Cardiac function and survival are affected by crude oil in larval red drum, Sciaenops ocellatus

Exposure to the Polychlorinated biphenyl mixture Aroclor 1254 elicits neurological and cardiac developmental effects in early life stage zebrafish (Danio rerio)

The goal of this study was to compare the bioaccumulation of the PCB mixture Aroclor 1254 in zebrafish to cardiac and neurologic outcomes. The establishment of effect concentrations (ECs) for cardiac and neurotoxic effects of PCBs in early life stage fish is challenging due to a lack of measured PCB concentrations in test media (e.g., fish tissue), the lack of standard exposure methods, and the propensity of PCBs to adsorb to test glassware and materials resulting in discrepancies in ECs from different studies with similar endpoints. Reporting tissue concentrations in test organisms will allow for standardization across different tests and thus may improve estimations of effect thresholds. Early life stage zebrafish (Danio rerio) are a common environmental toxicological model well represented within the literature, making them ideal for comparisons across multiple studies. Embryos were exposed at 6 h post fertilization (hpf) to aqueous Aroclor 1254 for 96 h with or without renewal in addition to a PCB 126 positive control for cardiotoxicity. PCB concentrations were measured in both exposure solutions and tissue samples. Measured concentrations of Aroclor 1254 in test solutions ranged from 8.7% to 870% of nominal concentrations. Heart rate, pericardial edema, and neurological endpoints (eye tremors) were measured in 102 hpf larvae. Pericardial edema was not present in Aroclor 1254-treated zebrafish but was observed in those exposed to PCB-126. Concentration-dependent bradycardia was observed in zebrafish exposed to Aroclor 1254 and PCB-126. Similarly, a concentration-dependent increase in eye tremor behavior was observed in embryos exposed to Aroclor 1254. Data produced by this study demonstrate novel toxicological effects of Aroclor 1254 and highlight the importance of measuring PCBs in both exposure and receptor media.

Toxicity of the oil spilled on the Brazilian coast at different degrees of natural weathering to early life stages of the zebrafish Danio rerio

Toxicity of water accommodated fractions (WAF) from the oil spilled on the Brazilian coast at different stages of weathering were investigated using Danio rerio. Weathering stages included emulsified oil that reached the coast (OM) and oil collected 50 days later deposited on beach sand (OS) or adhered to shore rocks (OR). Parent and alkylated naphthalenes decreased whereas phenanthrenes increased from less weathered WAF-OM to more weathered WAF-OS and WAF-OR. More weathered WAF-OS and WAF-OR were more potent inducers of zebrafish developmental delay, suggesting that parent and alkylated phenanthrenes are involved. However, less weathered WAF-OM was a more potent inducer of failure in swim-bladder inflation than more weathered WAF-OS and WAF-OR, suggesting that parent and alkylated naphthalenes are involved. Decreases in heart rates and increased heart and skeletal deformities were observed in exposed larvae. Lowest observed effect concentrations for different developmental toxicity endpoints are within environmentally relevant polycyclic aromatic hydrocarbon concentrations.

A larval zebrafish model of cardiac physiological recovery following cardiac arrest and myocardial hypoxic damage

Contemporary cardiac injury models in zebrafish larvae include cryoinjury, laser ablation, pharmacological treatment and cardiac dysfunction mutations. Although effective in damaging cardiomyocytes, these models lack the important element of myocardial hypoxia, which induces critical molecular cascades within cardiac muscle. We have developed a novel, tractable, high throughput in vivo model of hypoxia-induced cardiac damage that can subsequently be used in screening cardioactive drugs and testing recovery therapies. Our potentially more realistic model for studying cardiac arrest and recovery involves larval zebrafish (Danio rerio) acutely exposed to severe hypoxia (PO2=5-7 mmHg). Such exposure induces loss of mobility quickly followed by cardiac arrest occurring within 120 min in 5 days post fertilization (dpf) and within 40 min at 10 dpf. Approximately 90% of 5 dpf larvae survive acute hypoxic exposure, but survival fell to 30% by 10 dpf. Upon return to air-saturated water, only a subset of larvae resumed heartbeat, occurring within 4 min (5 dpf) and 6-8 min (8-10 dpf). Heart rate, stroke volume and cardiac output in control larvae before hypoxic exposure were 188±5 bpm, 0.20±0.001 nL and 35.5±2.2 nL/min (n=35), respectively. After briefly falling to zero upon severe hypoxic exposure, heart rate returned to control values by 24 h of recovery. However, reflecting the severe cardiac damage induced by the hypoxic episode, stroke volume and cardiac output remained depressed by ∼50% from control values at 24 h of recovery, and full restoration of cardiac function ultimately required 72 h post-cardiac arrest. Immunohistological staining showed co-localization of Troponin C (identifying cardiomyocytes) and Capase-3 (identifying cellular apoptosis). As an alternative to models employing mechanical or pharmacological damage to the developing myocardium, the highly reproducible cardiac effects of acute hypoxia-induced cardiac arrest in the larval zebrafish represent an alternative, potentially more realistic model that mimics the cellular and molecular consequences of an infarction for studying cardiac tissue hypoxia injury and recovery of function.

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.

Dual effect of polyaromatic hydrocarbons on sarco(endo)plasmic reticulum calcium ATPase (SERCA) activity of a teleost fish (Oncorhynchus mykiss)

Polycyclic aromatic hydrocarbons (PAHs) are embryo- and cardiotoxic to fish that might be associated with improper intracellular Ca2+ management. Since sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a major regulator of intracellular Ca2+, the SERCA activity and the contractile properties of rainbow trout (Oncorhynchus mykiss) ventricle were measured in the presence of 3- and 4-cyclic PAHs. In unfractionated ventricular homogenates, acute exposure of SERCA to 0.1-1.0 μM phenanthrene (Phe), retene (Ret), fluoranthene (Flu), or pyrene (Pyr) resulted in concentration-dependent increase in SERCA activity, except for the Flu exposure, with maximal effects of 49.7-83 % at 1 μM. However, PAH mixture did not affect the contractile parameters of trout ventricular strips. Similarly, all PAHs, except Ret, increased the myotomal SERCA activity, but with lower effect (27.8-40.8 % at 1 μM). To investigate the putative chronic effects of PAHs on SERCA, the atp2a2a gene encoding trout cardiac SERCA was expressed in human embryonic kidney (HEK) cells. Culture of HEK cells in the presence of 0.3-1.0 μM Phe, Ret, Flu, and Pyr for 4 days suppressed SERCA expression in a concentration-dependent manner, with maximal inhibition of 49 %, 65 %, 39 % (P < 0.05), and 18 % (P > 0.05), respectively at 1 μM. Current findings indicate divergent effects of submicromolar PAH concentrations on SERCA: stimulation of SERCA activity in acute exposure and inhibition of SERCA expression in chronic exposure. The depressed expression of SERCA is likely to contribute to the embryo- and cardiotoxicity of PAHs by depressing muscle function and altering gene expression.

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.

