction catalyzed by crude enzymes, containing EDDS lyase and fumarase. After performing metal affinity chromatography-mediated purification, we thoroughly eliminated the fumarase activity, which could result in the unnecessary formation of malate. Then, the purified EDDS lyase was immobilized on a glutaraldehyde-activated amino carrier, and the immobilized enzyme was used in 11 batches (864.5 h). After optimization, 209.3 g/L EDDS was obtained in a 100 mL reaction system, resulting in 20.2 g of EDDS product with a purity of 99.8 % after isolation. The yields of reaction and isolation were 94.0 % and 91.8 %, respectively. In conclusion, this study describes a promising bioproduction process for industrial-level EDDS production.
To determine whether grafting increases cadmium (Cd) accumulation in the post-grafting generation of hyperaccumulator plants, the effects of grafting on Cd accumulation characteristics of post-grafting generations of a potential Cd-hyperaccumulator Solanum photeinocarpum were evaluated in pot and field experiments. The following four grafting combinations were examined: ungrafted (UG), self-rooted grafting involving one S. photeinocarpum seedling (SG), self-rooted grafting involving two S. photeinocarpum seedling developmental stages (DG), and grafting on wild potato rootstock (PG). Grafting did not induce genetic changes in S. photeinocarpum, and increased the shoot biomass and the amount of Cd extracted by the shoots of the first, second, and third generations of S. photeinocarpum (PG > DG > SG > UG). Additionally, enhanced superoxide dismutase, peroxidase, and catalase activities and increased soluble protein contents of the first post-grafting generation were observed for the DG and PG, whereas only enhanced superoxide dismutase and peroxidase activities were observed for the SG. Grafting increased the DNA methylation levels by inducing hypermethylation in the first post-grafting generation (PG > DG > SG > UG). Therefore, grafting can enhance the Cd accumulation (phytoremediation) ability of post-grafting generations of S. photeinocarpum by enhancing DNA methylation levels, especially when wild potato rootstock is used.
Selecting (inter-varietal) Brassica juncea for tolerance to metal-contamination has been proposed as a strategy to develop superior genotypes for phytoextraction of lead (Pb) through selection and breeding techniques. To understand the differences among accessions of a single species to Pb accumulation, a pot experiment was conducted with three B. juncea accessions under levels of Pb added to the soil (0, 90, 180, and 540 mg kg-1). The duration of the growth period was 100 d. Pb concentration levels did not affect the flowering of B. juncea accessions. Plant height, shoot dry matter, and root dry matter were reduced linearly when soil Pb concentration increased to 540 mg kg-1. A significant interaction between Pb concentration levels and accessions was observed for Pb concentration in shoots and roots, indicating genotypic variation in Pb absorption. The concentration of Pb in shoots in accession PI 180266 was 51% higher compared to
accessions PI 649105 and PI 432379 when soil Pb concentration increased to 540 mg kg-1. It can be concluded that the B. juncea accessions differed significantly in Pb uptake, and the selection of tolerant cultivars might be helpful for Pb phytoremediation of contaminated soils.
Several species from the Brassica genus are very important agricultural crops in different parts of the world and are also known to be heavy metal accumulators. There have been a large number of studies regarding the tolerance, uptake and defense mechanism in several of these species, notably Brassica juncea and B. napus, against the stress induced by heavy metals. Numerous studies have also been published about the capacity of these species to be used for phytoremediation purposes but with mixed results. This review will focus on the latest developments in the study of the uptake capacity, oxidative damage and biochemical and physiological tolerance and defense mechanisms to heavy metal toxicity on six economically important species: B. juncea, B. napus, B. oleracea, B. carinata, B. rapa and B. nigra.
