EROD activity and antioxidant defenses of sea bass (Dicentrarchus labrax) after an in vivo chronic hydrocarbon pollution followed by a post-exposure period

Multi-biomarker analysis of sub-chronic PAH mixture effects in fish at environmentally relevant levels

Polycyclic Aromatic Hydrocarbons (PAHs) are persistent pollutants in aquatic ecosystems, occurring as complex mixtures with unpredictable toxicity. Although PAHs are procarcinogenic, their harmful effects require metabolic activation, leading to reactive metabolites and reactive oxygen species (ROS) that can cause DNA damage. This study assessed the toxic effects of individual PAHs (Phenanthrene and Benzo[a]pyrene) and their mixtures (1:2 and 2:1 ratios) on juvenile seabream (Sparus aurata) after 42 days of exposure at 0.2nmol.L-1 . Biomarkers related to oxidative stress, detoxification, and lipid peroxidation were analysed in the liver and gills (e.g., glutathione (GSH), glutathione peroxidase (GPx), glutathione-S-transferase (GST), catalase (CAT), lipoperoxidation (LPO). Liver gene expression (Cytochromes P450 (CYP1A), GST3, tumour protein p53 (TP53) and blood cell DNA damage were also studied. Correlation analyses and Non-Metric Multidimensional Scaling (NMDS) were used to relate treatments and biomarkers. Results suggested differences in organ responses, with the gills generally showing the most significant changes in GSH levels, GST activity, and LPO compared to the control group. DNA repair mechanisms appeared to prevent significant genotoxicity as assessed by the comet assay. However, erythrocytic nuclear anomalies (ENAs) were notably higher in fish exposed to Phe, B[a]P, and the 2:1 B[a]P:Phe mixture compared to the control group. Interestingly, the 2:1 Phe:B[a]P mixture appeared to have an enhanced effect, showing a marked upregulation of GST3 mRNA (up to 7-fold), possibly influenced by the higher proportion of Phe. MDS analysis proved to be a valuable tool in identifying patterns among biological responses, offering insight into how fish cope with PAH exposure and helping to uncover the unpredictable effects of chemical mixtures. This study highlights the need for further research into the interactions of PAH mixtures, employing multi-analysis approach and underscores the importance of revising environmental guidelines to account for their effects.

Toxic effect of fluorene on Perinereis aibuhitensis body wall and its corresponding defense mechanisms: A metabolomics perspective

Fluorene is a coastal sediment pollutant with high ecological risk. Perinereis aibuhitensis is an ecotoxicological model used for polycyclic aromatic hydrocarbon bioremediation; however, the effects of fluorene on the physiological metabolism of P. aibuhitensis and its corresponding responses remain unclear. This study explored the tolerance and defense responses of P. aibuhitensis in sediments with different fluorene concentrations using histology, ecological biomarkers, and metabolic responses. Metabolomics analyses revealed that P. aibuhitensis has high tolerance to fluorene in sediments. Fluorene stress disrupted the normal metabolism of the P. aibuhitensis body wall, resulting in excessive glycosphospholipid and stearamide accumulation and elevated oxygen consumption rates. To mitigate this, P. aibuhitensis has adopted tail cutting, yellowing, and modulation of metabolite contents in the body wall. This study provides novel insights into the potential ecological risk of fluorene pollution in marine sediments and proposes the use of P. aibuhitensis in the bioremediation of fluorene-contaminated sediments.

Emerging studies on oil pollution biomonitoring: A systematic review

In the last decade, several methods were applied to monitor the impact of oil pollution on marine organisms. Recent studies showed an eminent need to standardize these methods to produce comparable results. Here we present the first thorough systematic review of the literature on oil pollution monitoring methods in the last decade. The literature search resulted on 390 selected original articles, categorized according to the analytical method employed. Except for Ecosystem-level analyses, most methods are used on short-term studies. The combination of Biomarker and Bioaccumulation analysis is the most frequently adopted strategy for oil pollution biomonitoring, followed by Omic analyses. This systematic review describes the principles of the most frequently used monitoring tools, presents their advantages, limitations, and main findings and, as such, could be used as a guideline for future researches on the field.

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.

