Application of Floating Aquatic Plants in Phytoremediation of Heavy Metals Polluted Water: A Review

In situ phytoextraction of Mn and NH4+-N from aqueous electrolytic manganese residue solution by Pistia stratiotes: Effects of Fe/Co presence and rhizospheric microbe synergistic involvement

The electrolytic manganese industry produces a large amount of electrolytic manganese residue (EMR). Soluble Mn, NH4+-N, and other pollutants may be released from the open-air stacked EMR and transported to the environment along with rainfall or surface runoff. Aqueous EMR solution (AES) generally contains various elements required for plant growth, and phytoremediation can be applied to remove these pollutants from AES. Since the contents of Fe and Co vary greatly in AES depending on the ore sources as well as the pre-treatment processes, the presence of bioavailable Fe and Co at different levels may affect plant growth, the rhizosphere microbes, and pollutant removal. The present study investigated the in-situ removal of Mn(II) and NH4+-N from AES solution using free floating aquatic plant Pistia stratiotes, focusing especially on the effects of Fe/Co presence and rhizospheric microbe synergistic involvement on contaminant removal. The results showed that 69.08% of Mn and 94.99% of NH4+-N were removed by P. stratiotes in 24 d. Both the presence of Fe(II) and Co(II) facilitated the Mn(II) immobilization and increased Mn(II) removal by 19-31% due to the enhanced peroxidase activity and the increased Mn accumulating in roots The complete removal of Mn from AES was found in the presence of Fe(II) at 2 mg L-1 or Co(II) at 0.5 mg L-1 and more than 51% accumulated Mn in the roots was stored in the vacuole and cytoplasm. BioMnOx was found on the surface of the roots, revealing that rhizofiltration, rhizospheric plaque/biofilm formation, and Mn biogeochemical cycle exert synergic effects on Mn(II) immobilization. The findings of the present study demonstrate the feasibility of using P. stratiotes in the treatment of aqueous EMR solutions and the presence of an appropriate amount of bio-available Fe and Co can promote the removal of Mn(II) and NH4+-N.

Global impact of water hyacinth (Eichhornia Crassipes) on rural communities and mitigation strategies: a systematic review

The proliferation of water hyacinths (Eichhornia crassipes), recognized as one of the most invasive aquatic plants worldwide, presents profound ecological and socioeconomic challenges across diverse ecosystems, particularly in rural communities. This systematic review examines the extensive global impacts and explores various mitigation strategies to manage and utilize this pervasive species. Ecologically, water hyacinth disrupts aquatic ecosystems by depleting oxygen levels, obstructing sunlight, and displacing native species, which in turn compromises water quality and biodiversity. Economically, its rapid spread affects agriculture, fishing, and navigation, imposing significant costs on local economies and livelihoods. In response, this review assesses integrated management approaches combining mechanical, chemical, and biological controls that have been implemented to curb its growth. Moreover, innovative strategies that repurpose the biomass for bioenergy, handicrafts, and bio-remediation are discussed, highlighting their potential to transform an ecological menace into an economic resource. These strategies not only mitigate the plant's negative impacts but also contribute to sustainable development by providing economic opportunities and enhancing ecosystem services. This review stresses the necessity for a holistic approach to water hyacinth management that is adaptive, sustainable, and beneficial to affected communities.

Green solutions for antibiotic pollution: Assessing the phytoremediation potential of aquatic macrophytes in wastewater treatment plants

We compared the ability of one emergent (Sagittaria montevidensis), two floating (Salvinia minima and Lemna gibba), and one heterophyllous species (Myriophyllum aquaticum) to simultaneously remove sulfamethoxazole, sulfadiazine, ciprofloxacin, enrofloxacin, norfloxacin, levofloxacin, oxytetracycline, tetracycline, doxycycline, azithromycin, amoxicillin, and meropenem from wastewater in a mesocosm-scale constructed wetland over 28 days. Antibiotic concentrations in plants and effluent were analyzed using an LC-MS/MS to assess the removal rates and phytoremediation capacities. M. aquaticum did not effectively mitigate contamination due to poor tolerance and survival in effluent conditions. S. minima and L. gibba demonstrated superior efficiency, reducing the antibiotic concentrations to undetectable levels within 14 days, while S. montevidensis achieved this result by day 28. Floating macrophytes emerge as the preferable choice for remediation of antibiotics compared to emergent and heterophyllous species. Antibiotics were detected in plant tissues at concentrations ranging from 0.32 to 29.32 ng g-1 fresh weight, highlighting macrophytes' ability to uptake and accumulate these contaminants. Conversely, non-planted systems exhibited a maximum removal rate of 65%, underscoring the persistence of these molecules in natural environments, even after the entire experimental period. Additionally, macrophytes improved effluent quality regardless of species by reducing total soluble solids and phosphate concentrations and mitigating ecotoxicological effects. This study underscores the potential of using macrophytes in wastewater treatment plants to enhance overall efficiency and prevent environmental contamination by antibiotics, thereby mitigating the harmful impact on biota and antibiotic resistance. Selecting appropriate plant species is crucial for successful phytoremediation in constructed wetlands, and actual implementation is essential to validate their effectiveness and practical applicability.

Potential strategies for phytoremediation of heavy metals from wastewater with circular bioeconomy approach

Water pollution is an inextricable problem that stems from natural and human-related factors. Unfortunately, with rapid industrialization, the problem has escalated to alarming levels. The pollutants that contribute to water pollution include heavy metals (HMs), chemicals, pesticides, pharmaceuticals, and other industrial byproducts. Numerous methods are used for treating HMs in wastewater, like ion exchange, membrane filtration, chemical precipitation, adsorption, and electrochemical treatment. But the remediation through the plant, i.e., phytoremediation is the most sustainable approach to remove the contaminants from wastewater. Aquatic plants illustrate the capacity to absorb excess pollutants including organic and inorganic compounds, HMs, and pharmaceutical residues present in agricultural, residential, and industrial discharges. The extensive exploitation of these hyperaccumulator plants can be attributed to their abundance, invasive mechanisms, potential for bioaccumulation, and biomass production. Post-phytoremediation, plant biomass can be toxic to both water bodies and soil. Therefore, the circular bioeconomy approach can be applied to reuse and repurpose the toxic plant biomass into different circular bioeconomy byproducts such as biochar, biogas, bioethanol, and biodiesel is essential. In this regard, the current review highlights the potential strategies for the phytoremediation of HMs in wastewater and various strategies to efficiently reuse metal-enriched biomass material and produce commercially valuable products. The implementation of circular bioeconomy practices can help overcome significant obstacles and build a new platform for an eco-friendlier lifestyle.

Unveiling Metal Tolerance Mechanisms in Leersia hexandra Swartz under Cr/Ni Co-Pollution by Studying Endophytes and Plant Metabolites

Heavy metal pollution poses significant environmental challenges, and understanding how plants and endophytic bacteria interact to mitigate these challenges is of utmost importance. In this study, we investigated the roles of endophytic bacteria, particularly Chryseobacterium and Comamonas, in Leersia hexandra Swartz (L. hexandra) in response to chromium and nickel co-pollution. Our results demonstrated the remarkable tolerance of Chryseobacterium and Comamonas to heavy metals, and their potential to become dominant species in the presence of co-pollution. We observed a close relationship between these endophytic bacteria and the significant differences in metabolites, particularly carbohydrates, flavonoids, and amino acids in L. hexandra. These findings shed light on the potential of endophytic bacteria to promote the production of aspartic acid and other metabolites in plants as a response to abiotic stressors. Furthermore, our study presents a new direction for plant and bioremediation strategies in heavy metal pollution and enhances our understanding of L. hexandra's mechanisms for heavy metal tolerance.

Sorption capacity of Eichhornia crassipes (Mart.) Solms for zinc removal from electroplating industry wastewater

Various industrial operations in the dye, fertilizer, pesticide, battery, mining, and chemical industries have been associated with releasing heavy metals in wastewater, such as lead, zinc, copper, arsenic, cadmium, chromium, nickel, and mercury. These metals are dangerous to aquatic life as well as to humans, who may consume them directly or indirectly. Therefore, before being released into open water and land resources, it is necessary to minimize the concentration of toxic ions below the discharge limit. This study used Eichhornia crassipes (Mart.) Solms to remove zinc from wastewater from the electroplating industry in a constructed wetland. Experimental investigations were conducted for removing zinc ions from electroplating industry wastewater using various process parameters such as nutrient dosages, dilution ratios, potential of hydrogen ions, biomasses, and contact times. The outcome of this study revealed that the maximum zinc removal percentage in electroplating industrial wastewater was found for the optimum nutrient dosages of 60 g, dilution ratios of 10, potential hydrogen ion levels of 8, and biomass amounts of 100 g. The maximum zinc removal by Eichhornia crassipes (Mart.) Solms was found to be 88.3 ± 0.6 and 93.4 ± 0.4% at the optimum parameter values for the electroplating industry wastewater and the aqueous solution, respectively, against the optimum contact time of 22 days. This study suggests using this phytoremediation technology to remove all pollutants from industrial wastewater in general, not just wastewater from the electroplating industry.

