Cardiac arrhythmia is the primary response of embryonic Pacific herring (Clupea pallasi) exposed to crude oil during weathering

Early life stages of an arctic keystone species (Boreogadus saida) show high sensitivity to a water-soluble fraction of crude oil

Increasing anthropogenic activities in the Arctic represent an enhanced threat for oil pollution in a marine environment that is already at risk from climate warming. In particular, this applies to species with free-living pelagic larvae that aggregate in surface waters and under the sea ice where hydrocarbons are likely to remain for extended periods of time due to low temperatures. We exposed the positively buoyant eggs of polar cod (Boreogadus saida), an arctic keystone species, to realistic concentrations of a crude oil water-soluble fraction (WSF), mimicking exposure of eggs aggregating under the ice to oil WSF leaking from brine channels following encapsulation in ice. Total hydrocarbon and polycyclic aromatic hydrocarbon levels were in the ng/L range, with most exposure concentrations below the limits of detection throughout the experiment for all treatments. The proportion of viable, free-swimming larvae decreased significantly with dose and showed increases in the incidence and severity of spine curvature, yolk sac alterations and a reduction in spine length. These effects are expected to compromise the motility, feeding capacity, and predator avoidance during critical early life stages for this important species. Our results imply that the viability and fitness of polar cod early life stages is significantly reduced when exposed to extremely low and environmentally realistic levels of aqueous hydrocarbons, which may have important implications for arctic food web dynamics and ecosystem functioning.

Toxicity assessment of water-accommodated fractions from two different oils using a zebrafish (Danio rerio) embryo-larval bioassay with a multilevel approach

Petroleum compounds from chronic discharges and oil spills represent an important source of environmental pollution. To better understand the deleterious effects of these compounds, the toxicity of water-accommodated fractions (WAF) from two different oils (brut Arabian Light and Erika heavy fuel oils) were used in this study. Zebrafish embryos (Danio rerio) were exposed during 96h at three WAF concentrations (1, 10 and 100% for Arabian Light and 10, 50 and 100% for Erika) in order to cover a wide range of polycyclic aromatic hydrocarbon (PAH) concentrations, representative of the levels found after environmental oil spills. Several endpoints were recorded at different levels of biological organization, including lethal endpoints, morphological abnormalities, photomotor behavioral responses, cardiac activity, DNA damage and exposure level measurements (EROD activity, cyp1a and PAH metabolites). Neither morphological nor behavioral or physiological alterations were observed after exposure to Arabian Light fractions. In contrast, the Erika fractions led a high degree of toxicity in early life stages of zebrafish. Despite of defense mechanisms induced by oil, acute toxic effects have been recorded including mortality, delayed hatching, high rates of developmental abnormalities, disrupted locomotor activity and cardiac failures at the highest PAH concentrations (∑TPAHs=257,029±47,231ng·L(-1)). Such differences in toxicity are likely related to the oil composition. The use of developing zebrafish is a good tool to identify wide range of detrimental effects and elucidate their underlying foundations. Our work highlights once more, the cardiotoxic action (and potentially neurotoxic) of petroleum-related PAHs.

Impacts of Deepwater Horizon crude oil exposure on adult mahi-mahi (Coryphaena hippurus) swim performance

The temporal and geographic attributes of the Deepwater Horizon incident in 2010 likely exposed pelagic game fish species, such as mahi-mahi, to crude oil. Although much of the research assessing the effects of the spill has focused on early life stages of fish, studies examining whole-animal physiological responses of adult marine fish species are lacking. Using swim chamber respirometry, the present study demonstrates that acute exposure to a sublethal concentration of the water accommodated fraction of Deepwater Horizon crude oil results in significant swim performance impacts on young adult mahi-mahi, representing the first report of acute sublethal toxicity on adult pelagic fish in the Gulf of Mexico following the spill. At an exposure concentration of 8.4 ± 0.6 µg L^-1 sum of 50 selected polycyclic aromatic hydrocarbons (PAHs; mean of geometric means ± standard error of the mean), significant decreases in the critical and optimal swimming speeds of 14% and 10%, respectively (p < 0.05), were observed. In addition, a 20% reduction in the maximum metabolic rate and a 29% reduction in aerobic scope resulted from exposure to this level of ΣPAHs. Using environmentally relevant crude oil exposure concentrations and a commercially and ecologically valuable Gulf of Mexico fish species, the present results provide insight into the effects of the Deepwater Horizon oil spill on adult pelagic fish. Environ Toxicol Chem 2016;35:2613-2622. © 2016 SETAC.

Developing a polycyclic aromatic hydrocarbon exposure dose-response model for fish health and growth

One of the more important steps in understanding the ecosystem-level effects of anthropogenic disturbances on resident species is developing an accurate representation of the lethal and sub-lethal effects of these stressors. We develop methods for describing the impacts of oil on growth and mortality rates in fishes. We conducted a literature search to determine potential relationships between direct and indirect effects of exposure to oil, based on the frequency of lesions and body growth reduction. Data examining these effects with different exposure mediums were assessed and then input into four potential response models (a linear, step-wise, hockey-stick, and exponential model). We assessed the models using the Akaike Information Criterion. The most parsimonious and best fit model was the hockey-stick. This analysis will aid in identifying where future research on the impact of oil on fish should focus and also aid the development of ecosystem models on impacts of oil spills.

Crude oil exposures reveal roles for intracellular calcium cycling in haddock craniofacial and cardiac development

Recent studies have shown that crude oil exposure affects cardiac development in fish by disrupting excitation-contraction (EC) coupling. We previously found that eggs of Atlantic haddock (Melanogrammus aeglefinus) bind dispersed oil droplets, potentially leading to more profound toxic effects from uptake of polycyclic aromatic hydrocarbons (PAHs). Using lower concentrations of dispersed crude oil (0.7-7 μg/L ∑PAH), here we exposed a broader range of developmental stages over both short and prolonged durations. We quantified effects on cardiac function and morphogenesis, characterized novel craniofacial defects, and examined the expression of genes encoding potential targets underlying cardiac and craniofacial defects. Because of oil droplet binding, a 24-hr exposure was sufficient to create severe cardiac and craniofacial abnormalities. The specific nature of the craniofacial abnormalities suggests that crude oil may target common craniofacial and cardiac precursor cells either directly or indirectly by affecting ion channels and intracellular calcium in particular. Furthermore, down-regulation of genes encoding specific components of the EC coupling machinery suggests that crude oil disrupts excitation-transcription coupling or normal feedback regulation of ion channels blocked by PAHs. These data support a unifying hypothesis whereby depletion of intracellular calcium pools by crude oil-derived PAHs disrupts several pathways critical for organogenesis in fish.

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

The developing fish heart is vulnerable to a diverse array of toxic chemical contaminants in freshwater, estuarine, and marine habitats. Globally occurring examples of cardiotoxic agents include dioxins, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). The disruption of cardiac function during the process of heart morphogenesis can lead to adverse outcome pathways (AOPs) that can negatively affect fish survival at hatching as well as later life stages. Proximal impacts include cardiogenic fluid accumulation (edema) and defects of the body axis and jaw that preclude larval feeding. More subtle changes in heart development can produce permanent structural defects in the heart that reduce cardiac output and swimming performance in older fish. In recent decades, the presence of edema in fish embryos and larvae has been a very common bioindicator of cardiotoxicity. However, the different ways that edema forms in fish from different habitats (i.e., freshwater vs. marine, pelagic vs. demersal) has not been rigorously examined. Oil spills are an important source of PAHs in fish spawning areas worldwide, and research is revealing how patterns of cardiogenic edema are shaped by species-specific differences in developmental anatomy and ionoregulatory physiology. Here we review the visible evidence for circulatory disruption across nine freshwater and marine fish species, exposed to crude oils from different parts of the world. We focus on the close interconnectedness of the cardiovascular and osmoregulatory systems during early development, and corresponding implications for fish in hyperosmotic and hyposmotic habitats. Finally, we suggest there may be poorly understood adverse outcomes pathways related to osmotic gradients and water movement within embryos, the latter causing extreme shifts in tissue osmolality.

Comparison of Diluted Bitumen (Dilbit) and Conventional Crude Oil Toxicity to Developing Zebrafish

To facilitate pipeline transport of bitumen, it is diluted with natural gas condensate, and the resulting mixture, "dilbit", differs greatly in chemical composition to conventional crude oil. Despite the risk of accidental dilbit release, the effects of dilbit on aquatic animals are largely unknown. In this study, we compared the toxicity of water accommodated fractions (WAFs) of dilbit and two conventional crude oils, medium sour composite and mixed sweet blend, to developing zebrafish. Mortality and pericardial edema was lowest in dilbit WAF-exposed embryonic zebrafish but yolk sac edema was similar in all exposures. Shelter-seeking behavior was decreased by dilbit and conventional crude WAF exposures, and continuous swimming behavior was affected by all tested WAF exposures. Regardless of WAF type, monoaromatic hydrocarbon content (largely made up of benzene, toluene, ethylbenzene, and xylene (BTEX)) was a more accurate predictor of lethality and pericardial edema than polycyclic aromatic hydrocarbon (PAH) content. Our results suggest that the toxicity of dilbit to a model fish is less than or similar to that of conventional crudes.

