Heavy Metal Hyperaccumulation Research Articles

ASSESSMENT OF BIOCONCENTRATION FACTOR FOR SELECTED HEAVY METALS IN Talinum triangulare (WATER LEAF) GROWN IN THE VICINITY OF AUTOMOBILE WORKSHOP IN OLUKU, BENIN CITY

Sensitive vegetables grown in heavy metals polluted soils tend to accumulate heavy metals which are harmful to the human body even at low concentrations. In this study, the bioconcentration factor (Transfer Factor) was used to assess the accumulation of some heavy metals in Talinum triangulare grown in the vicinity of an automobile workshop in Oluku, Benin City. Physical and chemical parameters found to affect the interactions and mobility of heavy metals in the soil mass were also examined. A pH of 6.17±0.2 was obtained for the topsoil while the middle and bottom soil samples were 5.93±0.4 and 6.00±0.1 respectively, The values of CEC obtained for top, middle, and bottom soil samples were 5.58±0.54, 4.56±0.11, and 3.65±0.14 meq/100g respectively. Soil samples were randomly collected from three depths of 0-10 cm, 10-20 cm, and 20-30 cm with the aid of a soil auger; and T. triangulare were collected within the soil sampling locations. The concentrations of heavy metal were evaluated through the use of atomic absorption spectrophotometer after the samples were subjected to tri-acid digestion techniques. Particle size analysis showed that the soil is a sandy loam texture. High Transfer factor values were ascertained for some metals but none was greater than one. Therefore T. triangulare cannot be considered a hyperaccumulator of heavy metals investigated in this study. However, all metals found in T. triangulare were highly significant (p<0.05), and higher than the permissible limits recommended by FAO/WHO/EC/CODEX. Consumption of T. triangulare harvested from the vicinity of automobile workshops should be highly discouraged to avoid public health hazards.

Agronomic, breeding, and biotechnological interventions to mitigate heavy metal toxicity problems in agriculture

Heavy metal toxicity (HMT) is a major threat to agriculture production and productivity worldwide; it affects the yield potential of the major food crops. It impairs the plant's physiological function, reduces seed germination, produces oxidative stress, and hinders the plant's photosynthetic ability. Plants absorb these heavy metals from the contaminated soils and cause severe health complications to those consuming the products grown out of the contaminated sites. The major contributor to HMT is human and human-related activities. Therefore, it is very important to address the HMT problem in agriculture. Agronomic interventions such as bioremediation using either plants (phytoremediation) or microbes (microbial bioremediation) is one of the effective methods to remove heavy metals from the soil. More than 400 plant species were reported as hyperaccumulators of various heavy metals. Breeders may develop heavy metal tolerant crop cultivars through breeding and biotechnological interventions for wider adaptation. Several heavy metal tolerant crop cultivars have been developed and commercialized for various economically important food crops. Leveraging omics, gene editing, and high throughput screening tools may speed up the cultivar development. Therefore, we focus on reviewing the agronomic, breeding, and biotechnological interventions to mitigate the HMT problem in agriculture, along with sensors for heavy metal detection to speed up the screening process. • Heavy metal toxicity is a major threat to agriculture production and productivity worldwide; it affects the yield potential of the major food crops. • Plants absorb heavy metals from the contaminated soils and cause severe health complications to those consuming the products grown out of the contaminated sites. • Agronomic interventions include phytoextraction, phytostabilization, phytostimulation, phytovolatilization, phytofiltration, and phytodegradation are very effective in removing heavy metals from contaminated sites. • Breeding interventions are vital to identify the resistant sources from the gene pool and develop resistant cultivars; breeders developed heavy metal tolerant cultivars in many economically important crop species. • Biotechnological (gene targets and genetic engineering) and engineering (real-time sensors for heavy metal detection and quantification) interventions are the need of the hour to improve and mitigate the heavy metal toxicity problem in agriculture.

