Accumulation Of Heavy Metals In Plants Research Articles

Combined Application of Biochar and Plant Growth-Promoting Rhizobacteria Improves Heavy Metal and Drought Stress Tolerance in Zea mays.

Plants are often exposed to multiple stresses, including heavy metals (HM) and drought, which limit the plant growth and productivity. Though biochar or plant growth-promoting rhizobacteria (PGPR) have been widely used for alleviating HM or drought stress in plants, the study of the effects of combined treatment with biochar and PGPR under simultaneous HM and drought stress is limited. This study investigated individual and combined effects of groundnut shell biochar (GS-BC) and PGPR Bacillus pseudomycoides strain ARN7 on Zea mays growth, physiology, and HM accumulation, along with their impact on soil enzymes under HM (Ni and Zn), drought, or HM+drought stress. It was observed that even under HM+drought stress, Z. mays growth, total chlorophyll, proteins, phenolics, and relative water contents were increased in response to combined GS-BC and ARN7 treatment. Furthermore, the combined treatment positively influenced plant superoxide dismutase, ascorbate peroxidase, and catalase activities, while reducing electrolyte leakage and phenolics, malondialdehyde, and proline under HM, drought, or HM+drought stress. Interestingly, the combined GS-BC and ARN7 treatment decreased HM accumulation and the bioaccumulation factor in Z. mays, highlighting that the combined treatment is suitable for improving HM phytostabilization. Additionally, GS-BC increased soil enzymatic activities and ARN7 colonization irrespective of HM and drought stress. As far as we know, this study is the first to illustrate that combined biochar and PGPR treatment could lessen the adverse effects of both HM and drought, suggesting that such treatment can be used in water-deficient HM-contaminated areas to improve plant growth and reduce HM accumulation in plants.

Effect of Bacillus pumilus Strains on Heavy Metal Accumulation in Lettuce Grown on Contaminated Soil

Increasing number of heavy metal on land needs to be addressed through sustainable ways and various species of Bacillus can be used to mitigate heavy metals. The research work entitled “Effect of Bacillus pumilus strains on heavy metal accumulation in lettuce grown on contaminated soil” focuses on functional role of Bacillus pumilus strains inoculated with lettuce seed in mitigating heavy metal present in chromite mining soil. This experiment was conducted at ornamental horticulture nursery, the University of Agriculture Peshawar. In this experiment, factor A was three Bacillus pumilus strains (sequence C-2PMW-8, C-1 SSK-8 and C-1 PWK-7) while soil used for this experiment was collected from Prang Ghar mining site and lettuce seeds were grown in three levels of chromite mining soil (2.27, 4.65 and 7.14 %).The experimental design used during this research was randomized complete block design with two factors and was replicated thrice. The collected data related to effect of chromite mining soil and Bacillus pumilus strains indicated that these both factors have significant influence on growth parameters. For mining soil minimum days to germinate (14 days) was noted in lettuce grown on garden soil inoculated with sequence. Maximum germination percentage noted was (100%) for C-1 SSK-8 grown on garden soil, dry weight of lettuce leaf (5.0 g) for lettuce inoculated with C-1 SSK-8 and C-1 PWK-7 strains, survival percentage (77.9%) for C-1 SSK-8 treated lettuce for sequence C-2 PMW-8. Maximum germination percentage noted was (88%) for garden soil, fresh leaf weight (17.3g), dry leaf weight (6.5g), number of leaf per plant (16), leaf area (49.0 cm2) were noted in garden soil with no chromite mining soil. Results related to heavy metals accumulation showed that minimum chromium was (2.3 mg kg-1) in lettuce and (1.9 mg kg-1) in soil for all three sequences. It can be concluded that chromite mining soil significantly reduced the growth and survival of lettuce, but when lettuce was inoculated with Bacillus.pumilus strains it enhances the growth and survival. Similarly, minimum heavy metal accumulation in plant and soil, regardless of type of B. pumilus used, all three sequences has same mitigating effect on heavy metal in both soil and lettuce. All the three Bacillus pumilus strains ensured reduction in heavy metals content (Cr) in lettuce, below the maximum permissible limits of WHO/FAO 2011.