The effects of CYP1A inhibition on alkyl-phenanthrene metabolism and embryotoxicity in marine medaka (Oryzias melastigma)

Alkylated polycyclic aromatic hydrocarbons (alkyl-PAHs) are the predominant form of PAHs in crude oils, of which, 3-5 ring alkyl-PAH may cause dioxin-like toxicity to early life stages of fish. Retene (7-isopropyl-1-methylphenanthrene), a typical alkyl-phenanthrene compound, can be more toxic than phenanthrene, and the mechanism of retene toxicity is likely related to its rapid biotransformation by cytochrome P450 (CYP) enzymes to metabolites with a wide array of structures and potential toxicities. Here, we investigated how α-naphthoflavone (ANF), a cytochrome P450 1A (CYP1A) inhibitor, affected the embryotoxicity of retene and the role that CYP1A inhibition may play in the interactions. Marine medaka (Oryzias melastigma) embryos were exposed, separately or together, to 200 μg/L retene with 0, 5, 10, 100, and 200 μg/L ANF for 14 days. The results showed that ANF significantly inhibited the induction of CYP1A activity by retene; however, ANF interacted with retene to induce significant developmental toxicity and genotoxicity at 10, 100, and 200 μg/L (p < 0.01). Tissue concentrations of retene and its metabolites and lipid hydroperoxide (LPO) activity also increased, whereas the inhibition of the glutathione S-transferase (GST) activity and the alteration in metabolic profiles of retene were observed. The interactions of retene with ANF indicate that CYP1A inhibition was possibly act through different mechanisms to produce similar developmental effects and genotoxicity. Retene metabolites and altered metabolic profile were likely responsible for retene embryotoxicity to marine medaka. Therefore, elevated toxicity of alkyl-phenanthrene under CYP1A inhibitor suggested that the ecotoxicity of PAHs in coastal water may have underestimated the threat of PAHs to fish or ecosystem.

Advances in the Study of Heart Development and Disease Using Zebrafish

Animal models of cardiovascular disease are key players in the translational medicine pipeline used to define the conserved genetic and molecular basis of disease. Congenital heart diseases (CHDs) are the most common type of human birth defect and feature structural abnormalities that arise during cardiac development and maturation. The zebrafish, Danio rerio, is a valuable vertebrate model organism, offering advantages over traditional mammalian models. These advantages include the rapid, stereotyped and external development of transparent embryos produced in large numbers from inexpensively housed adults, vast capacity for genetic manipulation, and amenability to high-throughput screening. With the help of modern genetics and a sequenced genome, zebrafish have led to insights in cardiovascular diseases ranging from CHDs to arrhythmia and cardiomyopathy. Here, we discuss the utility of zebrafish as a model system and summarize zebrafish cardiac morphogenesis with emphasis on parallels to human heart diseases. Additionally, we discuss the specific tools and experimental platforms utilized in the zebrafish model including forward screens, functional characterization of candidate genes, and high throughput applications.

Confirmation of Stormwater Bioretention Treatment Effectiveness Using Molecular Indicators of Cardiovascular Toxicity in Developing Fish

Urban stormwater runoff is a globally significant threat to the ecological integrity of aquatic habitats. Green stormwater infrastructure methods such as bioretention are increasingly used to improve water quality by filtering chemical contaminants that may be harmful to fish and other species. Ubiquitous examples of toxics in runoff from highways and other impervious surfaces include polycyclic aromatic hydrocarbons (PAHs). Certain PAHs are known to cause functional and structural defects in developing fish hearts. Therefore, abnormal heart development in fish can be a sensitive measure of clean water technology effectiveness. Here we use the zebrafish experimental model to assess the effects of untreated runoff on the expression of genes that are classically responsive to contaminant exposures, as well as heart-related genes that may underpin the familiar cardiotoxicity phenotype. Further, we assess the effectiveness of soil bioretention for treating runoff, as measured by prevention of both visible cardiac toxicity and corresponding gene regulation. We find that contaminants in the dissolved phase of runoff (e.g., PAHs) are cardiotoxic and that soil bioretention protects against these harmful effects. Molecular markers were more sensitive than visible toxicity indicators, and several cardiac-related genes show promise as novel tools for evaluating the effectiveness of evolving stormwater mitigation strategies.

The effects of weathering and chemical dispersion on Deepwater Horizon crude oil toxicity to mahi-mahi (Coryphaena hippurus) early life stages

To better understand the impact of the Deepwater Horizon (DWH) incident on commercially and ecologically important pelagic fish species, a mahi-mahi spawning program was developed to assess the effect of embryonic exposure to DWH crude oil with particular emphasis on the effects of weathering and dispersant on the magnitude of toxicity. Acute lethality (96 h LC50) ranged from 45.8 (28.4-63.1) μg l(-1) ΣPAH for wellhead (source) oil to 8.8 (7.4-10.3) μg l(-1) ΣPAH for samples collected from the surface slick, reinforcing previous work that weathered oil is more toxic on a ΣPAH basis. Differences in toxicity appear related to the amount of dissolved 3 ringed PAHs. The dispersant Corexit 9500 did not influence acute lethality of oil preparations. Embryonic oil exposure resulted in cardiotoxicity after 48 h, as evident from pericardial edema and reduced atrial contractility. Whereas pericardial edema appeared to correlate well with acute lethality at 96 h, atrial contractility did not. However, sub-lethal cardiotoxicity may impact long-term performance and survival. Dispersant did not affect the occurrence of pericardial edema; however, there was an apparent reduction in atrial contractility at 48 h of exposure. Pericardial edema at 48 h and lethality at 96 h were equally sensitive endpoints in mahi-mahi.

Developmental exposure to a complex PAH mixture causes persistent behavioral effects in naive Fundulus heteroclitus (killifish) but not in a population of PAH-adapted killifish

Acute exposures to some individual polycyclic aromatic hydrocarbons (PAHs) and complex PAH mixtures are known to cause cardiac malformations and edema in the developing fish embryo. However, the heart is not the only organ impacted by developmental PAH exposure. The developing brain is also affected, resulting in lasting behavioral dysfunction. While acute exposures to some PAHs are teratogenically lethal in fish, little is known about the later life consequences of early life, lower dose subteratogenic PAH exposures. We sought to determine and characterize the long-term behavioral consequences of subteratogenic developmental PAH mixture exposure in both naive killifish and PAH-adapted killifish using sediment pore water derived from the Atlantic Wood Industries Superfund Site. Killifish offspring were embryonically treated with two low-level PAH mixture dilutions of Elizabeth River sediment extract (ERSE) (TPAH 5.04 μg/L and 50.4 μg/L) at 24h post fertilization. Following exposure, killifish were raised to larval, juvenile, and adult life stages and subjected to a series of behavioral tests including: a locomotor activity test (4 days post-hatch), a sensorimotor response tap/habituation test (3 months post hatch), and a novel tank diving and exploration test (3months post hatch). Killifish were also monitored for survival at 1, 2, and 5 months over 5-month rearing period. Developmental PAH exposure caused short-term as well as persistent behavioral impairments in naive killifish. In contrast, the PAH-adapted killifish did not show behavioral alterations following PAH exposure. PAH mixture exposure caused increased mortality in reference killifish over time; yet, the PAH-adapted killifish, while demonstrating long-term rearing mortality, had no significant changes in mortality associated with ERSE exposure. This study demonstrated that early embryonic exposure to PAH-contaminated sediment pore water caused long-term locomotor and behavioral alterations in killifish, and that locomotor alterations could be observed in early larval stages. Additionally, our study highlights the resistance to behavioral alterations caused by low-level PAH mixture exposure in the adapted killifish population. Furthermore, this is the first longitudinal behavioral study to use killifish, an environmentally important estuarine teleost fish, and this testing framework can be used for future contaminant assessment.