NOD-like receptor signaling pathway activation: A potential mechanism underlying negative effects of benzo(α)pyrene on zebrafish

Benzo(α)pyrene (BaP) is one of typical polycyclic aromatic hydrocarbons (PAHs) in aquatic environments and has been shown to cause toxic effects to aquatic animals. Although the negative effects of BaP have been investigated, the potential toxic mechanisms remain uncharacterized. To explore the potential mechanisms mediating the toxic effects of BaP, zebrafish (Danio rerio) were exposed to BaP for 15 days and the toxic effects of BaP in zebrafish liver were investigated using physiological and transcriptomic analyses. After 15-day BaP exposure, zebrafish liver exhibited abnormalities including increased cytoplasmic vacuolation, inflammatory cell infiltration, swelled nuclei and irregular pigmentation. BaP exposure also induced oxidative stress to the liver of zebrafish. Transcriptomic profiles revealed 5129 differentially expressed genes (DEGs) after 15-days of BaP exposure, and the vast majority of DEGs were up-regulated under BaP treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggest that genes related to immune response were significantly dysregulated. Furthermore, the nucleotide-binding, oligomerization domain (NOD)-like receptor signaling pathway was significantly enriched and most of the genes in this pathway exhibited enhanced expression after BaP exposure. These results partially explained the mechanisms underlying the toxic effects of BaP on zebrafish liver. In conclusion, BaP has the potential to induce physiological responses in zebrafish liver through altering associated genes.

Effects of 9,10-phenanthrenequione on antioxidant indices and metabolite profiles in Takifugu obscurus plasma

Derived from polycyclic aromatic hydrocarbons (PAHs), oxygenated-PAHs (oxy-PAHs) may pose hazards to aquatic organisms, which remain largely unknown. Takifugu obscurus is an important anadromous fish species of high economic and ecological values. In the present study, T. obscurus was acutely exposed to 44.29 µg l-1 9,10-phenanthrenequione (9,10-PQ) for 96 h. Changes of antioxidant indices and metabolite profiles in plasma were compared between 9,10-PQ treatment and the control. The results showed that 9,10-PQ treatment significantly increased malondialdehyde (MDA) content during 6 to 96 h, increased superoxide dismutase (SOD) and catalase (CAT) activities at 6 h, but decreased them at 96 h. These results indicated that 9,10-PQ induced oxidative stress to fish. Ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) analysis revealed that four metabolic pathways were influenced in response to treatment with 9,10-PQ, including glycerophospholipid metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, purine metabolism and sulfur metabolism. These pathways are associated with antioxidant mechanisms, biosynthesis of neurotransmitters and innate immune functions. Thus, the as-obtained results confirmed that 9,10-PQ induced oxidative stress and raised concerns of neurotoxicity and immunotoxicity to fish. Overall, the present study posed a high environmental risk of oxy-PAHs to aquatic ecosystems.

Histological, oxidative and immune changes in response to 9,10-phenanthrenequione, retene and phenanthrene in Takifugu obscurus liver

Polycyclic aromatic hydrocarbons (PAHs) are typical pollutants and may be alkylated and oxygenated to form alkyl-PAHs and oxygenated-PAHs (oxy-PAHs), respectively. Takifugu obscurus is an important anadromous fish species and displays a high risk of being exposed to PAHs-contaminated areas. In the present study, the effects of acute exposure to 44.29 µg L^-1 9,10-phenanthrenequione (9,10-PQ), retene and phenanthrene (Phe) on T. obscurus liver histology, antioxidant enzymes and immune indices were compared. After exposure to these three compounds, histological sections showed damages of hepatocyte, and the activities of alanine and aspartate aminotransferase increased in plasma, indicating direct hepatic toxicity. Hepatic malondialdehyde (MDA) content increased, but superoxide dismutase (SOD) and catalase (CAT) activities decreased in response to treatments with Phe, retene and 9,10-PQ. These results revealed peroxidative effects on T. obscurus hepatocytes. In addition, total immunoglobulin content and lysozyme activity in plasma increased in treatments with Phe, retene and 9,10-PQ, which might be resulted from the damaged liver cells and the subsequently hepatic inflammation. Besides, the changes were more severe in treatment with 9,10-PQ than those with Phe and retene, demonstrating higher toxicity of 9,10-PQ than the other two compounds. Overall, the present study posed a high environmental risk of PAH derivatives to aquatic ecosystems.

