Danio rerio as a model in aquatic toxicology and sediment research

Developmental and organ toxicity of fenpropimorph in zebrafish: Involvement of apoptosis and inflammation

Pesticides are increasingly the focus as a prominent factor in environmental pollution. Fenpropimorph, a widely utilized morpholine fungicide, is a significant water pollutant. Because of its extensive usage, fenpropimorph is readily detected in diverse aquatic ecosystems. Despite its well-known toxicity to aquatic organisms, its toxicity to zebrafish development and accompanying mechanics remain unexplored. To assess fenpropimorph's toxicity and potential mechanism, we employed the zebrafish model, a representative tool in toxicological studies. Our results showed that exposure to fenpropimorph reduced embryonic viability during the early stages of development and reduced head and body size. Moreover, fenpropimorph triggered apoptosis, DNA fragmentation, and inflammation. Aberrations in the vascular network were observed in the fli1:eGFP transgenic zebrafish model. Additionally, neurotoxic impacts were further assessed using transgenic olig2:dsRed zebrafish, accompanied by a reduction of liver size and fluorescence intensity of fabp10a:dsRed zebrafish. mRNA expression analysis related to corresponding organ development further supported our data. Overall, our research suggests that fenpropimorph may cause aberrations in aquatic organisms.

Chronic dimethomorph exposure induced behaviors abnormalities and cognitive performance alterations in adult zebrafish (Danio rerio)

Dimethomorph is a systematic fungicide that inhibits sterol synthesis in fungi and unfortunately, there was only scarce data regarding its toxicity. Therefore, considering its extensive application in agriculture and its presence in food residues and the environment, its toxicities in non-target organisms, including aquatic animals, are required to be evaluated since they are sensitive indicators of ecological change. In this study, we evaluated the toxicities of dimethomorph after chronic exposure to adult zebrafish (Danio rerio) by conducting various behavioral assays, a passive avoidance test, and biochemical assays by ELISA. From the results, ∼ 2 weeks exposure to dimethomorph caused lower locomotion, aggressiveness, and conspecific social interaction, and more robust predator avoidance behaviors. Furthermore, alterations in color preferences and short-term memory loss were also observed in the treated fish. In helping to elucidate the mechanism, the expression level of several important neurotransmitters in the brain tissue was measured. Interestingly, increment in several biomarkers, including serotonin, kisspeptin, epinephrine, norepinephrine, and dopamine was observed in the treated group along with a slight increase in other tested neurotransmitters, which were catalase, acetylcholine, and melatonin, which might play a role in the observed behavior alterations. Nevertheless, the results from the current study suggested possible alterations in the central nervous system by dimethomorph, and thus, consideration is required prior to the usage of this fungicide in the agricultural fields surrounding natural freshwater reservoirs.

Bioavailability assessment of propiconazole to Limnobium laevigatum and zebrafish (Danio rerio) in aquatic microcosms

Residues of the triazole fungicide propiconazole (PCZ) in the environment can easily enter aquatic ecosystems through various pathways and accumulate in sediments, thus threatening ecosystem stability. The method of using passive sampling techniques to measure the freely dissolved concentration (Cfree) of pollutants in aquatic environments for assessing their bioavailability has been widely utilized in environmental risk assessments. This study employs oleic acid-embedded cellulose acetate membrane (OECAM) as a tool to determine the Cfree of PCZ in water. By establishing sediment spiking concentrations of 0.1 and 0.5 mg/kg in an aquatic microcosm, the distribution and bioaccumulation of PCZ in zebrafish (Danio rerio) and the aquatic plant Limnobium laevigatum (L. laevigatum) were examined over a 7-day period. During the experimental period, the concentrations of PCZ in the water for the 0.1 mg/kg and 0.5 mg/kg treatment groups remained approximately 0.9 μg/L and 10.0 μg/L, respectively. After 7 days, the PCZ content in the sediments decreased by 22.74% and 14.94%, respectively. In both zebrafish and L. laevigatum, the concentration of PCZ initially increased and then gradually stabilized, with both species exhibiting moderate accumulation ability for PCZ. The bioconcentration factor (BCF) for zebrafish in the 0.1 mg/kg and 0.5 mg/kg treatment groups ranged from 9.25 to 13.96 and 7.84-16.05, respectively, while those for L. laevigatum ranged from 28.17 to 31.40 and 23.01-36.11, respectively. By the end of the 7-day experiment, the total PCZ content in both treatment groups decreased by an average of 17.51%. Among them, L. laevigatum contributed significantly, highlighting its potential in accelerating the removal of PCZ from aquatic ecosystems.

