Metabolites analysis, metabolic enzyme activities and bioaccumulation in the clam Ruditapes philippinarum exposed to benzo[a]pyrene

Biomarker responsiveness in Norwegian Sea mussels, Mytilus edulis, exposed at low temperatures to aqueous fractions of crude oil alone and combined with dispersant

Biological effects of aqueous fractions of a crude oil, alone or in combination with dispersant, were investigated in mussels, Mytilus edulis, exposed at three temperatures (5, 10 and 15 °C). Polycyclic aromatic hydrocarbons (PAHs) tissue concentrations were determined, together with genotoxicity, oxidative stress and general stress biomarkers and the Integrated Biological Response (IBR) index. The bioaccumulation of individual PAHs varied depending on the exposure temperature, with relevant bioaccumulation of phenantrene and fluoranthene at 5 °C and heavier (e.g. 5-rings) PAHs at 15 °C. The values and response profiles of each particular biomarker varied with exposure time, concentration of the oil aqueous fraction and dispersant addition, as well as with exposure temperature. Indeed, PAH bioaccumulation and biomarker responsiveness exhibited specific recognizable patterns in mussels exposed at low temperatures. Thus, genotoxicity was recorded early and transient at 5 °C and delayed but unremitting at 10-15 °C. Catalase activity presented a temperature-dependent response profile similar to the genotoxicity biomarker; however, glutathione-S-transferase responsiveness was more intricate. Lysosomal membrane stability in digestive cells decreased more markedly at 5 °C than at higher temperatures and the histological appearance of the digestive gland tissue was temperature-specific, which was interpreted as the combined effects of PAH toxicity and cold stress. It can be concluded that the profile and level of the biological effects are definitely different at low temperatures naturally occurring in the Arctic/Subarctic region (e.g. 5 °C) than at higher temperatures closer to the thermal optimum of this species (10-15 °C).

Effect of salinity on the toxicokinetics, oxidative stress, and metallothionein gene expression in Meretrix meretrix exposed to cadmium

To understand the effect of salinity on the toxicokinetics, oxidative stress, and detoxification of cadmium-exposed Meretrix meretrix, M. meretrix were acclimatized to different salinities (8, 14, 20, 26, and 32 ppt) for 14 d, exposed to 10 μg/L Cd for 7 d, followed by a 28-day depuration period. The internal Cd concentration was determined, and the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione-S-transferase (GST)), and the malondialdehyde (MDA) content were measured. The mRNA expression levels of antioxidant enzyme (Cu/Zn SOD, CAT) and detoxification-related genes metallothionein (MT) were analyzed. The mean concentrations of Cd in M. meretrix tissues were in the order gill > digestive gland > mantle > axe foot. The Cd uptake rate in the four tissues decreased with increasing salinity (range: 14-26 ppt). The Cd elimination half-lives were the highest at 8 ppt and 14 ppt salinity. Cadmium activated the four oxidative stress-related related enzymes in the gills. At the end of accumulation period, Cd exposure at 20 ppt salinity significantly increased the expression of Cu/Zn SOD. CAT expression was significantly inhibited at 20 ppt salinity, but was induced at 32 ppt. MT mRNA expression was only induced under Cd at 20 ppt salinity. At the end of depuration period, Cu/Zn SOD expression was inhibited at salinities of 8, 14, and 26 ppt. The results indicated that SOD, CAT, GST, MDA, Cu/Zn SOD, CAT, and MT were sensitive to cadmium in a water environment, and can be used as indicators of marine heavy metal pollution.

Toxic effects of triclocarban on the histological morphology, physiological and immune response in the gills of the black tiger shrimp Penaeus monodon

Triclocarban (TCC) is a widely used broad-spectrum antimicrobial agent that has become a pollutant threatening the health of aquatic animals. However, the toxic effects of TCC on Penaeus monodon are still lacking. In this study, we exposed P. monodon to 1 μg/L (TCC-1) and 10 μg/L TCC (TCC-10) for 14 days, and the changes of histological morphology, physiological and immune responses in the gills were investigated. The results showed that TCC exposure caused the deformation of the gill vessels and the disordered arrangement of the gill filaments. Oxidative stress biochemical indexes such as H2O2 content, CAT and GPx activity and the relative expression levels of antioxidant-related genes (SOD, GPx and Nrf2) were increased in the TCC-1 and TCC-10 groups; the levels of CAT and HSP70 genes were increased but POD activity was decreased in the TCC-10 group. The relative expression levels of endoplasmic reticulum (ER) stress indexes such as ERP15 and ATF-6 genes were increased in the TCC-10 group, while the level of GRP78 gene was decreased in the TCC-1 and TCC-10 groups. The relative expression levels of apoptosis indexes such as p53 and JNK genes were increased, but CytC and Casp-3 genes were decreased in the TCC-1 and TCC-10 groups. Furthermore, the relative expression levels of detoxification metabolism-related genes (cytP450 and GST) and osmotic regulation-related genes (NKA-α, NKA-β, CA, AQP, CLC and CCP) were increased in the TCC-10 group. The results showed that TCC exposure could affect the physiological homeostasis in the gills of P. monodon, probably via damaging histological morphology, inducing oxidative stress, and disordering ER stress, apoptosis, detoxification and osmotic regulation.

ChIP-seq identifies McSLC35E2 as a novel target gene of McNrf2 in Mytilus coruscus, highlighting its role in the regulation of oxidative stress response in marine mollusks

NF-E2-related factor 2 (Nrf2) plays a crucial role in the oxidative regulatory process, which could trigger hundreds of antioxidant elements to confront xenobiotics. In the previous study, we identified Nrf2 from the marine mussel Mytilus coruscus, and the findings demonstrated that McNrf2 effectively protected the mussels against oxidative stress induced by benzopyrene (Bap). In order to delve deeper into the underlying mechanism, we utilized Chromatin Immunoprecipitation followed by sequencing (ChIP-seq) technology to systematically identify potential novel target genes of McNrf2. A total of 3,465 potential target genes were screened, of which 219 owned binding sites located within the promoter region. During subsequent experimental verification, it was found that McSLC35E2, a candidate target gene of McNrf2, exhibited negative regulation by McNrf2, as confirmed through dual luciferase and qRT-PCR detection. Further, the enzyme activity tests demonstrated that McNrf2 could counteract Bap induced oxidative stress by inhibiting McSLC35E2. The current study provides valuable insights into the application of ChIP-seq technology in the research of marine mollusks, advancing our understanding of the key role of Nrf2 in antioxidant defense mechanisms, and highlighting the significance of SLC35E2 in the highly sophisticated regulation of oxidative stress response in marine invertebrates.