Cadmium/lead tolerance of six Dianthus species and detoxification mechanism in Dianthus spiculifolius

Toxic heavy metal contaminants seriously affect plant growth and human health. Reducing the accumulation of toxic metals by phytoremediation is an effective way to solve this environmental problem. Dianthus spiculifolius Schur is an ornamental plant with strong cold and drought tolerance. Because of its fast growth, well-developed root system, and large accumulation of biomass, D. spiculifolius has potential applications as a heavy metal hyperaccumulator. Therefore, the aim of this study was evaluate the ability of D. spiculifolius and other Dianthus species to remediate heavy metals, with an ultimate goal to identify available genetic resources for toxic metal removal. The cadmium (Cd) and lead (Pb) tolerance and accumulation of six Dianthus species were analyzed comparatively in physiological and biochemical experiments. Compared with the other Dianthus species, D. spiculifolius showed higher tolerance to, and greater accumulation of, Cd and Pb. Second-generation transcriptome analysis indicated that glutathione transferase activity was increased and the glutathione metabolism pathway was enriched with genes encoding antioxidant enzymes (DsGST, DsGST3, DsGSTU10, DsGGCT2-1, and DsIDH-2) that were up-regulated under Cd/Pb treatment by RT-qPCR in D. spiculifolius. When expressed in yeast, DsGST, DsGST3, DsGSTU10 and DsIDH-2 enhanced Cd or Pb tolerance. These results indicate that D. spiculifolius has potential applications as a new ornamental hyperaccumulator plant, and that antioxidant enzymes might be involved in regulating Cd/Pb accumulation and detoxification. The findings of this study reveal some novel genetic resources that can be used to breed new plant varieties that tolerate and accumulate heavy metals.

Insight into the synergistic effect and products distribution during co-pyrolysis of phytoremediation residue and municipal sewage sludge through experiment and reaction force field simulation

We co-pyrolyzed municipal sewage sludge (MS) and Sedum Alfredii L. (SA, a heavy metal hyperaccumulator plant) for the first time to solve their disposal issue. Experimental and simulation results show that synergistic effects exist during the co-pyrolysis process. The thermal decomposition mechanism, kinetics, and product distribution of MS and SA at different mixing ratios (1:0, 3:1, 1:1, 1:3, 0:1) were investigated by thermogravimetric analysis and co-pyrolysis experiments. According to thermogravimetric results, the decomposition of all feedstocks can be divided into three stages. FWO method and Master plot method were used to calculate the activation energy and determine the reaction mechanism. When the addition ratio of SA was 75 %, the difference between theoretical and practical activation energies was greatest, indicating that the best synergy could be achieved at this mixing ratio. Co-pyrolysis experiment shows that more bio-oil and gas were produced. The synergistic effect between MS and different fractions of SA was studied using Reaction Force Field simulation, revealing that the free radicals generated by MS and SA advance the MS decomposition time while increasing the decomposition degree of SA. In addition, we built an artificial neural network with a 3 × 21 × 1 structure to predict the degradation process of various mixtures, which exhibits a high agreement with the experimental results. This study can provide a new idea for the disposal of SA and MS, i.e., co-pyrolysis, by solving their disposal issue while obtaining valuable products.

An ecological remediation model combining optimal substrate amelioration and native hyperaccumulator colonization in non-ferrous metal tailings pond

The vegetation deterioration and pollution expansion from non-ferrous metal tailings pond have been found in many countries leading to water soil erosion and human health risk. Conventional ecological remediation technologies of mine tailings such as capping were costly and elusive. This study provided an economic and effective model as an alternative by substrate amelioration and vegetation restoration. A field experiment was carried out on a silver tailings pond in southwest China. Tailings substrate was ameliorated by adding organic matter (decomposed chicken manure, DCM), structural conditioner (polyacrylamide, PAM), water-retaining agent (acrylic acid-bentonite water-retaining agent, AAB), and heavy metal immobilizer (biofuel ash, BFA), which were optimized by laboratory experiment. Native heavy metal hyperaccumulator, Bidens pilosa, was colonized. Vegetation coverage and plant height of Bidens pilosa reached about 80% and over 30 cm respectively after 3 months, and the turbidity of tailings leaching solution decreased by 60%. The practice showed that the proportion of available heavy metals in tailings substrate was significantly lower than that in the soil surrounding mining area. Immobilization didn't have stabilization effect on Cd, Zn, and Pb, and As was only 0.002%, phytoremediation had stabilization effect of Cd, Zn, As, and Pb were 2.5–3.5%, 1–2%, 0.25–0.5%, and 0.25–0.75%. Phytoremediation was more effective significantly in controlling heavy metal pollution risk of tailings than immobilization. These results provided a new ecological remediation OSA-NHC model, meaning a combination of optimal substrate amelioration and native hyperaccumulator colonization, which could achieve vegetation restoration and augment heavy metal pollution control in non-ferrous metal tailings pond.