Among metals, Ni has been indicated as one of the most dangerous for the environment, and plants exposed to this metal are frequently reported to undergo a severe stress condition. In this work, the tolerance responses to different Ni concentrations at physiological and biochemical levels were evaluated in Amaranthus paniculatus L., a plant species previously characterised for their ability to phytoremove Ni from metal-spiked water. Results indicated a good metal tolerance of this plant species at environmentally relevant Ni concentrations, while clear symptoms of oxidative damages were detected at higher Ni concentrations, both in roots and leaves, by measuring lipid peroxide content. At the photosynthetic level, pigment content determination, chlorophyll fluorescence image analysis and gas-exchange parameter measurements revealed a progressive impairment of the photosynthetic machinery at increasing Ni concentrations in the solution. Regarding biochemical mechanisms involved in antioxidative defence and metal binding, antioxidative enzyme (ascorbate peroxidase, APX; catalase, CAT; guaiacol peroxidase, GPX; superoxide dismutase, SOD) activity, polyamine (PA) content, polyamine oxidase (PAO) activity and organic acid (OA) content were differently affected by Ni concentration in the growth solution. A role for GPX, SOD, PAs, and oxalic and citric acid in Ni detoxification is suggested. These results can contribute to elucidate the tolerance mechanisms carried out by plants when facing environmentally relevant Ni concentrations and to identify some traits characterising the physiological and biochemical responses of Amaranthus plants to the presence and bioaccumulation of Ni.
Referee: Professor Alan J.M. Baker, School of Botany, The University of Melbourne, VIC 3010, Australia A relatively small yet diverse group of plants are capable of sequestering metals in their shoot tissues at remarkably high concentrations that would be toxic to most organisms. This process, known as metal hyperaccumulation, is of interest for several reasons, including its relevance to the phytoremediation of metalpolluted soils. Most research on hyperaccumulators has focused on the physiological mechanisms of metal uptake, transport, and sequestration, but relatively little is known regarding the genetic basis of hyperaccumulation. There are no known cases of major genetic polymorphisms in which some members of a species are capable of hyperaccumulation and others are not. This is in contrast to the related phenomenon of metal tolerance, in which most species that possess any metal tolerance are polymorphic, evolving tolerance only in local populations on metalliferous soil. However, although some degree of hyperaccumulation occurs in all members of the species that can hyperaccumulate, there is evidence of quantitative genetic variation in ability to hyperaccumulate, both between and within populations. Such variation does not appear to correlate positively with either the metal concentration in the soil or the degree of metal tolerance in the plant. Studies using controlled crosses, interspecific hybrids, and molecular markers are beginning to shed light on the genetic control of this variation. As molecular physiology provides greater insights into the specific genes that control metal accumulation, we may learn more about the genetic and regulatory factors that influence variable expression of the hyperaccumulation phenotype.
In this study, a novel experimental setup (one pot placed above another) was used to investigate the residual effects of EDDS application on plant growth and metal uptake. Two plant species, garland chrysanthemum and ryegrass, were grown in the upper pots (mimicking the upper soil layers) and were harvested 7days after EDDS application. During this period the upper pots were watered twice. The lower pots (mimicking the subsoil under the upper soil layers) served as leachate collectors. Thereafter, the two pots were separated, and the same plants were grown in the upper and lower pots in two continuous croppings. Results showed that EDDS application restrained the growth of the first crop and resulted in a dramatic enhancement of Cu accumulation in plants grown in the upper pots. However, no negative growth effects were identified for the second and third crops, which were harvested 81 and 204days after the EDDS application, respectively. In the lower pots, the leachate from the upper pots after EDDS application exhibited the increased total and CaCl(2)-extractable Cu concentrations in the soil. However, the growth of garland chrysanthemum and ryegrass, and their shoot Cu concentrations were unaffected. These data suggest that the residual risk associated with EDDS application was limited, and that subsoil to which EDDS leachate was applied may exhibit reduced Cu bioavailability for plants due to the biodegradation of EDDS.