Evaluation of the toxicity of di-iso-pentyl-phthalate (DiPeP) using the fish Danio rerio as an experimental model

The presence of phthalates constitutes a risk to the health of aquatic environments and organisms. This work aimed to evaluate the toxic effects of di-iso-pentyl-phthalate (DiPeP) at environmentally relevant concentrations of 5, 25, and 125 µg/L in Danio rerio after subchronic exposure for 14 days. DiPeP altered the antioxidant system in the liver (125 μg/L), intestine (25 μg/L), brain, and gills in all concentrations tested. In animals exposed to 125 μg/L, DNA damage was identified in the gills. In addition, loss of cell boundary of hepatocytes, vascular congestion, necrosis in the liver, and presence of immune cells in the intestinal lumen were observed. Erythrocytic nuclear alterations in the blood occurred in animals exposed to 25 μg/L. DiPeP was quantified in muscle tissue at all exposure concentrations, appearing in a concentration-dependent manner. Contaminants such as DiPeP will still be used for a long time, mainly by industries, being a challenge for industry versus environmental health.

Bioaccumulation, Detoxification, and Biological Macromolecular Damage of Benzo[a]pyrene in Exposure in Tissues and Subcellular Fractions of Scallop Chlamys farreri

Because of the persistence and high toxicity of benzo[a]pyrene (B[a]P), the bioaccumulation and detoxification mechanisms of B[a]P have been studied extensively at the tissue level; but the data at the subcellular level in bivalves have not been reported. The present study was conducted to investigate the effects of B[a]P exposure on bioaccumulation, detoxification, and biomacromolecular damage in gills, digestive glands, and their subcellular fractions of the scallop Chlamys farreri. The subcellular fraction contains cytoplasm, mitochondria, microsome, nucleus, cell membrane, and overall organelle. The results demonstrated that B[a]P accumulation showed a clear time-dose effect. Based on the time-dependent accumulation of B[a]P in subcellular fractions, we speculated that the intracellular migration order of B[a]P was cell membrane, organelle, and nucleus in turn. Considering the difference of B[a]P accumulation may be related to B[a]P metabolism, we have further confirmed that the activities of B[a]P metabolizing enzymes in scallop tissues and subcellular fractions were significantly tempted by B[a]P (p < 0.05), including 7-ethoxyresorufin O-deethylase (increased), glutathione-S-transferase (GST; decreased), and superoxide dismutase (increased). First, GST was detected in bivalve cytoplasm and microsome. Second, B[a]P exposure also caused biomacromolecules damage. The results demonstrated that mitochondria and microsome were more vulnerable to lipid peroxidation than cell membrane and nucleus. Taken together, the present study fills some of the gaps in our knowledge of the bioaccumulation and detoxification mechanisms of C. farreri exposed to B[a]P in subcellular fractions and deeply explores the transportation and the main metabolic and damage sites of polycyclic aromatic hydrocarbons (PAHs) in cells, which helped us to comprehensively understand the toxic mechanism of PAHs on bivalves. Environ Toxicol Chem 2022;41:2353-2364. © 2022 SETAC.

The Role of the Ecotoxicology Applied to Seafood as a Tool for Human Health Risk Assessments Concerning Polycyclic Aromatic Hydrocarbons

Background: Polycyclic aromatic hydrocarbons (PAHs) are persistent pollutants routinely detected in aquatic ecosystems. It is, therefore, necessary to assess the link between deleterious marine biota PAH effects, especially in commercialized and consumed animals, environmental health status, and potential human health risks originating from the consumption of contaminated seafood products. Thus, this review seeks to verify the relationships of ecotoxicological studies in determining effect and safety concentrations on animals routinely consumed by humans. Methods: A total of 52 published studies between 2011 and 2021, indexed in three databases, were selected following the PICO methodology, and information on test animals, evaluated PAH, and endpoints were extracted. Results: Benzo(a)pyrene and phenanthrene were the most investigated PAHs in terms of biomarkers and test organisms, and mussels were the most evaluated bioindicator species, with an emphasis on reproductive responses. Furthermore, despite the apparent correlation between environmental PAH dynamics and effects on aquatic biota and human health, few assessments have been performed in a multidisciplinary manner to evaluate these three variables together. Conclusions: The links between human and environmental sciences must be strengthened to enable complete and realistic toxicity assessments as despite the application of seafood assessments, especially to mussels, in bioassays, the connection between toxicological animal responses and risks associated with their consumption is still understudied.

Integration of chemical and biological methods: A case study of polycyclic aromatic hydrocarbons pollution monitoring in Shandong Peninsula, China

Polycyclic aromatic hydrocarbons (PAHs), as persistent toxic substances (PTS), have been widely monitored in coastal environment, including seawater and sediment. However, scientific monitoring methods, like ecological risk assessment and integrated biomarker response, still need massive researches to verify their availabilities. This study was performed in March, May, August and October of 2018 at eight sites, Yellow River estuary (S1), Guangli Port (S2), Xiaying (S3), Laizhou (S4), Inner Bay (S5), Outer Bay (S6), Hongdao (S7) and Hongshiya (S8) of Shandong Peninsula, China. The contents of 16 priority PAHs in local seawater and sediment were determined, by which ecological risk assessment risk quotient (RQ) for seawater and sediment quality guidelines (SQGs) were calculated to characterize the PAHs pollution. Meanwhile, multiple biomarkers in the digestive gland of clam Ruditapes philippinarum were measured to represent different biological endpoints, including ethoxyresorufin-O-deethylase (EROD), glutathione S-transferase (GST), sulfotransferase (SULT), superoxide dismutase (SOD) and lipid peroxidation (LPO), by which integrated biomarker response (IBR) was calculated to provide a comprehensive assessment of environmental quality. Taken together, these results revealed the heaviest pollution at S2 as both PAHs concentrations and biomarkers responses reflected, and supported the integrated biomarker response as a useful tool for marine environmental monitoring, through its integration with SQGs.

Gene expression and functional analysis of different heat shock protein (HSPs) in Ruditapes philippinarum under BaP stress

Heat shock proteins (HSPs) are a class of highly conserved proteins which can protect cells against various types of stress. However, little information on the mechanism involved in the organic contaminants stress response of HSPs is available, especially in marine invertebrates. The present study was conducted to evaluate the responses of HSPs in clams (Ruditapes philippinarum) under Benzo[a] pyrene (BaP) exposure. The clams were exposed to BaP (concentrations: 0, 0.1, 1, 10 μg/L) for 15 days. 6 HSPs mRNA were classified, and the results of tissue distribution indicated that 4 HSPs gene expressed most in the digestive glands. The transcription level of 6 HSPs (HSP22-1, HSP22-2, HSP40A, HSP60, HSP70, HSP90) genes and the aryl hydrocarbon receptor signaling pathway-related genes, and detoxification system-related enzymes activities were analyzed at 0, 1, 3, 6, 10 and 15 days. The activities of phase II detoxification metabolic enzymes and signaling pathway related genes in clams were severely affected by BaP stress and presented significant difference. Our result suggested that HSPs were produced in the presence of BaP and participated in the process of detoxification metabolism to a certain extent. Additionally, the transcription of HSP40A gene may be used as a potential biomarker of BaP exposure due to its evident concentration- and time-dependent expression pattern. Overall, the study investigated the classification of HSPs in R. philippinarum, provided information about the expression profiles of various HSPs after BaP exposure and broadened the understanding mechanism of HSPs in detoxification defense system under PAHs stress in mollusks.

