Evaluation of Fish Early Life-Stage Toxicity Models of Chronic Embryonic Exposures to Complex Polycyclic Aromatic Hydrocarbon Mixtures

First Record of Malformation in Seahorses Attributed to the Oil Spill off the Brazilian Coast in 2019

In 2019, there was an environmental catastrophe in Brazil, when more than 5000 tons of unknown origin crude oil invaded beaches and mangroves. Two years later, two monitoring areas were selected to study seahorses' offspring: Massangana River estuary (apparently healthy area) and Cocaia Island (affected area). Thirty-six reproductive events of Hippocampus reidi (Syngnathidae) couples from these two areas were monitored to analyze the offspring. At the apparently healthy area, no newborns with malformations were found. However, the offspring from Cocaia Island showed a mean of 19.73% (±5.23) malformations in newborns. It is argued that the toxic/teratogenic effects of polycyclic aromatic hydrocarbons have affected the population in two ways: directly through the induction of mutations in the germ cells of the species and through a drastic reduction of the population (bottleneck effect) whose density observed today recovered through consanguineous couplings, potentiating deleterious genotypes in the offspring. Environ Toxicol Chem 2024;43:1996-2004. © 2024 SETAC.

A Quantitative Adverse Outcome Pathway for Embryonic Activation of the Aryl Hydrocarbon Receptor of Fishes by Polycyclic Aromatic Hydrocarbons Leading to Decreased Fecundity at Adulthood

Quantitative adverse outcome pathways (qAOPs) describe the response-response relationships that link the magnitude and/or duration of chemical interaction with a specific molecular target to the probability and/or severity of the resulting apical-level toxicity of regulatory relevance. The present study developed the first qAOP for latent toxicities showing that early life exposure adversely affects health at adulthood. Specifically, a qAOP for embryonic activation of the aryl hydrocarbon receptor 2 (AHR2) of fishes by polycyclic aromatic hydrocarbons (PAHs) leading to decreased fecundity of females at adulthood was developed by building on existing qAOPs for (1) activation of the AHR leading to early life mortality in birds and fishes, and (2) inhibition of cytochrome P450 aromatase activity leading to decreased fecundity in fishes. Using zebrafish (Danio rerio) as a model species and benzo[a]pyrene as a model PAH, three linked quantitative relationships were developed: (1) plasma estrogen in adult females as a function of embryonic exposure, (2) plasma vitellogenin in adult females as a function of plasma estrogen, and (3) fecundity of adult females as a function of plasma vitellogenin. A fourth quantitative relationship was developed for early life mortality as a function of sensitivity to activation of the AHR2 in a standardized in vitro AHR transactivation assay to integrate toxic equivalence calculations that would allow prediction of effects of exposure to untested PAHs. The accuracy of the predictions from the resulting qAOP were evaluated using experimental data from zebrafish exposed as embryos to another PAH, benzo[k]fluoranthene. The qAOP developed in the present study demonstrates the potential of the AOP framework in enabling consideration of latent toxicities in quantitative ecological risk assessments and regulatory decision-making. Environ Toxicol Chem 2024;00:1-12. © 2024 SETAC.

Toxicity evaluation of water-accommodated fraction of heavy and light oils on the rainbow trout fish cell line RTL-W1

Fish are currently used models for the toxicity assessment of chemicals, including polycyclic aromatic hydrocarbons (PAHs). Alternative methods including fish cell lines are currently used to provide fast and reliable results on the toxic properties of chemicals while respecting ethical concerns about animal testing. The Rainbow trout liver cell line RTLW1 was used to analyze the effects of two water-accommodated fractions from two crude oils: Arabian Light crude oil (LO) and refined oil from Erika (HO). Several toxicity endpoints were assessed in this study, including cytotoxicity, EROD activity, DNA damage (comet and micronucleus assays), and ROS production. RTL-W1 cells were exposed for 24 h at two or three dilutions of WAF at 1000 µg/L (0.1% (1 μg/L), 1% (10 μg/L), and 10% (100 μg/L)) for cytotoxicity and EROD activity and 1% and 10% for ROS production and genotoxicity). Exposure of RTL-W1 cells to LO WAF induced a significant increase of EROD activity and ROS production and altered DNA integrity as revealed by both the comet assay and the micronucleus test for 10 µg/L of LO. On the other hand, HO WAF exhibited limited toxic effects except for an EROD induction for 1% WAF dilution. These results confirmed the usefulness of RTL-W1 cells for in vitro toxicological assessment of chemical mixtures.

Growth of Pacific staghorn sculpin (Leptocottus armatus) is reduced at contaminated sites in the Lower Duwamish River, Washington

The Lower Duwamish River is a highly industrialized waterway flowing into the densely urbanized Puget Sound waterfront of Seattle, Washington, USA. The river has been profoundly altered from its natural state following more than a century of channelization, recurrent dredging, shoreline armoring, and pollution discharges. As part of a Natural Resource Damage Assessment addressing historical pollution at three designated Superfund sites (i.e., the assessment area), juvenile Pacific staghorn sculpin (Leptocottus armatus) were sampled throughout the lower river in order to evaluate injury from exposure to polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDTs), and butyltins (BTs). Sculpin live in close association with the river sediments within and upriver of the assessment area. Fish were collected for analysis of contaminant concentrations in composited whole bodies and stomach contents, as well as individual fish health metrics including daily somatic growth rates measured from otoliths. Sediment contaminant concentrations were also measured at sites near to fishing locations. Fish growth rates varied from 0.65 to 1.05 mm/day, and were significantly lower at unremediated downriver sites compared to upriver and remediated locations. Sculpin growth rates were negatively correlated with concentrations of PCBs in fish bodies, PAHs in stomach contents, as well as PCBs, DDTs and PAHs in sediment. Mixed effects models for whole-body and stomach content contaminants showed positive correlations between growth rate and water temperature. Temperature was not a significant confounding variable for the relationship between growth rate and sediment contaminants. Overall, these results show that juvenile sculpin are harmed by contaminant exposure in the Lower Duwamish River. Furthermore, this study demonstrates the utility of using paired biological and chemical indicators of pollutant-induced injury in a resident fish to inform a complex Natural Resource Damage Assessment and associated restoration efforts.

Modeling chronic oil pollution from ships

Stochastic simulations of virtual oil spills from ships were performed for the Adriatic Sea over 2017-2020, applying the European Marine Observation and Data Network vessel densities as a proxy for starting locations of operational spillage. The MEDSLIK-II oil spill model was run using high-resolution currents provided by the Copernicus Marine Service and the European Centre for Medium-Range Weather Forecasts winds. Chronic exposure to operational oil spills was reported in terms of hazard indices for five vessel groups: pleasure and passenger ships, cargo and service vessels, the fishing fleet, tankers, and other ships. The northernmost Adriatic expectedly showed the highest hazard values, including the areas of Trieste and Venice, where cargo and service ships were the dominant polluters. The Croatian coastal waters were more chronically polluted than the Italian coastal waters; the predominant contribution was from coastwise pleasure and passenger ships.

