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

Potent phototoxicity of marine bunker oil to translucent herring embryos after prolonged weathering

Pacific herring embryos (Clupea pallasi) spawned three months following the Cosco Busan bunker oil spill in San Francisco Bay showed high rates of late embryonic mortality in the intertidal zone at oiled sites. Dead embryos developed to the hatching stage (e.g. fully pigmented eyes) before suffering extensive tissue deterioration. In contrast, embryos incubated subtidally at oiled sites showed evidence of sublethal oil exposure (petroleum-induced cardiac toxicity) with very low rates of mortality. These field findings suggested an enhancement of oil toxicity through an interaction between oil and another environmental stressor in the intertidal zone, such as higher levels of sunlight-derived ultraviolet (UV) radiation. We tested this hypothesis by exposing herring embryos to both trace levels of weathered Cosco Busan bunker oil and sunlight, with and without protection from UV radiation. Cosco Busan oil and UV co-exposure were both necessary and sufficient to induce an acutely lethal necrotic syndrome in hatching stage embryos that closely mimicked the condition of dead embryos sampled from oiled sites. Tissue levels of known phototoxic polycyclic aromatic compounds were too low to explain the observed degree of phototoxicity, indicating the presence of other unidentified or unmeasured phototoxic compounds derived from bunker oil. These findings provide a parsimonious explanation for the unexpectedly high losses of intertidal herring spawn following the Cosco Busan spill. The chemical composition and associated toxicity of bunker oils should be more thoroughly evaluated to better understand and anticipate the ecological impacts of vessel-derived spills associated with an expanding global transportation network.

Unexpectedly high mortality in Pacific herring embryos exposed to the 2007 Cosco Busan oil spill in San Francisco Bay

In November 2007, the container ship Cosco Busan released 54,000 gallons of bunker fuel oil into San Francisco Bay. The accident oiled shoreline near spawning habitats for the largest population of Pacific herring on the west coast of the continental United States. We assessed the health and viability of herring embryos from oiled and unoiled locations that were either deposited by natural spawning or incubated in subtidal cages. Three months after the spill, caged embryos at oiled sites showed sublethal cardiac toxicity, as expected from exposure to oil-derived polycyclic aromatic compounds (PACs). By contrast, embryos from the adjacent and shallower intertidal zone showed unexpectedly high rates of tissue necrosis and lethality unrelated to cardiotoxicity. No toxicity was observed in embryos from unoiled sites. Patterns of PACs at oiled sites were consistent with oil exposure against a background of urban sources, although tissue concentrations were lower than expected to cause lethality. Embryos sampled 2 y later from oiled sites showed modest sublethal cardiotoxicity but no elevated necrosis or mortality. Bunker oil contains the chemically uncharacterized remains of crude oil refinement, and one or more of these unidentified chemicals likely interacted with natural sunlight in the intertidal zone to kill herring embryos. This reveals an important discrepancy between the resolving power of current forensic analytical chemistry and biological responses of keystone ecological species in oiled habitats. Nevertheless, we successfully delineated the biological impacts of an oil spill in an urbanized coastal estuary with an overlapping backdrop of atmospheric, vessel, and land-based sources of PAC pollution.

Recurrent die-offs of adult coho salmon returning to spawn in Puget Sound lowland urban streams

