Valuation of banana peels as an effective biosorbent for mercury removal under low environmental concentrations

Mercury's poisonous pulse: Blazing a new path for aquatic conservation with eco-friendly mitigation strategies

Many compounds and inorganic elements released from natural and anthropogenic origins contaminate the environment and are implicated in catastrophes involving most biologically driven ecological processes and public health. One such element is Mercury. Mercury exists in both inorganic elemental form and the more metabolically active molecular form e.g. methyl mercury. They enjoy wide applications in medicine and form key components of numerous electrical and electronic devices. Unfortunately, severe health and adverse physiological conditions have developed from the impacts of mercury on the flora and fauna of both aquatic and terrestrial organisms. Despite being present in tiny amounts in water bodies, mercury undergoes a process of trophic amplification where its concentration increases significantly as it moves up the food chain through processes like biomethylation, bioaccumulation, and biomagnification. Most current methods for removing mercury through physical and chemical means have significant drawbacks, including high costs, complex technical requirements, and harmful secondary effects on the environment. Therefore, only environmentally friendly and sustainable approaches are acceptable to mitigate the risks to public health and ecosystem damage. Bioremediation involves the use of biological systems, i.e., plants and microbes, to recover mercury from the environment. The application of microorganisms in remediation is the hallmark of all mitigation strategies targeted at mercury pollution in the soil and aquatic matrices. The present paper provides a comprehensive overview of the current knowledge on mercury pollution in the environment (i.e., atmosphere, soil, water, and sediments). Many symptoms of mercury poisoning in fish, birds, and other animals, including man, were extensively treated. Information on the existing physico-chemical treatment methods, as well as the more ecologically friendly bioremediation measures available, was summarized. The importance of strengthening existing international policies, commitments, protocols, and alignments on the control of anthropogenic generation, treatment, and reduction of mercury discharges to the environment was highlighted.

Eco-friendly banana peel biochar for adsorption of toxic metals from landfill treatment pond leachate

Adsorption is one of the most efficient ways to eliminate hazardous metals. The study evaluated the effectiveness of banana peel biochar as a cheap adsorbent to remove hazardous metals from landfill leachate. The landfill leachate of 100 mg/L was mixed with banana peel biochar (0.50, 1.50, and 3.00 g each) and placed in a water bath for 15, 30, and 45 min at a constant temperature of 30 °C and 35 °C. The adsorption efficiency of banana peel biochar for nickel in the leachate ranged from 98.76% to 98.96% and chromium ranged from 99.71% to 99.77% at a temperature of 30 °C for 15 mins and 99.07% to 99.27% for Ni and 99.71% to 99.73% for Cr at a temperature of 35 °C for 45 min. Banana peel biochar maximum adsorption capacity of nickel ranged from 1.15 × 10-5 mg/g to 5.27 × 10-6 mg/g, and 1.05 × 10-5 mg/g to 6.76 × 10-6 mg/g for chromium. Adsorbent made from less expensive banana peel can affordably remove nickel and chromium from landfill leachate. To acquire a broad understanding of the adsorbent's application, more adsorptive research utilizing banana peels as an adsorbent to treat various wastes ought to be conducted.

Optimization of divalent mercury removal from synthetic wastewater using desirability function in central composite design of response surface methodology