The effect of chemical dispersion and temperature on the metabolic and cardiac responses to physically dispersed crude oil exposure in larval American lobster (Homarus americanus)

Despite their potential vulnerability to oil spills, little is known about the physiological effects of petroleum exposure and spill responses in cold-water marine animal larvae. We investigated the effects of physically dispersed (water-accommodated fraction, WAF) and chemically dispersed (chemically enhanced WAF, CEWAF; using Slickgone EW) conventional heavy crude oil on the routine metabolic rate and heart rate of stage I larval American lobster (Homarus americanus). We found no effects of 24-h exposure to sublethal concentrations of crude oil WAF or CEWAF at 12 °C. We then investigated the effect of sublethal concentrations of WAFs at three environmentally relevant temperatures (9, 12, 15 °C). The highest WAF concentration increased metabolic rate at 9 °C, whereas it decreased heart rate and increased mortality at 15 °C. Overall, metabolic and cardiac function of American lobster larvae is relatively resilient to conventional heavy crude oil and Slickgone EW exposure, but responses to WAF may be temperature-dependent.

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.

Bridging the lab to field divide: Advancing oil spill biological effects models requires revisiting aquatic toxicity testing

Oil fate and exposure modeling addresses the complexities of oil composition, weathering, partitioning in the environment, and the distributions and behaviors of aquatic biota to estimate exposure histories, i.e., oil component concentrations and environmental conditions experienced over time. Several approaches with increasing levels of complexity (i.e., aquatic toxicity model tiers, corresponding to varying purposes and applications) have been and continue to be developed to predict adverse effects resulting from these exposures. At Tiers 1 and 2, toxicity-based screening thresholds for assumed representative oil component compositions are used to inform spill response and risk evaluations, requiring limited toxicity data, analytical oil characterizations, and computer resources. Concentration-response relationships are employed in Tier 3 to quantify effects of assumed oil component mixture compositions. Oil spill modeling capabilities presently allow predictions of spatial and temporal compositional changes during exposure, which support mixture-based modeling frameworks. Such approaches rely on summed effects of components using toxic units to enable more realistic analyses (Tier 4). This review provides guidance for toxicological studies to inform the development of, provide input to, and validate Tier 4 aquatic toxicity models for assessing oil spill effects on aquatic biota. Evaluation of organisms' exposure histories using a toxic unit model reflects the current state-of the-science and provides an improved approach for quantifying effects of oil constituents on aquatic organisms. Since the mixture compositions in toxicity tests are not representative of field exposures, modelers rely on studies using single compounds to build toxicity models accounting for the additive effects of dynamic mixture exposures that occur after spills. Single compound toxicity data are needed to quantify the influence of exposure duration and modifying environmental factors (e.g., temperature, light) on observed effects for advancing use of this framework. Well-characterized whole oil bioassay data should be used to validate and refine these models.

Acute and Chronic Effects of Crude Oil Water-Accommodated Fractions on the Early Life Stages of Marine Medaka (Oryzias melastigma, McClelland, 1839)

Oil spill is a major marine environmental pollution issue. Research regarding the long-term effects of oil spills on the early life stage of marine fish is still limited. In this study, the potential adverse impact of crude oil from one oil spill accident which occurred in the Bohai Sea on the early life stages of marine medaka (Oryzias melastigma, McClelland, 1839) was evaluated. A 96-h acute test (larvae) and a 21-d chronic test (embryo-larvae) of water-accommodated fractions (WAFs) from crude oil were conducted, respectively. The results of the acute test showed that only the highest concentration of WAFs (100.00%) significantly affected the mortality of larvae (p < 0.01) and that the 96 h-LC₅₀ was 68.92% (4.11 mg·L^-1 expressed as total petroleum hydrocarbons (TPHs)). Larval heart demonstrated histopathological alterations in all WAF-exposed groups. The chronic test results showed that, except for larval mortality, the total hatching success (%)/hatching time of embryos in WAF treatments was not significantly different from those of the control group (p > 0.05), and no malformation was found in surviving larvae after 21 d of exposure. Nevertheless, the exposed embryos and larvae in the highest concentration of WAFs (60.00%) demonstrated significantly reduced heart rate (p < 0.05) and increased mortality (p < 0.01), respectively. Overall, our results indicated that both acute and chronic WAF exposures had adverse impacts on the survival of marine medaka. In the early life stages, the heart of the marine medaka was the most sensitive organ which showed both structural alteration and cardiac dysfunction.

Latent impacts on juvenile rainbow trout (Oncorhynchus mykiss) cardio-respiratory function and swimming performance following embryonic exposures to hydraulic fracturing flowback and produced water

Technologies associated with hydraulic fracturing continue to be prevalent in many regions worldwide. As a result, the production of flowback and produced water (FPW) - a wastewater generated once pressure is released from subterranean wellbores - continues to rise in regions experiencing fracturing activities, while waste management strategies attempt to mitigate compounding burdens of increased FPW production. The heightened production of FPW increases the potential for release to the environment. However, relatively few studies have directly investigated how ecosystems and organisms may be latently affected long after exposures occur. The current study examines rainbow trout exposed in ovo at select critical cardiac developmental time points to differing dilutions and lengths of time (acute versus chronic) to determine how FPW-mediated exposure in ovo may alter later cardiac function and development. After exposure, we allowed fish to grow for ∼ 8 months post-fertilization and measured fish swimming performance, aerobic scope, and cardiac structure of juvenile trout. Acute 48 h embryonic 5% FPW exposure at either 3 days post-fertilization (dpf) or 10 dpf significantly reduced later swimming performance and aerobic scope in juvenile trout. In ovo exposure to 2.5% FPW at 3 dpf yielded significant decreases in these metrics as well, while exposing trout to 2.5% FPW at 10 dpf did not induce as significant effects. Morphometric analyses of heart muscle tissue in all treatments decreased compact myocardium thickness. Chronic 1% FPW in ovo exposure for 28 days induced similar reductions in swimming performance, aerobic scope, and decreased compact myocardium thickness as acute exposures. Overall, our results demonstrate that FPW exposure during egg development ultimately results in persistently impaired heart morphology and resulting physiological (swimming) performance.

Transcriptomic profiling of miR-203a inhibitor and miR-34b-injected zebrafish (Danio rerio) validates oil-induced neurological, cardiovascular and eye toxicity response pathways

The global sequencing of microRNA (miRNA; miR) and integration to downstream mRNA expression profiles in early life stages (ELS) of fish following exposure to crude oil determined consistently dysregulated miRNAs regardless of the oil source or fish species. The overlay of differentially expressed miRNAs and mRNAs into in silico software determined that the key roles of these miRNAs were predicted to be involved in cardiovascular, neurological and visually-mediated pathways. Of these, altered expression of miRNAs, miR-203a and miR-34b were predicted to be primary targets of crude oil. To better characterize the effect of these miRNAs to downstream transcript changes, zebrafish embryos were microinjected at 1 h post fertilization (hpf) with either a miR-203a inhibitor or miR-34b. Since both miRs have been shown to be associated with aryl hydrocarbon receptor (AhR) function, benzo(a)pyrene (BaP), a potent AhR agonist, was used as a potential positive control. Transcriptomic profiling was conducted on injected and exposed larvae at 7 and 72 hpf, and eye morphology assessed following exposure at 72 hpf. The top predicted physiological system disease and functions between differentially expressed genes (DEGs) shared with miR-203a inhibitor-injected and miR-34b-injected embryos were involved in brain formation, and the development of the central nervous system and neurons. When DEGs of miR-203a inhibitor-injected embryos were compared with BaP-exposed DEGs, alterations in nervous system development and function, and abnormal morphology of the neurosensory retina, eye and nervous tissue were predicted, consistent with both AhR and non-AhR pathways. When assessed morphologically, the eye area of miR-203a inhibitor and miR-34b-injected and BaP-exposed embryos were significantly reduced. These results suggest that miR-203a inhibition and miR-34b overexpression contribute to neurological, cardiovascular and eye toxicity responses that are caused by oil and PAH exposure in ELS fish, and are likely mediated through both AhR and non-AhR pathways.