Cadmium contributes to heat tolerance of a hyperaccumulator plant species Sedum alfredii

Hyperaccumulators are plant species that tolerate and accumulate very high concentrations of toxic metals, including Cd. Hyperaccumulation of heavy metals is reported to benefit plant biotic resistance; however, no prior study has examined the possible role of toxic metals on abiotic stress resistance in hyperaccumulators. A preliminary experiment found that Cd significantly improved plant growth of a hyperaccumulator, Sedum alfredii Hance, under heat stress. This study investigated the possible role of Cd in S. alfredii’s heat resistance, using infrared thermography, transmission electron microscopy (TEM), real-time quantitative polymerase chain reaction (RTqPCR), and high-throughput sequencing. The results showed that high temperatures irreversibly damaged stomatal function, chloroplast structure, photosynthesis in S. alfredii, and lowered survival rates to 25%. However, Cd application significantly decreased the leaf temperature of S. alfredii and increased the survival rate to 75%. Cd penetrated the guard cells, restored stomatal function, and mitigated excessive water loss from S. alfredii under heat stress. Moreover, it activated antioxidant enzymes, promoted phytohormone biosynthesis, and upregulated a series of unigenes, thereby augmenting heat resistance in S. alfredii. These results indicate that Cd effectively improved thermotolerance in S. alfredii by regulating stomatal movement and antioxidant systems via upregulation of phytohormones and heat shock proteins.

Thinking for the future: Phytoextraction of cadmium using primed plants for sustainable soil clean-up.

Cadmium (Cd) soil contamination is a global problem for food security due to its ubiquity, toxicity at low levels, persistence, and bioaccumulation in living organisms. Humans' intake of heavy metals is usually due to direct contact with contaminated soil, through the food chain (Cd accumulation in crops and edible plants) or through drinking water in cases of coupled groundwater-surface water systems. Phytoextraction is one of the eco-friendly, sustainable solutions that can be used as a method for soil clean-up with the possibility of re-use of extracted metals through phytomining. Phytoextraction is often limited by the tolerance level of hyperaccumulating plants and the restriction of their growth. Mechanisms of hyperaccumulation of heavy metals in tolerant species have been studied, but there are almost no data on mechanisms of further improvement of the accumulation capacity of such plants. Priming can influence plant stress tolerance by the initiation of mild stress cues resulting in acclimation of the plant. The potential of plant priming in abiotic stress tolerance has been extensively investigated using different types of molecules that are supplemented exogenously to plant organs (roots, leaves, etc.), resulting in enhanced tolerance of abiotic stress. This review focuses on mechanisms of enhancement of plant stress tolerance in hyperaccumulating plants for their exploitation in phytoextraction processes.

Elemental bioimaging of Zn and Cd in leaves of hyperaccumulator Arabidopsis halleri using laser ablation-inductively coupled plasma-mass spectrometry and referencing strategies

The spatial distribution of Zn and Cd in leaves of the heavy metal hyperaccumulator species Arabidopsis halleri, a land plant in the Brassicaceae family of angiosperms, is determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Detected intensities of nuclides of the environmental pollutants Zn and Cd are referenced to nuclides of the naturally abundant elements C, Mg, P, Ca, and Rb as internal standards, in order to compensate for widespread experimental issues in whole-leaf laser ablation. Referencing occurs by dividing the signal intensity of the analyte by the corresponding intensity of the internal standard. In order to avoid large quotients that occur during division by small numbers, quotients of pixels for which the internal standard is no higher than the background are set to zero. The effects of referencing on a loss of laser focus, overlapping layers of leaf tissue and cell damage within the imaged leaf tissue are addressed specifically. It is reported that referencing to 25Mg, 31P, 44Ca or 85Rb can skew the results of Zn and Cd distribution because of their different ion mobility within leaves or other element-specific effects. This is particularly valid in the leaf venation and in regions of leaves where cell damage has occurred. Considering all aspects, 13C was found to be best suited among the investigated elements for referencing of leaves, because it stabilizes the resulting distributions of Zn and Cd even in samples affected by experimental issues.