Corresponding morphological and molecular indicators of crude oil toxicity to the developing hearts of mahi mahi

Crude oils from distinct geological sources worldwide are toxic to developing fish hearts. When oil spills occur in fish spawning habitats, natural resource injury assessments often rely on conventional morphometric analyses of heart form and function. The extent to which visible indicators correspond to molecular markers for cardiovascular stress is unknown for pelagic predators from the Gulf of Mexico. Here we exposed mahi (Coryphaena hippurus) embryos to field-collected crude oil samples from the 2010 Deepwater Horizon disaster. We compared visible heart defects (edema, abnormal looping, reduced contractility) to changes in expression of cardiac-specific genes that are diagnostic of heart failure in humans or associated with loss-of-function zebrafish cardiac mutants. Mahi exposed to crude oil during embryogenesis displayed typical symptoms of cardiogenic syndrome as larvae. Contractility, looping, and circulatory defects were evident, but larval mahi did not exhibit downstream craniofacial and body axis abnormalities. A gradation of oil exposures yielded concentration-responsive changes in morphometric and molecular responses, with relative sensitivity being influenced by age. Our findings suggest that 1) morphometric analyses of cardiac function are more sensitive to proximal effects of crude oil-derived chemicals on the developing heart, and 2) molecular indicators reveal a longer-term adverse shift in cardiogenesis trajectory.

Differential Toxicokinetics Determines the Sensitivity of Two Marine Embryonic Fish Exposed to Iranian Heavy Crude Oil

Interspecific difference in the developmental toxicity of crude oil to embryonic fish allows the prediction of injury extent to a number of resident fish species in oil spill sites. This study clarifies the comparative developmental effects of Iranian heavy crude oil (IHCO) on the differences of biouptake and toxic sensitivity between embryonic spotted sea bass (Lateolabrax maculates) and olive flounder (Paralichthys olivaceus). From 24 h after exposure to IHCO, several morphological defects were observed in both species of embryonic fish, including pericardial edema, dorsal curvature of the trunk, developmental delay, and reduced finfolds. The severity of defects was greater in flounder compared to that in sea bass. While flounder embryos accumulated higher embryo PAH concentrations than sea bass, the former showed significantly lower levels of CYP1A expression. Although bioconcentration ratios were similar between the two species for some PAHs, phenanthrenes and dibenzothiophenes showed selectively higher bioconcentration ratios in flounder, suggesting that this species has a reduced metabolic capacity for these compounds. While consistent with a conserved cardiotoxic mechanism for petrogenic PAHs across diverse marine and freshwater species, these findings indicate that species-specific differences in toxicokinetics can be an important factor underlying species' sensitivity to crude oil.

Coho salmon spawner mortality in western US urban watersheds: bioinfiltration prevents lethal storm water impacts

Adult coho salmon Oncorhynchus kisutch return each autumn to freshwater spawning habitats throughout western North America. The migration coincides with increasing seasonal rainfall, which in turn increases storm water run-off, particularly in urban watersheds with extensive impervious land cover. Previous field assessments in urban stream networks have shown that adult coho are dying prematurely at high rates (>50%). Despite significant management concerns for the long-term conservation of threatened wild coho populations, a causal role for toxic run-off in the mortality syndrome has not been demonstrated.We exposed otherwise healthy coho spawners to: (i) artificial storm water containing mixtures of metals and petroleum hydrocarbons, at or above concentrations previously measured in urban run-off; (ii) undiluted storm water collected from a high traffic volume urban arterial road (i.e. highway run-off); and (iii) highway run-off that was first pre-treated via bioinfiltration through experimental soil columns to remove pollutants.We find that mixtures of metals and petroleum hydrocarbons - conventional toxic constituents in urban storm water - are not sufficient to cause the spawner mortality syndrome. By contrast, untreated highway run-off collected during nine distinct storm events was universally lethal to adult coho relative to unexposed controls. Lastly, the mortality syndrome was prevented when highway run-off was pretreated by soil infiltration, a conventional green storm water infrastructure technology.Our results are the first direct evidence that: (i) toxic run-off is killing adult coho in urban watersheds, and (ii) inexpensive mitigation measures can improve water quality and promote salmon survival. Synthesis and applications. Coho salmon, an iconic species with exceptional economic and cultural significance, are an ecological sentinel for the harmful effects of untreated urban run-off. Wild coho populations cannot withstand the high rates of mortality that are now regularly occurring in urban spawning habitats. Green storm water infrastructure or similar pollution prevention methods should be incorporated to the maximal extent practicable, at the watershed scale, for all future development and redevelopment projects, particularly those involving transportation infrastructure.

Very low embryonic crude oil exposures cause lasting cardiac defects in salmon and herring

The 1989 Exxon Valdez disaster exposed embryos of pink salmon and Pacific herring to crude oil in shoreline spawning habitats throughout Prince William Sound, Alaska. The herring fishery collapsed four years later. The role of the spill, if any, in this decline remains one of the most controversial unanswered questions in modern natural resource injury assessment. Crude oil disrupts excitation-contraction coupling in fish heart muscle cells, and we show here that salmon and herring exposed as embryos to trace levels of crude oil grow into juveniles with abnormal hearts and reduced cardiorespiratory function, the latter a key determinant of individual survival and population recruitment. Oil exposure during cardiogenesis led to specific defects in the outflow tract and compact myocardium, and a hypertrophic response in spongy myocardium, evident in juveniles 7 to 9 months after exposure. The thresholds for developmental cardiotoxicity were remarkably low, suggesting the scale of the Exxon Valdez impact in shoreline spawning habitats was much greater than previously appreciated. Moreover, an irreversible loss of cardiac fitness and consequent increases in delayed mortality in oil-exposed cohorts may have been important contributors to the delayed decline of pink salmon and herring stocks in Prince William Sound.

Spilled Oils: Static Mixtures or Dynamic Weathering and Bioavailability?

Polynuclear aromatic hydrocarbons (PAHs) from sequestered MV Selendang Ayu oil were biologically available in 2008, 3.6 y after it was spilled along Unalaska Island, Alaska. Thermodynamically driven weathering was the most probable mechanism of organism exposure to PAHs. Alkane and PAH composition in oil changed over time as smaller constituents were preferentially lost, indicative of weathering. In contrast, composition of the largest compounds (biomarkers) including triterpanes, hopanes, and steranes remained unchanged. Smaller molecules (the PAHs) lost from stranded oil were observed in indigenous mussels and passive samplers deployed in July 2008. Concentration and composition of PAHs were significantly different than in a non-oiled reference area and patterns observed in mussels were repeated in passive samplers deployed in three zones (intertidal, subtidal, and water). Thus, hydrocarbons lost from one compartment (sequestered whole oil) were detectable in another (mussels and passive samplers) implying aqueous transfer. Quantities of mobile oil constituents were small, yielding uptake concentrations that are likely inconsequential for mussels, but the sensitivity provided by bioaccumulation and passive sampler uptake ensured that dissolved hydrocarbons were detectable.

Effect of dispersed crude oil on cardiac function in seabass Dicentrarchus labrax

In this study, the impact of dispersed oil was assessed in Dicentrarchus labrax, a fish frequently used as an oil contamination indicator species. Fish were exposed for 48h to (mechanically and chemically) dispersed oil and dispersant alone. The impact of these exposure conditions was assessed on cardiac function by measuring (i) the contraction strength, the contraction and the relaxation speeds (ii) the cardiac energy metabolism using respirometry on permeabilized cardiac fibers. Compared to control, the increase of polycyclic aromatic metabolites observed in the bile indicated oil contamination in our fish. Following 48h of oil exposure at realistic oil concentrations, alterations of cardiac performances were observed. A decrease in contraction strength, contraction and relaxation speeds was observed in the presence of oil without effect of dispersant on these three parameters. Looking at cardiac energy metabolism, dispersant alone decreases all the activity of the respiratory chain and increases the proton leak. From these results, it appears that the observed decrease in cardiac performance in fish exposed to oil was not linked to a decrease in energy availability.

Parental trophic exposure to three aromatic fractions of polycyclic aromatic hydrocarbons in the zebrafish: Consequences for the offspring

In recent decades, PAH emissions due to extensive anthropogenic activities have risen sharply causing considerable pollution of aquatic ecosystems. This pollution represents a threat for organisms, among them are fish. Consequently, prenatal stress can have important repercussions, and may impact survival and population recruitment. To investigate this point, eggs were collected from zebrafish exposed during 6 months by trophic route to three aromatic fractions from two different origins, pyrolytic (PY) and petrogenic (light (BAL) and heavy (HFO) fractions) sources. Chronic dietary exposure of the parents was performed at environmentally relevant concentrations (0.3×, 1× and 3×; 1× represents an environmental concentration measured in French estuary). In order to explore the consequences of parental exposure for the next first generation, toxic responses were studied in both embryos and larvae using a multiscale approach. Toxic effects were assessed by looking at hatching success, developmental abnormalities, photomotor response and heartbeat. The level of PAH metabolites and EROD activity in fish larvae were measured to assess exposure to PAHs. Egg production of parents was significantly reduced compared to the Control; hence little information was available for BAL and HFO offspring. The size of larvae from PY parents was found to increase despite a reduced yolk sac compared to Control larvae. Furthermore, a high level of behavioral stress was observed in larvae originating from parents exposed to three-fold the environmental concentration. The cardiac activity was reduced in a concentration-dependent manner for the PY exposure group. No effect was however observed on biotransformation markers (cyp1a, EROD), nor on the level of DNA damage for all PY, BAL and HFO offspring. The absence of significant differences in metabolite levels may indicate a potential early depuration of transferred compounds or no PAH-transmission. The disruptions observed at the individual level in the next generation could impact on the longer-term, surviving population.