Parental transfer of an antibiotic mixture induces cardiotoxicity in early life-stage zebrafish: A cross-generational study

Antibiotic residues in the aquatic environment have been shown to induce significant adverse effects on the early-life stage development of aquatic organisms, though the underlying molecular mechanisms of these effects have not been well characterized. In this study, we performed global mRNA-miRNA sequencing, canonical pathway analyses, morphological, physiological, immunohistochemical, and behavioral analyses to comprehensively assess the cross-generational cardiotoxicity and mechanisms of antibiotic mixtures in zebrafish. Following parental treatment to 1 and 100 μg/L antibiotic mixtures (15 of the most commonly detected antibiotics) for 150 days, all 15 assessed antibiotics were detected in the F1 eggs, indicating the cross-generational transfer of antibiotics. Global mRNA-miRNA sequencing functional analysis predicted cardiotoxicity in the F1 generation by using the F1 whole fish. Consistent with canonical pathway analyses, significant cardiotoxicity was observed in F1 larvae, as well as the apoptosis of cardiac cells. Furthermore, let-7a-5p regulated the cardiac hypertrophy signaling pathway, suggesting mechanisms of miRNA of let-7 family mediating cross-generational cardiotoxicity of antibiotics in zebrafish. This study lays some groundwork for developing interventions to prevent parental exposure to environmental pollutants such as antibiotics from adversely affecting offspring development.

Early life-stage Deepwater Horizon crude oil exposure induces latent osmoregulatory defects in larval red drum (Sciaenops ocellatus)

Crude oil is known to induce developmental defects in teleost fish exposed during early-life stages (ELSs). A recent study has demonstrated that zebrafish (Danio rerio) larvae acutely exposed to Deepwater Horizon (DHW) crude oil showed transcriptional changes in key genes involved in early kidney (pronephros) development and function, which were coupled with pronephric morphological defects. Given the osmoregulatory importance of the kidney, it is unknown whether ELS effects arising from short-term crude exposures result in long-term osmoregulatory defects, particularly within estuarine fishes likely exposed to DWH oil following the spill. To address this knowledge gap, an acute 72 h exposure to red drum (Sciaenops ocellatus) larvae was performed using high-energy water-accommodated fractions (HEWAFs) of DWH weathered oil to analyze transcriptional changes in genes involved in pronephros development and function by quantitative PCR. To test the latent effects of oil exposure on osmoregulation ability, red drum larvae were first exposed to HEWAF for 24 h. Larvae were then reared in clean seawater for two weeks and a 96 h acute osmotic challenge test was performed by exposing the fish to waters with varying salinities. Latent effects of ELS crude oil exposure on osmoregulation were assessed by quantifying survival during the acute osmotic challenge test and analyzing transcriptional changes at 14 dpf. Results demonstrated that ELS crude oil exposure reduced survival of red drum larvae when challenged in hypoosmotic waters and that latent transcriptional changes in some target pronephric genes were evident, indicating that an affected kidney likely contributed to the increased mortality.

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.

Intraspecific Variation in the Sublethal Effects of Physically and Chemically Dispersed Crude Oil on Early Life Stages of Atlantic Cod (Gadus morhua)

The offshore oil industry in Atlantic Canada necessitates a greater understanding of the potential impacts of oil exposure and spill response measures on cold-water marine species. We used a standardized scoring index to characterize sublethal developmental impacts of physically and chemically dispersed crude oil in early life stages of Atlantic cod (Gadus morhua) and assessed intraspecific variation in the response among cod families. Cod (origin: Scotian Shelf, Canada) were laboratory-crossed to produce embryos from five specific families, which were subsequently exposed prehatch to gradient dilutions of a water-accommodated fraction (WAF) and a chemically enhanced WAF (CEWAF; prepared with Corexit 9500A) for 24 h. Postexposure, live embryos were transferred into filtered seawater and monitored to hatch; then, all live fish had sublethal endpoints assessed using the blue-sac disease (BSD) severity index. In both WAF and CEWAF groups, increasing exposure concentrations (measured as total petroleum hydrocarbons) resulted in an increased incidence of BSD symptoms (impaired swimming ability, increased degree of spinal curvature, yolk-sac edemas) in cod across all families. This positive concentration-dependent increase in BSD was similar between physically (WAF) versus chemically (CEWAF) dispersed oil exposures, indicating that dispersant addition does not exacerbate the effect of crude oil on BSD incidence in cod. Sensitivity varied between families, with some families having less BSD than others with increasing exposure concentrations. To our knowledge, our study is the first to demonstrate the occurrence in fishes of intraspecific variation among families in sublethal responses to oil and dispersant exposure. Our results suggest that sublethal effects of crude oil exposure will not be uniformly observed across cod populations and that sensitivity depends on genetic background. Environ Toxicol Chem 2022;41:1967-1976. © 2022 SETAC.

Counter-historical study of alternative dispersant use in the Deepwater Horizon oil spill response

Recent completion of oil fate modeling and a mass budget of the Deepwater Horizon (DWH) oil spill allows for a counter-historical study using quantitative Comparative Risk Assessment (CRA) methodology. Novel application of subsea dispersant injection (SSDI) during the response reduced surfacing oil, volatile organic carbon emissions, and oil on shorelines. The effectiveness of that application, and potential alternatives had dispersant not been used or been used more aggressively, were evaluated by modifying and comparing the validated oil fate model under different SSDI strategies. A comparison of mass balance results, exposure metrics, and CRA scoring for Valued Ecological Components (VECs) shows the value of SSDI in achieving risk reduction and tradeoffs that were made. Actual SSDI applied during the DWH oil spill reduced exposures to varying degrees for different VECs. Exposures and relative risks across the ecosystem would have been substantially reduced with more effective SSDI.

Transcriptomic responses and apoptosis in larval red drum (Sciaenops ocellatus) co-exposed to crude oil and ultraviolet (UV) radiation

Ultraviolet (UV) radiation can significantly increase the toxicity of polycyclic aromatic hydrocarbons (PAHs) in crude oil to early life stage (ELS) fishes through photo-induced /photo-enhanced toxicity. However, little is known about the sub-lethal effects and mechanisms of photo-induced PAH toxicity in ELS fishes. The present study investigated apoptosis and global transcriptomic effects in larval red drum (Sciaenops ocellatus) (24-72 h post-fertilization) following co-exposure to oil (0.29-0.30 μg/L ∑PAH₅₀) and UV. Apoptosis was quantified using the TUNEL assay, and transcriptomic effects were assessed using RNA sequencing analysis. Apoptotic fluorescence was greatest in the eyes and skin following 24 and 48 h co-exposure to oil and UV, indicating photo-induced toxicity. Consistent with these phenotypic responses, pathways associated with phototransduction, eye development, and dermatological disease were among the top predicted pathways impacted. The present study is the first to provide global transcriptomic analysis of UV and oil co-exposure in an ELS fish.