Identification and functional analysis of cation-efflux transporter 1 from Brassica juncea L.

BackgroundBrassica juncea behaves as a moderate-level accumulator of various heavy metal ions and is frequently used for remediation. To investigate the roles of metal ion transporters in B. juncea, a cation-efflux family gene, BjCET1, was cloned and functionally characterized.ResultsBjCET1 contains 382 amino acid residues, including a signature motif of the cation diffusion facilitator protein family, six classic trans-membrane-spanning structures and a cation-efflux domain. A phylogenetic analysis showed that BjCET1 has a high similarity level with metal tolerance proteins from other Brassica plants, indicating that this protein family is highly conserved in Brassica. BjCET1 expression significantly increased at very early stages during both cadmium and zinc treatments. Green fluorescence detection in transgenic tobacco leaves revealed that BjCET1 is a plasma membrane-localized protein. The heterologous expression of BjCET1 in a yeast mutant increased the heavy-metal tolerance and decreased the cadmium or zinc accumulations in yeast cells, suggesting that BjCET1 is a metal ion transporter. The constitutive expression of BjCET1 rescued the heavy-metal tolerance capability of transgenic tobacco plants.ConclusionsThe data suggest that BjCET1 is a membrane-localized efflux transporter that plays essential roles in heavy metal ion homeostasis and hyper-accumulation.

Complete chloroplast genome features of the model heavy metal hyperaccumulator Arabis paniculata Franch and its phylogenetic relationships with other Brassicaceae species.

The online version contains supplementary material available at 10.1007/s12298-022-01151-1.

Cadmium transfer between maize and soybean plants via common mycorrhizal networks

More than 80% terrestrial plants establish mutualistic symbiosis with soil-borne arbuscular mycorrhizal fungi (AMF). These fungi not only significantly improve plant nutrient acquisition and stress resistance, but also mitigate heavy metal phytotoxicity, Furthermore, the extraradical mycorrhizal mycelia can form common mycorrhizal networks (CMNs) that link roots of multiple plants in a community. Here we show that the networks mediate migration of heavy metal cadmium (Cd) from maize (Zea mays L.) to soybean (Glycine max (Linn.) Merr.) plants. CMNs between maize and soybean plants were established after inoculation of maize plants with AMF Funneliformis mosseae. Application of CdCl2 in maize plants led to 64.4% increase in the shoots and 48.2% increase in the roots in Cd content in CMNs-connected soybean plants compared to the control without Cd treatment in maize. Meanwhile, although the CMNs-connected soybean plants did not directly receive Cd supply, they upregulated transcriptional levels of Cd transport-related genes HATPase and RSTK 2.13- and 5.96-fold, respectively, induced activities of POD by 44.8% in the leaves, and increased MDA by 146.2% in the roots. Furthermore, Cd addition inhibited maize growth but mycorrhizal colonization improved plant performance in presence of Cd stress. This finding demonstrates that mycorrhizal networks mediate the transfer of Cd between plants of different species, suggesting a potential to use CMNs as a conduit to transfer toxic heavy metals from main food crops to heavy metal hyperaccumulators via intercropping.