Heavy metals exist in the ecosystem both naturally and due to anthropogenic activities and as recalcitrant pollutants; they are non-biodegradable and cause acute and chronic diseases to human beings and many lifeforms. A statistical experimental approach was applied in this current study to optimize the detoxification of mercury [Hg(II)] from mono-component biosorption system by a novel hybrid granular activated carbon (biosorbent) prepared from maize plant residues. The analysis of variance by the application of central composite design shows that all the studied independent factors greatly influence Hg(II) removal efficiency and uptake capacity. The optimum experimental condition of 30 min contact time, 0.5 g/L biosorbent dosage, and 15 mg/L initial Hg(II) concentration were achieved after seeking 20 optimization solutions at 0.903 desirability. The optimum percentage removal and uptake capacity of Hg(II) at the optimal experimental setup was 96.7% and 10.8 mg/g, respectively. To confirm the quadratic models developed for the prediction of the responses as a function of the independent factors, confirmatory laboratory experiments were performed at the optimum condition. The results show that at the established best experimental condition, the optimum Hg(II) removal efficiency of 98.3% and uptake capacity of 11.2 mg/g were attained, which were within the prediction intervals indicating the suitability of the quadratic models in predicting future cases. The TEM and XRD analyses show that the Hg(II) ions were adsorbed by the biosorbent successfully and this suggests the potential and applicability of this novel biosorbent in treating water contaminants, especially heavy metals.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40201-023-00888-5.

Green composite aerogel based on citrus peel/chitosan/bentonite for sustainable removal Cu(II) from water matrices

Here, we propose a green and sustainable 3D porous aerogel based on citrus peel (CP), chitosan (CS), and bentonite (BT). This aerogel is prepared through a simple sol-gel and freeze-drying process and is designed for efficient capture of Cu(II) ions from water matrices. CCBA-2, with its abundance of active binding sites, exhibits an impressive Cu(II) adsorption yield of 861.58 mg/g. The adsorption isotherm and kinetics follow the Freundlich and pseudo-second-order models, respectively. In the presence of coexisting mixed-metal ions, CCBA-2 demonstrates a significantly higher selectivity coefficient (KdCu = 1138.5) for removing Cu(II) ions compared to other toxic metal ions. Furthermore, the adsorption of Cu(II) ions by CCBA-2 is not significantly affected by coexisting cations/anions, ionic strength, organic matter, or different water matrices. Dynamic fixed-bed column experiments show that the adsorption capacity of Cu(II) ions reaches 377.4 mg/g, and the Yoon-Nelson model accurately describes the adsorption process and breakthrough curve. Through experiments, FTIR, and XPS analyses, we propose a reasonable binding mechanism between CCBA-2 and metal cations, involving electrostatic attraction and chemical chelation between Cu(II) and the functional groups of the aerogel. CCBA-2 saturated with Cu(II) ions can be successfully regenerated by elution with 1 M HNO3, with only a slight decrease in adsorption efficiency (5.3%) after 5 adsorption-desorption cycles. Therefore, CCBA-2 offers a cost-effective and environmentally friendly material that can be considered as a viable alternative for the green and efficient removal of toxic Cu(II) ions from wastewater.

Utilization of electron beam irradiated carboxymethyl cellulose/polyvinyl alcohol/banana peels composite film for remediation of dyes from wastewater

In this work, polymeric composite films were fabricated utilizing stable, non-toxic, soluble, low-cost, good mechanical, and biocompatible polymers such as CMC and PVA with the waste of one of the most current fruits consumed worldwide banana peel waste (BP) as a filler. Sequences of carboxymethyl cellulose/polyvinyl alcohol/banana peel (CMC/PVA/BP) composite films with various amounts of BP utilizing eco-friendly technique (electron beam) (EB) irradiation were prepared to eliminate common hazardous organic pollutants such as methylene blue (MB) dye from its solutions. Physical characteristics like; swelling and gel % were examined. The chemical structure, thermal stability, and surface morphology were examined utilizing FT-IR, TGA, DSC, XRD, EDX, and SEM. Additionally, the UV/Vis spectroscopy study was investigated to study the impact of the various parameters such as irradiation, contact time, pH, temperature, adsorbent dosage, and initial concentration on removal efficiency % of MB dye onto the prepared composite films. The adsorption process fitted with the Langmuir model, pseudo-second-order kinetic model, endothermic, favorable, and spontaneous. The adsorption capacity of MB dye onto the CMC/PVA/BP composite film was 19.6 mg/g at the optimum conditions: irradiation dose = 20 kGy, contact time = 120 min, pH = 10, temperature = 25 °C, adsorbent dosage = 0.1 g and initial conc. = 10 mg/L.