Global perspective of municipal solid waste and landfill leachate: generation, composition, eco-toxicity, and sustainable management strategies

Globally, more than 2 billion tonnes of municipal solid waste (MSW) are generated each year, with that amount anticipated to reach around 3.5 billion tonnes by 2050. On a worldwide scale, food and green waste contribute the major proportion of MSW, which accounts for 44% of global waste, followed by recycling waste (38%), which includes plastic, glass, cardboard, and paper, and 18% of other materials. Population growth, urbanization, and industrial expansion are the principal drivers of the ever-increasing production of MSW across the world. Among the different practices employed for the management of waste, landfill disposal has been the most popular and easiest method across the world. Waste management practices differ significantly depending on the income level. In high-income nations, only 2% of waste is dumped, whereas in low-income nations, approximately 93% of waste is burned or dumped. However, the unscientific disposal of waste in landfills causes the generation of gases, heat, and leachate and results in a variety of ecotoxicological problems, including global warming, water pollution, fire hazards, and health effects that are hazardous to both the environment and public health. Therefore, sustainable management of MSW and landfill leachate is critical, necessitating the use of more advanced techniques to lessen waste production and maximize recycling to assure environmental sustainability. The present review provides an updated overview of the global perspective of municipal waste generation, composition, landfill heat and leachate formation, and ecotoxicological effects, and also discusses integrated-waste management approaches for the sustainable management of municipal waste and landfill leachate.

Domestic wastewater treatment by Pistia stratiotes in constructed wetland

The objective of the study was to evaluate the performance of Pistia stratiotes for treatment of domestic wastewater in a free surface water flow constructed wetland. The objective of the study was to evaluate contaminants removal efficiency of the constructed wetland vegetated with P. stratiotes in treatment of domestic wastewater against Hydraulic retention time (HRT) of 10, 20 and 30 days was investigated. This asks for newer and efficient low-cost nature-based water treatment system which along with cost takes into consideration the sustainability of the ecosystem. Five constructed wetland setups improved the wastewater quality and purify it significantly by reducing the TDS by 83%, TSS by 82%, BOD by 82%, COD by 81%, Chloride by 80%, Sulfate by 77%, NH3 by 84% and Total Oil and Grease by 74%. There was an increase in pH of about 11.9%. Color and odor of wastewater was also improved significantly and effectively. It was observed that 30 days' HRT was optimum for the treatment of domestic wastewater. The final effluent was found to be suitable as per national environmental quality standards and recycled for watering plants and crop irrigation but not for drinking purposes. The treatment in constructed wetland system was found to be economical, as the cost of construction only was involved and operational and maintenance cost very minimal. Even this research was conducted on the sole purpose of commuting the efficiency of pollutant removal in short span time.

Heavy metals/-metalloids (As) phytoremediation with Landoltia punctata and Lemna sp. (duckweeds): coupling with biorefinery prospects for sustainable phytotechnologies

Heavy metals/-metalloids can result in serious human health hazards. Phytoremediation is green bioresource technology for the remediation of heavy metals and arsenic (As). However, there exists a knowledge gap and systematic information on duckweed-based metal phytoremediation in an eco-sustainable way. Therefore, the present review offers a critical discussion on the effective use of duckweeds (genera Landoltia and Lemna)-based phytoremediation to decontaminate metallic contaminants from wastewater. Phytoextraction and rhizofiltration were the major mechanism in 'duckweed bioreactors' that can be dependent on physico-chemical factors and plant-microbe interactions. The biotechnological advances such as gene manipulations can accelerate the duckweed-based phytoremediation process. High starch and protein contents of the metal-loaded duckweed biomass facilitate their use as feedstock in biorefinery. Biorefinery prospects such as bioenergy production, value-added products, and biofertilizers can augment the circular economy approach. Coupling duckweed-based phytoremediation with biorefinery can help achieve Sustainable Development Goals (SDGs) and human well-being.

Efficiency of sodium phytate in the remediation of As, Mn, and Cu contamination in acid mine drainage using water hyacinth

The accumulation and uptake efficiency of heavy metals, including As, Mn, and Cu, in water hyacinth (Eichhornia crassipes (Mart.) Solms) grown in synthetic acidic wastewater supplemented with sodium phytate (SP) was examined. Three treatments were studied using synthetic acidic wastewater containing 0.25, 5.0, and 1.0 mg/L of As, Mn, and Cu, respectively, (SM + heavy metals) and having pH in the range of 4-6, which comprised of (1) control treatments using SM + heavy metals at pH 4, 5, 6 without SP, and treatments using SM + heavy metals at pH 4, 5, 6 with SP: Cu (2) in a 1:3 M ratio and (3) a 1:6 M ratio. The translocation factor (TF < 1) indicated that plants had a lower capacity to transport heavy metals from the roots to the stems. The shoots of water hyacinth exhibited the highest capacity to absorb and store As in the pH 4-treatment with SP (SP:Cu1:3 mol), whereas the roots showed the greatest capacity at pH 4 without SP. The roots and shoots of the water hyacinth showed the greatest capacity to take up and store Mn in the pH 5-treatment with a 1:3 M ratio of SP:Cu. The roots showed the greatest capacity to take up and store Cu in the pH 6-treatment, and the shoots showed the highest capability in the pH 5-treatment with 1:3 M ratio of SP:Cu. Moreover, analysis of the chemical forms revealed that As accumulated in the arsenate form, whereas Mn accumulated in the divalent form.

Integrating phytoremediation and mycoremediation with biosurfactant-producing fungi for hydrocarbon removal and the potential production of secondary resources

Treatment of petroleum-contaminated soil to a less toxic medium via physical and chemical treatment is too costly and requires posttreatment. This review focuses on the employment of phytoremediation and mycoremediation technologies in cleaning hydrocarbon-contaminated soil which is currently rare. It is considered environmentally beneficial and possibly cost-effective as it implements the synergistic interaction between plants and biosurfactant producing mycorrhiza to degrade hydrocarbon contaminants. This review also covers possible sources of hydrocarbon pollution in water and soil, toxicity effects, and current technologies for hydrocarbon removal and degradation. In addition to these problems, this review also discusses the challenges and opportunities of transforming the resultant treated sludge and treating plants into potential by-products for a higher quality of life for future generations.

Microbes-assisted phytoremediation of lead and petroleum hydrocarbons contaminated water by water hyacinth

An experiment was carried out to explore the impact of petroleum hydrocarbons (PHs)-degrading microbial consortium (MC) on phytoremediation ability and growth of water hyacinth (WH) plants in water contaminated with lead (Pb) and PHs. Buckets (12-L capacity) were filled with water and WH plants, PHs (2,400 mg L-1) and Pb (10 mg L-1) in respective buckets. Plants were harvested after 30 days of transplanting and results showed that PHs and Pb substantially reduced the agronomic (up to 62%) and physiological (up to 49%) attributes of WH plants. However, the application of MC resulted in a substantial increase in growth (38%) and physiology (22%) of WH plants over uninoculated contaminated control. The WH + MC were able to accumulate 93% Pb and degrade/accumulate 72% of PHs as compared to initial concentration. Furthermore, combined use of WH plants and MC in co-contamination of PHs and Pb, reduced Pb and PHs contents in water by 74% and 68%, respectively, than that of initially applied concentration. Our findings suggest that the WH in combination with PHs-degrading MC could be a suitable nature-based water remediation technology for organic and inorganic contaminants and in future it can be used for decontamination of mix pollutants from water bodies.

