Heavy Metal Contamination in the Aquatic Ecosystem: Toxicity and Its Remediation Using Eco-Friendly Approaches

Impacts of solid waste management site on some toxic elements contamination of the surrounding soil in Akure, Nigeria

The distribution of potentially toxic elements (PTEs) such as zinc (Zn), copper (Cu), lead (Pb), nickel (Ni), cadmium (Cd), and chromium (Cr), their potential bioavailability, extent of contamination and potential risk of dumpsite and surrounding soil samples were appraised. Three (3) soil samples were collected randomly from within the dumpsite and three (3) soil samples were also obtained 50 m away from the perimeter fence of the dumpsite. PTEs in the bulk and fractionated portions were determined using inductively coupled plasma - optical emission spectrometry (ICP-OES). The results showed that the concentrations of all the PTEs analysed were higher in the dumpsite soil samples than the surrounding samples, suggesting an impact of the dumpsite activities on the soil. The distribution of PTEs varied significantly within the different fractions of both the surrounding and dumpsite soils and their presence were more of anthropogenic than geogenic. The calculated contamination factor/pollution load index (CF/PLI) revealed that the surrounding soil samples fell within the range of moderate contamination, except for Cu and Cr which showed very high contamination. Cd showed the highest value (60.4) for potential ecological risk index (PERI) at the surrounding area. However, the value of Cd in the surrounding soil samples indicated a low ecological risk. The total concentrations of the PTEs were lower than their corresponding target values for both national and international standards, except for Cd (0.15 mg/kg) and Cu (37.3 mg/kg). The study concluded that the dumping of various wastes at the dumpsite was found to be a contributing factor to PTEs contamination of soil at the study area. Hence, an engineered landfill for Akure metropolis is recommended to replace the existing practice.

Metagenomic landscape of sediments of river Ganga reveals microbial diversity, potential plastic and xenobiotic degradation enzymes

The Ganga is the largest river in India, serves as a lifeline for agriculture, drinking water, and religious rites. However, it became highly polluted due to the influx of industrial wastes and untreated sewages, leading to the decline of aquatic biodiversity. This study investigated the microbial diversity and plastic-xenobiotic degrading enzymes of six sediment metagenomes of river Ganga at Prayagraj (RDG, TSG, SDG) and Devprayag (KRG, BNG, BRG). The water quality parameters, higher values of BOD (1.8-3.7 ppm), COD (23-29.2 ppm) and organic carbon (0.18-0.51%) were recorded at Prayagraj. Comparative analysis of microbial community structure between Prayagraj and Devprayag revealed significant differences between Bacteroidetes and Firmicutes, which emerging as the predominant bacterial phyla across six sediment samples. Notably, their prevalence was highest in the BRG samples. Furthermore, 25 OTUs at genus level were consistent across all six samples. Alpha diversity exhibited minimal variation among samples, while beta diversity indicated an inverse relationship between species richness and diversity. Co-occurrence network analysis established that genera from the same and different groups of phyla show positive co-relations with each other. Thirteen plastic degrading enzymes, including Laccase, Alkane-1 monooxygenase and Alkane monooxygenase, were identified from six sediment metagenomes of river Ganga, which can degrade non-biodegradable plastic viz. Polyethylene, Polystyrene and Low-density Polyethelene. Further, 18 xenobiotic degradation enzymes were identified for the degradation of Bisphenol, Xylene, Toluene, Polycyclic aromatic hydrocarbon, Styrene, Atrazene and Dioxin etc. This is the first report on the identification of non-biodegradable plastic degrading enzymes from sediment metagenomes of river Ganga, India. The findings of this study would help in pollution abatement and sustainable management of riverine ecosystem.

Insects to the rescue? Insights into applications, mechanisms, and prospects of insect-driven remediation of organic contaminants

