Congo red dye diversely affects organisms of different trophic levels: a comparative study with microalgae, cladocerans, and zebrafish embryos

Unveiling the impact of dyes on aquatic ecosystems through zebrafish - A comprehensive review

Dye industry plays an essential role in industrial development, contributing significantly to economic growth and progress. However, its rapid expansion has led to significant environmental concerns, especially water pollution and ecosystem degradation due to the discharge of untreated or inadequately treated dye effluents. The effluents introduce various harmful chemicals altering water quality, depleting oxygen levels, harming aquatic organisms, and disrupting food chains. Dye contamination can also persist in the environment for extended periods, leading to long-term ecological damage and threatening biodiversity. Therefore, the complex effects of dye pollutants on aquatic ecosystems have been comprehensively studied. Recently, zebrafish (Danio rerio) has proved to be an effective biomedical model for this study due to its transparent embryos allowing real-time observation of developmental processes and genetic proximity (approx. 87%) to humans for studying diverse biological responses. This review highlights the various toxicological effects of industrial dyes, including cardiovascular toxicity, neurotoxicity, genotoxicity, hepatotoxicity, and developmental toxicity. These effects have been observed at different developmental stages and dye concentrations in zebrafish. The review underscores that the structure, stability and chemical composition of dyes significantly influence toxicological impact, emphasizing the need for detailed investigation into dye degradation to better understand and mitigate the environmental and health risks posed by dye pollutants.

Fabrication of eco-friendly nanocellulose-chitosan-calcium phosphate ternary nanocomposite for wastewater remediation

Nanocomposites have emerged as promising materials for pollutant removal due to their unique properties. However, conventional synthesis methods often involve toxic solvents or expensive materials. In this study, we present a novel ternary nanocomposite synthesized via a simple, cost-effective vacuum filtration method. The composite consists of calcium phosphate (CaP), biowaste-derived nanocellulose (diameter <50 nm) (NC), and chitosan (CH). The nanocomposite exhibited exceptional pollutant removal capabilities due to the hybrid approach of combining adsorption and size exclusion that widens and accelerates pollutant removal. When tested with synthetic wastewater containing 10 ppm of Ni ions and 10 ppm of Congo red (CR) dye, it achieved impressive removal rates of 98.7% for Ni ions and 100% for CR dye. Moreover, the nanocomposite effectively removed heavy metals such as Cd, Ag, Al, Fe, Hg, Mo, Li, and Se at 100%, and Ba, Be, P, and Zn at 80%, 92%, 87%, and 97%, respectively, from real-world municipal wastewater. Importantly, this green nanocomposite membrane was synthesized without the use of harmful chemicals or complex modifications and operated at a high flux rate of 146 L/m2.h.MPa. Its outstanding performance highlights its potential for sustainable pollutant removal applications.

Deciphering the ecological impact of azo dye pollution through microbial community analysis in water-sediment microcosms

The uncontrolled release of untreated dyeing wastewater into aquatic ecosystems poses global environmental risks. It alters native microbial communities and associated ecological processes, often going unnoticed. Therefore, the influence of acid orange 7 dye (AO7) contamination on the natural microbial community was investigated using a water-sediment microcosm. Compared to sterile microcosms, complete dye decolourization in natural microcosms showed microbial communities' significance in combating xenobiotic contamination. Proteobacteria dominated the water community, whereas Firmicutes dominated the sediment. AO7 exposure induced notable shifts in the structural composition of the bacterial community in both water and sediment. Niveispirillum exhibited a marked decrease, and Pseudomonas demonstrated a notable increase. The - 9.0 log2FC in Niveispirillum, a nitrogen-fixing bacterium, from 24.4% in the control to 0.1% post-treatment, may disrupt nutrient balance, plant growth, and ecosystem productivity. Conversely, elevated levels of Pseudomonas sp. resulting from azo dye exposure demonstrate its ability to tolerate and bioremediate organic pollutants, highlighting its resilience. Functional profiling via KEGG pathway analysis revealed differential expression patterns under AO7 stress. Specifically, valine, leucine, and isoleucine degradation pathways in water decreased by 52.2%, and cysteine and methionine metabolism ceased expression entirely, indicating reduced protein metabolism and nutrient bioavailability under dye exposure. Furthermore, in sediment, glutathione metabolism ceased, indicating increased oxidative stress following AO7 infusion. However, C5-branched dibasic acid metabolism and limonene and pinene degradation were uniquely expressed in sediment. Decreased methane metabolism exacerbates the effects of global warming on aquatic ecosystems. Further, ceased-butanoate metabolic pathways reflect the textile dye wastewater-induced adverse impact on ecological processes, such as organic matter decomposition, energy flow, nutrient cycling, and community dynamics that help maintain self-purification and ecological balance in river ecosystems. These findings underscore the critical need for more comprehensive environmental monitoring and management strategies to mitigate ecological risks posed by textile dyes in aquatic ecosystems, which remain unnoticed.