Prospects of algae-based green synthesis of nanoparticles for environmental applications

Green synthesis of nanoparticles (NPs) has emerged as an eco-friendly alternative to produce nanomaterials with diverse physical, chemical, and biological characteristics. Previously used, physical and chemical methods involve the production of toxic byproducts, costly instrumentation, and energy-intensive experimental processes thereby, limiting their applicability. Biogenic synthesis of nanoparticles has come forward as a potential alternative, providing an eco-friendly, cost-effective, and energy-efficient approach for the synthesis of a diverse range of NPs. Several biological entities are employed in the biosynthesis of NPs including bacteria, fungi, and algae. However, the distinguishing characteristics of microalgae and cyanobacteria make them promising candidates for NPs synthesis because of their higher growth rate, substantially higher rate of sequestering CO2, hyperaccumulation of heavy metals, absence of toxic byproducts, minimum energy input, and employment of biomolecules (pigments and enzymes) as reducing and capping agents. Algal extract, being a natural reducing and capping agent, serves as a living cell factory for the efficient green synthesis of nanoparticles. Physiological and biological methods allow algal cells to uptake heavy metals and utilize them as nutrient source to generate biomass by regulating their metabolic processes. Despite their enormous potential, studies on the microalgae-based synthesis of nanoparticles for the removal of toxic pollutants from wastewater remained an unexplored research area in the literature. This review was aimed to summarize the recent advancements and prospects in the algae-based synthesis of nanoparticles for environmental applications particularly treating the wastewater.

Health Risk Effect of Heavy Metals from Pesticides in Vegetables and Soils: A Review

Vegetables are vital to the human diet, and in particular provide the well-known nutrients to maintain normal physiological functions. The prolonged application of large amount of pesticides has resulted in heavy metal accumulation in vegetable farms. Exposure to heavy metals by the consumption of contaminated vegetables and its toxicity is a serious concern. This article reviews the effect of pesticides, heavy metals, heavy metals in vegetables, heavy metals in soil and transfer of heavy metals from soil to plants. However, a limited number of studies were found in the data base that examined the reduction of nutrients in vegetables due to heavy metal contamination. The heavy metals were found in leafy and fruit vegetables in different regions of the world and levels were above permissible limits in most of the vegetables. Specific study to human toxicity due to the contamination of heavy metals may be conducted. Furthermore, strategy and policy should be devised to control the heavy metals in vegetables, and those vegetables that are hyper-accumulators of heavy metals should be identified for awareness purposes.
 Keywords: Vegetables, Heavy metals, Permissible limit, Toxicity, Contamination and Hyper-accumulators

Accumulation of Heavy Metals in Agricultural Crops and Ecological Series of Crops Placement

The accumulation of toxic elements in vegetables and melons grown in agriculture, Brassica rapa - turnip, Solanum lycopersicum - tomato, Citrullus lanatus - watermelon, Capsicum annuum - bell pepper, Daucus carota - carrots, Cucurbita pepo - pumpkin, Cucumis melo - melon, and also Prunus armeniaca - apricot from fruit trees were analyzed. The excess of maximum allowable concentrations in agricultural crops of the element As by 1.65-1.75, Cd - 1.6-2.3, Cr -1.2-2.35, Cu -1.6-3.3, Ni - 1.16-3.53, Pb - 1.54-3.08, Al - 1.36-3.5, Sb - 2.0-33, Se - 1.1-3.3 times was established. The maximum allowable concentration of mercury in vegetables and melons was equal to 0.02 mg/kg, and in the chosen plants this indicator was close to the maximum allowable concentration (MAC). An ecological series of vegetable and melon crops (tomatoes → pumpkin → turnips → bell peppers → melons → watermelons → carrots) has been developed for their placement on fields contaminated with heavy metals Se, As, Pb, Cd, Zn, included in the first class in terms of the degree of danger to human health, while Ni, Cu, Cr metals were from the second class, and metal Mn from the third class. Agricultural crops in the ecological series are placed in inverse proportion to the regularities of the hyper accumulation of heavy metals in them.

Использование технологий фиторемедиации для очистки почв загрязненных тяжелыми металлами

Heavy metals are among the most toxic pollutants in the environment. This paper presents data on contaminated soils with heavy metals of the Republic of Kazakhstan. The ways of their solution are proposed and characterized. Soil contamination with heavy metals is one of the urgent problems of geoecology, they will be transferred to the soil around the storage facility and pose a great threat to the ecosystem, agricultural system and human health. Several methods are already being used to clean the environment of these types of pollutants, but most of them are expensive and far from their optimal performance. The use of plants for cleaning the environment became an effective and cost-effective method only after hyperaccumulative plants were discovered, capable of accumulating up to 5% of nickel, zinc or copper in their tissues in terms of dry weight, that is, tens of times more than ordinary plants. The article provides an overview of phytoremediation technology as an improved method of soil purification. Different types of plants are considered as hyperaccumulators. Hyperaccumulating plants are found in different families and each of them plays an important role in phytoremediation. Since each of them is unique in its own way and each has its own response to the presence of heavy metals in the soil. The increased interest in this new technology is also explained by the fact that plants are hyperaccumulators of heavy metals, with high efficiency can be used on large areas. This property increases the efficiency of this technology and increases the demand.

