The influence of heart developmental anatomy on cardiotoxicity-based adverse outcome pathways in fish

Innovative transgenic zebrafish biosensor for heavy metal detection

Heavy metal contamination is an urgent environmental issue that poses a significant threat to human health and the ecosystem. To mitigate the adverse impacts of heavy metal pollution, the aim of this research was to develop genetically engineered zebrafish as biosensors, which offer a promising alternative for detecting heavy metal exposure, specifically Cd2⁺ and Zn2⁺. A novel heavy metal-sensitive gene construct metallothionine 2 promoter with DsRed reporter gene (mt2-DsRed2) was synthesized and integrated into zebrafish embryos using a Tol2 transposon transposase system with the transgenic zebrafish line subjected to biosensing applications for Cd2+ and Zn2+. The biosensor showed specific responses with linear correlation heavy metal concentration and DsRed fluorescence signal for Cd2+ and Zn2+ with (p < 0.01) a minimum detection limit of 4 ppb for each metal ion but not for the non-specific metal ion Ni2+, which makes it suitable for laboratory-based heavy metal assessment assays in the low heavy metal concentration ranges of 0-10 ppb. Additionally, the study investigated the toxicity of heavy metals on zebrafish early developmental stages applying a modified version of the OECD Fish Embryo Toxicity (FET-236) test. Accordingly, Cd2+, Zn2+, and Ni2+ exhibited no significant toxicity effects on zebrafish embryos within the low dose range of 2-10 ppb confirming the biocompatibility of the transgenic zebrafish biosensor for heavy metal sensing applications. Thus, the developed transgenic zebrafish line can accurately sense heavy metals Cd2+ and Zn2+ within the low dose range, making it a promising alternative laboratory assay for environmental monitoring and risk assessment.

Stranded heavy fuel oil exposure causes deformities, cardiac dysfunction, and oxidative stress in marine medaka Oryzias melastigma using an oiled-gravel-column system

Heavy fuel oil (HFO) stranded on the coastline poses a potential threat to the health of marine fish after an oil spill. In this study, an oiled-gravel-column (OGC) system was established to investigate the toxic effects of stranded HFO on marine medaka Oryzias melastigma. HFO 380# (sulfur content 2.9%) was chosen as one type of high sulfur fuel oil for acute toxicity tests. The marine medaka larvae were exposed to the OGC system effluents with oil loading rates of 0 (control), 400, 800, 1600, and 3200 µg HFO/g gravel for 144 h, respectively. Results showed that a prevalence of blue sac disease signs presented teratogenic effects, including decreased circulation, ventricular stretch, cardiac hemorrhage, and pericardial edema. Moreover, the treatments (800, 1600, and 3200 µg oil/g gravel) induced severe cardiotoxicity, characterized by significant bradycardia and reduced stroke volume with an overt decrease in cardiac output. Additionally, the antioxidant enzyme activities, including catalase (CAT), peroxidase (POD), and glutathione S-transferase (GST) were significantly upregulated at 800-3200 µg oil/g gravel except for a marked inhibition of CAT activity at 3200 µg oil/g gravel. Furthermore, significantly elevated protein carbonyl (PCO) levels were detected, suggesting that the organisms suffered severe protein oxidative damage subjected to the exposure. Overall, stranded HFO 380# exposure activated the antioxidant defense system (up-regulated POD and GST activities) of marine medaka and disrupted CAT activity, which could result in an oxidative stress state (elevated PCO levels) and might further contribute to cardiac dysfunction, deformities, and mortality.

Transcriptome analysis unveils the mechanisms of oxidative stress, immunotoxicity and neurotoxicity induced by benzotriazole UV stabilizer-328 in zebrafish embryos

As an emerging pollutant, ultraviolet stabilizer-328 (UV-328) has been frequently detected in aquatic environments and attracted great attention. Nevertheless, the toxicity and mechanisms of UV-328 to aquatic organisms are still not fully understood. In particular, the immunotoxicity and neurotoxicity of UV-328 to aquatic organisms and their mechanisms have not been reported yet. In this experiment, the developmental toxicity, oxidative stress, apoptosis, immunotoxicity and neurotoxicity in zebrafish embryos exposed to UV-328 with concentrations of 0.01, 0.1, 1, 10 and 100 µg/L for 120 h were studied. By measuring the growth and developmental indices, production of ROS, enzyme activities, MDA content and expression of genes related to oxidative, immune and nerve, and histopathological analysis, it was found that UV-328 had developmental toxicity to zebrafish larvae, and could induce oxidative stress, immunotoxicity and neurotoxicity to zebrafish larvae even at environmental concentrations with concentration-dependent effects. Moreover, the results of transcriptome analysis and qRT-PCR validation suggested that immune and nerve disorders were caused by UV-328 in zebrafish larvae through regulating the RIG-I-like receptor signaling pathway and neuroactive ligand-receptor interaction, respectively. In addition, transcriptome analysis further revealed that UV-328 could mediate the RIG-I to induce oxidative stress through p38-MAPK/p53 signaling pathway, leading to apoptosis and oxidative damage. In addition, the p38-MAPK signaling pathway enhanced ROS production and activated inflammatory cytokines to induce immunotoxicity. The results of the present work provided important information for understanding the toxicity of UV-328 to aquatic organisms and evaluating its ecological risk in aquatic environment.

Use of cardiac cell cultures from salmonids to measure the cardiotoxic effect of environmental pollutants

Environmental stressors such as micro- and nanosized plastic particles (MNPs) or crude oil have a detrimental effect on aquatic animals; however, the impact upon the cardiovascular system of fish remains relatively under-researched. This study presents a novel approach for investigating the effect of crude oil and MNPs on the cardiac system of fish. We used salmonid larvae and cardiac cell cultures derived from hearts of salmonid fish and exposed them to environmental stressors. Following exposure to plastic particles or crude oil, the larvae exhibited some variation in contraction rate. In contrast, significant alterations in the contraction rate were observed in all cardiac cell cultures. The greatest differences between the control and treatment groups were observed in cardiac cell cultures derived from older brown trout. Following 7 days of exposure to MNPs or crude oil in Atlantic salmon larval hearts or cardiac cell cultures, there were only minor responses noted in mRNA expression of the selected marker genes. These findings show the use of a novel in vitro technique contributing to the existing body of knowledge on the impact of MNPs and crude oil on the cardiovascular system of salmonids and the associated risk.

Toxicity of crude oil-derived polar unresolved complex mixtures to Pacific herring embryos: Insights beyond polycyclic aromatic hydrocarbons

Crude oil toxicity to early life stage fish is commonly attributed to polycyclic aromatic hydrocarbons (PAHs). However, it remains unclear how the polar unresolved complex mixture (UCM), which constitutes the bulk of the water-soluble fraction of crude oil, contributes to crude oil toxicity. Additionally, the role of photomodification-induced toxicity in relation to the polar UCM is not well understood. This study addresses these knowledge gaps by assessing the toxicity of two laboratory generated polar UCMs from Cook Inlet crude oil, representing the readily water-soluble fraction of crude oil and photoproduced hydrocarbon oxidation products (HOPs), to Pacific herring (Clupea pallasii) embryos. A small-scale semi-static exposure design was utilized with a range of polar UCM concentrations (0.5-14 mg/L) in nonvolatile dissolved organic carbon (NVDOC) units, quantifying the entire polar UCM. Compositional analyses revealed a photochemical-driven shift toward more complex aromatic compositions, naphthenic acids, and no detectable levels of PAHs (above 0.3 μg/L). Exposure to the dark polar UCM resulted in higher mortality than exposure to the light polar UCM. Both dark and light polar UCMs induced developmental abnormalities commonly attributed to the PAH fraction, including edema, reduced heart rate, body axis defects, and decreased body lengths, with these effects observed at the lowest dose group (0.5 mg/L NVDOC). These responses suggest photomodification-induced toxicity is driven by exposure to increased concentrations of dissolved HOPs rather than photochemical induced compositional changes. Gene expression analyses focusing on xenobiotic metabolism and cardiac morphogenesis yielded results consistent with previous studies examining the biological mechanisms of crude oil toxicity. In summary, these phenotypic and genotypic responses in Pacific herring embryos indicate that the polar UCM is a significant driver of crude oil toxicity. These findings emphasize the importance of considering the polar UCM in future studies, metric reporting, and risk assessments related to crude oil toxicity.

PCBs contamination in water and Mytilus edulis along the north Portuguese Atlantic Ocean coastline and analysis of potential carcinogenic risk to human health

Seven seawater polychlorinated biphenyls (PCBs) were measured in water (DAP), suspended particulate matter (SPM), and blue mussels (Mytilus edulis) collected from four beaches in northwest Portugal. PCBs were extracted using solid-phase-extraction, ultrasound-extraction and QuEChERS before GC-MS analysis. The two-year annual average concentrations of PCBs in DAP, SPM and the four-year analysis in mussels were ∼ 4.4 ng/L, ∼15.9 μg/kg, and ∼ 56.0 μg/kg. The results suggest higher concentrations of PCBs in summer for SPM and in spring for mussels, mainly those collected close to the Ave River estuary. The origins of PCBs remain uncertain. Risk assessment shows that PCBs in water are unlikely to harm local biota due to their low thyroid hormone toxicity equivalents (TEQ-TH; ∼1.4E-04 ng/L and ∼ 4.1E-04 μg/kg) and on WHO toxicity equivalents (TEQ-WHO; ∼2.1E-05 ng/L and ∼ 4.9E-05 μg/kg). However, the lifetime carcinogenic risk (LCR) for humans consuming local bivalves is concerning, as it exceeds 1.0E-06.