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

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

Co-Exposure of Phenanthrene and the cyp-Inducer 3-Methylchrysene Leads to Altered Biotransformation and Increased Toxicity in Fish Egg and Larvae

Polycyclic aromatic hydrocarbons (PAHs) have frequently been suspected of governing crude oil toxicity because of similar morphological defects in fish. However, PAH concentrations are often not high enough to explain the observed crude oil toxicity. We hypothesize that one PAH can enhance the metabolism and toxicity of another PAH when administered as a mixture. Early life stage Atlantic haddock (Melanogrammus aeglefinus) were in this study exposed to phenanthrene in the presence and absence of 3-methylchrysene that is known to induce the metabolic enzyme cytochrome P450 1A via cyp1a gene expression. Uptake, metabolism, and multiple toxicity endpoints were then measured in a time-course study up to 3 days post-hatching. Passive dosing provided aqueous concentrations ≈180 μg/L for phenanthrene and ≈0.6 μg/L for 3-methylchrysene, which resulted in tissue concentrations ≈60 μg/g ww for phenanthrene and ≈0.15 μg/g ww for 3-methylchrysene. The low concentration of 3-methylchrysene led to the elevated expression of cyp1a but no toxicity. Levels of phenanthrene metabolites were 5-fold higher, and morphological defects and cardiotoxicity were consistently greater when co-exposed to both compounds relative to phenanthrene alone. This work highlights the metabolic activation of PAH toxicity by a co-occurring PAH, which can lead to excess toxicity, synergistic effects, and the overproportional contribution of PAHs to crude oil toxicity.

Effect of polycyclic aromatic hydrocarbons on homeobox gene expression during embryonic development of cuttlefish, Sepia officinalis

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants (POPs) commonly found in marine environments. Their bioaccumulation can cause harm to aquatic organisms, including invertebrates, particularly during the early stages of embryonic development. In this study, we evaluated, for the first time, the patterns of PAH accumulation in both capsule and embryo of common cuttlefish (Sepia officinalis). In addition, we explored the effects of PAHs by analysing the expression profiles of seven homeobox genes [i.e., gastrulation brain homeobox (GBX), paralogy group labial/Hox1 (HOX1), paralogy group Hox3 (HOX3), dorsal root ganglia homeobox (DRGX), visual system homeobox (VSX), aristaless-like homeobox (ARX) and LIM-homeodomain transcription factor (LHX3/4)]. We found that PAH levels in egg capsules were higher than those observed in chorion membranes (35.1 ± 13.3 ng/g vs 16.4 ± 5.9 ng/g). Furthermore, PAHs were also found in perivitellin fluid (11.5 ± 5.0 ng/ml). Naphthalene and acenaphthene were the congeners present at highest concentrations in each analysed egg component suggesting higher bioaccumulation rates. Embryos with high concentrations of PAHs also showed a significant increase in mRNA expression for each of the analysed homeobox genes. In particular, we observed a 15-fold increase in the ARX expression levels. Additionally, the statistically significant variation in homeobox gene expression patterns was accompanied by a concomitant increase in mRNA levels of both aryl hydrocarbon receptor (AhR) and estrogen receptor (ER). These findings suggest that bioaccumulation of PAHs may modulate developmental processes of cuttlefish embryos by targeting homeobox gene-mediated transcriptional outcomes. Mechanisms underlying the upregulation of homeobox genes could be related to the ability of PAHs to directly activate AhR- or ER-related signaling pathways.

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

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

Embryonic exposure to environmentally relevant levels of tributyltin affects embryonic tributyltin bioaccumulation and the physiological responses of juveniles in cuttlefish (Sepia pharaonis)

Tributyltin (TBT) is a typical organic pollutant that persists in aquatic sediments due to its wide usage as an antifouling fungicide during the past few decades. Despite increased awareness of the serious negative consequences of TBT on aquatic species, studies on the effects of TBT exposure on cephalopod embryonic development and juvenile physiological performance are scarce. To investigate the lasting effects of TBT toxicity on Sepia pharaonis from embryo to hatchling, embryos (gastrula stage, 3-5 h post fertilization) were exposed to four levels of TBT until hatching: 0 (control), 30 (environmental level), 60, and 120 ng/L. Subsequently, juvenile growth performance endpoints and behavioral alterations were assessed over 15 days post-hatching. Egg hatchability was significantly reduced and embryonic development (i.e., premature hatching) was accelerated in response to 30 ng/L TBT exposure. Meanwhile, TBT-induced alterations in embryonic morphology primarily included yolk-sac lysis, embryonic malformations, and uneven pigment distributions. During the pre-middle stage of embryonic development, the eggshell serves as an effective barrier to safeguard the embryo from exposure to 30-60 ng/L TBT, according to patterns of TBT accumulation and distribution in the egg compartment. However, even environmental relevant levels of TBT (30 ng/L) exposure during embryonic development had a negative impact on juvenile behavior and growth, including slowing growth, shortening eating times, causing more irregular movements, and increasing inking times. These findings indicate that after TBT exposure, negative long-lasting effects on S. pharaonis development from embryo to hatchling persist, suggesting that long-lasting toxic effects endure from S. pharaonis embryos to hatchlings.

Impacts of water pollutants on chondrichthyans species from South America: A review

This is the first research that extensively compiles all the available scientific literature on the presence of trace metals (TMs), persistent organic pollutants (POPs), and plastic debris in Chondrichthyan species inhabiting South America (including the Atlantic and Pacific Oceans), providing an insight into Chondrichthyans as bioindicators of pollutants as well as the impacts of pollutant exposure on the organisms. Seventy-three studies were published in South America between 1986 and 2022. While 68.5% focused on TMs, 17.8% on POPs, and 9.6% on plastic debris. Brazil and Argentina were at the top in terms of the number of publications; however, there is an absence of information regarding pollutants for Chondrichthyans in Venezuela, Guyana, and French Guiana. Of the 65 Chondrichthyan species reported, 98.5% belong to the Elasmobranch group, and 1.5% from the Holocephalans. Most studies focused on Chondrichthyans of economic importance, and the most analyzed organs were the muscle and liver. There is a lack of studies on Chondrichthyan species with low economic value and critical conservation status. Due to their ecological relevance, distribution, accessibility, high trophic position, capacity to accumulate high levels of pollutants, and the number of studies published, Prionace glauca and Mustelus schmitii seem to be adequate to serve as bioindicators. For TMs, POPs, and plastic debris there is a lack of studies focusing on the pollutant levels as well as their effect on Chondrichthyans. Future research reporting TMs, POPs, and plastic debris occurrences in Chondrichthyan species are required in order to increase the scarce databases about pollutants in this group, with a clear need for further research on the responses of chondrichthyans to pollutants, as well as making inferences about the potential risks to the ecosystems and human health.