Exploring integrated methodology for phytoremediation and biofuel production potential of Eichhornia crassipes

Eichhornia crassipes (EC) is a well-known invasive weed in different aquatic ecosystems. Its effective and complete eradication remains a challenge. The plant is a heavy metal (HM) hyperaccumulator in water bodies; however, studies regarding its biomass utilisation post-phytoremediation remain limited. The abundant growth rate and biochemical composition make EC a promising lignocellulosic feedstock for biofuel production; hence could be a deterministic approach for solving the twin problems of water pollution and higher energy demand, which are the global pressing issues in today’s scenario. The present study aimed at evaluating the phytoremediation potential of EC followed by proximate and biochemical analysis to investigate its suitability for biofuel production. After two weeks, the EC removed above 90% of Lead (Pb) and 60% of Cadmium (Cd) at all experimental doses. Lower doses of HMs, especially Pb, showed stimulatory effects on E. crassipes leaf biomass (ECLB). The recovered ECLB from Pb contaminated water (1 mg L−1) was further analysed for moisture (89.23±0.86%), dry matter (10.77±0.60%), ash (11.91±1.20%), organic carbon (51.56±1.08%), cellulose (21.89±0.64%), hemicellulose (26.50±1.13%), lignin (5.62±0.83%), total carbohydrate (32.00±1.58%), and protein (20.83±0.52%) content. SEM imaging of harvested ECLB confirmed compact and rigid structure. The recorded peaks in FTIR-spectra (1015.21, 1153.71, 1246.01, 1339.63, 1419.71, 1540.71, 1646.80, 1736.73, 2933.03, and 3263.72 cm−1) indicate the presence of lignocellulosic biomass. XRD peak at 21.55 confirmed the crystalline fraction of cellulose in ECLB. The results of theoretical yields of H2 and CH4 co-generation (HMG) (210.85 mLH2/g DW and 150.28 mL CH4/g DW) and Bioethanol (0.278 g/g DW) derived from cellulose and hemicellulose content of ECLB were comparable to those in reported studies. Overall, this work demonstrates an integrated methodology of phytoremediation followed by biofuel production from the recovered phytobiomass.

Effect of heavy metals on soil and crop pollution in Ukraine – a review

The presented review discusses current situation with heavy metal pollution in the various regions of Ukraine and possible pollution of important crop. It is suggested that violent conflict of 2022 in Ukraine may cause development of polluted areas with Pb, Ni, Cr, Cu. Especially such tendency is dangerous for Ukrainian regions with high level of heavy metals level where is military conflict was in an active phase: Donetsk, Zaporizhia, Kyiv, Lugansk, Sumy, Kharkiv, Kherson, Chernihiv, Mykolaiv, Zhytomyr, Dnipropetrovsk, and Odessa regions. The analysis of monitoring data related heavy metals pollution has been described in regions of Ukraine. Current ccharacteristics of major crop production areas in Ukraine regarding their possible yield production and presence of heavy metals in the soil are presented. Near 70% of planted areas for major exported plants in the areas of conflict may be under additional increased effects of heavy metals. The wheat, corn, barley, rapeseed, sunflower have been presented and discussed their cultivation potential as major crops in Ukraine. It is recommended to use modern technologies of phytoremediation with use crop rotation of plants hyperaccumulators of heavy metals at these areas afterword's.