Water-accommodated fractions of crude oil and its mixture with chemical dispersant impairs oxidase stress and energy metabolism disorders in Oryzias melastigma embryos

In this study, marine medaka (Oryzias melastigma) embryos were exposed to different concentrations of water-accommodated fractions (WAFs) and chemically enhanced water-accommodated fractions (CEWAFs) of Oman crude oil for 14 d by semi-static exposure methods. The effects on growth and development and energy metabolism process were evaluated. Results showed that embryo survival and hatchability were decreased in a dose-dependent manner with an increase in the concentration of petroleum hydrocarbon compounds, whereas the malformation exhibited a dose-dependent increase. Compared to the control, the adenosine triphosphate (ATP) content and Na+-K+-ATPase (NKA) activities of embryos exposed to both WAFs and CEWAFs were reduced, while intracellular reactive oxygen species (ROS) levels and NADH oxidase (NOX) activities were increased. Our study demonstrated that exposure to crude oil dispersed by chemical dispersant affected the growth and development of marine medaka embryos, caused oxidative stress while produced a series of malformations in the body and dysregulation in energy metabolism. In comparison, the toxic effects of chemically dispersed crude oil might be more severe than the oil itself in the equivalent diluted concentration treatment solution. These would provide more valuable and reliable reference data for the use of chemical dispersants in oil spills.

Impacts of UV light on the effects of either conventional or nano-enabled azoxystrobin on Daphnia magna

Agri-chemicals such as fungicides are applied in natural settings and hence are exposed to the environment's ultraviolet (UV) light. Recently, many fungicides in commerce are being modified as nano-enabled formulations to increase agricultural productivity and reduce potential off-target effects. The present study investigated the impacts of sunlight-grade UV emission on the effects of either conventional or nano-enabled azoxystrobin (Az or nAz, respectively), a commonly applied agricultural fungicide, on Daphnia magna. Daphnids were exposed to increasing concentrations of Az or nAz under either full-spectrum (Vis) or full-spectrum Vis + UV (Vis + UV) lighting regimes to evaluate LC50s. Az LC50 was calculated at 268.8 and 234.2 μg/L in Vis or Vis + UV, respectively, while LC50 for nAz was 485.6 and 431.0 μg/L under Vis or Vis + UV light, respectively. Daphnids were exposed to 10% LC50 of either Az or nAz under Vis or Vis + UV lighting regime for 48 h or 21 d (acute and chronic, respectively). By 48 h, both Az and nAz reduced O2 consumption and increased TBARS. Heart rate was increased in Az-exposed daphnids but not in nAz groups. Neither of the two chemicals impacted thoracic limb activity. In 21 d exposures, Az significantly reduced biomass production and fecundity, but nAz groups were not significantly different from controls. The results of the present study demonstrate that conventional Az is more toxic to D. magna at lethal and sub-lethal levels in acute and chronic exposures, and sunlight strength UV can potentiate both acute and chronic effects of Az and nAz on D. magna.

Isomer-specific cardiotoxicity induced by tricresyl phosphate in zebrafish embryos/larvae

Tricresyl phosphate (TCP) has received extensive attentions due to its potential adverse effects, while the toxicological information of TCP isomers is limited. In this study, 2 h post-fertilization zebrafish embryos were exposed to tri-o-cresyl phosphate (ToCP), tri-m-cresyl phosphate (TmCP) or tri-p-cresyl phosphate (TpCP) at concentrations of 0, 100, 300 and 600 μg/L until 120 hpf, and the cardiotoxicity and mechanism of TCP isomers in zebrafish embryos/larvae were evaluated. The results showed that ToCP or TmCP exposure induced cardiac morphological defects and dysfunction in zebrafish, characterized by increased distance between sinus venosus and bulbus arteriosis, increased atrium and pericardial sac area, trabecular defects, and decreased heart rate and blood flow velocity, while no adverse effects of TpCP on zebrafish heart were found. Transcriptomic results revealed that extracellular matrix (ECM) and motor proteins, as well as PPAR signaling pathways, were included in the cardiac morphological defects and dysfunction induced by ToCP and TmCP. Co-exposure test with D-mannitol indicated that the inhibition of energy metabolism by ToCP and TmCP affected cardiac morphology and function by decreasing osmoregulation. This study is the first to report the cardiotoxicity induced by TCP in zebrafish from an isomer perspective, providing a new insight into the toxicity of TCP isomers and highlighting the importance of evaluating the toxicity of different isomers.

Microscopic photoplethysmography-based evaluation of cardiotoxicity in whitefish larvae induced by acute exposure to cadmium and phenol

Toxic environmental pollutants pose a health risk for both humans and animals. Accumulation of industrial contaminants in freshwater fish may become a significant threat to biodiversity. Comprehensive monitoring of the impact of environmental stressors on fish functional systems is important and use of non-invasive tools that can detect the presence of these toxicants in vivo is desirable. The blood circulatory system, by virtue of its sensitivity to the external stimuli, could be an informative indicator of chemical exposure. In this study, microscopic photoplethysmography-based approach was used to investigate the cardiac activity in broad whitefish larvae (Coregonus nasus) under acute exposure to cadmium and phenol. We identified contamination-induced abnormalities in the rhythms of the ventricle and atrium. Our results allow introducing additional endpoints to evaluate the cardiac dysfunction in fish larvae and contribute to the non-invasive evaluation of the toxic effects of industrial pollutants on bioaccumulation and aquatic life.

Detrimental impacts and QSAR baseline toxicity assessment of Japanese medaka embryos exposed to methylparaben and its halogenated byproducts

Despite the theoretical risk of forming halogenated methylparabens (halo-MePs) during water chlorination in the absence or presence of bromide ions, there remains a lack of in vivo toxicological assessments on vertebrate organisms for halo-MePs. This research addresses these gaps by investigating the lethal (assessed by embryo coagulation) or sub-lethal (assessed by hatching success/heartbeat rate) toxicity and teratogenicity (assessed by deformity rate) of MeP and its mono- and di-halogen derivatives (Cl- or Br-) using Japanese medaka embryos. In assessing selected apical endpoints to discern patterns in physiological or biochemical alterations, heightened toxic impacts were observed for halo-MePs compared to MeP. These include a higher incidence of embryo coagulation (4-36 fold), heartbeat rate decrement (11-36 fold), deformity rate increment (32-223 fold), hatching success decrement (11-59 fold), and an increase in Reactive Oxygen Species (ROS) level (1.2-7.4 fold)/Catalase (CAT) activity (1.7-2.8 fold). Experimentally determined LC50 values are correlated and predicted using a Quantitative Structure Activity Relationship (QSAR) based on the speciation-corrected liposome-water distribution ratio (Dlipw, pH 7.5). The QSAR baseline toxicity aligns well with (sub)lethal toxicity and teratogenicity, as evidenced by toxic ratio (TR) analysis showing TR < 10 for MeP exposure in all cases, while significant specific or reactive toxicity was found for halo-MeP exposure, with TR > 10 observed (excepting three values). Our extensive findings contribute novel insights into the intricate interplay of embryonic toxicity during the early-life-stage of Japanese medaka, with a specific focus on highlighting the potential hazards associated with halo-MePs compared to the parent compound MeP.

Oil droplet fouling on lesser sandeel (Ammodytes marinus) eggshells does not enhance the crude oil induced developmental toxicity

The oil industry's expansion and increased operational activity at older installations, along with their demolition, contribute to rising cumulative pollution and a heightened risk of accidental oil spills. The lesser sandeel (Ammodytes marinus) is a keystone prey species in the North Sea and coastal systems. Their eggs adhere to the seabed substrate making them particularly vulnerable to oil exposure during embryonic development. We evaluated the sensitivity of sandeel embryos to crude oil in a laboratory by exposing them to dispersed oil at concentrations of 0, 15, 50, and 150 µg/L oil between 2 and 16 days post-fertilization. We assessed water and tissue concentrations of THC and tPAH, cyp1a expression, lipid distribution in the eyes, head and trunk, and morphological and functional deformities. Oil droplets accumulated on the eggshell in all oil treatment groups, to which the embryo responded by a dose-dependent rise in cyp1a expression. The oil exposure led to only minor sublethal deformities in the upper jaw and otic vesicle. The findings suggest that lesser sandeel embryos are resilient to crude oil exposure. The lowest observed effect level documented in this study was 36 µg THC/L and 3 µg tPAH/L. The inclusion of these species-specific data in risk assessment models will enhance the precision of risk evaluations for the North Atlantic ecosystems.

Emerging disinfection byproducts 3-bromine carbazole induces cardiac developmental toxicity via aryl hydrocarbon receptor activation in zebrafish larvae

3-bromine carbazole (3-BCZ) represents a group of emerging aromatic disinfection byproducts (DBP) detected in drinking water; however, limited information is available regarding its potential cardiotoxicity. To assess its impacts, zebrafish embryos were exposed to 0, 0.06, 0.14, 0.29, 0.58, 1.44 or 2.88 mg/L of 3-BCZ for 120 h post fertilization (hpf). Our results revealed that ≥1.44 mg/L 3-BCZ exposure induced a higher incidence of heart malformation and an elevated pericardial area in zebrafish larvae; it also decreased the number of cardiac muscle cells and thins the walls of the ventricle and atrium while increasing cardiac output and impeding cardiac looping. Furthermore, 3-BCZ exposure also exhibited significant effects on the transcriptional levels of genes related to both cardiac development (nkx2.5, vmhc, gata4, tbx5, tbx2b, bmp4, bmp10, and bmp2b) and cardiac function (cacna1ab, cacna1da, atp2a1l, atp1b2b, atp1a3b, and tnnc1a). Notably, N-acetyl-L-cysteine, a reactive oxygen species scavenger, may alleviate the failure of cardiac looping induced by 3-BCZ but not the associated cardiac dysfunction or malformation; conversely, the aryl hydrocarbon receptor agonist CH131229 can completely eliminate the cardiotoxicity caused by 3-BCZ. This study provides new evidence for potential risks associated with ingesting 3-BCZ as well as revealing underlying mechanisms responsible for its cardiotoxic effects on zebrafish embryos.