Banana Peel Powder Biosorbent for Removal of Hazardous Organic Pollutants from Wastewater

Disposing of pollutants in water sources poses risks to human health and the environment, but biosorption has emerged as an eco-friendly, cost-effective, and green alternative for wastewater treatment. This work shows the ability of banana peel powder (BPP) biosorbents for efficient sorption of methylene blue (MB), atrazine, and glyphosate pollutants. The biosorbent highlights several surface chemical functional groups and morphologies containing agglomerated microsized particles and microporous structures. BPP showed a 66% elimination of MB in 60 min, with an adsorption capacity (qe) of ~33 mg g-1, and a combination of film diffusion and chemisorption governed the sorption process. The biosorbent removed 91% and 97% of atrazine and glyphosate pesticides after 120 min, with qe of 3.26 and 3.02 mg g-1, respectively. The glyphosate and atrazine uptake best followed the Elovich and the pseudo-first-order kinetic, respectively, revealing different sorption mechanisms. Our results suggest that BPP is a low-cost biomaterial for green and environmentally friendly wastewater treatment.

P/Pb transport at the interface of water and Al-substituted ferrihydrite: Effect of P/Pb loading sequence

Sediment mineral such as Al-substituted ferrihydrite plays a critical role for contaminant transport in the river systems. Heavy metals and nutrient pollutants often coexisted in the natural aquatic environment, and they may enter the river at different time frames, altering the fate and transport of each other subsequently discharged into the river. However, most studies focused on the simultaneous adsorption of co-existing pollutants instead of their loading sequence. In this study, the transport of P and Pb at the interface of Al-substituted ferrihydrite and water was investigated under different P and Pb loading sequences. The results showed that preloaded P provided additional adsorption sites for the following adsorption of Pb, with enhanced Pb adsorption amount and accelerated adsorption process. Moreover, Pb preferred to be bounded with the preloaded P to form P-O-Pb ternary complexes rather than directly reacted with Fe-OH. The formation of the ternary complexes effectively prevented the release of Pb once adsorbed. However, the adsorption of P was slightly affected by the preloaded Pb, and most of the P were adsorbed onto Al-substituted ferrihydrite directly with the formation of Fe/Al-O-P. Moreover, the release process of the preloaded Pb was significantly inhibited by the following adsorbed P due to the formation of Pb-O-P. Meanwhile, the release of P was not detected from all P and Pb loaded samples of different adding sequence due to the high affinity between P and the mineral. Thus, the transport of Pb at the interface of Al-substituted ferrihydrite was seriously influenced by the adding sequence of Pb and P, while the transport of P was not sensitive to the adding sequence. The results provided important information for the transport of heavy metal and nutrients in river system with different discharging sequence, and offered new insights to further understand the secondary pollution in multi-contaminated river.

Mercury Removal from Contaminated Water by Wood-Based Biochar Depends on Natural Organic Matter and Ionic Composition

