Phytostabilization potential of two ecotypes of Vetiveria zizanioides in cadmium-contaminated soils: greenhouse and field experiments

Phytotoxicity of radionuclides: A review of sources, impacts and remediation strategies

Various anthropogenic activities and natural sources contribute to the presence of radioactive materials in the environment, posing a serious threat to phytotoxicity. Contamination of soil and water by radioactive isotopes degrades the environmental quality and biodiversity. They persist in soils for a considerable amount of time and disturb the fauna and flora of any affected area. Hence, their removal from the contaminated medium is inevitable to prevent their entry into the food chain and the organisms at higher levels of the food chain. Physicochemical methods for radioactive element remediation are effective; however, they are not eco-friendly, can be expensive and impractical for large-scale remediation. Contrastingly, different bioremediation approaches, such as phytoremediation using appropriate plant species for removing the radionuclides from the polluted sites, and microbe-based remediation, represent promising alternatives for cleanup. In this review, sources of radionuclides in soil as well as their hazardous impacts on plants are discussed. Moreover, various conventional physicochemical approaches used for remediation discussed in detail. Similarly, the effectiveness and superiority of various bioremediation approaches, such as phytoremediation and microbe-based remediation, over traditional approaches have been explained in detail. In the end, future perspectives related to enhancing the efficiency of the phytoremediation process have been elaborated.

Differential physiological responses and tolerance to potentially toxic elements in Primula forbesii Franch

Environmental pollution caused by potentially toxic elements (PTEs) has become a global problem that endangers environmental sustainability due to industrial, agricultural, and urban pollution. Primula forbesii Franch. (a synonym of Primula filipes G. Watt.) is a biennial flower native to China with excellent stress resistance and ornamental value. In this study, we examined the phenotypic traits, growth indexes, and physiological properties of P. forbesii in response to five representative PTEs (Cd, Ni, Cr(III), Cu, and Zn) under hydroponic culture conditions. High concentrations of Zn and Cr had little effect on the growth and physiological properties of P. forbesii, indicating that the species has strong tolerance to Zn and Cr stress. Alternatively, high concentrations of Cd, Ni, and Cu seriously affected plant growth and development, resulting in leaf chlorosis and even death, and therefore may have a serious negative impact on the growth of P. forbesii. However, activity levels of some antioxidant enzymes and osmotic regulatory substances remained high, indicating that P. forbesii resisted PTE stress by regulating physiological and biochemical metabolism to a certain extent. Furthermore, principal component analysis and membership function were used to comprehensively evaluate P. forbesii resistance to PTEs. These analyses revealed that P. forbesii exhibits distinct sensitivities and physiological responses to different PTEs and suggested that the resistance to five PTEs in decreasing order is Zn > Cr > Cd > Cu > Ni. These results provide a theoretical basis for the future application of P. forbesii in environments with PTE pollution and may expand its practical utilization.

Improving capacity for phytoremediation of Vetiver grass and Indian mustard in heavy metal (Al and Mn) contaminated water through the application of clay minerals

One of the consequences of mining is the release of heavy metals into the environment, especially water bodies. Phytoremediation of areas contaminated by heavy metals using Vetiver grass and Indian mustard is cost-effective and environmentally friendly. This study aimed at enhancing remediation of heavy metal contaminated water through the simultaneous hybrid application of clay minerals (attapulgite and bentonite) and Vetiver grass or Indian mustard. A 21-day greenhouse experiment was carried out to investigate the effectiveness of the clay minerals to improve heavy metal phytoremediation. The highest accumulation of aluminium (Al) by Vetiver grass was 371.8 mg/kg in the BT2.5VT treatment, while for Mn, the highest accumulation of 34.71 mg/kg was observed in the AT1VT treatment. However, Indian mustard showed no significant uptake of heavy metals, but suffered heavy metal toxicity despite the addition of clay minerals. From this study, it was evident that bentonite added at 2.5% (w/v) could improve the phytoremediation capacity of Vetiver grass for Al and Mn polluted water. The current laboratory-scale findings provided a basis for field trials earmarked for remediation in a post-mining coal environment in South Africa. This remediation approach can also be adopted in other places.

Compost and microbial biostimulant applications improve plant growth and soil biological fertility of a grass-based phytostabilization system

In this work, a grass-based phytoremediation system integrated with an organic amendment and biostimulants was evaluated for remediating contaminated sites. Plant growth and biological fertility were monitored to assess the efficacy of a vegetative cap used as a safety measure to reduce sanitary and environmental risks of industrially contaminated soils and soil-washing sludges. Both matrices were potentially contaminated with Pb and Zn with an ecological risk index from low to moderate. According to potentially toxic elements (PTEs) bioaccessibility tests, the exposure to the released fine particulate matter may cause serious risks to human beings, in particular to children. The grass mixture was well adapted to both the substrates and a low PTEs mobility was detected, thus, reducing the leaching risk to ground water sources. Compost addition augmented significantly nitrogenase reductase (nifH) and ammonia monooxygenase (amoA) gene expression abundance in both substrates. Furthermore, a positive interaction between compost fertilization and a Trichoderma-based biostimulant inoculation was recorded in sludges resulting in a significant stimulation of nitrogen-fixing and ammonia-oxidizing bacteria. The application of compost and biostimulant increased soil fertility and plant growth. Furthermore, there was a slight reduction in PTE bioaccessibility, thus, improving the efficiency of the phytostabilization, limiting the resuspension and dispersion of the health-risk soil particulate.