Structure-activity relationships for alkyl-phenanthrenes support two independent but interacting synergistic models for PAC mixture potency

Multiple lines of evidence at whole animal, cellular and molecular levels implicate polycyclic aromatic compounds (PACs) with three rings as drivers of crude oil toxicity to developing fish. Phenanthrene (P0) and its alkylated homologs (C1- through C4-phenanthrenes) comprise the most prominent subfraction of tricyclic PACs in crude oils. Among this family, P0 has been studied intensively, with more limited detail available for the C4-phenanthrene 1-methyl-7-isopropyl-phenanthrene (1-M,7-IP, or retene). While both compounds are cardiotoxic, P0 impacts embryonic cardiac function and development through direct blockade of K+ and Ca2+ currents that regulate cardiomyocyte contractions. In contrast, 1-M,7-IP dysregulates aryl hydrocarbon receptor (AHR) activation in developing ventricular cardiomyocytes. Although no other compounds have been assessed in detail across the larger family of alkylated phenanthrenes, increasing alkylation might be expected to shift phenanthrene family member activity from K+/Ca2+ ion current blockade to AHR activation. Using embryos of two distantly related fish species, zebrafish and Atlantic haddock, we tested 14 alkyl-phenanthrenes in both acute and latent developmental cardiotoxicity assays. All compounds were cardiotoxic, and effects were resolved into impacts on multiple, highly specific aspects of heart development or function. Craniofacial defects were clearly linked to developmental cardiotoxicity. Based on these findings, we suggest a novel framework to delineate the developmental toxicity of petrogenic PAC mixtures in fish, which incorporates multi-mechanistic pathways that produce interactive synergism at the organ level. In addition, relationships among measured embryo tissue concentrations, cytochrome P4501A mRNA induction, and cardiotoxic responses suggest a two-compartment toxicokinetic model that independently predicts high potency of PAC mixtures through classical metabolic synergism. These two modes of synergism, specific to the sub-fraction of phenanthrenes, are sufficient to explain the high embryotoxic potency of crude oils, independent of as-yet unmeasured compounds in these complex environmental mixtures.

Newly synthesized derivatives with a thiosemicarbazide group reduce the viability of cancer cell lines. Acute toxicity assessment in Zebrafish (Danio rerio) early life stages

Due to the variability and ability of tumor to mutate, as well as the heterogeneity of tumor tissue, such drugs are sought that would act selectively and multidirectionally on the cancer cell. Therefore, two newly synthesized semicarbazide structured substances were evaluated for anticancer properties in our study: 1a and 1b. In order to evaluate the cytotoxicity and selectivity of the tested compounds, MTT and Neutral Red uptake assay on cell lines (HEK293, LN229, 769-P, HepG2 and NCI-H1563) and cell cycle analysis were performed. Acute toxicity and cardiotoxicity were also evaluated in the zebrafish model. The tested compounds (1a, 1b) showed cytotoxic activity, with the greatest selectivity noted against the glioblastoma multiforme cell line (LN229). However, compound 1b showed stronger selective activity than 1a. Both of compounds were shown to significantly affect the M phase of the cell cycle. Whereas, the conducted toxicological examination of newly synthesized thiosemicarbazide derivates showed, that direct exposition of Danio rerio embryos to compound 1a, but not 1b, causes a concentration-dependent increase in developmental malformations, indicating possible teratogenic effects.

Validation of a zebrafish developmental defects assay as a qualified alternative test for its regulatory use following the ICH S5(R3) guideline

Zebrafish is a popular toxicology model and provides an ethically acceptable small-scale analysis system with the complexity of a complete organism. Our goal is to further validate this model for its regulatory use for reproductive and developmental defects by testing the compounds indicated in the "Guideline on detection of reproductive and developmental toxicity for human pharmaceuticals" (ICH S5(R3) guideline.) To determine the embryotoxic and developmental risk of the 32 reference compounds listed in the ICH S5(R3) guideline, the presence of morphological alterations in zebrafish embryos was analyzed at two different stages to calculateLC50 and EC50 values for each stage. Teratogenic Indexes were established as the ratio between LC50 and EC50 critical for the proper compound classification as teratogenic when it is ≥ 2. A total of three biological replicates have been conducted to study the reproducibility of the assay. The chemicals' concentration in the medium and internally in the zebrafish embryos was evaluated. In this study, the 3 negative compounds were properly categorized while 23 compounds out of the 29 reference ones (sensitivity of 79.31%) were classified as teratogenic in zebrafish. The 6 that had false-negative results were classified 4 as inconclusive, 1 as not toxic, and 1 compound resulted toxic for zebrafish embryos under testing conditions. After the bioavailability experiments, some of the obtained inconclusive results were refined. The developmental defects assay in zebrafish gives an accuracy of 89.66%, sensitivity of 88.46%, specificity and repeatability of 100% compared to mammals; therefore, this is a well-integrated strategy using New Alternative Methods, to minimize the use of animals in developmental toxicity studies.

Transcriptomic and proteomic fingerprints induced by the fungicides difenoconazole and metalaxyl in zebrafish embryos

In this study, we applied OMICs analysis to identify substance-specific biomarker candidates, which may act as early indicators for specific ecotoxic modes of actions (MoA). Zebrafish embryos were exposed to two sublethal concentrations of difenoconazole and metalaxyl according to a modified protocol of the OECD test guideline No. 236. At the end of exposure, total RNA and protein were extracted, followed by transcriptomics and proteomics analysis. The analysis of significantly differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) revealed a positive exposure-response correlation in all test concentrations for both fungicides. Similarly, also a positive correlation between the obtained transcriptome and proteome data was observed, highlighting the robustness of our approach. From the detected DEGs, candidate biomarkers specific for difenoconazole (apoa1b, gatm, mylpfb and acta1b) and metalaxyl (lgals2b, abat, fabp1b.1 and myh9a) were selected, and their biological functions were discussed to assess the predictive potential.

Biological Responses of Pacific Herring Embryos to Crude Oil Are Quantifiable at Exposure Levels Below Conventional Limits of Quantitation for PAHs in Water and Tissues

Pacific herring (Clupea pallasii), a cornerstone of marine food webs, generally spawn on marine macroalgae in shallow nearshore areas that are disproportionately at risk from oil spills. Herring embryos are also highly susceptible to toxicity from chemicals leaching from oil stranded in intertidal and subtidal zones. The water-soluble components of crude oil trigger an adverse outcome pathway that involves disruption of the physiological functions of cardiomyocytes in the embryonic herring heart. In previous studies, impaired ionoregulation (calcium and potassium cycling) in response to specific polycyclic aromatic hydrocarbons (PAHs) corresponds to lethal embryolarval heart failure or subtle chamber malformations at the high and low ends of the PAH exposure range, respectively. Sublethal cardiotoxicity, which involves an abnormal outgrowth (ballooning) of the cardiac ventricular chamber soon after hatching, subsequently compromises juvenile heart structure and function, leading to pathological hypertrophy of the ventricle and reduced individual fitness, measured as cardiorespiratory performance. Previous studies have not established a threshold for these sublethal and delayed-in-time effects, even with total (∑)PAH exposures as low as 29 ng/g of wet weight (tissue dose). Here, we extend these earlier findings showing that (1) cyp1a gene expression provides an oil exposure metric that is more sensitive than typical quantitation of PAHs via GC-MS and (2) heart morphometrics in herring embryos provide a similarly sensitive measure of toxic response. Early life stage injury to herring (impaired heart development) thus occurs below the quantitation limits for PAHs in both water and embryonic tissues as a conventional basis for assessing oil-induced losses to coastal marine ecosystems.

Lethal and sublethal effects towards zebrafish larvae of microcystins and other cyanopeptides produced by cyanobacteria

Cyanobacterial blooms affect aquatic ecosystems across the globe and one major concern relates to their toxins such as microcystins (MC). Yet, the ecotoxicological risks, particularly non-lethal effects, associated with other co-produced secondary metabolites remain mostly unknown. Here, we assessed survival, morphological alterations, swimming behaviour and cardiovascular functions of zebrafish (Danio rerio) upon exposure to cyanobacterial extracts of two Brazilian Microcystis strains. We verified that only MIRS-04 produced MCs and identified other co-produced cyanopeptides also for the MC non-producer NPCD-01 by LC-HRMS/MS analysis. Both cyanobacterial extracts, from the MC-producer and non-producer, caused acute toxicity in zebrafish with LC50 values of 0.49 and 0.98 mgdw_biomass/mL, respectively. After exposure to MC-producer extract, additional decreased locomotor activity was observed. The cyanopeptolin (micropeptin K139) contributed 52% of the overall mortality and caused oedemas of the pericardial region. Oedemas of the pericardial area and prevented hatching were also observed upon exposure to the fraction with high abundance of a microginin (Nostoginin BN741) in the extract of the MC non-producer. Our results further add to the yet sparse understanding of lethal and sublethal effects caused by cyanobacterial metabolites other than MCs and the need to better understand the underlying mechanisms of the toxicity. We emphasize the importance of considering mixture toxicity of co-produced metabolites in the ecotoxicological risk assessment of cyanobacterial bloom events, given the importance for predicting adverse outcomes in fish and other organisms.