Comparison of the acute effects of benzo-a-pyrene on adult zebrafish (Danio rerio) cardiorespiratory function following intraperitoneal injection versus aqueous exposure

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants. PAH exposure causes developmental toxicity in multiple fish species, while acute adult fish toxicity is thought to be minimal. The literature increasingly suggests sublethal PAH effects may occur, but differences in exposure route may confound conclusions. We hypothesized that acute PAH exposure in adult fish will cause cardiorespiratory impairment that will not differ with exposure route. In order to investigate this hypothesis, adult zebrafish (Danio rerio) were injected intraperitoneal (i.p.) twice with increasing concentrations of the prototypical PAH, benzo-a-pyrene (BaP; 0.1, 10, and 1000μg/kg) or exposed aqueously (static, renewal at 24h; 16.2 and 162μg/L) for 48h and compared to corresponding dimethylsulfoxide controls. No mortalities or significant effects on weight of the fish were noted at any exposure concentration or route. At 48h, fish were subjected to swimming tests with concurrent oxygen consumption measurement (n=10 fish/treatment) or echocardiography (n=12 fish/treatment). Oxygen consumption (MO2) was increased at three swimming speeds in BaP-injected groups compared to control (p<0.01 in Fisher's LSD tests after two-way ANOVA). In contrast, aqueously BaP-exposed fish showed increased MO2 under only basal conditions. Despite increased oxygen demand, ventricular heart rate was significantly decreased in BaP-exposed fish, both injected and aqueously-exposed. Analysis of BaP body burdens in fish tissue allowed for identification of an overlapping dose group between exposure routes, through which comparisons of cardiorespiratory toxicity were then made. This comparison revealed most effects were similar between the two exposures routes, although minor differences were noted. At similar BaP body burdens, injected fish suffered from more severe bradycardia than aqueously exposed fish and had greater levels of increases in cytochrome P4501A (CYP1A) mRNA levels in liver and heart tissue compared to aqueous exposed fish. In conclusion, acute BaP exposure in adult zebrafish had negative effects on cardiorespiratory function. Differences in effect between exposure routes were attributed primarily to differences in bioavailability, since overall, similar effects were noted between the two exposure routes when similar BaP body burdens were achieved.

Tissue PAH, blood cell and tissue changes following exposure to water accommodated fractions of crude oil in alligator gar, Atractosteus spatula

Alligator gar Atractosteus spatula acclimated to brackish water (9 ppt) were exposed to water accommodated fraction oil loadings (surrogate to Macondo Deepwater Horizon, northern Gulf of Mexico) of 0.5 and 4.0 gm oil/L tank water for 48 h. The surrogate oil was approximately 98% alkanes and alkynes and 2% petroleum aromatic hydrocarbons. The 2% petroleum aromatic hydrocarbons were predominately naphthalene. After 48 h, naphthalene levels in fish liver exposed to 0.5 or 4 gm oil/L were 547.79 and 910.68 ppb, while muscle levels were 214.11 and 253.84 ppb. There was a significant decrease in peripheral blood lymphocyte numbers and a significant reduction of granulocytes in the kidney marrow of the same fish. Tissue changes included hepatocellular vacuolization and necrosis, necrotizing pancreatitis, renal eosinophilia, and splenic congestion. After 7 days recovery, liver naphthalene levels decreased to 43.59 and 43.20 ppb, while muscle levels decreased to 9.74, and 16.78 ppb for oil exposures of 0, 0.5 or 4 g/L. In peripheral blood and kidney marrow, blood cell counts returned to normal. The severity of liver and kidney lesions lessened after 7 days recovery in non-oiled water, but splenic congestion remained in all gar.

Zebrafish cardiotoxicity: the effects of CYP1A inhibition and AHR2 knockdown following exposure to weak aryl hydrocarbon receptor agonists

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates many of the toxic effects of dioxin-like compounds (DLCs) and some polycyclic aromatic hydrocarbons (PAHs). Strong AHR agonists, such as certain polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), cause severe cardiac teratogenesis in fish embryos. Moderately strong AHR agonists, such as benzo[a]pyrene and β-naphthoflavone, have been shown to cause similar cardiotoxic effects when coupled with a cytochrome P450 1A (CYP1A) inhibitor, such as fluoranthene (FL). We sought to determine if weak AHR agonists, when combined with a CYP1A inhibitor (FL) or CYP1A morpholino gene knockdown, are capable of causing cardiac deformities similar to moderately strong AHR agonists (Wassenberg and Di Giulio Environ Health Perspect 112(17):1658-1664, 2004a; Wassenberg and Di Giulio Res 58(2-5):163-168, 2004b; Billiard et al. Toxicol Sci 92(2):526-536, 2006; Van Tiem and Di Giulio Toxicol Appl Pharmacol 254(3):280-287, 2011). The weak AHR agonists included the following: carbaryl, phenanthrene, 2-methylindole, 3-methylindole, indigo, and indirubin. Danio rerio (zebrafish) embryos were first exposed to weak AHR agonists at equimolar concentrations. The agonists were assessed for their relative potency as inducers of CYP1 enzyme activity, measured by the ethoxyresorufin-O-deethylase (EROD) assay, and cardiac deformities. Carbaryl, 2-methylindole, and 3-methylindole induced the highest CYP1A activity in zebrafish. Experiments were then conducted to determine the individual cardiotoxicity of each compound. Next, zebrafish were coexposed to each agonist (at concentrations below those determined to be cardiotoxic) and FL in combination to assess if CYP1A inhibition could induce cardiac deformities. Carbaryl, 2-methylindole, 3-methylindole, and phenanthrene significantly increased pericardial edema relative to controls when combined with FL. To further evaluate the interaction of the weak AHR agonists and CYP1A inhibition, a morpholino was used to knockdown CYP1A expression, and embryos were then exposed to each agonist individually. In embryos exposed to 2-methylindole, CYP1A knockdown caused a similar level of pericardial edema to that caused by exposure to 2-methylindole and FL. The results showed a complex pattern of cardiotoxic response to weak agonist inhibitor exposure and morpholino-knockdown. However, CYP1A knockdown in phenanthrene and 3-methylindole only moderately increased pericardial edema relative to coexposure to FL. AHR2 expression was also knocked down using a morpholino to determine its role in mediating the observed cardiac teratogenesis. Knockdown of AHR2 did not rescue the pericardial edema as previously observed with strong AHR agonists. While some of the cardiotoxicity observed may be attributed to the combination of weak AHR agonism and CYP1A inhibition, other weak AHR agonists appear to be causing cardiotoxicity through an AHR2-independent mechanism. The data show that CYP1A is protective of the cardiac toxicity associated with weak AHR agonists and that knockdown can generate pericardial edema, but these findings are also suggestive of differing mechanisms of cardiac toxicity among known AHR agonists.

Reproductive and transgenerational toxicities of phenanthrene on female marine medaka (Oryzias melastigma)

Phenanthrene (PHE) is one of the most abundant polycyclic aromatic hydrocarbons in the aquatic environment and often results from oil spills. To assess the effects of PHE on fish, marine medaka (Oryzias melastigma) was exposed to PHE at 0.06, 0.6, 6 and 60 μg/L. The reproductive functions and transgenerational effects were investigated. After 80 days exposure, the percentage of previtellogenic and vitellogenic oocytes in the ovary showed a significant decrease in the 0.06 and 60 μg/L groups. The mRNA levels of salmon-type gonadotropin releasing hormone, the follicle-stimulating hormone FSHβ, and the luteinizing hormone LHβ in the brain; the cytochrome P450 aromatase gene CYP19A and the estrogen receptor α (ERα) in the ovary; and ERα and vitellogenin VTG1 and 2 in the liver all exhibited significant down-regulation in the 0.06 and 60 μg/L groups, but did not significantly change in the 6 μg/L group compared to the control, which was quite consistent with development of the oocytes. A significant elevation of PHE accumulation in the brain in the 0.06 and 60 μg/L groups gave a reasonable explanation for the nonmonotonic dose-response and also elucidated the action pathway via the brain-pituitary-gonadal axis. The reduction of the time to hatch and the increased cardiac rhythm of embryos were in accord with the PHE accumulative levels in the eggs. The results demonstrated that exposure to PHE at both low and high concentrations can inhibit ovary development. In addition, PHE can be maternally transferred to embryos and influence the health and sustainability of the next generation.