Several Seattle-area streams in Puget Sound were the focus of habitat restoration projects in the 1990s. Post-project effectiveness monitoring surveys revealed anomalous behaviors among adult coho salmon returning to spawn in restored reaches. These included erratic surface swimming, gaping, fin splaying, and loss of orientation and equilibrium. Affected fish died within hours, and female carcasses generally showed high rates (>90%) of egg retention. Beginning in the fall of 2002, systematic spawner surveys were conducted to 1) assess the severity of the adult die-offs, 2) compare spawner mortality in urban vs. non-urban streams, and 3) identify water quality and spawner condition factors that might be associated with the recurrent fish kills. The forensic investigation focused on conventional water quality parameters (e.g., dissolved oxygen, temperature, ammonia), fish condition, pathogen exposure and disease status, and exposures to metals, polycyclic aromatic hydrocarbons, and current use pesticides. Daily surveys of a representative urban stream (Longfellow Creek) from 2002-2009 revealed premature spawner mortality rates that ranged from 60-100% of each fall run. The comparable rate in a non-urban stream was <1% (Fortson Creek, surveyed in 2002). Conventional water quality, pesticide exposure, disease, and spawner condition showed no relationship to the syndrome. Coho salmon did show evidence of exposure to metals and petroleum hydrocarbons, both of which commonly originate from motor vehicles in urban landscapes. The weight of evidence suggests that freshwater-transitional coho are particularly vulnerable to an as-yet unidentified toxic contaminant (or contaminant mixture) in urban runoff. Stormwater may therefore place important constraints on efforts to conserve and recover coho populations in urban and urbanizing watersheds throughout the western United States.

Transcriptional evidence for low contribution of oil droplets to acute toxicity from dispersed oil in first feeding Atlantic cod (Gadus morhua) larvae

We evaluated the potential contribution of oil droplets to the toxicity of dispersed oil to first feeding fish larvae. Atlantic cod larvae were exposed to five concentrations of either artificially weathered (200°C residue) dispersed oil (D1-D5) containing oil droplets [medium size 11-13 μm based on volume] and water-soluble fraction [WSF] or the filtered dispersions containing only the corresponding equilibrium WSFs only (W1-W5). The larvae were exposed for 4 days and harvested for transcriptional analysis at 13 days post hatching. The most significant differently expressed genes were observed in cod larvae exposed to the highest concentration of the dispersed oil (containing 10.41 ± 0.46 μg ∑PAH/L), with CYP1A showing the strongest response. Functional analysis further showed that the top scored network as analyzed with Ingenuity Pathway Analysis was "Drug Metabolism, Endocrine System Development and Function, Lipid Metabolism". Oil exposure also increased the expression of genes involved in bone resorption and decreased the expression of genes related to bone formation. In conclusion, oil exposure affects drug metabolism, endocrine regulation, cell differentiation and proliferation, apoptosis, fatty acid biosynthesis and tissue development in Atlantic cod larvae. The altered gene transcription was dominated by the WSF and the corresponding oil droplet fraction only had a moderate contribution to the observed changes.

Cardiac toxicity of 5-ring polycyclic aromatic hydrocarbons is differentially dependent on the aryl hydrocarbon receptor 2 isoform during zebrafish development

Petroleum-derived compounds, including polycyclic aromatic hydrocarbons (PAHs), commonly occur as complex mixtures in the environment. Recent studies using the zebrafish experimental model have shown that PAHs are toxic to the embryonic cardiovascular system, and that the severity and nature of this developmental cardiotoxicity varies by individual PAH. In the present study we characterize the toxicity of the relatively higher molecular weight 5-ring PAHs benzo[a]pyrene (BaP), benzo[e]pyrene (BeP), and benzo[k]fluoranthene (BkF). While all three compounds target the cardiovascular system, the underlying role of the ligand-activated aryl hydrocarbon receptor (AHR2) and the tissue-specific induction of the cytochrome p450 metabolic pathway (CYP1A) were distinct for each. BaP exposure (40μM) produced AHR2-dependent bradycardia, pericardial edema, and myocardial CYP1A immunofluorescence. By contrast, BkF exposure (4-40μM) caused more severe pericardial edema, looping defects, and erythrocyte regurgitation through the atrioventricular valve that were AHR2-independent (i.e., absent myocardial or endocardial CYP1A induction). Lastly, exposure to BeP (40μM) yielded a low level of CYP1A+ signal in the vascular endothelium of the head and trunk, without evident toxic effects on cardiac function or morphogenesis. Combined with earlier work on 3- and 4-ring PAHs, our findings provide a more complete picture of how individual PAHs may drive the cardiotoxicity of mixtures in which they predominate. This will improve toxic injury assessments and risk assessments for wild fish populations that spawn in habitats altered by overlapping petroleum-related human impacts such as oil spills, urban stormwater runoff, or sediments contaminated by legacy industrial activities.