Local and landscape factors influencing mercury distribution in water, bottom sediment, and biota from lakes of the Araguaia River floodplain, Central Brazil

Mercury (Hg) is a chemical element widely present in the Earth's crust. However, its high toxicity and ability to accumulate in organisms and biomagnify through food chains characterize it as a global pollutant of primary control. We assessed total mercury concentrations ([THg]) in abiotic and biotic compartments from 98 floodplain lakes associated with the Araguaia River and six tributaries (Midwest Brazil). [THg] quantification in water was performed by cold vapor atomic fluorescence spectroscopy. [THg] in bottom sediment was assessed using cold vapor generation atomic absorption spectrophotometry, while [THg] in macrophyte, periphyton, and plankton were quantified by thermal decomposition atomic absorption spectrometry. Hotspots of [THg] in water, bottom sediment, and macrophytes were determined in areas impacted by pasture and urban areas. In contrast, hotspots of [THg] in periphyton and forest fires were determined in preserved areas downstream. [THg] in plankton did not show a clear spatial distribution pattern. The mean bioaccumulation factor order was plankton (2.3 ± 1.8) > periphyton (1.3 ± 0.9) > macrophytes (0.7 ± 0.4) (KW = 55.09, p < 0.0001). Higher [THg] in water and bottom sediment were associated with high pH (R2adj = 0.118, p = 0.004) and organic matter (R2adj = 0.244, p < 0.0001). [THg] in macrophytes were positively influenced by [THg] in water (R2adj = 0.063, p = 0.024) and sediment (R2adj = 0.105, p = 0.007). [THg] in periphyton are positively related to forest fires (R2adj = 0.156, p = 0.009) and [THg] in macrophytes (R2adj = 0.061, p = 0.03) and negatively related to lake depth (R2adj = 0.045, p = 0.02). The transfer of Hg from water and sediment to the biota is limited. However, the progressive increase of the bioaccumulation factor between macrophyte, periphyton, and plankton may indicate Hg biomagnification along the food chain of the Araguaia River floodplain.

The Metallotolerance and Biosorption of As(V) and Cr(VI) by Black Fungi

A collection of 34 melanized fungi isolated previously from anthropogenic contaminated sites were assessed for their tolerance to toxic concentrations of As(V) and Cr(VI) anions. Three strains of the species Cyphellophora olivacea, Rhinocladiella similis, and Exophiala mesophila (Chaetothyriales) were identified as hyper-metallotolerant, with estimated IC50 values that ranged from 11.2 to 16.9 g L-1 for As(V) and from 2.0 to 3.4 g L-1 for Cr(VI). E. mesophila and R. similis were selected for subsequent assays on their biosorption capacity and kinetics under different pH values (4.0 and 6.5) and types of biomass (active and dead cells and melanin extracts). The fungal biosorption of As(V) was relatively ineffective, but significant removal of Cr(VI) was observed from liquid cultures. The Langmuir model with second-order kinetics showed maximum sorption capacities of 39.81 mg Cr6+ g-1 for R. similis and 95.26 mg Cr6+ g-1 for E. mesophila on a dry matter basis, respectively, while the kinetic constant for these two fungi was 1.32 × 10-6 and 1.39 × 10-7 g (mg Cr6+ min)-1. Similar experiments with melanin extracts of E. mesophila showed maximum sorption capacities of 544.84 mg Cr6+ g-1 and a kinetic constant of 1.67 × 10-6 g (mg Cr6+ min)-1. These results were compared to bibliographic data, suggesting that metallotolerance in black fungi might be the result of an outer cell-wall barrier to reduce the diffusion of toxic metals into the cytoplasm, as well as the inner cell wall biosorption of leaked metals by melanin.

The decomposition of algae has a greater impact on heavy metal transformation in freshwater lake sediments than that of macrophytes

Heavy metal (HM) pollution is a major concern in freshwater ecosystem management. The different types of endogenous organic matter and the way their decomposition affects HM transformation in freshwater lakes is not well understood. An ex situ mesocosm study was conducted to compare HM transformation in sediments during anaerobic decomposition of cyanobacterial bloom biomass (CBB) and submerged cyanobacterial vegetation in Lake Taihu, known as Potamogeton malaianus (PM). Microbial community structures were examined through Illumina sequencing of 16S rDNA. Results indicate that Zn had a remarkably higher amount of potential mobile fraction than other heavy metals (Cr, Pb, Cu, Ni, and Cd) detected in sediments, especially in sediments collected from CBB-dominated areas (approximately 150 mg kg-1). CBB decomposition has caused a significant increase in exchangeable Zn content in sediments and a decrease in reducible Zn that was three times greater than PM decomposition. Additionally, oxidizable Zn content declined during CBB decomposition but increased during PM decomposition. Furthermore, the relative abundance of the main fermentative bacteria and some sulfate-reducing bacteria genera (e.g., Desulfomicrobium) were significantly associated with the HM content of exchangeable and reducible fractions during CBB decomposition. Overall, the findings indicate that Zn is more susceptible to endogenous organic matter decomposition than other metals in freshwater lakes, and the impacts of CBB decomposition on the transformation of heavy metals in sediment are greater than that of submerged macrophyte decomposition.

Industrial wastewater treatment using floating wetlands: a review

Industrial wastewater generated from various production processes is often associated with elevated pollutant concentrations and environmental hazards, necessitating efficient treatment. Floating wetlands (FWs) have emerged as a promising and eco-friendly solution for industrial wastewater treatment, with numerous successful field applications. This article comprehensively reviews the removal mechanisms and treatment performance in the use of FWs for the treatment of diverse industrial wastewaters. Our findings highlight that the performance of FWs relies on proper plant selection, design, aeration, season and temperature, plants harvesting and disposal, and maintenance. Well-designed FWs demonstrate remarkable effectiveness in removing organic matter (COD and BOD), suspended solids, nutrients, and heavy metals from industrial wastewater. This effectiveness is attributed to the intricate physical and metabolic interactions between plants and microbial communities within FWs. A significant portion of the reported applications of FWs revolve around the treatment of textile and oily wastewater. In particular, the application reports of FWs are mainly concentrated in temperate developing countries, where FWs can serve as a feasible and cost-effective industrial wastewater treatment technology, replacing high-cost traditional technologies. Furthermore, our analysis reveals that the treatment efficiency of FWs can be significantly enhanced through strategies like bacterial inoculation, aeration, and co-plantation of specific plant species. These techniques offer promising directions for further research. To advance the field, we recommend future research efforts focus on developing novel floating materials, optimizing the selection and combination of plants and microorganisms, exploring flexible disposal methods for harvested biomass, and designing multi-functional FW systems.

A review on existing and emerging approaches for textile wastewater treatments: challenges and future perspectives

This comprehensive review explores the complex environment of textile wastewater treatment technologies, highlighting both well-established and emerging techniques. Textile wastewater poses a significant environmental challenge, containing diverse contaminants and chemicals. The review presents a detailed examination of conventional treatments such as coagulation, flocculation, and biological processes, highlighting their effectiveness and limitations. In textile industry, various textile operations such as sizing, de-sizing, dyeing, bleaching, and mercerization consume large quantities of water generating effluent high in color, chemical oxygen demand, and solids. The dyes, mordants, and variety of other chemicals used in textile processing lead to effluent variable in characteristics. Furthermore, it explores innovative and emerging techniques, including advanced oxidation processes, membrane filtration, and nanotechnology-based solutions. Future perspectives in textile wastewater treatment are discussed in-depth, emphasizing the importance of interdisciplinary research, technological advancements, and the integration of circular economy principles. Numerous dyes used in the textile industry have been shown to have mutagenic, cytotoxic, and ecotoxic potential in studies. Therefore, it is necessary to assess the methods used to remediate textile waste water. Major topics including the chemical composition of textile waste water, the chemistry of the dye molecules, the selection of a treatment technique, the benefits and drawbacks of the various treatment options, and the cost of operation are also addressed. Overall, this review offers a valuable resource for researchers and industry professionals working in the textile industry, pointing towards a more sustainable and environmentally responsible future.