Hydrothermal Treatment of the Pristine and Contaminated Cd/Zn Hyperaccumulators for Bio-Oil Production and Heavy Metal Separation

Hydrothermal conversion is a promising technology to dispose of biomass wastes. To achieve the harmless treatment of heavy metal (HM) hyperaccumulators and production of bio-oil, hydrothermal conversion of two types of Sedum alfredii [i.e., uncontaminated S. alfredii (SAL) and the harvested S. alfredii after phytoremediation (SAH)] at 210–300 °C was conducted in this study. Only 0.53–1.59% of Cd and 0.34–5.94% of Zn in SAH migrated to bio-oils, which were much lower than those in hydrochar and the aqueous products. High hydrothermal conversion temperature promoted the bio-oil yield, and the S. alfredii-derived bio-oils showed considerable higher heating values (32.07–33.83 MJ/kg). The main components of bio-oils were aliphatic hydrocarbons, followed by oxygen-containing compounds (e.g., alcohols, phenols, and ketones/aldehydes) and nitrogen-containing compounds. The bio-oils derived from SAL contained a higher content of aliphatic hydrocarbons (56.39–60.11%) and N-containing compounds (9.03–15.17%), while the SAH-derived bio-oils had more ketones/aldehydes (15.17–19.79%), which could be ascribed to the component difference of feedstocks and the catalytic effect of Zn. Moreover, the distillable fraction (boiling point <538 °C) in the bio-oils was up to 79.89–86.90%. These results suggest that hydrothermal conversion of S. alfredii could be a promising technique for the HM separation and value-added bio-oil production.

Eichhornia crassipes leaves biomass harvested from heavy metal contaminated water for biodiesel production potential

Energy is crucial for life and the issues related to fossil fuels (coal, gas and mineral oils) like limited availability, increasing prices, etc., have necessitated the need for some alternative energy sources. Eichhornia crassipes is known as widespread aquatic weed and a well known heavy metal hyperaccumulator. Its leaves biomass reported to have biochemical profile to be utilized for bioenergy generation. Therefore, the present study was conducted at the Institute campus during 2017–2020 with an aim to materialize the prolific growth of this aquatic weed to generate bioenergy sources such as Biodiesel from heavy metal contaminated water, thus proposing a strategy of its control through utilization. GC-MS screening of E. crassipes leaves extract showed the presence of methyl esters such as 8-Octadecenoic acid; 9,12-Octadecadienoic acid (Z, Z)-Hexadecanoic acid. Lower TL content (∼16%) was observed in E. crassipes leaves biomass raised at T2 culture (4 ppm Pb) as compared to T1 culture (1 ppm Pb). Characterization of the produced biodiesel using FTIR, confirmed the presence of the ester group. The FA analysis of esterified lipid showed the presence of C16:0, C18:1 and C18:3, which are known to be the common FAs present in biodiesel. The findings of the present study could provide a promising way of utilizing E. crassipes growing in wastewater contaminated with a lower concentration of heavy metal (lead) for biodiesel production.

Risk assessments and health impacts of heavy metal pollution

<p indent="0mm">Heavy metal pollution is a serious global environmental issue, posing huge risks to food security and human health. As a typical biomarker of heavy metals, soil nematodes develop complex defenses in response to heavy metal exposures. Meanwhile, their gut microbiomes assist host resistance to heavy metals. Here we review the pollution status and assessment methods of heavy metals at home and abroad and summarize their effects on the behavior, physiology, and biochemistry of soil nematodes. Additionally, defense mechanisms of organisms against heavy metals are reviewed, including barrier functions of the cell wall and membrane, changes in active substances, metallothionein overexpression, and noncoding RNA regulation. We propose that the diversity and composition of the nematode gut microbiome can be used as a new indicator of heavy metal toxicity. Furthermore, long-term heavy metal exposure could lead to adaptive evolution, such as the emergence and enrichment of heavy metal hyperaccumulation, resistance, and detoxification genes. Additionally, we can map genetic changes, such as resistance mutations in genes and synergies of resistance, by quantifying the genome-level response of genetic variation under environmental stresses. Finally, we provide a prospect on the ecotoxicology of heavy metals and indicate that future research should focus on the current ecological environment and human health, explore the ecological role of soil fauna gut microbiome, and further understand the potential mechanism of occurrence and development of heavy metal toxicity and biological detoxification.