Arsenic (As) toxicity and its biochemical effects have been mostly evaluated in ferns and a few higher plants. In this study,
we investigated the effect of As (10.0 and 50.0μM) on seedling growth, root anatomy, lipid peroxidation (malondialdehyde
and conjugated dienes), electrolyte leakage, H2O2 content, root oxidizability and the activities of antioxidant enzymes in mung bean (Phaseolus aureus Roxb.). Arsenic significantly enhanced lipid peroxidation (by 52% at 50.0μM As), electrolyte leakage and oxidizability in
roots. However, there was no significant change in H2O2 content. Arsenic toxicity was associated with an increase in the activities of superoxide dismutase (SOD), guaiacol peroxidase
(GPX) and glutathione reductase (GR). In response to 50.0μM As, the activities of SOD and GR increased by over 60% and 90%,
respectively. At 10.0μM As, the activity of ascorbate peroxidase (APX) increased by 83%, whereas at 50.0μM it declined significantly.
The catalase (CAT) activity, on the other hand, decreased in response to As exposure, and it corresponded to the observed
decrease in H2O2 content. We conclude that As causes a reduction in root elongation by inducing an oxidative stress that is related to enhanced
lipid peroxidation, but not to H2O2 accumulation.
Twelve Mediterranean hydrophyte species collected inLebanon were evaluated for their potential asbioindicator species for heavy metal pollution innutrient cultures enriched with 1 ppm Cr, Ni and Cd.These were: Nasturtium officinale R.Br, Apium nodiflorum L., Veronica beccabunga L., Veronica anagallis aquatica L., Veronicalysimachioides L., Veronica anagalloides L., Mentha longifolia L., Mentha aquatica L., Mentha pulegium L., Potentilla reptansL., Mentha sylvestris L., and Cardamine uliginosa L.. Large variability in responseto exposure to the heavy metals was observed. Growthrates remained high during the experimental period,indicating that the plants were little affected by thepresence of the metal at the experimentalconcentration. Metal accumulation and bioconcentrationvaried within at least one order of magnitude, andranged from less than 10 to over 200. Cr waspreferentially accumulated in the roots. All speciesbut M. pulegium, P. reptans and V. anagallisaquatica accumulated and bioconcentrated sufficientCr to qualify as bioindicator species. Five of thespecies that accumulated Cr also accumulated Ni, withthe same partitioning into the root. These were: N. officinale, C. uliginosa sp., M. longifolia, M. aquatica and M. sylvestris, all of which mayalso be used as bioindicators of Ni pollution. Onlyone species, M. aquatica, accumulated Cdsignificantly, and may, therefore, be used as abioindicator for all three metals.
Background, Aims and ScopePhytoremediation is a promising means for the treatment of heavy metal contamination. Although several species have been identified as hyperaccumulators, most studies have been conducted with only one metal. Experiments were conducted to investigate the ability of Helianthus annuus and Thlaspi caerulescens to simultaneously uptake Cd, Cr and Ni. Materials and Methods
The efficiency of plants grown in a sandy-loam soil was investigated. The ability of two EDTA concentrations (0.1 and 0.3 g kg−1) for enhancing the phytoremediation of Cd, Cr and Ni at two different metal concentrations (24.75 mg kg−1 and 90 mg kg−1) was studied. ResultsThlaspi hyperaccumulated Ni with 0.1 g kg−1 EDTA. When the EDTA dosage was increased to 0.3 g kg−1, Thlaspi was able to hyperaccumulate both Ni and Cr. Since Thlaspi is a low-biomass plant, it was considered insufficient for full-scale applications. Helianthus annuus hyperacummulated Cr (with 0.1 g kg−1 EDTA) and Cd (0.3 g kg−1 EDTA). DiscussionWhen the contamination was 8.25 mg kg−1 per metal, the total metal uptake was 10–25% (1.35 to 2.12 mg) higher and had the same uptake selectivity (Cr>>Cd>Ni) for both EDTA levels. It was hypothesized that complexation with EDTA interfered with Ni translocation. For these experiments, the optimal results were obtained with the H. annuus-0.1 g kg−1 EDTA combination. Conclusions
Although the use of EDTA did increase the amount of metal that could be extracted, care should be taken during in-situ field applications. Chelators can also increase the amount of metals that are leached past the root zone. Metal leaching and subsequent migration could lead to ground water contamination as well as lead to new soil contamination. Recommendations and PerspectivesAdditional research to identify the optimal EDTA dosage for field applications is warranted. This is necessary to ensure that the metals do not leach past the root zone.Identification of a plant that can hyperaccumulate multiple metals is critical for phytoremediation to be a viable remediation alternative. In addition to being able to hyperaccumulate multiple metals, the optimal plant must be fast growing with sufficient biomass to sequester the heavy metals.