Biomarker responses and histological damage in the gill, liver, and gonad of Cyprinus carpio with benzo(a)pyrene exposure

The risk of polycyclic aromatic hydrocarbon exposure in aquatic organisms is a global concern. In this study, we investigated the toxic effects of different doses of benzo(a)pyrene (BaP) on Cyprinus carpio in microcosms from the following aspects: superoxide dismutase (SOD) and peroxidase (POD) activity, malondialdehyde (MDA) content in the gill, liver, and gonad; glutathione s-transferase (GST), aromatic hydroxylase (AHH), and 7-ethoxyresorufin-O-deethylase (EROD) activity in the liver; and altered tissue and cellular structures of the gill, liver,and gonad. SOD and POD activity in the gill, liver, and gonad increased in low-dose BaP groups and significantly decreased with an increase in BaP. MDA content increased continuously with an increase in BaP in the gill, liver, and gonad. The activity of enzymes related to detoxification, specifically GST, AHH, and EROD, gradually increased in the liver with an increase in BaP. Upon exposure to BaP, gill hypertrophy, bulging, necrosis, and cavitation occurred, gonadal cells became larger, with an increase in pyknotic or vacuolar nuclei, bulging and cavitation of organelles, and cytoplasm leakage, and nuclear membrane lysis was observed in the liver. Collectively, BaP exposure changed the SOD and POD activity in the gill, liver, and gonad of carp with increases in MDA content, increased GST, AHH, and EROD activity in liver, and damaged the tissue and cellular structures of the gill, liver, and gonad, revealing the toxic effects of BaP exposure on carp.

Exposure radius of a local coal mine in an Arctic coastal system; correlation between PAHs and mercury as a marker for a local mercury source

Mercury in the Arctic originates from emissions and releases at lower latitudes and, to a lesser extent, from local and regional sources. The relationship between mercury (Hg) and polycyclic aromatic hydrocarbons (PAHs) in sediment can be applied as an indicator of the mercury source. This research examines the Hg contamination gradient from a land-based coal mine to the surrounding coastal environment to quantify the impact of local sources. Total mercury and PAH (Σ₁₄PAH) were measured in terrestrial and marine sediments as well as in marine biota. Samples were collected at the mine and two reference sites. Mercury and Σ₁₄PAH concentrations in samples collected at the mine site were significantly higher than those at the reference sites. This was also found in the biota samples, although less pronounced. This work addresses the complexities of interpreting data concerning very low contaminant levels in a relatively pristine environment. A clear correlation between PAH and Hg concentration in sediment was found, although a large number of samples had levels below detection limits. PAH profiles, hierarchical clustering, and molecular diagnostic ratios provided further insight into the origin of PAHs and Hg, showing that signatures in sediments from the nearest reference site were more similar to the mine, which was not the case for the other reference site. The observed exposure radius from the mine was small and diluted from land to water to marine biota. Due to low contamination levels and variable PAH profiles, marine biota was less suitable for tracing the exposure radius for this local land-based Hg source. With an expected increase in mobility and availability of contaminants in the warming Arctic, changes in input of PAHs and Hg from land-based sources to the marine system need close monitoring.

Effects of BαP and TBBPA on multixenobiotic resistance (MXR) related efflux transporter activity and gene expressions in gill cells of scallop Chlamys farreri

The multixenobiotic resistance mechanism (MXR) provides aquatic organisms with the capacity to adapt to polluted environments, which can be inhibited by chemosensitizers. In the present study, the effect of two typical marine persistent organic pollutants, benzo(a)pyrene (BaP) and tetrabromobisphenol A (TBBPA), on the most relevant ABC transporters, ABCB1, ABCC1, and ABCG2 of scallop Chlamys farreri was tested. MXR transporter efflux activity of cultured gill cells of the scallops was evaluated by measuring the intracellular fluorescent intensity of Calcein-AM and rhodamine 123 with flow cytometry. The results showed that ABCB1 and ABCC1 transporters demonstrated increased activity compared with ABCG2 in mediating MXR efflux activity. BaP and TBBPA were able to suppress the efflux transporter activity of ABC transporters significantly, of which BaP revealed block effects by acting on the ABCB1 transporter. Additionally, exposure of BaP and TBBPA only significantly upregulated the expression level of ABCC1 gene. This study demonstrated the promising utility of efflux transporter activity in conjunction with biomarkers such as mRNA levels in identification of chemosensitizer.

Effects of Nrf2-Keap1 signaling pathway on antioxidant defense system and oxidative damage in the clams Ruditapes philippinarum exposure to PAHs

NF-E2-related factor 2 (Nrf2) is a master regulator of antioxidant defense system which can maintain the oxidation balance in the cell. In our previous study, we first cloned the Nrf2 gene in clams and preliminarily explored the role of the Nrf2 at the transcription level. In this study, RNA interference (RNAi) technology was used to interfere with the expression of Nrf2 after being exposed to benzo(a)pyrene (BaP) for 5 days to verify the role of Nrf2 in the antioxidant defense system. Besides, we examined the mRNA expression and enzyme activities of antioxidases and the oxidative damage. The positive correlations between the Nrf2 with the mRNA expression and the enzyme activities of antioxidases indicated that Nrf2 was required for the induction of these antioxidant genes. Additionally, the mRNA expression and the enzyme activities of the glutathione peroxidase (GPx) in the Nrf2-dsRNA group were significantly higher than those in the control groups on the fifth day, indicating that the GPx is more sensitive to oxidative stress. Moreover, the oxidative damage in the RpNrf2-dsRNA group was markedly increased than control groups, indicating that Nrf2 transcriptional regulation may play an essential role in defending against oxidative damage. This study provides a foundation for further research on the mechanism of detoxification and antioxidation of polycyclic aromatic hydrocarbons (PAHs) in the clams at the transcription level and the protein level.