Increase in Cd Tolerance through Seed-Borne Endophytic Fungus Epichloë gansuensis Affected Root Exudates and Rhizosphere Bacterial Community of Achnatherum inebrians

Soil cadmium (Cd) pollution is a serious environmental problem imperiling food safety and human health. The endophyte Epichloë gansuensis can improve the tolerance of Achnatherum inebrians to Cd stress. However, it is still unknown whether and how the endophyte helps host plants build up a specific bacterial community when challenged by CdCl2. In this study, the responses of the structure and function of bacterial community and root exudates of E+ (E. gansuensis infected) and E- (E. gansuensis uninfected) plants to Cd stress were investigated. Analysis of bacterial community structure indicated that the rhizosphere bacterial community predominated over the root endosphere bacterial community in enhancing the resistance of CdCl2 in a host mediated by E. gansuensis. E+ plant strengthened the interspecific cooperation of rhizosphere bacterial species. Moreover, the analysis of root exudates demonstrated E. gansuensis and increased the contents of organic acids and amino acids under Cd stress, and most root exudates were significantly correlated with rhizosphere bacteria. These results suggested that E. gansuensis employed a specific strategy to recruit distinct rhizosphere bacterial species and relevant functions by affecting root exudates to improve the tolerance of the host to Cd stress. This study provides a firm foundation for the potential application of symbionts in improving phytostabilization efficiency.

Organic amendment additions to cadmium-contaminated soils for phytostabilization of three bioenergy crops

The effects of organic amendments on the phytoremediation of cadmium (Cd) in acacia (Acacia mangium), jatropha (Jatropha curcas), and cassava (Manihot esculenta) were investigated. The bone meal/bat manure and leonardite/bat manure amendments resulted in better growth performance in both acacia and cassava (growth rate in dry biomass; GRDB 24.2 and 22.2, respectively), while bone meal (GRDB 17.2) was best for jatropha. The lower root/shoot ratio values of jatropha and acacia suggest that these species were better suited than cassava on Cd-contaminated soil. Cassava experienced toxicity symptoms after harvest (3 months). Acacia root accumulated somewhat greater Cd concentrations (up to 5.1 mg kg^-1) than cassava and jatropha roots (2.2-3.9 and 2.7-4.1 mg kg^-1, respectively). The bone meal and chicken manure (BMCM) treatment for jatropha had the highest bioconcentration factor for root (1.3) and the lowest translocation factor (0.7). Despite the fact that this treatment had substantial Cd concentrations in the soil (3.1 mg kg^-1), low Cd accumulation value (3.2 mg kg^-1) and the lowest Cd uptake value (127.8 mg plant^-1) were observed, clearly indicating that this amendment reduced Cd bioavailability. When growth performance of the study plants is considered, jatropha and acacia may be suitable for phytomanagement of Cd-contaminated soil.

Cadmium uptake by a hyperaccumulator and three Pennisetum grasses with associated rhizosphere effects

Pennisetum grasses (P. purpureum Schumach. 'Purple', P. alopecuroides (L.) Spreng. 'Liren' and P. alopecuroides (L.) Spreng. 'Changsui'), and a cadmium (Cd) hyperaccumulator (Thlaspi caerulescens J.Presl & C.Presl), were grown in soil with four Cd addition levels of 0, 2, 20 and 200 mg/kg. Toxicity symptoms were not observed although growth of all plants decreased as Cd addition increased. Shoot bioconcentration factor (BCFS), the translocation factor (TF) and shoot accumulation of Cd for most plants first increased and then declined as Cd concentrations increased. In contrast, the root bioconcentration factor (BCFR) for T. caerulescens declined and root Cd accumulation for T. caerulescens and two P. alopecuroides cultivars increased consistently as Cd levels increased. P. purpureum had the largest biomass with shoot Cd accumulation similar to that of T. caerulescens, despite lower foliar Cd concentration. Although shoot Cd concentrations of two P. alopecuroides cultivars were lower than for P. purpureum, root Cd concentrations were greater. P. purpureum had Cd BCFS and TF (> 1) at 2- and 20-mg/kg Cd addition treatments, similar to T. caerulescens. P. alopecuroides cultivars had Cd BCFR (> 1) and TF (< 1) at all Cd levels. Roots did not affect rhizosphere pH. However, concentrations of acid extractable Cd in rhizosphere soil were lower than those of corresponding non-rhizosphere soil at all Cd levels for T. caerulescens and P. purpureum; T. caerulescens and P. purpureum did not affect less bioavailable Cd fractions. Concentrations of acid extractable Cd in the rhizosphere of the P. alopecuroides cultivars were not reduced at any Cd level. Differences in Cd accumulation among the three Pennisetum grasses were mainly attributable to root biomass and Cd TFs rather than rhizosphere Cd mobility.