The influence of 50 and 100μM Ni on the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase
(GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), alanine aminotransferase (AlaAT) and aspartate aminotransferase
(AspAT) was studied in the wheat roots. Root fresh weight, tissue Ni, nitrate, ammonium, glutamate and protein concentrations
were also determined. Exposure to Ni resulted in a marked reduction in fresh weight of the roots accompanied by a rapid accumulation
of Ni in these organs. Both nitrate and ammonium contents in the root tissue were considerably enhanced by Ni stress. While
protein content was not significantly influenced by Ni application, glutamate concentration was slightly reduced on the first
day after treatment with the higher Ni dose. Treatment of the wheat seedlings with 100μM Ni led to a decrease in NR activity;
however, it did not alter the activation state of this enzyme. Decline in NiR activity observed after application of 100μM
Ni was more pronounced than that in NR. The activities of GS and NADH-GOGAT also showed substantial decreases in response
to Ni stress with the latter being more susceptible to this metal. Starting from the fourth day, both aminating and deaminating
GDH activities in the roots of the seedlings supplemented with Ni were lower in comparison to the control. While the activity
of AspAT remained unaltered after Ni application that of AlaAT showed a considerable enhancement. The results indicate that
exposure of the wheat seedlings to Ni resulted in a general depression of nitrogen assimilation in the roots. Increase in
the glutamate-producing activity of AlaAT may suggest its involvement in supplying the wheat roots with this amino acid under
Ni stress.
Nickel even though recognized as a trace element, its metabolism is very decisive for certain enzyme activities, maintaining proper cellular redox state and various other biochemical, physiological and growth responses. Study of the aspects related with uptake, transport and distributive localization of Ni is very important in various cellular metabolic processes particularly under increased nitrogen metabolism. This review article, in core, encompasses the dual behavior of Ni in plants emphasizing its systemic partitioning, essentiality and ill effects. However, the core mechanism of molecules involved and the successive physiological conditions required starting from the soil absorption, neutralization and toxicity generated is still elusive, and varies among the plants.
Coronopus didymus was examined in terms of its ability to remediate Pb-contaminated soils. Pot experiments were conducted for 4 and 6 weeks to compare the growth, biomass, photosynthetic efficiency, lead (Pb) uptake and accumulation by C. didymus plants. The plants grew well having no visible toxic symptoms and 100% survivability, exposed to different Pb-spiked soils 100, 350, 1500 and 2500 mg kg⁻¹, supplied as lead nitrate. After 4 weeks, root and shoot concentrations reached 1652 and 502 mg Pb kg⁻¹ DW while after 6 weeks they increased upto 3091 and 527 mg Pb kg⁻¹ DW respectively, at highest Pb concentration. As compared to the 4 week experiments, the plant growth and biomass yield were higher after 6 weeks of Pb exposure. However, the chlorophyll content of leaves decreased but only a slight decline in photosynthetic efficiency was observed on exposure to Pb at both 4 and 6 weeks. The Pb accumulation was higher in roots than in the shoots. The bioconcentration factor of Pb was > 1 in all the plant samples but the translocation factor was < 1. This suggested C. didymus as a good candidate for phytoremediation of Pb-contaminated soils and can be used for future remediation purposes.