Arsenic pollution cycle, toxicity and sustainable remediation technologies: A comprehensive review and bibliometric analysis

Arsenic pollution and its allied impacts on health are widely reported and have gained global attention in the last few decades. Although the natural distribution of arsenic is limited, anthropogenic activities have increased its mobility to distant locations, thereby increasing the number of people affected by arsenic pollution. Arsenic has a complex biogeochemical cycle which has a significant role in pollution. Therefore, this review paper has comprehensively analysed the biogeochemical cycle of arsenic which can dictate the occurrence of arsenic pollution. Considering the toxicity and nature of arsenic, the present work has also analysed the current status of arsenic pollution around the world. It is noted that the south of Asia, West-central Africa, west of Europe and Latin America are major hot spots of arsenic pollution. Bibliometric analysis was performed by using scopus database with specific search for keywords such as arsenic pollution, health hazards to obtain the relevant data. Scopus database was searched for the period of 20 years from year 2003-2023 and total of 1839 articles were finally selected for further analysis using VOS viewer. Bibliometric analysis of arsenic pollution and its health hazards has revealed that arsenic pollution is primarily caused by anthropogenic sources and the key sources of arsenic exposure are drinking water, sea food and agricultural produces. Arsenic pollution was found to be associated with severe health hazards such as cancer and other health issues. Thus considering the severity of the issue, few sustainable remediation technologies such as adsorption using microbes, biological waste material, nanomaterial, constructed wetland, phytoremediation and microorganism bioremediation are proposed for treating arsenic pollution. These approaches are environmentally friendly and highly sustainable, thus making them suitable for the current scenario of environmental crisis.

Phytoremediation for antibiotics removal from aqueous solutions: A meta-analysis

Antibiotics are widely used as drugs and enter water bodies through various routes, leading to environmental pollution. As a green in-situ remediation technology, phytoremediation has been proven to be highly effective in removing antibiotics present in the aqueous phase. However, these data are distributed in various studies and lack systematic analysis, which could provide a more comprehensive understanding of the current status and trends in the research field. Based on this, a meta-analysis was conducted from three perspectives in this study: the factors influencing antibiotics removal by phytoremediation, the effect of antibiotics on plant physiological indexes, and the accumulation and translocation of antibiotics in plants. The results showed that plants have a significant effect on antibiotics removal, which is influenced by plant species, running time, biomass, antibiotic types and antibiotic concentration. Although some physiological indexes of plants changed under stress from high antibiotic concentrations, most plant species demonstrated resistance to antibiotic concentrations below 100 μgL-1. Additionally, the amount of antibiotics accumulated in plants was extremely little, so the risk of secondary pollution was minimal during phytoremediation. The results of this study reveal the main factors influencing antibiotics removal by phytoremediation and plant physiological responses to antibiotics, providing a reference for improving the rational application of phytoremediation for antibiotics removal. In addition, it will provide concepts and directions for improving the efficiency of sustainable and environmentally friendly remediation methods for treating antibiotic pollution.

Enhanced nitrogen and phosphorus removal by a novel ecological floating bed integrated with three-dimensional biofilm electrode system

The ecological floating bed (EFB) has been used extensively for the purification of eutrophication water. However, the traditional EFB (T-EFB) often exhibits a decline in nitrogen and phosphorus removal because of the limited adsorption capacity of fillers and inadequate electron donors. In the present study, a series of electrolysis-ecological floating beds (EC-EFBs) were constructed to investigate the decontamination performance of conventional pollutants. EC-EFB outperformed T-EFB in terms of nitrogen and phosphorus removal. Its removal efficiency of total nitrogen and total phosphorus was 20.51-32.95% and 45.06-96.20%, which were higher than that in T-EFB.. Moreover, the plants in EC-EFB demonstrated higher metabolic activity than those in T-EFB. Under the electrolysis condition of 0.51 mA/cm2 for 24 h, the malondialdehyde content and superoxide dismutase activity in EC-EFB were 6.08 nmol/g and 22.61 U/g, which were significantly lower compared to T-EFB (38.65 nmol/g and 26.13 U/g). And the soluble protein content of plant leaves increased from 3.31 mg/g to 5.72 mg/g in EC-EFB. Microbial analysis revealed that electrolysis could significantly change the microbial community and facilitate the proliferation of nitrogen-functional microbes, such as Thermomonas, Hydrogenophaga, Deinococcus, and Zoogloea. It is important to highlight that the hydrogen evolution reaction at the cathode area facilitated phosphorus removal in EC-EFB, thereby inhibiting phosphorus leaching. This study provides a promising and innovative technology for the purification of eutrophic water.

Biotechnology to reduce logistics burden and promote environmental stewardship for Air Force civil engineering requirements

This review provides discussion of advances in biotechnology with specific application to civil engineering requirements for airfield and airbase operations. The broad objectives are soil stabilization, waste management, and environmental protection. The biotechnology focal areas address (1) treatment of soil and sand by biomineralization and biopolymer addition, (2) reduction of solid organic waste by anaerobic digestion, (3) application of microbes and higher plants for biological processing of contaminated wastewater, and (4) use of indigenous materials for airbase construction and repair. The consideration of these methods in military operating scenarios, including austere environments, involves comparison with conventional techniques. All four focal areas potentially reduce logistics burden, increase environmental sustainability, and may provide energy source, or energy-neutral practices that benefit military operations.

Gene co-expression networks unravel the molecular responses of freshwater hydrophytes to combined stress of salinity and cadmium

Salinization in freshwater lakes is becoming a serious global environmental problem, especially in lakes of plateaus such as south-western plateau of China. However, limited information is available about the molecular response of freshwater hydrophytes to salinity under multiple stress. In the present study, a weighted gene co-expression network (WGCNA) was used to identify the modules of co-expressed genes in the physiological and biochemical indicators of Pistia stratiotes to determine its molecular response to salinity (NaCl) alone and when combined with cadmium (Cd). The physiological and biochemical indicators showed that P. stratiotes improved its salt tolerance by enhancing photosynthetic abilities, reducing oxidative stress, and inducing osmoprotectant generation. Morever, addition of NaCl reduced the Cd accumulation in P. stratiotes. Transcriptome and WGCNA analysis revealed that the pathways of alpha-linolenic acid metabolism, ribosomal, flavonoid biosynthesis, and phenylpropanoid biosynthesis were significantly enriched in both treatments. Genes associated with photosynthesis-antenna proteins, nitrogen metabolism, and the acid cycle pathways were only expressed under salinity stress alone, while the proteasome pathway was only significantly enriched in the combined salinity and Cd treatment. Our findings provide novel insights into the effects of salinization on aquatic plants in freshwater ecosystems and the management of aquatic ecosystems under global change.

O, Asma K.A.A A, Eida Mohammad A, Ali Khan MW. Optimization of Pseudomonas aeruginosa isolated for bioremediation from Ha'il region of Saudi Arabia

Majority of dyes are toxic to all the living organisms and inherently resistant to microbial degradation. Hence, decolorization and degradation of textile dye methyl red were evaluated using isolated bacterial strain Pseudomonas aeruginosa (P. aeruginosa). Methyl red dye decolorization by P. aeruginosa with respect to various parameters was optimized. Data shows that maximum possible decolorization was seen at 50 ppm dye concentration, 1400 mg/l glucose concentration, 700 mg/l sodium chloride (NaCl) concentration, pH 9, temperature 38°C, 1000 mg/l urea concentration P. aeruginosa AM-1 strain. The highest percent (91.1%) of bioremediation was achieved at 40 ppm dye concentration in Allium cepa test. These findings suggest P. aeruginosa strain (AM-1) has the potential to be used in the biological treatment of highly toxic dye which is main constituent of dyeing mill effluents due to its high decolorization activity with simple conditions. Strain AW-1 strain also has potential to bioremediate other wastewater containing methyl red dye.

Bacterial Communities Associated with the Roots of Typha spp. and Its Relationship in Phytoremediation Processes

Heavy metal pollution is a severe concern worldwide, owing to its harmful effects on ecosystems. Phytoremediation has been applied to remove heavy metals from water, soils, and sediments by using plants and associated microorganisms to restore contaminated sites. The Typha genus is one of the most important genera used in phytoremediation strategies because of its rapid growth rate, high biomass production, and the accumulation of heavy metals in its roots. Plant growth-promoting rhizobacteria have attracted much attention because they exert biochemical activities that improve plant growth, tolerance, and the accumulation of heavy metals in plant tissues. Because of their beneficial effects on plants, some studies have identified bacterial communities associated with the roots of Typha species growing in the presence of heavy metals. This review describes in detail the phytoremediation process and highlights the application of Typha species. Then, it describes bacterial communities associated with roots of Typha growing in natural ecosystems and wetlands contaminated with heavy metals. Data indicated that bacteria from the phylum Proteobacteria are the primary colonizers of the rhizosphere and root-endosphere of Typha species growing in contaminated and non-contaminated environments. Proteobacteria include bacteria that can grow in different environments due to their ability to use various carbon sources. Some bacterial species exert biochemical activities that contribute to plant growth and tolerance to heavy metals and enhance phytoremediation.

