Effects of diluted bitumen exposure and recovery on the seawater acclimation response of Atlantic salmon smolts

Metabolomics perspectives of the ecotoxicological risks of polycyclic aromatic hydrocarbons: A scoping review

Polycyclic Aromatic Hydrocarbons (PAHs) represent persistent environmental pollutants ubiquitously distributed in the environment. Their presence alongside various other contaminants gives rise to intricate interactions, culminating in profound deleterious consequences. The combination effects of different PAH mixtures on biota remains a relatively unexplored domain. Recent studies have harnessed the exceptional sensitivity of metabolomic techniques to unveil the significant ecotoxicological perils of PAH pollution confronting both human populations and ecosystems. This article furnishes a comprehensive overview of current literature focused on the metabolic repercussions stemming from exposure to complex mixtures of PAHs or PAH-pollution sources using metabolomics approaches. These insights are obtained through a wide range of models, including in vitro assessments, animal studies, investigations on human subjects, botanical specimens, and soil environments. The findings underscore that PAH mixtures induce cellular stress responses and systemic effects, leading to metabolic dysregulations in amino acids, carbohydrates, lipids, and other key metabolites (e.g., organic acids, purines), with specific variations observed based on the organism and PAH compounds involved. Additionally, the ecological consequences of PAH pollutants on plant and soil microbial responses are emphasized, revealing significant changes in stress-related metabolites and nutrient cycling in soil ecosystems. The complex interplay of various PAHs and their metabolic effects on several models, as elucidated through metabolomics, highlight the urgency of further research and the need for comprehensive strategies to mitigate the risks posed by these widespread environmental pollutants.

Exploring the Impact of Naphthalene (Polycyclic Aromatic Hydrocarbons) on Anabas testudineus (Bloch) through Dose-Specific Bioenzymological Analysis

This study addresses the increasing concern about naphthalene, a polycyclic aromatic hydrocarbon (PAH), highlighting its growing threats to the environment and aquatic life. The research examines its impact on Anabas testudineus (Bloch) through a detailed dose-specific bioenzymological analysis. Experimental fish groups were exposed to T1 (0.71 mg/L) and T2 (1.42 mg/L) naphthalene concentrations, representing 25 and 50% of the LC50 value, respectively, over a 1-21 day period. Following the experiment, water samples underwent physicochemical analysis, while fish tissues were examined for diverse bioenzymological parameters. Among these parameters, aspirate aminotransferase (AST) and alanine aminotransferase (ALT) serve as crucial indicators for monitoring the physiological status of fish and addressing pollution induced by PAHs, especially naphthalene. Statistical significance was observed in morpho-pathological changes and erythrocyte alterations, particularly the presence of tear-drop appearance (Tr) positively interacting with swelled cells (Sc), vacuolated cells (Va), and sickle cells (Sk) (P < 0.05). These findings highlight tear-drop appearance (Tr) as a significant biomarker in response to naphthalene exposure. The observed changes in A. testudineus tissue bioenzymology, apoptosis, and erythrocytic alterations were exposure and dose-dependent. The research highlights the significance of overseeing and controlling PAH concentrations in aquatic ecosystems to ensure the well-being of A. testudineus (Bloch).

Salinity-dependent mitigation of naphthalene toxicity in migratory Takifugu obscurus juveniles: Implications for survival, oxidative stress, and osmoregulation

Naphthalene, an environmental pollutant classified as a polycyclic aromatic hydrocarbon (PAH), can induce toxicity in fish and other aquatic organisms. Through our investigation, we determined how Takifugu obscurus juveniles were affected by naphthalene (0, 2 mg L-1) exposure in terms of oxidative stress biomarkers and Na+/K+-ATPase activity in various tissues (gill, liver, kidney and muscle) under dissimilar salinities (0, 10 psu). Results suggest that naphthalene exposure significantly affects the survival of T. obscurus juveniles and leads to significant changes in the levels of malondialdehyde, superoxide dismutase, catalase, glutathione, and Na+/K+-ATPase activity, which are indicative of oxidative stress and emphasized the risks associated with osmoregulatory function. The higher salinity affected on the noxious effects of naphthalene can be observed, resulting in decreased biomarker levels and increased Na+/K+-ATPase activity. Salinity levels affected the uptake of naphthalene and its impact on different tissues, with high salinity conditions having mitigating effects on oxidative stress and naphthalene uptake in the liver and kidney tissues. Increased Na+/K+-ATPase activity was observed in all tissues treated with 10 psu and 2 mg L-1 naphthalene. Our findings deepen the understanding of T. obscurus juveniles' physiological responses to naphthalene exposure, and highlight the potential mitigating effects of salinity. These insights can inform the development of appropriate conservation and management practices to protect aquatic organisms from susceptibility.