Risk assessment of polycyclic aromatic hydrocarbon infested sediments along the coast of Goa, India

Goa, a small state in India, is a tourist hotspot known for its coastline and beaches. Anthropogenic activities lead to pollution in the environment. Amongst many other pollutants, polycyclic aromatic hydrocarbons represent a major class of contaminants owing to their widespread distribution and protracted environmental persistence. No information is available about the levels of Polycyclic aromatic hydrocarbon (PAH) contamination in the sediments along the coastline of Goa. The study aimed to establish a baseline for PAH concentrations in the sediments along the shoreline to help comment on the pollution levels caused and thereby understand the risk and their impact on the marine life therein. The total concentration of PAHs along the selected sampling sites of the Goa coastline was 1.00 to 875 μg g-1. Maximum PAH concentrations were detected in the Divar island mangrove (875 μg g-1); the least was observed at Galgibaga beach (365 μg g-1). The results revealed that the sediment of the Goa coastline is heavily contaminated with PAH. Source apportionment of PAHs was analysed based on diagnostic ratios, and results exhibited that petroleum products and their combustion were primarily responsible for their generation. The results of risk quotients showed that the values are way above effect range median (ER-M), indicating these could pose a high risk to the ecosystem.

Interplay between Nrf2 and αB-crystallin in the lens and heart of zebrafish under proteostatic stress

A coordinated oxidative stress response, partly triggered by the transcription factor Nrf2, protects cells from the continual production of reactive oxygen species. Left unbuffered, reactive oxygen species can lead to protein aggregation that has been implicated in a spectrum of diseases such as cataract of the ocular lens and myopathy of the heart. While proteostasis is maintained by diverse families of heat shock proteins, the interplay between the oxidative and proteostatic stress responses in the lens and heart has not been investigated. Capitalizing on multiple zebrafish lines that have compromised function of Nrf2 and/or the two zebrafish small heat shock proteins αBa- and αBb-crystallin, we uncovered a transcriptional relationship that leads to a substantial increase in αBb-crystallin transcripts in the heart in response to compromised function of Nrf2. In the lens, the concomitant loss of function of Nrf2 and αBa-crystallin leads to upregulation of the cholesterol biosynthesis pathway, thus mitigating the phenotypic consequences of the αBa-crystallin knockout. By contrast, abrogation of Nrf2 function accentuates the penetrance of a heart edema phenotype characteristic of embryos of αB-crystallin knockout lines. Multiple molecular pathways, such as genes involved in extracellular interactions and implicated in cardiomyopathy, are revealed from transcriptome profiling, thus identifying novel targets for further investigation. Together, our transcriptome/phenotypic analysis establishes an intersection between oxidative stress and chaperone responses in the lens and heart.

Characterization of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)-induced cardiotoxicity in larval zebrafish (Danio rerio)

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is a type of p-phenylenediamine (PPD), which is widely used in the manufacture of rubber tires owing to its excellent antiozonant properties. In this study, the developmental cardiotoxicity of 6PPD was evaluated in zebrafish larvae, and the LC50 was approximately 737 μg/L for the larvae at 96 h post fertilization (hpf). In the 6PPD treatment of 100 μg/L, the accumulation concentrations of 6PPD were up to 2658 ng/g in zebrafish larvae, and 6PPD induced significant oxidative stress and cell apoptosis in the early developmental stages of zebrafish. Transcriptome analysis showed that 6PPD exposure could potentially cause cardiotoxicity in larval zebrafish by affecting the transcription of the genes related to the calcium signal pathway and cardiac muscle contraction. The genes related to calcium signaling pathway (slc8a2b, cacna1ab, cacna1da, and pln) were verified by qRT-PCR, which were significantly downregulated in larval zebrafish after exposing to 100 μg/L of 6PPD. Simultaneously, the mRNA levels of the genes related to cardiac functions (myl7, sox9, bmp10, and myh71) also respond accordingly. H&E staining and heart morphology investigation indicated that cardiac malformation occurred in zebrafish larvae exposed to 100 μg/L of 6PPD. Furthermore, the phenotypic observation of transgenic Tg (myl7: EGFP) zebrafish also confirmed that 100 μg/L of 6PPD exposure could change the distance of atria and ventricles of the heart and inhibit some key genes (cacnb3a, ATP2a1l, ryr1b) related to cardiac function in larval zebrafish. These results revealed the toxic effects of 6PPD on the cardiac system of zebrafish larvae.

Cardiac toxicity of phenanthrene depends on developmental stage in Atlantic cod (Gadus morhua)

Complex mixtures like crude oil, and single components such as Phenanthrene (Phe), induce cardiotoxicity by interfering with excitation-contraction coupling. However, recent work has demonstrated that the timing of pollutant exposure during embryogenesis greatly impacts the degree of cardiac dysfunction caused. Here, we aimed to clarify the temporal dependence of Phe toxicity and the downstream effects of cardiac dysfunction using Atlantic cod (Gadus morhua). Phe (nominal concentration, 1.12 μmol/L), or the L-type‑calcium channel blocker Nicardipine (Nic) (nominal concentration, 2 and 4 μmol/L), were individually applied to cod embryos either during cardiogenesis (early) or after the onset of cardiac function (late). Phe toxicity was highly dependent on the timing of exposure. Exposure after the onset of cardiac function (i.e. late) caused more severe cardiac and extracardiac abnormalities at 3 days post hatching (dph) than early exposure. Late Phe exposure resulted in a smaller ventricle, eliminated ventricular contraction, and reduced atrial contraction. In contrast, early Phe exposure did not have an effect on cardiac development and function. This temporal difference was not as evident in the Nic treatment. Early Nic exposure created similar morphological phenotypes to the late Phe exposure. The two treatments (early Nic and late Phe) also shared a cardiofunctional phenotype, comprised of eliminated ventricular, and reduced atrial, contraction. These data suggest that extracardiac abnormalities, such as the craniofacial deformities seen after late embryonic exposure to cardiotoxic oil components and mixtures, are mostly downstream effects of cardiac dysfunction.

Toxicity identification evaluation for hydraulic fracturing flowback and produced water during shale gas exploitation in China: Evidence from tissue residues and gene expression

Hydraulic fracturing flowback and produced water (HF-FPW) from shale gas extraction processes is a highly complex medium with potential threats to the environment. Current research on ecological risks of FPW in China is limited, and the link between major components of FPW and their toxicological effects on freshwater organisms is largely unknown. By integrating chemical and biological analyses, toxicity identification evaluation (TIE) was used to reveal causality between toxicity and contaminants, potentially disentangling the complex toxicological nature of FPW. Here, FPW from different shale gas wells, treated FPW effluent, and a leachate from HF sludge were collected from southwest China, and TIE was applied to obtain a comprehensive toxicity evaluation in freshwater organisms. Our results showed that FPW from the same geographic zone could cause significantly different toxicity. Salinity, solid phase particulates, and organic contaminants were identified as the main contributors to the toxicity of FPW. In addition to water chemistry, internal alkanes, PAHs, and HF additives (e.g., biocides and surfactants) were quantified in exposed embryonic fish by target and non-target tissue analyses. The treated FPW failed to mitigate the toxicity associated with organic contaminants. Transcriptomic results illustrated that organic compounds induced toxicity pathways in FPW-exposed embryonic zebrafish. Similar zebrafish gene ontologies were affected between treated and untreated FPW, again confirming that sewage treatment did not effectively remove organic chemicals from FPW. Thus, zebrafish transcriptome analyses revealed organic toxicant-induced adverse outcome pathways and served as evidence for TIE confirmation in complex mixtures under data-poor scenarios.

No observed developmental effects in early life stages of capelin (Mallotus villosus) exposed to a water-soluble fraction of crude oil during embryonic development

The rise in offshore oil and gas operations, maritime shipping, and tourism in northern latitudes enhances the risk of oil spills to sub-Arctic and Arctic coastal environments. Therefore, there is a need to understand the potential adverse effects of petroleum on key species in these areas. Here, we investigated the effects of oil exposure on the early life stages of capelin (Mallotus villosus), an ecologically and commercially important Barents Sea forage fish species that spawns along the coast of Northern Norway. Capelin embryos were exposed to five different concentrations (corresponding to 0.5-19 µg/L total PAHs) of water-soluble fraction (WSF) of crude oil from 6 days post fertilization (dpf) until hatch (25 dpf), and development of larvae in clean seawater was monitored until 52 dpf. None of the investigated endpoints (embryo development, larval length, heart rate, arrhythmia, and larval mortality) showed any effects. Our results suggest that the early life stages of capelin may be more robust to crude oil exposure than similar life stages of other fish species.