Metabolic responses to crude oil during early life stages reveal critical developmental windows in the zebrafish (Danio rerio)

Morphological effects of crude oil exposure on early development in fishes have been well documented, but crude oil's metabolic effects and when in early development these effects might be most prominent remains unclear. We hypothesized that zebrafish (Danio rerio) exposed to crude oil as a high energy water accommodated fraction (HEWAF) would show increased routine oxygen consumption (ṀO₂) and critical oxygen tension (P_Crit) and this effect would be dependent upon day of HEWAF exposure, revealing critical windows of development for exposure effects. Zebrafish were exposed to 0%, 10%, 25%, 50% or 100% HEWAF for 24 h during one of the first six days post-fertilization (dpf). Survival rate, body mass, routine ṀO₂, and P_Crit were then measured at 7 dpf. Survival rate and especially body mass were both decreased based on both exposure concentration and day of crude oil exposure, with the largest decrease when HEWAF exposure occurred at 3 dpf. HEWAF effects on routine ṀO₂ also differed depending upon exposure day. The largest effect occurred at 3 dpf, when ṀO₂ increased significantly by ~60% from 10.1 ± 0.8 μmol O₂/g/h compared to control group value of 6.3 ± 0.4 μmol O₂/g/h. No significant effects of HEWAF exposure on any day were evident for P_Crit (85 ± 4 mmHg in the control population). Overall, the main effects on body mass and ṀO₂ measured at 7 dpf occurred when HEWAF exposures occurred at ~3 dpf. This critical window for metabolism in zebrafish larvae coincides with time of hatching, which may represent an especially vulnerable period in development.

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.

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.

Exposure of zebrafish larvae to water accommodated fractions of weathered crude oil alters steroid hormone concentrations with minimal effect on cholesterol

Crude oil has multiple toxic effects in fish, particularly during their early life stages. Recent transcriptomics studies have highlighted a potential effect on cholesterol homeostasis and biosynthesis, but have not investigated effects on steroid hormones, which are biosynthetically downstream metabolites of cholesterol. We exposed zebrafish (Danio rerio) embryos and larvae to 3 concentrations of a high energy water accommodated fraction (HEWAF) of crude oil and measured effects on cholesterol and steroid hormones at 48 and 96 h post fertilization (hpf). HEWAF exposure caused a small decrease in cholesterol at 96 hpf but not 48 hpf. HEWAF-exposed larvae had higher levels of androstenedione, testosterone, estradiol, cortisol, corticosterone, and progesterone at 96 hpf compared to controls, while effects at 48 hpf were more modest or not present. 2-Methoxyestradiol was lower following HEWAF exposure at both time points. Dihydrotestosterone was elevated in one HEWAF concentration at 48 hpf only. Our results suggest that hormone imbalance may be an important toxic effect of oil HEWAF exposure despite no major effect on their biosynthetic precursor cholesterol.

Acute Exposure to Crude Oil Induces Epigenetic, Transcriptional and Metabolic Changes in Juvenile Sciaenops ocellatus

In this study, we report molecular and metabolic responses of Sciaenops ocellatus during an acute oil exposure bioassay (100, 800 and 8000 mg 1^-1 of crude oil). The global DNA methylation and expression profiles of key genes of the xenobiotic biotransformation system (cytochrome P450 1A [cyp1a] and glutathione S-tranferase [gst]), oxidative stress system (glutathione peroxidase [gpx], catalase [cat], aldehyde dehydrogenase [aldh]) and reproductive system (vitellogenin [vtg]) were evaluated. At the metabolic level, we evaluated the concentration of four polycyclic aromatic hydrocarbon (PAH) metabolites -hydroxybenzo[a]pyrene, hydroxypyrene, hydroxynaphthalene and hydroxyphenanthrene- in fish bile. The results of this study revealed that fish exposed to crude oil exhibited hypomethylation of DNA, up-regulation of cyp1a and gst and down-regulation of gpx, cat, aldh and vtg and high concentrations of PAH metabolites with respect to the control.

Exposure to Deepwater Horizon crude oil increases free cholesterol in larval red drum (Sciaenops ocellatus)

The 2010 Deepwater Horizon oil spill impacted over 2100 km of shoreline along the northern Gulf of Mexico, which coincided with the spawning season of many coastal species, including red drum (Sciaenops ocellatus). Red drum develop rapidly and are sensitive to crude oil exposure during the embryonic and larval periods. This study investigates the predictions from recent transcriptomic studies that cholesterol biosynthetic processes are impacted by oil exposure in fish early life stages. We found that red drum larvae exposed for 72 h to ΣPAH₅₀ 3.55-15.45 µg L^-1 exhibited significantly increased pericardial area, a cardiotoxicity metric, but the expression of several genes targeted in the cholesterol synthesis pathway was not affected. However, whole-mount staining revealed significant increases in free cholesterol throughout the larval body (ΣPAH₅₀ 4.71-16.15 µg L^-1), and total cholesterol followed an increasing trend (ΣPAH₅₀ 3.55-15.45 µg L^-1). Cholesterol plays a critical role in fish embryo development and ion channel function. Therefore, the disruption of cholesterol homeostasis, as observed here, could play a role in the oil toxicity phenotype observed across many fish species.

A review of the toxicology of oil in vertebrates: what we have learned following the Deepwater Horizon oil spill

In the wake of the Deepwater Horizon (DWH) oil spill, a number of government agencies, academic institutions, consultants, and nonprofit organizations conducted lab- and field-based research to understand the toxic effects of the oil. Lab testing was performed with a variety of fish, birds, turtles, and vertebrate cell lines (as well as invertebrates); field biologists conducted observations on fish, birds, turtles, and marine mammals; and epidemiologists carried out observational studies in humans. Eight years after the spill, scientists and resource managers held a workshop to summarize the similarities and differences in the effects of DWH oil on vertebrate taxa and to identify remaining gaps in our understanding of oil toxicity in wildlife and humans, building upon the cross-taxonomic synthesis initiated during the Natural Resource Damage Assessment. Across the studies, consistency was found in the types of toxic response observed in the different organisms. Impairment of stress responses and adrenal gland function, cardiotoxicity, immune system dysfunction, disruption of blood cells and their function, effects on locomotion, and oxidative damage were observed across taxa. This consistency suggests conservation in the mechanisms of action and disease pathogenesis. From a toxicological perspective, a logical progression of impacts was noted: from molecular and cellular effects that manifest as organ dysfunction, to systemic effects that compromise fitness, growth, reproductive potential, and survival. From a clinical perspective, adverse health effects from DWH oil spill exposure formed a suite of signs/symptomatic responses that at the highest doses/concentrations resulted in multi-organ system failure.

miR133b Microinjection during Early Development Targets Transcripts of Cardiomyocyte Ion Channels and Induces Oil-like Cardiotoxicity in Zebrafish (Danio rerio) Embryos

Previous studies have shown that altered expression of a family of small noncoding RNAs (microRNAs, or miRs) regulates the expression of downstream mRNAs and is associated with diseases and developmental disorders. miR133b is highly expressed in mammalian cardiac and skeletal muscle, and aberrant expression is associated with cardiac disorders and electrophysiological changes in cardiomyocytes. Similarly, cardiac dysfunction has been observed in early life-stage mahi-mahi (Coryphaena hippurus) exposed to crude oil, a phenotype that has been associated with an upregulation of miR133b as well as subsequent downregulation of a delayed rectifier potassium channel (I_Kr) and calcium signaling genes that are important for proper heart development during embryogenesis. To examine the potential role of miR133b in oil-induced early life-stage cardiotoxicity in fish, cleavage-stage zebrafish (Danio rerio) embryos were either (1) microinjected with ∼3 nL of negative control miR (75 μM) or miR133b (75 μM) or (2) exposed to a treatment solution containing 5 μM benzo(a)pyrene (BaP), a model polycyclic aromatic hydrocarbon, as a positive control. At 72 h post fertilization (hpf), miR133b-injected fish exhibited BaP-like cardiovascular malformations, including a significantly increased pericardial area relative to negative control miR-injected embryos, as well as a significantly reduced eye area. qPCR revealed that miR133b microinjection decreased the abundance of cardiac-specific I_Kr kcnh6 at 5 hpf, which may contribute to action potential elongation in oil-exposed cardiomyocytes. Additionally, ryanodine receptor 2, a crucial calcium receptor in the sarcoplasmic reticulum, was also downregulated by miR133b. These results indicate that an oil-induced increase in miR133b may contribute to cardiac abnormalities in oil-exposed fish by targeting cardiac-specific genes essential for proper heart development.