Combined Effects of Elevated Temperature and Crude Oil Pollution on Oxidative Stress and Apoptosis in Sea Cucumber (Apostichopus japonicus, Selenka)

Currently, global climate change and oil pollution are two main environmental concerns for sea cucumber (Apostichopus japonicus) aquaculture. However, no study has been conducted on the combined effects of elevated temperature and oil pollution on sea cucumber. Therefore, in the present study, we treated sea cucumber with elevated temperature (26 °C) alone, water-accommodated fractions (WAF) of Oman crude oil at an optimal temperature of 16 °C, and Oman crude oil WAF at an elevated temperature of 26 °C for 24 h. Results showed that reactive oxygen species (ROS) level and total antioxidant capacity in WAF at 26 °C treatment were higher than that in WAF at 16 °C treatment, as evidenced by 6.03- and 1.31-fold-higher values, respectively. Oxidative damage assessments manifested that WAF at 26 °C treatment caused much severer oxidative damage of the biomacromolecules (including DNA, proteins, and lipids) than 26 °C or WAF at 16 °C treatments did. Moreover, compared to 26 °C or WAF at 16 °C treatments, WAF at 26 °C treatment induced a significant increase in cellular apoptosis by detecting the caspase-3 activity. Our results revealed that co-exposure to elevated temperature and crude oil could simulate higher ROS levels and subsequently cause much severer oxidative damage and cellular apoptosis than crude oil alone on sea cucumber.

Antioxidant defenses of flame scallop Ctenoides scaber (Born, 1778) exposed to the water-soluble fraction of used vehicle crankcase oils

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This paper evaluated effects of a WSF-UVCO on the antioxidant responses of the scallop Lima scabra.

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The antioxidant defenses in L. scabra seem be highly sensitive to low doses of to WSF-UVCO.

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Digestive gland and gill show stronger antioxidant responses in L. scabra exposed to WSF-UVCO.

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L. scabra could be good sensor for screening pollutant impacts along the Caribbean coastline.

Used vehicle crankcase oils are a source of contamination in Caribbean marine environments and may alter the oxidative balance of organism that inhabiting coastal ecosystems. This paper aims to evaluate effects of a water-soluble fraction of used vehicle crankcase oils (WSF-UVCO) on the antioxidant responses of the flame scallop Ctenoides scaber. The organisms were exposed to ascending sublethal concentrations 0, 0.001, 0.01 and 0.1 % of WSF-UVCO in a static system of aquaria during one week. Subsequently activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST) as well as concentrations of reduced glutathione (GSH) and thiobarbituric acid reactive substances (TBARS) were determined in the digestive gland, adductor muscle and gills. SOD, CAT, GST and TBARS increased in digestive gland of organisms exposed to WSF-UVCO at medium and highest concentrations, with a concomitant decrease in GPX and GR activities. In adductor muscle CAT decreased, but GR rose with exposure to 0.01 and 0.1 % WSF-UVCO; in gills, GST rose through all WSF-UVCO concentrations, and SOD, CAT and GR increased only at 0.1 %. The fluctuations in antioxidant enzymes and GST activities point out possible adjustments to control ROS production and detoxification of xenobiotics. These biochemical responses may guarantee the oxidative balance in flame scallop during short term exposure to low concentrations of WSF-UVCO. C. scaber appears suitable as an experimental organism for evaluating biological risks of sublethal exposure to hazardous xenobiotics in tropical marine environments.

Quantitative biomonitoring of polycyclic aromatic compounds (PACs) using the Sydney rock oyster (Saccostrea glomerata)

Increasing our understanding of the bioavailable fractions of polycyclic aromatic compounds (PACs) in an aquatic environment is important for the assessment of the environmental and human health risks posed by PACs. More importantly, the behaviour of polar polycyclic aromatic hydrocarbons (polar PAHs), which are metabolites of legacy PAHs, are yet to be understood. We, therefore, carried out a study involving Sydney rock oysters (Saccostrea glomerata) sourced from two locations, that had been exposed to PAH contamination, within an Australian south-east estuary. Biomonitoring of these oysters, following relocation from the estuary to a relatively isolated waterway, was done at 24 and 72 h after deployment and subsequently at 7, 14, 28, 52 and 86 days. Control samples from Camden Haven River were sampled for PAC analyses just before deployment, after 28 days and at the end of the study (day 86). Lipid-normalised concentrations in oyster tissues across the 86-day sampling duration, elimination rate constants (k₂), biological half-lives (t_1/2) and time required to reach 95% of steady-state (t₉₅) were reported for parent PAHs and the less-monitored polar PAHs including nitrated/oxygenated/heterocyclic PAHs (NPAHs, oxyPAHs and HPAHs) for the three differently sourced oyster types. Most of the depurating PAHs and NPAHs, as well as 9-FLO (oxyPAH), had k₂ values significantly different from zero (p < 0.05). All other oxyPAHs and HPAHs showed no clear depuration, with their concentrations remaining similar. The non-depuration of polar PAHs from oyster tissues could imply greater human health risk compared to their parent analogues.

In vitro-in vivo and cross-life stage extrapolation of uptake and biotransformation of benzo[a]pyrene in the fathead minnow (Pimephales promelas)

Understanding internal dose metrics is integral to adequately assess effects environmental contaminants might have on aquatic wildlife, including fish. In silico toxicokinetic (TK) models are a leading approach for quantifying internal exposure metrics for fishes; however, they often do not adequately consider chemicals that are actively biotransformed and have not been validated against early-life stages (ELS) that are often considered the most sensitive to the exposure to contaminants. To address these uncertainties, TK models were parameterized for the rapidly biotransformed chemical benzo[a]pyrene (B[a]P) in embryo-larval and adult life stages of fathead minnows. Biotransformation of B[a]P was determined through measurements of in vitro clearance. Using in vitro-in vivo extrapolation, in vitro clearance was integrated into a multi-compartment TK model for adult fish and a one-compartment model for ELS. Model predictions were validated using measurements of B[a]P metabolites from in vivo flow-through exposures to graded concentrations of water-borne B[a]P. Significantly greater amounts of B[a]P metabolites were observed with exposure to greater concentrations of parent compound in both life stages. However, when assessing biotransformation capacity, no differences in phase I or phase II biotransformation were observed with greater exposures to B[a]P. Results of modelling suggested that biotransformation of B[a]P can be successfully implemented into in silico models to accurately predict life stage-specific abundances of B[a]P metabolites in either whole-body larvae or the bile of adult fish. Models developed increase the scope of applications in which TK models can be used to support environmental risk assessments.