Magnetic field treatment on horticultural and agricultural crops: its benefits and challenges

ABSTRACT Magnetic field (MF) treatment, as an efficient and pollution-free treatment method, has received extensive attention from researchers and found broad prospects in horticultural and agricultural development. According to relevant studies, mainstream research direction is aimed at utilizing MF treatment to improve the economic traits of horticultural and agricultural crops. MF has positive effects, for example, on seed germination, seedling growth, crop yield and quality and plant tolerance to stress. In recent years, more and more researchers have focused their work on using seed MF or magnetised water (MW) irrigation treatment to improve plant tolerance to salt or heavy metal stresses, to achieve the purpose of soil restoration by plant heavy metal accumulation. In this review, the most commonly utilised MF or MW treatment methods have been described in detail, and the effects of MF treatment on horticultural and agricultural crops have been presented. Furthermore, new prospects for MF treatment and the associated molecular basis have been presented. Since different species or cultivars have different optimal dose requirements for MF treatment, it is still a challenge presently to promote MF treatment use in commercial applications. For successful implementation of MF treatments, it is essential to conduct a large number of screening experiments and more in-depth research on the effects of MF on cultivated plants.

Bioponic systems with biochar: Insights into nutrient recovery, heavy metal reduction, and microbial interactions in digestate-based bioponics

Bioponics is a nutrient-recovery technology that transforms nutrient-rich organic waste into plant biomass/bioproducts. Integrating biochar with digestate from anaerobic wastewater treatment process can improve resource recovery while mitigating heavy metal contamination. The overarching goal of this study was to investigate the application of biochar in digestate-based bioponics, focusing on its efficacy in nutrient recovery and heavy metal removal, while also exploring the microbial community dynamics. In this study, biochar was applied at 50 % w/w with 500 g dry weight of digestate during two 28-day crop cycles (uncontrolled pH and pH 5.5) using white stem pak choi (Brassica rapa var. chinensis) as a model crop. The results showed that the digestate provided sufficient phosphorus and nitrogen, supporting plant growth. Biochar amendment improved plant yield and phosphate solubilization and reduced nitrogen loss, especially at the pH 5.5. Furthermore, biochar reduced the heavy metal accumulation in plants, while concentrating these metals in the residual sludge. However, owing to potential non-carcinogenic and carcinogenic health risks, it is still not recommended to directly consume plants cultivated in digestate-based bioponic systems. Additionally, biochar amendment exhibited pronounced impact on the microbial community, promoting microbes responsible for nutrient solubilization and cycling (e.g., Tetrasphaera, Herpetosiphon, Hyphomicrobium, and Pseudorhodoplanes) and heavy metal stabilization (e.g., Leptolinea, Fonticella, Romboutsia, and Desulfurispora) in both the residual sludge and plants. Overall, the addition of biochar enhanced the microbial community and facilitated the metal stabilization and the cycling of nutrients within both residual sludge and root systems, thereby improving the overall efficiency of the bioponics.

Phytoremediation of heavy metal and tetracycline co‐contaminated soil by Solanum nigrum L.: Response of tetracycline‐resistant genes