Environmental modulators of diluted bitumen effects in juvenile pink salmon (Oncorhynchus gorbuscha)

Recent and potential expansions in the transportation of diluted bitumen (dilbit) through marine terminals in coastal regions of British Columbia require the examination of potential risks to estuarine species such as Pacific salmon. The estuarine habitat of out-migrated pink salmon (Oncorhynchus gorbuscha) exhibits dynamic temperature and salinity regimes, possibly modifying dilbit exposure, bioavailability and/or its effects. To examine dilbit toxicity and its modification by environmental stressors, juvenile pinks were subchronically exposed for 3 months to the water-accommodated fraction (WAF) of Cold Lake Blend dilbit (winter) in seawater at three salinities (7, 14, and 28‰ [temperature 12.5 °C]) and three temperatures (8.5, 12.5, and 16.5 °C [salinity of 28‰]). Temperature and salinity alone did not affect any measured endpoints in control fish. Dilbit exposure induced higher mortality at high (16.5 °C) and low temperatures (8.5 °C) as well as at higher salinity (28‰) in fish exposed to the highest dilution of WAF [total polycyclic aromatic compounds (TPAC) = 128.9 μg/L]. A concentration-dependent reduction of growth was evident in fish exposed to the medium (TPAC = 97.3 μg/L) and high dilution of WAF at higher temperatures (12.5 and 16.5 °C) and high salinity (28‰). At 28‰, swimming performance (U_burst) was decreased in fish exposed to the highest concentration of dilbit at all 3 temperatures. Gill Na⁺-K⁺-ATPase activity, white muscle lactate, glycogen, and triglyceride concentrations were altered by dilbit exposure and modified by temperature and salinity. In addition, gene expression associated with phase I biotransformation, energy metabolism, mitochondrial activity, and inflammation showed significant upregulation with exposure and temperature stress. Dilbit exposure at PAC concentrations in the ppb range, affected pink salmon at the molecular, biochemical, and whole organism level; effects that were exacerbated by environmental temperature and salinity.

Behavioral Changes in a Coastal Marine Fish Lead to Increased Predation Risk Following Oil Exposure

Fishes exposed to crude oil have shown reduced sociability and poor habitat selection, which corresponded with increased predation risk. However, the contribution of oil-induced cardiorespiratory impairments to these findings is uncertain. This study explores the effect of oil exposure on predation risk in a model fish species, Sciaenops ocellatus, across a suite of physiological and behavioral end points to elucidate the mechanisms through which any observed effects are manifested. Using mesocosms to assess group predator avoidance, oil exposure to 36.3 μg l^-1 ΣPAH reduced the time to 50% mortality from a mean time of 80.0 (74.1-86.0 95% confidence interval [CI]) min to 39.2 (35.6-42.8 95% CI) min. The influence of oil impaired cardiorespiratory and behavioral pathways on predation risk was assessed based on respiratory performance, swim performance, sociability, and routine activity. Swim trials demonstrated that cardiorespiratory and swim performance were unaffected by exposures to 26.6 or 100.8 μg l^-1 ΣPAH. Interestingly, behavioral tests revealed that exposure to 26.6 μg l^-1 ΣPAH increased distance moved, speed, acceleration, and burst activity. These data indicate that behavioral impairment is more sensitive than cardiorespiratory injury and may be a more important driver of downstream ecological risk following oil exposure in marine species.

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.

Comparative toxicity assessment of in situ burn residues to initial and dispersed heavy fuel oil using zebrafish embryos as test organisms

In situ burning (ISB) is discussed to be one of the most suitable response strategies to combat oil spills in extreme conditions. After burning, a highly viscous and sticky residue is left and may over time pose a risk of exposing aquatic biota to toxic oil compounds. Scientific information about the impact of burn residues on the environment is scarce. In this context, a comprehensive ISB field experiment with approx. 1000L IFO 180 was conducted in a fjord in Greenland. The present study investigated the toxicity of collected ISB residues to early life stages of zebrafish (Danio rerio) as a model for potentially exposed pelagic organisms. The toxicity of ISB residues on zebrafish embryos was compared with the toxicity of the initial (unweathered) IFO 180 and chemically dispersed IFO 180. Morphological malformations, hatching success, swimming behavior, and biomarkers for exposure (CYP1A activity, AChE inhibition) were evaluated in order to cover the toxic response on different biological organization levels. Across all endpoints, ISB residues did not induce greater toxicity in zebrafish embryos compared with the initial oil. The application of a chemical dispersant increased the acute toxicity most likely due to a higher bioavailability of dissolved and particulate oil components. The results provide insight into the adverse effects of ISB residues on sensitive life stages of fish in comparison with chemical dispersant application.

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.

Effects of polycyclic aromatic hydrocarbons and abiotic stressors on Fundulus grandis cardiac transcriptomics

Following the 2010 Deepwater Horizon oil spill, extensive research has been conducted on the toxicity of oil and polycyclic aromatic hydrocarbons (PAHs) in the aquatic environment. Many studies have identified the toxicological effects of PAHs in estuarine and marine fishes, however, only recently has work begun to identify the combinatorial effect of PAHs and abiotic environmental factors such as hypoxia, salinity, and temperature. This study aims to characterize the combined effects of abiotic stressors and PAH exposure on the cardiac transcriptomes of developing Fundulus grandis larvae. In this study, F. grandis larvae were exposed to varying environmental conditions (dissolved oxygen (DO) 2, 6 ppm; temperature 20, 30 °C; and salinity 3, 30 ppt) as well as to a single concentration of high energy water accommodated fraction (HEWAF) (∑PAHs 15 ppb). Whole larvae were sampled for RNA and transcriptional changes were quantified using RNA-Seq followed by qPCR for a set of target genes. Analysis revealed that exposure to oil and abiotic stressors impacts signaling pathways associated with cardiovascular function. Specifically, combined exposures appear to reduce development of the systemic vasculature as well as strongly impact the cardiac musculature through cardiomyocyte proliferation resulting in inhibited cardiac function and modulated blood pressure maintenance. Results of this study provide a holistic view of impacts of PAHs and common environmental stressors on the cardiac system in early life stage estuarine species. To our knowledge, this study is one of the first to simultaneously manipulate oil exposure with abiotic factors (DO, salinity, temperature) and the first to analyze cardiac transcriptional responses under these co-exposures.

Effects of crude oil vapors on the cardiovascular flow of embryonic Gulf killifish

Direct contact with toxicants in crude oil during embryogenesis causes cardiovascular defects, but the effects of exposure to airborne volatile organic compounds released from spilled oil are not well understood. The effects of crude oil-derived airborne toxicants on peripheral blood flow were examined in Gulf killifish (Fundulus grandis) since this model completes embryogenesis in the air. Particle image velocimetry was used to measure in vivo blood flow in intersegmental arteries of control and oil-exposed embryos. Significant effects in oil-exposed embryos included increased pulse rate, reduced mean blood flow speed and volumetric flow rate, and decreased pulsatility, demonstrating that normal-appearing oil-exposed embryos retain underlying cardiovascular defects. Further, hematocrit moderately increased in oil-exposed embryos. This study highlights the potential for fine-scale physiological measurement techniques to better understand the sub-lethal effects of oil exposure and demonstrates the efficacy of Gulf killifish as a unique teleost model for aerial toxicant exposure studies.

