Biochemical and behavioral responses of the Amazonian fish Colossoma macropomum to crude oil: the effect of oil layer on water surface

Biological-based techniques for real-time water-quality studies: Assessment of non-invasive (swimming consistency and respiration) and toxicity (antioxidants) biomarkers of zebrafish

Swimming consistency and respiration of fish are recognized as the non-invasive stress biomarkers. Their alterations could directly indicate the presence of pollutants in the water ecosystem. Since these biomarkers are a routine process for fish, it is difficult to monitor their activity manually. For this reason, experts employ engineering technologies to create sensors that can monitor the regular activities of fish. Knowing the importance of these non-invasive stress biomarkers, we developed online biological behavior monitoring system-OBBMS and online biological respiratory response monitoring system-OBRRMS to monitor real-time swimming consistency and respiratory response of fish, respectively. We continuously monitored the swimming consistency and respiration (OCR, CER and RQ) of zebrafish (control and atrazine-treatments) for 7 days using our homemade real-time biological response monitoring systems. Furthermore, we analyzed oxidative stress indicators (SOD, CAT and POD) within the vital tissues (gills, brain and muscle) of zebrafish during stipulated sampling periods. The differences in the swimming consistency and respiratory rate of zebrafish between the control and atrazine treatments could be precisely differentiated on the real-time datasets of OBBMS and OBRRMS. The zebrafish exposed to atrazine toxin showed a concentration-dependent effect (hypoactivity). The OCR and CER were increased in the atrazine treated zebrafish. Both Treatment I and II received a negative response for RQ. Atrazine toxicity let to a rise in the levels of SOD, CAT and POD in the vital tissues of zebrafish. The continuous acquisition of fish signals is achieved which is one of the main merits of our OBBMS and OBRRMS. Additionally, no special data processing was done, the real-time data sets were directly used on statistical tools and the differences between the factors (groups, photoperiods, exposure periods and their interactions) were identified precisely. Hence, our OBBMS and OBRRMS could be a promising tool for biological response-based real-time water quality monitoring studies.

Detrimental influence of industrial effluents, especially heavy metals, on limnological parameters of water and nutritional profile in addition to enzymatic activities of fish, Sperata seenghala (Sykes, 1839) from diverse Ramsar sites, India (Punjab)

The present research was designed to determine the nutritive value of the liver and intestine of fish, Sperata seenghala, the impact of effluence load on limnological parameters of water and proximate composition of fish organs, especially on fatty acids, liver enzymatic activities, seasonal variations in the nutritional profile of fish, and to check and compare the pollution status of Ramsar sites in Punjab by calculating the water quality index, heavy metal pollution index, and metal index from June 2018 to August 2020. WQI of Harike wetland was found to be 53.95, which depicts that water quality in this region is "poor". At Nangal wetland, water quality index was reported to be "excellent" quality water and fit for the whole ecological unit. Overall heavy metal pollution index for Harike wetland was reported 174.569, whereas for Nangal wetland it was 5.994, depicting massive contaminant loads in a polluted region. MI value was also recorded as being higher (6.9336) in polluted habitat than in control habitat (0.8175). In fish liver, significant (p < 0.05) higher mean total lipids (6.73%), total proteins (3.98%), moisture (77.69%), ash (3.56%), and carbohydrates (3.79%) were observed in the samples from Nangal wetland than Harike wetland. A similar trend was reported in all biochemical contents of the fish intestine. Enzyme activities such as aspartate-aminotransferase and alanine-aminotransferase were significantly elevated (p < 0.05) in the specimens collected from the polluted region. The mean total n-3 (except in spring), n-6 polyunsaturated fatty acids (except in winter), and average monounsaturated and saturated fatty acids diminished significantly (p < 0.05) in the liver of fish from contaminated habitat than control site. In the intestine of fish collected from the polluted region, significant reductions in the mean total n-3 (except in autumn as well as summer), total n-6 PUFAs (in autumn and winter), and total SFAs were reported than control site.