Photochemical modification of tea waste by tungsten oxide nanoparticle as a novel, low-cost and green photocatalyst for degradation of dye pollutant

So far, many adsorbents and nanocomposites have been synthesized by different methods and used to remove or degradation of dye pollutants. Nowadays, the use of natural adsorbents and their modification with simple methods based on metal oxides are of interest to many researchers. In this study, for the first time, we report the simple and low-cost modification of tea pomace waste (TPW) with tungsten oxide (WO3) based on the photochemical method as a green, cost-effective, and biodegradable photocatalyst for the degradation of Rh B dye pollutant. The results obtained from FE-SEM, EDAX, XRD, XPS, PL, BET and UV-Vis Diffusive Reflectance (DRS) analyses confirmed the successful modification of the TPW surface with WO3 (WO3/TPW). The parameters affecting the photocatalytic behavior of WO3/TPW, including the time of photochemical modification and the type of radiation on its photocatalytic activity, were carefully optimized. WO3/TPW showed excellent photocatalytic activity compared to TPW for the degradation of Rh B dye pollutant under UV light for 30 min (94 %). Finally, the effective parameters on the value of Rh B dye degradation by WO3/TPW photocatalyst including pH, adsorbent dosage, the concentration of dye pollutant, and the kinetics of the degradation process were studied. It is expected that this type of photochemical modification method and natural WO3/TPW photocatalyst will be a promising path for the synthesis, modification, and increase of the photocatalytic performance of natural adsorbents.

Indigo dyes: Toxicity, teratogenicity, and genotoxicity studies in zebrafish embryos

Wastewater released by textile dyeing industries is a major source of pollution. Untreated wastewater released from indigo dyeing operations affects aquatic ecosystems and threatens their biodiversity. We have assessed the toxicity of natural and synthetic indigo dye in zebrafish embryos, using the endpoints of teratogenicity, genotoxicity, and histopathology. The zebrafish embryo toxicity test (ZFET) was conducted, exposing embryos to ten concentrations of natural and synthetic indigo dyes; the 96-hour LC50 values were approximately 350 and 300 mg/L, respectively. Both dyes were teratogenic, causing egg coagulation, tail detachment, yolk sac edema, pericardial edema, and tail bend, with no significant difference in effects between the natural and synthetic dyes. Both dyes were genotoxic (using comet assay for DNA damage). Real-time RT-PCR studies showed upregulation of the DNA-repair genes FEN1 and ERCC1. Severe histological changes were seen in zebrafish larvae following exposure to the dyes. Our results show that indigo dyes may be teratogenic and genotoxic to aquatic organisms, underscoring the need for development of sustainable practices and policies for mitigating the environmental impacts of textile dyeing.

Nickel-doped magnetic carbon aerogel derived from xanthan gum: a competent catalyst for the degradation of single and binary dye-based water pollutants

Toxic organic dyes (colorants) are one of the main causes of water pollution that releases destructive effluents in the environment. To overcome this issue, a fundamental need to produce a novel, efficient catalyst for the degradation and mineralization of dye mixtures has arisen. The objective of this research is to develop an eminent Ni-doped magnetic carbon aerogel (Ni-MCA) catalyst using graft co-polymerization method having xanthan gum as backbone doped with Ni-magnetic nanoparticles (Ni-MNPs), that do not show agglomeration and easy to separate. The examination revealed that Ni-MCA provided exceptional magnetic characteristics (Ms = 52.75 emu/g) and potent catalytic activity for the degradation of mono- as well as binary-dye solutions of Congo red (CR) and methyl green (MG) dyes. The formation was verified by various characterization techniques such as FTIR, VSM, XRD, XPS, SEM, TEM, and EDX mapping. Interestingly, Ni-MCA shows faster result on anionic dye CR up to 97% with degradation rate of 5.647 × 10-1 min-1, and MG dye shows degradation of 95.7% with the degradation rate of 2.169 × 10-1 min-1, while dye mixture is showing 90% degradation with rate of 2.159 × 10-1 min-1.