Traditional and emerging contaminants pose significant human and environmental health risks. Conventional physical, chemical, and bioremediation techniques have been extensively studied for contaminant remediation. However, entomo- or insect-driven remediation has received limited research and public attention. Entomo-remediation refers to the use of insects, their associated gut microbiota, and enzymes to remove or mitigate organic contaminants. This novel approach shows potential as an eco-friendly method for mitigating contaminated media. However, a comprehensive review of the status, applications, and challenges of entomo-remediation is lacking. This paper addresses this research gap by examining and discussing the evidence on entomo-remediation of various legacy and emerging organic contaminants. The results demonstrate the successful application of entomo-remediation to remove legacy organic contaminants such as persistent organic pollutants. Moreover, entomo-remediation shows promise in removing various groups of emerging contaminants, including microplastics, persistent and emerging organic micropollutants (e.g., antibiotics, pesticides), and nanomaterials. Entomo-remediation involves several insect-mediated processes, including bio-uptake, biotransfer, bioaccumulation, and biotransformation of contaminants. The mechanisms underlying the biotransformation of contaminants are complex and rely on the insect gut microbiota and associated enzymes. Notably, while insects facilitate the remediation of contaminants, they may also be exposed to the ecotoxicological effects of these substances, which is often overlooked in research. As an emerging field of research, entomo-remediation has several knowledge gaps. Therefore, this review proposes ten key research questions to guide future perspectives and advance the field. These questions address areas such as process optimization, assessment of ecotoxicological effects on insects, and evaluation of potential human exposure and health risks.

Toxicological effects and mechanisms of lithium on growth, photosynthesis and antioxidant system in the freshwater microalga Chromochloris zofingiensis

The growing prevalence of lithium (Li) batteries has drawn public attention to Li as an emerging pollutant. The present study investigates the toxicity of Li+ on Chromochloris zofingiensis, examining physiological, biochemical and omics aspects. Results reveal hormesis effects of Li+ on C. zofingiensis growth. At Li+ concentrations below 5 mg L-1, Li+ can enhance chlorophyll content, mitochondrial activity, and antioxidant capacity, leading to increased dry cell weight and cell number. Conversely, when it exceeded 10 mg L-1, Li+ can reduce chlorophyll content, induce oxidative stress, and disrupt chloroplast and mitochondria structure and function, ultimately impeding cell growth. In addition, under 50 mg L-1 Li+ stress, microalgae optimize absorbed light energy use (increasing Fv/Fm and E TR ) and respond to stress by up-regulating genes in starch and lipid biosynthesis pathways, promoting the accumulation of storage components. Weighted gene co-expression network analysis indicates that peptidylprolyl cis/trans isomerase, GTPase and L-ascorbate oxidase might be the key regulators in response to Li+ stress. This research marks the toxic effects and molecular mechanisms of Li+ on freshwater microalga, which would improve our understanding of Li's toxicology and contributing to the establishment of Li pollution standards.

An Update in Computational Methods for Environmental Monitoring: Theoretical Evaluation of the Molecular and Electronic Structures of Natural Pigment-Metal Complexes

Metals are beneficial to life, but the presence of these elements in excessive amounts can harm both organisms and the environment; therefore, detecting the presence of metals is essential. Currently, metal detection methods employ powerful instrumental techniques that require a lot of time and money. Hence, the development of efficient and effective metal indicators is essential. Several synthetic metal detectors have been made, but due to their risk of harm, the use of natural pigments is considered a potential alternative. Experiments are needed for their development, but they are expensive and time-consuming. This review explores various computational methods and approaches that can be used to investigate metal-pigment interactions because choosing the right methods and approaches will affect the reliability of the results. The results show that quantum mechanical methods (ab initio, density functional theory, and semiempirical approaches) and molecular dynamics simulations have been used. Among the available methods, the density functional theory approach with the B3LYP functional and the LANL2DZ ECP and basis set is the most promising combination due to its good accuracy and cost-effectiveness. Various experimental studies were also in good agreement with the results of computational methods. However, deeper analysis still needs to be carried out to find the best combination of functions and basis sets.

Impact of heavy metals (Cu, Fe, Pb, Zn) on carbon and nitrogen uptake of the diatom-bearing benthic foraminifera Heterosteginadepressa