Environmental fluoxetine promotes skin cell proliferation and wound healing

This study investigates the effects of environmentally-relevant concentrations of fluoxetine (FLX, commercial name: Prozac) on wound healing. Pollution of water systems with pharmaceutical and personal care products, including antidepressants such as FLX and other selective serotonin reuptake inhibitors, is a growing environmental concern. Environmentally-relevant FLX concentrations are known to impact physiological functions and behaviour of aquatic animals, however, the effects of exposure on humans are currently unknown. Using a combination of human skin biopsies and a human keratinocyte cell line, we show that exposure to environmental FLX promotes wound closure. We show dose-dependent increases in wound closure with FLX concentrations from 125 ng/l. Using several -omics and pharmaceutical approaches, we demonstrate that the mechanisms underlying enhanced wound closure are increased cell proliferation and serotonin signalling. Transcriptomic analysis revealed 350 differentially expressed genes after exposure. Downregulated genes were enriched in pathways related to mitochondrial function and metabolism, while upregulated genes were associated with cell proliferation and tissue morphogenesis. Kinase profiling showed altered phosphorylation of kinases linked to the MAPK pathway. Consistent with this, phosphoproteomic analyses identified 235 differentially phosphorylated proteins after exposure, with enriched GO terms related to cell cycle, division, and protein biosynthesis. Treatment of skin biopsies and keratinocytes with ketanserin, a serotonin receptor antagonist, reversed the increase in wound closure observed upon exposure. These findings collectively show that exposure to environmental FLX promotes wound healing through modulating serotonin signalling, gene expression and protein phosphorylation, leading to enhanced cell proliferation. Our results justify a transition from the study of behavioural effects of environmental FLX in aquatic animals to the investigation of effects of exposure on wound healing in aquatic and terrestrial animals, including direct impacts on human health.

A fish perspective on SARS-CoV-2: Toxicity of benzalkonium chloride on Danio rerio

SARS-CoV-2 outbreak led to an increased marketing of disinfectants, creating a potential environmental problem. For instance, pre-pandemic environmental levels of the disinfectant benzalkonium chloride (BAC) ranging from 0.5 to 5 mgL-1 in effluents were expected to further increase threatening aquatic life. Our aim was to characterize potential adverse effects after an acute exposure of zebrafish to different concentrations of BAC. An increase in the overall swimming activity, thigmotaxis behavior, and erratic movements were observed. An increase in CYP1A1 and catalase activities, but inhibitions of CY1A2, GSTs and GPx activities were also noticed. BAC is metabolized by CYP1A1, increasing the production of H2O2, thereby activating the antioxidant enzyme CAT. Data also showed an increase of AChE activity. Our study highlights adverse embryonic, behavioral, and metabolic effects of noteworthy environmental significance, especially considering that the use and release of BAC is most likely to increase in a near future.

Thiobencarb induces phenotypic abnormalities, apoptosis, and cardiovascular toxicity in zebrafish embryos through oxidative stress and inflammation

Thiobencarb is a representative herbicide used on rice paddies. Because thiobencarb is used extensively on agricultural lands, especially on paddy fields, there is a high risk of unintended leaks into aquatic ecosystems. For this reason, several studies have investigated and reported on the toxicity of thiobencarb to aquatic species. In European eels, thiobencarb affected acetylcholinesterase levels in plasma and impaired adenosine triphosphatase activity in their gills. In medaka, thiobencarb-exposed embryos showed lower viability. However, molecular mechanisms underlying thiobencarb-mediated embryotoxicity have yet to be clarified. Therefore, the objective of our study was to investigate its mechanism of toxicity using zebrafish embryos. The viability of zebrafish embryos decreased upon exposure to thiobencarb and various phenotypic abnormalities were observed at concentrations lower than the lethal dose. The developmental toxicity of thiobencarb was mediated by pro-inflammatory cytokines (il1b, cxcl8, cxcl18b, and cox2a) and excessive generation of reactive oxygen species due to the downregulation of genes such as catalase, sod1, and sod2, which encode antioxidant enzymes. In addition, severe defects of the cardiovascular system were identified in response to thiobencarb exposure. Specifically, deformed cardiac looping, delayed common cardinal vein (CCV) regression, and interrupted dorsal aorta (DA)-posterior cardinal vein (PCV) segregation were observed. Our results provide an essential resource that demonstrates molecular mechanisms underlying the toxicity of thiobencarb on non-target organisms, which may contribute to the establishment of a mitigation strategy.