Sorption Behavior of Azo Dye Congo Red onto Activated Biochar from Haematoxylum campechianum Waste: Gradient Boosting Machine Learning-Assisted Bayesian Optimization for Improved Adsorption Process

This work aimed to describe the adsorption behavior of Congo red (CR) onto activated biochar material prepared from Haematoxylum campechianum waste (ABHC). The carbon precursor was soaked with phosphoric acid, followed by pyrolysis to convert the precursor into activated biochar. The surface morphology of the adsorbent (before and after dye adsorption) was characterized by scanning electron microscopy (SEM/EDS), BET method, X-ray powder diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) and, lastly, pHpzc was also determined. Batch studies were carried out in the following intervals of pH = 4-10, temperature = 300.15-330.15 K, the dose of adsorbent = 1-10 g/L, and isotherms evaluated the adsorption process to determine the maximum adsorption capacity (Qmax, mg/g). Kinetic studies were performed starting from two different initial concentrations (25 and 50 mg/L) and at a maximum contact time of 48 h. The reusability potential of activated biochar was evaluated by adsorption-desorption cycles. The maximum adsorption capacity obtained with the Langmuir adsorption isotherm model was 114.8 mg/g at 300.15 K, pH = 5.4, and a dose of activated biochar of 1.0 g/L. This study also highlights the application of advanced machine learning techniques to optimize a chemical removal process. Leveraging a comprehensive dataset, a Gradient Boosting regression model was developed and fine-tuned using Bayesian optimization within a Python programming environment. The optimization algorithm efficiently navigated the input space to maximize the removal percentage, resulting in a predicted efficiency of approximately 90.47% under optimal conditions. These findings offer promising insights for enhancing efficiency in similar removal processes, showcasing the potential of machine learning in process optimization and environmental remediation.

Upcycling of sugar refining mud solid waste as a novel adsorbent for removing methylene blue and Congo red from wastewater

The feasibility of utilizing the mud solid waste (MSW) produced during the carbonation process of sugar refining as a cost-effective and environmentally friendly alternative for the water removal of methylene blue (MB) and Congo red (CR), being highly utilized organic dyes representing cationic and anionic species, respectively is presented. Prior to its use, the MSW was dried at 110 °C for 24 h and sieved through a 100-mesh screen. The chief constituent of the MSW utilized was CaCO3, with a point of zero charge (PZC) found at pH 8.4 and 7.96 m2 g-1 total surface area. XRD and FTIR data indicate the presence of interactions between the dyes and the MSW surface, indicating effective adsorption. Different variables, such as initial dye concentration, MSW weight, solution pH, contact time, and temperature, were all examined to determine the optimal dye removal conditions. A central composite design (CCD) approach based on response surface methodology (RSM) modeling was utilized to identify statistically significant parameters for MB and CR adsorption capacities onto the MSW adsorbent. The removal equilibrium was typically reached in 120 minutes, with the greatest removal efficiency of CR taking place at pH 2 and 328 K, while the highest MB removal efficiency was obtained at pH 12 and 296 K. Kinetic studies suggest the adsorption of both dyes on the MSW follow pseudo-second-order rates, as evident through the high correlations obtained. Linearized and non-linearized Langmuir models showed strong correlations indicating maximum adsorption capacities of 86.6 and 72.3 mg g-1 for MB and CR, respectively. High regeneration and reusability potential of the MSW was demonstrated especially for the adsorption of CR, where the removal efficiency was nearly constant throughout five adsorption cycles, ranging from 93 to 91%, while the reduction in the removal for MB was much more significantly impacted, diminishing from 95 to 79% after the five cycles.

Emerging pollutants in textile wastewater: an ecotoxicological assessment focusing on surfactants

Water and several chemicals, including dyestuffs, surfactants, acids, and salts, are required during textile dyeing processes. Surfactants are harmful to the aquatic environment and induce several negative biological effects in exposed biota. In this context, the present study aimed to assess acute effects of five surfactants, comprising anionic and nonionic classes, and other auxiliary products used in fiber dyeing processes to aquatic organisms Vibrio fischeri (bacteria) and Daphnia similis (cladocerans). The toxicities of binary surfactant mixtures containing the anionic surfactant dodecylbenzene sulfonate + nonionic fatty alcohol ethoxylate and dodecylbenzene sulfonate + nonionic alkylene oxide were also evaluated. Nonionic surfactants were more toxic than anionic compounds for both organisms. Acute nonionic toxicity ranged from 1.3 mg/L (fatty alcohol ethoxylate surfactant) to 2.6 mg/L (ethoxylate surfactant) for V. fischeri and from 1.9 mg/L (alkylene oxide surfactant) to 12.5 mg/L (alkyl aryl ethoxylated and aromatic sulfonate surfactant) for D. similis, while the anionic dodecylbenzene sulfonate EC50s were determined as 66.2 mg/L and 19.7 mg/L, respectively. Both mixtures were very toxic for the exposed organisms: the EC50 average in the anionic + fatty alcohol ethoxylate mixture was of 1.0 mg/L ± 0.11 for V. fischeri and 4.09 mg/L ± 0.69 for D. similis. While the anionic + alkylene oxide mixture, EC50 of 3.34 mg/L for D. similis and 3.60 mg/L for V. fischeri. These toxicity data suggested that the concentration addition was the best model to explain the action that is more likely to occur for mixture for the dodecylbenzene sulfonate and alkylene oxide mixtures in both organisms. Our findings also suggest that textile wastewater surfactants may interact and produce different responses in aquatic organisms, such as synergism and antagonism. Ecotoxicological assays provide relevant information concerning hazardous pollutants, which may then be adequately treated and suitably managed to reduce toxic loads, associated to suitable management plans.