Alkyl-phenanthrenes in early life stage fish: differential toxicity in Atlantic haddock (Melanogrammus aeglefinus) embryos

Tricyclic polycyclic aromatic hydrocarbons (PAHs) are believed to be the primary toxic components of crude oil. Such compounds including phenanthrene are known to have direct effects on cardiac tissue, which lead to malformations during organogenesis in early life stage fish. We tested a suite of 13 alkyl-phenanthrenes to compare uptake and developmental toxicity in early life stage haddock (Melanogrammus aeglefinus) embryos during gastrulation/organogenesis beginning at 2 days post fertilization via passive dosing. The alkyl-phenanthrenes were tested at their solubility limits, and three of them also at lower concentrations. Measured body burdens were linearly related to measured water concentrations. All compounds elicited one or more significant morphological defects or functional impairment, such as decreased length, smaller eye area, shorter jaw length, and increased incidence of body axis deformities and eye deformities. The profile of developmental toxicities appeared unrelated to the position of alkyl substitution, and gene expression of cytochrome 1 a (cyp1a) was low regardless of alkylation. Mortality and sublethal effects were observed below the expected range for baseline toxicity, thus indicating excess toxicity. Additionally, PAH concentrations that resulted in toxic effects here were far greater than when measured in whole crude oil exposures that cause toxicity. This work demonstrates that, while these phenanthrenes are toxic to early life stage fish, they cannot individually account for most of the developmental toxicity of crude oil, and that other compounds and/or mixture effects should be given more consideration.

Impacts of dispersants on microbial communities and ecological systems

Accidental oil spills can result in catastrophic ecological insults and therefore require rapid intervention to mitigate the potential impacts to aquatic ecosystems. One of the largest oil spills, known as the Deepwater Horizon oil spill, occurred in the Spring of 2010 near the coast of Louisiana (USA) due to an explosion during oil drilling activities. Millions of gallons of oil were released into the Gulf of Mexico, impacting thousands of ocean miles and coastal areas linked to the gulf. Among the actions taken during the remediation efforts was the unprecedented large use of Corexit dispersants, including at the subsurface to prevent oil from reaching the surface. While there is evidence that dispersants can accelerate the biodegradation of oil, reports on their potential toxicity to aquatic biota and to microbial functions have also been documented. In this review, we will examine the most recent literature on the impact of dispersants on microbial communities implicated in oil degradation and overall ecological networks. The primary focus will be on studies using Corexit but other dispersants will be discussed if data are available. We will share the literature gaps identified and discuss future work that is needed to reconcile some of the discrepancies found on the effectiveness of dispersants on oil degradation and their potential toxicity. KEY POINTS: • Chemical dispersants have been applied as a chemical response measure for oil spills. • The effects of chemical dispersants on microbial communities have been the subject of substantial research. • This work seeks to review recent work on the impact of chemical dispersants on oil biodegradation, microbial communities, and ecosystems.

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

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

An annual profile of the impacts of simulated oil spills on the Northeast Arctic cod and haddock fisheries

We simulate the combined natural and pollutant-induced survival of early life stages of NEA cod and haddock, and the impact on the adult populations in response to the time of a major oil spill in a single year. Our simulations reveal how dynamic ocean processes, controlling both oil transport and fate and the frequency of interactions of oil with drifting fish eggs and larvae, mediate the magnitude of population losses due to an oil spill. The largest impacts on fish early life stages occurred for spills initiated in Feb-Mar, concomitant with the initial rise in marine productivity and the earliest phase of the spawning season. The reproductive health of the adult fish populations was maintained in all scenarios. The study demonstrates the application of a simulation system that provides managers with information for the planning of development activities and for the protection of fisheries resources from potential impacts.

Effects of lubricant oil and diesel on macrofaunal communities in marine sediments: A five year field experiment in Antarctica

Hydrocarbons pose significant risks to marine ecosystems. A field experiment investigated the effects of four different hydrocarbon products (diesel fuel and three lubricating oils: Unused, Used and Biodegradable) on sediment macrofaunal communities over a five year period, in a shallow Antarctic marine embayment. Sediments were defaunated, treated with a hydrocarbon and deployed in trays (including a control) on the seabed. Diesel fuel had the biggest initial impact on communities, with strong effects at 5 weeks and 1 year, in particular on annelids, but also on amphipods, ostracods and cumaceans. By five years, however, the effect of diesel was less than that of lubrication oils and showed more recovery than oiled treatments and the biggest effect was from the Used oil. There was an effect of hydrocarbons on diversity, especially diesel, at 5 weeks and 1 year, but by 2 and 5 years diversity was not different or greater in hydrocarbon treatments than controls. Total abundance was always lower in hydrocarbon treatments than controls, especially for crustaceans, but annelids were more abundant in oil treatments than controls at 5 years. Oils, and in some cases diesel, enhanced the abundance of some taxa at 2-5 years, including molluscs, some polychaete families (capitellids, cirratulids, dorvilleids), oligochaetes, as well as ostracods, cumaceans and isopods. Amphipods and tanaids were most sensitive to hydrocarbons, and annelids were very sensitive to diesel. The Biodegradable oil had similar magnitude community effects to standard oil at 5 years, but annelids were more affected by Biodegradable oil, particularly at 1 and 2 years, and it did not enhance annelid or mollusc abundance at 5 years like the other oils, except for some polychaete families. Impacts of spilled hydrocarbons in Antarctica will persist well beyond 5 years, but diesel impacts will recover faster than oil.

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

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

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

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

Alkylation of Benz[a]anthracene Affects Toxicity to Early-Life Stage Zebrafish and In Vitro Aryl Hydrocarbon Receptor 2 Transactivation in a Position-Dependent Manner

Polycyclic aromatic hydrocarbons (PAHs) are structurally diverse organic chemicals that can have adverse effects on the health of fishes through activation of aryl hydrocarbon receptor 2 (AhR2). They are ubiquitous in the environment, but alkyl PAHs are more abundant in some environmental matrices. However, relatively little is known regarding the effects of alkylation on the toxicity of PAHs to fishes in vivo and how this relates to potency for activation of AhR2 in vitro. Therefore, the objectives of the present study were to determine the toxicity of benz[a]anthracene and three alkylated homologs representing various alkylation positions to early life stages of zebrafish (Danio rerio) and to assess the potency of each for activation of the zebrafish AhR2 in a standardized in vitro AhR transactivation assay. Exposure of embryos to each of the PAHs caused a dose-dependent increase in mortality and malformations characteristic of AhR2 activation. Each alkyl homolog had in vivo toxicities and in vitro AhR2 activation potencies different from those of the parent PAH in a position-dependent manner. However, there was no statistically significant linear relationship between responses measured in these assays. The results suggest a need for further investigation into the effect of alkylation on the toxicity of PAHs to fishes and greater consideration of the contribution of alkylated homologs in ecological risk assessments. Environ Toxicol Chem 2022;41:1993-2002. © 2022 SETAC.

Short-Term Exposure Effects of the Environmental Endocrine Disruptor Benzo(a)Pyrene on Thyroid Axis Function in Zebrafish

Benzo(a)Pyrene (BaP) is one of the most widespread polycyclic aromatic hydrocarbons (PAHs) with endocrine disrupting properties and carcinogenic effects. In the present study, we tested the effect of BaP on thyroid development and function, using zebrafish as a model system. Zebrafish embryos were treated with 50 nM BaP from 2.5 to 72 h post fertilization (hpf) and compared to 1.2% DMSO controls. The expression profiles of markers of thyroid primordium specification, thyroid hormone (TH) synthesis, hypothalamus-pituitary-thyroid (HPT) axis, TH transport and metabolism, and TH action were analyzed in pools of treated and control embryos at different developmental stages. BaP treatment did not affect early markers of thyroid differentiation but resulted in a significant decrease of markers of TH synthesis (tg and nis) likely secondary to defective expression of the central stimulatory hormones of thyroid axis (trh, tshba) and of TH metabolism (dio2). Consequently, immunofluorescence of BaP treated larvae showed a low number of follicles immunoreactive to T4. In conclusion, our results revealed that the short-term exposure to BaP significantly affects thyroid function in zebrafish, but the primary toxic effects would be exerted at the hypothalamic-pituitary level thus creating a model of central hypothyroidism.