Biochars can remove potentially toxic elements, such as inorganic mercury [Hg(II)] from contaminated waters. However, their performance in complex water matrices is rarely investigated, and the combined roles of natural organic matter (NOM) and ionic composition in the removal of Hg(II) by biochar remain unclear. Here, we investigate the influence of NOM and major ions such as chloride (Cl^-), nitrate (NO₃^-), calcium (Ca²⁺), and sodium (Na⁺) on Hg(II) removal by a wood-based biochar (SWP700). Multiple sorption sites containing sulfur (S) were located within the porous SWP700. In the absence of NOM, Hg(II) removal was driven by these sites. Ca²⁺ bridging was important in enhancing removal of negatively charged Hg(II)-chloro complexes. In the presence of NOM, formation of soluble Hg-NOM complexes (as seen from speciation calculations), which have limited access to biochar pores, suppressed Hg(II) removal, but Cl^- and Ca²⁺ could still facilitate it. The ability of Ca²⁺ to aggregate NOM, including Hg-NOM complexes, promoted Hg(II) removal from the dissolved fraction (<0.45 μm). Hg(II) removal in the presence of Cl^- followed a stepwise mechanism. Weakly bound oxygen functional groups in NOM were outcompeted by Cl^-, forming smaller-sized Hg(II)-chloro complexes, which could access additional intraparticle sorption sites. Therein, Cl^- was outcompeted by S, which finally immobilized Hg(II) in SWP700 as confirmed by extended X-ray absorption fine structure spectroscopy. We conclude that in NOM containing oxic waters, with relatively high molar ratios of Cl^-: NOM and Ca²⁺: NOM, Hg(II) removal can still be effective with SWP700.

Influence of UV degradation of bioplastics on the amplification of mercury bioavailability in aquatic environments

Bioplastics have emerged to minimize the ecological footprint of non-degradable plastics. However, the effect of their degradation in aquatic systems, including the interaction with toxic metals, is still unexplored. In this work, the influence of UV-aging on structure, chemistry, wettability, rigidity, and Hg-sorption of commercially available bioplastic (BIO)- and polyethylene (PE)-based films was studied. To mimetize the materials disposal in fresh-/saltwaters, non-saline/saline aqueous solutions were used in Hg-sorption studies. ATR-FTIR spectra revealed that the BIO film was a coblended starch/polyester-based material, whose microstructure, physicochemical, and mechanical properties changed after UV-aging to a higher extent than in PE film. AFM and kinetic modelling pointed out electrostatic interactions/complexation as the mechanisms involved in the increased Hg-sorption by the UV-aged BIO film. An increased salinity did not impair its Hg-sorption. Therefore, when disposed in aquatic systems, starch/polyester-based bioplastics can play a potential vector for amplifying Hg along the food chain.

Utilization of Phyllanthus emblica fruit stone as a Potential Biomaterial for Sustainable Remediation of Lead and Cadmium Ions from Aqueous Solutions

In the present work, an effort has been made to utilize Phyllanthus emblica (PE) fruit stone as a potential biomaterial for the sustainable remediation of noxious heavy metals viz. Pb(II) and Cd(II) from the aqueous solution using adsorption methodology. Further, to elucidate the adsorption potential of Phyllanthus emblica fruit stone (PEFS), effective parameters, such as contact time, initial metal concentration, temperature, etc., were investigated and optimized using a simple batch adsorption method. It was observed that 80% removal for both the heavy metal ions was carried out within 60 min of contact time at an optimized pH 6. Moreover, the thermodynamic parameters results indicated that the adsorption process in the present study was endothermic, spontaneous, and feasible in nature. The positive value of entropy further reflects the high adsorbent-adsorbate interaction. Thus, based on the findings obtained, it can be concluded that the biosorbent may be considered a potential material for the remediation of these noxious impurities and can further be applied or extrapolated to other impurities.

Impact of chemical elements released by the volcanic eruption of La Palma (Canary Islands, Spain) on banana agriculture and European consumers

The recent volcanic eruption on the island of La Palma has aroused the concern of banana producers and consumers, given that in its area of influence there are thousands of hectares of banana plantations with an annual production of about 100 million kilos for export. Since volcanoes are one of the main natural sources of heavy metal contamination, we sampled bananas from the affected area and determined the concentrations of 50 elements (Ag, Al, As, Au, Ba, Be, Bi, Cd, Ce, Co, Cr, Cu, Cu, Dy, Er, Eu, Fe, Ga, Gd, Hg, Ho, In, La, Lu, Mn, Mo, Nb, Nd, Ni, Os, Pb, Pd, Pm, Pr, Pt, Sb, Sc, Se, Sm, Sn, Sr, Ta, Tb, Th, Ti, Tl, Tm, U, Y, Yb and Zn). The levels of 36 elements were elevated but the washing implemented after the eruption can remove a good part. After the washout, bananas have elevated levels of Fe, Al, Ti, V, Ba, Pb, most of the rare earth elements, Mo, and Co. In all cases, except Mo, the elevation is much higher in the peel than in the flesh. In the case of Mo, the elevation in banana flesh would translate into a higher nutritional intake of this trace element, which could represent up to 35% of the daily nutritional requirements. Exposure to toxic or potentially toxic elements, does not represent a health risk, since would not exceed 5% of the tolerable daily intake, even in the worst-case scenario.