Phytoremediation for Co-contaminated Soils of Cadmium and Polychlorinated Biphenyls Using the Ornamental Plant Tagetes patula L

In this study, pot-culture experiments were conducted to investigate the single effect of Cd, PCBs, and the combined effect of Cd-PCBs with Tagetes patula L. The study highlights that the minimum concentration of PCBs (100 µg kg^-1) could enable the growth of the plant with an increase in biomass by 27.76% when compared with the control. In all the experiments performed, the Cd concentrations over the surface parts were found to be above 100 mg kg^-1. Significant positive correlations were observed between the Cd and PCBs concentrations accumulated in tissues of the soil and plants (p < 0.05). T. patula exhibited high tolerance to Cd and PCBs, and the plant promoted the removal rate of PCBs. The removal rates of PCB18 and PCB28 were up to 42.72 and 42.29%, respectively. The study highlights the potential and suitability of T. patula for phytoremediation of Cd and PCBs in contaminated soils.

Nickel and cadmium phytoextraction efficiencies of vetiver and lemongrass grown on Ni-Cd battery waste contaminated soil: A comparative study of linear and nonlinear models

A comparative assessment of the phytoremediation efficiency of two tolerant grass species viz. vetiver and lemongrass were performed in pots against simulated Ni-Cd battery electrolyte waste (EW) contaminated soil (EW1%, EW2% and EW4% w/w). Ni (μg g^-1) accumulation was higher in shoots (36.8) and roots (252.9) of vetiver than in lemongrass (12.5 and 79.7, respectively). While the same trend was true for Cd (μg g^-1) accumulation in vetiver and lemon grass roots (232.2 and 147.2, respectively), however, the accumulation in vetiver shoot (43.4) was less than in lemongrass (99.9). The bioaccumulation factor of metals in both grasses increased with EW contamination. Vetiver was tolerant towards EW toxicity than lemongrass, as it exhibited lesser decline in morphological parameters, lesser rise in TBARS against the doses of EW. The activities of SOD, APX, POD enzymes were higher in vetiver whereas, only GR in lemongrass. Multiple linear regression model show, pH had strong and positive influence over the Ni and Cd uptake by the plants whereas, phosphate, OM and bioavailable metals influenced negatively. The higher R² (>0.9) and Chi-square values ≤ 1 in sigmoid non-linear model demonstrates robustness of the model for predicting the Ni and Cd accumulation (M_HM) in both the grasses. Ni accumulation was higher than Cd, roots had greater accumulation of heavy metal and vetiver was a greater accumulator of Ni and Cd from EW the contaminated soil than lemongrass.

Effects of soil amendments on leaf anatomical characteristics of marigolds cultivated in cadmium-spiked soils

The marigolds (Tagetes spp.) in this study were classified as excluders for cadmium (Cd); however, their leaves also accumulated substantial Cd content. Among the experimental treatments (i.e., control, cattle manure, pig manure, and leonardite which served as soil amendments), pig manure resulted in significantly increased growth performance for all marigold cultivars as seen by relative growth rates (119-132.3%) and showed positive effects on leaf anatomy modifications, e.g., thickness of spongy and palisade mesophyll, size of vein area and diameter of xylem cells. This may be due to substantially higher essential nutrient content, e.g., total nitrogen (N) and extractable phosphorus (P), in pig manure that aided all marigold cultivars, particularly the French cultivar which exhibited the highest relative growth rate (132.3%). In the Cd-only treatment, cell disorganization was observed in vascular bundles as well as in palisade and spongy mesophyll, which may have been responsible for the lowest plant growth performance recorded in this study, particularly among the American and Honey cultivars (RGR = 73% and 77.3%, respectively).

Potential of ornamental monocot plants for rhizofiltration of cadmium and zinc in hydroponic systems

Cadmium (Cd) and zinc (Zn) accumulation and uptake ability have been investigated in three ornamental monocot plants (Heliconia psittacorum x H. spathocircinata, Echinodorus cordifolius, and Pontederia cordata) grown in hydroponic systems. All study plants in the highest heavy metal treatments were found to be excluders for Cd and Zn with translocation factor values < 1 and bioconcentration factor (BCF) values > 100. The highest Cd and Zn accumulations were found in roots of E. cordifolius (4766.6 mg Zn kg^-1 and 6141.6 mg Cd kg^-1), followed by H. psittacorum x H. spathocircinata (4313.5 mg Zn kg^-1) and P. cordata (3673.3 mg Cd kg^-1), respectively, whereas shoots had lower performances. However, P. cordata had the lowest dry biomass production compared to the other two plant species in this study. As a result of dilution effects, heavy metal accumulation for all study plants was lower in the combined heavy metal treatments than in solely Cd and Zn only treatments. At the end of experiments, the highest uptakes of Cd and Zn were found in H. psittacorum x H. spathocircinata (62.1% Zn²⁺ from 10 mg Zn L^-1 solution) and E. cordifolius (27.3% Cd²⁺ from 2 mg Cd L^-1 solution). Low percentage metal uptakes were found in P. cordata; therefore, E. cordifolius and H. psittacorum x H. spathocircinata are clearly better suited for removing Cd and/or Zn from contaminated waters and hydroponic systems.