The effects of acute crude oil exposure on growth and competition in red drum, Sciaenops ocellatus

Crude oil is a well-known toxicant that reduces cardiorespiratory performance in acutely exposed fishes. While toxic effects can manifest in death in severe cases, the ecological consequences of sub-lethal exposure remain uncertain. This study investigated the impact of crude oil exposure on long-term social competition, growth, and metabolic performance in a coastal species, the red drum (Sciaenops ocellatus). Fish were acutely exposed to either control or one of two environmentally relevant oil concentrations and reared together in groups of 15 (5 from each exposure concentration) for eight weeks under resource-rich or resource-limited scenarios. Relative to controls, a 41.3% and 45.9% reduction in the specific growth rate was-observed following exposure to 25.3 and 53.4 μg l^-1 ΣPAH respectively under resource-limited conditions. These fish were subsequently sampled for metabolic performance and common indicators of social subordination including reduced glucocorticoid receptors in the gill and caudal fin damage. The reduction in specific growth rate coincided with a 15.1% and 17.3% reduction in standard metabolic rate; however, maximum metabolic rate and aerobic scope were unaffected. Additionally, measures of social subordination showed no differences between oil-exposed and control fish. These results reinforce the hypothesis that acute oil exposure can have prolonged sub-lethal effects that compromise the ability of exposed individuals to perform effectively in their environment, including gathering and/or metabolizing food. Furthermore, this work highlights the premise that oil spills can be more detrimental in already at-risk ecosystems.

Investigating the Potential Toxicity of Hydraulic Fracturing Flowback and Produced Water Spills to Aquatic Animals in Freshwater Environments: A North American Perspective

Unconventional methods of oil and natural gas extraction have been a growing part of North America's energy sector for the past 20-30 years. Technologies such as horizontal hydraulic fracturing have facilitated the exploitation of geologic reserves that were previously resistant to standard drilling approaches. However, the environmental risks associated with hydraulic fracturing are relatively understudied. One such hazard is the wastewater by-product of hydraulic fracturing processes: flowback and produced water (FPW). During FPW production, transport, and storage, there are many potential pathways for environmental exposure. In the current review, toxicological hazards associated with FPW surface water contamination events and potential effects on freshwater biota are assessed. This review contains an extensive survey of chemicals commonly associated with FPW samples from shale formations across North America and median 50% lethal concentration values (LC₅₀) of corresponding chemicals for many freshwater organisms. We identify the characteristics of FPW which may have the greatest potential to be drivers of toxicity to freshwater organisms. Notably, components associated with salinity, the organic fraction, and metal species are reviewed. Additionally, we examine the current state of FPW production in North America and identify the most significant obstacles impeding proper risk assessment development when environmental contamination events of this wastewater occur. Findings within this study will serve to catalyze further work on areas currently lacking in FPW research, including expanded whole effluent testing, repeated and chronic FPW exposure studies, and toxicity identification evaluations.

Physiological Responses of Fish to Oil Spills

Millions of tons of oil are spilled in aquatic environments every decade, and this oil has the potential to greatly impact fish populations. Here, we review available information on the physiological effects of oil and polycyclic aromatic hydrocarbons on fish. Oil toxicity affects multiple biological systems, including cardiac function, cholesterol biosynthesis, peripheral and central nervous system function, the stress response, and osmoregulatory and acid-base balance processes. We propose that cholesterol depletion may be a significant contributor to impacts on cardiac, neuronal, and synaptic function as well as reduced cortisol production and release. Furthermore, it is possible that intracellular calcium homeostasis-a part of cardiotoxic and neuronal function that is affected by oil exposure-may be related to cholesterol depletion. A detailed understanding of oil impacts and affected physiological processes is emerging, but knowledge of their combined effects on fish in natural habitats is largely lacking. We identify key areas deserving attention in future research.

Effects of Dissolved Organic Carbon, Ultraviolet Light and their Co-Exposure on Deepwater Horizon crude oil acute toxicity to larval red drum (Sciaenops ocellatus)

In the aquatic environment, ubiquitous natural factors such as ultraviolet light (UV) and dissolved organic carbon (DOC) are likely to influence crude oil toxicity. The present study examined the interactive effects of DOC, UV, and DOC-UV co-exposure on the acute toxicity of Deepwater Horizon crude oil in larval red drum (Sciaenops ocellatus). Although DOC alone did not influence crude oil toxicity, it mildly reduced UV photo-enhanced toxicity. Environ Toxicol Chem 2020;39:2509-2515. © 2020 SETAC.

The effects of exposure to crude oil or PAHs on fish swim bladder development and function

The failure of the swim bladder to inflate during fish development is a common and sensitive response to exposure to petrochemicals. Here, we review potential mechanisms by which petrochemicals or their toxic components (polycyclic aromatic hydrocarbons; PAHs) may affect swim bladder inflation, particularly during early life stages. Surface films formed by oil can cause a physical barrier to primary inflation by air gulping, and are likely important during oil spills. The act of swimming to the surface for primary inflation can be arduous for some species, and may prevent inflation if this behavior is limited by toxic effects on vision or musculature. Some studies have noted altered gene expression in the swim bladder in response to PAHs, and Cytochrome P450 1A (CYP1A) can be induced in swim bladder or rete mirabile tissue, suggesting that PAHs can have direct effects on swim bladder development. Swim bladder inflation failure can also occur secondarily to the failure of other systems; cardiovascular impairment is the best elucidated of these mechanisms, but other mechanisms might include non-inflation as a sequela of disruption to thyroid signaling or cholesterol metabolism. Failed swim bladder inflation has the potential to lead to chronic sublethal effects that are as yet unstudied.

The additive effects of oil exposure and hypoxia on aerobic performance in red drum (Sciaenops ocellatus)

Aerobic scope, the difference between standard metabolic requirements and maximum metabolic capacity, is considered a particularly important metric influencing ecological success in fishes. Crude oil exposure can impair cardiorespiratory function in fishes, which reduces maximum metabolic rate, aerobic scope, and may impair ecological performance. Oil exposure is not the only environmental stressor that can affect aerobic scope, especially in areas affected by crude oil spills. Hypoxia (low dissolved oxygen) is also known to constrain maximum metabolic rate, yet there has been little effort to explore how hypoxia may influence the magnitude of metabolic injury following oil exposure. Therefore, our goal was to investigate the effects of acute oil exposure and hypoxia on the metabolic performance of red drum (Sciaenops ocellatus), an economically important fish common in the Gulf of Mexico. Here, sub-adult red drum were exposed to crude oil for 24 h before being exposed to hypoxic conditions following exhaustive exercise. Our results show that hypoxia exposure combined with crude oil exposure results in significantly reduced aerobic scope, which was additive compared to the reductions caused by each stressor alone. We also quantified hypoxia tolerance among treatments following exposure, and our results showed no changes to hypoxia tolerance among individuals, regardless of exposure to hypoxia or oil. These data offer insight into the metabolic constraints facing fishes exposed to oil while concurrently subjected to hypoxia, a notable climate change stressor.