Coronopus didymus has been emerged as a promising wild, unpalatable plant species to alleviate lead (Pb) from the contaminated soils. This work investigated the hypothesis regarding various metabolic adaptations of C. didymus under lead (Pb) stress. In pot experiments, we assessed the effect of Pb at varied concentrations (500–2900 mg kg−1) on growth, photosynthetic pigments, alteration of macromolecular (protein and carbohydrate) content, and activities of enzymes like protease, α-and β-amylase, peroxidase (POX), and polyphenol oxidase (PPO) in C. didymus for 6 weeks. Results revealed that Pb exposure enhanced the growth, protein, and carbohydrate level, but decreased the leaf pigment concentration and activities of hydrolytic enzymes. The activities of POX and PPO in roots increased progressively by ~337 and 675%, respectively, over the control, at 2900 mg kg−1 Pb treatment. Likewise, contemporaneous findings were noticed in shoots of C. didymus, strongly indicating its inherent potential to cope Pb-induced stress. Furthermore, the altered plant biochemical status and upregulated metabolic activities of POX and PPO indulged in polyphenol peroxidation elucidate their role in allocating protection and conferring resistance against Pb instigated stress. The current work suggests that stress induced by Pb in C. didymus stimulated the POX and PPO activities which impart a decisive role in detoxification of peaked Pb levels, perhaps, by forming physical barrier or lignifications.
In a screenhouse experiment, we investigated the role of two environment friendly chelants, Ammonium molybdate and EDDS for Pb mobilisation and its extraction by Coronopus didymus under completely randomized controlled conditions. Seedlings of C. didymus were grown in pots having Pb-contaminated soil (1200 and 2200 mg kg⁻¹) for 6 weeks. Plants were harvested, 1 week after the addition of A. molybdate and EDDS. Results revealed that A. molybdate and EDDS enhanced the uptake and accumulation of Pb in roots and shoots of C. didymus. At 2200 mg kg⁻¹ Pb level, compared to Pb-alone treatment, the maximal concentration of Pb was increased upto ∼10% and ∼19%, in roots whereas ∼8% and ∼18%, respectively, in shoots on addition of 2 mmol kg⁻¹ A. molybdate and EDDS. Additionally, Pb + EDDS treatments enhanced the plant biomass and triggered strong antioxidative response, more efficaciously than Pb + A. molybdate and Pb-alone treated plants. In this study, EDDS relative to A. molybdate was more efficient in mobilising and extracting Pb from soil. Although, EDDS followed by A. molybdate had good efficacy in mitigating Pb from contaminated soils but C. didymus itself has the inherent affinity to tolerate and accumulate Pb from contaminated soils and hence in future, can be used either alone or with some other eco-friendly amendments for soil remediation purposes.
Phytoextraction is a green remediation technology for cleaning contaminated soils. Application of chelating agents increases metal solubility and enhances phytoextraction. Following a successful greenhouse experiment, a panel study under field weather elucidated the efficiency of the chelating agent ethylenediaminedisuccinic acid (EDDS) on phytoextraction of lead (Pb) by vetiver grass, a hyperaccumulator of Pb, and a nonaccumulator fescue grass from residential soils contaminated with Pb-based paint from Baltimore, MD and San Antonio, TX. Three soils from each city with Pb content between 1000 and 2400 mg kg⁻¹ were chosen for the panel study. Sequential extraction revealed that Fe-Mn oxide (60–63%) and carbonate (25–33%) fractions of Pb dominated in Baltimore soils, whereas in San Antonio soils, Pb was primarily bound to the organic fraction (64–70%) because organic content was greater and, secondarily, to the Fe-Mn oxide (15–20%) fraction. Vetiver and fescue grasses were transplanted and grown on wood panels in the field with EDDS applied after 3 months and 13 months. Soil and leachate results indicated that EDDS applications increased Pb solubility in soils. Plant tissues results indicated enhanced the uptake of Pb by vetiver and showed that EDDS application promoted translocation of Pb from root to shoot. Average Pb concentration increased by 53% and 203% in shoots and by 73% and 84% in roots of vetiver after the first and second applications of EDDS, respectively. Concentrations in roots and shoots increased in all tested soils, regardless of soil pH or clay content. After the second application, average Pb concentrations in vetiver were higher than those in fescue by 3.6x in shoots and 8.3x in roots. Visual phytotoxic symptoms from increased bioavailable Pb from EDSS applications were observed in fescue but not in vetiver. This study demonstrated the potential of a chemically-catalyzed phytoremediation system as a cleanup method for lead-contaminated soils.