Phytoremediation Perspectives of Seven Aquatic Macrophytes for Removal of Heavy Metals from Polluted Drains in the Nile Delta of Egypt

Simple Summary

Some main drains in the Nile Delta of Egypt are subjected to heavy pollution loads and used to irrigate crops and vegetables. Here, we assessed the pollution level and the ability of some wild aquatic macrophytes (Cyperus alopecuroides, Echinochloa stagnina, Eichhornia crassipes, Ludwigia stolonifera, Phragmites australis, Ranunculus sceleratus, and Typha domingensis) to accumulate eight heavy metals (Fe, Cu, Zn, Mn, Co, Cd, Ni, and Pb) in three of the polluted drains (Amar, El-Westany, and Omar-Beck). The sediment in the three drains exceeded the worldwide permissible ranges of Cu, Zn, and Pb, but it ranged within safe limits for Mn, Cd, Ni, and Co. P. australis accumulated the highest levels of Fe, Co, Cd, and Ni, while E. crassipes contained the highest concentrations of Cu, Zn, Mn and Pb. The bioaccumulation factor was > 1 for the investigated heavy metals (except Cu) in all species, except C. alopecuroides. Accordingly, these species could be applied for the accumulation and phytostabilization of these metals.

Abstract

The current study addressed the heavy metals accumulation potentials of seven perennial aquatic macrophytes (Cyperus alopecuroides, Echinochloa stagnina, Eichhornia crassipes, Ludwigia stolonifera, Phragmites australis, Ranunculus sceleratus and Typha domingensis) and the pollution status of three drains (Amar, El-Westany and Omar-Beck) in the Nile Delta of Egypt. Nine sites at each drain were sampled for sediment and plant analyses. Concentrations of eight metals (Fe, Cu, Zn, Mn, Co, Cd, Ni, and Pb) were determined in the sediment and the aboveground and belowground tissues of the selected macrophytes. Bioaccumulation factor (BF) and translocation factor (TF) were computed for each species. The sediment heavy metals concentrations of the three drains occurred in the following order: El-Westany > Amar > Omar-Beck. The concentrations of sediment heavy metals in the three drains were ordered as follows: Fe (438.45–615.17 mg kg⁻¹) > Mn (341.22–481.09 mg kg⁻¹) > Zn (245.08–383.19 mg kg⁻¹) > Cu (205.41–289.56 mg kg⁻¹) > Pb (31.49–97.73 mg kg⁻¹) > Cd (13.97–55.99 mg kg⁻¹) > Ni (14.36–39.34 mg kg⁻¹) > Co (1.25–3.51 mg kg⁻¹). The sediment exceeded the worldwide permissible ranges of Cu, Zn and Pb, but ranged within safe limits for Mn, Cd, Ni and Co. P. australis accumulated the highest concentrations of Fe, Co, Cd and Ni, while E. crassipes contained the highest concentrations of Cu, Zn, Mn, and Pb. Except for C. alopecuroides and Cu metal, the studied species had BF values greater than one for the investigated heavy metals. Nevertheless, the TFs of all species (except Cd in L. stolonifera) were less than one. Hence, the studied species are appropriate for accumulation, biomonitoring, and phytostabilization of the investigated metals.

Improvement of the Cu and Cd phytostabilization efficiency of perennial ryegrass through the inoculation of three metal-resistant PGPR strains

To explore a novel strategy for the remediation of soils polluted with Cu and Cd, three strains of plant-growth-promoting rhizobacteria (PGPRs) isolated from contaminated mines and two grass species (perennial ryegrass and tall fescue) were selected in this study. The performance of PGPR strains in metal adsorption, maintaining promotion traits under stress, and ameliorating phytostabilization potential was evaluated. Cd²⁺ exerted a stronger deleterious effect on microbial growth than Cu²⁺, but the opposite occurred for grass seedlings. Adsorption experiment showed that the growing PGPR strains were able to immobilize maximum 79.49% Cu and 81.35% Cd owing to biosorption or bioaccumulation. The strains exhibited the ability to secrete indole-3-acetic acid (IAA) and dissolve phosphorus in the absence and presence of metals, and IAA production was even enhanced in the presence of low Cu²⁺ (5 mg L^-1). However, the siderophore-producing ability of the isolates was strongly suppressed under Cu and Cd exposure. Ryegrass was further selected for pot experiments owing to its higher germination rate and tolerance under Cu and Cd stress than fescue. Pot-experiment results revealed that PGPR addition significantly increased the shoot and root biomasses of ryegrass by 11.49%-44.50% and 43.53%-90.29% in soil co-contaminated with 800 mg Cu kg^-1 and 30 mg Cd kg^-1, respectively. Metal uptake and translocation in inoculated ryegrass significantly decreased owing to the reduced diethylenetriamine pentaacetic acid-extractable metal content and increased residual metal-fraction percentage mediated by PGPR. Interestingly, stress mitigation was observed in these inoculated plants; in particular, their malondialdehyde content and superoxide dismutase activity were even significantly lower than those of ryegrass under normal conditions. Therefore, PGPR could be a promising option to enhance the phytostabilization efficiency of Cu and Cd in heavily polluted soils.