Development of Fe3O4/CAC nanocomposite for the effective removal of contaminants of emerging concerns (Ce3+) from water: An ecotoxicological assessment

Contaminants of emerging concerns present in the ecosystems causes various adverse effects on all living organisms. In current study, removal of Ce³⁺ from water was performed using Fe₃O₄/CAC nanocomposite (MCAC) synthesized by co-precipitation technique. The synthesized MCAC was characterized using various analytical techniques. The magnetic behavior of the nanocomposite which is a crucial advantage in separation of MCAC after adsorption of Ce³⁺ from water was determined using vibrating sample magnetometer. MCAC was polycrystalline comprising both amorphous and crystalline regions with elements like C, O, Fe and N. The influence of process parameters was optimized through batch mode with the adsorption capacity of 86.206 mg/g. Ecotoxicological studies were performed using Danio rerio (Zebra fish) and seeds of Vigna mungo and Vigna radiata to assess the harmful effects of Ce³⁺ before and after adsorption process. The phytotoxicity studies on seeds revealed that inhibition of growth ranges from 50.39% to 12.55% (before adsorption) and 28.57%-3.89% (after adsorption). After 96 h the LC₅₀ value of Ce³⁺ on the Danio rerio before and after adsorption was 2.44 and 77.85 mg/L. Thus, the current study investigated the effective removal of Ce³⁺ by MCAC and evaluates its ecotoxicological effects.

Cleaner Approach for Atrazine Removal Using Recycling Biowaste/Waste in Permeable Barriers

This work addresses the rehabilitation of water contaminated with atrazine, entrapping it in a permeable and sustainable barrier designed with waste materials (sepiolite) and with biomaterials (cork and pine bark). Atrazine adsorption was assessed by kinetics and equilibrium assays and desorption was tested with different extraction solvents. Adsorbed atrazine was 100% recovered from sepiolite using 20% acetonitrile solution, while 40% acetonitrile was needed to leach it from cork (98%) and pine bark (94%). Continuous fixed-bed experiments using those sorbents as PRB were performed to evaluate atrazine removal for up-scale applications. The modified dose-response model properly described the breakthrough data. The highest adsorption capacity was achieved by sepiolite (23.3 (±0.8) mg/g), followed by pine bark (14.8 (±0.6) mg/g) and cork (13.0 (±0.9) mg/g). Recyclability of sorbents was evaluated by adsorption-desorption cycles. After two regenerations, sepiolite achieved 81% of atrazine removal, followed by pine with 78% and cork with 54%. Sepiolite had the best performance in terms of adsorption capacity/stability. SEM and FTIR analyses confirmed no significant differences in material morphology and structure. This study demonstrates that recycling waste/biowaste is a sustainable option for wastewater treatment, with waste valorization and environmental protection.