Nitro blue tetrazolium has been used to intercept O2⁻ generated enzymically or photochemically. The reduction of NBT by O2⁻ has been utilized as the basis of assays for superoxide dismutase, which exposes its presence by inhibiting the reduction of NBT. Superoxide dismutase could thus be assayed either in crude extracts or in purified protein fractions. The assays described are sensitive to ng/ml levels of super-oxide dismutase and were applicable in free solution or on polyacrylamide gels. The staining procedure for localizing superoxide dismutase on polyacrylamide electrophoretograms has been applied to extracts obtained from a variety of sources. E. coli has been found to contain two superoxide dismutases whereas bovine heart, brain, lung, and erthrocytes contain only one.
A photo-induced cyclic peroxidation in isolated chloroplasts is described. In an osmotic buffered medium, chloroplasts upon illumination produce malondialdehyde (MDA)—a decomposition product of tri-unsaturated fatty acid hydroperoxides—bleach endogenous chlorophyll, and consume oxygen. These processes show (a) no reaction in the absence of illumination; (b) an initial lag phase upon illumination of 10-20 minutes duration; (c) a linear phase in which the rate is proportional to the square root of the light intensity; (d) cessation of reaction occurring within 3 minutes after illumination ceases; and (e) a termination phase after several hours of illumination. The kinetics of the above processes fit a cyclic peroxidation equation with velocity coefficients near those for chemical peroxidation.
The stoichiometry of MDA/O2 = 0.02, and O2/Chlbleached = 6.9 correlates well with MDA production efficiency in other biological systems and with the molar ratio of unsaturated fatty acids to chlorophyll. The energies of activation for the lag and linear phases are 17 and 0 kcal/mole, respectively, the same as that for autoxidation. During the linear phase of oxygen uptake the dependence upon temperature and O2 concentration indicates that during the reaction, oxygen tension at the site of peroxidation is 100-fold lower than in the aqueous phase.
It is concluded that isolated chloroplasts upon illumination can undergo a cyclic peroxidation initiated by the light absorbed by chlorophyll. Photoperoxidation results in a destruction of the chlorophyll and tri-unsaturated fatty acids of the chloroplast membranes.
We studied chelate effects on castor bean (Ricinus communis L.) growth. These effects included Cd and Pb accumulation in plant tissues and the chemical behavior of Cd and Pb in the plant rhizosphere and non-rhizosphere. Tests were conducted in a glasshouse using the rhizobag method. Two castor bean cultivars (Zibo-3 and Zibo-9) were grown in soil contaminated with 3.53mg/kg Cd and 274mg/kg Pb. The soil was treated with citric acid (CA), ethylenediamine disuccinic acid (EDDS) or ethylenediamine tetraacetic acid (EDTA) (5mmol/kg). EDDS-treated soil produced 28.8% and 59.4% greater biomass for Zibo-3 and Zibo-9 respectively. In contrast, CA and EDTA inhibited the growth of the two cultivars. Zibo-9 had greater tolerance than Zibo-3 to chelate toxicity. Based on Cd and Pb plant uptake, EDDS could substitute for EDTA for phytoremediation of Cd in soil. EDTA was the most effective of the three chelates for Pb phytoremediation but it is less suitable for field use due to toxicology environmental persistence. Acid extractable Cd and Pb in the rhizosphere or reducible Cd and Pb in the non-rhizosphere of soil were the main influences on Cd and Pb accumulation in castor bean.