Uptake and release of chromium and nickel by Vetiver grass (Chrysopogon zizanioides (L.) Roberty)

The effectiveness of using Vetiver grass (Chrysopogon zizanioides) in phytoremediation of wastewater has been proven. In this study, the phytoremediation potential of C. zizanioides planted in Cr- and Ni-contaminated soil was evaluated through investigating the behaviors on uptake and release of metals. Three treatments: control, Cr, and Ni, with three concentrations (50, 150, and 300 ppm), were applied. The potential of C. zizanioides is assessed by the determination of metal uptake rate, metal release rate, bioconcentration factor (BCF), biological absorption coefficient (BAC), and translocation factor (TF). The experiment showed that Cr uptake was higher than release rate and on the other hand low in uptake and release of Ni. Accumulation of Cr and Ni was 167.8 mg kg−1 and 66.3 mg kg−1, respectively. Excess of Cr in the soil was absorbed in high uptake rate making vetiver grass suitable for Cr phytoremediation. During 28-day uptake and 28-day release periods, it was found that BCF, BAC, and TF values in some treatments showed greater than 1 (one) and Ni-treated plants were able to translocate Ni to aerial plant parts supported by its high TF value. Low acidity of soil causes low solubility and low mobility of metals, resulting in low metal absorption. C. zizanioides has shown the potential as a heavy metal-tolerant species and could be potentially used as phytoremediation alternative species at least in lightly polluted areas.

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

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

Morphological Responses and Gene Expression of Grain Amaranth (Amaranthus spp.) Growing under Cd

Phytoremediation efficiency depends on the ability of plants to accumulate, translocate and resist high levels of metals without symptoms of toxicity. This study was conducted to evaluate the potential of grain amaranth for remediation of soils contaminated with Cd. Three grain amaranth varieties, “Pribina” (A. cruentus), “Zobor” (A. hypochondriacus x A. hybridus) and Plainsman (A. hypochondriacus x A. hybridus) were tested under different level of Cd (0, 5, 10 and 15 mg/L) in a hydroponic experimental treatment. All could be classified as Cd excluders or Cd-hypertolerant varieties able to grow and accumulate significant amounts of Cd from the hydroponic solution, preferentially in the roots. Under the highest level of Cd exposure, qRT-PCR expression analysis of five stress-related genes was examined in above- and below-ground biomass. The results show that the Cd concentration significantly increased the mRNA level of chitinase 5 (Chit 5) in amaranth roots as the primary site of metal stress. The involvement of phytochelatin synthase (PCS1) in Cd detoxification is suggested. Based on our findings, we can conclude that variety “Pribina” is the most Cd-tolerant among three tested and can be expected to be used in the phytomanagement of Cd loaded soils as an effective phytostabiliser.

Effect of Serratia sp. K3 combined with organic materials on cadmium migration in soil-vetiveria zizanioides L. system and bacterial community in contaminated soil

Phytoremediation is an economical strategy to harvest cadmium (Cd) from contaminated soil, but the efficiency of phytoremediation was affected by many factors. This study investigated the potential of Serratia sp. K3 (K3) assisted with straw biogas residue (SBR) or leavening fertilizer (LF) on improving the Cd migration efficiency and micro-environment in soil-vetiveria zizanioides L. system. The results showed that the acid soluble Cd in soil was increased by 2.83-29.79% in treatments compared with control (CK). In addition, Cd accumulation in the roots and shoots of vetiveria zizanioides were significantly enhanced by the combination of K3 and SBR/LF. Especially, the translocation factor of Cd increased by 21.53-62.37% in groups with K3 compared with the groups without K3, correspondingly. Furthermore, SBR/LF effectively changed bacterial community structure, and improved bacterial abundance. Relative abundance of functional genes related with carbohydrate/energy/amino acid metabolism were increased in groups of SBRB/LFB rhizosphere compared with CK. These results provide insight into the change of phytoremediation efficiency and soil bacterial communities in the vetiveria zizanioides rhizosphere after inoculation. This study may provide a promising method for improving phytoremediation in Cd contaminated soil.

The potential of an energy crop "Conocarpus erectus" for lead phytoextraction and phytostabilization of chromium, nickel, and cadmium: An excellent option for the management of multi-metal contaminated soils

Past studies have thoroughly explored the phytoextraction/phytostabilization potentials of different plant species for particular metals. However, none of the plants was able to tackle the problem of multi-metal in contaminated soils. We report herewith the potential of Conocarpus erectus to extract lead (Pb) while having the capability to stabilize chromium (Cr), nickel (Ni) and cadmium (Cd) in polluted soil. The C. erectus was subjected to grow for 120 days in a soil spiked with four different levels of each metal i.e. Pb (0, 600, 1200 and 2400 mg kg^-1), Ni (0, 50, 100 and 200 mg kg^-1), Cr (0, 150, 300 and 600 mg kg^-1) and Cd (0, 20, 40 and 80 mg kg^-1). Data related to plant growth, physiology, biochemistry and antioxidants activities revealed that forenamed parameters were significantly reduced with increasing spiking levels. Contrarily, metal speciation in plant parts (metal concentrations in shoots and roots, and metal contents in these corresponding plant parts), metal removal per pot, and DTPA-extractable metals from the soil were significantly increased with increasing spiking level upon the termination of the experiment. Curiously, each spiking level demonstrated elevated Pb concentrations in shoots than roots, while the concentrations of other metals (Cr, Ni, and Cd) were found higher in roots than in the shoots. Likewise, at each spiking level, C. erectus showed both bioconcentration factor (BCF) and translocation factor (TF) values greater than 1 for Pb, while these values were ever lower than 1 for Cr, Ni, and Cd. Moreover, the percentages of Pb removal were ever higher than other metals at each spiking level. Outcomes of our experiment suggest that C. erectus has immense potential for the phytoextraction of Pb and phytostabilization of Cr, Ni, and Cd in polluted soil. It is suggested that this plant can be used to tackle the problem of multi-metal pollution in soils.