Foraminifera are protists primarily living in benthic marine and estuarine environments. We studied uptake of inorganic carbon (C) and nitrogen (N) of the photosymbiont-bearing benthic coral reef foraminifera Heterostegina depressa in the presence of heavy metals. Incubation experiments were accomplished with artificial seawater enriched with copper, iron, lead and zinc at two different concentration levels (10 and 100 fold enriched in contrast to the usual culture medium). Additionally, isotopically labelled 13C-sodium bicarbonate and 15N-ammonium chloride were added to trace their assimilation over time (1 d, 3 d, 5 d, 7 d). Pulse-amplified modulated fluorescence measurements were performed to measure the potential impacts of heavy metals on chlorophyll fluorescence of the photosymbiont. Increased levels of copper (430.5 μg Cu/l) exhibited the greatest toxicity, while for low levels no effect on the overall metabolism of the foraminifera and the fluorescence activity of the photosymbiont could be detected. Iron (III) increased the symbiont activity, independent of concentration applied (44.5 and 513.3 μg Fe/l), which indicates Fe-limitation of the algal symbiont. Lead enrichment showed no detectable effect even at high concentration. Low concentrations of zinc (35.1 μg Zn/l) promoted the metabolism of the foraminifera, while high concentrations (598.4 μg Zn/l) were toxic. At low levels, two metals (Fe and Zn) promoted symbiont activity, at high levels, iron still boosted photosynthesis, but Zn and Cu had a negative impact on the obligatory photosynthetic symbionts.

A New Approach of Complexing Polymers Used for the Removal of Cu2+ Ions

This study presents two modified polymers for Cu2+ ion removal from aqueous media. Shredded maize stalk (MC) and a strong-base anionic resin (SAX) were modified with indigo carmine (IC) in order to obtain two different complexing polymers, i.e., IC-MC and SAX-IC. Initially, the complex reaction between IC and Cu2+ in the solution was studied. Additionally, the complex formation Cu2+-IC in liquid solutions was evaluated at different pH ranges of 1.5, 4.0, 6.0, 8.0, and 10.0, respectively. For Cu2+ ions, adsorption onto the IC-MC and IC-SAX batch experiments were conducted. The contact time for evaluating the optimum adsorption for Cu2+ ions on the complexing materials was established at 1 h. Efficient Cu2+ ion adsorption on the IC-MC and SAX-IC at pH = 10 was achieved. The adsorption of Cu2+ ions depends on the quantity of IC retained on MC and SAX. At 2.63 mg IC/g MC(S4) and 22 mg IC/g SAX(SR2), a high amount of Cu2+ ion adsorption was reported. The highest adsorption capacity (Qe) of IC-MC was obtained at 0.73 mg/g, and for IC-SAX, it was attained at 10.8 mg/g. Reusability experiments were performed using the HCl (0.5 M) solution. High regeneration and reusability studies of IC-MC and IC-SAX were confirmed, suggesting that they can be used many times to remove Cu2+ ions from aqueous matrices. Therefore, the development of complexing materials could be suitable for Cu2+ ion removal from wastewater.

Performance and mechanism of amphiphilic polymeric chelator for enhanced removal of high concentrations of Cu(II) from wastewater

An amphiphilic polymeric chelator (APC16-g-SX) grafted with sodium xanthate (SX) groups was successfully prepared for the efficient removal of high concentrations of Cu(II) from wastewater. The ordinary polymeric chelator (PAM-g-SX) based on linear polyacrylamide (PAM) was also prepared for comparative studies. The polymeric chelators were characterized by Fourier transform infrared spectroscopy (FT-IR), solid-state nuclear magnetic resonance (13C-NMR), gel permeation chromatography (GPC), elemental analyzer, and scanning electron microscope (SEM). The chelating performance of these polymeric chelators was investigated, and the mechanism of APC16-g-SX for enhanced removal of Cu(II) from wastewater was proposed based on fluorescence spectroscopy, cryo-scanning electron microscope (Cryo-SEM), energy-dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS) tests. The results show that as the initial Cu(II) concentration in the wastewater increases, APC16-g-SX shows more excellent chelating performance than ordinary PAM-g-SX. For the wastewater with an initial Cu(II) concentration of 200 mg/L, the removal rate of Cu(II) was 99.82% and 89.34% for both 500 mg/L APC16-g-SX and PAM-g-SX, respectively. The pH of the system has a very great influence on the chelating performance of the polymeric chelators, and the increase in pH of the system helps to improve the chelating performance. The results of EDS and XPS tests also show that N, O, and S atoms in APC16-g-SX were involved in the chelation of Cu(II). The mechanism of enhanced removal of Cu(II) by APC16-g-SX can be attributed to the spatial network structure constructed by the self-association of hydrophobic groups that enhances the utilization of chelation sites.