Differences in biomarker and behavioral responses to native and chemically dispersed crude and refined fossil oils in zebrafish early life stages

Petroleum products including crude oils and refined distillates are unique environmental pollutants consisting of thousands of compounds with varying physical-chemical properties and resulting toxicity for aquatic biota. Hence, for a reliable risk assessment individual petroleum product toxicity profiles are needed. Furthermore, the influence of oil spill response strategies like the application of chemical dispersants has to be implemented. The present study addressed the toxicity of water-accommodated fractions (WAFs) of two different oil types on fish early life stages on different biological organization levels in the laboratory model species Danio rerio. Experiments with a 3^rd generation dispersant used in loading rated resembling the exposure in experiments with chemically dispersed oils were included, enabling a direct comparability of results. This approach is of high importance as especially the investigation of dispersant toxicity in relevant exposure concentrations is rather scarce. Zebrafish embryos were exposed to different WAFs shortly after and up to 120 hour post fertilization (hpf). Besides phenotypic effects including edema and spine deformations, reduced responses to dark stimuli, increased CYP1A activity and marginal AChE inhibition were observed in sublethal effect concentrations. Both oil types had varying strength of toxicity, which did not correlate with corresponding chemical analysis of target PAHs. Chemically dispersed oils induced stronger acute toxicity in zebrafish embryos compared to native (initial) oil exposure, which was further reflected by very low exposure concentrations for biomarker endpoints. Based on a comparison to the dispersant alone, a higher toxicity of dispersed oils was related to a combination of dispersant toxicity and an elevated crude oil compound bioavailability, due to dispersion-related partitioning kinetics. In contrast to LEWAF and CEWAF neither typical morphological effects nor mechanism-specific toxicity were observed for the dispersant alone, indicating narcosis as the responsible cause of effects.

Exposure to Crude Oil Induces Retinal Apoptosis and Impairs Visual Function in Fish

Polycyclic aromatic hydrocarbons (PAHs) present in crude oil are known to impair visual development in fish. However, the underlying mechanism of PAH-induced toxicity to the visual system of fish is not understood. Embryonic zebrafish (Danio rerio) at 4 h post fertilization were exposed to weathered crude oil and assessed for visual function using an optokinetic response, with subsequent samples taken for immunohistochemistry and gene expression analysis. Cardiotoxicity was also assessed by measuring the heart rate, stroke volume, and cardiac output, as cardiac performance has been proposed to be a contributing factor to eye-associated malformations following oil exposure. Larvae exposed to the highest concentrations of crude oil (89.8 μg/L) exhibited an increased occurrence of bradycardia, though no changes in stroke volume or cardiac output were observed. However, genes important in eye development and phototransduction were downregulated in oil-exposed larvae, with an increased occurrence of cellular apoptosis, reduced neuronal connection, and reduced optokinetic behavioral response in zebrafish larvae.

Molecular level determination of water accommodated fraction with embryonic developmental toxicity generated by photooxidation of spilled oil

In this study, developmental toxicity was increased as the oil was further degraded under natural sunlight. Detailed chemical composition of the degraded oils was examined by use of gas chromatography (GC) and (-) electrospray ionization ultrahigh resolution mass spectrometry (UHR-MS). Baseline toxicities were estimated based on chemical activities of polycyclic aromatic hydrocarbons, and it was obvious that the predicted chemical activities can not explain increased toxicity alone. However, the ultrahigh resolution mass spectral abundance of polar compounds including O₃ and O₄ class compounds was significantly increased as the photodegradation proceeded. Further examination of double bond equivalence values of the compounds showed that polar compounds with both non-aromatic and aromatic polar structures were increased. Statistical analysis indicates that the increased toxicity can be well explained by the increased polar compounds. Therefore, the oxygenated compounds identified in this study can play an important role in toxicity of degraded oils.

Exposure to water-accommodated fractions of two different crude oils alters morphology, cardiac function and swim bladder development in early-life stages of zebrafish

The present study investigated the developmental toxicity of water-accommodated fractions (WAFs) of Oman crude oil (OCO) and Merey crude oil (MCO) on zebrafish (Danio rerio) in early-life stages (ELS). Based on total petroleum hydrocarbons (TPH), LC₅₀ values manifested that OCO WAF was 1.2-fold more lethal to zebrafish embryos than MCO WAF. As for hatching rate, EC₅₀ value for OCO WAF was 5.7-fold lower than that for MCO WAF. To evaluate the sublethal morphological effects, semi-quantitative extended general morphological score (GMS) and general teratogenic score (GTS) systems were adopted. The GMS and GTS scores indicated that the WAFs caused remarkable developmental delay and high frequencies of malformation in a dose-dependent manner. Additionally, OCO and MCO WAFs exposure exhibited severe bradycardia (reduced heart rate) and overt reduction of stroke volume, with a concomitant decrease in the cardiac output. Meanwhile, the WAFs also induced dose-dependent down-regulated expressions of several key functional genes of excitation-contraction coupling in cardiomyocytes, including ryr2, atp2a2a, atp2a2b, ncx1h, and kcnh2. For key gene markers of swim bladder development, results showed that high dose of TPH induced significant down-regulation of hb9 and anxa5 with no obvious change of acta2, suggesting that the WAFs could affect the specification and development of epithelium and outer mesothelium of swim bladder in zebrafish ELS. A strong negative relationship between the failure of swim bladder inflation and cardiac dysfunction via cardiac output was found. All these findings provide novel insights into the complicated mechanisms of the developmental toxicity of crude oil on fish in ELS.

Impacts of deepwater horizon oil on fish

An explosion on the Deepwater Horizon (DWH) oil rig in 2010 lead to the largest marine oil spill to occur in US history, resulting in significant impacts to the ecosystems and organisms in the Northern Gulf of Mexico (GoM). The present review sought to summarize and discuss findings from the 50+ peer-reviewed publications reporting effects of DWH oil exposure on teleost fish, and concludes that oil toxicity is a multi-target, multi-organ syndrome with substantial species-specific sensitivity differences. Of the 15 species tested with characterized exposures, 20% show effects at concentrations <1 μg l^-1 while 50% display effects at <8.6 μg l^-1 ΣPAH₅₀, concentrations well within the range of reported environmental levels during the spill. Cardiotoxic effects are among the most frequently reported endpoints in DWH oil exposure studies and are thought to have significant downstream effects on fitness and survival. However, additional and possibly cardio-toxic independent impacts on sensory function and behavior are reported at very low exposure concentrations (< 1 μg l^-1 ∑PAH₅₀) and are clearly deserving of further study. Available information about modes of action leading to different categories of effects are summarized in the present review. An overview of the literature illustrates that early life stages (ELS) are approximately 1-order of magnitude more sensitive than corresponding later life stages, but also illustrates that adults can be impacted at concentrations as low as 4 μg l^-1 ΣPAH₅₀. The majority of studies exploring DWH oil toxicity in fish are performed using acute exposures (1-2 days), mid-range test temperatures (26-28 °C) and measure effects at the molecular to organismal levels, leaving a pressing need for more long-term exposures, exposures at the upper and lower levels of GoM relevant temperatures, and studies investigating population level impacts.