Bioavailability of polycyclic aromatic compounds (PACs) to the Sydney rock oyster (Saccostrea glomerata) from sediment matrices of an economically important Australian estuary

Improving risk assessment and remediation rests on better understanding of contaminant bioavailability. Despite their strong toxicological attributes, little is known about the partitioning behaviour and bioavailability of polar polycyclic aromatic hydrocarbons (PAHs) in aquatic environments. The present study provides an insight into the bioavailable fractions of polar PAHs and their parent analogues in the tissues of the Sydney rock oyster, Saccostrea glomerata, a model aquatic bio-indicator organism. The concentration and distribution patterns of parent and polar PAHs including oxygenated PAHs (oxyPAHs), nitrated PAHs (NPAHs) and heterocyclic PAHs (HPAHs) were determined in water, sediment and oysters from an ecologically and economically important estuary of New South Wales, Australia. Total concentrations of PAHs, oxyPAHs, NPAHs and HPAHs were higher in sediments compared to oyster tissue and water. For most polar PAHs, total concentrations for water, sediment and oyster samples were <1 μg/g (μg/l for water) while parent PAH concentrations were several orders of magnitude higher. Computed biota-sediment accumulation factors (BSAFs) on lipid-normalized oyster concentrations revealed that while ∑oxyPAHs and ∑HPAHs exhibited low accumulation from sediment to oyster tissues (BSAF <1), ∑PAHs and ∑NPAH were found to be accumulated at high levels (BSAF >1). BSAF individual computation showed that bioaccumulation of nine investigated HPAHs in oyster tissues were relatively low and only 2-EAQ (oxyPAH) and 1N-NAP (NPAH) showed high levels of accumulation in oyster tissues, similar to parent PAHs. To the best of our knowledge, this is the first known study on the bioavailability of polar and non-polar PAHs in an Australian aquatic environment. The outcome of this study might be a useful indicator of the potential risks of polar PAHs to humans and other living organisms.

Genotoxic, metabolic, and biological responses of Chironomus sancticaroli Strixino & Strixino, 1981 (Diptera: Chironomidae) after exposure to BBP

Benzyl butyl phthalate (BBP), which is widely used in industrial production, reaches the aquatic environment, mainly owing to improper disposal of plastic products. In the water, it remains adsorbed to sedimentary particles causing toxic effects in aquatic invertebrates such as Chironomidae, which are important in maintaining ecosystem dynamics and are an important link in the food chain. However, the effects of BBP on Chironomidae are still poorly known. Thus, the toxic effects of BBP on Chironomus sancticaroli at acute (48 h), subchronic (8 d), and chronic (25 d) exposures of concentrations between 0.1 and 2000 μg·L^-1 were determined. Genotoxicity effects, changes in the oxidative stress pathway, and development and emergence of organisms were evaluated. Biochemical markers showed a reduction in cholinesterase (ChE) activity, indicating a neurotoxic effect on acute exposure (1-1000 μg·L^-1). The antioxidant pathway, glutathione S-transferase (GST) activity showed reduction on acute (0.1; 1-2000 μg·L^-1) and subchronic (1-2000 μg·L^-1) exposures and reduction in superoxide dismutase (SOD) activity at all evaluated concentrations, suggesting oxidative stress. In contrast, lipid peroxidation was not observed. DNA damage occurred on acute (10 μg·L^-1) and subchronic (10-2000 μg·L^-1) exposures, indicating genotoxic effects. At concentrations above 10 μg·L^-1, no emergence of adults occurred, while lower concentrations (0.1 and 1 μg·L^-1) showed a reduction in the number of adults, mainly males. The observed effects indicate that BBP is genotoxic and causes biochemical alterations presenting high toxicity at the population level.

The molecular mechanism of AhR-ARNT-XREs signaling pathway in the detoxification response induced by polycyclic aromatic hydrocarbons (PAHs) in clam Ruditapes philippinarum

The aryl hydrocarbon receptor (AhR) has been known primarily for its role in the regulation of several drug and xenobiotic metabolizing enzymes to mitigate environmental stresses. In this study, we interfere the expression of AhR gene to investigate the mechanism of AhR signaling pathway in the detoxification and antioxidation defense system that induced by Polycyclic Aromatic Hydrocarbons (PAHs) exposure by RNA interference (RNAi). The gene expressions of aryl hydrocarbon receptor nuclear translocator (ARNT), heat shock protein 90 (Hsp90) were evaluated after being exposed to benzo(a)pyrene (BaP) (4 μg/L) for 5 days and the positive correlations between AhR, ARNT, HSP90 indirectly indicating that AhR may have the ability to bind to ligands such as PAHs in Ruditapes philippinarum (R. philippinarum). Besides, the activities of detoxification enzymes were determined to investigate the role of AhR signaling pathway played in the metabolic detoxification. What's more, the gene expressions of protein kinase C (PKC) signaling pathway, mitogen-activated protein kinase (MAPKs) signaling pathway, NF-E2-related factor 2 (Nrf2) signaling pathway and antioxidant defense system indicated that AhR may regulate the Nrf2-Keap1 signaling pathway through Kelch-like ECH-associated protein-1 (Keap1) and MAPKs, PKC signaling pathways. In conclusion, adoption of RNA interference technology to explore the role of RpAhR gene played in the detoxification and antioxidation defense system under the PAHs stress at different time points can informe molecular endpoints for application towards ecotoxicology monitoring of bivalves.

Modulatory Effects of Silymarin on Benzo[a]pyrene-Induced Hepatotoxicity

Benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon, is a group 1 carcinogen that introduces mutagenic DNA adducts into the genome. In this study, we investigated the molecular mechanisms underlying the involvement of silymarin in the reduction of DNA adduct formation by B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE), induced by B[a]P. B[a]P exhibited toxicity in HepG2 cells, whereas co-treatment of the cells with B[a]P and silymarin reduced the formation of BPDE-DNA adducts, thereby increasing cell viability. Determination of the level of major B[a]P metabolites in the treated cells showed that BPDE levels were reduced by silymarin. Nuclear factor erythroid 2-related factor 2 (Nrf2) and pregnane X receptor (PXR) were found to be involved in the activation of detoxifying genes against B[a]P-mediated toxicity. Silymarin did not increase the expression of these major transcription factors, but greatly facilitated their nuclear translocation. In this manner, treatment of HepG2 cells with silymarin modulated detoxification enzymes through NRF2 and PXR to eliminate B[a]P metabolites. Knockdown of Nrf2 abolished the preventive effect of silymarin on BPDE-DNA adduct formation, indicating that activation of the Nrf2 pathway plays a key role in preventing B[a]P-induced genotoxicity. Our results suggest that silymarin has anti-genotoxic effects, as it prevents BPDE-DNA adduct formation by modulating the Nrf2 and PXR signaling pathways.