Unexpected interaction with dispersed crude oil droplets drives severe toxicity in Atlantic haddock embryos

The toxicity resulting from exposure to oil droplets in marine fish embryos and larvae is still subject for debate. The most detailed studies have investigated the effects of water-dissolved components of crude oil in water accommodated fractions (WAFs) that lack bulk oil droplets. Although exposure to dissolved petroleum compounds alone is sufficient to cause the characteristic developmental toxicity of crude oil, few studies have addressed whether physical interaction with oil micro-droplets are a relevant exposure pathway for open water marine speices. Here we used controlled delivery of mechanically dispersed crude oil to expose pelagic embryos and larvae of a marine teleost, the Atlantic haddock (Melanogrammus aeglefinus). Haddock embryos were exposed continuously to two different concentrations of dispersed crude oil, high and low, or in pulses. By 24 hours of exposure, micro-droplets of oil were observed adhering and accumulating on the chorion, accompanied by highly elevated levels of cyp1a, a biomarker for exposure to aromatic hydrocarbons. Embryos from all treatment groups showed abnormalities representative of crude oil cardiotoxicity at hatch (5 days of exposure), such as pericardial and yolk sac edema. Compared to other species, the frequency and severity of toxic effects was higher than expected for the waterborne PAH concentrations (e.g., 100% of larvae had edema at the low treatment). These findings suggest an enhanced tissue uptake of PAHs and/or other petroleum compounds from attached oil droplets. These studies highlight a novel property of haddock embryos that leads to greater than expected impact from dispersed crude oil. Given the very limited number of marine species tested in similar exposures, the likelihood of other species with similar properties could be high. This unanticipated result therefore has implications for assessing the ecological impacts of oil spills and the use of methods for dispersing oil in the open sea.

Acute effects of β-naphthoflavone on cardiorespiratory function and metabolism in adult zebrafish (Danio rerio)

Aryl hydrocarbon receptor (AhR) agonists are known to cause lethal cardiovascular deformities in fish after developmental exposure. Acute adult fish toxicity of AhR agonists is thought to be minimal, but limited evidence suggests sublethal effects may also involve the cardiac system in fish. In the present study, adult zebrafish (Danio rerio) were aqueously exposed to solvent control or three nominal concentrations of the commonly used model AhR agonist, β-naphthoflavone (BNF), for 48 h. Following exposure, fish were subjected to echocardiography to determine cardiac function or swimming tests with concurrent oxygen consumption measurement. Critical swimming speed and standard metabolic rate were not significantly changed, while active metabolic rate decreased with increasing BNF exposure, reaching statistical significance at the highest BNF exposure. Factorial aerobic scope was the most sensitive end-point and was decreased at even lower BNF concentrations, indicating a reduced aerobic capacity after acute AhR agonist exposure in adult fish. The highest BNF concentration caused a significant decrease in cardiac output, while increasing the ratio of atrial to ventricular heart rate (indicating atrioventricular conduction blockade). In conclusion, the effect of acute BNF exposure on zebrafish metabolic capacity and cardiac function is likely to be physiologically important given that fish have a critical need for adequate oxygen to fuel essential survival behaviors such as swimming, growth, and reproduction. Future studies should be directed at examining the effects of other polycyclic aromatic hydrocarbons on fish cardiorespiratory function to determine whether their effects and modes of action are similar to BNF.

Long-term disruption of growth, reproduction, and behavior after embryonic exposure of zebrafish to PAH-spiked sediment

A natural sediment spiked with three individual polycyclic aromatic hydrocarbons (PAHs; pyrene, phenanthrene and benzo[a]pyrene) was used to expose zebrafish embryos and larvae during 4 days. The total PAH concentration was 4.4 μg g(-1) which is in the range found in sediment from contaminated areas. Quantification of metabolites in the larvae after exposure confirmed the actual contamination of the larvae and indicated an active metabolism especially for pyrene and benzo[a]pyrene. After a transfer in a clean medium, the larvae were reared to adulthood and evaluated for survival, growth, reproduction, and behavior. Measured endpoints revealed a late disruption of growth (appearing at 5 months) and a trend toward a lower reproductive ability. Adults of embryos exposed to sediment spiked with PAHs displayed lethargic and/or anxiety-like behaviors. This latter behavior was also identified in offspring at larval stage. All together, these effects could have detrimental consequences on fish performances and contribution to recruitment.

Chronic dietary exposure to pyrolytic and petrogenic mixtures of PAHs causes physiological disruption in zebrafish--part I: Survival and growth

The release of polycyclic aromatic hydrocarbons (PAHs) into the environment has increased very substantially over the last decades leading to high concentrations in sediments of contaminated areas. To evaluate the consequences of long-term chronic exposure to PAHs, zebrafish were exposed, from their first meal at 5 days post fertilisation until they became reproducing adults, to diets spiked with three PAH fractions at three environmentally relevant concentrations with the medium concentration being in the range of 4.6-6.7 μg g(-1) for total quantified PAHs including the 16 US-EPA indicator PAHs and alkylated derivatives. The fractions used were representative of PAHs of pyrolytic (PY) origin or of two different oils of differing compositions, a heavy fuel (HO) and a light crude oil (LO). Fish growth was inhibited by all PAH fractions and the effects were sex specific: as determined with 9-month-old adults, exposure to the highest PY inhibited growth of females; exposure to the highest HO and LO inhibited growth of males; also, the highest HO dramatically reduced survival. Morphological analysis indicated a disruption of jaw growth in larvae and malformations in adults. Intestinal and pancreatic enzyme activities were abnormal in 2-month-old exposed fish. These effects may contribute to poor growth. Finally, our results indicate that PAH mixtures of different compositions, representative of situations encountered in the wild, can promote lethal and sublethal effects which are likely to be detrimental for fish recruitment.

Developmental toxicity of PAH mixtures in fish early life stages. Part I: adverse effects in rainbow trout

A new gravel-contact assay using rainbow trout, Oncorhynchus mykiss, embryos was developed to assess the toxicity of polycyclic aromatic hydrocarbons (PAHs) and other hydrophobic compounds. Environmentally realistic exposure conditions were mimicked with a direct exposure of eyed rainbow trout embryos incubated onto chemical-spiked gravels until hatching at 10 °C. Several endpoints were recorded including survival, hatching delay, hatching success, biometry, developmental abnormalities, and DNA damage (comet and micronucleus assays). This bioassay was firstly tested with two model PAHs, fluoranthene and benzo[a]pyrene. Then, the method was applied to compare the toxicity of three PAH complex mixtures characterized by different PAH compositions: a pyrolytic extract from a PAH-contaminated sediment (Seine estuary, France) and two petrogenic extracts from Arabian Light and Erika oils, at two environmental concentrations, 3 and 10 μg g(-1) sum of PAHs. The degree and spectrum of toxicity were different according to the extract considered. Acute effects including embryo mortality and decreased hatching success were observed only for Erika oil extract. Arabian Light and pyrolytic extracts induced mainly sublethal effects including reduced larvae size and hemorrhages. Arabian Light and Erika extracts both induced repairable DNA damage as revealed by the comet assay versus the micronucleus assay. The concentration and proportion of methylphenanthrenes and methylanthracenes appeared to drive the toxicity of the three PAH fractions tested, featuring a toxic gradient as follows: pyrolytic < Arabian Light < Erika. The minimal concentration causing developmental defects was as low as 0.7 μg g(-1) sum of PAHs, indicating the high sensitivity of the assay and validating its use for toxicity assessment of particle-bound pollutants.

An evaluation of background levels and sources of polycyclic aromatic hydrocarbons in naturally spawned embryos of Pacific herring (Clupea pallasii) from Puget Sound, Washington, USA

Pacific herring embryos spawned in nearshore habitats may be exposed to toxic contaminants as they develop, from exogenous sources in spawning habitats and from maternal transfer. Determining baseline concentrations of these toxic contaminants is important for evaluating the health of this species, especially during this sensitive life stage. In this study we compared concentrations of polycyclic aromatic hydrocarbons, or PAHs, in naturally spawned herring embryos from five spawning areas across Puget Sound. The summed values of 31 PAH analytes (Σ31PAH) in early- to late-stage development embryos ranged from 1.1 to 140 ng/g, wet weight. Σ31PAH concentrations increased with development time in embryos from one spawning area where the greatest concentrations were observed, and the relative abundance of PAH chemicals in late-stage embryos was similar to those in nearby sediments, suggesting accumulation from local environmental sources. PAHs in both sediments and late-stage embryos appeared to exhibit a pyrogenic pattern. Although maternal transfer of PAHs appeared to be a negligible source to embryos in spawning areas with the greatest embryo PAH concentrations, maternal transfer may have been the dominant source in embryos from spawning areas where the lowest levels of embryo-PAHs occurred. Chronic embryo mortality has been reported in spawning habitats where we observed the greatest concentration of PAHs in embryos, and necrotic tissue in herring embryos from one such location was similar in description to phototoxic PAH necrosis reported elsewhere for embryonic zebrafish.