Crude oil exposure of early life stages of Atlantic haddock suggests threshold levels for developmental toxicity as low as 0.1 μg total polyaromatic hydrocarbon (TPAH)/L

Atlantic haddock (Melanogrammus aeglefinus) embryos bind dispersed crude oil droplets to the eggshell and are consequently highly susceptible to toxicity from spilled oil. We established thresholds for developmental toxicity and identified any potential long-term or latent adverse effects that could impair the growth and survival of individuals. Embryos were exposed to oil for eight days (10, 80 and 300 μg oil/L, equivalent to 0.1, 0.8 and 3.0 μg TPAH/L). Acute and delayed mortality were observed at embryonic, larval, and juvenile stages with IC₅₀ = 2.2, 0.39, and 0.27 μg TPAH/L, respectively. Exposure to 0.1 μg TPAH/L had no negative effect on growth or survival. However, yolk sac larvae showed significant reduction in the outgrowth (ballooning) of the cardiac ventricle in the absence of other extracardiac morphological defects. Due to this propensity for latent sublethal developmental toxicity, we recommend an effect threshold of 0.1 μg TPAH/L for risk assessment models.

Evaluation of cadmium and mercury on cardiovascular and neurological systems: Effects on humans and fish

Chemicals are at the top of public health concerns and metals have received much attention in terms of toxicological studies. Cadmium (Cd) and mercury (Hg) are among the most toxic heavy metals and are widely distributed in the environment. They are considered important factors involved in several organ disturbances. Heart and brain tissues are not among the first exposure sites to Cd and Hg but they are directly affected and may manifest intoxication reactions leading to death. Many cases of human intoxication with Cd and Hg showed that these metals have potential cardiotoxic and neurotoxic effects. Human exposure to heavy metals is through fish consumption which is considered as an excellent source of human nutrients. In the current review, we will summarize the most known cases of human intoxication with Cd and Hg, highlight their toxic effects on fish, and investigate the common signal pathways of both Cd and Hg to affect heart and brain tissues. Also, we will present the most common biomarkers used in the assessment of cardiotoxicity and neurotoxicity using Zebrafish model.

Mepanipyrim induces cardiotoxicity of zebrafish (Danio rerio) larvae via promoting AhR-regulated COX expression pathway

The wide use of pesticides has seriously threatened human health and the survival of beneficial organisms. The fungicide mepanipyrim is widely used in viticulture practices. Studies of mepanipyrim-induced toxicity in organisms are still scarce, especially studies on cardiotoxicity. In this study, we aimed to investigate mepanipyrim-induced cardiotoxicity in zebrafish (Danio rerio) larvae. We found that mepanipyrim could induce cardiotoxicity by altering the heart rate and cardiomyocyte diameter of larvae. Meanwhile, RNA sequencing and RT-qPCR data indicated that mepanipyrim exposure could dramatically alter the mRNA expression of calcium signaling pathway-, cardiac muscle contraction-, and oxidative respiratory chain-related genes. Interestingly, by the CALUX cell bioassay, we found that most cytochrome c oxidase (COX) family genes exhibited potential AhR-regulated activity, suggesting that mepanipyrim induced cardiotoxicity via a novel AhR-regulated manner in larvae. Additionally, the AhR antagonist CH223191 could effectively prevent mepanipyrim-induced cardiotoxicity in zebrafish larvae. In conclusion, the AhR agonist mepanipyrim could induce cardiotoxicity in a novel unreported AhR-regulated manner, which could specifically affect the expression of COX family genes involved in the mitochondrial oxidative respiratory chain. Our data will help explain the toxic effects of mepanipyrim on organisms and provide new insight into the AhR agonistic activity pesticide-induced cardiotoxicity.

Acute exposure of early-life stage zebrafish (Danio rerio) to Deepwater Horizon crude oil impairs glomerular filtration and renal fluid clearance capacity

The pronephros (early-stage kidney) is an important osmoregulatory organ, and the onset of its function occurs relatively early in some teleost fishes. As such, any defects in kidney development and function are likely associated with a decreased ability to osmoregulate. Previous work has shown that early-life stage (ELS) zebrafish (Danio rerio) acutely exposed to Deepwater Horizon (DWH) crude oil exhibit transcriptional changes in key genes involved in pronephros development and function, as well as pronephric morphological defects and whole-animal osmoregulatory impairment. The objective of this study was to examine the acute effects of crude oil exposure during zebrafish ELS on pronephros function by assessing its fluid clearance capacity and glomerular filtration integrity. Following a 72-h exposure to control conditions, 20% or 40% dilutions of high-energy water-accommodated fractions (HEWAF) of DWH crude oil, zebrafish were injected into the common cardinal vein either with fluorescein-labeled (FITC) 70-kDa dextran to assess glomerular filtration integrity or with FITC-inulin to assess pronephric clearance capacity. Fluorescence was quantified after the injections at predetermined time intervals by fluorescence microscopy. The results demonstrated a diminished pronephric fluid clearance capacity and failed glomerular perfusion when larvae were exposed to 40% HEWAF dilutions, whereas only a reduced glomerular filtration selectivity was observed in zebrafish previously exposed to the 20% HEWAF dilution.

Microplastics: A Matter of the Heart (and Vascular System)

Plastic use dramatically increased over the past few years. Besides obvious benefits, the consequent plastic waste and mismanagement in disposal have caused ecological problems. Plastic abandoned in the environment is prone to segregation, leading to the generation of microplastics (MPs) and nanoplastics (NPs), which can reach aquatic and terrestrial organisms. MPs/NPs in water can access fish's bodies through the gills, triggering an inflammatory response in loco. Furthermore, from the gills, plastic fragments can be transported within the circulatory system altering blood biochemical parameters and hormone levels and leading to compromised immunocompetence and angiogenesis. In addition, it was also possible to observe an unbalanced ROS production, damage in vascular structure, and enhanced thrombosis. MPs/NPs led to cardiotoxicity, pericardial oedema, and impaired heart rate in fish cardiac tissue. MPs/NPs effects on aquatic organisms pose serious health hazards and ecological consequences because they constitute the food chain for humans. Once present in the mammalian body, plastic particles can interact with circulating cells, eliciting an inflammatory response, with genotoxicity and cytotoxicity of immune cells, enhanced haemolysis, and endothelium adhesion. The interaction of MPs/NPs with plasma proteins allows their transport to distant organs, including the heart. As a consequence of plastic fragment internalisation into cardiomyocytes, oxidative stress was increased, and metabolic parameters were altered. In this scenario, myocardial damage, fibrosis and impaired electrophysiological values were observed. In summary, MPs/NPs are an environmental stressor for cardiac function in living organisms, and a risk assessment of their influence on the cardiovascular system certainly merits further analysis.

Study on the mechanism of liver toxicity induced by acenaphthene in zebrafish

Acenaphthene is a polycyclic aromatic hydrocarbon (PAH) that is a widely distributed environmental pollutant that accumulates in organisms and leads to health risks in humans. Although acenaphthene is reported to be toxic to aquatic organisms, its effects of acenaphthene on the livers of these organisms have not been evaluated. Here, zebrafish were used as an experimental model. Zebrafish larvae were exposed to 4.5, 5.5, and 6.5 mg/L acenaphthene for 72 h while adult zebrafish were exposed to 1.5, 2, and 2.5 mg/L acenaphthene for 28 days. We investigated the mechanism by which acenaphthene causes liver toxicity in zebrafish. The results showed that acenaphthene affected the early development of zebrafish and led to mitochondrial damage by promoting the production of reactive oxygen species (ROS) resulting in oxidative stress. The expression of genes related to inflammation and apoptosis was analyzed, observing up-regulation of the pro-inflammatory factors IL-8, TNF-α, and IL-6. The pro-apoptotic genes p53, Caspase-3, and Bax and the Bax/Bcl-2 ratio were up-regulated, while the anti-apoptotic gene Bcl-2 was down-regulated. In addition, we investigated the effects of acenaphthene on liver metabolism. When exposed to acenaphthene, the glycogen content of the liver decreased, while lipid accumulation increased together with alterations in related indicators of liver metabolism. In conclusion, acenaphthene induced oxidative stress through ROS production, leading to mitochondrial damage and activation of pathways associated with inflammation and apoptosis, resulting in hepatotoxicity. This affects normal liver metabolism. Our results revealed the mechanism of hepatotoxicity in zebrafish acenaphthene, and provided new evidence for a more comprehensive understanding of the hepatotoxicity of acenaphthene.

Evaluation of developmental toxicity in zebrafish embryos and antiproliferative potential against human tumor cell lines of new derivatives containing 4-nitrophenyl group

The aim of the studies was to evaluate the antiproliferative potential against human tumor cell lines of newly synthetized derivatives containing 4-nitrophenyl group, as well as its impact on developmental toxicity in zebrafish model. We selected 1-(4-nitrobenzoyl)-4-ethylsemicarbazide (APS-1) and 1-[(4-nitrophenyl)acetyl]-4-hexyl-thiosemicarbazide (APS-18) for research. The antiproliferative properties of semicarbazide derivatives were assessed against human cancer cell lines derived from hepatocellular adenocarcinoma (HepG2), renal cell carcinoma (769-P), non-small cell lung cancer (NCI-H1563) and glioblastoma multiforme (LN229) in comparison to the physiological human embryonic kidney (HEK-293) cell line. The influence of the tested substances on the cell cycle and apoptosis was also evaluated. Fish embryo acute toxicity test (FET) was performed based on OECD Guidelines (Test No. 236), and was carried out for the first 5 days post fertilization. The following concentrations of APS-1 and APS-18 were tested: 125-2000 μM and 0.125-1000 μM, respectively. The presented studies on the antiproliferative properties of the new semicarbazide derivatives showed that the compounds APS-1 and APS-18 reduce the viability of human tumor lines. Particularly noteworthy is the strong and selective antiproliferative activity of APS-18 against all neoplastic cell lines, in particular against glioblastoma. Against this tumor line, the compound APS-1 showed an effective inhibitory effect. In the FET we noted that the direct exposure of zebrafish embryos to APS-1 and APS-18 in used range of concentration did not cause morphological abnormalities, including cardiotoxicity. On basis of obtained outcomes it could be concluded that APS-1 and APS-18 may constitute models for further research, design and synthesis of new, safer drugs with more favorable anticancer properties.