Identification, expression and functional characterisation of CYP1A in grass carp (Ctenopharyngodon idella)

In mammal, CYP1A has attracted special attention due to its important roles in the oxidative metabolism. In fish, the researches on CYP1A are more focus on its roles in pollution in water environments, but the immune function is unclear. In the study, CiCYP1A gene was cloned from grass carp (Ctenopharyngodon idella). Tissue distribution exhibited an overwhelmingly high basal expression levels in the liver. After GCRV infection, CiCYP1A showed a potent response, indicating CiCYP1A was involved in GCRV-induced immunity. Subcellular localisation showed CiCYP1A was distributed in the cytoplasm. Besides, dual-luciferase activity assays revealed CYP1A was relevant for IFN-I signaling pathway modulation, furthermore, overexpressed CYP1A potently suppressed the mRNA expression of IRF3 and IFN-I but not IRF7. The results provide new sights into exploring immune function of CiCYP1A in teleosts.

Interactions of oxidative DNA damage and CYP1A gene expression with the liver enzymes in Klunzinger's mullet exposed to benzo[a]pyrene

Benzo[a]pyrene (B[a]P) is an important contaminant whose liver biotransformation is dependent on the species, the route of exposure and the concentration. The goal of this study was to assess the interactions of oxidative DNA damage and CYP1A gene expression with the liver enzymes in Klunzinger’s mullet (Liza klunzingeri) exposed to benzo[a]pyrene. Sublethal doses of B[a]P (5, 10 and 50 mg/kg) were intraperitoneally administered to the fish for 14 days. The alterations in antioxidant enzymes’ activity (SOD, CAT, and GPX), hepatic enzymes’ activity (ALT, AST and ALP), DNA damage (measured by comet assay and cellProfiler software) and CYP1A gene expression in the fish liver were studied on the 1st, 3rd, 7th and 14th days. The determination of these parameters in the liver showed that most of these parameters significantly increased mostly in a time-dependent manner. Multiple regression analysis showed that DNA damage and CYP1A gene expression had positive correlations with the liver enzymes in this fish species intraperitoneally exposed to these concentrations. Moreover, these interactions indicated that theses parameters are sensitive biomarkers for the exposure to B[a]P in Klunzinger's mullet. However, other possible factors and B[a]P metabolites should be considered in future studies for better elucidating the biotransformation mechanisms and introducing better biomarkers of B[a]P.

The effect of hypoxia and hydrocarbons on the anti-predator performance of European sea bass (Dicentrarchus labrax)

Hydrocarbons contamination and hypoxia are two stressors that can coexist in coastal ecosystems. At present, few studies evaluated the combined impact of these stressors on fish physiology and behavior. Here, we tested the effect of the combination of hypoxia and petrogenic hydrocarbons on the anti-predator locomotor performance of fish. Specifically, two groups of European sea bass (Dicentrarchus labrax) were exposed to clean water (Ctrl) or oil-contaminated water (Oil). Subsequently, fish of both groups were placed in normoxic (norx) or hypoxic (hyp) experimental tanks (i.e. four groups of fish were formed: Ctrl norx, Ctrl hyp, Oil norx, Oil hyp). In these tanks, escape response was elicited by a mechano-acoustic stimulus and recorded with a high speed camera. Several variables were analyzed: escape response duration, responsiveness (percentage of fish responding to the stimulation), latency (time taken by the fish to initiate a response), directionality (defined as away or toward the stimulus), distance-time variables (such as speed and acceleration), maneuverability variables (such as turning rate), escape trajectory (angle of flight) and distancing of the fish from the stimulus. Results revealed (i) effects of stressors (Ctrl hyp, Oil norx and Oil hyp) on the directionality; (ii) effects of Oil norx and Oil hyp on maneuverability and (iii) effects of Oil hyp on distancing. These results suggest that individual stressors could alter the escape response of fish and that their combination could strengthen these effects. Such an impact could decrease the probability of prey escape success. By investigating the effects of hydrocarbons (and the interaction with hypoxia) on the anti-predator behavior of fish, this work increases our understanding of the biological impact of oil spill. Additionally, the results of this study are of interest for oil spill impact evaluation and also for developing new ecotoxicological tools of ecological significance.