Diluted Bitumen Affects Multiple Physiological Systems in Sockeye Salmon (Oncorhynchus nerka) Embryo to Juvenile Life Stages

An understanding of the risks associated with diluted bitumen (dilbit) transport through Pacific salmon habitat necessitates the identification and quantification of hazards posed to early life stages. Sockeye from the embryo to juvenile stage (8 months old) were exposed to four concentrations of the water-soluble fraction of Cold Lake dilbit (summer blend; concentrations of 0, 13.7, 34.7, and 124.5 μg/L total polycyclic aromatic compounds). Significant mortality (up to 18% over controls) only occurred in the embryo to swim-up fry stage. Impaired growth was seen in the alevin, swim-up, and juvenile stages (maximum reduction 15% in mass but not fork length). Reductions in both critical (maximum 24% reductions) and burst (maximum 47% reductions) swimming speed in swim-up fry and juveniles were seen. Alterations in energy substrate reserves (reductions in soluble protein and glycogen content, elevations in whole-body lipid and triglyceride levels) at all stages may underlie the effects seen in swimming and growth. Dilbit exposure induced a preexercise physiological stress response that affected the recovery of postexercise biochemistry (cortisol, glycogen, lactate, triglyceride concentrations). The transcript abundance of the cytochrome P450 1A gene (cyp1a) was quantified in alevin head regions (containing the heart) and in the hearts of swim-up fry and juveniles and showed a concentration-dependent increase in the expression of cyp1a at all life stages. Environ Toxicol Chem 2022;41:1937-1949. © 2022 SETAC.

PAHs impacts on aquatic organisms: contamination and risk assessment of seafood following an oil spill accident

Oil spills, intrinsically related to the petroleum production chain, represent a risk to the marine environment and a potential threat to humans through seafood consumption. We revised the NE Brazil oil spill and other accidents along the Brazilian coast, with a focus on seafood contamination, covering topics such as bioaccumulation, bioaccessibility, and risk analysis. Comprehensive knowledge of the impacts of spills helps in the interpretation of the dynamics of hydrocarbons released into the sea, contributing to actions to control their negative impacts. Currently, no legal limits have been established permanently in Brazil for PAHs in seafood edible tissues.

Diluted bitumen-induced alterations in aerobic capacity, swimming performance, and post-exercise recovery in juvenile sockeye salmon (Oncorhynchus nerka)

The transportation of heavy crudes such as diluted bitumen (dilbit) sourced from Canadian oil sands through freshwater habitat requires the generation of information that will contribute to risk assessments, spill modelling, management, and remediation for the protection of aquatic organisms. Juvenile sockeye salmon (Oncorhynchus nerka) were exposed acutely (96 h) or subchronically (28 d) to the water-soluble fraction (WSFd) of Cold Lake Blend dilbit at initial total polycyclic aromatic compound (TPAC) concentrations of 0, 13.7, 34.7, and 124.5 µg/L. A significant induction (>3-fold) of hepatic liver ethoxyresorufin-O-deethylase (EROD) activity was induced by 96 h in fish exposed to [TPAC] ≥ 34.7 µg/L and at ≥13.7 µg/L for a 28 d exposure. Exposure resulted in a typical physiological stress response and disturbance of ion homeostasis; this included elevations in plasma [cortisol], [lactate], [Na⁺], and [Cl^-], and significant reductions in muscle [glycogen]. Critical swimming speed (U_crit) was significantly reduced (28.4%) in the acute exposure at [TPAC] 124.5 µg/L; reductions of 14.2% and 35.4% were seen in fish subchronically exposed at the two highest concentrations. Reductions in U_crit were related to significant reductions in aerobic scope (24.3-46.6%) at [TPAC]s of 34.7 and 124.5 µg/L, respectively. Exposure did not impair the ability to mount a secondary stress response following burst exercise, however, the time required for biochemical parameters to return to baseline values was prolonged. Alterations in critical systems supporting swimming, exercise recovery and the physiological stress response could result in decreased salmonid fitness and contribute to population declines if a dilbit spill occurs.

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.

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

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

Acetylcholinesterase activity in fish species exposed to crude oil hydrocarbons: A review and new perspectives

Crude oil and its derivatives are primary energy resources for humans, and processes involving these materials could affect aquatic environments. Acetyl cholinesterase (AChE) activity is a suitable biomarker for exposure to organophosphate pesticides. Under controlled conditions, fish exposed to polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene, pyrene and anthracene, showed inhibition of this biomarker; however, PAHs with a low molecular weight did not induce changes or cause stimulation of AChE activity. Diverse responses of fish exposed to soluble fractions of crude oil, fuels or gasoline were documented. Most studies in which AChE activity was considered for environmental monitoring have been performed to evaluate the presence of pesticides, and the effects of petroleum hydrocarbons are unclear. The objective of this review was to provide the recent status of research on this topic and suggest proposals for future investigations. To establish the suitability of this biomarker in fish species exposed to these pollutants and to determine their neurotoxic effects, researchers must determinate the mechanism involved in the AChE inhibition by petroleum hydrocarbons, unify criteria concerning the experimental in vitro and in vivo designs and apply multivariate statistical and correlation analyses between these pollutants with AChE activity in field studies.