Soil amendments for cadmium phytostabilization by five marigold cultivars

In recent years, ornamental plants have come under investigation as phytoremediation agents. In addition to reducing contaminant concentrations in soil, such plants support local economies by serving social (e.g., religious) and decorative purposes. Greenhouse studies investigated the phytostabilization potential of soil cadmium (Cd) by five cultivars of marigold (Tagetes erecta), a common ornamental flower in Asia. The effects of organic (cattle manure and pig manure) and inorganic (leonardite and Osmocote®) amendments in supporting plant growth and enhancing Cd uptake were also examined. Marigold cultivars Babuda and Sunshine grown in soil supplemented with pig manure produced the greatest biomass and experienced greatest Cd accumulation and flower production. In all treatments, plant parts accumulated Cd in the following order: root > shoot ≈ flower. Furthermore, Babuda and Sunshine cultivars had a high phytostabilization potential as evidenced by translocation factors < 1 and bioconcentration factors > 1 for roots. It is proposed that Babuda and Sunshine marigold cultivars be applied toward Cd phytostabilization while enhancing local economies as an ornamental species.

Root system architecture influencing cadmium accumulation in rice (Oryza sativa L.)

Cadmium (Cd) contamination in paddy fields affects human health because of the consumption of Cd-contaminated rice. In the current study, we demonstrated that variation in root system architecture (RSA) influenced Cd uptake by rice. Rice cultivars consisting of KDML105, Mali Dang, Pitsanulok2 and Niaw San-pah-tawng were assessed in hydroponics and mesocosms while KDML 105, Pitsanulok2, and RD53 were used in field experiments. In hydroponics, root number and root weight were positively correlated with Cd uptake. In mesocosms, we found that the effects of Cd on RSA depended on rice varieties. Among different rice varieties, Mali Dang consistently accumulated high concentration of Cd, while Niaw San-pah-tawng tended to accumulate much lower amount in its shoot in both hydroponics and mesocosms. Correlation analysis indicates that Cd concentrations in shoot was positively correlated with root weight (R² = 0.95), crown root number (R² = 0.74), and negatively correlated with root depth (R² = 0.86). In the field, Cd is most abundant at a depth of 10-20 cm. and root distribution influenced Cd uptake as evidenced by high root Cd content in the RD53 variety. We propose that low crown root number and deep RSA could be promising traits for selection and breeding for low Cd uptake rice.

Phytoremediation of landfill leachate waste contaminants through floating bed technique using water hyacinth and water lettuce

In the present study, the effectiveness of water hyacinth and water lettuce was tested for the phytoremediation of landfill leachate for the period of 15 days. Fifteen plastic containers were used in experimental setup where aquatic plants were fitted as a floating bed with the help of thermo-pole sheet. It was observed that both plants significantly (p < 0.05/p < 0.01/p < 0.001) reduce the physicochemical parameters pH, TDS, BOD, COD and heavy metals like Zn, Pb, Fe, Cu and Ni from landfill leachate. Maximum reduction in these parameters was obtained at 50% and 75% landfill leachate treatment and their removal rate gradually increased from day 3 to day 15 of the experiment. The maximum removal rate for heavy metals such as for Zn (80-90%), Fe (83-87%) and Pb (76-84%) was attained by Eichhornia crassipes and Pistia stratiotes. Value of bioconcentration and translocation factor was less than 1 which indicates the low transport of heavy metals from roots to the above-ground parts of the plants. Both these plants accumulate heavy metals inside their body without showing much reduction in growth and showing tolerance to all the present metals. Therefore, results obtained from the study suggest that these aquatic plants are suitable candidate for the removal of pollution load from landfill leachate.

Ralstonia eutropha Q2-8 reduces wheat plant above-ground tissue cadmium and arsenic uptake and increases the expression of the plant root cell wall organization and biosynthesis-related proteins

In this study, the molecular mechanisms involved in Ralstonia eutropha Q2-8-induced increased biomass and reduced cadmium (Cd) and arsenic (As) uptake in wheat plants (Triticum aestivum cv. Yangmai 16) were investigated in growth chambers. Strain Q2-8 significantly increased plant biomass (22-75%) without and with Cd (5 μM) + As (10 μM) stress and reduced plant above-ground tissue Cd (37%) and As (34%) contents compared to those in the controls. Strain Q2-8 significantly increased the proportions of Cd and As in wheat root cell walls. Under Cd and As stress, 109 root proteins were differentially expressed among which those involved in metabolisms, stress and defence, and energy were dominant in the presence of strain Q2-8. Furthermore, energy-, defence-, and cell wall biosynthesis-related proteins were found to be up-regulated. Notably, differentially expressed cell wall biosynthesis-related proteins in roots were only found in bacteria-inoculated plants under Cd and As stress. The results suggest that strain Q2-8 can alleviate Cd and As toxicity to wheat plant seedlings and reduce above-ground tissue Cd and As uptake by increasing the efficiency of root energy metabolism, defence, and cell wall biosynthesis under Cd and As stress.