Evaluating toxicity of heavy fuel oil fractions using complementary modeling and biomimetic extraction methods

The toxicity of chemically dispersed heavy fuel oil (HFO) and 3 distillate fractions to rainbow trout (Oncorhynchus mykiss) embryos was evaluated using the PETROTOX model and a biomimetic extraction technique that involved passive sampling of oil-contaminated test media with solid-phase microextraction (SPME) fibers. Test solutions for toxicity testing were generated using a combination of dispersant and high-energy mixing. The resulting water accommodated fractions (WAF) provided complex exposure regimens that included both dissolved hydrocarbons and oil droplets. The toxicity of the various fractions differed by approximately 3 orders of magnitude when expressed on the basis of WAF dilution. Using detailed compositional data, the PETROTOX model predicted the speciation of hydrocarbons between dissolved and oil droplet phases and explained observed toxicity based on computed dissolved phase toxic units (TUs). A key finding from model calculations was that dissolved hydrocarbon exposures and associated TUs were a nonlinear function of WAF dilution, because dissolved hydrocarbons were largely controlled by the dissolution of oil droplets that were transferred in WAF dilutions. Hence, oil droplets served to "buffer" dissolved concentrations in WAF dilutions at loadings greater than 1 mg/L, resulting in higher dissolved concentrations and TUs than expected based on dilution. The TUs computed at each WAF dilution explained the observed toxicity among the HFO and fractions to within a factor of 3. Dissolved material measured by SPME showed a consistent relationship with model-predicted TUs, confirming the utility of this approach for providing an integrated measure of exposure to bioavailable hydrocarbons. These 2 approaches provide complementary tools for better defining bioavailability of complex petroleum substance.

NADPH oxidase 4 induces cardiac arrhythmic phenotype in zebrafish

Oxidative stress has been implicated in cardiac arrhythmia, although a causal relationship remains undefined. We have recently demonstrated a marked up-regulation of NADPH oxidase isoform 4 (NOX4) in patients with atrial fibrillation, which is accompanied by overproduction of reactive oxygen species (ROS). In this study, we investigated the impact on the cardiac phenotype of NOX4 overexpression in zebrafish. One-cell stage embryos were injected with NOX4 RNA prior to video recording of a GFP-labeled (myl7:GFP zebrafish line) beating heart in real time at 24-31 h post-fertilization. Intriguingly, NOX4 embryos developed cardiac arrhythmia that is characterized by irregular heartbeats. When quantitatively analyzed by an established LQ-1 program, the NOX4 embryos displayed much more variable beat-to-beat intervals (mean S.D. of beat-to-beat intervals was 0.027 s/beat in control embryos versus 0.038 s/beat in NOX4 embryos). Both the phenotype and the increased ROS in NOX4 embryos were attenuated by NOX4 morpholino co-injection, treatments of the embryos with polyethylene glycol-conjugated superoxide dismutase, or NOX4 inhibitors fulvene-5, 6-dimethylamino-fulvene, and proton sponge blue. Injection of NOX4-P437H mutant RNA had no effect on the cardiac phenotype or ROS production. In addition, phosphorylation of calcium/calmodulin-dependent protein kinase II was increased in NOX4 embryos but diminished by polyethylene glycol-conjugated superoxide dismutase, whereas its inhibitor KN93 or AIP abolished the arrhythmic phenotype. Taken together, our data for the first time uncover a novel pathway that underlies the development of cardiac arrhythmia, namely NOX4 activation, subsequent NOX4-specific NADPH-driven ROS production, and redox-sensitive CaMKII activation. These findings may ultimately lead to novel therapeutics targeting cardiac arrhythmia.

Acute embryonic or juvenile exposure to Deepwater Horizon crude oil impairs the swimming performance of mahi-mahi (Coryphaena hippurus)

The Deepwater Horizon incident likely resulted in exposure of commercially and ecologically important fish species to crude oil during the sensitive early life stages. We show that brief exposure of a water-accommodated fraction of oil from the spill to mahi-mahi as juveniles, or as embryos/larvae that were then raised for ∼25 days to juveniles, reduces their swimming performance. These physiological deficits, likely attributable to polycyclic aromatic hydrocarbons (PAHs), occurred at environmentally realistic exposure concentrations. Specifically, a 48 h exposure of 1.2 ± 0.6 μg L(-1) ΣPAHs (geometric mean ± SEM) to embryos/larvae that were then raised to juvenile stage or a 24 h exposure of 30 ± 7 μg L(-1) ΣPAHs (geometric mean ± SEM) directly to juveniles resulted in 37% and 22% decreases in critical swimming velocities (Ucrit), respectively. Oil-exposed larvae from the 48 h exposure showed a 4.5-fold increase in the incidence of pericardial and yolk sac edema relative to controls. However, this larval cardiotoxicity did not manifest in a reduced aerobic scope in the surviving juveniles. Instead, respirometric analyses point to a reduction in swimming efficiency as a potential alternative or contributing mechanism for the observed decreases in Ucrit.

Deepwater Horizon crude oil impacts the developing hearts of large predatory pelagic fish

The Deepwater Horizon disaster released more than 636 million L of crude oil into the northern Gulf of Mexico. The spill oiled upper surface water spawning habitats for many commercially and ecologically important pelagic fish species. Consequently, the developing spawn (embryos and larvae) of tunas, swordfish, and other large predators were potentially exposed to crude oil-derived polycyclic aromatic hydrocarbons (PAHs). Fish embryos are generally very sensitive to PAH-induced cardiotoxicity, and adverse changes in heart physiology and morphology can cause both acute and delayed mortality. Cardiac function is particularly important for fast-swimming pelagic predators with high aerobic demand. Offspring for these species develop rapidly at relatively high temperatures, and their vulnerability to crude oil toxicity is unknown. We assessed the impacts of field-collected Deepwater Horizon (MC252) oil samples on embryos of three pelagic fish: bluefin tuna, yellowfin tuna, and an amberjack. We show that environmentally realistic exposures (1-15 µg/L total PAH) cause specific dose-dependent defects in cardiac function in all three species, with circulatory disruption culminating in pericardial edema and other secondary malformations. Each species displayed an irregular atrial arrhythmia following oil exposure, indicating a highly conserved response to oil toxicity. A considerable portion of Gulf water samples collected during the spill had PAH concentrations exceeding toxicity thresholds observed here, indicating the potential for losses of pelagic fish larvae. Vulnerability assessments in other ocean habitats, including the Arctic, should focus on the developing heart of resident fish species as an exceptionally sensitive and consistent indicator of crude oil impacts.

Crude oil impairs cardiac excitation-contraction coupling in fish

Crude oil is known to disrupt cardiac function in fish embryos. Large oil spills, such as the Deepwater Horizon (DWH) disaster that occurred in 2010 in the Gulf of Mexico, could severely affect fish at impacted spawning sites. The physiological mechanisms underlying such potential cardiotoxic effects remain unclear. Here, we show that crude oil samples collected from the DWH spill prolonged the action potential of isolated cardiomyocytes from juvenile bluefin and yellowfin tunas, through the blocking of the delayed rectifier potassium current (I(Kr)). Crude oil exposure also decreased calcium current (I(Ca)) and calcium cycling, which disrupted excitation-contraction coupling in cardiomyocytes. Our findings demonstrate a cardiotoxic mechanism by which crude oil affects the regulation of cellular excitability, with implications for life-threatening arrhythmias in vertebrates.