Newly Hatched Stage I American Lobster (Homarus americanus) Survival Following Exposure to Physically and Chemically Dispersed Crude Oil

Standard model species are commonly used in toxicity tests due to their biological and technical advantages but studying native species increases the specificity and relevance of results generated for the potential risk assessment to an ecosystem. Accounting for intraspecies variability and other factors, such as chemical and physical characterization of test medium, is necessary to develop a reproducible bioassay for toxicity testing with native species. In this study, larval stage I American lobster (Homarus americanus), a commercially important and native species of Atlantic Canada, was used as the test species. Toxicity tests were first conducted by exposing lobster larvae to a reference toxicant of copper sulphate (CuSO₄) and then to physically and chemically (using Corexit 9500A) dispersed oil (WAF and CEWAF, respectively). The effect on larval survival was estimated by calculating the 24-h median effect concentration (24-h EC50), and there was no difference between WAF or CEWAF exposure when the results are reported on a total petroleum hydrocarbon (TPH) basis. The 24-h EC50s ranged from 2.54 to 9.73 mg TPH/L when all trials (n = 19) are considered together. The HC5 (hazardous concentration for 5 per cent of the population) value was 2.52 mg TPH/L and similar to the EC50 value when all trials were pooled. To evaluate the reproducibility of the lobster toxicity tests, inter-trial variability was determined, and the resultant coefficients of variation (%CV) were compared to those reported for two standard test species, mysid shrimp (Americamysis bahia) and inland silverside (Menidia beryillina). This comparison showed that the %CV for the lobster toxicity tests were lower than those for the standard species tests indicating that the described larval lobster toxicity bioassay produces reliable and repeatable results.

Acute and subchronic effects of petroleum on the freshwater fish Hoplias aff. malabaricus

Abstract Petroleum water soluble fraction (WSF) impairs organisms, but damages may vary among cell and tissue levels. The aim of the present study was to evaluate the acute (24 h, 48 h, 72 h) and subchronic effects (36 days) of WSF (0%, 25% and 100%) in juveniles of the Neotropical top predator fish Hoplias aff. malabaricus. The effects of WSF were evaluated at a molecular level using the comet assay and micronucleus test for genome damage; and at a morphological level through histological identification of liver pathologic lesions. In both acute and subchronic exposure we found low levels of DNA damage (< 10% of comet tail) and non-significant frequency of micronucleus in WSF exposed fish. The most significant liver lesions in WSF exposed fish were fatty vacuolization, hypertrophy and focal necrosis. Since these tissue injuries were progressive and persistent, their irreversibility may negatively affect fish recruitment, even in a such resistant top predator.

Effect of petroleum wastewater treated with gravity separation and magnetite nanoparticles adsorption methods on the blood biochemical response of mrigal fish (Cirrhinus cirrhosus)

Drainage of treated wastewater to surface water is a severe threat to the health of aquatic organisms. This study aimed to evaluate the effects of 0.5 and 1% water-soluble fractions of crude oil (WSFO), WSFO treated with magnetic nanoparticles of Fe₃O₄ (TWSFO-Fe₃O₄) and with the gravity separation method (TWSFO-GSM) on Cirrhinus cirrhosis for 21 days. The rate of erythrocyte hemolysis in fish exposed to untreated 0.5 and 1% WSFO were significantly high. The activities of alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT), alkaline phosphatase (ALP) were significantly increased in the groups exposed to TWSFO-GSM compared to the control group, while lactate dehydrogenase (LDH) was reduced. No significant differences in LDH, ALT, ALP, and GGT activities were observed in the fish treated with TWSFO-Fe₃O₄. The aspartate aminotransferase activity was significantly increased after exposure to TWSFO-Fe₃O₄ (1%) and TWSFO-GSM. The levels of triglyceride were decreased, whereas glucose, cholesterol, and cholinesterase activity increased in fish after both treatments. The total protein and albumin contents significantly decreased in fish under exposure to both doses of TWSFO-Fe₃O₄ and TWSFO-GSM. The globulin level decreased in fish exposed to TWSFO-Fe₃O₄ (1%) and TWSFO-GSM. Glutathione peroxidase, catalase, glucose-6-phosphate dehydrogenase activities, and total antioxidant levels were significantly reduced in the hepatocytes of fish exposed to TWSFO-Fe₃O₄, TWSFO-GSM, and WSFO, while superoxide dismutase activity and malondialdehyde content were increased. This study showed that despite removing oil drips from the WSFO, the xenobiotics present in the effluent treated by gravitational or nano-magnetite methods caused changes in biochemical parameters and induced oxidative stress. Therefore, it is recommended to prevent the discharge of treated effluent from the oil and petrochemical industries to aquatic ecosystems.

New insights into benzo[⍺]pyrene osteotoxicity in zebrafish

Persistent and ubiquitous organic pollutants, such as the polycyclic aromatic hydrocarbon benzo[⍺]pyrene (BaP), represent a major threat to aquatic organisms and human health. Beside some well-documented adverse effects on the development and reproduction of aquatic organisms, BaP was recently shown to affect fish bone formation and skeletal development through mechanisms that remain poorly understood. In this work, zebrafish bone-related in vivo assays were used to evaluate the osteotoxic effects of BaP during bone development and regeneration. Acute exposure of zebrafish larvae to BaP from 3 to 6 days post-fertilization (dpf) induced a dose-dependent reduction of the opercular bone size and a depletion of osteocalcin-positive cells, indicating an effect on osteoblast maturation. Chronic exposure of zebrafish larvae to BaP from 3 to 30 dpf affected the development of the axial skeleton and increased the incidence and severity of skeletal deformities. In young adults, BaP affected the mineralization of newly formed fin rays and scales, and impaired fin ray patterning and scale shape, through mechanisms that involve an imbalanced bone remodeling. Gene expression analyses indicated that BaP induced the activation of xenobiotic and metabolic pathways, while negatively impacting extracellular matrix formation and organization. Interestingly, BaP exposure positively regulated inflammation markers in larvae and increased the recruitment of neutrophils. A direct interaction between neutrophils and bone extracellular matrix or bone forming cells was observed in vivo, suggesting a role for neutrophils in the mechanisms underlying BaP osteotoxicity. Our work provides novel data on the cellular and molecular players involved in BaP osteotoxicity and brings new insights into a possible role for neutrophils in inflammatory bone reduction.