Functional and molecular characterization of the Atlantic salmon gill epithelium cell line ASG-10; a tool for in vitro gill research

Fish gills are not only the respiratory organ, but also essential for ion-regulation, acid-base control, detoxification, waste excretion and host defense. Multifactorial gill diseases are common in farmed Atlantic salmon, and still poorly understood. Understanding gill pathophysiology is of paramount importance, but the sacrifice of large numbers of experimental animals for this purpose should be avoided. Therefore, in vitro models, such as cell lines, are urgently required to replace fish trials. An Atlantic salmon gill epithelial cell line, ASG-10, was established at the Norwegian Veterinary institute in 2018. This cell line forms a monolayer expressing cytokeratin, e-cadherin and desmosomes, hallmarks of a functional epithelial barrier. To determine the value of ASG-10 for comparative studies of gill functions, the characterization of ASG-10 was taken one step further by performing functional assays and comparing the cell proteome and transcriptome with those of gills from juvenile freshwater Atlantic salmon. The ASG-10 cell line appear to be a homogenous cell line consisting of epithelial cells, which express tight junction proteins. We demonstrated that ASG-10 forms a barrier, both alone and in co-culture with the Atlantic salmon gill fibroblast cell line ASG-13. ASG-10 cells can phagocytose and express several ATP-binding cassette transport proteins. Additionally, ASG-10 expresses genes involved in biotransformation of xenobiotics and immune responses. Taken together, this study provides an overview of functions that can be studied using ASG-10, which will be an important contribution to in vitro gill epithelial research of Atlantic salmon.

Dynamic cyp1a1 transcript responses in the caudal fin of coho salmon (Oncorhynchus kisutch) smolts to low sulfur marine diesel water accommodated fraction exposures and depuration

Oil spills that occur in high traffic coastal environments can have profound consequences for the health of marine ecosystems and the commercial and social interests that are dependent upon these habitats. Given that the global reliance on marine fuels is not abating, it is imperative to develop sensitive and robust tools to monitor oil contamination and remediation in a timely manner. Such tools are increasingly important for ascertaining the immediate and long-term effects of oil contamination on species of interest and local habitats as water-soluble components of oils, such as polycyclic aromatic hydrocarbons (PAHs), can persist post-remediation. We previously demonstrated that 3-methylcholanthrene responsive cytochrome P450-1a (cyp1a1) transcript abundance in the liver and caudal fin of coho salmon smolts (Onchorhynchus kisutch) was sensitive to exposure to low sulfur marine diesel (LSMD) seawater accommodated fractions (seaWAF) in cold water. We expanded upon this paradigm by assessing the utility of the cyp1a1 transcript to track both exposure to LSMD seaWAF and recovery from exposure by measuring cyp1a1 abundance in coho smolts using quantitative polymerase chain reaction (qPCR). Smolts were exposed to either 100 mg/L LSMD seaWAF or clean seawater (control) for 4 days. Fish were then transferred to clean seawater for depuration and tissues sampled at 0, 1, 2, 4, and 8 days from both treatments. Livers and caudal fins were dissected from 40 smolts per group (n_total = 400 smolts). The LSMD seaWAF-induced cyp1a1 transcript levels significantly decreased one day after depuration in the liver and caudal fin in a sex-independent manner in genotyped females and males. After four days of depuration, cyp1a1 transcript abundance decreased to baseline control levels, regardless of tissue or sex. The present study demonstrates the value of using the caudal fin as a reliable, sensitive, and non-lethal sampling and monitoring tool.

Early developmental toxicity of Atlantic salmon exposed to conventional and unconventional oils