Exxon Valdez to Deepwater Horizon: comparable toxicity of both crude oils to fish early life stages

The 2010 Deepwater Horizon disaster in the Gulf of Mexico was the largest oil spill in United States history. Crude oils are highly toxic to developing fish embryos, and many pelagic fish species were spawning in the northern Gulf in the months before containment of the damaged Mississippi Canyon 252 (MC252) wellhead (April-July). The largest prior U.S. spill was the 1989 grounding of the Exxon Valdez that released 11 million gallons of Alaska North Slope crude oil (ANSCO) into Prince William Sound. Numerous studies in the aftermath of the Exxon Valdez spill defined a conventional crude oil injury phenotype in fish early life stages, mediated primarily by toxicity to the developing heart. To determine whether this type of injury extends to fishes exposed to crude oil from the Deepwater Horizon - MC252 incident, we used zebrafish to compare the embryotoxicity of ANSCO alongside unweathered and weathered MC252 oil. We also developed a standardized protocol for generating dispersed oil water-accommodated fractions containing microdroplets of crude oil in the size range of those detected in subsurface plumes in the Gulf. We show here that MC252 oil and ANSCO cause similar cardiotoxicity and photo-induced toxicity in zebrafish embryos. Morphological defects and patterns of cytochrome P450 induction were largely indistinguishable and generally correlated with polycyclic aromatic compound (PAC) composition of each oil type. Analyses of embryos exposed during different developmental windows provided additional insight into mechanisms of crude oil cardiotoxicity. These findings indicate that the impacts of MC252 crude oil on fish embryos and larvae are consistent with the canonical ANSCO cardiac injury phenotype. For those marine fish species that spawned in the northern Gulf of Mexico during and after the Deepwater Horizon incident, the established literature can therefore inform the assessment of natural resource injury in the form of potential year-class losses.

Phenanthrene exposure causes cardiac arrhythmia in embryonic zebrafish via perturbing calcium handling

Phenanthrene (Phe) is one of the most abundant and ubiquitous polycyclic aromatic hydrocarbons in the aquatic environment. It is known that Phe has cardiotoxic effects, but knowledge concerning the mechanism of cardiac dysfunction caused by Phe is still limited. In this study, zebrafish embryos were exposed to environmentally relevant concentrations of Phe, and an increase of an irregular rhythm was observed in Phe treated embryos. Disordered calcium (Ca(2+)) handling characterized by impaired sarcoplasmic reticulum Ca(2+) uptake, and obvious Ca(2+) accumulation in the cytoplasm was observed in rat embryonic cardiac myoblasts (H9C2) exposed to Phe. The mRNA level as well as protein expression of the SERCA2a Ca(2+) pump in zebrafish hearts or H9C2 cells was significantly decreased by Phe exposure. The activity of Ca(2+)-ATPase in H9C2 cells was inhibited by Phe. Both the mRNA and protein levels of TBX5, a direct regulator of SERCA2a, were significantly decreased by Phe exposure. These results suggested that exposure to Phe could lead to arrhythmia in zebrafish embryos via perturbing the calcium handling pathway.

Spatial, temporal, and habitat-related variation in abundance of pelagic fishes in the Gulf of Mexico: potential implications of the deepwater horizon oil spill

Time-series data collected over a four-year period were used to characterize patterns of abundance for pelagic fishes in the northern Gulf of Mexico (GoM) before (2007-2009) and after (2010) the Deepwater Horizon oil spill. Four numerically dominant pelagic species (blackfin tuna, blue marlin, dolphinfish, and sailfish) were included in our assessment, and larval density of each species was lower in 2010 than any of the three years prior to the oil spill, although larval abundance in 2010 was often statistically similar to other years surveyed. To assess potential overlap between suitable habitat of pelagic fish larvae and surface oil, generalized additive models (GAMs) were developed to evaluate the influence of ocean conditions on the abundance of larvae from 2007-2009. Explanatory variables from GAMs were then linked to environmental data from 2010 to predict the probability of occurrence for each species. The spatial extent of surface oil overlapped with early life habitat of each species, possibly indicating that the availability of high quality habitat was affected by the DH oil spill. Shifts in the distribution of spawning adults is another factor known to influence the abundance of larvae, and the spatial occurrence of a model pelagic predator (blue marlin) was characterized over the same four-year period using electronic tags. The spatial extent of oil coincided with areas used by adult blue marlin from 2007-2009, and the occurrence of blue marlin in areas impacted by the DH oil spill was lower in 2010 relative to pre-spill years.

Effects of low-level hexabromocyclododecane (HBCD) exposure on cardiac development in zebrafish embryos

Hexabromocyclododecane (HBCD) is one of the most widely used brominated flame retardants. In the present study, zebrafish embryos were exposed to HBCD at the low concentrations of 0, 2, 20 and 200 nM. The results showed HBCD exposure resulted in an increase in heart rate and cardiac arrhythmia after exposure for 72 h, though the survival rate and the whole malformation rate were not significantly affected. These results demonstrated that the heart might be a target of HBCD. Low-level HBCD exposure may not share the same mechanisms as exposure to high concentrations, since no obvious increase of apoptotic cells around the heart was observed in the HBCD-treated groups. It was observed that the expression of Tbx5 and Nkx2.5 was significantly elevated by HBCD treatment in a dose-dependent manner using real-time quantitative PCR, which may be mainly responsible for the alteration of heart rate, given that Tbx5 and Nkx2.5 are two factors regulating ventricle conduction. The mRNA expression of RyR2 and Atp2a2b (SERCA2a) was up-regulated in the exposure group, which may be one of reasons to affect the normal heart rate, since SERCA2a and RyR2 play an important role in calcium ion transport of cadiomyocytes. However, HBCD exposure did not significantly change the expression of Actc1l, Tnnt2, and Myh6, which are mainly muscle contractile genes that play key roles in the formation of cardiac structure. These results were consistent with the lack of effect seen on the other measurements of cardiac function, end diastolic volume, end-systolic volume, stroke volume, and cardiac output.

Phenanthrene exposure produces cardiac defects during embryo development of zebrafish (Danio rerio) through activation of MMP-9

Phenanthrene (Phe) is one of the most abundant polycyclic aromatic hydrocarbons in the aquatic environment as a result of human activities. It is widely accepted that Phe has cardiotoxic effects. Even so, knowledge concerning the mechanism(s) of cardiac development toxicity is still limited. In this study, we exposed zebrafish embryos to environmentally relevant concentrations of Phe and then investigated its cardiotoxic effects and the mechanism(s) involved. Some cardiac morphogenetic defects, which was characterized by an abnormally looped and enlarged heart, dilated and thinner ventricular wall, and increased interstitial fibrosis, were observed in the Phe treated groups. The mRNA and protein expression levels of matrix metalloproteinase-9 (MMP-9), as well as the MMP-9 activity, were induced. Moreover, during co-treatment of the zebrafish embryos with MMP-9 inhibitor, the cardiac defects caused by Phe were attenuated. In addition, Phe exposure led to an up-regulation of transforming growth factor β (TGF-β), which plays a crucial role in mediating cardiac fibrosis. Taken together, our data indicated that the exposure to Phe of zebrafish embryos disrupted normal cardiac development, and that the cardiac defects induced by Phe were mediated by the MMP-9, while TGF-β was also involved in these cardiac defects.

Multitissue molecular, genomic, and developmental effects of the Deepwater Horizon oil spill on resident Gulf killifish (Fundulus grandis)

The Deepwater Horizon oil rig disaster resulted in crude oil contamination along the Gulf coast in sensitive estuaries. Toxicity from exposure to crude oil can affect populations of fish that live or breed in oiled habitats as seen following the Exxon Valdez oil spill. In an ongoing study of the effects of Deepwater Horizon crude oil on fish, Gulf killifish ( Fundulus grandis ) were collected from an oiled site (Grande Terre, LA) and two reference locations (coastal MS and AL) and monitored for measures of exposure to crude oil. Killifish collected from Grande Terre had divergent gene expression in the liver and gill tissue coincident with the arrival of contaminating oil and up-regulation of cytochrome P4501A (CYP1A) protein in gill, liver, intestine, and head kidney for over one year following peak landfall of oil (August 2011) compared to fish collected from reference sites. Furthermore, laboratory exposures of Gulf killifish embryos to field-collected sediments from Grande Terre and Barataria Bay, LA, also resulted in increased CYP1A and developmental abnormalities when exposed to sediments collected from oiled sites compared to exposure to sediments collected from a reference site. These data are predictive of population-level impacts in fish exposed to sediments from oiled locations along the Gulf of Mexico coast.

Structurally distinct polycyclic aromatic hydrocarbons induce differential transcriptional responses in developing zebrafish

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment as components of fossil fuels and by-products of combustion. These multi-ring chemicals differentially activate the aryl hydrocarbon receptor (AHR) in a structurally dependent manner, and induce toxicity via both AHR-dependent and -independent mechanisms. PAH exposure is known to induce developmental malformations in zebrafish embryos, and recent studies have shown cardiac toxicity induced by compounds with low AHR affinity. Unraveling the potentially diverse molecular mechanisms of PAH toxicity is essential for understanding the hazard posed by complex PAH mixtures present in the environment. We analyzed transcriptional responses to PAH exposure in zebrafish embryos exposed to benz(a)anthracene (BAA), dibenzothiophene (DBT) and pyrene (PYR) at concentrations that induced developmental malformations by 120 h post-fertilization (hpf). Whole genome microarray analysis of mRNA expression at 24 and 48 hpf identified genes that were differentially regulated over time and in response to the three PAH structures. PAH body burdens were analyzed at both time points using GC-MS, and demonstrated differences in PAH uptake into the embryos. This was important for discerning dose-related differences from those that represented unique molecular mechanisms. While BAA misregulated the least number of transcripts, it caused strong induction of cyp1a and other genes known to be downstream of the AHR, which were not induced by the other two PAHs. Analysis of functional roles of misregulated genes and their predicted regulatory transcription factors also distinguished the BAA response from regulatory networks disrupted by DBT and PYR exposure. These results indicate that systems approaches can be used to classify the toxicity of PAHs based on the networks perturbed following exposure, and may provide a path for unraveling the toxicity of complex PAH mixtures.