Differential responses in the biotransformation systems of the oyster Crassostrea gasar (Adanson, 1757) elicited by pyrene and fluorene: molecular, biochemical and histological approach - Part I

Polycyclic aromatic hydrocarbons (PAHs) are among the main contaminants in aquatic environments. PAHs can affect organisms due to their carcinogenic, mutagenic and/or teratogenic characteristics. Depending on the PAHs, concentration, and period of exposure, biological damage can occur leading to histopathologic alterations. This study aimed to evaluate the molecular, biochemical and histological responses of the oyster Crassostrea gasar exposed to pyrene (0.25 and 0.5 μM) and fluorene (0.6 and 1.2 μM), after exposure for 24 and 96 h. Concentrations of both PAHs were quantified in the water and in oyster tissues. Transcript levels of phase I (CYP3475C1, CYP2-like, CYP2AU1 and CYP356A) and phase II (GSTO-like, MGST-like and SULT-like) biotransformation-related genes and the activities of ethoxyresorufin-O-deethylase (EROD), total and microsomal glutathione S-transferase (GST and MGST) were evaluated in the gills. Also, histological changes and localization of mRNA transcripts CYP2AU1 in gills, mantle, and digestive diverticula were evaluated. Both PAHs accumulated in oyster tissues. Pyrene half-life in water was significantly lower than fluorene. Transcript levels of all genes were higher in oysters exposed to of pyrene 0.5 μM (24 h). Only CYP2AU1 gene was up-regulated by fluorene exposure. EROD and MGST activities were higher in oysters exposed to pyrene. Tubular atrophy in the digestive diverticula and an increased number of mucous cells in the mantle were observed in oysters exposed to pyrene. CYP2AU1 transcripts were observed in different tissues of pyrene-exposed oysters. A significant correlation was observed between tubular atrophy and the CYP2AU1 hybridization signal in oysters exposed to pyrene, suggesting the sensibility of the species to this PAH. These results suggest an important role of biotransformation-related genes and enzymes and tissue alterations associated to pyrene metabolism but not fluorene. In addition, it reinforces the role of CYP2AU1 gene in the biotransformation process of PAHs in the gills of C. gasar.

The molecular mechanism of Nrf2-Keap1 signaling pathway in the antioxidant defense response induced by BaP in the scallop Chlamys farreri

In this study, we cloned the full-length cDNA of the Kelch-like ECH-associated protein 1 (Keap1) from the scallops Chlamys farreri (C. farreri). Sequences alignment and phylogenetic analysis showed that CfKeap1 was highly specific in the scallops, and the amino acid sequence identity value is closer to that in zebrafish Keap1b and Nothobranchius furzeri Keap1b than Keap1a. The highest transcription level of CfKeap1 expression was detected in the digestive glands. The gene expressions of CfKeap1, NF-E2-related nuclear factor 2 (Nrf2), Superoxide Dismutase (SOD), Catalase (CAT) and Glutathione Peroxidase (GPx) in digestive glands were evaluated by quantitative real-time PCR (qRT-PCR) after being exposed to benzo(a)pyrene (BaP) (0.25, 1and 4 μg/L) for 15 days, which indicated that the activation of Nrf2 and Keap1 expression can be significantly induced under BaP exposure. RNA interference (RNAi) experiments were conducted to examine the expression profiles of CfKeap1, Nrf2, antioxidant genes (Cu/Zn-SOD, CAT and GPx), mitogen-activated protein kinase (MAPKs) and protein kinase C (PKC) signaling pathways key genes in digestive glands and gills when exposed to BaP. Results showed that the mRNA level of CfKeap1 was significantly decreased by 60.69% and59.485%. The changes of CfKeap1 and Nrf2 suggested that the enhancement of Keap1 expression stimulating Nrf2 degradation. Furthermore, the expression of antioxidant genes were consistent with the Nrf2 gene, which suggesting that Nrf2-Keap1 signaling pathway is required for the induction of antioxidant genes. Besides, the changes of PKC, c-Jun N-terminal kinase (JNK) and p38 genes expression suggested that PKC and MAPKs signaling pathways played a synergistic role with Nrf2-Keap1 signaling pathway in the anti-oxidative defense system of bivalve molluscs. In conclusion, these data demonstrated that Keap1 can sense nucleophilic or oxidative stress factors to regulate the Nrf2 signaling pathway together with Cul3-based E3 Ubiquitin Ligase (E3), and the Nrf2-Keap1 signaling pathway played an important role in modulating gene expression of antioxidant enzymes in bivalve mollusks.

A passive sampling model to predict PAHs in butter clams (Saxidomus giganteus), a traditional food source for Native American tribes of the Salish Sea Region

Native Americans face disproportionate exposures to environmental pollution through traditional subsistence practices including shellfish harvesting. In this study, the collection of butter clams (Saxidomus giganteus) was spatially and temporally paired with deployment of sediment pore water passive samplers at 20 locations in the Puget Sound region of the Salish Sea in the Pacific Northwest, USA, within adjudicated usual and accustomed tribal fishing grounds and stations. Clams and passive samplers were analyzed for 62 individual PAHs. A linear regression model was constructed to predict PAH concentrations in the edible fraction of butter clams from the freely dissolved fraction (C_free) in porewater. PAH concentrations can be predicted within a factor of 1.9 ± 0.2 on average from the freely dissolved PAH concentration in porewater using the following equation: PAHClam=4.1±0.1×PAHporewater This model offers a simplified, cost effective, and low impact approach to assess contaminant levels in butter clams which are an important traditional food.

The influence of short-term experimental fasting on biomarker responsiveness in oil WAF exposed mussels

Mussels are widely used in toxicological experimentation; however, experimental setups are not standardized yet. Although there is evidence of changes in biomarker values during food digestion and depending on the mussel nutritive status, the mode of feeding differs among toxicological experiments. Typically, mussels are fed with different diets in different long-term experiments, while fasting is the most common approach for short-term studies. Consequently, comparisons among experiments and reliable interpretations of biomarker results are often unfeasible. The present investigation aimed at determining the influence of fasting (against feeding with Isochrysis galbana) on biomarkers and their responsiveness in mussels exposed for 96 h to the water accommodated fraction (WAF) of a heavy fuel oil (0%, 6.25%, 12.5% and 25% WAF in sea water). PAH tissue levels in digestive gland and a battery of biomarkers were compared. WAF exposure led to decrease of cytochrome-C-oxidase activity, modulated glutathione-S-transferase activity, augmented lipid peroxidation, inhibited acetyl cholinesterase (AChE) activity, and led to lysosomal enlargement (Vv_LYS and S/V_LYS) and membrane destabilisation, lipofuscin accumulation, and histopathological alterations (Vv_BAS, MLR/MET and CTD ratio) in the digestive gland epithelium; and were integrated as IBR/n (biological response index). Overall, no significant changes were recorded in AChE activity, S/V_LYS and CTD ratio in any experimental treatment, while all the other biomarkers showed significant changes depending on the fasting/feeding condition, the exposure to WAF and/or their interaction. As a result, the integrated biomarker index IBR/n was higher at increasing WAF exposure levels both in fasted and fed mussels albeit the response was more marked in the latter. The response profiles were qualitatively similar between fasted and fed mussels but quantitatively more pronounced in fed mussels, especially upon exposure to the highest concentration (25% WAF). Therefore, it is highly recommended that mussels are also supplied with food during short-term, like during long-term toxicological experiments. This practice would avoid the interference of fasting with biological responses elicited by the tested chemicals and allow for reliable comparison with data obtained in long-term experiments and monitoring programmes.