Adsorption of Heavy Metals on Alkali-Activated Zeolite Foams

Elevated concentrations of heavy metals in natural waters can cause significant ecological problems. It is therefore essential to ensure their removal from any water discharged into the environment immediately, especially in case of an accident, where there is a risk of releasing large quantities or high concentrations. The aim of this paper is to test a newly developed adsorbent for the removal of heavy metals from aqueous solutions-in particular, it is very fast adsorption, and thus efficiency, during clean-ups. The alkali-activated foamed zeolite adsorbent was laboratory-prepared and -tested in both batch and flow-through arrangements on single and multi-component solutions and compared with natural zeolite. The experimental setup for batch adsorption consisted of a set of samples and solutions containing iron, cobalt, manganese, zinc and nickel. The samples were put on a horizontal shaker with a 500 mg adsorbent loading in a 50 mL solution. The column adsorption experimental setup consisted of a glass column with an inside diameter of 15 mm and a bed length of 165 mm. A measured amount of each adsorbent was added to the column to achieve a filter fixed-bed height of 160 mm. The high efficiency of the tested adsorbent on various heavy metals was confirmed. The adsorbent has a high potential for use in decontamination processes, water protection and landscape revitalization. Due to its rapid precipitation and subsequent fixation of metal cations in the form of insoluble oxide or hydroxide, it can be used as an emergency adsorbent, the great advantage of which is its low production cost and natural origin.

Mitigating chromium toxicity in rice (Oryza sativa L.) via ABA and 6-BAP: Unveiling synergistic benefits on morphophysiological traits and ASA-GSH cycle

In recent years, the use of plant hormones, such as abscisic acid (ABA) and 6-benzylaminopurine (6-BAP), has gained significant attention for their role in mitigating abiotic stresses across various plant species. These hormones have been shown to play a vital role in enhancing the ascorbate-glutathione cycle and eliciting a wide range of plant growth and biomass, photosynthetic efficiency, oxidative stress and response of antioxidants and other physiological responses. While previous research has been conducted on the individual impact of ABA and 6-BAP in metal stress resistance among various crop species, their combined effects in the context of heavy metal-stressed conditions remain underexplored. The current investigation is to assess the beneficial effects of single and combined ABA (5 and 10 μM L-1) and 6-BAP (5 and 10 μM L-1) applications in rice (Oryza sativa L.) cultivated in chromium (Cr)-contaminated soil (100 μM). Our results showed that the Cr toxicity in the soil showed a significant declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in O. sativa. However, Cr toxicity significantly increased oxidative stress biomarkers, organic acids, enzymatic and non-enzymatic antioxidants including their gene expression in O. sativa seedlings. Although, the application of ABA and 6-BAP showed a significant increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, And Cr uptake. In addition, individual or combined application of ABA and 6-BAP enhanced the cellular fractionation and decreases the proline metabolism and AsA-GSH cycle in rice plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Mechanism of Cr(VI) removal by efficient Cr(VI)-resistant Bacillus mobilis CR3

Cr(VI) is a hazardous environmental pollutant that poses significant risks to ecosystems and human health. We successfully isolated a novel strain of Bacillus mobilis, strain CR3, from Cr(VI)-contaminated soil. Strain CR3 showed 86.70% removal capacity at 200 mg/L Cr(VI), and a good Cr(VI) removal capacity at different pH, temperature, coexisting ions, and electron donor conditions. Different concentrations of Cr(VI) affected the activity of CR3 cells and the removal rate of Cr(VI), and approximately 3.46% of total Cr was immobilized at the end of the reaction. The combination of SEM-EDS and TEM-EDS analysis showed that Cr accumulated both on the cell surface and inside the cells after treatment with Cr(VI). XPS analysis showed that both Cr(III) and Cr(VI) were present on the cell surface, and FTIR results indicated that the presence of Cr on the cell surface was mainly related to functional groups, such as O-H, phosphate, and -COOH. The removal of Cr(VI) was mainly achieved through bioreduction, which primarily occurred outside the cell. Metabolomics analysis revealed the upregulation of five metabolites, including phenol and L-carnosine, was closely associated with Cr(VI) reduction, heavy metal chelation, and detoxification mechanisms. In addition, numerous metabolites were linked to cellular homeostasis exhibited differential expression. Cr(VI) exerted inhibitory effects on the division rate and influenced critical pathways, including energy metabolism, nucleotide metabolism, and amino acid synthesis and catabolism. These findings reveal the molecular mechanism of Cr(VI) removal by strain CR3 and provide valuable insights to guide the remediation of Cr(VI)-contaminated sites.