Atlantic salmon is an important species for Canadian culture and economy and its importance extends beyond Canada to Scandinavia and Western Europe. However, it is a vulnerable species facing decline due to habitat contamination and destruction. Existing and new Canadian pipeline projects pose a threat to salmonid habitat. The effects of diluted bitumen (dilbit), the main oil circulating in pipelines, are less studied than those of conventional oils, especially during the critical early embryonic developmental stage occurring in freshwater ecosystems. Therefore, this study aimed to compare the effects of water-accommodated fractions (WAF) of the Clearwater McMurray dilbit and the Lloydminster Heavy conventional oil on Atlantic salmon embryos exposed either from fertilization or from eyed stage. The dilbit contained the highest concentrations of low molecular weight (LMW) compounds (including BTEX and C₆-C₁₀), while the conventional oil contained the highest concentrations of PAHs. The Clearwater dilbit caused a higher percentage of mortality and malformations than the conventional oil at similar WAF concentrations. In addition, the embryos exposed from fertilization suffered a higher mortality rate, more developmental delays, and malformations than embryos exposed from the eyed stage, suggesting that early development is the most sensitive developmental stage to oil exposure. Gene expression and enzymatic activity of the detoxification phase I and II enzymes (CYP1A and GST) were measured. Data showed increases in both cyp1a expression and GST activity with increasing WAF concentrations, while gst expression was not affected by the exposures. Also, gene expression of proteins involved in the biotransformation of vitamin A and DNA damage repair were modified by the oil exposures. Overall, this study indicates that Atlantic salmon is mostly affected by oil exposure at the beginning of its development, during which embryos accumulate deformities that may impact their survival at later life stages.

Age matters: Comparing life-stage responses to diluted bitumen exposure in coho salmon (Oncorhynchus kisutch)

Millions of liters of diluted bitumen (dilbit), a crude oil product from Canada's oil sands region, is transported through critical Pacific salmon habitat each day. While the toxicity of the water-soluble fraction of dilbit (WSFd) to early life-stages of salmon is known, quantitative data on life-stage differences in sensitivity to WSFd is missing. To fill this knowledge gap, we exposed two juvenile life-stages of coho salmon (O. kisutch) in parallel to very low (parts per billion), environmentally-relevant concentrations of WSFd for acute (48 h) and sub-chronic (4 wk) durations. The relative sensitivities of the two life-stages (fry and parr) were assessed by comparing the timing and magnitude of biological responses using common organismal and molecular endpoints of crude oil exposure. A significant reduction in body condition occurred in both fry and parr after 4 wk exposure to WSFd. Both life-stages also experienced a concentration-dependent decrease in time-to-loss-of-equilibrium during a hypoxia challenge test at both 48 h and 4 wk of exposure. Although organismal responses were similar, molecular responses were distinct between life-stages. In general, unexposed fry had higher baseline values of hepatic phase I biotransformation indicators than unexposed parr, but induction of EROD activity and cyp1a mRNA expression in response to WSFd exposure was greater in parr than in fry. Neither gst nor hsp70 mRNA expression, markers of phase II biotransformation and cell stress, respectively, were reliably altered by WSFd exposure in either life-stage. Taken together, results of this study do not support differential sensitivities of coho fry and parr to WSFd. All the same, the potential for ontogenic differences in the expression and induction of phase I biotransformation need to be considered because age does matter for these endpoints if they are used as bioindicators of exposure in post-spill impact assessments.

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.

Lethal and sublethal effects in Pink salmon (Oncorhynchus gorbuscha) following exposure to five aquaculture chemotherapeutants

Early life stages of Pink salmon (Oncorhynchus gorbuscha) are at risk of exposure to the active ingredients of chemotherapeutant formulations (hydrogen peroxide [HP], azamethiphos [AZ], emamectin benzoate [EB], cypermethrin [CP] and deltamethrin [DM]) used to control sea lice in salmon aquaculture. LC50 values (95% confidence intervals) for acute 48-h water exposures in order of least to most toxic to seawater-adapted pink salmon fry were: HP (227 [138-418] mg/L), EB (1090 [676-2006] µg/L), AZ (80 [52-161] µg/L), CP (5.1 [3.0-10.5] µg/L), and DM (980 [640-1800] ng/L), and in subchronic 10-d lethality sediment exposure tests: EB (2065 [1384-3720] µg/kg), CP (97 [58-190] µg/kg), and DM (1035 [640-2000] ng/kg). Alterations in behaviour varied between chemicals; no chemical attracted pink salmon fry; fish avoided HP to a limited extent at 50 mg/L), as well as EB (300 µg/L), and AZ (50 µg/L). Significant concentration-dependent decreases in olfactory responsiveness to food extract were seen following AZ, CP and DM exposures that occurred at lower concentrations with longer exposure periods (10 µg/L, 0.5 µg/L and 100 ng/L thresholds at 7 d). Following 10-d sediment exposures, olfaction was only affected by CP exposure at 50 µg/kg. Significant decreases in swimming performance (Ucrit) occured for HP, AZ, CP and DM at concentrations as low as 100 mg/L, 10 µg/L, 2 µg/L and 200 ng/L, respectively. This study provides comprehensive data on the lethal and sublethal effects of aquaculture chemotherapeutant exposure in early life stage pink salmon.