Detoxification and Immune Transcriptomic Response of the Gill Tissue of Bay Scallop (Argopecten irradians) Following Exposure to the Algicide Palmitoleic Acid

Palmitoleic acid (PA) is an effective algicide against Alexandrium tamarense. However, the toxicological mechanism of PA exposure is unclear. The transcript abundance and differentially expressed genes (DEGs) in gills of bay scallop were investigated following 80 mg/L PA exposure up to 48 h using the Illumina HiSeq 4000 deep-sequencing platform with the recommended read length of 100 bp. De novo assembly of paired-end reads yielded 62,099 unigenes; 5414 genes were identified as being significantly increased, and 4452 were decreased. Based on gene ontology classification and enrichment analysis, the ‘cellular process’, ‘metabolic process’, ‘response to stimulus’, and ‘catalytic process’ with particularly high functional enrichment were revealed. The DEGs, which are related to detoxification and immune responses, revealed that acid phosphatase, fibrinogen C domain-containing protein, cyclic AMP-responsive element-binding protein, glutathione reductase, ATP-binding cassette, nuclear factor erythroid 2-related factor, NADPH2:quinone reductase, and cytochrome P450 4F22, 4B1, and 2C8-related gene expression decreased. In contrast, some genes related to glutathione S-transferase, C-type lectin, superoxide dismutase, toll-like receptors, and cytochrome P450 2C14, 2U1, 3A24 and 4A2 increased. The results of current research will be a valuable resource for the investigation of gene expression stimulated by PA, and will help understanding of the molecular mechanisms underlying the scallops’ response to PA exposure.

Comparative transcriptome analysis between the short-term stress and long-term adaptation of the Ruditapes philippinarum in response to benzo[a]pyrene

In order to monitor the pollution of polycyclic aromatic hydrocarbons (PAHs) in the seawater environment, screening biomarkers capable of monitoring PAHs is the focus of many studies. The transcriptomic profiles of the digestive gland tissue from the R. philippinarum groups after the exposure to BaP (4 μg/L) at four time points (0, 0.5, 6 and 15 days) were investigated to globally screen the key genes and pathways involved in the responses to short-term stress and long-term adaptation of BaP resistance. By comparative transcriptome analysis, 233, 282 and 58 differentially expressed genes (DEGs) were identified at 0.5 day, 6 day and 15 day (vs 0 day). The differential expression genes were related to stress response, detoxification metabolic process and innate immunity. DEGs of each group at different stages were clustered in six profiles based on gene expression pattern. Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis were used on all genes to determine the biological functions and processes. We selected Multidrug resistance protein 3 (MRP3), transcriptional regulator ATRX-like isoform X2 (ATRX) as biomarker indicator genes for short-term pollution monitoring and NADH dehydrogenase [ubiquinone] 1 (NQO1), Complement C1q-like protein 4 (C1q), Glutathione-S-transferase theta (GST), E3 ubiquitin-protein ligase (E3) for long-term pollution monitoring based on the different expression patterns and the function in detoxification and antioxidant defense system. Besides, the expression of seven genes was measured through Quantitative real-time PCR (qPCR) according to their gene expression patterns which was confirmed by the DGE analysis. Taken together, adoption of transcriptomic analysis to explore the bivalves' mRNA abundance changes and detoxification metabolic mechanism under the BaP stress at different time points can aid the development of sensitive and informed molecular endpoints for application towards ecotoxicogenomic monitoring of bivalves.

The role of Nrf2-Keap1 signaling pathway in the antioxidant defense response induced by PAHs in the calm Ruditapes philippinarum

The NF-E2-related factor 2 (Nrf2) is a master regulator of cellular responses against environmental stresses. In this study we cloned the full-length cDNAs of the RpNrf2 encompassed 2823 bp from the clam Ruditapes philippinarum (R. philippinarum). Sequences alignment and phylogenetic analysis showed that Nrf2 was highly specific in the clams. RpNrf2 expression was detected in gill, digestive gland, mantle and adductor, which the highest transcription level was observed in gill and digestive gland. The gene expressions of RpNrf2, Kelch-like-ECH-associated Protein 1 (Keap1), Cul3-based E3 Ubiquitin Ligase (E3), Glutathione S-transferase (GST-pi), Superoxide Dismutase (SOD), Catalase (CAT) and Glutathione Peroxidase (GPx) in digestive gland was evaluated by real-time PCR after being exposed to benzo(a)pyrene (BaP) (0.25, 1and 4 μg/L) for 15 days, which showed that the expression of Nrf2 significantly increased at day 1 and day 6 after exposure (p < 0.05), and there was a negative relationship between the mRNA levels of Nrf2 and Keap1 that indicates the enhancement of Keap1 expression stimulating Nrf2 degradation. RNA interference experiments were conducted to examine the expression profiles of RpNrf2, antioxidant and detoxification genes (GST-pi, Cu/Zn-SOD, CAT and GPx) and Lipid Peroxidase (LPO) level in digestive gland exposed to BaP. The results showed that the mRNA level of Nrf2 was significantly decreased by 63.2%, and the changes of antioxidant and detoxification genes expression were consistent with the Nrf2 gene suggesting that Nrf2 is required for the induction of antioxidant and detoxification genes. Besides, the LPO levels expressed by malondialdehyde (MDA) contents were significant higher compared with the control group at 72 h post dsRNA-Nrf2 injection. In conclusion, our data demonstrated that Keap1 can sense nucleophilic or oxidative stress factors to regulate the Nrf2 signaling pathway together with E3 and Nrf2 signaling pathway plays an important role in modulating gene expression of antioxidant enzymes in bivalve mollusks.