Identification and evaluation of cyp1a transcript expression in fish as molecular biomarker for petroleum contamination in tropical fresh water ecosystems

In order to monitor potential contamination deriving from exploration and transport of oil in the Urucu region (Brazil), there is a need to establish suitable biomarkers for native Amazonian fish. Therefore, the transcript expression of various potentially sensitive genes (ahr2(1), cyp1a, hmox1, hsp70, maft, mt, nfe212, gstp1 and nqo1) in fish exposed to water soluble fractions of oil (WSF) was compared. The analysis was first performed in an established laboratory model, the zebrafish embryo. The cyp1a gene proved to be the most sensitive and robust marker for oil contamination and, hence, was selected to study the effect of oil-derived contaminants in the Amazonian cichlid Astronotus ocellatus. Induction of cyp1a transcript expression was observed for ≥0.0061% (v/v) WSFs. In liver samples of fish, collected from different lakes in the Urucu oil mining area, no elevated expression of cyp1a transcripts was observed. The data demonstrate the high sensitivity of cyp1a as indicator of oil exposure; further studies should be considered to test its usefulness at known contaminated sites and to evaluate influential factors by, e.g. mesocosm experiments.

Sublethal exposure to crude oil during embryonic development alters cardiac morphology and reduces aerobic capacity in adult fish

Exposure to high concentrations of crude oil produces a lethal syndrome of heart failure in fish embryos. Mortality is caused by cardiotoxic polycyclic aromatic hydrocarbons (PAHs), ubiquitous components of petroleum. Here, we show that transient embryonic exposure to very low concentrations of oil causes toxicity that is sublethal, delayed, and not counteracted by the protective effects of cytochrome P450 induction. Nearly a year after embryonic oil exposure, adult zebrafish showed subtle changes in heart shape and a significant reduction in swimming performance, indicative of reduced cardiac output. These delayed physiological impacts on cardiovascular performance at later life stages provide a potential mechanism linking reduced individual survival to population-level ecosystem responses of fish species to chronic, low-level oil pollution.

Methods for conducting bioassays using embryos and larvae of Pacific herring, Clupea pallasi

The rapid decrease of several stocks of Pacific herring, Clupea pallasi, in Puget Sound, Washington, has led to concerns about the effects of industrial and nonpoint source contamination on the embryo and larval stages of this and related forage fish species. To address these concerns, the state of Washington and several industries have funded efforts to develop embryo and larval bioassay protocols that can be used by commercial laboratories for routine effluent testing. This article presents the results of research to develop herring embryo and larval bioassay protocols. Factors evaluated during protocol development included temperature, salinity, dissolved oxygen (DO), light intensity, photoperiod, larval feeding regimes, use of brine and artificial sea salts, gonad sources, collection methods, and egg quality.

Inhibition by polycyclic aromatic hydrocarbons of ATPase activities in Sebastiscus marmoratus larvae: relationship with the development of early life stages

Sebastiscus marmoratus larvae were exposed to waterborne polycyclic aromatic hydrocarbons (PAHs) containing 3-5 rings, benzo[a]pyrene (BaP), pyrene (Py) or phenanthrene (Phe), respectively at 0.01, 0.1 and 1 μg L⁻¹. Cumulative mortality, frequency of dorsal curvature and rate of pericardial and yolk sac edema in larvae treated for 8 days were significantly increased in a dose-dependent manner. All three PAHs resulted in reduction of the lower jaw, and the extent of reduction increased with increasing concentrations of the PAHs. Na+/K+-ATPase and Ca²+-ATPase activity in larvae exposed to the three PAHs were all significantly inhibited in a dose-dependent manner. Analysis using the Pearson correlation coefficient indicated a significant correlation between the rate of the dorsal curvature and edema and the inhibition of Na+/K+-ATPase and Ca²+-ATPase activity, suggesting that the developmental defects caused by PAHs were related to their inhibition of Na+/K+-ATPase and Ca²+-ATPase activity.