Modeling competitive biosorption for methylene blue removal on rape straw powders using response surface methodology in a ternary dye aqueous solution

The improvement of biosorption efficiency for selective dye removal in a multi-dye aqueous system has become an increasingly significant research topic. However, the competitive effects of coexisting dyes and the target dye in such systems remain uncertain due to complex interactions between adsorbent and coexisting dyes. Therefore, in this research, response surface methodology (RSM) model was effectively employed to investigate the competitive effects of allura red (AR) and malachite green (MG) on methylene blue (MB) removal in a ternary dye aqueous system using three different parts of rape straw powders. In the current design of RSM, the initial concentrations of AR and MG dyes ranging from 0 mg·L-1 to 500 mg·L-1 were considered as influencing factors, while the removal rates of MB on adsorbents at an initial concentration of 500 mg·L-1 were established as response values. The RSM models exhibited high correlation coefficients with adjusted R2 values of 0.9908 (pith core), 0.9870 (seedpods), and 0.9902 (shells), respectively, indicating a close fitted between predicted and actual values. The proposed models indicated that the perturbation effects of initial AR and MG concentrations were observed on the removal rates of MB by three types of rape straw powders in a ternary dye aqueous system, resulting in a decrease in MB removal rates, particularly at higher initial AR concentration due to stronger competitive effects compared to initial MG concentration. The structures of rape straw powders, including pith core, seedpods and shell, were analyzed using scanning eletron microscoe (SEM), energy dispersive spectroscopy (EDS), N2 physisorption isotherm, frourier transform infared spectroscopy (FTIR), Zeta potential classes and fluorescence spectrum before and after adsorption of MB in various dye aqueous systems. The characteristics of rape straw powders suggested that similar adsorption mechanisms, such as electrostatic attraction, pore diffusion, and group complex formation for MB, AR, and MG, respectively, occurred on the surfaces of adsorbents during their respective adsorption processes. This leads to significant competitive effects on the removal rates of MB in a ternary dye aqueous system, which are particularly influenced by initial AR concentrations as confirmed through fluorescence spectrum analysis.

Emerging micropollutants in aquatic ecosystems and nanotechnology-based removal alternatives: A review

There is a significant concern about the accessibility of uncontaminated and safe drinking water, a fundamental necessity for human beings. This concern is attributed to the toxic micropollutants from several emission sources, including industrial toxins, agricultural runoff, wastewater discharges, sewer overflows, landfills, algal blooms and microbiota. Emerging micropollutants (EMs) encompass a broad spectrum of compounds, including pharmaceutically active chemicals, personal care products, pesticides, industrial chemicals, steroid hormones, toxic nanomaterials, microplastics, heavy metals, and microorganisms. The pervasive and enduring nature of EMs has resulted in a detrimental impact on global urban water systems. Of late, these contaminants are receiving more attention due to their inherent potential to generate environmental toxicity and adverse health effects on humans and aquatic life. Although little progress has been made in discovering removal methodologies for EMs, a basic categorization procedure is required to identify and restrict the EMs to tackle the problem of these emerging contaminants. The present review paper provides a crude classification of EMs and their associated negative impact on aquatic life. Furthermore, it delves into various nanotechnology-based approaches as effective solutions to address the challenge of removing EMs from water, thereby ensuring potable drinking water. To conclude, this review paper addresses the challenges associated with the commercialization of nanomaterial, such as toxicity, high cost, inadequate government policies, and incompatibility with the present water purification system and recommends crucial directions for further research that should be pursued.