Toxic effects and mechanisms of common pesticides (Roundup and chlorpyrifos) and their mixtures in a zebrafish model (Danio rerio)

Agrochemicals can adversely affect biodiversity, environment and human health, and commonly occur in mixtures with poorly characterized toxic mechanisms and health hazards. Here, we evaluated the individual and mixture toxicities of Roundup and chlorpyrifos in environmentally relevant concentrations to zebrafish using molecular and biochemical indices. Studied pesticides alone and in combination caused depletion of total antioxidant capacity and cellular thiols, overproduction of ROS, accumulation of oxidative lesions and elevated DNA damage in zebrafish liver. Notably, low concentration of Roundup induced a hormesis-like effect by stimulating the protective cellular mechanisms. Chlorpyrifos showed stronger prooxidant effects than Roundup and additionally caused nitrosative and carbonyl stress in zebrafish. At the organismal level, studied pesticides and their mixtures induced hepato- and neurotoxicity. The effects of the studied pesticides on biomarkers of apoptosis, endocrine disruption and immune disorders were generally weak and inconsistent. The multibiomarker assessment showed that chlorpyrifos is considerably more toxic than Roundup to zebrafish. The toxic effects of the pesticide mixtures were mostly driven by chlorpyrifos, with minimal or mitigating effects of Roundup addition. These findings elucidate the toxic mechanisms of common pesticides in a model vertebrate and demonstrate that health hazards of pesticide mixtures cannot be predicted from the effects of single pesticides.

Behavioural impairment and oxidative stress by acute exposure of zebrafish to a commercial formulation of tebuconazole

Tebuconazole is a systemic follicular fungicide known to cause diverse problems in non-target organisms namely associated to the pure active ingredient. As such, the objective of this work was to evaluate developmental changes induced by a tebuconazole commercial formulation to a non-target animal model. Zebrafish embryos at ± 2 h post-fertilization were exposed to tebuconazole wettable powder concentrations (0.05, 0.5 and 5 mg L^-1) for 96 h with developmental toxicity assessed throughout the exposure period and biochemical parameters evaluated at the end of the exposure. Behavioural assessment (spatial exploration and response to stimuli) was conducted 24 h after the end of the exposure. While no developmental and physiological alterations were observed, exposure to tebuconazole resulted in an increased generation of reactive oxidative species at the 0.05 and 0.5 mg L^-1 concentrations and a decreased GPx activity at the 0.5 mg L^-1 concentration suggesting a potential protection mechanism. There was also a change in the avoidance-escape behaviour supporting an anxiolytic effect suggesting possible alterations in the central nervous system development demanding further studies.

Hematotoxic, oxidative and genotoxic damage in rainbow trout (Oncorhynchus mykiss) after exposure to 3-benzoylpyridine