Gills CYP1A of Oncorhynchus mykiss as a sensitive biomarker of crude oil pollution in freshwater environments

The induction of CYP1A activity (EROD) and protein expression was compared in liver and gills of rainbow trout from a stream polluted with crude oil, and through laboratory exposures to 1% and 5% of water accommodated fraction of the crude oil (WAF) for 1 and 4 days. Gills EROD increased 1.6-2.7-fold in fish from the polluted stream and during experiments, while liver EROD was induced only by 1% WAF at day 1 (1.5-fold). Contrastingly, crude oil pollution strongly induced both liver and gills CYP1A protein expression in the field (14-36-fold) and in experiments (4-25-fold). This highlights that crude oil induced CYP1A activity markedly in gills but only slightly or not at all in the liver, suggesting that differences between organ EROD activities are related to the modulation of CYP1A enzyme activity but not to the regulation at transcriptional or translational levels.

Influence of crude oil exposure on cardiac function and thermal tolerance of juvenile rainbow trout and European sea bass

Oil spills pose a threat to aquatic organisms. However, the physiological effects of crude oil on cardiac function and on thermal tolerance of juvenile fish are still poorly understood. Consequently, in this paper, we will present results of two separate experiments where we exposed juvenile rainbow trout and European sea bass to crude oil and made cardiac thermal tolerances and maximum heart rate (f _Hmax) measurements after 1 week (rainbow trout) and 6-month recovery (sea bass). In both species, the f _Hmax was lower in crude oil-exposed fish than in the control ones at temperatures below the optimum but this difference disappeared at higher temperatures. More importantly, the oil-exposed fish had significantly higher Arrhenius break point temperature for f _Hmax, which gave an estimate for optimum temperature, than the control fish in both species even though the exposure conditions and recovery times differed between species. The results indicated that exposure of juvenile fish to crude oil did not have a significant negative impact upon their cardiac performance in high temperatures and upper thermal tolerance increased when the fish were tested 1 week or 6 months after the exposure. Our findings suggest that the cardiac function and thermal tolerance of juvenile fish are relatively resistant to a crude oil exposure.

A multi-year study of hepatic biomarkers in coastal fishes from the Gulf of Mexico after the Deepwater Horizon Oil Spill

Following the 2010 Gulf of Mexico oil spill, concerns were raised regarding exposure of fish to crude oil components, particularly polycyclic aromatic hydrocarbons (PAHs). This three year study examined hepatic enzymes in post-mitochondrial supernatant fractions from red snapper (Lutjanus campechanus) and gray triggerfish (Balistes capriscus) collected in the north central Gulf of Mexico between 2011 and 2014. Biomarker activities evaluated included benzo(a)pyrene hydroxylase (AHH), ethoxyresorufin O-deethylase (EROD), glutathione transferase (GST), and glutathione peroxidase (GPx). Mean EROD activity was higher in gray triggerfish (12.97 ± 7.15 pmol/min/mg protein [mean ± SD], n = 115) than red snapper (2.75 ± 1.92 pmol/min/mg protein, n = 194), p < 0.0001. In both species, EROD declined over time between 2011 and 2014. Declines in GST and GPx activities were also noted over this time period for both species. Gray triggerfish liver was fatty, and heptane extracts of the liver fat contained fluorescent substances with properties similar to known PAHs, however the origin of these PAHs is unknown.

Biomarker responses to environmental contamination in estuaries: A comparative multi-taxa approach

Estuaries are highly productive ecosystems subjected to numerous anthropogenic pressures with consequent environmental quality degradation. In this study, multiple biomarker responses [superoxide dismutase (SOD), catalase (CAT), ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST) activities, as well as lipid peroxidation (LPO) and DNA damage (DNAd)] were determined in two fish (Dicentrarchus labrax and Pomatoschistus microps) and four macroinvertebrate species (Carcinus maenas, Crangon crangon, Hediste diversicolor and Scrobicularia plana) from the Ria de Aveiro and Tejo estuaries over distinct months. Two sites per estuarine system were selected based on anthropogenic pressures and magnitude of environmental contamination. Antioxidant enzyme activities in fish species suggested a ubiquitous response to oxidative stress, while biotransformation and effect biomarkers exhibited higher spatial and temporal variation. In invertebrate species, biotransformation enzyme activity was clearly less variable than in fish evidencing lower xenobiotic transformation capability. Overall, largest biomarker responses were found in the most contaminated sites (Tejo), yet species-specific patterns were evident. These should be factored in multi-taxa approaches, considering that the differential functional traits of species, such as habitat use, life-stage, feeding or physiology can influence exposure routes and biomarker responses. The Integrated Biomarker Response index highlighted patterns in biomarker responses which were not immediately evident when analyzing biomarkers individually. Overall, results provided insights into the complexity of species responses to contamination in naturally varying estuarine environments. Ultimately, multi-taxa and multi-biomarker approaches provide a comprehensive and complementary view of ecosystem health, encompassing diverse forms of biological integration and exposure routes, and allow the validation of results among markers and species.