Review of ecologically relevant in vitro bioassays to supplement current in vivo tests for whole effluent toxicity testing - Part 1: Apical endpoints

Whole effluent toxicity (WET) testing is commonly used to ensure that wastewater discharges do not pose an unacceptable risk to receiving environments. Traditional WET testing involves exposing animals to (waste)water samples to assess four major ecologically relevant apical endpoints: mortality, growth, development, and reproduction. Recently, with the widespread implementation of the 3Rs to replace, reduce and refine the use of animals in research and testing, there has been a global shift away from in vivo testing towards in vitro alternatives. However, prior to the inclusion of in vitro bioassays in regulatory frameworks, it is critical to establish their ecological relevance and technical suitability. This is part 1 of a two-part review that aims to identify in vitro bioassays that can be used in WET testing and relate them to ecologically relevant endpoints through toxicity pathways, providing the reader with a high-level overview of current capabilities. Part 1 of this review focuses on four apical endpoints currently included in WET testing: mortality, growth, development, and reproduction. For each endpoint, the link between responses at the molecular or cellular level, that can be measured in vitro, and the adverse outcome at the organism level were established through simplified toxicity pathways. Additionally, literature from 2015 to 2020 on the use of in vitro bioassays for water quality assessments was reviewed to identify a list of suitable bioassays for each endpoint. This review will enable the prioritization of relevant endpoints and bioassays for incorporation into WET testing.

Age matters: Comparing life-stage responses to diluted bitumen exposure in coho salmon (Oncorhynchus kisutch)

Millions of liters of diluted bitumen (dilbit), a crude oil product from Canada's oil sands region, is transported through critical Pacific salmon habitat each day. While the toxicity of the water-soluble fraction of dilbit (WSFd) to early life-stages of salmon is known, quantitative data on life-stage differences in sensitivity to WSFd is missing. To fill this knowledge gap, we exposed two juvenile life-stages of coho salmon (O. kisutch) in parallel to very low (parts per billion), environmentally-relevant concentrations of WSFd for acute (48 h) and sub-chronic (4 wk) durations. The relative sensitivities of the two life-stages (fry and parr) were assessed by comparing the timing and magnitude of biological responses using common organismal and molecular endpoints of crude oil exposure. A significant reduction in body condition occurred in both fry and parr after 4 wk exposure to WSFd. Both life-stages also experienced a concentration-dependent decrease in time-to-loss-of-equilibrium during a hypoxia challenge test at both 48 h and 4 wk of exposure. Although organismal responses were similar, molecular responses were distinct between life-stages. In general, unexposed fry had higher baseline values of hepatic phase I biotransformation indicators than unexposed parr, but induction of EROD activity and cyp1a mRNA expression in response to WSFd exposure was greater in parr than in fry. Neither gst nor hsp70 mRNA expression, markers of phase II biotransformation and cell stress, respectively, were reliably altered by WSFd exposure in either life-stage. Taken together, results of this study do not support differential sensitivities of coho fry and parr to WSFd. All the same, the potential for ontogenic differences in the expression and induction of phase I biotransformation need to be considered because age does matter for these endpoints if they are used as bioindicators of exposure in post-spill impact assessments.

Emerging bio-dispersant and bioremediation technologies as environmentally friendly management responses toward marine oil spill: A comprehensive review

Marine oil spills emanating from wells, pipelines, freighters, tankers, and storage facilities draw public attention and necessitate quick and environmentally friendly response measures. It is sometimes feasible to contain the oil with booms and collect it with skimmers or burn it, but this is impracticable in many circumstances, and all that can be done without causing further environmental damage is adopting natural attenuation, particularly through microbial biodegradation. Biodegradation can be aided by carefully supplying biologically accessible nitrogen and phosphorus to alleviate some of the microbial growth constraints at the shoreline. This review discussed the characteristics of oil spills, origin, ecotoxicology, health impact of marine oils spills, and responses, including the variety of remedies and responses to oil spills using biological techniques. The different bioremediation and bio-dispersant treatment technologies are then described, with a focus on the use of green surfactants and their advances, benefits/drawbacks. These technologies were thoroughly explained, with a timeline of research and recent studies. Finally, the hurdles that persist as a result of spills are explored, as well as the measures that must be taken and the potential for the development of existing treatment technologies, all of which must be linked to the application of integrated procedures.

Embryonic cardio-respiratory impairments in rainbow trout (Oncorhynchus mykiss) following exposure to hydraulic fracturing flowback and produced water

During hydraulic fracturing, wastewaters - termed flowback and produced water (FPW) - are created as a by-product during hydrocarbon extraction. Given the large volumes of FPW that a single well can produce, and the history of FPW release to surface water bodies, it is imperative to understand the hazards that hydraulic fracturing and FPW pose to aquatic biota. Using rainbow trout embryos as model organisms, we investigated impacts to cardio-respiratory system development and function following acute (48 h) and sub-chronic (28-day) FPW exposure by examining occurrences of developmental deformities, rates of embryonic respiration (MO₂), and changes in expression of critical cardiac-specific genes. FPW-exposed embryos had significantly increased rates of pericardial edema, yolk-sac edema, and tail/trunk curvatures at hatch. Furthermore, when exposed at three days post-fertilization (dpf), acute 5% FPW exposures significantly increased embryonic MO₂ through development until 15 dpf, where a switch to significantly reduced MO₂ rates was subsequently recorded. A similar trend was observed during sub-chronic 1% FPW exposures. Interestingly, at certain specific developmental timepoints, previous salinity exposure seemed to affect embryonic MO₂; a result not previously observed. Following acute FPW exposures, embryonic genes for cardiac development and function were significantly altered, although at termination of sub-chronic exposures, significant changes to these same genes were not found. Together, our evidence of induced developmental deformities, modified embryonic MO₂, and altered cardiac transcript expression suggest that cardio-respiratory tissues are toxicologically targeted following FPW exposure in developing rainbow trout. These results may be helpful to regulatory bodies when developing hazard identification and risk management protocols concerning hydraulic fracturing activities.

Pyrene drives reduced brain size during early life exposure in an estuarine fish, the red drum (Sciaenops ocellatus)

Crude oil and the constituent polycyclic aromatic hydrocarbons (PAHs) induce a consistent suite of sub-lethal effects in early life stage fishes. It has been suggested that 3-ring PAHs drive cardiotoxicity and that all other impacts are downstream consequences of these cardiac effects. However, recent studies have documented behavioral alterations that may not be linked to cardiotoxicity. This raises the question of whether the 3-ring PAHs that drive cardiotoxicity are also responsible for the observed neurological impairments. To explore this question, we exposed embryonic red drum (Sciaenops ocellatus) - a species that exhibits greater sensitivity to craniofacial malformations than cardiotoxicity - to individual 2-ring, 3-ring, and 4-ring PAHs for 48 h after which they were assessed for sub-lethal developmental malformations. No effects were observed following exposure to naphthalene, anthracene, dibenzothiophene, phenanthrene and fluorene at doses equivalent to the ΣPAH₅₀ effective concentration 50 for craniofacial malformation in red drum. Conversely, pyrene caused complete lethality at the original dose, and a 5× diluted dose resulted in significantly reduced brain size and spine length. Similar sub-lethal effects were also observed in chrysene at the 1× dose. These results indicate that 4-ring PAHs are driving malformations in developing red drum and suggest oil induced impairments in this species are not a downstream consequence of 3-ring PAH induced cardiac malformations.

Transgenerational effects of parental crude oil exposure on the morphology of adult Fundulus grandis

The current study involved exposing adult F0 Gulf killifish (Fundulus grandis) to Macondo-252 oil for 36 to 44 days and assessing the effects of this oiling on the swimming performance and morphology in two generations of progeny reared in clean water. Following exposure to oil, the F0 fish were used as broodstock to generate four lineages of F1 fish using a full-matrix mating design derived from the gametes of clean and oil-exposed parents. Later, the four lineages of F1 fish were used as broodstock to create an F2 generation of the same four lineages. We found few differences in embryonic outcome (% dead,% hatched, and% unhatched) in any of the four lineages of F1 and F2 fish. However, as adults, F1 and F2 fish derived from oil-exposed males from the F0 generation had significantly lower critical swimming speeds (U_crit) than both the control and maternally oil-exposed lineages. Additionally, progeny of oil-exposed fish had altered body shape based on the statistical analysis of two-dimensional landmark-based geometric morphometrics. Fish from oil-exposed lineages showed increased body depth, altered spinal curvature, and changes in the upward angle of projection of the head. Both generations had a significant main effect of maternal and paternal oil exposure on shape; however, F0 paternal oil exposure explained more of the variance in shape across both generations relative to F0 maternal exposure. Our findings demonstrate that parental exposure to oil can impact the shape and aerobic swimming capacity of offspring for at least two generations after the original paternal oiling.