Recent progress on the microbial mitigation of heavy metal stress in soybean: overview and implications

Plants are adapted to defend themselves through programming, reprogramming, and stress tolerance against numerous environmental stresses, including heavy metal toxicity. Heavy metal stress is a kind of abiotic stress that continuously reduces various crops' productivity, including soybeans. Beneficial microbes play an essential role in improving plant productivity as well as mitigating abiotic stress. The simultaneous effect of abiotic stress from heavy metals on soybeans is rarely explored. Moreover, reducing metal contamination in soybean seeds through a sustainable approach is extremely needed. The present article describes the initiation of heavy metal tolerance mediated by plant inoculation with endophytes and plant growth-promoting rhizobacteria, the identification of plant transduction pathways via sensing annotation, and contemporary changes from molecular to genomics. The results suggest that the inoculation of beneficial microbes plays a significant role in rescuing soybeans under heavy metal stress. They create a dynamic, complex interaction with plants via a cascade called plant-microbial interaction. It enhances stress metal tolerance via the production of phytohormones, gene expression, and secondary metabolites. Overall, microbial inoculation is essential in mediating plant protection responses to heavy metal stress produced by a fluctuating climate.

A review of the effects of environmental hazards on humans, their remediation for sustainable development, and risk assessment

In the race for economic development and prosperity, our earth is becoming more polluted with each passing day. Technological advances in agriculture and rapid industrialization have drastically polluted the two pillars of natural resources, land and water. Toxic chemicals and microbial contaminants/agents created by natural and anthropogenic activities are rapidly becoming environmental hazards (EH) with increased potential to affect the natural environment and human health. This review has attempted to describe the various agents (chemical, biological, and physical) responsible for environmental contamination, remediation methods, and risk assessment techniques (RA). The main focus is on finding ways to mitigate the harmful effects of EHs through the simultaneous application of remediation methods and RA for sustainable development. It is recommended to apply the combination of different remediation methods using RA techniques to promote recycling and reuse of different resources for sustainable development. The report advocates for the development of site-specific, farmer-driven, sequential, and plant-based remediation strategies along with policy support for effective decontamination. This review also focuses on the fact that the lack of knowledge about environmental health is directly related to public health risks and, therefore, focuses on promoting awareness of effective ways to reduce anthropological burden and pollution and on providing valuable data that can be used in environmental monitoring assessments and lead to sustainable development.

2,4-D mediated moderation of aluminum tolerance in Salvinia molesta D. Mitch. with regards to bioexclusion and related physiological and metabolic changes

We examined the efficacy of 2,4-dichlorophenoxy acetic acid (2,4-D; 500 µM) in enhancing the potential of Salvinia species for tolerance to aluminum (Al) toxicity (240 and 480 µM, seven days). Salvinia showed better efficacy in removal of toxicity of Al by sorption mechanism with changes of bond energy shifting on cell wall residues and surface structure. Plants recorded tolerance to Al concentration (480 µM) when pretreated with 2,4-D through adjustment of relative water content, proline content, osmotic potential, and improved the pigment fluorescence for energy utilization under Al stress. Photosynthetic activities with regards to NADP-malic enzyme and malic dehydrogenase and sugar metabolism with wall and cytosolic invertase activities were strongly correlated with compatible solutes. A less membrane peroxidation and protein carbonylation had reduced ionic loss over the membrane that was studied with reduced electrolyte leakage with 2,4-D pretreated plants. Membrane stabilization was also recorded with higher ratio of K+ to Na+, thereby suggesting roles of 2,4-D in ionic balance. Better sustenance of enzymatic antioxidation with peroxidase and glutathione metabolism reduced reactive oxygen species accumulation and save the plant for oxidative damages. Moreover, gene polymorphism for antioxidant, induced by 2,4-D varied through Al concentrations would suggest an improved biomarker for tolerance. Collectively, analysis and discussion of plant's responses assumed that auxin herbicide could be a potential phytoprotectant for Salvinia as well as improving the stability to Al toxicity and its bioremediation efficacy.

ETDA as a legacy soil chelatant: a comparative study to a more environmentally sensitive alternative for metal removal by Pistia stratiotes L

The accuracy of environmental risk assessment depends upon selecting appropriate matrices to extract the most risk-relevant portion of contaminant(s) from the soil. Here, we applied the chelatants EDTA and tartaric acid to extract a metal-contaminated soil. Pistia stratiotes was applied as an indicator plant to measure accumulation from the metal-laden bulk solutions generated, in a hydroponic experiment lasting 15 days. Speciation modeling was used to elucidate key geo-chemical mechanisms impacting matrix and metal-specific uptake revealed by experimental work. The highest concentrations of soil-borne metals were extracted from soil by EDTA (7.4% for Cd), but their uptake and translocation to the plant were restricted due to the formation of stable metal complexes predominantly with DOC. Tartaric acid solubilized metals to a lesser extent (4.6% for Cd), but a higher proportion was plant available due to its presence mainly in the form of bivalent metal cations. The water extraction showed the lowest metal extraction (e.g., 3.9% for Cd), but the metal species behaved similarly to those extracted by tartaric acid. This study demonstrates that not all extractions are equal and that metal-specific speciation will impact accurate risk assessment in soil (water)-plant systems. In the case of EDTA, a deleterious impact on DOC leaching is an obvious drawback. As such, further work should now determine soil and not only metal-specific impacts of chelatants on the extraction of environmentally relevant portions of metal(loid)s.

Fungal community remediate quartz tailings soil under plant combined with urban sludge treatments

Introduction

Tailings can cause extensive damage to soil structure and microbial community. Phytoremediation is an effective strategy for remedied tailings soil due to its environmentally friendly and low-cost advantage. Fungi play a crucial role in nutrient cycling, stress resistance, stabilizing soil structure, and promoting plant growth. However, the fungal community variation in phytoremediation remains largely unexplored.

Methods

We analyzed soil fungal community based on high-throughput sequencing during three plant species combined with urban sludge to remediate quartz tailings soil.

Results

The results indicated that the fungal diversity was significantly increased with plant diversity, and the highest fungal diversity was in the three plant species combination treatments. Moreover, the fungal diversity was significantly decreased with the addition of urban sludge compared with plant treatments, while the abundance of potential beneficial fungi such as Cutaneotrichosporon, Apiotrichum, and Alternaria were increased. Notably, the fungal community composition in different plant species combination treatments were significant difference at the genus level. The addition of urban sludge increased pH, available phosphorus (AP), and available nitrogen (AN) content that were the main drivers for fungal community composition. Furthermore, the fungal networks of the plant treatments had more nodes and edges, higher connectedness, and lower modularity than plant combined with urban sludge treatments.

Conclusion

Our results showed that three plant species combined with urban sludge treatments improved fungal community and soil properties. Our results provide insights for quartz tailings soil remediation using plant-fungi- urban sludge.

Process variables that defined the phytofiltration efficiency of invasive macrophytes in aquatic system

Phytofiltration is an eco-friendly and cost-effective approach to the management of pollutants in aquatic system. The present study aimed at elucidating the process variables that defined the phytofiltration efficiency of invasive macrophytes in aquatic system. The invasion of macrophytes, such as Pistia stratiotes, of water bodies is an undesirable experience because of the challenges synonymous with their occurrence. Owing to the unfettered proliferation, high and rich biomass generation, and nutrient uptake capability, these macrophytes outcompete the native vegetation and reduce the distinctiveness of the biological communities at various scales. However, these same intrinsic features positioned them as an ideal phytofiltration species for the decontamination of polluted aqua systems. Herein, we provided an overview of the process of phytofiltration in an aquatic system, and the need to create a balanced ecological system through the exploitation of the potentials of macrophytes as phytoremediators. The translocation factor, type, and concentration of pollutants in the matrix, pH value, type of macrophyte employed are among the factors identified as determinants of the success or failure of invasive macrophytes as pollutant remediators in the aqua system. Therefore, the optimization of these variables, to enhance the phytoremediation potentials of the different macrophytes were critically appraised.

Phytoremediation of toxic chemicals in aquatic environment with special emphasis on duckweed mediated approaches

The discharge of toxic chemicals into water bodies and their linked detrimental effects on health is a global concern. Phytoremediation, an environment-friendly plant-based technology, has gained intensive interest over the last decades. For the aquatic phytoremediation process, the commonly available duckweeds have recently attracted significant attention due to their capacity to grow in diverse ecological niches, fast growth characteristics, suitable morphology for easy handling of biomass, and capacity to remove and detoxify various potential toxic elements and compounds. This review presents the progress of duckweed-assisted aquatic phytoremediation of toxic chemicals. A brief background of general phytoremediation processes, including the different phytoremediation methods and advances in understanding their underlying mechanisms, has been described. A summary of different approaches commonly practiced to assess the growth of the plants and their metal removal capacity in the phytoremediation process has also been included. A vast majority of studies have established that duckweed is an efficient plant catalyst to accumulate toxic heavy metals and organic contaminants, such as pesticides, fluorides, toxins, and aromatic compounds, reducing their toxicity from water bodies. The potential of this plant-based phytoremediation process for its downstream applications in generating value-added products for the rural economy and industrial interest has been identified.