Polycyclic Aromatic Hydrocarbons Phenanthrene and Retene Modify the Action Potential via Multiple Ion Currents in Rainbow Trout Oncorhynchus mykiss Cardiac Myocytes

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants in aqueous environments. They affect cardiovascular development and function in fishes. The 3-ring PAH phenanthrene has recently been shown to impair cardiac excitation-contraction coupling by inhibiting Ca²⁺ and K⁺ currents in marine warm-water scombrid fishes. To see if similar events take place in a boreal freshwater fish, we studied whether the PAHs phenanthrene and retene (an alkylated phenanthrene) modify the action potential (AP) via effects on Na⁺ (I_Na ), Ca²⁺ (I_CaL ), or K⁺ (I_Kr , I_K1 ) currents in the ventricular myocytes of the rainbow trout (Oncorhynchus mykiss) heart. Electrophysiological characteristics of myocytes were measured using whole-cell patch clamp. Micromolar concentrations of phenanthrene and retene modified the shape of the ventricular AP, and retene profoundly shortened the AP at low micromolar concentrations. Both PAHs increased I_Na and reduced I_CaL and I_Kr , but retene was more potent. Neither of the PAHs had an effect on I_K1 . Our results show that phenanthrene and retene affect cardiac function in rainbow trout by a mechanism that involves multiple cardiac ion channels, and the final outcome of these changes (shortening of AP) is opposite to that observed in scombrid fishes (prolongation of AP). The results also show that retene and aryl hydrocarbon receptor (AhR) agonist have an additional mechanism of toxicity besides the previously known AhR-mediated, transcription-dependent one. Environ Toxicol Chem 2019;38:2145-2153. © 2019 SETAC.

Characterizing Crude Oil Toxicity to Early-Life Stage Fish Based On a Complex Mixture: Are We Making Unsupported Assumptions?

Numerous studies of the water-soluble fraction (WSF) from crude oil have concluded that polycyclic aromatic hydrocarbons (PAHs) are the primary causative agents for early life stage (ELS) fish toxicity. Noteworthy is the lack of studies demonstrating that the sum of PAHs are capable of causing toxic effects in ELS fish at the low levels claimed (0.1-5 μg/L) without being part of a complex crude oil mixture. Crude oil and the WSF are composed of thousands of other compounds that co-occur and likely contribute to crude oil toxicity. Based on the available data, it appears that the syndrome of effects (lower heart rate, edemas, and morphological abnormalities) for ELS fish exposed to the aqueous fraction of a crude oil mixture is commonly observed in studies exposing fish embryos to high concentrations of a variety of compounds and may be a nonspecific response. We conclude that the available data support the hypothesis that this syndrome of effects is likely the result of baseline toxicity (not receptor based) due to membrane disruption and resulting alteration in ion (e.g., calcium and potassium) homeostasis. We acknowledge the possibility of some compounds in the WSF capable of causing a specific receptor based toxicity response to ELS fish; however, such compounds have not been identified nor their receptor characterized. Concluding that PAHs are the main toxic compounds for crude oil exposure is misleading and does not result in guideline values that can be useful for environmental protection. Water quality guidelines for any single chemical or suite of chemicals must be based on a complete understanding of exposure concentrations, mechanism of action, potency, and resulting response. This review focuses on the toxic effects reported for fish embryos and the purported toxic concentrations observed in the aqueous phase of an oil/water mixture, the known levels of toxicity for individual PAHs, a toxic unit approach for characterizing mixtures, and the potential molecular initiating event for ELS toxicity in fish. This review also has implications for a large number of studies exposing ELS fish to a variety of compounds at high concentrations that result in a common baseline toxic response.

Oil exposure alters social group cohesion in fish

Many animal taxa live in groups to increase foraging and reproductive success and aid in predator avoidance. For fish, a large proportion of species spend all or part of their lives in groups, with group coordination playing an important role in the emergent benefits of group-living. Group cohesion can be altered by an array of factors, including exposure to toxic environmental contaminants. Oil spills are one of the most serious forms of pollution in aquatic systems, and while a range of effects of acute oil exposure on animal physiology have been demonstrated, sub-lethal effects on animal behavior are relatively under-studied. Here we used an open-field behavioral assay to explore influence of acute oil exposure on social behavior in a gregarious fish native to the Gulf of Mexico, Atlantic croaker (Micropogonias undulatus). We used two oil concentrations (0.7% and 2% oil dilution, or 6.0 ± 0.9 and 32.9 ± 5.9 μg l-1 ΣPAH50 respectively) and assays were performed when all members of a group were exposed, when only one member was exposed, and when no individuals were exposed. Shoal cohesion, as assessed via mean neighbor distance, showed significant impairment following acute exposure to 2% oil. Fish in oil-exposed groups also showed reduced voluntary movement speed. Importantly, overall group cohesion was disrupted when even one fish within a shoal was exposed to 2% oil, and the behavior of unexposed in mixed groups, in terms of movement speed and proximity to the arena wall, was affected by the presence of these exposed fish. These results demonstrate that oil exposure can have adverse effects on fish behavior that may lead to reduced ecological success.

Parental stressor exposure simultaneously conveys both adaptive and maladaptive larval phenotypes through epigenetic inheritance in the zebrafish (Danio rerio)

Genomic modifications occur slowly across generations, whereas short-term epigenetic inheritance of adaptive phenotypes may be immediately beneficial to large numbers of individuals, acting as a bridge for survival when adverse environments occur. In the present study, crude oil was used as an example of an environmental stressor. Adult zebrafish (P₀) were dietarily exposed for 3 weeks to no, low, medium or high concentrations of crude oil. The F₁ offspring obtained from the P₀ groups were then assessed for transgenerational epigenetic transfer of oil-induced phenotypes. The exposure did not alter body length, body and organ mass or condition factor in the P₀ groups. However, the P₀ fecundity of both sexes decreased in proportion to the amount of oil fed. The F₁ larvae from each P₀ were then exposed from 3 hpf to 5 dpf to oil in their ambient water. Remarkably, F₁ larvae derived from oil-exposed parents, when reared in oiled water, showed a 30% enhanced survival compared with controls (P<0.001). Unexpectedly, from day 3 to 5 of exposure, F₁ larvae from oil-exposed parents showed poorer survival in clean water (up to 55% decreased survival). Additionally, parental oil exposure induced bradycardia (presumably maladaptive) in F₁ larvae in both clean and oiled water. We conclude that epigenetic transgenerational inheritance can lead to an immediate and simultaneous inheritance of both beneficial and maladaptive traits in a large proportion of the F₁ larvae. The adaptive responses may help fish populations survive when facing transient environmental stressors.

Accumulation and toxicity of monoaromatic petroleum hydrocarbons in early life stages of cod and haddock

A multitude of recent studies have documented the detrimental effects of crude oil exposure on early life stages of fish, including larvae and embryos. While polycyclic aromatic hydrocarbons (PAHs), particularly alkyl PAHs, are often considered the main cause of observed toxic effects, other crude oil derived organic compounds are usually overlooked. In the current study, comprehensive two-dimensional gas chromatography coupled to mass spectrometry was applied to investigate the body burden of a wide range of petrogenic compounds in Atlantic haddock (Melanogrammus aeglefinus) and cod (Gadus morhua) embryos that had been exposed to sublethal doses of dispersed crude oil. Several groups of alkylated monoaromatic compounds (e.g. alkyl tetralins, indanes and alkyl benzenes), as well as highly alkylated PAHs, were found to accumulate in the fish embryos upon crude oil exposure. To investigate the toxicity of the monoaromatic compounds, two models (1-isopropyl-4-methyltetralin and 1-isopropyl-4-methylindane) were synthesized and shown to bioaccumulate and cause delayed hatching in developing embryos. Minor developmental effects, including craniofacial and jaw deformations and pericardial edemas, were also observed at the highest studied concentrations of the alkylindane.