Development of PSA@PS-TiO2 nanocomposite photocatalyst: structure, mechanism, and application using response surface designs and molecular modeling

Using periwinkle shell ash (PSA) and polystyrene (PS), a new-fangled PSA@PS-TiO₂ photocatalyst was fabricated. The morphological images of all the samples studied using a high-resolution transmission electron microscope (HR-TEM) showed a size distribution of 50-200 nm for all samples. The SEM-EDX showed that the membrane substrate of PS was well dispersed, confirming the presence of anatase/rutile phases of TiO₂, and Ti and O₂ were the major composites. Given the very rough surface morphology (atomic force microscopy (AFM)) due to PSA, the main crystal phases (XRD) of TiO₂ (rutile and anatase), low bandgap (UVDRS), and beneficial functional groups (FTIR-ATR), the 2.5 wt.% of PSA@PS-TiO₂ exhibited better photocatalytic efficiency for methyl orange degradation. The photocatalyst, pH, and initial concentration were investigated and the PSA@PS-TiO₂ was reused for five cycles with the same efficiency. Regression modeling predicted 98% efficiency and computational modeling showed a nucleophilic initial attack initiated by a nitro group. Therefore, PSA@PS-TiO₂ nanocomposite is an industrially promising photocatalyst for treating azo dyes, particularly, methyl orange from an aqueous solution.

Development of a Novel Electrochemical Sensor Based on Gold Nanoparticle-Modified Carbon-Paste Electrode for the Detection of Congo Red Dye

In this study, gold nanoparticles (AuNPs) were electrodeposited on samples of a carbon-paste electrode (CPE) with different thicknesses. The prepared AuNPs were characterized using different analysis techniques, such as FTIR, UV-Vis, SEM, EDX, TEM images, and XRD analysis. The fabricated modified electrode AuNPs/CPE was used for the sensitive detection of Congo red (CR) dye. Electrochemical sensing was conducted using square-wave voltammetry (SWV) in a 0.1 M acetate buffer solution at pH 6.5. The proposed sensor exhibited high efficiency for the electrochemical determination of CR dye with high selectivity and sensitivity and a low detection limit of 0.07 μM in the concentration range of 1-30 μM and 0.7 μM in the concentration range of 50-200 μM. The practical application of the AuNPs/CPE was verified by detecting CR dye in various real samples involving jelly, candy, wastewater, and tap water. The calculated recoveries (88-106%) were within the acceptable range.

Silver Nanoparticle-Intercalated Cotton Fiber for Catalytic Degradation of Aqueous Organic Dyes for Water Pollution Mitigation

Azo dyes are commonly used in textile color processing for their wide array of vibrant colors. However, in recent years these dyes have become of concern in wastewater management given their toxicity to humans and the environment. In the present work, researchers remediated water contaminated with azo dyes using silver nanoparticles (Ag NPs) intercalated within cotton fabric as a catalyst, for their enhanced durability and reusability, in a reductive degradation method. Three azo dyes—methyl orange (MO), Congo red (CR), and Chicago Sky Blue 6B (CSBB)—were investigated. The azo degradation was monitored by UV/vis spectroscopy, degradation capacity, and turnover frequency (TOF). The Ag NP−cotton catalyst exhibited excellent degradation capacity for the dyes, i.e., MO (96.4% in 30 min), CR (96.5% in 18.5 min), and CSBB (99.8% in 21 min), with TOFs of 0.046 min−1, 0.082 min−1, and 0.056 min−1, respectively, using a 400 mg loading of catalyst for 100 mL of 25 mg L−1 dye. To keep their high reusability while maintaining high catalytic efficiency of >95% degradation after 10 cycles, Ag NPs immobilized within cotton fabric have promising potential as eco-friendly bio-embedded catalysts.

Toxicological assessment and adsorptive removal of lead (Pb) and Congo red (CR) from water by synthesized iron oxide/activated carbon (Fe3O4/AC) nanocomposite

Heavy metals and dyes are the persistent pollutants causing harmful effects on living organisms in different ecosystems. In current study, removal of Lead (Pb) and Congo Red (CR) from water was performed using Iron oxide/Activated Carbon (Fe₃O₄/AC) nanocomposite. Ferromagnetic behavior of the nanocomposite is the crucial advantage in separation of nanocomposite after biosorption process. The biosorbent was thermally stable till 800 °C of temperature. The synthesized biosorbent was polycrystalline in nature comprising of elements like C, O, Fe. The influence of various experimental conditions was optimized through batch study with the biosorption capacity of 144.92 mg/g (Pb) and 122.22 mg/g (CR) at pH 5-6, Fe₃O₄/AC dosage (0.04 g) for 40 mg/L of Pb and CR. Toxicological assessment was performed using Danio rerio and seeds to evaluate the harmful effects of pollutants on these organisms. The phytotoxicity results revealed that growth inhibition of seeds lies between 85.64% and 55.92% (Pb) and 77.94%-51.85% (CR). The LC₅₀ value of Pb on the Danio rerio was found to be 20.98 mg/L. In contrast, we observed significant increase in LC₅₀ value about 86.82 mg/L after biosorption of Pb onto biosorbent.