Pyridine is a basic heterocyclic organic compound. The pyridine ring is present in many important compounds, including agricultural chemicals, medicines and vitamins. Due to their widespread industrial use, bioaccumulation and non-target toxic effects are being considered as a great risk to human and environmental health. In this study, we aimed to evaluate the hematological, oxidative and genotoxic damage potentials by different concentrations (1, 1.5, and 2 g/L) of the ketone 3-Benzoylpyridine (3BP) on rainbow trout (Oncorhynchus mykiss). Alterations in the biomarker levels of oxidative DNA damage (8-hydroxy-2'-deoxyguanosine (8-OHdG)), apoptosis (Caspase-3), malondialdehyde (MDA) as well as antioxidant enzyme activities including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), myeloperoxidase (MPO), paraoxonase (PON), and arylesterase (AR) were assessed in brain, liver, gill and blood tissues. Acetylcholinesterase (AChE) activity was also determined in brain tissue. In addition, we analyzed micronucleus (MN) rates and hematological indices of total erythrocyte count (RBC), total leukocyte count (WBC), hemoglobin (Hb), hematocrit (Hct), total platelet count (PLT), mean cell hemoglobin concentration (MCHC), mean cell hemoglobin (MCH), and mean cell volume (MCV) in blood. LC₅₀-96h value of 3BP was calculated as 5.2 g/L from the data obtained. A significant decrease in brain AChE activity was determined in clear time and dose dependent manners. While SOD, CAT, GPx, PON, and AR levels were decreased, MDA, MPO, 8-OHdG and Caspase-3 levels were increased in all tissues (p < 0.05). Again, the 3BP led to increases of MN formation at all applied concentrations in the rates of between 45.4 and 72.7%. Significant differences (p < 0.05) were found out in between all studied hematology parameters between 3BP-exposed and the control fish. In conclusion, ours study firstly indicated that the treatment doses of 3BP induced distinct hematological and oxidative alterations as well as genotoxic damage in rainbow trout.

Influence of salinity on the toxicity of copper and cadmium to Zebrafish embryos

Salinization has become a serious worldwide environmental perturbation in freshwater ecosystems. Concomitantly, many of such ecosystems are already impacted by other toxicants, which together with increased salinity may result in synergistic, antagonistic or additive toxic effects to biota. This work intended to assess the influence of increasing salinity (by using NaCl) on the lethal and sublethal toxicity of two metallic elements (copper and cadmium) in embryos of the fish species Danio rerio. This goal was achieved by exposing zebrafish embryos to seven concentrations of NaCl, individually or combined with each metal, using a full factorial design. The following endpoints were monitored in the test organisms: mortality, hatching, malformations and the enzymatic activity of glutathione S-transferase (GST) and cholinesterase (ChE). Overall, moderate salinity levels alleviated the lethal toxicity of both copper and cadmium although this effect was stronger in the copper assay. This effect was also influenced, as expected, by the concentrations of the metals indicating that the protective effect of salt only reaches some levels, after what is overwhelmed by the high metal toxicity, especially with the non-essential metal cadmium. At sub-lethal concentrations, the interactive effect resulting from NaCl and metals was not consistent and varied with the endpoint analyzed and the metal tested. Overall, the interactions between the salt and metals seem complex and with more drastic effects (positive or negative) on lethal endpoints than sub-lethal.

Contamination and Toxicity of Surface Waters Along Rural and Urban Regions of the Capibaribe River in Tropical Northeastern Brazil

The Capibaribe River provides water to a population of 1.7 million people in the Brazilian northeast, while receiving agricultural runoff and industrial and domestic effluents along its 280 km. The present study evaluated the ecotoxicity of surface waters along ten sites in rural and urban areas using zebrafish (Danio rerio) early-life stages and related it to water quality indices and chemical abiotic variables. Lethality rates, delays in embryo-larval development quantified by the general morphology score (GMS), and frequencies of developmental abnormalities were analyzed. A correlation was detected between zebrafish GMS and water quality index (WQI), sensitivity to domestic sewage contamination, and trophic state index, focused on eutrophication. These indices agreed in identifying a spatial pattern of smaller impact in terms of ecotoxicity, domestic sewage contamination, and eutrophication risk at three sites in rural areas (mean GMS 16.9), an intermediate impact at four sites with urban and agricultural influence (mean GMS 16.4), and greatest impacts at three more urbanized sites (mean GMS 14.9). Most frequent developmental abnormalities included noninflation of the swim bladder, delayed hatching, nonprotrusion of the mouth, blood stasis, and nondevelopment of pectoral fins. Toxic NH₃ concentrations varied spatially, with higher concentrations in urban sites; and blood stasis correlated positively with NH₃ , suggesting a causal relationship. Polycyclic aromatic hydrocarbons were detected in both rural and urbanized sites, contributing to detected toxicity. The present study demonstrates the potential of zebrafish early-life stages as an ecotoxicological model that may contribute to a better understanding of surface water quality and ecotoxicity in tropical river systems. Environ Toxicol Chem 2021;40:3063-3077. © 2021 SETAC.