Biological effects of crude oil vapor. IV. Cardiovascular effects

Workers in the oil and gas extraction industry are at risk of inhaling volatile organic compounds. Epidemiological studies suggest oil vapor inhalation may affect cardiovascular health. Thus, in this hazard identification study we investigated the effects of inhalation of crude oil vapor (COV) on cardiovascular function. Male rats were exposed to air or COV (300 ppm) for 6 h (acute), or 6 h/day × 4 d/wk. × 4 wk. (sub-chronic). The effects of COV inhalation were assessed 1, 28, and 90 d post-exposure. Acute exposure to COV resulted in reductions in mean arterial and diastolic blood pressures 1 and 28 d after exposure, changes in nitrate-nitrite and H2O2 levels, and in the expression of transcripts and proteins that regulate inflammation, vascular remodeling, and the synthesis of nitric oxide (NO) in the heart and kidneys. The sub-chronic exposure resulted in a reduced sensitivity to α1-adrenoreceptor-mediated vasoconstriction in vitro 28 d post-exposure, and a reduction in oxidative stress in the heart. Sub-chronic COV exposure led to alterations in the expression of NO synthases and anti-oxidant enzymes, which regulate inflammation and oxidative stress in the heart and kidneys. There seems to be a balance between changes in the expression of transcripts associated with the generation of reactive oxygen species (ROS) and antioxidant enzymes. The ability of antioxidant enzymes to reduce or inhibit the effects of ROS may allow the cardiovascular system to adapt to acute COV exposures. However, sub-chronic exposures may result in longer-lasting negative health consequences on the cardiovascular system.

Morphological and cardiac alterations after crude oil exposure in the early-life stages of the tropical gar (Atractosteus tropicus)

Fish development can be affected by environmental pollutants such as crude oil (anthropogenic or natural sources), causing alterations especially in cardiac function and morphology. Most such studies have focused on saltwater species, whereas studies in freshwater fishes are scant. The objective of the current study was to evaluate the effects of crude oil exposure (as 0, 5, 10, 15, or 20% high-energy water accommodated fractions, HEWAF) on cardiac function and edema formation during two early periods of development (embryo and eleuteroembryo, 48 h each) individually using the tropical gar Atractosteus tropicus as a model. Embryos did not exhibit alterations in body mass, total length, condition factor, and cardiac function as a function of oil. In contrast, eleuteroembryos proved to be more sensitive and exhibited increased body mass, total length, and condition factor, decreased heart rate and phenotypic alterations such as cardiac dysmorphia (tubular hearts) and spine curvature at high concentrations of HEWAF. Moreover, edema formation was observed in both stages This study shows different functional responses of A. tropicus after crude oil exposure and provides useful information of the developmental impacts of these compounds on the early life stages of freshwater tropical fishes.

The developing zebrafish kidney is impaired by Deepwater Horizon crude oil early-life stage exposure: A molecular to whole-organism perspective

Crude oil is known to induce developmental defects in teleost fish exposed during early life stages (ELSs). While most studies in recent years have focused on cardiac endpoints, evidence from whole-animal transcriptomic analyses and studies with individual polycyclic aromatic hydrocarbons (PAHs) indicate that the developing kidney (i.e., pronephros) is also at risk. Considering the role of the pronephros in osmoregulation, and the common observance of edema in oil-exposed ELS fish, surprisingly little is known regarding the effects of oil exposure on pronephros development and function. Using zebrafish (Danio rerio) ELSs, we assessed the transcriptional and morphological responses to two dilutions of high-energy water accommodated fractions (HEWAF) of oil from the Deepwater Horizon oil spill using a combination of qPCR and whole-mount in situ hybridization (WM-ISH) of candidate genes involved in pronephros development and function, and immunohistochemistry (WM-IHC). To assess potential functional impacts on the pronephros, three 24 h osmotic challenges (2 hypo-osmotic, 1 near iso-osmotic) were implemented at two developmental time points (48 and 96 h post fertilization; hpf) following exposure to HEWAF. Changes in transcript expression level and location specific to different regions of the pronephros were observed by qPCR and WM-ISH. Further, pronephros morphology was altered in crude oil exposed larvae, characterized by failed glomerulus and neck segment formation, and straightening of the pronephric tubules. The osmotic challenges at 96 hpf greatly exacerbated edema in both HEWAF-exposed groups regardless of osmolarity. By contrast, larvae at 48 hpf exhibited no edema prior to the osmotic challenge, but previous HEWAF exposure elicited a concentration-response increase in edema at hypo-osmotic conditions that appeared to have been largely alleviated under near iso-osmotic conditions. In summary, ELS HEWAF exposure impaired proper pronephros development in zebrafish, which coupled with cardiotoxic effects, most likely reduced or inhibited pronephros fluid clearance capacity and increased edema formation.

Oil induced cardiac effects in embryonic sheepshead minnows, Cyprinodon variegatus

Following the Deepwater Horizon oil spill in April 2010, much research has been conducted on the cardiotoxic effects of oil on fish. Sensitive life history stages, such as the embryonic period, have been targeted to elucidate the effects of polycyclic aromatic hydrocarbons (PAHs) on the developing cardiovascular systems of fish. However, much of this research has focused on rapidly developing pelagic species, with little emphasis on estuarine species with longer embryological periods. Moreover, previous studies have used heart rate as the primary endpoint to measure cardiac performance in embryos and larvae; an endpoint that on its own may overlook impairment in cardiac performance. This study aims to fill these knowledge gaps and provide a more holistic approach for assessing the effects of PAHs on cardiac function by exposing sheepshead minnow (Cyprinodon variegatus) embryos to two oil doses (150 and 300 μg/L tPAH nominally) throughout embryonic development and measuring cardiac responses through the identification of cardiotoxic phenotypes (pericardial edema) as well as calculation of cardiac output at 4 days post fertilization. Results of this study show significant increases in pericardial edema at both oil doses relative to controls as well as significantly reduced cardiac output - driven by reductions in ventricular stroke volume. This study is one of the first to assess cardiac output in embryonic fish exposed to oil and methods described here allow for more physiologically relevant measures of cardiac performance in early life stages through established and non-invasive measures.

Evaluation of cardiotoxicity in Amazonian fish Bryconops caudomaculatus by acute exposure to aluminium in an acidic environment

Aluminium (Al) is soluble in acidic waters and may become toxic to organisms. In this study, the acute effects of two Al concentrations were evaluated in the Amazonian fish Bryconops caudomaculatus. Antioxidant responses and lipid damage were assessed in gills, liver and muscle, along with the electrocardiography (ECG) and characterization of cardiac complex and wave intervals. Fish were essayed as follows: two control groups at neutral and acidic pH and two exposure groups at acidic pH (0.3 mg/L and 3.0 mg/L Al). Water samples were collected at 0h, 24h and 48h, for chloride (Cl^-), fluoride (F^-) and sulphate (SO₄^2-) ion analyses, while total Al was quantified in muscle. Concentrations of Cl^- and SO₄^2- were constant over time whereas F^- was not detected. Total Al concentrations in water and muscle were concentration-dependent. Antioxidant responses, total antioxidant capacity against peroxyl radicals (ACAP) and glutathione S-transferase were not triggered in fish tissues exposed to 0.3 mg/L Al; however, fish exposed to 3.0 mg/L Al presented increased and reduced ACAP in gills and liver, respectively. No changes in lipoperoxidation levels occurred among groups. Fish exposed to 0.3 mg/L Al showed prolonged intervals in ECG as a reflection of low heart rate (HR), with sinus bradycardia. Moreover, there was a marked prolongation of the PQ interval (time between the atrial activity and the start of ventricular activity), indicating interference on the cardiac cell automaticity. Fish exposed to the highest concentration of Al showed reduced wave intervals as a consequence of increased HR, with sinus arrhythmia, while ECG tracings did not present P waves (atrial contraction), indicating an atrioventricular blockade. In conclusion, 48h exposure sufficed to cause cardiotoxicity in B. caudomaculatus at either Al concentration. However, as oxidative stress was not observed, such cardiac alterations seem to be reversible under the experimental conditions established herein.

Cardiac dysfunction affects eye development and vision by reducing supply of lipids in fish

Developing organisms are especially vulnerable to environmental stressors. Crude oil exposure in early life stages of fish result in multiple functional and developmental defects, including cardiac dysfunction and abnormal and smaller eyes. Phenanthrene (Phe) has a reversible impact on cardiac function, and under exposure Phe reduces cardiac contractility. Exposure to a known L-type channel blocker, nicardipine hydrochloride (Nic) also disrupts cardiac function and creates eye deformities. We aimed to investigate whether cardiac dysfunction was the major underlying mechanism of crude oil-, Phe- and Nic-induced eye malformations. We exposed Atlantic haddock (Melanogrammus aeglefinus) early embryos to Nic and crude oil (Oil) and late embryos/early larvae to Phe exposure. All three exposures resulted in cardiac abnormalities and lead to severe, eye, jaw and spinal deformities at early larval stages. At 3 days post hatching, larvae from the exposures and corresponding controls were dissected. Eyes, trunk, head and yolk sac were subjected to lipid profiling, and eyes were also subjected to transcriptomic profiling. Among most enriched pathways in the eye transcriptomes were fatty acid metabolism, calcium signaling and phototransduction. Changes in lipid profiles and the transcriptome suggested that the dysfunctional and abnormal eyes in our exposures were due to both disruption of signaling pathways and insufficient supply of essential fatty acids and other nutrients form the yolk.