Is this a Real Choice? Critical Exploration of the Social License to Operate in the Oil Extraction Context of the Ecuadorian Amazon

The purpose of this research was to critically analyze the social license to operate (SLO) for an oil company operating in Block 10, an oil concession located in the Ecuadorian Amazon. The specific study area is an important biodiversity hotspot, inhabited by indigenous villages. A mixed-methods approach was used to support a deeper understanding of SLO, grounded in participants’ direct experience. Semi-structured interviews (N = 53) were conducted with village leaders and members, indigenous associations, State institutions, and oil company staff, while household surveys were conducted with village residents (N = 346). The qualitative data informed a modified version of Moffat and Zhang’s SLO model, which was tested through structural equation modelling (SEM) analyses. Compared to the reference model, our findings revealed a more crucial role of procedural fairness in building community trust, as well as acceptance and approval of the company. Procedural fairness was found to be central in mediating the relationship between trust and the effects of essential services provided by the company (medical assistance, education, house availability) and sources of livelihoods (i.e., fishing, hunting, harvesting, cultivating, and waterway quality). The main results suggested that the concept of SLO may not appropriately apply without taking into account a community’s autonomy to decline company operation. To enhance procedural fairness and respect for the right of community self-determination, companies may need to consider the following: Establishing a meaningful and transparent dialogue with the local community; engaging the community in decision-making processes; enhancing fair distribution of project benefits; and properly addressing community concerns, even in the form of protests. The respect of the free prior informed consent procedure is also needed, through the collaboration of both the State and companies. The reduction of community dependence on companies (e.g., through the presence of developmental alternatives to oil extraction) is another important requirement to support an authentic SLO in the study area.

Physiological disturbances in juvenile sockeye salmon (Oncorhynchus nerka) exposed to the water-soluble fraction of diluted bitumen

Current and proposed transcontinental pipelines for the transport of diluted bitumen (dilbit) from the Canadian oil sands traverse the coastal watersheds of British Columbia, habitat essential to Pacific salmonids. To determine the potential risks posed to these keystone species, juvenile sockeye (Oncorhynchus nerka; 1+ parr) were acutely (24-96 h) or subchronically (21-42 d) exposed to 4 concentrations of the water-soluble fraction (WSF) of unweathered Cold Lake Blend dilbit (initial total PAC concentrations: 0, 13.7, 34.7 and 124.5 μg/L) in a flow-through system. Dilbit effects on iono-osmoregulation, the physiological stress response, and the immune system were assessed by both biochemical and functional assays. Hydrocarbon bioavailability was evidenced by a significant induction of liver ethoxyresorufin-O-deethylase (EROD) activity in exposed fish. Acute and subchronic exposure significantly reduced gill Na⁺-K⁺-ATPase activity and resulted in lower plasma osmolality, Cl^-, and Na⁺ concentrations. Acute exposure to dilbit resulted in a classic physiological stress response, however at 21 d of exposure, plasma cortisol remained elevated while other measured parameters had returned to baseline values. A compromised immune system was demonstrated by a 29.5 % higher mortality in fish challenged with Vibrio (Listonella) anguillarum following dilbit exposure compared to unexposed controls. Exposure of juvenile salmonids to the WSF of dilbit (at TPAC concentrations at the ppb level) resulted in sublethal effects that included a classic physiological stress response, and alterations in iono-osmoregulatory homeostasis and immunological performance.

Juvenile fish responses to sublethal leachate concentrations: comparison of sensitivity of different behavioral endpoints

The aim of the present study was to investigate changes in the locomotor activity of rainbow trout (Oncorhynchus mykiss) juveniles under the impact (2 h) of landfill leachate (as a multicomponent mixture) based on different endpoints such as average, maximum and angular velocities, movement duration, body mobility, and blood glucose level. Fish were exposed to five different sublethal leachate concentrations (0, 0.0625, 0.125, 0.25, and 0.5%). The locomotor activity of the leachate-exposed fish significantly decreased at 0.25 and 0.5% concentrations. Significant changes in fish behavior in response to sublethal leachate concentrations were determined during the first minutes of exposure. Angular velocity proved to be the most sensitive of all the endpoints tested. A positive correlation was observed among behavioral responses, but no correlation was established between the blood glucose level and behavioral endpoints. The blood glucose endpoint was found to be insensitive, and we suggest that it should be used only in combination with other endpoints to complement toxicity data. To enhance the understanding of rainbow trout behavioral characteristics in relation to time, and relations among behavioral endpoints of the fish under short-term exposure to a multicomponent mixture, in the current study, we investigated dynamics of the selected behavioral endpoints over time, relations among these endpoints and compared behavioral response rapidness and efficacy.