Bioaccumulation and physiological traits qualify Pistia stratiotes as a suitable species for phytoremediation and bioindication of iron-contaminated water

Serious concerns have recently been raised regarding the association of Fe excess with neurodegenerative diseases in mammals and nutritional and oxidative disorders in plants. Therefore, the current study aimed to understand the physiological changes induced by Fe excess in Pistia stratiotes, a species often employed in phytoremediation studies. P. stratiotes were subjected to five concentrations of Fe: 0.038 (control), 1.0, 3.0, 5.0 and 7.0 mM. Visual symptoms of Fe-toxicity such as bronzing of leaf edges in 5.0 and 7.0 mM-grown plants were observed after 5 days. Nevertheless, no major changes were observed in photosynthesis-related parameters at this time-point. In contrast, plants growing for 10 days in high Fe concentrations showed decreased chlorophyll concentrations and lower net CO₂ assimilation rate. Notwithstanding, P. stratiotes accumulated high amounts of Fe, especially in roots (maximum of 10,000 µg g^-1 DW) and displayed a robust induction of the enzymatic antioxidant system. In conclusion, we demonstrated that P. stratiotes can be applied to clean up Fe-contaminated water, as the species displays high Fe bioaccumulation, mostly in root apoplasts, and can maintain physiological processes under Fe excess. Our results further revealed that by monitoring visual symptoms, P. stratiotes could be applied for bioindication purposes.

Advances in studies on the plant rhizosphere microorganisms in wetlands: A visualization analysis based on CiteSpace

Rhizosphere microorganisms and their interactions with plants in wetlands have recently attracted much attention due to their importance in enhancing plant environmental adaptation, removing wetland pollutants, and alleviating climate change. However, the fluctuating hydrological environment of wetlands leads to more complex dynamics in the rhizosphere environment. Research progress and hotspots concerning plant-rhizosphere microorganisms under special wetland environments are still kept unclear. To better understand the current research status, hotspots and trends of rhizosphere microorganisms in wetlands, we used CiteSpace bibliometric software to visualize and analyze 231 English-language publications from the Web of Science core collection database. Here, we reviewed the role played by various countries, institutions, and scholars in the studies of plant rhizosphere microorganisms in wetlands based on cooperation network analysis. We discussed the shift from bioremediation and nutrient removal to rhizosphere microbial community composition as a research hotspot for plant rhizosphere microorganisms in wetlands according to keyword co-occurrence and clustering analysis. Finally, we highlighted that more attention should be paid to the ecological functions of rhizosphere microorganisms in different wetland ecosystems, and the plant‒microbe microinterface processes and interaction patterns should be explored in depth to provide new indicators for the evaluation of wetland ecosystem functions.

Removing Mn, Cu and Fe from Real Wastewaters with Macrophytes: Reviewing the Relationship between Environmental Factors and Plants' Uptake Capacity

Heavy metal pollution creates environmental health concerns. Among these, iron (Fe), copper (Cu) and manganese (Mn) are commonly found in aquatic environments due to the release of wastewaters. Phytoremediation in hydroponics uses macrophytes to treat contaminated environments, and this is influenced by environmental factors. However, the relationship between these factors and the removal of Fe, Cu and Mn by macrophytes is not known. Therefore, a meta-analysis serves to determine the correlations between environmental factors and the removal of these metals in real wastewater by macrophytes, as well as to identify the role of different aquatic forms of macrophytes in phytoremediation. Emergent macrophytes had higher concentrations of manganese in their tissues, and higher bioconcentrations factor of iron and manganese than floating plants. Regardless of the biotope, higher concentrations of Fe and Cu decreased the ability of plants to bioconcentrate them. The correlations among exposure time, pH, dissolved oxygen, nitrogen, phosphorus, photoperiod and metal phytoremediation by plants were also found. It can be concluded that the emergent macrophytes showed better performance in terms of the removal of Fe, Cu and Mn, and that the significant correlations between environmental factors and removal vary with the type of metal and the environmental factor analyzed.

Wastewater generation and treatment by various eco-friendly technologies: Possible health hazards and further reuse for environmental safety

The discharge of untreated wastewater as a result of various developmental activities such as urbanization, industrialization and changes in lifestyle poses great threats to aquatic ecosystems as well as humans. Currently, ∼380 billion m³ (380 trillion liters) of wastewater is generated globally every year. Around 70% of freshwater withdrawals are used for agricultural production throughout the world. The wastewater generated through agricultural run-off further pollutes freshwater resources. However, only 24% of the total wastewater generated from households and industries is treated before its disposal in rivers or reused in agriculture. The most problematic contaminants associated with ecological toxicity are heavy metals such as Cd, Cr, Cu, Ni, Zn, Fe, Pb, Hg, As and Mn. One of the most important issues linked with wastewater generation is the residual presence of pathogenic microorganisms which pose potential health hazards to consumers when they enter into the food chain. It is estimated that in India almost USD 600 million (48.60 billion INR) is spent per year to tackle waterborne diseases (WBD). In light of this, immediate action is needed to effectively treat wastewater and develop safer reuse prospects. Various wastewater treatment technologies have been established and they work well to provide an alternative water source to meet the growing demand. The main concern towards treating wastewater is to eliminate inorganic and organic substances and lower the nutrient concentration, total solids, and microbial pathogens to prevent freshwater pollution and health risks.

Phytoremediation of nitrogen and phosphorus pollutants from glass industry effluent by using water hyacinth (Eichhornia crassipes (Mart.) Solms): Application of RSM and ANN techniques for experimental optimization

The present study aimed to assess the efficiency of the water hyacinth (Eichhornia crassipes (Mart.) Solms) plant for the reduction of nitrogen and phosphorus pollutants from glass industry effluent (GIE) as batch mode phytoremediation experiments. For this, response surface methodology (RSM) and artificial neural networks (ANN) methods were adopted to evidence the optimization and prediction performances of E. crassipes for total Kjeldahl's nitrogen (TKN) and total phosphorus (TP) removal. The control parameters, i.e., GIE concentration (0, 50, and 100%) and plant density (1, 3, and 5 numbers) were used to optimize the best reduction conditions of TKN and TP. A quadratic model of RSM and feed-forward backpropagation algorithm-based logistic model (input layer: 2 neurons, hidden layer: 10 neurons, and output layer: 1 neuron) of ANN showed good fitness results for experimental optimization. Optimization results showed that maximum reduction of TKN (93.86%) and TP (87.43%) was achieved by using 60% of GIE concentration and nearly five plants. However, coefficient of determination (R²) values showed that ANN models (TKN: 0.9980; TP: 0.9899) were superior in terms of prediction performance as compared to RSM (TKN: 0.9888; TP: 0.9868). Therefore, the findings of this study concluded that E. crassipes can be effectively used to remediate nitrogen and phosphorus loads of GIE and minimize environmental hazards caused by its unsafe disposal.

Enhanced nickel removal and synchronous bioelectricity generation based on substrate types in microbial fuel cell coupled with constructed wetland: performance and microbial response

In this study, an attempt was made to clarify the impact of substrates on the microbial fuel cell coupled with constructed wetland (CW-MFC) towards the treatment of nickel-containing wastewater. Herein, zeolite (ZEO), coal cinder (COA), ceramsite (CER), and granular activated carbon (GAC) were respectively introduced into lab-scaled CW-MFCs to systematically investigate the operational performances and microbial community response. GAC was deemed as the most effective substrate, and the corresponding device yielded favorable nickel removal efficiencies over 99% at different initial concentrations of nickel. GAC-CW-MFC likewise produced a maximum output voltage of 573 mV, power density of 8.95 mW/m², and internal resistance of 177.9 Ω, respectively. The strong adsorptive capacity of nickel by GAC, accounting for 54.5% of total contaminant content, was mainly responsible for the favorable nickel removal performances of device GAC-CW-MFC. The high-valence Ni²⁺ was partially reduced to elemental Ni⁰ on the cathode, which provided evidence for the removal of heavy metals via the cathodic reduction of CW-MFC. The microbial community structure varied considerably as a result of substrates addition. For an introduction of GAC into the CW-MFC, a remarkably enriched population of genera Thermincola, norank_f__Geobacteraceae, Anaerovorax, Bacillus, etc. was noted. This study was dedicated to providing a theoretical guidance for an effective regulation of CW-MFC treatment on nickel-containing wastewater and accompanied by bioelectricity generation via the introduction of optimal substrate.