Accurate Removal of Toxic Organic Pollutants from Complex Water Matrices

Characteristic emerging pollutants at low concentration have raised much attention for causing a bottleneck in water remediation, especially in complex water matrices where high concentration of interferents coexist. In the future, tailored treatment methods are therefore of increasing significance for accurate removal of target pollutants in different water matrices. This critical review focuses on the overall strategies for accurately removing highly toxic emerging pollutants in the presence of typical interferents. The main difficulties hindering the improvement of selectivity in complex matrices are analyzed, implying that it is difficult to adopt a universal approach for multiple targets and water substrates. Selective methods based on assorted principles are proposed aiming to improve the anti-interference ability. Thus, typical approaches and fundamentals to achieve selectivity are subsequently summarized including their mechanism, superiority and inferior position, application scope, improvement method and the bottlenecks. The results show that different methods may be applicable to certain conditions and target pollutants. To better understand the mechanism of each selective method and further select the appropriate method, advanced methods for qualitative and quantitative characterization of selectivity are presented. The processes of adsorption, interaction, electron transfer, and bond breaking are discussed. Some comparable selective quantitative methods are helpful for promoting the development of related fields. The research framework of selectivity removal and its fundamentals are established. Presently, although continuous advances and remarkable achievements have been attained in the selective removal of characteristic organic pollutants, there are still various substantial challenges and opportunities. It is hopeful to inspire the researches on the new generation of water and wastewater treatment technology, which can selectively and preferentially treat characteristic pollutants, and establish a reliable research framework to lead the direction of environmental science.

Multiple adverse effects of textile effluents and reactive Red 239 dye to aquatic organisms

Textile dyeing consumes high volumes of water, generating proportional number of colored effluents which contain several hazardous chemical. These contaminants can implicate in significant changes in aquatic environmental, including several adverse effects to organisms in different trophic levels. The present study was developed to assess the ecotoxicological effects of textile effluent samples and reactive Red 239 dye (used in cotton dyeing) to aquatic organisms Vibrio fischeri bacteria, Daphnia similis crustacean, and Biomphalaria glabrata snail (adults and embryos). Chronic assays with lethal and sublethal effects for Daphnia similis were included and performed only for textile effluents samples. The mutagenicity was also evaluated with Salmonella/microsome assay (TA98, TA100, and YG1041 strains). V. fischeri bacteria was the most sensitive to reactive Red 239 dye (EC50 = 10.14 mg L^-1) followed by mollusk embryos at all stages (EC50 = 116.41 to 124.14 mg L^-1), D. similis (EC50= 389.42 mg L^-1), and less sensitive to adult snails (LC50= 517.19 mg L^-1). The textile effluent was toxic for all exposed organisms [E(L)C50 < 15%] and B. glabrata embryos showed different responses in the early stages of blastulae and gastrulae (EC50 = 7.60 and 7.08%) compared to advanced development stages trochophore and veliger (EC50 = 21.56 and 29.32%). Developmental and sublethal effects in B. glabrata embryos and D. similis were evidenced. In the chronic assay with effluent, the EC10/NOEC = 3% was obtained. Mutagenic effects were not detected for dye aqueous solutions neither for effluents samples. These data confirmed the importance of evaluating the effects in aquatic organisms from different trophic levels and reinforce the need for environmental aquatic protection.

Toxigenic Microcystis aeruginosa (Cyanobacteria) affects the population growth of two common green microalgae: Evidence of other allelopathic metabolites different to cyanotoxins

Agriculture runoffs and discharge of wastewaters are the major causes of eutrophication. Although eutrophication could promote the thriving of any phytoplankter, harmful algal blooms (HABs) are dominated frequently by cyanobacteria. Currently, HABs dominated by the toxigenic cyanobacterium Microcystis aeruginosa in lakes and reservoirs are the main environmental concerns worldwide. This study aimed to determine how M. aeruginosa (Ma) modifies the population growth of Pseudokirchneriella subcapitata (Ps) and Ankistrodesmus falcatus (Af). Growth kinetics were determined for each species and in the combinations: Ps-Ma, Af-Ma, Af-Ps, and Ps-Af-Ma. At the end of experiments, photosynthetic pigments, phycobiliproteins, and microcystins were quantified. A logistic equation significantly described the growth trend for all of the tested species, enabling the identification of negative effects on early stages in the population growth of co-cultures with the cyanobacterium; in addition, the interaction effects on the growth rate and in the maximum attainable population density were determined. The biomasses of A. falcatus and P. subcapitata were significantly higher when cultured individually than in all of the combinations with the cyanobacterium. The concentrations of chlorophyll a and b, as well as carotenoids, were lower in combined cultures, but phycobiliprotein content in the cultures with M. aeruginosa was not significantly affected. Microcystis aeruginosa negatively affected the growth of the microalgae, but A. falcatus was significantly more inhibited than P. subcapitata; however, microcystin concentrations were significantly reduced in the co-cultures with microalgae. These results could help to explain the displacements of microalgae when cyanobacteria are present, giving rise to cyanobacterial blooms in eutrophic freshwaters.