Bioaccumulation processes for mercury removal from saline waters by green, brown and red living marine macroalgae

Mercury is a very toxic metal that persists and accumulates in the living organisms present in the aquatic systems and its elimination is an urgent need. Two green (Ulva intestinalis and Ulva lactuca), brown (Fucus spiralis and Fucus vesiculosus), and red (Gracilaria sp. and Osmundea pinnatifida) marine macroalgae were tested for mercury removal from saline waters. The ability of each species was evaluated to the initial mercury concentrations of 50, 200, and 500 μg dm^-3 along 72 h. In general, all species exhibited good performances, removing 80.9-99.9% from solutions with 50 μg dm^-3, 79.3-98.6% from solutions with 200 μg dm^-3, and 69.8-97.7% from solutions containing 500 μg dm^-3 of mercury. Among the macroalgae, Ulva intestinalis showed the highest affinity to mercury and it presented an uptake ability up to 1888 μg g^-1 of Hg(II) and bioconcentration factors up to 3823, which proved its promising potential on Hg removal.

High affinity of 3D spongin scaffold towards Hg(II) in real waters

This study focuses on the ability of commercial natural bath sponges, which are made from the skeletons of marine sponges, to sorb Hg from natural waters. The main component of these bath sponges is spongin, which is a protein-based material, closely related to collagen, offering a plenitude of reactive sites from the great variety of amino acids in the protein chains, where the Hg ions can sorb. For a dose of 40 mg L^-1 and initial concentration of 50 μg L^-1 of Hg(II), marine spongin (MS) removed ~90% of Hg from 3 water matrixes (ultrapure, bottled, and seawater), corresponding to a residual concentration of ~5 μg L^-1, which tends to the recommend value for drinking water of 1 μg L^-1. This value was maintained even by increasing the MS dosage, suggesting the existence of a gradient concentration threshold below which the Hg sorption mechanism halts. Kinetic modelling showed that the Pseudo Second-Order equation was the best fit for all the water matrixes, which indicates that the sorption mechanism relies most probably on chemical interactions between the functional groups of spongin and the Hg ions. This material can also be regenerated in HNO₃ and reused for Hg sorption, with marginal losses in efficiency, at least for 3 consecutive cycles.

Adsorption and mass transfer studies of methylene blue onto comminuted seedpods from Luehea divaricata and Inga laurina

In this work, comminuted seedpods of the forest species Luehea divaricata (LDPR) and Inga laurina (ILPR) were used as alternative and environmental-friendly adsorbents for the methylene blue (MB) removal from aqueous solutions. Batch adsorption experiments were carried out at the native pH of the solution (pH = 8.7), with curves of removal and adsorption capacity crossed at 0.75 g L^-1, having 125 mg g^-1 for LDPR and 115 mg g^-1 for ILPR. The kinetic models of pseudo-first-order (PFO) and HSDM-Crank were the most adequate to represent MB dye concentration decay data for both biosorbents. The equilibrium curves were better adjusted by the Langmuir model for both adsorbents, with maximum adsorption capacity increased from 279 to 325 mg g^-1 for LDPR, and 199 to 233 mg g^-1 for ILPR, as a function of an increase in temperature from 298 to 328 K. The thermodynamic parameters showed that both systems are spontaneous with a dominance of physisorption. Mass transfer analysis indicates that the external mass transfer is the limiting step, with Bi < 0.5. Surface diffusion increased with the adsorption capacity, presenting linear and exponential behavior for the ILPR and PLPR adsorbents, respectively. Both materials proved to be efficient in treating a simulated effluent with similar industrial wastewater characteristics, reaching superior values at 70% of color removal.

Nutshells as Efficient Biosorbents to Remove Cadmium, Lead, and Mercury from Contaminated Solutions