Effects of short-duration oil exposure on bay anchovy (Anchoa mitchilli) embryos and larvae: mortality, malformation, and foraging

The Deepwater Horizon oil spill highlighted the need to understand the effects of oil exposure on marine eggs and larvae. To determine how short-duration exposure impacts the survivability of early life stages of the bay anchovy, Anchoa mitchilli, embryos and larvae ≤ 3-days-post-hatch (dph) were exposed to high-energy water accommodated fractions of weathered crude oil for 2 or 6 h. Lethal and sublethal effects of short-duration oil exposure were observed, including crippling malformations and altered optimal swimming and foraging behavior of larvae without malformation. The probability of mortality for larvae exposed as embryos (37.37 and 77.31 µg L^-1 total polycyclic aromatic hydrocarbons or 'TPAH'), assessed 48 h after exposure, increased from 0.06 to 0.15 (2 h) and 0.10-0.23 (6 h) relative to unoiled controls. When exposed as 1-dph larvae (8.80-37.37 µg L^-1 TPAH) and assessed 24 h after exposure, the probabilities increased from 0.20 to 0.76 (2 h) and 0.28-0.99 (6 h). Among surviving larvae, probabilities of yolk-sac, finfold, notochord, and cranio-facial malformations increased with exposure concentration, duration, and time after exposure by up to 0.07 immediately following exposure of 1-dph larvae and 0.55 24 h after exposure. When assessed 48 h after exposure as embryos, the probability of larval malformation reached 0.43. First-feeding (3-dph) foraging behavior was altered immediately and 24 h after 2 h exposures (8.80-77.31 µg L^-1 TPAH). Time spent in motion and swim speed increased with exposure concentration by up to 331% and 189%, respectively. The number of bursts min^-1 increased by 293% immediately and 152% 24 h after exposure. Burst distance decreased by 201%. Pause duration and burst speed decreased by 391% and 250% immediately and 124% and 109% 24 h after exposure. No effects were found for burst duration or tortuosity. Our results suggest potential cascading effects on fitness and trophic interactions.

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

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

Benzo[a]pyrene exposure and overcrowding stress impacts anxiety-like behavior and impairs learning and memory in adult zebrafish, Danio rerio

Benzo[a]pyrene (B[a]P), a prototype of polycyclic aromatic hydrocarbons and ubiquitous environmental pollutant, alters neurobehavioral responses in aquatic organisms like zebrafish. Increasing organic load on water bodies causes population explosion leading to overcrowding (OC) stress. The effect of OC stress on neurobehavioral alterations remains unclear. The objective of our study is to elucidate the impact of OC stress on behavioral alterations and neurodegenerative phenotypes on exposure to B[a]P in zebrafish. We demonstrate the effects of OC stress (12 fish/L) on acute waterborne exposure to B[a]P (0.2 mg L^-1 ) in adult wild zebrafish. Anxiety-like behavior, learning, and memory impairment were assayed by novel tank diving test, light/dark preference test, and T-maze test. Oxidative stress bio-markers were assayed along with histopathological changes in zebrafish brain. OC stress significantly impaired the learning ability and mood behavior by increasing the number of transition and time spent in the alter zones. Increased lipid peroxidation and protein carbonyl formation with significant decreased catalase activity and reduced glutathione level showed oxidative stress on exposure to OC stress and B[a]P. Pyknotic neuronal counts dramatically increased in periventricular grey zone of optic tectum brain region of zebrafish. Our findings showed that OC stress modulates the B[a]P-induced behavioral alterations causing learning and memory deficiency with histopathological changes in adult zebrafish brain. OC stress may act as an early risk factor for the eventual development of cognitive impairments and B[a]P exposure plays a key role in mediating both the facilitating and impairing actions of OC stress in memory processes.

1H NMR based metabolomic profiling of early life stage zebrafish (Danio rerio) exposed to a water-soluble fraction of weathered sediment-bound diluted bitumen

Spills of diluted bitumen (dilbit) from pipelines pose a risk to the health of aquatic organisms, including fish, and with expected increases in production and transportation of dilbit, these risks could increase. To date, the majority of studies have investigated effects of fresh dilbit on aquatic organisms, but little is known about effects of weathered sediment-bound dilbit, including mechanisms of toxicity. The goal of this study was to use 1H NMR based metabolomics to identify altered metabolites and pathways in early life-stages of zebrafish (Danio rerio) exposed to a sediment derived water-soluble fraction of dilbit (SDWSF) to better understand mechanisms of adverse effects. Zebrafish embryos exposed to the SDWSF until 120 h post-fertilization exhibited increased prevalence of pericardial edema, yolk sac edema, and swim bladder malformations that are typical of exposure to fresh dilbit. Concentrations of nine metabolites (alanine, glutamine, lysine, threonine, tyrosine, betaine, taurine, inosine, and glycerol) were significantly altered in embryos exposed to SDWSF. Pathway topology analysis revealed four potentially impacted pathways: 1) phenylalanine, tyrosine, and tryptophan biosynthesis, 2) taurine and hypotaurine metabolism, 3) alanine, aspartate, and glutamate metabolism, and 4) glycine, serine, and threonine metabolism. Altered metabolites were linked to several biological process, that when perturbed could be key events in mechanisms of developmental effects observed in embryos. Future studies should further investigate the role of perturbations to these metabolites and pathways to determine the specific role they might play in adverse effects of exposure to dilbit.

Effects of dispersant treated oil upon exploratory behaviour in juvenile European sea bass (Dicentrarchus labrax)

Accidental spills are pervasive pollution in aquatic ecosystems. Resorting to chemical dispersant is one of the most implemented strategies in response to oil spills, but it results in an increase in the bio-availability of oil compounds known to disturb fish neurosensory capacities and hence fish habitat use. While it has become well established that acute oil exposure can cause a range of physiological defects, sub-lethal consequences on animal behaviour have only received recent attention. Here we investigated the effect of an exposure to a 62 h- dispersant treated oil on the exploration tendency (exploratory activity, and avoidance of unfamiliar open areas) of juvenile European sea bass. Three different concentrations of chemically dispersed oil were tested, low and medium conditions bracketing the range of likely situations that fish encounter following an oil spill, the high dose representing a more severe condition. Fish recovery capacities were also evaluated during 2 weeks post-exposure. Our results suggest a dose-response relationship; the low dose (0.048 ± 0.007 g L^-1 of total petroleum hydrocarbons ([TPH])) had no effect on sea bass behavioural response to a novel environment while medium (0.243 ± 0.012 g L^-1 [TPH]) and high (0.902 ± 0.031 g L^-1 [TPH]) doses altered fish exploratory activity and their typical avoidance of unfamiliar open areas. Our experiment also suggest signs of recovery capacities in the first 10 days following oil exposure even if fish might need more time to fully recover from observed alterations. We discuss the possibility that observed alterations may result from a neurosensory or physiological known defects of oil exposure, causing anaesthetic-like sedative behaviours. Altogether, this study shows that juvenile sea bass exposed to oil spill exhibit transient behavioural impairments that may have major population-level consequences given the high mortality experienced by juveniles.

Previous oil exposure alters Gulf Killifish Fundulus grandis oil avoidance behavior

Oil spills threaten the structure and function of ecological communities. The Deepwater Horizon spill was predicted to have catastrophic consequences for nearshore fishes, but field studies indicate resilience in populations and communities. Previous research indicates many marsh fishes exhibit avoidance of oil contaminated areas, representing one potential mechanism for this resilience. Here, we test whether prior oil exposure of Gulf killifish Fundulus grandis alters this avoidance response. Using choice tests between unoiled and oiled sediments at one of three randomized concentrations (low: 0.1 L oil m^-2, medium: 0.5 L oil m^-2, or high: 3.0 L oil m^-2), we found that, even at low prior exposure levels, killifish lose recognition of oiled sediments compared to control, unexposed fish. Preference for unoiled sediments was absent across all oil concentrations after oil exposure, and some evidence for preference of oiled sediments at high exposure was demonstrated. These results highlight the lack of response to toxic environments in exposed individuals, indicating altered behavior despite organism survival. Future research should document additional sublethal consequences that affect ecosystem and food web functioning.