Assessment of Advanced Oxidation Processes Using Zebrafish in a Non-Forced Exposure System: A Proof of Concept

Water bodies and aquatic ecosystems are threatened by discharges of industrial waters. Ecotoxicological effects of components occurring in untreated and treated wastewaters are often not considered. The use of a linear, multi-compartmented, non-forced, static system constructed with PET bottles is proposed for the quality assessment of treated waters, to deal with such limitations. Two synthetic waters, one simulating wastewater from the textile industry and the other one simulating wastewater from the cassava starch industry, were prepared and treated by homogeneous Fenton process and heterogeneous photocatalysis, respectively. Untreated and treated synthetic waters and their dilutions were placed into compartments of the non-forced exposure system, in which zebrafish (Danio rerio), the indicator organism, could select the environment of its preference. Basic physical–chemical and chemical parameters of untreated and treated synthetic waters were measured. The preference and avoidance responses allowed verification of whether or not the quality of the water was improved due to the treatment. The results of these assays can be a complement to conventional parameters of water quality.

Textile dyes Maxilon blue 5G and Reactive blue 203 induce acute toxicity and DNA damage during embryonic development of Danio rerio

Common textile dyes used in various industrial sectors are organic compounds and considered for the aquatic environment as pollutants. The textile dye industry is one of the main sectors that have serious impacts on the environment due to a large amount of wastewater released into the ecosystem. Maxilon blue 5G (MB-5G) and Reactive Blue 203 (RB-203) are widely used textile dyes. However, their potential toxicity on living organisms remains to be elucidated. Here, we investigate the acute toxicity and genotoxicity of MB-5G and RB-203 dyes using the zebrafish embryos/larvae. Embryos treated with each dye for 96 h revealed LC₅₀ values of acute toxicity as 166.04 mg L^-1 and 278.32 mg L^-1 for MB-5G and RB 203, respectively. When exposed to MB-5G and RB-203 at different concentrations (1, 10, and 100 mg L^-1) for 96 h, the expression of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, significantly increased in brain tissues as compared to control. MB-5G and RB-203 resulted in common developmental abnormalities including tail malformation, microphthalmia, pericardial edema, curved body axis, and yolk sac/pericardial edemas. Moreover, at its highest dose (100 mg L^-1), RB-203 caused premature hatching after 48 h, while MG-5G did not. Our results collectively reveal that the textile dyes MB-5G and RB-203 cause genotoxicity and teratogenicity during embryonic and larval development of zebrafish. Thus, it is necessary to eliminate these compounds from wastewater or reduce their concentrations to safe levels before discharging the textile industry wastewater into the environment.

Auramine dyes induce toxic effects to aquatic organisms from different trophic levels: an application of predicted non-effect concentration (PNEC)

The dyes Auramine and Auramine O are used in several industrial products, despite the scarce information regarding their ecotoxicity. The aim of the present study was to assess the acute and chronic toxicity of both dyes to aquatic organisms from different trophic levels (Raphidocelis subcapitata, Daphnia similis, Hydra attenuata, and Danio rerio) and calculate their predicted non-effect concentrations (PNEC). Auramine and Auramine O induced toxicity to all selected test organisms with L(E)C50 values ranging from 300 to 4800 ug/L. Both dyes induced inhibition in the growth rate of exposed algae, negatively affecting the reproduction of D. similis and induced deformities in H. attenuata (clubbed tentacles and shortened tentacles) and D. rerio (edemas, tail malformation and delay in yolk sac absorption). PNEC values of 0.92 μg/L and 4.0 μg/L were obtained for Auramine and Auramine O, respectively, based on results of the most sensitive test system (algae). Test results were analyzed using the Criteria of Reporting and Evaluating Ecotoxicity Data (CRED), confirming their reliability and relevance. Thus, PNEC values can be used in future risk assessments of those substances in freshwater systems.