AbstractCo‐contamination with heavy metals (HMs) and tetracyclines (TCs) in soils has been widely reported and has resulted in serious consequences, such as the diffusion of tetracycline‐resistant genes (TRGs). Phytoremediation displays high potential for the remediation of co‐contaminated soils. Here, we chose a Cd hyperaccumulator (Solanum nigrum L.) to explore the accumulation of HMs in plants and the effect of TRG diffusion in HM‐TC‐contaminated soil by conducting a pot experiment. The results showed that the shoot biomass of S. nigrum L. decreased by 28.39%–73.00% in treatments with HM (Cd and Cu) contamination singly caused by the toxicity of a nontarget element (Cu). The Cd concentrations in S. nigrum L. shoots increased by 30 times, while the Cu concentrations increased by less than 3 times. The bioconcentration factors (BCFs) and translocation factors (TFs) of Cd ranged from 1.05 to 7.98 and 0.80 to 2.27, respectively, which decreased with increasing TC concentrations in most treatments. The TC residuals in soils increased greatly with increasing TC and HM concentrations. Their concentrations in S. nigrum L. tissues followed the order chlorotetracycline > tetracycline > oxytetracycline. Phytoremediation stimulated the growth of soil microorganisms and increased the abundance of mobile genetic elements (intI 1) and TRGs, especially efflux pump genes (tet C and tet G, which increased 2.97 and 4.13 logs after phytoremediation, respectively). Our results suggested that phytoremediation had a high potential for HM and TC removal; however, it increased the diffusion risk of TRGs, especially for efflux pump genes that functioned in both HM and TC resistance.

Sodium Silicate Improves Cucumber Seedling Growth and Substrate Nutrients and Reduces Heavy Metal Accumulation in Plants

The gasification filter cake (GFC) has great application potential for improving the characteristics of seedling substrates due to its nutrient richness and excellent water retention capacity. However, GFCs leach heavy metals easily and thus pose certain ecological risks. Sodium silicate can enhance plant resistance to heavy metal toxicity by fixing heavy metals. This study investigated the impact of sodium silicate on cucumber plant growth, the chemical characterization of the substrate, and the distribution and transfer of heavy metals. Sodium silicate was added to the seedling substrate mix at mass rates of 0 g/kg−1 (GFC0), 2 g/kg−1 (GFC2), 4 g/kg−1 (GFC4), and 8 g/kg−1 (GFC8). The seedling substrate was composed of a commercial matrix, caragana compost, and GFC (m:m 7:7:2). The GFC increased the content of total phosphorus (P), available phosphorus (P), and available potassium (K) in the substrate by 31.58%, 16.58%, and 80.10%, respectively. Conversely, the GFC decreased the plant height by 12.3%. Adding sodium silicate to the GFC increased the chlorophyll content of the plants, fixed heavy metals in the substrate, and promoted nutrient absorption and utilization by the plants. Compared with GFC0 without sodium silicate, adding sodium silicate at a mass rate of 2 g/kg−1 (GFC2) reduced the chromium, lead, and cadmium contents by 51.13%, 26.37%, and 90.04%, respectively, which effectively alleviated heavy metal stress and was more conducive to plant growth.

Altitude governs the air pollution tolerance and heavy metal accumulation in plants.

Plant response to changing air pollution is a function of various factors including meteorology, type of pollutants, plant species, soil chemistry, and geography. However, the impact of altitude on plant behavior has received little attention to date. A study was therefore conducted to evaluate the impact of altitude on the air pollution tolerance index (APTI), heavy metal accumulation, and deposition in plant species. The results favor the hypothesis of a definite impact of altitude on biochemical and heavy metal accumulation in plants. While a significant decline (p < 0.05) in the relative water content (RWC), APTI, and heavy metal accumulation with increasing altitude was evident in the studied plant species, the behavior of ascorbic acid, leaf extract pH, chlorophyll content, and the particle heavy metal deposition was erratic and did not display any statistically significant differences. The metal accumulation index was in the following order: Ni > Zn > Cu > Pb > Cd > Co. Similarly, the particle heavy metal deposition on the leaf surface (µg/cm2) displayed significant species variability (p < 0.05) and was in the order: Cu (0.303) > Pb (0.301) > Ni (0.269) > Zn (0.241) > Cd (0.044) > Co (0.025). The accumulated heavy metal and RWC showcased a significant positive correlation with the APTI, suggesting the dominant role of RWC in the plant's tolerance against air pollution in an altitudinal gradient. Future studies on the role of micrometeorological conditions in altering APTI may be fruitful in ascertaining these postulations.