The release of potentially toxic elements into the environment, and their effects on aquatic ecosystems still present a real threat. To avoid such contamination, the use of biological sorbents as an alternative to conventional and expensive water remediation techniques has been proposed. The present study evaluated the potential of 0.5 g L-1 of peanut, hazelnut, pistachio, walnut, and almond shells to remove the requisite concentrations of cadmium (Cd), lead (Pb), and mercury (Hg) from contaminated water. Hazelnut shells were identified as the sorbent with the highest potential and were evaluated in mono- and multi-contaminated mineral water. The influence of sorbent-intrinsic and solution-intrinsic characteristics were assessed. Differences among sorbents were attributed to varying percentages of their main components: cellulose, hemicellulose, and lignin. Matrix complexity increase caused a decrease in Cd removal, presumably due to the diminution in electrostatic interaction, and complexation with anions such as Cl-. When simultaneously present in the solution, contaminants competed, with Pb showing higher affinity to the sorbent than Hg. High efficiencies (>90%) obtained for hazelnut shells for all elements in ultrapure water and for Pb and Hg in mineral water) reveals the high potential of this low-cost and abundant waste for use in the remediation of contaminated waters (circular economy).

Mercury Removal from Aqueous Solution Using ETS-4 in the Presence of Cations of Distinct Sizes

The removal of the hazardous Hg²⁺ from aqueous solutions was studied by ion exchange using titanosilicate in sodium form (Na-ETS-4). Isothermal batch experiments at fixed pH were performed to measure equilibrium and kinetic data, considering two very distinct situations to assess the influence of competition effects: (i) the counter ions initially in solution are Na⁺ and Hg²⁺ (both are exchangeable); (ii) the initial counter ions in solution are tetrapropylammonium (TPA⁺) and Hg²⁺ (only Hg²⁺ is exchangeable, since TPA⁺ is larger than the ETS-4 micropores). The results confirmed that ETS-4 is highly selective for Hg²⁺, with more than 90% of the mercury being exchanged from the fluid phase. The final equilibrium attained under the presence of TPA⁺ or Na⁺ in solution was very similar, however, the Hg²⁺/Na⁺/ETS-4 system in the presence of Na⁺ required more 100 h to reach equilibrium than in the presence of TPA⁺. The Hg²⁺/Na⁺/ETS-4 system was modelled and analyzed in terms of equilibrium (mass action law) and mass transfer (Maxwell–Stefan (MS) formalism). Concerning equilibrium, no major deviations from ideality were found in the range of studied concentrations. On the other hand, the MS based model described successfully (average deviation of 5.81%) all kinetic curves of mercury removal.

Assessment of marine macroalgae potential for gadolinium removal from contaminated aquatic systems

Gadolinium (Gd) is a rare earth associated with hospital and urban wastewaters due to its application as a contrast agent for magnetic resonance imaging. In this work, the uptake of Gd from contaminated seawater by three living marine macroalgae, Ulva lactuca (Chlorophyta), Fucus spiralis (Phaeophyta) and Gracilaria sp. (Rhodophyta) was studied along 72 h. Surface analysis (FTIR), water content, kinetic modelling, and Gd quantification in seawater and biomass were performed. All species were able to accumulate Gd from seawater with 10, 157, and 500 μg Gd L^-1, although green and red macroalgae performed better, following the order: green > red > brown. Removal efficiencies reached 85%, corresponding to a bioconcentration factor of 1700. In more complex solutions that intended to mimic real contaminated environments, namely mixtures with other rare earth elements (Y, La, Ce, Pr, Nd, Eu, Tb, Dy), and with potentially toxic elements commonly found in wastewaters (Cr, Ni, Cu, Cd, Hg, Pb), at two salinities (10 and 30), the macroalgae kept its efficiency: 84% and 88% of removal by green and red macroalgae, respectively. Overall, findings evidence that living macroalgae could be a countermeasure to the increasing anthropogenic enrichment of Gd observed in the aquatic environment.