Aquatic plants for phytostabilization of cadmium and zinc in hydroponic experiments

Cadmium (Cd) may be toxic to aquatic plants even at modest concentrations, and excessive quantities of zinc (Zn) decrease plant performance. The Cd and Zn phytoremediation potential of several aquatic plant species (Thalia geniculate, Cyperus alternifolius, Canna indica, Eichhornia crassipes, Pistia stratiotes) and one grass species (Vetiveria zizanioides) was evaluated in hydroponic experiments. Vetiveria zizanioides, E. crassipes, and P. stratiotes experienced reduced growth performance in the presence of Cd as determined from biomass production, survival rate, and crown root number (CN); however, they accumulated high quantities of metals in their tissues, particularly in roots. Root accumulation is considered a key characteristic of so-called excluder species. In this study, only E. crassipes and P. stratiotes had bioconcentration factors and translocation factors (> 1000 and < 1, respectively) suitable for high phytostabilization of Cd. Furthermore, V. zizanioides and P. stratiotes showed the highest percent metal uptake from solution and removal capacity for Zn (~70% and ~2 mg d^-1 g^-1, respectively). Emergent aquatic species (particularly C. alternifolius and T. geniculate) adapted and lived well in Cd- and Zn-contaminated solution and took up high quantities of Cd and Zn in roots, and are therefore considered strong excluders. Beneficial uses of such species in contaminated wetlands include stabilizing toxic metals and limiting erosion. Plant tissue can be applied to other uses, including as a biomass fuel. In field situations, the candidate species may work best when grown together, since each plant genotype possesses a different potential to control Cd and Zn.

Differential distribution of metals in tree tissues growing on reclaimed coal mine overburden dumps, Jharia coal field (India)

Opencast bituminous coal mining invariably generates huge amount of metal-polluted waste rocks (stored as overburden (OB) dumps) and reclaimed by planting fast growing hardy tree species which accumulate metals in their tissues. In the present study, reclaimed OB dumps located in Jharia coal field (Jharkhand, India) were selected to assess the accumulation of selected metals (Pb, Zn, Mn, Cu and Co) in tissues (leaf, stem bark, stem wood, root bark and root wood) of two commonly planted tree species (Acacia auriculiformis A.Cunn. ex Benth. and Melia azedarach L.). In reclaimed mine soil (RMS), the concentrations of pseudo-total and available metals (DTPA-extractable) were found 182-498 and 196-1877% higher, respectively, than control soil (CS). The positive Spearman's correlation coefficients between pseudo-total concentration of Pb and Cu (r = 0.717; p < 0.05), Pb and Co (r = 0.650; p < 0.05), Zn and Mn (0.359), Cu and Co (r = 0.896; p < 0.01) suggested similar sources for Pb-Cu-Co and Mn-Zn. Among the five tree tissues considered, Pb selectively accumulated in root bark, stem bark and leaves; Zn and Mn in leaves; and Cu in root wood and stem wood. These results suggested metal accumulation to be "tissue-specific". The biological indices (BCF, TF_leaf, TF_{stem bark} and TF_{stem wood}) indicated variation in metal uptake potential of different tree tissues. The study indicated that A. auriculiformis could be employed for Mn phytoextraction (BCF, TF_leaf, TF_{stem bark} and TF_{stem wood} > 1). The applicability of both the trees in Cu phytostabilization (BCF > 1; TF_leaf, TF_{stem bark} and TF_{stem wood} < 1) was suggested. The study enhanced knowledge about the selection of tree species for the phytoremediation of coal mine OB dumps and specific tree tissues for monitoring metal pollution.

Trace metal accumulation by Ranunculus sceleratus: implications for phytostabilization

This study investigated the growth response of Ranunculus sceleratus to pollution and its capacity to accumulate trace metals for its use as a phytoremediator in Lake Maruit, Egypt. Three basins (main basin, fish farm, and southwestern basin) representing the natural distribution of the plant as well as the pollution loads in the lake, were chosen for collecting plant and sediment samples. In each basin ten quadrats (0.5 m × 0.5 m), distributed equally along two sites, were selected for measuring growth parameters, nutrients, and trace metal concentration. The highest biomass of the shoot and root (610 and 236 g m^-2) was recorded in the main basin and fish farm, respectively. R. sceleratus accumulated high concentrations of Cu and Pb (27.7 and 9.9 mg kg^-1), while toxic concentration of Mn (2508.0 mg kg^-1) in their roots compared to shoots. The bioaccumulation factor (BF) for the investigated metals was greater than one, and in the decreasing order: Ni (27.1) > Zn (20.0) > Cd (16.4) > Cu (7.7) > Mn (3.9) > Pb (3.6). The translocation factor of all analyzed trace metals was less than one. The ability of R. sceleratus to accumulate Mn, Ni, Cu, and Pb in its roots indicates the potential use of this species for phytostabilization of these metals (mainly Mn) in contaminated water bodies.

A review on moringa tree and vetiver grass - Potential biorefinery feedstocks

Plants and derivatives have been explored for unlimited purposes by mankind, from crop cultivation for providing food and animal feed, to the use for cosmetics, therapeutics and energy. Moringa tree and vetiver grass features, capabilities and applications were explored through a literature review. The suitability of these plants for the bioenergy industry products is evidenced, namely for bioethanol, biogas and biodiesel, given the lignocellulosic biomass content of these plants and characteristics of moringa seed oil. In addition, moringa leaves and pods are an important source for food and animal feed industries due to their high nutrient value. Thus, the co-cultivation of moringa and vetiver could provide energy and food security, and contribute to more sustainable agricultural practices and for the development of rural areas. Policymakers, institutions and scientific community must engage to promote the cultivation of multipurpose crops to cope with energy and food industries competition for biomass.