Assessment of sludge application in maize (Zea mays L.): influence on crop biomass and heavy metals bioavailability

ABSTRACT Increasing population and subsequent increase in waste necessitate recycling of waste products to minimize the environmental burden. This study was conducted in semi-arid tropics of Punjab to evaluate different rates of sludge application as a supplementary source of nutrients to conventional fertilizers in maize. The grain yield was significantly higher with the application of 5 t ha−1 sludge over control and marginally lower than in 10 t ha−1. Cadmium (Cd), chromium (Cr), lead (Pb), and nickel (Ni) in grains were below international standards even after maximum dose of sludge treatment and can be declared as safe for consumption. The bioconcentration factor of Cd and Ni increased by 82% and 49% with 10 t ha−1 over control, respectively while it remained same for Cr and Pb. Significant increase in exchangeable Cd, Pb in carbonate, and easily reducible oxide, Ni and Cr in residual fraction with 10 t ha−1 sludge over control were found. Mobility of only Pb and Cd increased with increasing sludge treatment. Conclusively, sludge application can be beneficial in increasing plant biomass, however heavy metal accumulation in plants may limit its use. Long-term effect of sludge applications as nutrient sources must be evaluated to get more in-depth insights.

Compost Formulation from Different Wastes to Enhance the Soil and Plant Productivity A Review

Different types and sources of compost are used to increase agricultural productivity. This review reveals different compost formulation methods and the incorporation of those methods into agriculture to reduce waste production, providing a better way to maintain soil fertility for better plant yield. This review furnishes an in-depth update on the impact of prepared compost from different ingredients like municipal waste, kitchen-based food waste, livestock waste, agricultural waste, algae, and industrial waste to find the effects on soil health, plant growth parameters (height, stem diameter, leaf number, chlorophyll content, etc.), and plant yield. Several studies have shown that compost significantly affects the soil’s health and improves different plants’ morphological (height, width, stem diameter, leaf shape, leaf size, leaf arrangement, root system), physiological (photosynthesis rate, transpiration rate, respiration rate, stomatal conductance, chlorophyll content, carbon dioxide assimilation, nutrient uptake, water use efficiency, flowering time, germination rate), and chemical properties (pH, macronutrient content, micronutrient content, carbohydrate content, protein content, lipid content, phytochemical content, essential oil content, pigment content). Produced compost from different ingredients has significant results for enhancing soil health, nutrient supply to plants, reducing heavy metal accumulation in plants, increasing plant yield, and reducing the environmental pollution. Overall, the results of this study demonstrate the potential of compost formulations made from different waste materials to enhance soil fertility and plant productivity. These findings have important implications for sustainable agriculture and waste management practices. Using compost as a soil amendment can help reduce waste and improve soil health, increasing plant yields and reducing the need for chemical fertilisers. However, the dose of compost prepared from various wastes in different climatic conditions should be optimized at the farm level, with particular emphasis on economic sustainability.

Assessment of environmental and toxicity impacts and potential health hazards of heavy metals pollution of agricultural drainage adjacent to industrial zones in Egypt

The objectives of this study were to assess the environmental impact of industrial wastewater disposal in the El-Khadrawiya agricultural drain, Menoufia Governorate, Egypt, as well as the effect on water, soil, and plant qualities in the drain's extension area, which was primarily adjacent to the industrial zone. The analyses results of wastewater at El-Khadrawiya drain revealed that heavy metal concentrations in water samples exceeded WHO permitted limits. Heavy metal levels followed the following pattern: (Pb > Zn > Cr > Cd > Ni > As), where Heavy metal levels average were: (1.8492 > 1.7857 > 0.1815 > 0.1578 > 0.059 > 0.0048. Wastewater, soil and plant samples were analyzed using (PerkinElmer AAnalyst 400 Atomic Absorption Spectrometer A Analyst 400), Heavy metal pollution evaluation indicators: Target hazard quotient (THQ), Hazard index (HI), Chronic daily intake (CDI), Carcinogenic risk (CR), and Heavy metals pollution index (HPI)) showed that a majority of samples discovered values referring to carcinogenic health risks for the population. In contrast, the soil contamination indices followed the same trend, with the contamination factor (CF) indicating that the majority of samples exposed low to medium levels of pollution for (Ni, Cd, and Zn), while Pb and Cr were between high and very high, and the contamination degree (Cd) and modified degree of contamination (mCd) indicating that the majority of samples revealed the medium level of pollution, with the exception of one site with a high level of contamination. The bioaccumulation factor (BAF) revealed that heavy metal accumulation in plants exceeds the critical range. This study should be expanded to include additional agricultural regions with comparable conditions in order to provide environmental monitoring of present challenges and work toward solutions.