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

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

Toxic Effects of Polychlorinated Biphenyl Congeners and Aroclors on Embryonic Growth and Development

Polychlorinated biphenyls (PCBs) cause significant health and reproductive problems in many vertebrates. Exposure during embryogenesis likely leads to defects in organ development, compromising survival and growth through adulthood. The present study identifies the impact of PCBs on the embryonic development of key organs and resulting consequences on survival and growth. Zebrafish embryos were treated with individual PCB congeners (126 or 104) or one of 4 Aroclor mixtures (1016, 1242, 1254, or 1260) and analyzed for changes in gross embryonic morphology. Specific organs were assessed for defects during embryonic development, using a variety of transgenic zebrafish to improve organ visualization. Resulting larvae were grown to adulthood while survival and growth were assayed. Embryonic gross development on PCB treatment was abnormal, with defects presenting in a concentration-dependent manner in the liver, pancreas, heart, and blood vessel organization. Polychlorinated biphenyl 126 treatment resulted in the most consistently severe and fatal phenotypes, whereas treatments with PCB 104 and Aroclors resulted in a range of more subtle organ defects. Survival of fish was highly variable although the growth rates of surviving fish were relatively normal, suggesting that maturing PCB-treated fish that survive develop compensatory strategies needed to reach adulthood. Life span analyses of fish from embryogenesis through adulthood, as in the present study, are scarce but important for the field because they help identify foci for further studies. Environ Toxicol Chem 2021;40:187-201. © 2020 SETAC.

Maternal transfer of polycyclic aromatic hydrocarbons in an endangered elasmobranch, the Brazilian guitarfish

Maternal transfer of contaminants is an important route of exposure for many species during embryonic development, which might compromise the organism throughout its life cycle. Here, we report the maternal offloading of polycyclic aromatic hydrocarbons (PAHs) in an elasmobranch, the Brazilian guitarfish Pseudobatos horkelii. Eighteen PAHs were determined by gas chromatography in maternal liver and uterine content (uterine eggs and early-stage development embryos) samples to determine the maternal transfer rate. The mean rate of PAHs offloaded to the offspring was of 13%, with high variability among individual congener transfer (0.7-29.9%) and benzo[b]fluoranthene attaining the highest maternal transfer rates. Differential transfer rates were attributed to physicochemical proprieties of each compound, with low molecular level PAHs presenting the highest rates. A depuration mechanism in which females decrease their maternal transfer rate as a function of size, related to consecutive reproductive cycles was not properly observed in this study. From a conservation perspective, these results indicate that elasmobranchs embryos of an endangered species can be exposed to PAHs during their development and, considering the possible harmful effects of these compounds to other early life stage organisms, deleterious effects could be a possibility, although this was not analyzed herein.

Impacts of Petroleum Fuels on Fertilization and Development of the Antarctic Sea Urchin Sterechinus neumayeri

Antarctic marine environments are at risk from petroleum fuel spills as shipping activities in the Southern Ocean increase. Knowledge of the sensitivity of Antarctic species to fuels under environmentally realistic exposure conditions is lacking. We determined the toxicity of 3 fuels, Special Antarctic Blend diesel (SAB), marine gas oil (MGO), and intermediate fuel oil (IFO 180) to a common Antarctic sea urchin, Sterechinus neumayeri. Sensitivity was estimated for early developmental stages from fertilization to the early 4-arm pluteus in toxicity tests of up to 24 d duration. The effects of the water accommodated fractions (WAFs) of fuels were investigated under different exposure scenarios to determine the relative sensitivity of stages and of different exposure regimes. Sensitivity to fuel WAFs increased through development. Both MGO and IFO 180 were more toxic than SAB, with median effect concentration values for the most sensitive pluteus stage of 3.5, 6.5, and 252 µg/L total hydrocarbon content, respectively. Exposure to a single pulse during fertilization and early embryonic development showed toxicity patterns similar to those observed from continuous exposure. The results show that exposure to fuel WAFs during critical early life stages affects the subsequent viability of larvae, with consequent implications for reproductive success. The sensitivity estimates for S. neumayeri that we generated can be utilized in risk assessments for the management of Antarctic marine ecosystems. Environ Toxicol Chem 2020;39:2527-2539. © 2020 SETAC.

Acute toxicities of fluorene, fluorene-1-carboxylic acid, and fluorene-9-carboxylic acid on zebrafish embryos (Danio rerio): Molecular mechanisms of developmental toxicities of fluorene-1-carboxylic acid

In this study, fluorene (FL), FL-1-carboxylic acid (FC-1), and FL-9-carboxylic acid (FC-9) were investigated to understand their acute toxicity by measuring inhibitory effects on hatching rates and developmental processes of zebrafish embryos (Danio rerio). For exposure concentrations up to 3000 μg/L, FC-1 alone showed acute toxicity at 1458 μg/L for LC₅₀ value. FC-1 caused yolk sac and spinal deformities, and pericardial edema. Molecular studies were undertaken to understand FC-1 toxicity examining 61 genes after exposure to 5 μM (equivalent to LC₂₀ value of FC-1) in embryos. In the FC-1-treated embryos, the expression of the cyp7a1 gene, involved in bile acid biosynthesis, was dramatically decreased, while the expression of the Il-1β gene involved in inflammation was remarkably increased. In addition to these findings, in FC-1-treated embryos, the expression of nppa gene related to the differentiation of the myocardium was 3-fold increased. On the other hand, cyp1a, cyp3a, ugt1a1, abcc4, mdr1, and sult1st1 responsible for detoxification of xenobiotics were upregulated in FC-9-treated embryos. Taken together, carboxylation on carbon 1 of FL increased acute toxicity in zebrafish embryos, and its toxicity might be related to morphological changes with modification of normal biological functions and lowered defense ability.