Toxicity and developmental effects of Arctic fuel oil types on early life stages of Atlantic cod (Gadus morhua)

Due to the heavy fuel oil (HFO) ban in Arctic maritime transport and new legislations restricting the sulphur content of fuel oils, new fuel oil types are continuously developed. However, the potential impacts of these new fuel oil types on marine ecosystems during accidental spills are largely unknown. In this study, we studied the toxicity of three marine fuel oils (two marine gas oils with low sulphur contents and a heavy fuel oil) in early life stages of cod (Gadus morhua). Embryos were exposed for 4 days to water-soluble fractions of fuel oils at concentrations ranging from 4.1 - 128.3 µg TPAH/L, followed by recovery in clean seawater until 17 days post fertilization. Exposure to all three fuel oils resulted in developmental toxicity, including severe morphological changes, deformations and cardiotoxicity. To assess underlying molecular mechanisms, we studied fuel oil-mediated activation of aryl hydrocarbon receptor (Ahr) gene battery and genes related to cardiovascular, angiogenesis and osteogenesis pathways. Overall, our results suggest comparable mechanisms of toxicity for the three fuel oils. All fuel oils caused concentration-dependant increases of cyp1a mRNA which paralleled ahrr, but not ahr1b transcript expression. On the angiogenesis and osteogenesis pathways, fuel oils produced concentration-specific transcriptional effects that were either increasing or decreasing, compared to control embryos. Based on the observed toxic responses, toxicity threshold values were estimated for individual endpoints to assess the most sensitive molecular and physiological effects, suggesting that unresolved petrogenic components may be significant contributors to the observed toxicity.

Gene co-expression network analysis reveals mechanisms underlying ozone-induced carbamazepine toxicity in zebrafish (Danio rerio) embryos

Sewage effluent ozonation can reduce concentrations of chemical pollutants including pharmaceutical residues. However, the formation of potentially toxic ozonation byproducts (OBPs) is a matter of concern. This study sought to elucidate toxicity mechanisms of ozonated carbamazepine (CBZ), an anti-epileptic drug frequently detected in sewage effluents and surface water, in zebrafish embryos (Danio rerio). Embryos were exposed to ozonated and non-ozonated CBZ from 3 h post-fertilization (hpf) until 144 hpf. Embryotoxicity endpoints (proportion of dead and malformed embryos) were assessed at 24, 48, and 144 hpf. Heart rate was recorded at 48 hpf. Exposure to ozonated CBZ gave rise to cardiovascular-related malformations and reduced heart rate. Moreover, embryo-larvae exposed to ozonated CBZ displayed a lack of swim bladder inflation. Hence, the expression patterns of CBZ target genes involved in cardiovascular and embryonal development were investigated through a stepwise gene co-expression analysis approach. Two co-expression networks and their upstream transcription regulators were identified, offering mechanistic explanations for the observed toxicity phenotypes. The study presents a novel application of gene co-expression analysis elucidating potential toxicity mechanisms of an ozonated pharmaceutical with environmental relevance. The resulting data was used to establish a putative adverse outcome pathway (AOP).

Low-level embryonic crude oil exposure disrupts ventricular ballooning and subsequent trabeculation in Pacific herring

There is a growing awareness that transient, sublethal embryonic exposure to crude oils cause subtle but important forms of delayed toxicity in fish. While the precise mechanisms for this loss of individual fitness are not well understood, they involve the disruption of early cardiogenesis and a subsequent pathological remodeling of the heart much later in juveniles. This developmental cardiotoxicity is attributable, in turn, to the inhibitory actions of crude oil-derived mixtures of polycyclic aromatic compounds (PACs) on specific ion channels and other proteins that collectively drive the rhythmic contractions of heart muscle cells via excitation-contraction coupling. Here we exposed Pacific herring (Clupea pallasi) embryos to oiled gravel effluent yielding ΣPAC concentrations as low as ~ 1 μg/L (64 ng/g in tissues). Upon hatching in clean seawater, and following the depuration of tissue PACs (as evidenced by basal levels of cyp1a gene expression), the ventricles of larval herring hearts showed a concentration-dependent reduction in posterior growth (ballooning). This was followed weeks later in feeding larvae by abnormal trabeculation, or formation of the finger-like projections of interior spongy myocardium, and months later with hypertrophy (overgrowth) of the spongy myocardium in early juveniles. Given that heart muscle cell differentiation and migration are driven by Ca²⁺-dependent intracellular signaling, the observed disruption of ventricular morphogenesis was likely a secondary (downstream) consequence of reduced calcium cycling and contractility in embryonic cardiomyocytes. We propose defective trabeculation as a promising phenotypic anchor for novel morphometric indicators of latent cardiac injury in oil-exposed herring, including an abnormal persistence of cardiac jelly in the ventricle wall and cardiomyocyte hyperproliferation. At a corresponding molecular level, quantitative expression assays in the present study also support biomarker roles for genes known to be involved in muscle contractility (atp2a2, myl7, myh7), cardiomyocyte precursor fate (nkx2.5) and ventricular trabeculation (nrg2, and hbegfa). Overall, our findings reinforce both proximal and indirect roles for dysregulated intracellular calcium cycling in the canonical fish early life stage crude oil toxicity syndrome. More work on Ca²⁺-mediated cellular dynamics and transcription in developing cardiomyocytes is needed. Nevertheless, the highly specific actions of ΣPAC mixtures on the heart at low, parts-per-billion tissue concentrations directly contravene classical assumptions of baseline (i.e., non-specific) crude oil toxicity.

Combined effects of crude oil exposure and warming on eggs and larvae of an arctic forage fish

Climate change, along with environmental pollution, can act synergistically on an organism to amplify adverse effects of exposure. The Arctic is undergoing profound climatic change and an increase in human activity, resulting in a heightened risk of accidental oil spills. Embryos and larvae of polar cod (Boreogadus saida), a key Arctic forage fish species, were exposed to low levels of crude oil concurrently with a 2.3 °C increase in water temperature. Here we show synergistic adverse effects of increased temperature and crude oil exposure on early life stages documented by an increased prevalence of malformations and mortality in exposed larvae. The combined effects of these stressors were most prevalent in the first feeding larval stages despite embryonic exposure, highlighting potential long-term consequences of exposure for survival, growth, and reproduction. Our findings suggest that a warmer Arctic with greater human activity will adversely impact early life stages of this circumpolar forage fish.

Environmental fate of cigarette butts and their toxicity in aquatic organisms: A comprehensive systematic review

Cigarette butts (CBs) are the most frequently littered pieces of environmental wastes which are released both directly and indirectly into the environment and finally may reach aquatic environments and contaminate aquatic biomes. However, to date, there is no comprehensive review on the extent and magnitude of the potential effects of CBs on aquatic organisms. Hence, a systematic review of published studies was conducted in this paper to survey the fate of CBs in the aquatic environments and also the impacts of exposure to CBs on survival, growth, and reproduction of aquatic organisms. The gathered data showed that the leachates of CBs in the aquatic environment could extremely be toxic for various organisms and increasing the exposure time, increases the mortality rate. In addition, smoked filtered CBs with tobacco remnants have higher mortality rate compared to unsmoked filtered butts (USFs) for Hymenochirus curtipes, Clarias gariepinus, tidepool snails, Atherinops affinis and Pimephales promelas. The fate of CBs in the aquatic environments is affected by various factors, and prior to sinking they are floated for a long time (long distance). Hence, CBs and their associated toxic chemicals might be ingested by diverse aquatic organisms. However, further studies are necessary to understand the exact toxicity of CBs on different freshwater and marine organisms and also their fate in the aquatic media. The results of this review showed the essentiality of regulations to prevent the release of chemical and toxic compounds into the aquatic environments.

Phenotypic and transcriptomic consequences in zebrafish early-life stages following exposure to crude oil and chemical dispersant at sublethal concentrations

To further understand the underlying mechanisms involved in the developmental toxicity of crude oil and chemically dispersed crude oil on fish early-life stages (ELS), zebrafish (Danio rerio) embryos were exposed to GM-2 chemical dispersant (DISP), low-energy water-accommodated fractions (LEWAF), and chemically enhanced WAF (CEWAF) of Merey crude oil at sublethal concentrations for 120 h. We employed the General Morphology Score (GMS) and General Teratogenic Score (GTS) systems in conjunction with high-throughput RNA-Seq analysis to evaluate the phenotypic and transcriptomic responses in zebrafish ELS. Results showed that ΣPAHs concentrations in LEWAF and CEWAF solutions were 507.63 ± 80.95 ng·L^-1 and 4039.51 ± 241.26 ng·L^-1, respectively. The GMS and GTS values indicated that CEWAF exposure caused more severe developmental delay and higher frequencies of teratogenic effects than LEWAF exposure. Moreover, no significant change in heart rate was observed in LEWAF treatment, while CEWAF exposure caused a significant reduction in heart rate. LEWAF and CEWAF exposure exhibited an overt change in eye area, with a reduction of 4.0% and 25.3% (relative to the control), respectively. Additionally, no obvious impact on phenotypic development was observed in zebrafish embryo-larvae following DISP exposure. Significant changes in gene expression were detected in LEWAF and CEWAF treatments, with a total of 957 and 2062 differentially expressed genes (DEGs), respectively, while DISP exposure altered only 91 DEGs. Functional enrichment analysis revealed that LEWAF and CEWAF exposure caused significant perturbations in the pathways associated with phototransduction, retinol metabolism, metabolism of xenobiotics by cytochrome P450, and immune response-related pathways. Our results provide more valid evidence to corroborate the previous suggestion that ocular impairment is an equal or possibly more sensitive biomarker than cardiotoxicity in fish ELS exposed to oil-derived PAHs. All these findings could gain further mechanistic insights into the effects of crude oil and chemical dispersant on fish ELS.