A banana peel/silicon glue coated stir bar for extraction of aspirin, diclofenac, ibuprofen and mefenamic acid followed by high performance liquid chromatography-UV detection

In the current study, a green, cost-effective, and bio-degradable additive was used for the preparation of a highly efficient sorbent based on silicon glue. Here, a banana peel was pretreated and mixed with silicon glue. It was proved that the prepared banana peel-silicon glue bar is a reliable sorbent for stir bar sorptive extraction of nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, diclofenac, ibuprofen and mefenamic acid in human urine and plasma. Compared to the lab-made sorbents, the prepared sorbent showed high extraction performance, high stability, and satisfactory reproducibility and involved easy preparation. In order to optimize the effective factors, different parameters such as (stirring rate, pH, extraction time, desorption time and elution solvent volume) were optimized using response surface methodology (RSM) through applying Central-Composite Design (CCD). Under the optimum conditions, the linear dynamic ranges of the target analytes were investigated in the range of 0.2-200 μg L^-1 with r² higher than 0.9929. Limits of detection (LODs) and limits of quantification (LOQs) of analytes were in the ranges of 0.04-0.5 and 0.15-1.65, respectively. The reproducibility of the method was also investigated by calculating the relative standard deviation. The RSD was measured to be lower than 4.9%. Bar-to-bar reproducibility at a 100 μg L^-1 concentration level was also evaluated to be lower than 5.3% (n = 3). Also, each prepared film can be used up to 64 times without any reduction in extraction performance. Finally, the method was successfully applied for the determination of selected drugs in different biological fluids including urine and plasma samples. The calculated relative recovery in real sample analysis was higher than 90%.

Green Graphene-Chitosan Sorbent Materials for Mercury Water Remediation

The development of new graphene-based nanocomposites able to provide synergistic effects for the adsorption of toxic heavy metals in realistic conditions (environment) is of higher demand for future applications. This work explores the preparation of a green nanocomposite based on the self-assembly of graphene oxide (GO) with chitosan (CH) for the remediation of Hg(II) in different water matrices, including ultrapure and natural waters (tap water, river water, and seawater). Starting at a concentration of 50 μg L^-1, the results showed that GO-CH nanocomposite has an excellent adsorption capacity of Hg (II) using very small doses (10 mg L^-1) in ultrapure water with a removal percentage (% R) of 97 % R after only two hours of contact time. In the case of tap water, the % R was 81.4% after four hours of contact time. In the case of river and seawater, the GO-CH nanocomposite showed a limited performance due the high complexity of the water matrices, leading to a residual removal of Hg(II). The obtained removal of Hg(II) at equilibrium in river and seawater for GO-CH was 13% R and 7% R, respectively. Our studies conducted with different mimicked sea waters revealed that the removal of mercury is not affected by the presence of NO₃^- and Na⁺ (>90% R of Hg(II)); however, in the presence of Cl^-, the mercury removal was virtually nonexistent (1% R of Hg(II)), most likely because of the formation of very stable chloro-complexes of Hg(II) with less affinity towards GO-CH.

Negligible effect of potentially toxic elements and rare earth elements on mercury removal from contaminated waters by green, brown and red living marine macroalgae

Mercury (Hg) removal by six different living marine macroalgae, namely, Ulva intestinalis, Ulva lactuca, Fucus spiralis, Fucus vesiculosus, Gracilaria sp., and Osmundea pinnatifida was investigated in mono and multi-contamination scenarios. All macroalgae were tested under the same experimental conditions, evaluating the competition effects with all elements at the same initial molar concentration of 1 μmol dm^-3. The presence of the main potentially toxic elements (Cd, Cr, Cu, Ni, and Pb) and rare earth elements (La, Ce, Pr, Nd, Eu, Gd, Tb, and Y) has not affected the removal of Hg. Characterizations of the macroalgae by FTIR before and after the biosorption/bioaccumulation assays suggest that Hg was mainly linked to sulfur-functional groups, while the removal of other elements was related with other functional groups. The mechanisms involved point to biosorption of Hg on the macroalgae surface followed by possible incorporation of this metal into the macroalgae by metabolically active processes. Globally, the green macroalgae (Ulva intestinalis, Ulva lactuca) showed the best performances for Hg, potential toxic elements and rare earth elements removal from synthetic seawater spiked with 1 μmol dm^-3 of each element, at room temperature and pH 8.5.