Zinc oxide-induced changes to sunscreen ingredient efficacy and toxicity under UV irradiation

Sunscreen safety and efficacy is generally evaluated based upon the properties of the individual chemicals in a formulation. However, the photostability of sunscreens has been shown to be highly dependent on the mixture of chemicals present. To better understand how sunscreen formulation influences stability, and to establish a foundation for probing the influence of zinc oxide additives, we formulated five different small-molecule based ultraviolet-filter (UV-filter) mixtures with a Sun Protection Factor (SPF) of 15. These mixtures contained active ingredients approved in either the United States or European Union and were designed to represent formulations of actual products on the market. We evaluated the photostability and toxicity of these mixtures in the absence and presence of zinc oxide after UV exposure for two hours. Changes in UV absorbance were minimal for all five small-molecule-based mixtures without zinc oxide. The presence of either micro- or nano-sized zinc oxide caused significant small-molecule photodegradation and the degraded mixtures exhibited higher levels of toxicity in embryonic zebrafish assays. This study suggests that caution must be taken when formulating sunscreens containing both zinc oxide and small-molecule UV-filters to avoid unintended consequences during use.

The Green toxicology approach: Insight towards the eco-toxicologically safe development of benign catalysts

Green toxicology is a novel approach increasingly applied for the development of materials and chemicals that are more benign to the environment and human health than their conventional counterparts. It includes predictive eco-toxicological assessments of chemicals during the early developmental process to exclude adverse effects. In the present study, two guanidine zinc catalysts for the ring-opening polymerization of lactide were investigated using eco-toxicological tools. Namely, the fish embryo toxicity assay for teratogenic effects, the ER (α) CALUX assay for endocrine activity and the Ames fluctuation assay for mutagenic potential were applied. Both complexes showed no endocrine activity, mutagenicity or acute aquatic toxicity, however a delayed hatch could be observed, therefore suggesting potential effects on a molecular level. This proof-of-concept study aims to assess the toxicity of guanidine zinc catalysts and is a first step towards the incorporation of toxicological assessments into chemical developmental processes to achieve a sustainable and safe production of catalysts.

Metabolomic Studies for the Evaluation of Toxicity Induced by Environmental Toxicants on Model Organisms

Environmental pollution causes significant toxicity to ecosystems. Thus, acquiring a deeper understanding of the concentration of environmental pollutants in ecosystems and, clarifying their potential toxicities is of great significance. Environmental metabolomics is a powerful technique in investigating the effects of pollutants on living organisms in the environment. In this review, we cover the different aspects of the environmental metabolomics approach, which allows the acquisition of reliable data. A step-by-step procedure from sample preparation to data interpretation is also discussed. Additionally, other factors, including model organisms and various types of emerging environmental toxicants are discussed. Moreover, we cover the considerations for successful environmental metabolomics as well as the identification of toxic effects based on data interpretation in combination with phenotype assays. Finally, the effects induced by various types of environmental toxicants in model organisms based on the application of environmental metabolomics are also discussed.

Comparative Lipid Peroxidation and Apoptosis in Embryo-Larval Zebrafish Exposed to 3 Azole Fungicides, Tebuconazole, Propiconazole, and Myclobutanil, at Environmentally Relevant Concentrations