Evaluation of the potential of two halophytes to extract Cd and Zn from contaminated saltwater

The contamination of saltwater by toxic heavy metals has become a worldwide problem. The application of phytoextraction to remove these pollutants seems to be more efficient and cheaper compared to physicochemical methods. In this work, we evaluated the potential of two halophyte species to accumulate cadmium and zinc from contaminated water. Seedlings of Carpobrotus edulis L. and Sesuvium portulacastrum L. were cultivated during 1 month on pots filled with saltwater (200 mM NaCl) containing different concentrations of Cd2+ (0, 50, 100 μM) and of Zn2+ (0, 200, and 400 μM) applied separately. Results showed that both halophytes were more resistant to Zn2+ than Cd2+ and that Sesuvium better tolerates the two metals. Zn2+ and Cd2+ concentrations in the shoot as well as the values of translocation factors suggest that these species are able to absorb and to concentrate Cd2+ and Zn2+ in their roots and shoots. Hence, after 1 month of culture on 50 μM Cd2+, plants were able to extract 31% and 21% of Cd, respectively, in S. portulacastrum and C. edulis. The Zn-extraction efficiency was less important and reached 18 and 19%, respectively, in S. portulacastrum and C. edulis cultivated under 200 μM Zn2+. Given together, data demonstrate the efficiency of the use of halophytes, especially S. portulacastrum, to extract Zn2+ and Cd2+ from salt wastewater.

Water Quality Degradation Due to Heavy Metal Contamination: Health Impacts and Eco-Friendly Approaches for Heavy Metal Remediation

Water quality depends on its physicochemical and biological parameters. Changes in parameters such as pH, temperature, and essential and non-essential trace metals in water can render it unfit for human use. Moreover, the characteristics of the local environment, geological processes, geochemistry, and hydrological properties of water sources also affect water quality. Generally, groundwater is utilized for drinking purposes all over the globe. The surface is also utilized for human use and industrial purposes. There are several natural and anthropogenic activities responsible for the heavy metal contamination of water. Industrial sources, including coal washery, steel industry, food processing industry, plastic processing, metallic work, leather tanning, etc., are responsible for heavy metal contamination in water. Domestic and agricultural waste is also responsible for hazardous metallic contamination in water. Contaminated water with heavy metal ions like Cr (VI), Cd (II), Pb (II), As (V and III), Hg (II), Ni (II), and Cu (II) is responsible for several health issues in humans, like liver failure, kidney damage, gastric and skin cancer, mental disorders and harmful effects on the reproductive system. Hence, the evaluation of heavy metal contamination in water and its removal is needed. There are several physicochemical methods that are available for the removal of heavy metals from water, but these methods are expensive and generate large amounts of secondary pollutants. Biological methods are considered cost-effective and eco-friendly methods for the remediation of metallic contaminants from water. In this review, we focused on water contamination with toxic heavy metals and their toxicity and eco-friendly bioremediation approaches.

Gill and hepatic histological alterations in Sciades herzbergii resulting from trace element contamination in the Port of São Luiz, Brazil

The objective of this study was to evaluate, through changes in the gills and livers of Sciades herzbergii, the environmental contamination to which estuarine organisms are exposed in two areas in São Marcos Bay - MA. Two collection areas located in São Marcos Bay were selected for this study: A1, an area close to the Port Complex, and A2, an area on Caranguejos Island (included in the Environmental Protection Area of Baixada Maranhense). Collections were carried out during rainy and dry periods. Sediments (for trace element analyses), surface water (for physico-chemical analyses), and specimens of S. herzbergii (for biometric measurements and identification of branchial and hepatic histopathology) were collected. Physico-chemical parameters (pH, dissolved oxygen, temperature and salinity) were within limits established by Brazilian legislation. Arsenic (in A1) and nickel (in A1 and A2) were above the legal standards in both periods. The highest percentage of histological alterations in the gills (aneurysms, lamellar fusion and detachment of the epithelium) occurred in the port area, in the rainy (93%) and dry (74%) periods. Liver alterations (melanomacrophage centers and necrosis) occurred only in specimens from the same area, in the rainy (41%) and dry (36%) periods. The highest histological indices of gill and liver changes were recorded in A1. This result was further supported by the total HI value of the lesions, which was higher in the port area compared to A2 (less impacted area), suggesting that the environmental conditions in that location are less favorable for the well-being of these organisms. Permanent environmental monitoring of the area is necessary to control environmental impacts efficiently.