A screenhouse experiment was conducted to assay the effect of Lead (Pb) on oxidative status, antioxidative response and metal accumulation in Coronopus didymus after 6 weeks. Results revealed a good Pb tolerance and accumulation potential of C. didymus towards the increasing Pb concentrations (500, 900, 1800, 2900 mg kg−1) in soil. The content of Pb in roots and shoots elevated with higher Pb levels and reached a maximum of 3684.3 mg kg−1 and 862.8 mg kg−1 Pb dry weight, respectively, at 2900 mg kg−1 treatment. Pb exposure stimulated electrolyte leakage, H2O2 level, MDA content and the activities of antioxidant machinery (SOD, CAT, APX, GPX and GR). However, at the highest Pb concentration, the activities of SOD and CAT declined. The H2O2 level and MDA content in roots increased significantly up to ∼500% and 213%, respectively, over the control, at 2900 mg kg−1 Pb treatment. Likewise, concurrent findings were noticed in shoots of C. didymus, with the increasing Pb concentration. The present work suggests that C. didymus exhibited a good accumulation potential for Pb and can tolerate Pb-induced oxidative stress by an effective antioxidant defense mechanism.
A simple, rapid method requiring few manipulations for the extraction of chlorophylls from fragmented leaf tissue of angiosperms and gymnosperms is compared with the widely used acetone method. Unlike the acetone method where grinding and subsequent centrifugation are essential, this method makes use of incubation at 65 °C of leaf tissue immersed in dimethyl sulphoxide. The new method was found to be as efficient as acetone for chlorophyll extraction and superior in terms of chlorophyll stability.
The effect of increasing level of nickel (Ni) in soil was studied on
biomass production, antioxidants, and Ni bioaccumulation and its translocation in
castor bean (Ricinus communis) as well as Indian mustard (Brassica juncea) in similar
agroclimatic conditions. The plants were exposed to 25, 50, 75, 100, and 150 mg
Ni kg¡1 soil for up to 60 days. It was found that R. communis produced higher
biomass during the same period at all the contamination levels than B. juncea, and
reduction in fresh and dry weights due to the metal contamination in soil was
significantly lower in R. communis than in B. juncea. Proline and malondialdehyde
in the leaves increased with increase in Ni level in both the species, whereas soluble
protein content was found decreased. A correlation between the protein and MDA
contents in the leaves and Ni contamination levels revealed that higher r
2 values for
protein and MDA were found in case of B. juncea, which indicates more toxic
effects of the metal in this species. R. communis was found to have enhanced proline
accumulation (higher correlation value, r
2
) at different Ni contamination levels.
The bioaccumulation of Ni was higher in B. juncea on the basis of the per unit
biomass; however, the total metal accumulation per plant was much higher in R.
communis than in B. juncea during the same growing periods. The translocation of
Ni from roots to shoots was higher in B. juncea at all Ni concentrations. R.
communis appeared more tolerant and capable to clean more Ni from the
contaminated soil in a given time and also in one crop cycle.
This is the first report on using Macleaya cordata for phytoextraction of uranium from the uranium contaminated soil in the greenhouse. Macleaya M. cordata was found to increase uranium concentration in the soil solution by increasing the dissolved organic carbon (DOC). The amendment experiments with citric acid (CA) and [S,S]-ethylenediamine disuccinic acid (EDDS) at the rates of 1.0, 2.5, 5.0, and 10.0 mmol kg−1 dry weight (DW) soil showed that EDDS was more efficient to increase uranium concentration in the shoot than CA when they were applied at the same rate. The applications of 5.0 mmol kg−1 EDDS and 10.0 mmol kg−1 CA were most appropriate for increasing uranium concentrations in the shoot of M. cordata. CA was more efficient to increase the solubility of uranium at the same application rates except for 2.5 mmol kg−1 application rate. There was a linear correlation between the uranium concentration in the shoot and the average uranium concentration of one planted pot during 14 days in soil solution after the application of different rates of EDDS and CA, respectively (r
2 = 0.972, P < 0.01; r
2 = 0.948, P < 0.01), indicating that uranium uptake was dependent on the soluble uranium concentration. The Fe-U-DOC and Mn-U-DOC complexes were probably formed after the application of CA. Soil solution pH and Fe, Mn, Ca, and DOC concentrations in soil solution were found to be changed by the chelates.