Azole fungicides have entered the aquatic environment through agricultural and residential runoff. In the present study, we compared the off-target toxicity of tebuconazole, propiconazole, and myclobutanil using embryo-larval zebrafish as a model. The aim of the present study was to investigate the relative toxicity of tebuconazole, propiconazole, and myclobutanil using multiple-level endpoints such as behavioral endpoints and enzymatic and molecular biomarkers associated with their mode of action. Zebrafish embryos were exposed to azoles at environmentally relevant and high concentrations, 0.3, 1.0, and 1000 µg/L, starting at 5 h postfertilization (hpf) up to 48 hpf, as well as 5 d postfertilization (dpf). Relative mRNA expressions of cytochrome P450 family 51 lanosterol-14α-demethylase, glutathione S-transferase, caspase 9, phosphoprotein p53, and BCL2-associated X protein were measured to assess toxicity attributable to fungicides at the mRNA level, whereas caspase 3/7 (apoptosis) and 3,4-methylene​dioxy​amphetamine (lipid peroxidation) levels were measured at the enzymatic level. Furthermore, mitochondrial dysfunction was measure through the Mito Stress test using the Seahorse XFe24 at 48 hpf. In addition, light to dark movement behavior was monitored at 5 dpf using Danio Vision® to understand adverse effects at the organismal level. There was no significant difference in the light to dark behavior with exposure to azoles compared to controls. The molecular biomarkers indicated that propiconazole and myclobutanil induced lipid peroxidation, oxidative stress, and potentially apoptosis at environmentally relevant concentrations (0.3 and 1 µg/L). The results from the mitochondrial respiration assay indicated a slight decrease in spare respiratory capacity with an acute exposure (48 hpf) to all 3 azoles at 1000 µg/L. Based on the present results, propiconazole and myclobutanil are acutely toxic compared to tebuconazole in aquatic organisms at environmentally relevant concentrations. Environ Toxicol Chem 2019;38:1455-1466. © 2019 SETAC.

YB-1 recruitment to stress granules in zebrafish cells reveals a differential adaptive response to stress

The survival of cells exposed to adverse environmental conditions entails various alterations in cellular function including major changes in the transcriptome as well as a radical reprogramming of protein translation. While in mammals this process has been extensively studied, stress responses in non-mammalian vertebrates remain poorly understood. One of the key cellular responses to many different types of stressors is the transient generation of structures called stress granules (SGs). These represent cytoplasmic foci where untranslated mRNAs are sorted or processed for re-initiation, degradation, or packaging into mRNPs. Here, using the evolutionarily conserved Y-box binding protein 1 (YB-1) and G3BP1 as markers, we have studied the formation of stress granules in zebrafish (D. rerio) in response to different environmental stressors. We show that following heat shock, zebrafish cells, like mammalian cells, form stress granules which contain both YB-1 and G3BP1 proteins. Moreover, zfYB-1 knockdown compromises cell viability, as well as recruitment of G3BP1 into SGs, under heat shock conditions highlighting the essential role played by YB-1 in SG assembly and cell survival. However, zebrafish PAC2 cells do not assemble YB-1-positive stress granules upon oxidative stress induced by arsenite, copper or hydrogen peroxide treatment. This contrasts with the situation in human cells where SG formation is robustly induced by exposure to oxidative stressors. Thus, our findings point to fundamental differences in the mechanisms whereby mammalian and zebrafish cells respond to oxidative stress.

A temporal high-resolution investigation of the Ah-receptor pathway during early development of zebrafish (Danio rerio)

In order to contribute to a comprehensive understanding of the regulating mechanisms of the aryl-hydrocarbon-receptor (AHR) in zebrafish embryos, we aimed to elucidate the interaction of proteins taking part in this signaling pathway during early development of the zebrafish (Danio rerio) after chemical exposure. We managed to illustrate initial transcription processes of the implemented proteins after exposure to two environmentally relevant chemicals: polychlorinated biphenyl 126 (PCB126) and β-Naphthoflavone (BNF). Using qPCR, we quantified mRNA every 4 h until 118 h post fertilization and found the expression of biotransformation enzymes (cyp1 family) and the repressor of the AHR (ahr-r) to be dependent on the duration of chemical exposure and the biodegradability of the compounds. PCB126 induced persistently increased amounts of transcripts as it is not metabolized, whereas activation by BNF was limited to the initial period of exposure. We did not find a clear relation between the amount of transcripts and activity of the induced CYP-proteins, so posttranscriptional mechanisms are likely to regulate biotransformation of BNF. With regard to zebrafish embryos and their application in risk assessment of hazardous chemicals, our examination of the AHR pathway especially supports the relevance of the time point or period of exposure that is used for bioanalytical investigations and consideration of chemical properties determining biodegradability.