Under ice spills of conventional crude oil and diluted bitumen: Physiological resilience of the blue mussel and transgenerational effects

Spillages at sea of diluted bitumen (dilbit) from oil sands have received little attention until now. To our best knowledge, there are no reports on the impact of a severe exposure to dilbit on the Blue mussel (Mytilus edulis). In this study, adult Blue mussels were exposed to one conventional crude oil (Heidrun) and two dilbits (Cold Lake Blend and Access Western Blend) for a period of 7 days in an ice-covered environment and then maintained for three months until the spawning season. The exposed mussels were monitored for aromatic hydrocarbon bioaccumulation, physiological energetic budget, cellular stress, byssus production and gametogenesis. In spring, spawning was induced to characterize breeding success. Bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) was detected after three days of exposure, with higher concentrations of PAHs associated to the conventional oil (5.49 ± 0.12 μg·g^-1 d.w.) compared to both dilbits (0.91 ± 0.02 μg·g^-1; 0.51 ± 0.03 μg·g^-1 d.w.). Despite a fast depuration rate and a good resilience of the exposed mussels, significant negative effects were observed at the cellular, physiological and fitness levels, especially in offspring. Our results suggest a higher toxicity of the diluted bitumen compared to the conventional crude despite the lower bioaccumulation of total PAHs. Dilbit treatments caused evident negative transgenerational effects on unexposed F1 generation.

Blood Biochemical and Erythrocytic Morpho-pathological Consequences of Naphthalene Intoxication in Indian Teleost, Anabas testudineus (Bloch)

Anabas testudineus (Bloch) was exposed to 0.71 mg/L and 1.42 mg/L (25 and 50% of LC₅₀ value respectively) naphthalene, a polycyclic aromatic hydrocarbon (PAH), for 21 days. Blood biochemical parameters and erythrocytic morphological alterations were assessed to describe the naphthalene toxicity. Biochemical analysis showed a significant increase in glutamic pyruvic transaminase, GPT (576.7 ± 11.79 and 608.9 ± 12.08 U/L, respectively) and alkaline phosphatase, ALP (12.9 ± 0.69 and 13.4 ± 0.64 U/L, respectively) activities under two doses compared with control. Protein and albumin (ALB) content in blood decreased significantly, in comparison with control value in the tune of 22.67 ± 1.04 and 23.97 ± 1.24 g/dl, respectively and 10.7 ± 0.79 and 11.1 ± 0.67 g/dl, respectively. Erythrocytes showed varied symptomatic morphological changes under naphthalene exposure, which included severe denaturation, swelling in cells, appearance of sickle and tear drop cells, and cellular vacuolation. In particularly, the changes were more prominent under higher naphthalene exposure. Following the results, it has been able to establish that GPT, ALP, protein and ALB, and the morphological manifestations of erythrocytes would be good tools of biomarker in monitoring toxicological paradigm, especially to naphthalene exposure in aquatic bodies.

Effects on Trout Alevins of Chronic Exposures to Chemically Dispersed Access Western Blend and Cold Lake Blend Diluted Bitumens

The present study assessed the chronic toxicity of 2 chemically enhanced water accommodated fractions (CEWAFs) of diluted bitumens (dilbits), Access Western Blend (AWB) and Cold Lake Blend (CLB), to rainbow trout alevins. Chemical dispersion was used to overcome the resistance to dispersion of dilbits and to generate test solutions that contained more and smaller oil droplets for increased partitioning of petroleum hydrocarbons into water. Test solutions were characterized by fluorescence spectroscopy, a rapid and inexpensive analytical tool to compare toxicity endpoints measured by fluorescence (total petroleum hydrocarbons measured by fluorescence [TPH-F]). Cumulative mortality and the prevalence and severity of malformations increased following exposure of alevins to dispersed dilbits. Toxicity curves overlapped for AWB and CLB when expressed as TPH-F and 22- to 24-d median lethal and effect concentrations ranged from 0.36 to 1.5 mg/L. Gene expression in alevins was also altered following exposure to dispersed dilbit, with relative cytochrome P450-1A mRNA levels increasing up to 170-fold for AWB and up to 240-fold for CLB. Access Western Blend and CLB caused similar toxicity to rainbow trout alevins as light to medium conventional crude oils, and rainbow trout alevins were more sensitive than yellow perch, Japanese medaka, and fathead minnow embryos exposed to dispersed AWB and CLB. The present study is the first to assess the embryotoxicity of dilbits to a Canadian freshwater salmonid species. Environ Toxicol Chem 2020;39:1620-1633. © 2020 SETAC.