Effects of dispersed oil exposure on biomarker responses and growth in juvenile wolfish Anarhichas denticulatus

This study evaluated the sensitivity of the wolfish Anarhichas denticulatus exposed to crude oil, comparing the effects of mechanically dispersed versus chemically dispersed oil using sub-lethal endpoints. To test the toxicity of this controversial technique, two experiments involving exposure of the organisms for 48 h were conducted. The first experiment assessed the effects of oil exposure on biomarker responses. The second experiment monitored the growth of juveniles over 5 weeks after exposure. Overall, this study demonstrated that polycyclic aromatic hydrocarbon (PAH) biliary metabolites, ethoxyresorufin-O-deethylase (EROD), and acetylcholinesterase (AChE) are appropriate biomarkers to assess exposure of A. denticulatus. Growth rate, both in length and weight, was significantly higher in control compared to oil exposure treatments. The lack of differences between chemically and mechanically dispersed oils in biomarker response and growth suggests that dispersant application is no more toxic than the natural oil dispersion. The results indicate the potential for population-level effects resulting from exposure to oil.

Hypoxia depresses CYP1A induction and enhances DNA damage, but has minimal effects on antioxidant responses in sheepshead minnow (Cyprinodon variegatus) larvae exposed to dispersed crude oil

The growing incidence of hypoxic regions in coastal areas receiving high volumes of anthropogenic discharges requires more focused risk assessment of multiple stressors. One area needing further study is the combined effect of hypoxia and oil exposure. This study examined the short-term sublethal effects of co-exposure to hypoxia and water accommodated fractions (WAF) and chemically enhanced WAFs (CEWAFs) of Southern Louisiana Crude oil on detoxification, antioxidant defenses and genotoxicity in early life stage sheepshead minnow (Cyprinodon variegatus). CYP1A induction (evaluated by measuring EROD activity), activity of a number of key antioxidant enzymes (GST, GR, GPx, SOD, CAT, and GCL), levels of antioxidants (tGSH, GSH, and GSSG), evidence of lipid peroxidation (evaluated using the TBARS assay), and DNA damage (evaluated using the comet assay) provided a broad assessment of responses. Contaminant detoxification pathways induced by oil exposure were inhibited by co-exposure to hypoxia, indicating a maladaptive response. The interactive effects of oil and hypoxia on antioxidant defenses were mixed, but generally indicated less pronounced alterations, with significant increases in lipid peroxidation not observed. Hypoxia significantly enhanced DNA damage induced by oil exposure indicating the potential for significant deleterious effects post exposure. This study demonstrates the importance of considering hypoxia as an enhanced risk factor in assessing the effects of contaminants in areas where seasonal hypoxia may be prevalent.

Integrating Multiple Biomarkers of Fish Health: A Case Study of Fish Health in Ports

Biomarkers of fish health are recognised as valuable biomonitoring tools that inform on the impact of pollution on biota. The integration of a suite of biomarkers in a statistical analysis that better illustrates the effects of exposure to xenobiotics on living organisms is most informative; however, most published ecotoxicological studies base the interpretation of results on individual biomarkers rather than on the information they carry as a set. To compare the interpretation of results from individual biomarkers with an interpretation based on multivariate analysis, a case study was selected where fish health was examined in two species of fish captured in two ports located in Western Australia. The suite of variables selected included chemical analysis of white muscle, body condition index, liver somatic index (LSI), hepatic ethoxyresorufin-O-deethylase activity, serum sorbitol dehydrogenase activity, biliary polycyclic aromatic hydrocarbon metabolites, oxidative DNA damage as measured by serum 8-oxo-dG, and stress protein HSP70 measured on gill tissue. Statistical analysis of individual biomarkers suggested little consistent evidence of the effects of contaminants on fish health. However, when biomarkers were integrated as a set by principal component analysis, there was evidence that the health status of fish in Fremantle port was compromised mainly due to increased LSI and greater oxidative DNA damage in fish captured within the port area relative to fish captured at a remote site. The conclusions achieved using the integrated set of biomarkers show the importance of viewing biomarkers of fish health as a set of variables rather than as isolated biomarkers of fish health.