Phytoremediation of contaminated industrial wastewater by duckweed (Lemna minor L.): Growth and physiological response under acetic acid application.

Extensive usage of heavy metals (HMs) in chemical reactions and processes eventually contaminate the environmental segments and is currently a major environmental concern. HMs such as cadmium (Cd), copper (Cu), lead (Pb), chromium (Cr) and nickel (Ni) are considered the most harmful pollutants as they have adequate potential of bioaccumulation. The current research was carried out to assess the HMs toxicity of textile and tannery wastewater and effect of acetic acid (AA) on phytoextraction of HMs by duckweed (Lemna minor L.) in a hydroponic system. Plants were treated with different treatments having different hydroponic concentrations of AA (5 and 10mM) and textile and tannery effluents, where these two effuents were equally mixed and then diluted with good quality water with different ratios (25, 50, 75, and 100%) along with three replications of each treatment. Results were recorded for growth attributes, chlorophylls, antioxidant enzymes, electrolytic leakage, reactive oxygen species and HMs accumulation in plants. HMs accumulation disrupts the growth parameters, chlorophyll contents and carotenoids contents along with increased activities of antioxidant enzyme such as catalases (CAT), superoxide dismutase (SOD), peroxidases (POD) and ascorbate peroxidase (APX). Addition of AA in the hydroponic experimental system significantly improves the antioxidant defense mechanism and alleviated the HM induced toxicity in plants. Cr, Cd, Pb, Cu and Ni concentrations were maximally increased up to 116 & 422%, 106 & 416%, 72 & 351%, 76 & 346%, and 41 & 328% respectively under AA (10mM) application. The results revealed that duckweed can be applied as potential phyto-remedy to treat industrial wastewater.

Development of melatonin nano-delivery systems to reduce cadmium accumulation in rice (Oryza sativa L.) seedlings: Insights from photosynthetic efficiency, antioxidative response and gene expression

Cadmium (Cd) contamination in paddy soil has become a worldwide problem for rice production. Foliar application has been reported as a practical approach to reducing Cd accumulation in rice. In the present study, we used mesoporous silica nanoparticles (MSN) and MSN-chitosan (MSN-CS) as carriers to deliver melatonin (MT) into rice plants through foliar spray. Both systems showed the potentials as controlled-release delivery vehicles, with MT@MSN-CS performing better in vitro. The hydroponic trial revealed that foliar spray of MT@MSN-CS could significantly reduce Cd concentration in rice leaves by 43.8%, which was better than those of MT and MT@MSN. The nano-delivery systems improved leaf photosynthesis efficiency, decreased malondialdehyde (MDA) content, enhanced the activity of antioxidative enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), as well as regulated the expression levels of Cd transport genes ( OsNramp1 , OsNramp5 , OsHMA2 , OsHMA3 , OsLCD and OsPCR1 ). Our results also suggested that the use of stimuli-responsive carriers, MSN-CS, for example, as MT-delivery systems may be a feasible option for the reduction of heavy metal accumulation in plants and can be potentially implemented in soil remediation. • MSN and MSN-CS were used as carriers to deliver melatonin into rice plants. • The foliar spray of MT@MSN-CS significantly reduced Cd concentration in rice leaves by 43.8%. • The nano-delivery systems improved photosynthesis efficiency and enhanced antioxidative enzyme activities. • The nano-delivery systems effectively regulated the expression levels of Cd transport genes.