Phytoremediation of Potentially Toxic Elements: Role, Status and Concerns

Environmental contamination with a myriad of potentially toxic elements (PTEs) is triggered by various natural and anthropogenic activities. However, the industrial revolution has increased the intensity of these hazardous elements and their concentration in the environment, which, in turn, could provoke potential ecological risks. Additionally, most PTEs pose a considerable nuisance to human beings and affect soil, aquatic organisms, and even nematodes and microbes. This comprehensive review aims to: (i) introduce potentially toxic elements; (ii) overview the major sources of PTEs in the major environmental compartments; (iii) briefly highlight the major impacts of PTEs on humans, plants, aquatic life, and the health of soil; (iv) appraise the major methods for tackling PTE-caused pollution; (v) discuss the concept and applications of the major eco-technological/green approaches (comprising phytoextraction, rhizofiltration, phytostabilization, phytovolatilization, and phytorestoration); (vi) highlight the role of microbes in phytoremediation under PTE stress; and (vii) enlighten the major role of genetic engineering in advancing the phytoremediation of varied PTEs. Overall, appropriate strategies must be developed in order to stop gene flow into wild species, and biosafety issues must be properly addressed. Additionally, consistent efforts should be undertaken to tackle the major issues (e.g., risk estimation, understanding, acceptance and feasibility) in order to guarantee the successful implementation of phytoremediation programs, raise awareness of this green technology among laymen, and to strengthen networking among scientists, stakeholders, industrialists, governments and non-government organizations.

Screening of structural and functional alterations in duckweed (Lemna minor) induced by per- and polyfluoroalkyl substances (PFASs) with FTIR spectroscopy

As a class of common emerging pollutants, per- and polyfluoroalkyl substances (PFASs) and their alternatives have been widely detected in various environmental matrices, exhibiting a great threat to the ecological environment and human health. Nevertheless, changes in biomolecular structure and function of duckweed caused by PFASs and their alternatives remain unknown thus far. Herein, the effects of four PFASs, including two common legacy PFASs (perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA)) and two PFASs alternatives (perfluorobutane sulfonic acid (PFBS) and 1H,1H,2H, 2H-perfluorooctane sulfonic acid (6:2 FTS)) on duckweed (Lemna minor) at biochemical level were investigated with Fourier transform infrared spectroscopy (FTIR). Although no obvious inhibitions were observed in the growth of L. minor with PFASs exposure at three levels of 1 μg L^-1, 100 μg L^-1, and 10 mg L^-1, significant structural and functional alterations were induced at the biochemical level. In response to PFASs exposure, lipid peroxidation, proteins aggregation and α-helix to β-sheet transformation of the protein conformation, as well as changes of DNA conformations were detected. Moreover, alterations in lipid, protein, and DNA were proved to be concentration-related and compound-specific. Compared to the two legacy PFASs (PFOS and PFOA), alternative ones exhibited greater effects on the biological macromolecules of L. minor. The findings of this study firstly reveal structural and functional alterations in L. minor induced by PFASs exposure, providing further understanding of their toxicity effects.

Short and long-term phytoremediation capacity of aquatic plants in Cu-polluted environments

Freshwater ecosystems face numerous threats from human populations, including heavy metal contamination. Phytoremediation, the use of plants to remediate contaminated soils and sediments, is an effective and low-cost means of removing chemical contaminants, including heavy metals, from polluted environments. However, key questions remain unanswered in the application of this technology in aquatic environments, such as the long-term fate of pollutants following plant uptake. In this study, using two common wetland plant species (duckweed and tape grass), we first examined the capacity of plants to remove copper (Cu) from polluted water. Next, we evaluated the leaching potential of plant tissues following decomposition and how it is affected by a simulated freeze-thaw cycle. Using phytoremediated water and leachates from senesced plants we assessed phytoremediation success and Cu leaching potential by conducting standard toxicity assays using pond snails (Physa acuta), a species with known Cu sensitivity. We found that duckweed outperformed tape grass as a phytoremediator at low Cu concentrations. In addition, for plants grown in low concentrations of Cu, leaching from decaying plant material did not negatively impact snail survival, while at high concentrations of Cu, leaching did result in toxicity. Lastly, we found that a simulated freeze-thaw cycle increased the release of Cu from plant tissue in the presence of high Cu concentrations only, resulting in reduced snail survival. Our results indicate that in moderately Cu-polluted environments, some aquatic plants can remove contaminants without a long-term risk of leaching. In contrast, phytoremediation in highly polluted environments will likely require removal of plant tissue to prevent leaching of previously accumulated metals. Land managers must not only consider plant species and degree of contamination, but also geographic location, as freeze-thaw cycles may enhance plant decomposition and increase the likelihood of contaminant leaching following phytoremediation efforts in aquatic ecosystems.

A critical review on the bio-mediated green synthesis and multiple applications of magnesium oxide nanoparticles

Nowadays, advancements in nanotechnology have efficiently solved many global problems, such as environmental pollution, climate change, and infectious diseases. Nano-scaled materials have played a central role in this evolution. Chemical synthesis of nanomaterials, however, required hazardous chemicals, unsafe, eco-unfriendly, and cost-ineffective, calling for green synthesis methods. Here, we review the green synthesis of MgO nanoparticles and their applications in biochemical, environmental remediation, catalysis, and energy production. Green MgO nanoparticles can be safely produced using biomolecules extracted from plants, fungus, bacteria, algae, and lichens. They exhibited fascinating and unique properties in morphology, surface area, particle size, and stabilization. Green MgO nanoparticles served as excellent antimicrobial agents, adsorbents, colorimetric sensors, and had enormous potential in biomedical therapies against cancers, oxidants, diseases, and the sensing detection of dopamine. In addition, green MgO nanoparticles are of great interests in plant pathogens, phytoremediation, plant cell and organ culture, and seed germination in the agricultural sector. This review also highlighted recent advances in using green MgO nanoparticles as nanocatalysts, nano-fertilizers, and nano-pesticides. Thanks to many emerging applications, green MgO nanoparticles can become a promising platform for future studies.

Mercury Sources, Emissions, Distribution and Bioavailability along an Estuarine Gradient under Semiarid Conditions in Northeast Brazil

In the semiarid coast of northeast Brazil, climate change and changes in land use in drainage basins affect river hydrodynamics and hydrochemistry, modifying the estuarine environment and its biogeochemistry and increasing the mobilization of mercury (Hg). This is particularly relevant to the largest semiarid-encroached basin of the region, the Jaguaribe River. Major Hg sources to the Jaguaribe estuary are solid waste disposal, sewage and shrimp farming, the latter emitting effluents directly into the estuary. Total annual emission reaches 300 kg. In that estuary, the distribution of Hg in sediment and suspended particulate matter decreases seaward, whereas dissolved Hg concentrations increase sharply seaward, suggesting higher mobilization at the marine-influenced, mangrove-dominated portion of the estuary, mostly in the dry season. Concentrations of Hg in rooted macrophytes respond to Hg concentrations in sediment, being higher in the fluvial endmember of the estuary, whereas in floating aquatic macrophytes, Hg concentrations followed dissolved Hg concentrations in water and were also higher in the dry season. Animals (fish and crustaceans) also showed higher concentrations and bioaccumulation in the marine-influenced portion of the estuary. The variability of Hg concentrations in plants and sediments agrees with continental sources of Hg. However, Hg fractionation in water and contents in the animals respond to higher Hg availability in the marine-dominated end of the estuary. The results suggest that the impact of anthropogenic sources on Hg bioavailability is modulated by regional and global environmental changes and results from a conjunction of biological, ecological and hydrological characteristics. Finally, increasing aridity due to global warming, observed in northeast Brazil, as well as in other semiarid littorals worldwide, in addition to increased water overuse, augment Hg bioavailability and environmental risk and exposure of the local biota and the tradition of human populations exploiting the estuary's biological resources.