Toxicity assessment of a novel oil dispersant based on silica nanoparticles using Fathead minnow

Oil spill accidents are a major concern for aquatic organisms. In recent history, the Deepwater Horizon blowout spilled 500 million liters of crude oil into the Gulf of Mexico. Corexit 9500A was used to disperse the oil since it was the method approved at that time, despite safety concerns about its use. A better solution is necessary for dispersing oil from spills that reduces the toxicity to exposed aquatic organisms. To address this challenge, novel engineered nanoparticles were designed using silica cores grafted with hyperbranched poly(glycidol) branches. Because the silica core and polymers are known to be biocompatible, we hypothesized that these particles are nontoxic to fathead minnows (Pimephales promelas) and would decrease their exposure to oil polyaromatic hydrocarbons. Fathead minnow embryos, juveniles and adult stages were exposed to the particles alone or in combination with a water-accommodated fraction of oil. Acute toxicity of nanoparticles to fish was tested by measuring mortality. Sub-lethal effects were also measured including gene expression of cytochrome P450 1a (cyp1a) mRNA and heart rate in embryos. In addition, a mixture of particles plus the water-accommodated fraction was directly introduced to adult female fathead minnows by gavage. Three different nanoparticle concentrations were used (2, 10, and 50 mg/L) in either artificial fresh water or the water-accommodated fraction of the oil. In addition, nanoparticle-free controls were carried out in the two solutions. No significant mortality was observed for any age group or nanoparticle concentration, suggesting the safety of the nanoparticles. In the presence of the water-accommodated fraction alone, juvenile and adult fathead minnows responded by increasing expression of cyp1a. The addition of nanoparticles to the water-accommodated fraction reduced cyp1a gene expression in treatments. Heart rate was also restored to normal parameters in embryos co-exposed to nanoparticles and to the water-accommodated fraction. Measurement of polyaromatic hydrocarbons confirmed their presence in the tested solutions and the reduction of available PAH in WAF treated with the nanoparticles. Our findings suggest the engineered nanoparticles may be protecting the fish by sequestering polyaromatic hydrocarbons from oil, measured indirectly by the induction of cypa1 mRNAs. Furthermore, chemical analysis showed a reduction in PAH content in the water accommodated fraction with the presence of nanoparticles.

Polycyclic aromatic compounds (PACs) in the Canadian environment: The challenges of ecological risk assessments

Ecological risk assessments (ERAs) of polycyclic aromatic compounds (PACs), as single congeners or in mixtures, present technical challenges that raise concerns about their accuracy and validity for Canadian environments. Of more than 100,000 possible PAC structures, the toxicity of fewer than 1% have been tested as individual compounds, limiting the assessment of complex mixtures. Because of the diversity in modes of PAC action, the additivity of mixtures cannot be assumed, and mixture compositions change rapidly with weathering. In vertebrates, PACs are rapidly oxygenated by cytochrome P450 enzymes, often to metabolites that are more toxic than the parent compound. The ability to predict the ecological fate, distribution and effects of PACs is limited by toxicity data derived from tests of a few responses with a limited array of test species, under optimal laboratory conditions. Although several models are available to predict PAC toxicity and rank species sensitivity, they were developed with data biased by test methods, and the reported toxicities of many PACs exceed their solubility limits. As a result, Canadian Environmental Quality Guidelines for a few individual PACs provide little support for ERAs of complex mixtures in emissions and at contaminated sites. These issues are illustrated by reviews of three case studies of PAC-contaminated sites relevant to Canadian ecosystems. Interactions among ecosystem characteristics, the behaviour, fate and distribution of PACs, and non-chemical stresses on PAC-exposed species prevented clear associations between cause and effect. The uncertainties of ERAs can only be reduced by estimating the toxicity of a wider array of PACs to species typical of Canada's diverse geography and environmental conditions. Improvements are needed to models that predict toxicity, and more field studies of contaminated sites in Canada are needed to understand the ecological effects of PAC mixtures.

Influence of Benz[a]anthracene on Bone Metabolism and on Liver Metabolism in Nibbler Fish, Girella punctata

It has been reported that spinal deformity was induced in developing fish by the addition of polycyclic aromatic hydrocarbons (PAHs). To examine the mechanism of the disruption of fish bone metabolism, the effect of benz[a]anthracene (BaA), a kind of PAH, on plasma calcium, inorganic phosphorus, osteoblasts, and osteoclasts was investigated in this study. We also measured several plasma components to analyze the toxicity of BaA on other metabolisms. BaA (1 or 10 ng/g body weight) was intraperitoneally injected (four times) into nibbler fish during breeding, for 10 days, and it was indicated, for the first time, that injecting high doses of BaA to nibbler fish induced both hypocalcemia and hypophosphatemia. Furthermore, in the scales of nibbler fish treated with high doses of BaA, both osteoclastic and osteoblastic marker messengerRNA (mRNA) expressions decreased. These results are a cause of disruption of bone metabolism and, perhaps, the induction of spinal deformities. In addition, we found that total protein, metabolic enzymes in the liver, total cholesterol, free cholesterol, and high-density lipoprotein cholesterol levels significantly decreased in BaA-injected fish. These results indicate that BaA may affect liver diseases and emphasize the importance of prevention of aquatic PAH pollution.

Toxicities of Polycyclic Aromatic Hydrocarbons for Aquatic Animals

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds that are widely distributed in the air, water, and soil. Recently, the amount of PAHs derived from fuels and from incomplete combustion processes is increasing. In the aquatic environment, oil spills directly cause PAH pollution and affect marine organisms. Oil spills correlate very well with the major shipping routes. Furthermore, accidental oil spills can seriously impact the marine environment toxicologically. Here, we describe PAH toxicities and related bioaccumulation properties in aquatic animals, including invertebrates. Recent studies have revealed the toxicity of PAHs, including endocrine disruption and tissue-specific toxicity, although researchers have mainly focused on the carcinogenic toxicity of PAHs. We summarize the toxicity of PAHs regarding these aspects. Additionally, the bioaccumulation properties of PAHs for organisms, including invertebrates, are important factors when considering PAH toxicity. In this review, we describe the bioaccumulation properties of PAHs in aquatic animals. Recently, microplastics have been the most concerning environmental problem in the aquatic ecosystem, and the vector effect of microplastics for lipophilic compounds is an emerging environmental issue. Here, we describe the correlation between PAHs and microplastics. Thus, we concluded that PAHs have a toxicity for aquatic animals, indicating that we should emphasize the prevention of aquatic PAH pollution.

Can the toxicity of naphthenic acids in oil sands process-affected water be mitigated by a green photocatalytic method?

Our study evaluates the efficacy of a “green” (i.e., sustainable, recyclable, and reusable) technology to treat waste waters produced by Canada’s oil sands industry. We examined the ability of a novel advanced oxidative method—ultra-violet photocatalysis over titanium dioxide (TiO2)-coated microparticles—to reduce the toxicity of naphthenic acid fraction components (NAFC) to early life stages of the fathead minnow ( Pimephales promelas). Lengthening the duration of photocatalysis resulted in greater removal of NAFC from bioassay exposure waters; low- and high-intensity treatments reduced NAFC concentrations to about 20 and 3 mg/L (by Fourier-transformed infrared spectroscopy, FTIR), respectively. Treatments reduced the acute lethality of NAFC to fathead minnows by over half after low-intensity treatment and three-fold after high-intensity treatment. However, incomplete degradation in low-intensity treatments increased the incidence of chronic toxicity relative to untreated NAFC solutions and cardiovascular abnormalities were common even with >80% of NAFC degraded. Our findings demonstrate that photocatalysis over TiO2 microparticles is a promising method for mitigating the toxicity of oil sands process-affected water-derived NAFC to fish native to the oil sands region, but the intensity of the photocatalytic treatment needs to be considered carefully to ensure adequate mineralization of toxic constituents.