Effect of sewage sludge-based fertilizers on biomass growth and heavy metal accumulation in plants

This study was focused on an assessment of the agronomic efficiency of organo-mineral fertilizers based on sewage sludge and possible accumulation of heavy metals in plant biomass. Fertilizers optimized for industrial crops (rape, maize, sunflower) were used in the study. The impact of fertilizers based on sewage sludge on early stage plant growth was assessed using germination tests, and the impact on further growth and development was assessed using pot trials. The germination index of cress, sorghum and mustard was in the range of 50–92% depending on the type and dose of fertilizer and on the plant tested, which corresponded to moderate to zero toxicity. The results of pot trials showed a significant impact of fertilizers based on sewage sludge on the biomass growth of selected plants. The use of fertilizers caused an increase in fresh mass of 75–138% for rape, 96–138% for maize and 23–54% for sunflower with respect to the control sample. An increase in the dose of fertilizers for rape did not significantly affect the heavy metal content in plants, except for the content of Ni. In the case of fertilizers optimized for maize and sunflower, an increase in the dose caused an accumulation of Cd, Ni, Pb and Cr in the biomass of the tested plants. However, it should be noted that the pollution level of plant biomass for all treatments was zero to medium (1.00–1.66).

Assessing heavy metal accumulation in plants and soil with sewage sludge application under rice–wheat system in an Indo-Gangetic Inceptisol

Assessing heavy metal accumulation in plants and soil with sewage sludge application under rice–wheat system in an Indo-Gangetic Inceptisol

Recent advances in physiological and molecular mechanisms of heavy metal accumulation in plants.

Among abiotic stress, the toxicity of metals impacts negatively on plants' growth and productivity. This toxicity promotes various perturbations in plants at different levels. To withstand stress, plants involve efficient mechanisms through the implication of various signaling pathways. These pathways enhance the expression of many target genes among them gene coding for metal transporters. Various metal transporters which are localized at the plasma membrane and/or at the tonoplast are crucial in metal stress response. Furthermore, metal detoxification is provided by metal-binding proteins like phytochelatins and metallothioneins. The understanding of the molecular basis of metal toxicities signaling pathways and tolerance mechanisms is crucial for genetic engineering to produce transgenic plants that enhance phytoremediation. This review presents an overview of the recent advances in our understanding of metal stress response. Firstly, we described the effect of metal stress on plants. Then, we highlight the mechanisms involved in metal detoxification and the importance of the regulation in the response to heavy metal stress. Finally, we mentioned the importance of genetic engineering for enhancing the phytoremediation technique. In the end, the response to heavy metal stress is complex and implicates various components. Thus, further studies are needed to better understand the mechanisms involved in response to this abiotic stress.

Efficiency of transporter genes and proteins in hyperaccumulator plants for metals tolerance in wastewater treatment: Sustainable technique for metal detoxification

Environmental contamination of heavy metals is now becoming increasingly a concern and a significant problem due to its harmful effects worldwide. The plant-meditated approach is encouraging to eliminate toxins avoiding side effects from polluted wastewater. For the development of appropriate plant species for the mechanisms of heavy metal absorption, transport, detoxification, identification, and signaling pathways would be important facts. Transporter genes like ATP-phosphoribosyl transferase (ATP-PRT), Yellow Stripe-like (YSL), NAS (nicotinamide synthase), SAMS (S-adenosyl-methionine synthetase), FER (ferritin Fe (III) binding), HMA (heavy metal ATPase), IREG (iron-regulated transporter), and proteins like cation diffusion facilitators (CDF), ZRT, IRT-like protein (ZIP), and natural resistance-associated macrophage protein (NRAMP) are active in heavy metal accumulation, translocalisation, sequestration, and resistance. Besides, chelating agents and metabolites can be used either to increase heavy metal bioavailability, which facilitates heavy metal accumulation in plants and further promote plant growth and fitness. This review paper addresses key roles and potential transporter genes and proteins for the remediation of heavy metals from hyperaccumulator plants. This review specifically focuses on the efficacy of transporter genes and proteins in hyperaccumulator plants in metal restoration, discussing the use of these plants for wastewater treatment processes. • Discusses the efficiency of hyperaccumulator plant for removal of metals. • Summarizes transporter gene and proteins in heavy metal uptake and tolerance. • Proposes improved prospects for wastewater treatment.