Chromosomal Mapping of Rex Retrotransposons in Tambaqui (Colossoma macropomum Cuvier, 1818) Exposed to Three Climate Change Scenarios

Greenhouse gas emissions are known to influence the planet's temperature, mainly due to human activities. To allow hypothesis testing, as well as to seek viable alternatives for mitigation, the Intergovernmental Panel on Climate Change (IPCC) suggested 3 main scenarios for changes projected for the year 2100. In this paper, we subjected Colossoma macropomum Cuvier, 1818 (tambaqui) individuals in a microcosm to IPCC scenarios B1 (mild), A1B (intermediate), and A2 (extreme) to test possible impacts on their genome. We found chromosome heterochromatinization in specimens exposed to the A2 scenario, where terminal blocks and interstitial bands were detected on several chromosome pairs. The behavior of Rex1 and Rex3 sequences differed between the test scenarios. Hybridization of Rex1 resulted in diffuse signals which showed a gradual increase in the tested scenarios. For Rex3, an increase was observed in the A2 scenario with blocks on several chromosomes, some of which coincided with heterochromatin. Heterochromatinization is an epigenetic process, which may have occurred as a mechanism for regulating Rex3 activity. The signal pattern of Rex6 did not change, suggesting that other mechanisms are acting to regulate its activity.

Ecophysiology, genotoxicity, histopathology, and gene responses of naphthalene injected Colossoma macropomum (Cuvier, 1818) exposed to hypoxia

The present study aimed to evaluate the biological responses of Colossoma macropomum to naphthalene injection and subsequent hypoxia exposure, emphasizing the expression of the tumor suppressor gene tp53. Tambaquis were intraperitoneally injected with naphthalene (50 mg/kg) and, after 96 hours, the fish were transferred to respirometry chambers and, submitted to progressive hypoxia for the determination of critical PO₂. In a subsequent experiment, the fish received an intraperitoneal injection of naphthalene and were kept for 96 hours under normoxia. Successively, fish were challenged with acute hypoxia (PO₂<PO₂ crit) during 6 hours. We observed that the PO₂ crit was not affected by naphthalene injection. Moreover, hematological parameters were modulated only in response to hypoxia. Fish with naphthalene injection plus hypoxia exposure presented altered activity of the GST and CAT enzymes. Exposure to naphthalene also resulted in DNA damages, which was not influenced by hypoxia. Hypoxia accentuated the hepatic lesions caused by naphthalene, as well as it also impaired the transcription of tp53 in naphtalene injected fish, demonstrating the risks of contaminating aquatic environments, especially environments where hypoxic conditions are common and occur on a daily or on seasonal basis, as in the Amazon basin.

Deltamethrin-induced nuclear erythrocyte alteration and damage to the gills and liver of Colossoma macropomum

Deltamethrin is one of the most commonly used pyrethroids in the world, and it has a high toxic potential, mainly on aquatic organism. Thus, the purpose of this study was to evaluate LC₅₀ values of deltamethrin on tambaqui (Colossoma macropomum) fingerlings and to investigate genotoxic effects and histopathological responses. Fish were exposed to different concentrations of deltamethrin (0, 6.16 × 10^-3; 6.44 × 10^-2; 1.34 × 10^-1, and 1.93 × 10^-1 mg L^-1) for 96 h. In addition, a genotoxicity analysis was carried out on peripheral blood erythrocytes and histopathological changes were classified by the severity degree of damage and organ functioning. The 96 h LC₅₀ value for tambaqui was estimated at 5.56 × 10^-2 mg L^-1 using a static test system. Nuclear abnormalities in exposed fish included micronuclei, blebbed, notched, 8-shaped, and binucleated nuclei forms. Deltamethrin significantly induced a notched nucleus compared to other abnormalities. A histopathological examination showed hepatic lesions and gill damage. Deltamethrin was found to be highly toxic; it induced genotoxicity and caused liver and gill inflammation in tambaqui.