AhR2-mediated, CYP1A-independent cardiovascular toxicity in zebrafish (Danio rerio) embryos exposed to retene

In the embryo-larval stages of fish, alkylphenanthrenes such as retene (7-isopropyl-1-methylphenanthrene) produce a suite of developmental abnormalities typical of exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), including pericardial and yolk sac edema, cardiovascular dysfunction, and skeletal deformities. To investigate the mechanism and target tissue of retene toxicity, we used observational, histological, and protein knockdown techniques in zebrafish (Danio rerio) embryos. The primary overt signs of toxicity are pericardial edema and reduced blood flow, first observed at 36 h post-fertilization (hpf). The most pronounced effects at this stage are a reduced layer of cardiac jelly in the atrium and reduced diastolic filling. Conversely, an increased layer of cardiac jelly is observed at 72 hpf in retene-exposed embryos. Induction of cytochrome P4501A (CYP1A) is apparent in a subset of cardiomyocytes by 48 hpf suggesting that early cardiac effects may be due to AhR activation in the myocardium. Myocardial CYP1A induction is transient, with only endocardial induction observed at 72 hpf. Knockdown of cyp1a by morpholino oligonucleotides does not affect retene toxicity; however, ahr2 knockdown prevents toxicity. Thus, the mechanism of retene cardiotoxicity is AhR2-mediated and CYP1A-independent, similar to TCDD; however, the onset and proximate signs of retene toxicity differ from those of TCDD. Retene cardiotoxicity also differs mechanistically from the cardiac effects of non-alkylated phenanthrane, illustrating that alkyl groups can alter toxic action. These findings have implications for understanding the toxicity of complex mixtures containing alkylated and non-alkylated polycyclic aromatic hydrocarbons.

Ecotoxicological mechanisms and models in an impact analysis tool for oil spills

In an international collaborative effort, an impact analysis tool is being developed to predict the effect of accidental oil spills on recruitment and production of Atlantic cod (Gadus morhua) in the Barents Sea. The tool consisted of three coupled ecological models that describe (1) plankton biomass dynamics, (2) cod larvae growth, and (3) fish stock dynamics. The discussions from a series of workshops are presented in which variables and parameters of the first two ecological models were listed that may be affected by oil-related compounds. In addition, ecotoxicological algorithms are suggested that may be used to quantify such effects and what the challenges and opportunities are for algorithm parameterization. Based on model exercises described in the literature, survival and individual growth of cod larvae, survival and reproduction of zooplankton, and phytoplankton population growth are denoted as variables and parameters from the ecological models that might be affected in case of an oil spill. Because toxicity databases mostly (67%) contain data for freshwater species in temperate environments, parameterization of the ecotoxicological algorithms describing effects on these endpoints in the subarctic marine environment is not straightforward. Therefore, it is proposed that metadata analyses be used to estimate the sensitivity of subarctic marine species from available databases. To perform such analyses and reduce associated uncertainty and variability, mechanistic models of varying complexity, possibly aided by new experimental data, are proposed. Lastly, examples are given of how seasonality in ecosystems may influence chemical effects, in particular in the subarctic environment. Food availability and length of day were identified as important characteristics as these determine nutritional status and phototoxicity, respectively.

Acute effects of COREXIT EC9500A on cardiovascular functions in rats

These studies characterized cardiovascular responses after an acute inhalation exposure to COREXIT EC9500A, the oil dispersant used in the Deepwater Horizon oil spill. Male Sprague-Dawley rats underwent a single 5-h inhalation exposure to COREXIT EC9500A (average exposure level 27.12 mg/m(3)) or air. On d 1 and 7 following the exposure, rats were implanted with indwelling catheters and changes in heart rate and blood pressure were assessed in response to increasing levels of adrenoreceptor agonists. A separate group of rats was euthanized at the same time points, ventral tail arteries were dissected, and vascular tone along with dose-dependent responses to vasoconstricting and dilating factors were assessed in vitro. Agonist-induced dose-dependent increases in heart rate and blood pressure were greater in COREXIT EC9500A-exposed than in air-exposed rats at 1 d but not 7 d after the exposure. COREXIT EC9500A exposure also induced a rise in basal tone and reduced responsiveness of tail arteries to acetylcholine-induced vasodilation at 1 d but not 7 d following the exposure. These findings demonstrate that an acute exposure to COREXIT EC9500A exerts transient effects on cardiovascular and peripheral vascular functions.