Copper biosorption by Bacillus pumilus OQ931870 and Bacillus subtilis OQ931871 isolated from Wadi Nakheil, Red Sea, Egypt

BACKGROUND

Despite being necessary, copper is a toxic heavy metal that, at high concentrations, harms the life system. The parameters that affect the bioreduction and biosorption of copper are highly copper-resistant bacteria.

RESULTS

In this work, the ability of the bacterial biomass, isolated from black shale, Wadi Nakheil, Red Sea, Egypt, for Cu2+ attachment, was investigated. Two Cu2+ resistance Bacillus species were isolated; Bacillus pumilus OQ931870 and Bacillus subtilis OQ931871. The most tolerant bacterial isolate to Cu2+ was B. pumilus. Different factors on Cu2+ biosorption were analyzed to estimate the maximum conditions for Cu biosorption. The qmax for Cu2+ by B. pumilus and B. subtilis determined from the Langmuir adsorption isotherm was 11.876 and 19.88 mg. g-1, respectively. According to r2, the biosorption equilibrium isotherms close-fitting with Langmuir and Freundlich model isotherm. Temkin isotherm fitted better to the equilibrium data of B. pumilus and B. subtilis adsorption. Additionally, the Dubinin-Radushkevich (D-R) isotherm suggested that adsorption mechanism of Cu2+ is predominately physisorption.

CONCLUSION

Therefore, the present work indicated that the biomass of two bacterial strains is an effective adsorbent for Cu2+ removal from aqueous solutions.

Study on the removal effect and mechanism of calcined pyrite powder on Cr(VI)

Pyrite exhibits considerable potential as an adsorbent in wastewater treatment. However, few pyrite adsorbents are directly obtained from natural pyrite, as most are composite materials that require a complex preparation process. To develop a pyrite-based adsorbent with a simple preparation process, pyrite was processed by calcination at 400, 600, and 800 °C for 4 h and ball-milled into a fine powder. The adsorption properties of the pyrite powder were systematically explored. The calcined pyrite powder was characterized by SEM-EDS and XRD. The results revealed that the pyrite calcined at 600 °C exhibited excellent adsorption properties and was primarily composed of Fe7S8. The optimum conditions for Cr(VI) removal were a temperature of 45 °C, an adsorbent dosage of 1 g, an equilibration time of 60 min, and an initial pH of 3. Moreover, the calcined pyrite powder exhibited excellent reusability, and the Cr(VI) removal rate exceeded 65% after three cycles. The Cr(VI) adsorption on pyrite can be well described by the Freundlich model and pseudo-second-order kinetic equation. The calcination temperature is the main factor affecting the adsorption performance of pyrite. Therefore, the calcined pyrite powder is expected to be an excellent adsorbent for Cr(VI) in the wastewater treatment industry.

SNAC3 Transcription Factor Enhances Arsenic Stress Tolerance and Grain Yield in Rice (Oryza sativa L.) through Regulating Physio-Biochemical Mechanisms, Stress-Responsive Genes, and Cryptochrome 1b

Arsenic (As) is one of the toxic heavy metal pollutants found in the environment. An excess of As poses serious threats to plants and diminishes their growth and productivity. NAC transcription factors revealed a pivotal role in enhancing crops tolerance to different environmental stresses. The present study investigated, for the first time, the functional role of SNAC3 in boosting As stress tolerance and grain productivity in rice (Oryza sativa L.). Two SNAC3-overexpressing (SNAC3-OX) and two SNAC3-RNAi transgenic lines were created and validated. The wild-type and transgenic rice plants were exposed to different As stress levels (0, 25, and 50 µM). The results revealed that SNAC3 overexpression significantly improved rice tolerance to As stress and boosted grain yield traits. Under both levels of As stress (25 and 50 µM), SNAC3-OX rice lines exhibited significantly lower levels of oxidative stress biomarkers and OsCRY1b (cryptochrome 1b) expression, but they revealed increased levels of gas exchange characters, chlorophyll, osmolytes (soluble sugars, proteins, proline, phenols, and flavonoids), antioxidant enzymes (SOD, CAT, APX, and POD), and stress-tolerant genes expression (OsSOD-Cu/Zn, OsCATA, OsCATB, OsAPX2, OsLEA3, OsDREB2B, OsDREB2A, OsSNAC2, and OsSNAC1) in comparison to wild-type plants. By contrast, SNAC3 suppression (RNAi) reduced grain yield components and reversed the aforementioned measured physio-biochemical and molecular traits. Taken together, this study is the first to demonstrate that SNAC3 plays a vital role in boosting As stress resistance and grain productivity in rice through modulating antioxidants, photosynthesis, osmolyte accumulation, and stress-related genes expression, and may be a useful candidate for further genetic enhancement of stress resistance in many crops.