Highly efficient and fast removal of colored pollutants from single and binary systems, using magnetic mesoporous silica

Magnetic mesoporous silica material was tested as adsorbent for removal of two usual colored compounds present in industrial wastewater. The magnetic mesoporous silica was synthesized by modified sol-gel method and characterized from the morpho-textural, structural and magnetic point of view. The specific surface area and the total pore volume indicate a good adsorption capacity of the material, and the obtained saturation magnetization strength value denotes a good magnetic separation from solution. The adsorption capacity of magnetic mesoporous silica increases with the increase of the initial dye concentration, and the removal efficiency of the dyes was dependent on the pH of the solution and decreased with increasing temperature. The pseudo-second-order kinetic model described best the adsorption mechanism, and the maximum adsorption capacities were determined from the Sips isotherm model, being 88.29 mg/g for Congo Red and 208.31 mg/g for Methylene Blue. A complete thermodynamic evaluation was performed, by determining the free energy, enthalpy and entropy, and the result showed a spontaneous and exothermic adsorption process. The recovery and reutilization of the adsorbent were estimated in five cycles of adsorption-desorption, and the results indicated a good stability and reusability of magnetic mesoporous silica. The new magnetic mesoporous silica can be easily separated from solution, via an external magnetic field, and may be effectively applied as adsorbent for elimination of dyes from colored polluted waters.

Toxicokinetics of Brominated Azo Dyes in the Early Life Stages of Zebrafish (Danio rerio) Is Prone to Aromatic Substituent Changes

Brominated azo dyes (BADs) have been identified as predominant indoor brominated pollutants in daycare dust; thus, their potential health risk to children is of concern. However, the toxicities of BADs remain elusive. In this study, the toxicokinetics of two predominant BADs, Disperse Blue 373 (DB373) and Disperse Violet 93 (DV93), and their suspect metabolite 2-bromo-4,6-dinitroaniline (BDNA) was investigated in embryos of zebrafish (Danio rerio). The bioconcentration factor of DV93 at 120 hpf is 6.2-fold lower than that of DB373. The nontarget analysis revealed distinct metabolism routes between DB373 and DV93 by reducing nitro groups to nitroso (DB373) or amine (DV93), despite their similar structures. NAD(P)H quinone oxidoreductase 1 (NQO1) and pyruvate dehydrogenase were predicted as the enzymes responsible for the reduction of DB373 and DV93 by correlating time courses of the metabolites and enzyme development. Further in vitro recombinant enzyme and in vivo inhibition results validated NQO1 as the enzyme specifically reducing DB373, but not DV93. Global proteome profiling revealed that the expression levels of proteins from the "apoptosis-induced DNA fragmentation" pathway were significantly upregulated by all three BADs, supporting the bioactivation of BADs to mutagenic aromatic amines. This study discovered the bioactivation of BADs via distinct eukaryotic enzymes, implying their potential health risks.

Evaluation of the supramolecular interaction of Congo red with cucurbiturils using mass spectrometry and spectroscopic methods

Cucurbit[n]urils decolourise aqueous solutions of Congo red by forming outer-surface adducts, which are also detected in gas-phase ESI-MS studies.

Exposure to the azo dye Direct blue 15 produces toxic effects on microalgae, cladocerans, and zebrafish embryos

Aquatic pollution caused by dyes has increased together with the growth of activities using colorants such as the textile, leather, food, and agrochemicals industries. Because most popular azo dyes are synthesized from benzidine, a carcinogenic compound, a threat to aquatic biota could be expected. The use of single species for toxicity assessment provides limited data, so a battery of test organisms, including representatives of different trophic levels such as algae, zooplankters, and fish, could undoubtedly provide more information. Therefore, our study was aimed at evaluating the toxic effect of the azo dye Direct blue 15 (DB15) on a battery of bioassays using a primary producer (Pseudokirchneriella subcapitata), a primary consumer (Ceriodaphnia dubia), and a secondary consumer (Danio rerio). P. subcapitata was more sensitive to DB15 (IC₅₀ = 15.99 mg L^-1) than C. dubia (LC₅₀: 450 mg L^-1). In the algae exposed to DB15, chlorophyll-a and -b were significantly increased, and carotenoids were reduced. The concentrations of protein, carbohydrates, and lipids per cell in P. subcapitata exposed to all DB15 concentrations were significantly higher than that measured in control. At 25 mg L^-1 of DB15, survival, total progeny, and the number of released clutches were significantly decreased, and the start of reproduction was delayed in C. dubia. DB15 did not induce lethal or sublethal effects in D. rerio embryos at any of the tested concentrations from 24 to 72 h post-fertilization (hpf), but from 96 to 144 hpf, the larvae exposed to 100 and 500 mg L^-1 developed yolk sac edema, curved tail, and skeletal deformations. After 144 hpf, DB15 produced a significant increase in embryos without a heartbeat, as the concentration of dye raised. The textile-used, azo dye DB15, caused toxic effects of different magnitude on microalgae, cladocerans, and zebrafish embryos; for this reason, the discharge of this colorant into waterbodies should be regulated to prevent environmental impacts.