Oil pollution in soils and sediments from the Northern Peruvian Amazon

Oil has been extracted from the Northern Peruvian Amazon for over four decades. However, few scientific studies have assessed the impacts of such activities in the environment and health of indigenous communities in the region. We have investigated the occurrence of petrogenic hydrocarbon pollution in soils and sediments from areas favoured as hunting or fishing grounds by local indigenous inhabitants. The study was conducted in one of the most productive oil blocks in Peru, located in the headwaters of the Amazon river. Soils and river sediments, in the vicinity of oil extraction and processing infrastructure, contained an oil pollution signature as attested by the occurrence of hopanes and steranes. Given the lack of any other significant source of oil pollution in the region, the sources of hydrocarbons are likely to be the activities of the oil industry in the oil block, from voluntary discharges or accidental spills. Spillage of produced water was commonplace until 2009. Moreover, petrogenic compounds were absent in control samples in sites far removed from any oil infrastructure in the oil block. Our findings suggest that wildlife and indigenous populations in this region of the Amazon are exposed to the ingestion of oil polluted soils and sediments. The data obtained supports previous claims that the local spillage of oil and produced waters in the water courses in the Corrientes and Pastaza basins could have eventually reached the main water course of the Amazon.

Exposure of European sea bass (Dicentrarchus labrax) to chemically dispersed oil has a chronic residual effect on hypoxia tolerance but not aerobic scope

We tested the hypothesis that the chronic residual effects of an acute exposure of European sea bass (Dicentrarchus labrax) to chemically dispersed crude oil is manifest in indices of hypoxic performance rather than aerobic performance. Sea bass were pre-screened with a hypoxia challenge test to establish their incipient lethal oxygen saturation (ILOS), but on discovering a wide breadth for individual ILOS values (2.6-11.0% O₂ saturation), fish were subsequently subdivided into either hypoxia sensitive (HS) or hypoxia tolerant (HT) phenotypes, traits that were shown to be experimentally repeatable. The HT phenotype had a lower ILOS and critical oxygen saturation (O_2crit) compared with the HS phenotype and switched to glycolytic metabolism at a lower dissolved oxygen, even though both phenotypes accumulated lactate and glucose to the same plasma concentrations at ILOS. As initially hypothesized, and regardless of the phenotype considered, we found no residual effect of oil on any of the indices of aerobic performance. Contrary to our hypothesis, however, oil exposure had no residual effect on any of the indices of hypoxic performance in the HS phenotype. In the HT phenotype, on the other hand, oil exposure had residual effects as illustrated by the impaired repeatability of hypoxia tolerance and also by the 24% increase in O_2crit, the 40% increase in scope for oxygen deficit, the 17% increase in factorial scope for oxygen deficit and the 57% increase in accumulated oxygen deficit. Thus, sea bass with a HT phenotype remained chronically impaired for a minimum of 167days following an acute 24-h oil exposure while the HS phenotypes did not. We reasoned that impaired oxygen extraction at gill due to oil exposure activates glycolytic metabolism at a higher dissolved oxygen, conferring on the HT phenotype an inferior hypoxia resistance that might eventually compromise their ability to survive hypoxic episodes.

What is the most efficient respiratory organ for the loricariid air-breathing fish Pterygoplichthys anisitsi, gills or stomach? A quantitative morphological study

The purpose of the present study was to evaluate the morphometric respiratory potential of gills compared to the stomach in obtaining oxygen for aerobic metabolism in Pterygoplichthys anisitsi, a facultative air-breathing fish. The measurements were done using stereological methods. The gills showed greater total volume, volume-to-body mass ratio, potential surface area, and surface-to-volume ratio than the stomach. The water-blood diffusion barrier of the gills is thicker than the air-blood diffusion barrier of the stomach. Taken together, the surface area, the surface-to-volume ratio and the diffusion distance for O₂ transfer from the respiratory medium to blood yield a greater diffusing capacity for gills than for the stomach, suggesting greater importance of aquatic respiration in this species. On the other hand, water breathing is energetically more expensive than breathing air. Under severe hypoxic conditions, O₂ uptake by the stomach is more efficient than by the gills, although the stomach has a much lower diffusing capacity. Thus, P. anisitsi uses gills under normoxic conditions but the stomach may also support aerobic metabolism depending on environmental conditions.

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

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