Preparation of Eco-Friendly Chelating Resins and Their Applications for Water Treatment

In the present study, two chelating resins were prepared and used for simultaneous adsorption of toxic metal ions, i.e., Cr³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ (M^X+). In the first step, chelating resins were prepared starting with styrene-divinylbenzene resin, a strong basic anion exchanger Amberlite IRA 402(Cl^-) with two chelating agents, i.e., tartrazine (TAR) and amido black 10B (AB 10B). Key parameters such as contact time, pH, initial concentration, and stability were evaluated for the obtained chelating resins (IRA 402/TAR and IRA 402/AB 10B). The obtained chelating resins show excellent stability in 2M HCl, 2M NaOH, and also in ethanol (EtOH) medium. The stability of the chelating resins decreased when the combined mixture (2M HCl:EtOH = 2:1) was added. The above-mentioned aspect was more evident for IRA 402/TAR compared to IRA 402/AB 10B. Taking into account the higher stability of the IRA 402/TAR and IRA 402/AB 10B resins, in a second step, adsorption studies were carried out on complex acid effluents polluted with M^X+. The adsorption of M^X+ from an acidic aqueous medium on the chelating resins was evaluated using the ICP-MS method. The following affinity series under competitive analysis for IRA 402/TAR was obtained: Fe³⁺(44 µg/g) > Ni²⁺(39.8 µg/g) > Cd²⁺(34 µg/g) > Cr³⁺(33.2 µg/g) > Pb²⁺(32.7 µg/g) > Cu²⁺ (32.5 µg/g) > Mn²⁺(31 µg/g) > Co²⁺(29 µg/g) > Zn²⁺ (27.5 µg/g). While for IRA 402/AB 10B, the following behavior was observed: Fe³⁺(58 µg/g) > Ni²⁺(43.5 µg/g) > Cd²⁺(43 µg/g) > Cu²⁺(38 µg/g) > Cr³⁺(35 µg/g) > Pb²⁺(34.5 µg/g) > Co²⁺(32.8 µg/g) > Mn²⁺(33 µg/g) > Zn²⁺(32 µg/g), consistent with the decreasing affinity of M^X+ for chelate resin. The chelating resins were characterized using TG, FTIR, and SEM analysis. The obtained results showed that the chelating resins prepared have promising potential for wastewater treatment in the context of the circular economy approach.

Enhanced Chromium (VI) Adsorption onto Waste Pomegranate-Peel-Derived Biochar for Wastewater Treatment: Performance and Mechanism

Surface chemical modification allows for the rational construction of biochar with desirable structures and functionalities for environment purification. Fruit-peel-derived adsorbing material has been well studied in the adsorption of heavy-metal removal due to its abundance and non-toxicity, but its precise mechanism in removing chromium-containing pollutants remains unclear. Herein, we explored the potential application of engineered biochar prepared from fruit waste via chemical modification to remove chromium (Cr) from an aqueous solution. By synthesizing two types of agricultural residue-derived adsorbents, including pomegranate peel adsorbent (PG) and its modified product, pomegranate-peel-derived biochar (PG-B), via chemical and thermal decomposition methods, we elucidated the adsorption property of Cr(VI) on the studied materials and identified the cation retention mechanism of the adsorption process. Batch experiments and varied characterizations demonstrated that superior activity was exhibited in PG-B, which can contribute to the porous surfaces caused by pyrolysis and effective active sites resulting from alkalization. The highest Cr(VI) adsorption capacity is obtained at pH 4, a dosage of 6.25 g L^-1, and a contact time of 30 min. The maximum adsorption efficiency of 90.50% in a short period (30 min) was obtained on PG-B, while PG reached a removal performance of 78.01% at 60 min. The results from kinetic and isotherm models suggested that monolayer chemisorption dominated the adsorption process. The Langmuir maximum adsorption capacity is 16.23 mg g^-1. This study shortened the adsorption equilibrium time of pomegranate-based biosorbents and presents positive significance in designing and optimizing waste fruit-peel-derived adsorption materials for water purification.