Geologically distinct crude oils cause a common cardiotoxicity syndrome in developing zebrafish

Crude oils from different geological formations vary in composition, yet most crude oils contain a polycyclic aromatic hydrocarbon (PAH) fraction that would be expected to produce cardiotoxic effects in developing fish. To determine whether different crude oils or PAH compositions produce common or distinct effects, we used zebrafish embryos to directly compare two crude oils at different states of weathering. Iranian heavy crude oil (IHCO) spilled in the Yellow Sea following the 2007 Hebei Spirit accident was compared to the intensively studied Alaska North Slope crude oil (ANSCO) using two different exposure methods, water-accommodated fractions containing dispersed oil microdroplets and oiled gravel effluent. Overall, both crude oils produced a largely overlapping suite of defects, marked by the well-known effects of PAH exposure on cardiac function. Specific cardiotoxicity phenotypes were nearly identical between the two oils, including impacts on ventricular contractility and looping of the cardiac chambers. However, with increased weathering, tissue-specific patterns of aryl hydrocarbon receptor (AHR) activation in the heart changed, with myocardial AHR activation evident when alkyl-PAHs dominated the mixture. Our findings suggest that mechanisms of cardiotoxicity may shift from a predominantly AHR-independent mode during early weathering to a multiple pathway or synergistic mode with prolonged weathering and increased proportions of dissolved alkyl-PAHs. Despite continued need for comparisons of crude oils from different sources, the results here indicate that the body of knowledge already acquired from studies of ANSCO is directly relevant to understanding the impacts of other crude oil spills on the early life history stages of fish.

Influence of exposure and toxicokinetics on measures of aquatic toxicity for organic contaminants: a case study review

This theoretical and case study review of dynamic exposures of aquatic organisms to organic contaminants examines variables important for interpreting exposure and therefore toxicity. The timing and magnitude of the absorbed dose change when the dynamics of exposure change. Thus, the dose metric for interpreting toxic responses observed during such exposure conditions is generally limited to the specific experiment and cannot be extrapolated to either other experiments with different exposure dynamics or to field exposures where exposure dynamics usually are different. This is particularly true for mixture exposures, for which the concentration and composition and, therefore, the timing and magnitude of exposure to individual components of different potency and potentially different mechanisms of action can vary. Aquatic toxicology needs studies that develop temporal thresholds for absorbed toxicant doses to allow for better extrapolation between conditions of dynamic exposure. Improved experimental designs are required that include high-quality temporal measures of both the exposure and the absorbed dose to allow better interpretation of data. For the short term, initial water concentration can be considered a conservative measure of exposure, although the extent to which this is true cannot be estimated specifically unless the dynamics of exposure as well as the toxicokinetics of the chemicals in the exposure scenario for the organism of interest are known. A better, but still limited, metric for interpreting the exposure and, therefore, toxicity is the peak absorbed dose, although this neglects toxicodynamics, requires appropriate temporal measures of accumulated dose to determine the peak concentration, and requires temporal thresholds for critical body residue for each component of the mixture.

Toxicological effects of crude oil and oil dispersant: biomarkers in the heart of the juvenile golden grey mullet (Liza aurata)

Dispersant use is a controversial oil spill response technique in coastal areas. Using an experimental approach, this study evaluated the toxicity of dispersant use upon juveniles of golden grey mullet (Liza aurata). Fish were exposed for 48 h to either dispersant only, chemically dispersed oil, mechanically dispersed oil, the water soluble fraction of oil or to control conditions. Following exposure and a depuration period, biomarkers were assessed in fish hearts, namely the total glutathione content and the activity of four enzymes (glutathione S-transferase, superoxide dismutase, catalase and glutathione peroxides). Comparing biomarker responses between the different treatments, this study revealed that 48 h exposure to dispersed oil (whether mechanically or chemically dispersed) resulted in a toxicity that was still detectable after a 14 days depuration period. Comparing biomarkers responses after an exposure to chemically and mechanically dispersed oil, this study suggests that chemical dispersion of the oil slick would not be more toxic than its natural dispersion under certain turbulent meteorological conditions (e.g. waves). Furthermore, the results indicated that the heart could be a target organ of interest in further studies investigating the toxicity of hydrocarbons. This study, which has been integrated into the DISCOBIOL project (Dispersant et techniques de lutte en milieu côtier: effets biologiques et apport à la réglementation), presents information of interest when attempting to provide a framework for dispersant applications in coastal areas.

Low-level pyrene exposure causes cardiac toxicity in zebrafish (Danio rerio) embryos

It is widely accepted that the most abundant polycyclic aromatic hydrocarbons (PAHs) in weathered crude oils is cardiotoxic. Although PAHs toxic endpoints show strong correlation with the aryl hydrocarbon receptor (AhR), a ligand activated transcription factor, and is thought to be a potent inducer of cytochrome P4501A, the action mechanism of PAHs on vertebrate cardiovascular development and disease is unclear. Herein, we address the cardiac developmental effects of exposure to the weak AhR agonist pyrene on the early life-stages of zebrafish. Embryos were exposed to 0, 0.05, 0.5, 5, and 50 nmol/L pyrene up to 72h post-fertilization (hpf). Pyrene-treated embryos showed dose-dependent heart abnormalities, such as pericardial edema and cardiac looping defects. Changes in AhR1a, AhR1b, AhR2, and Cyp1A expression were assessed by real-time RT-PCR. The results showed that low-level pyrene failed to alter these genes expression. However, the homeodomain transcription factor Nkx2.5, which plays an essential role in the development of the cardiovascular system, was down-regulated in a dose-dependent manner by pyrene exposure. The bone morphogenetic protein 2b (Bmp2b), which has been identified as the upstream gene of Nkx2.5, also was inhibited in a dose-dependent manner after treatment with pyrene. Taken together, these data indicated that embryonic exposure of zebrafish to low-level environmental pyrene disrupt normal cardiac development and alter expression of defective cardiac differentiation related genes.

Macondo crude oil from the Deepwater Horizon oil spill disrupts specific developmental processes during zebrafish embryogenesis

Background

The Deepwater Horizon disaster was the largest marine oil spill in history, and total vertical exposure of oil to the water column suggests it could impact an enormous diversity of ecosystems. The most vulnerable organisms are those encountering these pollutants during their early life stages. Water-soluble components of crude oil and specific polycyclic aromatic hydrocarbons have been shown to cause defects in cardiovascular and craniofacial development in a variety of teleost species, but the developmental origins of these defects have yet to be determined. We have adopted zebrafish, Danio rerio, as a model to test whether water accumulated fractions (WAF) of the Deepwater Horizon oil could impact specific embryonic developmental processes. While not a native species to the Gulf waters, the developmental biology of zebrafish has been well characterized and makes it a powerful model system to reveal the cellular and molecular mechanisms behind Macondo crude toxicity.

Results

WAF of Macondo crude oil sampled during the oil spill was used to treat zebrafish throughout embryonic and larval development. Our results indicate that the Macondo crude oil causes a variety of significant defects in zebrafish embryogenesis, but these defects have specific developmental origins. WAF treatments caused defects in craniofacial development and circulatory function similar to previous reports, but we extend these results to show they are likely derived from an earlier defect in neural crest cell development. Moreover, we demonstrate that exposure to WAFs causes a variety of novel deformations in specific developmental processes, including programmed cell death, locomotor behavior, sensory and motor axon pathfinding, somitogenesis and muscle patterning. Interestingly, the severity of cell death and muscle phenotypes decreased over several months of repeated analysis, which was correlated with a rapid drop-off in the aromatic and alkane hydrocarbon components of the oil.

Conclusions

Whether these teratogenic effects are unique to the oil from the Deepwater Horizon oil spill or generalizable for most crude oil types remains to be determined. This work establishes a model for further investigation into the molecular mechanisms behind crude oil mediated deformations. In addition, due to the high conservation of genetic and cellular processes between zebrafish and other vertebrates, our work also provides a platform for more focused assessment of the impact that the Deepwater Horizon oil spill has had on the early life stages of native fish species in the Gulf of Mexico and the Atlantic Ocean.