Evaluation of apoptosis, oxidative stress responses, AChE activity and body malformations in zebrafish (Danio rerio) embryos exposed to deltamethrin

In this study, we observed the zebrafish embryo/larvae (Danio rerio) exposed to Deltamethrin (DM) used as pesticide in agricultural fields. We determined respectively, changes in body morphology, cell apoptosis, antioxidant enzyme (SOD, CAT, GPx) activities, MDA and acetylcholinesterase (AChE) levels after 96h of DM exposure. The embryos were exposed to 2.5 μg/l - 10 μg/l - 25 μg/l - 50 μg/l of DM concentration for 96 h. Survival and hatching rates, and body malformations were determined under a stereo microscope for in 24, 48, 72 and 96th hours. DM caused the cellular apoptosis and an increase in MDA levels while inhibiting SOD, CAT, GPx enzyme activities and AChE level (P < 0.05). In addition, pericardial edema, yolk sac edema, spinal cord curvature and body malformations were determined in the embryo by depending on the dose of pesticide. As conclusion it can be concluded that DM inhibits the antioxidant enzyme mechanism, increases the cellular apoptosis, malformations. This study may provide enable us for understanding toxic mechanisms of DM in zebrafish embryos.

Stabilized landfill leachate treatment by coagulation-flocculation coupled with UV-based sulfate radical oxidation process

In this work, the feasibility of coagulation-flocculation coupled with UV-based sulfate radical oxidation process (UV/SRAOP) in the removal of chemical oxygen demand (COD) of stabilized landfill leachate (SLL) was evaluated. For coagulation-flocculation, ferric chloride (FeCl₃) was used as the coagulant. The effect of initial pH of SLL and COD:FeCl₃ ratio on the COD removal was evaluated. The result revealed that COD:FeCl₃ ratio of 1:1.3 effectively removed 76.9% of COD at pH 6. The pre-treated SLL was then subjected to UV/SRAOP treatment. For UV/SRAOP, the sulfate radical (SR) was generated using UV-activated persulfate (UV/PS) and peroxymonosulfate (UV/PMS). The dosage of oxidant and reaction time were found to be the main parameters that influence the efficiency of COD removal. On the other hand, the effect of initial pH (3-7) and the type of oxidant (PS and PMS) was found to have no significant influence on COD removal efficiency. At optimum conditions, approximately 90.9 and 91.5% of COD was successfully removed by coagulation-flocculation coupled with UV/PS and UV/PMS system, respectively. Ecotoxicity study using zebrafish showed a reduction in toxicity of SLL from 10.1 to 1.74 toxicity unit (TU) after coagulation-flocculation. The TU remained unchanged after UV/PS treatment but slightly increased to 1.80 after UV/PMS treatment due to the presence of residual sulfate ion in the treated effluent. In general, it can be concluded that coagulation-flocculation coupled with UV/SRAOP could be a potential water treatment method for SLL treatment.

Removal of organic matter from stabilized landfill leachate using Coagulation-Flocculation-Fenton coupled with activated charcoal adsorption

The treatment of stabilized landfill leachate (SLL) by conventional biological treatment is often inefficient due to the presence of bio-recalcitrant substances. In this study, the feasibility of coagulation-flocculation coupled with the Fenton reaction in the treatment of SLL was evaluated. The efficiency of the selected treatment methods was evaluated through total organic carbon (TOC) removal from SLL. With ferric chloride as the coagulant, coagulation-flocculation was found to achieve the highest TOC removal of 71% at pH 6. Then, the pretreated SLL was subjected to the Fenton reaction. Nearly 50% of TOC removal was achieved when the reaction was carried out at pH 3, H₂O₂:Fe²⁺ ratio of 20:1, H₂O₂ dosage of 240 mM and 1 h of reaction time. By coupling the coagulation-flocculation with the Fenton reaction, the removal of TOC, COD (chemical oxygen demand) and turbidity of SLL were 85%, 84% and 100%, respectively. The ecotoxicity study performed using zebrafish revealed that 96 h LC₅₀ for raw SLL was 1.40% (v/v). After coagulation-flocculation, the LC₅₀ of the pretreated SLL was increased to 25.44%. However, after the Fenton reaction, the LC₅₀ of the treated SLL was found to decrease to 10.96% due to the presence of H₂O₂ residue. In this study, H₂O₂ residue was removed using powdered activated charcoal. This method increased the LC₅₀ of treated effluent to 34.48% and the removal of TOC and COD was further increased to 90%. This finding demonstrated that the combination of the selected treatment methods can be an efficient treatment method for SLL.