Oil spills and fish health: exposing the heart of the matter

The chemical complexity of crude oil and its fuel products poses many important challenges for exposure science in marine ecosystems that support productive fisheries throughout the world. Meeting these challenges will enable better decisions on approaches to protecting and restoring these ecosystems.

Natural sunlight and residual fuel oils are an acutely lethal combination for fish embryos

The majority of studies characterizing the mechanisms of oil toxicity in fish embryos and larvae have focused largely on unrefined crude oil. Few studies have addressed the toxicity of modern bunker fuels, which contain residual oils that are the highly processed and chemically distinct remains of the crude oil refinement process. Here we use zebrafish embryos to investigate potential toxicological differences between unrefined crude and residual fuel oils, and test the effects of sunlight as an additional stressor. Using mechanically dispersed oil preparations, the embryotoxicity of two bunker oils was compared to a standard crude oil from the Alaska North Slope. In the absence of sunlight, all three oils produced the stereotypical cardiac toxicity that has been linked to the fraction of tricyclic aromatic compounds in an oil mixture. However, the cardiotoxicity of bunker oils did not correlate strictly with the concentrations of tricyclic compounds. Moreover, when embryos were sequentially exposed to oil and natural sunlight, the bunker oils produced a rapid onset cell-lethal toxicity not observed with crude oil. To investigate the chemical basis of this differential toxicity, a GC/MS full scan analysis was used to identify a range of compounds that were enriched in the bunker oils. The much higher phototoxic potential of chemically distinct bunker oils observed here suggests that this mode of action should be considered in the assessment of bunker oil spill impacts, and indicates the need for a broader approach to understanding the aquatic toxicity of different oils.

Anthropogenically sourced low concentration PAHS: In situ bioavailability to juvenile Pacific salmon

Gill 7-ethoxyresorufin O-deethylase (EROD) activity of juvenile Chinook salmon caged in Auke Lake, AK was used as a biomarker of polycyclic aromatic hydrocarbon (PAH) exposure. Biomarker measurements in conjunction with a comprehensive sampling program that included grab water and sediment samples, and passive sampling devices were used to determine PAH concentrations, source(s), bioavailability, and resulting biological response. PAHs were detected at all lake locations except the reference site upstream of anthropogenic activity. Water samples were the best predictor of a biological response and EROD activity correlated to corresponding parts per trillion water pyrene concentrations (r(2)=0.9662; p=0.0004). Sediment samples yielded the clearest indication of PAH sources and amalgamated contaminant magnitude, and passive samplers served as accumulators of retrospective aqueous conditions. Results suggest that salmon stocks are being exposed to chronic low-concentrations of anthropogenically sourced PAHs during sensitive life-stages, which may be in part a contributor to their declining numbers.

Impacts of suspended sediments on fertilization, embryonic development, and early larval life stages of the pacific herring, Clupea pallasi

Pacific herring reproduce in the San Francisco Bay estuary during times of the year when suspended sediment loads are highest due to freshwater input, yet little is known about the effects of sediment on herring early life stages. During the first 2 h after eggs contacted water, embryos were adhesive and susceptible to having sediment particles attach permanently to the chorion. Treatment with suspended San Francisco Bay dredged sediments at ecologically relevant concentrations of 250 or 500 mg/l during this time period increased self-aggregation of the eggs and led to sublethal and lethal effects. After the first 2 h in water, sediments that contacted embryos did not attach to chorions and did not have an observable impact. Sediment treatment during the first 2 h was not linked statistically to declines in fertilization or total larval hatch rate, but it did produce significant sublethal effects that included increases in precocious larval hatch and higher percentages of abnormal larvae, as well as an increase in larval mortality.