Root damages induced by extended phytotoxic effects of cadmium pre-exposure against subsequent lindane uptake in rice seedlings

The heavy metal accumulation in plants via uptake generally poses some phytotoxic effects on plant roots, which may in turn impact the plant uptake process. The present study was conducted to evaluate the phytotoxic effects of cadmium (Cd) pre-exposure (2 and 40 mg L−1) on rice (Oryza sativa) root at organ, tissue and cellular levels, and to investigate the subsequent uptake performance of the affected rice seedlings by re-exposing to lindane (4 mg L−1). Biomass, relative water content (RWC), fatty acid (FA) profiles were quantified as the indicators for phytotoxicity. Following the Cd pretreatment, varying degrees of water deficit and lipid peroxidation of rice seedlings were found compared to the control, as evidenced by the decrease in RWC and the increase in FA saturation degree, with no significant effect on root biomass. Meanwhile, damages to root tissue structure were confirmed microscopically. All these symptoms did not show any signs of recovery after the Cd stress was removed, but even deteriorated especially in the high-level Cd pretreatment. The root function of uptake, which was interrelated to the above indicators, was consequently impaired, verified by the decrease in active root uptake area (ARUA). In addition, pre-exposure to much higher levels of Cd brought about lower lindane uptake in roots and lower lindane root-to-shoot translocation. After 5-d lindane exposure, lindane concentrations decreased by 15.8 ± 0.5 % and 30.3 ± 0.4 % respectively compared to the control in seedling roots of two Cd pretreatments, and 34.1 ± 0.6 % and 59.2 ± 1.2 % respectively in shoots. The lindane proportions in shoots of Cd pretreatment were approximately 20 % and 40 % while that from the control exceeded 45 %. These results demonstrated the “uptake-phytotoxicity” cycle, and indicated that the hampered uptake and translocation progresses in plant appeared to depend on the severity of root damages, which was induced by the extended phytotoxic effects.

Enhanced phytoextraction of multi-metal contaminated soils under increased atmospheric temperature by bioaugmentation with plant growth promoting Bacillus cereus

The co-occurrence of environmental stresses such as heavy metals (HM) and increased atmospheric temperature (IAT) pose serious implications on plant growth and productivity. In this work, we evaluated the role of plant growth-promoting bacteria (PGPB) and its effectiveness on Zea mays growth, stress tolerance and phytoremediation potential in multi-metal (MM) contaminated soils under IAT stress conditions. The PGPB strain TCU11 was isolated from metal contaminated soils and identified as Bacillus cereus. TCU11 was able to resist abiotic stresses such as IAT (45 °C), MM (Pb, Zn, Ni, Cu, and Cd), antibiotics and induced in vitro plant growth promotion (PGP) by producing siderophores (catechol and hydroxymate) and indole 3-acetic acid even in the presence of MM under IAT. Inoculation of TCU11 significantly increased the biomass, chlorophyll, carotenoids, and protein content of Z. mays compared to the respective control under MM, IAT, and MM + IAT stress. A decrease of malondialdehyde and over-accumulation of total phenolics, proline along with the increased activity of superoxide dismutase, catalase and ascorbic peroxidase were observed in TCU11 inoculated plants under stress conditions. These results suggested MM and/or IAT significantly reduced the maize growth, whereas TCU11 inoculation mitigated the combined stress effects on maize performance. Moreover, the inoculation of TCU11 under IAT stress increased the MM (Pb, Zn, Ni, Cu, and Cd) accumulation in plant tissues and also increased the translocation of HM from root to shoot except for Ni. The results of soil HM mobilization further indicates that IAT increased the HM mobilizing activity of TCU11, thus increasing the concentrations of bio-available HM in soil. These results suggested that TCU11 not only alleviates MM and IAT stresses but also enhances the biomass production and HM accumulation in plants. Therefore, TCU11 can be exploited as inoculums for improving the phytoremediation efficiency in MM polluted soils under IAT conditions.