Weatherfish (Misgurnus fossilis) as a new species for toxicity testing?

Selection of appropriate test species is a critical issue when assessing effects of environmental contamination on fish because the ecological relevance of commonly used test species might be restricted due to their exotic origin. In the present study, a European freshwater fish with frequent occurrence in agricultural areas is suggested as a potential alternative: the European weatherfish (Misgurnus fossilis). Its suitability for acute embryo toxicity tests (FET) was investigated with regard to practical implementation, sensitivity to contaminants and tolerance against environmental conditions of concern. For this purpose, weatherfish embryos were exposed (72h) to the reference substance 3,4-dichloroaniline (DCA) in three independent tests. Furthermore, the effects of dissolved oxygen (DO) deficiency on weatherfish embryos were studied to evaluate their suitability e.g. for sediment bioassays. Obtained results revealed that the sensitivity of weatherfish embryos towards DCA (72 h-EC₅₀=0.52mg/l; 72 h-LC₅₀=0.71mg/l) was highest compared to other species and three times higher than that reported for the commonly used zebrafish (Danio rerio). Even though knowledge of DO requirements during the embryonic period of European fish species is scarce, weatherfish can be stated as one of the most tolerant native species (LC₉₀ for DO=0.53mg/l after 48h exposure plus 72h post-exposure). Its high ecological relevance for Europe, the particular sensitivity towards DCA and high tolerance against DO depletion highlight the potential of weatherfish as additional species for toxicity testing.

Investigations on sediment toxicity of German rivers applying a standardized bioassay battery

River sediments may contain a huge variety of environmental contaminants and play a key role in the ecological status of aquatic ecosystems. Contaminants adsorbed to sediments and suspended solids may contribute directly or after remobilization to an adverse ecological and chemical status of surface water. In this subproject of the joint research project DanTox, acetonic Soxhlet extracts from three German river sediments from the River Rhine (Altrip and Ehrenbreitstein with moderate contamination) and River Elbe (Veringkanal Hamburg heavily contaminated) were prepared and redissolved in dimethyl sulfoxide (DMSO). These extracts were analyzed with a standard bioassay battery with organisms from different trophic levels (bacteria, algae, Daphnia, fish) as well as in the Ames test and the umuC test for bacterial mutagenicity and genotoxicity according to the respective OECD and ISO guidelines. In total, 0.01% (standard) up to 0.25% (only fish embryo test) of the DMSO sediment extract was dosed to the test systems resulting in maximum sediment equivalent concentrations (SEQ) of 2 up to 50 g l(-1). The sediment of Veringkanal near Hamburg harbor was significantly more toxic in most tests compared to the sediment extracts from Altrip and Ehrenbreitstein from the River Rhine. The most toxic effect found for Veringkanal was in the algae test with an ErC50 (72 h) of 0.00226 g l(-1) SEQ. Ehrenbreitstein and Altrip samples were about factor 1,000 less toxic. In the Daphnia, Lemna, and acute fish toxicity tests, no toxicity at all was found at 2 g l(-1) SEQ. corresponding to 0.01% DMSO. Only when increasing the DMSO concentration the fish embryo test showed a 22-fold higher toxicity for Veringkanal than for Ehrenbreitstein and Altrip samples, while the toxicity difference was less evident for the Daphnia test due to the overlaying solvent toxicity above 0.05% dimethyl sulfoxide (DMSO). The higher toxicities observed with the Veringkanal sample are supported by the PAH and PCB concentrations analyzed in the sediments. The sediment extracts of Altrip and Veringkanal were mutagenic in the Ames tester strain TA98 with metabolic activation (S9-mix). The findings allow a better ecotoxicological characterization of the sediments extensively analyzed in all subprojects of the DanTox project (e.g., Garcia-Kaeufer et al. Environ Sci Pollut Res. doi: 10.1007/s11356-014-3894-4 , 2014; Schiwy et al. Environ Sci Pollut Res. doi: 10.1007/s11356-014-3185-0 , 2014; Hollert and Keiter 2015). In the absence of agreed limit values for sediment extracts in standard tests, further data with unpolluted reference sediments are required for a quantitative risk assessment of the investigated polluted sediments.