Saline soils often constitute sites of accumulation of industrial and urban wastes contaminated by heavy metals. Halophytes, i.e. native salt-tolerant species, could be more suitable for heavy metal phytoextraction from saline areas than glycophytes, most frequently used so far. In the framework of this approach, we assess here the Ni phytoextraction potential in the halophyte Mesembryanthemum crystallinum compared with the model species Brassica juncea. Plants were hydroponically maintained for 21 days at 0, 25, 50, and 100 μM NiCl2. Nickel addition significantly restricted the growth activity of both species, and to a higher extent in M. crystallinum, which did not, however, show Ni-related toxicity symptoms on leaves. Interestingly, photosynthesis activity, chlorophyll content and photosystem II integrity assessed by chlorophyll fluorescence were less impacted in Ni-treated M. crystallinum as compared to B. juncea. The plant mineral nutrition was differently affected by NiCl2 exposure depending on the element, the species investigated and even the organ. In both species, roots were the preferential sites of Ni2+ accumulation, but the fraction translocated to shoots was higher in B. juncea than in M. crystallinum. The relatively good tolerance of M. crystallinum to Ni suggests that this halophyte species could be used in the phytoextraction of moderately polluted saline soils.
The effects and mechanisms of indole-3-acetic (IAA), kinetin (KN) and spermidine (Spd) assisted with ethylenediamine disuccinic acid (EDDS) on Cd and Pb accumulation in ramie were investigated by a pot experiment. In the first stage, the optimum concentrations of IAA, KN, and Spd were determined. And the effects of IAA, KN, and Spd at their optimum concentration on the antioxidant enzymes, non-enzymatic antioxidants, and metal accumulation in ramie were evaluated in the secondary stage. The results show that the translocation factor (TF) of Cd and Pb were increased by approximately 47 and 112%, respectively, at the presence of KN in combination with EDDS. In comparison with IAA treatment, Cd and Pb in root symplast were increased, approximately 2.02 and 2.62 times upon the combined application of IAA and EDDS. In addition, the contents of antioxidant enzymes and non-enzymatic antioxidant were increased dramatically through the addition of IAA, KN, and Spd plus EDDS. On the whole, IAA, KN, and Spd assisted with EDDS could significantly alleviate the oxidative stress induced by Cd and Pb in ramie.
Soil amendment with chelating agents can increase metal uptake and translocation in biomass species through increased metal bioavailability together with possible increases in metal leaching. In this study, we assessed the efficiency and environmental risk of the fast-degradable [S,S]-EDDS. Cu, Pb and Zn uptake in pot-cultivated Brassica carinata A. Braun, residual substrate metal bioavailability and leaching were investigated after one cycle of EDDS-assisted phytoextraction in mixed metal-contaminated pyrite waste, which is characterised by high Fe content. The chelator was supplied at doses of 2.5 and 5 mmol EDDS kg(-1) waste 1 week before harvest and 1 mmol EDDS kg(-1) waste repeated five times at 5- and 10-day intervals during the growing cycle. Here we demonstrate that EDDS generally increases shoot metal concentrations-especially of Cu-but only seldom improves removals because of markedly impaired growth. Considerable phytotoxicity and Cu leaching occurred under repeated EDDS treatments, although environmental risks may also arise from the single, close-to-harvest applications as Cu bioavailability in waste at plant harvest still remained very high (up to +67 % at 5 mmol EDDS kg(-1) vs. untreated controls). The residual bioavailability of Zn and Pb was instead generally reduced, perhaps due to shifts in cation exchange, whereas Fe mobility was not apparently affected. The amount of metals removed by plants represented a small fraction of the bioavailable pool (<1 %), and mobilised metals quickly reached deep layers in the substrate. We conclude that EDDS assistance can provide only some limited opportunities for improving phytoremediation of pyrite waste, major benefits being achieved by low doses to be traditionally applied shortly before harvest, with due attention to limiting groundwater pollution.