Impacts of deepwater horizon oil on fish

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

Toxicity in aquatic model species exposed to a temporal series of three different flowback and produced water samples collected from a horizontal hydraulically fractured well

In the present study, we compared the toxicity and associated chemical characterizations of flowback and produced water (FPW) collected from a single horizontal hydraulically fractured well at different time points during FPW production. Since few studies on whole mixture toxicity related to FPW exist, our aims were to determine both overall toxicity of the FPW mixture in a suite of organisms (Daphnia magna, Lumbriculus variegatus, Danio rerio, and Oncorhynchus mykiss) and also determine if toxicity changes depending on variation in FPW chemical properties as a function of time sampled (1.33, 72, and 228 h FPW samples collected immediately post-well production onset were analyzed in current study). FPW chemical composition was determined via quadra-pole inductively coupled plasma - mass spectrometry/mass spectrometry (ICP-MS/MS), full-scan high performance liquid chromatography/Orbitrap mass spectrometry (HPLC/Orbitrap-MS), and gas chromatography-mass spectrometry (GC-MS). We observed that FPW sampled later in the production process contained higher ion and total dissolved solids concentrations, whereas the highest concentrations of dissolved organic compounds were observed in the earliest FPW sample analyzed. Toxicity associated with FPW exposure was deemed to be species-specific to a certain extent, but general trends revealed the earliest FPW sampled contained highest toxic potential. Accordingly, we theorize that although the saline conditions of FPW are the foremost toxicological drivers to freshwater organisms, dissolved organics associated with FPW significantly contribute to the overall toxicity of exposed organisms.

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

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

Analysis of Sublethal Toxicity in Developing Zebrafish Embryos Exposed to a Range of Petroleum Substances

The Organisation for Economic Co-operation and Development (OECD) test guideline 236 (fish embryo acute toxicity test; 2013) relies on 4 endpoints to describe exposure-related effects (coagulation, lack of somite formation, tail-bud detachment from the yolk sac, and the presence of a heartbeat). Danio rerio (zebrafish) embryos were used to investigate these endpoints along with a number of additional sublethal effects (cardiac dysfunction, pericardial edema, yolk sac edema, tail curvature, hatch success, pericardial edema area, craniofacial malformation, swim bladder development, fin development, and heart rate) following 5-d exposures to 7 petroleum substances. The substances investigated included 2 crude oils, 3 gas oils, a diluted bitumen, and a petrochemical containing a mixture of branched alcohols. Biomimetic extraction-solid-phase microextraction (BE-SPME) was used to quantify freely dissolved concentrations of test substances as the exposure metric. The results indicated that the most prevalent effects observed were pericardial and yolk sac edema, tail curvature, and lack of embryo viability. A BE-SPME threshold was determined to characterize sublethal morphological alterations that preceded embryo mortality. Our results aid in the understanding of aquatic hazards of petroleum substances to developing zebrafish beyond traditional OECD test guideline 236 endpoints and show the applicability of BE-SPME as a simple analytical tool that can be used to predict sublethal embryo toxicity. Environ Toxicol Chem 2019;38:1302-1312. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Biological Effects of Elevated Major Ions in Surface Water Contaminated by a Produced Water from Oil Production

Produced water (PW) from oil and gas extraction processes has been shown to contain elevated concentrations of major ions. The objective of this study was to determine the potential effects of elevated major ions in PW-contaminated surface water on a fish (fathead minnow, Pimephales promelas) and a unionid mussel (fatmucket, Lampsilis siliquoidea) in short-term (7-day) exposures. The test organisms were exposed in 3 reconstituted waters formulated with 1, 2, and 4 times the major ions measured at a PW-contaminated stream site 1 month after a PW spill from an oil production wastewater pipeline in the Williston Basin, North Dakota. A reconstituted water mimicking the ionic composition of an upstream site from the spill was used as a reference water. Significant reductions in survival and growth of the fish were observed in the 4× treatment compared with the reference. The mussels were more sensitive than the fish, with significant reductions in survival in the 2× and 4× treatments, and significant reductions in length in the 1× and 2× treatments. Overall, these results indicate that elevated concentrations of major ions in PW-contaminated surface waters could adversely affect the fish and mussels tested and potentially other aquatic organisms.

Field-collected crude oil, weathered oil and dispersants differentially affect the early life stages of freshwater and saltwater fishes

The Deepwater Horizon (DWH) oil spill was the biggest in US history and released 3.19 million barrels of light crude oil into the Gulf of Mexico. In this study, we compared the toxicity of water accommodated fractions (WAFs) of naturally weathered crude oils, source oil, and source oil with dispersant mixtures and their effects on developing sheepshead minnow and zebrafish. Although a freshwater fish, zebrafish has been used as a model for marine oil spills owing to the molecular and genetic tools available and their amenability to lab care. Our study not only aimed to determine the effect of crude oil on early life stages of these two fish species, but also aimed to determine whether dissolved crude oil constituents were similar in fresh and saltwater, and if freshwater fish might be a suitable model to study marine spills. Weathering and dispersant had similar effects on WAF composition in both fresh and saltwater, except that the saltwater source oil + dispersant WAF had markedly higher PAH levels than the freshwater equivalent. WAF exposure differentially affected survival, as the LC50 values in %WAF for the zebrafish and sheepshead minnow exposures were 44.9% WAF (95% confidence interval (C.I.) 42.1-47.9) and 16.8% WAF (95% C.I. 13.7-20.5); respectively. Exposure increased heart rate of zebrafish embryos, whereas in sheepshead, source oil exposure had the opposite effect. WAF exposure altered mRNA expression of biotransformation makers, vitellogenin and neurodevelopment genes in both species. Muscle deformations were only found in oil-exposed zebrafish. This is one of the most comprehensive studies to date on crude oil toxicity, and highlights the species-specific differences in cardiotoxicity, estrogenic effects, biotransformation enzyme induction and potential neurotoxicity of crude oil exposure.

Morphological and molecular effects of two diluted bitumens on developing fathead minnow (Pimephales promelas)

Canada has experienced a significant increase in the transport of diluted bitumen (dilbit), a predominant oil sands product that combines bitumen with diluents derived from oil-gas condensates and other proprietary compounds. The toxicity of dilbit to fish embryos, which are immobile and thus at a high risk of exposure to oil in the event of a spill, remains largely unknown for most species. This study assessed the toxicity of water accommodated fractions (WAF) and chemically enhanced water accommodated fractions (CEWAF) of two winter dilbit blends, Access Western Blend (AWB) and Cold Lake Blend (CLB), to fathead minnow (Pimephales promelas) embryos. The TPH-F EC50s for malformations were 834 and 1058 μg/L for AWB WAF and CEWAF, respectively, and 500 and 715 μg/L for CLB WAF and CEWAF, respectively. Levels of cyp1a mRNA increased up to 46- and 69-fold, respectively, reflecting increasing exposure to polycyclic aromatic compounds (PACs) in AWB and CLB. Similarly, levels of gst mRNA were elevated up to 3.8-fold and 2.7-fold with increasing total concentrations of PACs in AWB and CLB, respectively. However, there were no significant changes in mRNA levels of p53, sod, cat, and gsr. These results suggest that the expression of cyp1a and gst may serve as biomarkers for dilbit exposure in fathead minnow, furthering our understanding of dilbit-responsive indicators of toxicity in fish species native to North America. This study is important as it utilizes the same exposure methodology to examine the toxicity of two commonly used Canadian dilbits, facilitating comparison of dilbit toxicity.