Phytomanagement of radionuclides and heavy metals in mangrove sediments of Pattani Bay, Thailand using Avicennia marina and Pluchea indica

This study determines uptake and accumulation of radionuclides and heavy metals by Pluchea indica and Avicennia marina and evaluates phytoremediation potential via greenhouse and field experiments. P. indica and A. marina are considered excluders for ⁴⁰K and ²⁶²Ra, and Pb since roots accumulated them in higher quantities compared to other plant parts, and the bioconcentration factor (BCF) and transfer factor (TF) values for Pb, and ⁴⁰K and ²⁶²Ra were >1, respectively. Absorbed dose rate in air (D) showed significant values in sediments, which were generally over the maximum recommended value of 55nGyh^-1. Phytostabilization of radionuclides and heavy metals may serve as an appropriate strategy for mangrove-polluted areas. D values in sediments were considered sufficiently high to recommend long-term monitoring. Radionuclide activities may increase in the food chain via uptake and accumulation of edible plants, ultimately resulting in harm to human health.

The influence of particle size and feedstock of biochar on the accumulation of Cd, Zn, Pb, and As by Brassica chinensis L

Biochar produced from rice straw (RC) and maize stalk (MC) was amended to the heavy metal-contaminated soil to investigate the effects of different biochar feedstock and particle size (fine, moderate, coarse) on the accumulation of Cd, Zn, Pb, and As in Brassica chinensis L. (Chinese cabbage). The concentrations of Cd, Zn, and Pb in shoot were decreased by up to 57, 75, and 63%, respectively, after biochar addition (4%). Only MC decreased As concentration in B. chinensis L. shoots by up to 61%. Biochar treatments significantly decreased NH₄NO₃-extractable concentrations of Cd, Zn, and Pb in soil by 47-62, 33-66, and 38-71%, respectively, yet increased that of As by up to 147%. Amendment of RC was more effective on immobilizing Cd, Zn, and Pb, but mobilizing soil As, than MC. A decrease in biochar particle size greatly contributed to the immobilization of Cd, Zn, and Pb in soil and thereby the reduction of their accumulations in B. chinensis L. shoots, especially RC. Increases in soil pH and extractable P induced by biochar addition contributed to the sequestration of Cd, Zn, and Pb and the mobilization of As. Shoot biomass, root biomass, and root system of B. chinensis L. were enhanced with biochar amendments, especially RC. This study indicates that biochar addition could potentially decrease Cd, Zn, Pb, and As accumulations in B. chinensis L., and simultaneously increase its yield. A decrease in biochar particle size is favorable to improve the immobilization of heavy metals (except As). The reduction in Cd, Zn, Pb, and As levels in B. chinensis L. shoots by biochar amendment could be mainly attributed to a function of heavy metal mobility in soil, plant translocation factor, and root uptake.

Influence of amendments on Cd and Zn uptake and accumulation in rice (Oryza sativa L.) in contaminated soil

Cadmium is a toxic metallic element that poses serious human health risks via consumption of contaminated agricultural products. The effect of mixtures of dicalcium phosphate and organic amendments, namely cow manure (MD) and leonardite (LD), on Cd and Zn uptake of three rice cultivars (KDML105, KD53, and PSL2) was examined in mesocosm experiments. Plant growth, Cd and Zn accumulation, and physicochemical properties of the test soils were investigated before and after plant harvest. Amendment application was found to improve soil physicochemical properties; in particular, soil organic matter content and nutrient (N, P, K, Ca, and Mg) concentrations increased significantly. The MD treatment was optimal in terms of increasing plant growth; the MD and LD treatments decreased soil Cd concentration by 3.3-fold and 1.6-fold, respectively. For all treatments, all rice cultivars accumulated greater quantities of Cd and Zn in roots compared with panicles and shoots. Among the three cultivars, RD53 accumulated the lowest quantity of Cd. Translocation factors (<0.28) and bioconcentration coefficients of roots (>1) indicate that the three rice cultivars are Cd excluders. Our results suggest that a mixture of organic and inorganic amendments can be used to enhance rice growth while reducing accumulation of heavy metals when grown in contaminated soil.

Radionuclide (226Ra, 232Th, 40K) accumulation among plant species in mangrove ecosystems of Pattani Bay, Thailand

Little is known regarding phytoremediation of radionuclides from soil; even less is known about radionuclide contamination and removal in tropical ecosystems such as mangrove forests. In mangrove forests in Pattani Bay, Thailand, 18 plant species from 17 genera were evaluated for radionuclide concentrations within selected plant parts. Two shrub species, Avicennia marina and Pluchea indica, accumulated the highest ²³²Th (24.6Bqkg^-1) and ⁴⁰K (220.7Bqkg^-1) activity concentrations in roots, respectively. Furthermore, the aquatic species Typha angustifolia accumulated highest ²³²Th, ⁴⁰K and ²²⁶Ra activity concentrations (85.2, 363.5, 16.6Bqkg^-1, respectively) with the highest transfer factors (TFs) (3.0, 2.0, 5.9, respectively) in leaves. Leaves of T. angustifolia had an absorbed dose rate in air (D) over the recommended value (74.8nGyh^-1) that was considered sufficiently high to be of concern for human consumption.