Leymus chinensis resists degraded soil stress by modulating root exudate components to attract beneficial microorganisms

Phytoremediation is an effective means to improve degraded soil nutrients and soil structure. Here, we investigated the remediation effects of Leymus chinensis on the physicochemical properties and structure of degraded soil after 3 years of cultivation and explored the bacterial and fungal drivers in root exudates by metabolomics and high-throughput sequencing. The results showed that root exudates increased soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP) and soil aggregates, and organic acids in root exudates reduced pH and activated insoluble nutrients into forms that are available to plants, such as available nitrogen (NH₄ ⁺-N), nitrate nitrogen (NO₃ ^--N), and available phosphorus (AP). The cultivation of L. chinensis restored the diversity and richness of soil microorganisms and recruited potential beneficial bacteria and fungi to resist degraded soil stress, and L. chinensis also regulated the abundances of organic acids, amino acids and fatty acids in root exudates to remediate degraded soils. Spearman correlation analysis indicated that glutaric acid, 3-hydroxybutyric acid and 4-methylcatechol in root exudates attracted Haliangium, Nitrospira and Mortierella to the rhizosphere and dispersed the relative abundance of the harmful microorganisms Fusicolla and Fusarium. Our results demonstrate that L. chinensis enhances soil fertility, improves soil structure, promotes microbial diversity and abundance, and recruits potentially beneficial microorganisms by modulating root exudate components.

Duckweed: a potential phytosensor for heavy metals

Globally, heavy metal (HM) contamination is one of the primary causes of environmental pollution leading to decreased quality of life for those affected. In particular, HM contamination in groundwater poses a serious risk to human health and the potential for destabilization of aquatic ecosystems. At present, strategies to remove HM contamination from wastewater are inefficient, costly, laborious, and often the removal poses as much risk to the environment as the initial contamination. Phytoremediation, plant-based removal of contaminants from soil or water, has long been viewed as an economical and sustainable solution to remove toxic metals from the environment. However, to date, phytoremediation has demonstrated limited successes despite a large volume of literature supporting its potential. A key aspect for achieving robust and meaningful phytoremediation is the selection of a plant species that is well suited to the task. For the removal of pollutants from wastewater, hydrophytes, like duckweed, exhibit significant potential due to their rapid growth on nutrient-rich water, ease of collection, and ability to survive in various ecosystems. As a model for ecotoxicity studies, duckweed is an ideal candidate, as it is easy to cultivate under controlled and even sterile conditions, and the rapid growth enables multi-generational studies. Similarly, recent advances in the genetic engineering and genome-editing of duckweed will enable the transition from fundamental ecotoxicity studies to engineered solutions for phytoremediation of HMs. This review will provide insight into the suitability of duckweeds for phytoremediation of HMs and strategies for engineering next-generation duckweed to provide real-world environmental solutions.

Development of Ion Character Property Relationship (IC-PR) for Removal of 13-Metal Ions by Employing a Novel Green Adsorbent Aerva javanica

The novel Aerva javanica absorbent was applied for the removal of thirteen selected metal ions from a distilled water solution of each metal by the batch adsorption method. The optimization remediation parameters of the metal ions for the batch adsorption approach were developed, which were the initial concentrations (60 ppm), contact time (60 min) and pH (7). The basic properties of metal ion affected the adsorption results; therefore, 21 properties of metal ions were selected, which are called "descriptors". The most significant descriptors were selected that were vital for the adsorption results, such as covalent index, polarizability and ion charge. The developed model equation by the descriptors provided more than 80% accuracy in the predicted results. Furthermore, Freundlich and Langmuir adsorption models were also applied on the results. Constants of the Freundlich and Langmuir models were also used for model generation, and the results revealed the importance of a covalent index for the removal phenomenon of metal ions. The current study provided a suitable Ion Character Property Relationship (IC-PR) for the removal of metal ions, and future predictions can be achieved on the proposed adsorbent with significant accuracy. The ecofriendly and cost effective Aerva javanica absorbent in the batch experimental model of the current study predicted that this novel absorbent can be used for the removal of a wide spectrum of heavy metal ions from different sources of waste waters.

Biomass valorization of Eichhornia crassipes root using thermogravimetric analysis

Present study focused on the thermo-chemical potential of waste biomass of Eichhornia crassipes or water hyacinth root (WHR). The pyrolysis-kinetic parameters are investigated using thermo-gravimetric analysis at the various heating rates (5, 10, 15, and 20 °C/min). Three model-free techniques, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Starink, were used for the thermal kinetic analysis of biomass. The average activation energy for WHR biomass was determined using KAS, FWO, and Starink, with the values of 57.87, 64.69, and 58.27 kJ/mol, respectively. From the study it is observed that the roots of water hyacinth have rich in carbon, oxygen and hydrogen composition around 24%, 70% and 4% respectively. The higher heating value of water hyacinth root was observed around 15 MJ/kg.

Lithium Accumulation in Salvinia natans Free-Floating Aquatic Plant

The new context of the intensive use of lithium-based batteries led to increased production of Li and Li-containing wastes. All these activities are potential sources of environmental pollution with Li. However, the negative impact of Li on ecosystems, its specific role in the plants' development, uptake mechanism, and response to the induced stress are not fully understood. In this sense, the Li uptake and changes induced by Li exposure in the major and trace element contents, photosynthetic pigments, antioxidant activity, and elemental composition of Salvinia natans were also investigated. The results showed that Salvinia natans grown in Li-enriched nutrient solutions accumulated much higher Li contents than those grown in spring waters with a low Li content. However, the Li bioaccumulation factor in Salvinia natans grown in Li-enriched nutrient solutions was lower (13.3-29.5) than in spring waters (13.0-42.2). The plants exposed to high Li contents showed a decrease in their K and photosynthetic pigments content, while their total antioxidant activity did not change substantially.

Continuous Systems Bioremediation of Wastewaters Loaded with Heavy Metals Using Microorganisms

Heavy metal pollution is a serious concern of the modern era due to its widespread negative effects on human health and to the environment. Conventional technologies applied for the uptake of this category of persistent pollutants are complex, often expensive, and inefficient at low metal concentrations. In the last few years, non-conventional alternatives have been studied in search of better solutions in terms of costs and sustainability. Microbial adsorbents are one of the biomass-based sorbents that have extensively demonstrated excellent heavy metals removal capacity even at low concentrations. However, most of the carried-out research regarding their application in wastewater treatment has been performed in discontinuous systems. The use of microorganisms for the uptake of metal ions in continuous systems could be an important step for the upscale of the remediation processes since it facilitates a faster remediation of higher quantities of wastewaters loaded with heavy metals, in comparison with batch systems removal. Thus, the current research aims to analyze the available studies focusing on the removal of metal ions from wastewaters using microorganisms, in continuous systems, with a focus on obtained performances, optimized experimental conditions, and the sustainability of the bioremoval process. The present work found that microbial-based remediation processes have demonstrated very good performances in continuous systems. Further sustainability analyses are required in order to apply the bioremediation technology in an optimized environmentally friendly way in large-scale facilities.

Cu and Pb accumulation and removal from aqueous medium by Enydra fluctuans Lour. (Asteraceae) - a medicinal plant with potential for phytoremediation

Enydra fluctuans Lour. (Asteraceae) is an edible semi-aquatic floating or trailing herbaceous plant widely distributed in tropical Africa, South and South East Asia, and Australia. Its leaves, which are consumed as a vegetable, are also used in traditional medicine to treat several diseases. The efficacy of this plant in removal of copper and lead from aqueous medium was tested in the present study. The plants were exposed to graded measured concentrations of 0.55-10.2 mg Cu L^-1 and 11.5-50.2 mg Pb L^-1 in hydroponic systems. Controls without added Cu and Pb were maintained under identical conditions. Cu and Pb were estimated by atomic absorption spectrometry, and the bioconcentration factor (BCF) and the translocation factor (TF) were calculated for each element at the different concentrations. Accumulation of both Cu and Pb was significantly higher in root than that in leaf and stem. Though all the bioconcentration factor (BCF) values were greater than unity, none of the translocation factor (TF) values was greater than unity, indicating that this plant could not be considered a hyperaccumulator of these metals. Nevertheless, E. fluctuans could remove Cu from aqueous medium at rates ranging from 98.8 to 99.7%, with a mean reduction of 99.2% after 96-h exposure at various concentrations. The removal of Pb ranged from 97.1 to 99.1%, with a mean reduction of 98.2%. Thus, E. fluctuans showed high potential for removal of Cu and Pb from aqueous medium and has the prospect of being used in phytoremediation of these metals.