Rhizosphere properties and heavy metal accumulation of plants growing in the fly ash dumpsite, Morupule power plant, Botswana.

Discarding fly ash from a coal power plant into a dumpsite does not only contribute to deforestation and loss of productive land but also leads to contamination of air, soil, and groundwater. Therefore, fly ash should be managed properly to avoid the migration of contaminants. One management option is phytoremediation using adapted plants and as a prerequisite, there is a need to identify suitable plants that can be used for revegetation of fly ash dumpsites. To identify prospective plants, a survey was carried out by assessing the plants growing in Morupule B fly ash dumpsite based on their ability to accumulate heavy metals and their bioconcentration (BAF) and translocation factors (TF). Of the twenty-two-plant species growing in the fly ash dumpsite of Morupule B power plant station, N. glauca is a potential phytoextraction agent for Cu (TFCu = 1.02; BAFCu = 2.16) and Pb (TFPb = 1.38; BAFPb = 1.65); P. burchellii for Pb (TFPb = 1.61, BAFPb = 0.9) and Zn (TFZn = 1.35; BAFZn = 5.74); I. pes-tigridis for Pb (TFPb = 1.35; BAFPb = 1.56) and Zn (TFZn = 1.62; BAFZn = 7.43); A. pungens for Cr (TFCr = 1.22; BAFCr = 0.11), Cu (TFCu = 2.18; BAFCu = 1.14), and Zn (TFZn = 1.04; BAFZn = 1.44); E. hirta for Zn (TFZn = 1.54, BAFZn = 2.44); A. spinosus for Pb (TFPb = 1.29; BAFPb = 1.55); C. dactylon for Cu (TFCu = 1.86; BAFCu = 1.07) and Zn (TFZn = 1.00; BAFZn = 2.46); and D. aegyptium for Pb (TFPb = 1.19; BAFPb = 2.57). Other plants growing in the fly ash dumpsite are potential candidates for phytostabilization as they can tolerate a high concentration of metals and low essential nutrients. Also, different plant groups variably modified the pH, EC, OM, and exchangeable fractions of metals in the rhizosphere wherein grasses can increase the OM at higher rates, and it has a higher capacity to acidify and solubilize heavy metals in the rhizosphere leading to higher EC and available metals compared to other plant groups. Overall, the information presented is useful in identifying plants or their combinations for the phytoremediation of fly ash and other heavy metal-polluted environments.

Characteristics of heavy metal accumulation in five wild plants in Huize Lead-Zinc mining area

In order to screen out the plants used to repair heavy metal pollution in the soil, five plants and surface soil were collected in the Huize lead-zinc mine area, centered on the hyperaccumulator plant Arabis alpina L. var. parviflora Franch, measured the heavy metal content of in shoot and root of plant and surface soil, and analyzed the characteristics of heavy metal accumulation in plants. The results showed that the soil Cd pollution in the Huize lead-zinc mining area was the most serious; among the five plants, the Cd bioconcentration factor(BCF) and translocation factor(TF) of A. alpina were more than 1, and the TF of Pb was more than 1; the TF of Anaphalis margaritacea, Cyananthus inflatus and Arenaria orbiculata to Cu and Zn were more than 1, the TF of Juncus effusus to Cd and Zn were more than 1. These five plants had good tolerance to heavy metals and were of great significance to the remediation and restoration of heavy metal contaminated soil in lead-zinc mining areas.