Detoxification- and Immune-Related Transcriptomic Analysis of Gills from Bay Scallops (Argopectenirradians) in Response to Algal Toxin Okadaic Acid

To reveal the molecular mechanisms triggered by okadaic acid (OA)-exposure in the detoxification and immune system of bay scallops, we studied differentially-expressed genes (DEGs) and the transcriptomic profile in bay scallop gill tissue after 48 h exposure to 500 nM of OA using the Illumina HiSeq 4000 deep-sequencing platform. De novo assembly of paired-end reads yielded 55,876 unigenes, of which 3204 and 2620 genes were found to be significantly up- or down-regulated, respectively. Gene ontology classification and enrichment analysis of the DEGs detected in bay scallops exposed to OA revealed four ontologies with particularly high functional enrichment, which were ‘cellular process’ (cellular component), ‘metabolic process’ (biological process), ‘immune system process’ (biological process), and ‘catalytic process’ (molecular function). The DEGs revealed that cyclic AMP-responsive element-binding proteins, acid phosphatase, toll-like receptors, nuclear erythroid 2-related factor, and the NADPH2 quinone reductase-related gene were upregulated. In contrast, the expression of some genes related to glutathione S-transferase 1, C-type lectin, complement C1q tumor necrosis factor-related protein, Superoxide dismutase 2 and fibrinogen C domain-containing protein, decreased. The outcomes of this study will be a valuable resource for the study of gene expression induced by marine toxins, and will help understanding of the molecular mechanisms underlying the scallops’ response to OA exposure.

Relationship between metabolic enzyme activities and bioaccumulation kinetics of PAHs in zebrafish (Danio rerio)

Many studies have investigated bioaccumulation and metabolism of polycyclic aromatic hydrocarbons (PAHs) in aquatic organisms. However, lack of studies investigated both processes simultaneously, and the interaction between these two processes is less understood so far. This study investigated the bioaccumulation kinetics of PAHs and metabolic enzyme activities, including total cytochrome P450 (CYPs) and total superoxide dismutase (T-SOD), in zebrafish. Mature zebrafish were exposed to the mixture of phenanthrene and anthracene under constant concentration maintained by passive dosing systems for 16days. The results showed that PAH concentrations in zebrafish experienced a peak value after exposure for 1.5days, and then decreased gradually. The bioaccumulation equilibrium was achieved after exposure for 12days. Both of the uptake rate constants (k_u) and the elimination rate constants (k_e) decreased after the peak value. The variation of PAH concentrations and metabolic enzyme activities in zebrafish had an interactive relationship. The activities of CYPs and T-SOD increased initially with the increase of PAH concentrations, but decreased to the lowest state when PAH concentrations reached the peak value. When the bioaccumulation equilibrium of PAHs was achieved, CYPs and T-SOD activities also reached the steady state. In general, CYPs and T-SOD activities were activated after exposure to PAHs. The decrease of PAH concentrations in zebrafish after the peak value may be attributed to the great drop of k_u and the variation of CYPs activities. This study suggests that an interactive relationship exists between bioaccumulation kinetics of PAHs and metabolic enzyme activities in aquatic organisms.

Benzo(a)pyrene Exposure Causes Genotoxic and Biochemical Changes in the Midge Larvae of Chironomus sancticaroli Strixino & Strixino (Diptera: Chironomidae)

Benzo(a)pyrene (BaP) is a carcinogenic polycyclic aromatic hydrocarbon, also found in nature due to human activities. BaP adheres to sediments showing toxic effects on benthic organisms, including midge larvae of the family Chironomidae. We tested for toxic effects of benzo(a)pyrene on Chironomus sancticaroli Strixino & Strixino 1981 using biochemical and genotoxic biomarkers, to identify changes in metabolic and antioxidant pathways, besides neurotoxic and DNA damage. Enzyme activity was compared by exposing larvae to four nominal concentrations (0.47, 2.13, 3.41, and 4.73 μg l^-1) and DNA damage to two concentrations (0.47 and 4.73 μg l^-1), after exposure at 24, 48, 72, and 96 h. BaP caused neurotoxic effect, showing acetylcholinesterase alterations at different treatments. Changes in the biotransformation pathway were detected, with an increased activity of alpha and beta esterase in 48 h and reduction of glutathione-S-transferase activity in all periods at the highest concentrations. Damage to the antioxidant system was observed by the increase of the superoxide dismutase and reduction of the catalase, in 48 h. Genotoxicity was detected by an increased DNA damage at 48 and 72 h. The lowest concentration (0.47 μg l^-1), even presenting low mortality, also altered the biochemical parameters of the larvae. Thus, these results indicate that BaP causes metabolic, neurotoxic, and genotoxic effects on C. sancticaroli, even at low concentrations and short-term exposure. BaP can cause damage of immature invertebrates, and the ecological dynamics can be affected, since these organisms have trophic importance in the aquatic environment.

Three simple biomarkers useful in conducting water quality assessments with bivalve mollusks

While biomarkers are undeniably key tools in aquatic ecotoxicology to measure adverse effects linked to contamination events, their application is often inhibited by monetary constraints negating the possibility of having access to dedicated equipment, special wares, and/or expensive reagents. To offset this bottleneck, we propose three simple physiological biomarkers, quantifiable in bivalves, that are free of cost considerations and that can provide basic knowledge on animal health and water quality. Indeed, condition index (CI), growth index (GI), and SOS response (air-time survival) comprise measurements straightforward enough to perform by any laboratory or science body on the planet. Long-term monitoring or screening studies can be carried out with these biomarkers and they are able to provide robust information notably after exposure of bivalves to either singular or multiple agents of contamination. By highlighting examples of data generated in aquatic studies conducted in Eastern Canada under both laboratory and field situations with different species of marine and freshwater mollusks, we establish the suitability of these biomarkers for assessing environmental contamination. Their relationships with other biomarkers are also shown which further corroborate their value as reliable indicators of ecosystem health.

Multi-biomarker approach in the scallop Chlamys farreri to assess PAHs pollution in Qingdao coastal areas of China

A multi-biomarker approach was conducted in the scallop Chlamys farreri from three sites, denoted here as S1, S2, and S3, in Qingdao coastal areas of China in March, June, September and December 2014 to assess pollution from polycyclic aromatic hydrocarbons (PAHs) and to select appropriate biomarkers. A suite of biological responses of the gills and digestive glands of the scallops was assayed, including: (i) phase I detoxification enzymes of 7-ethoxyresorufin-O-deethylase (EROD), epoxide hydrolase (EH), and dihydrodiol dehydrogenase (DD) and phase II detoxification enzymes of glutathione-S-transferase (GST) and sulfotransferase (SULT); (ii) antioxidant enzymes: catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx); (iii) oxidative damage parameters: lipid peroxidation (LPO) expressed by malondialdehyde (MDA) contents, protein carbonylation (PC) and DNA damage (F value); and (iv) the metabolism-related genes of EH, DD, GST, SULT and SOD. Simultaneously, the concentrations of total PAHs along with 16 types of PAHs previously identified by the US Environmental Protection Agency (USEPA) and environmental parameters, including temperature and salinity together with pH, were measured. Using Principle Component Analysis (PCA), it was revealed that S2 was the most PAH-contaminated site, while S1 was identified as the least PAH-polluted site, which was consistent with the results utilizing the Biomarker Response Index (BRI); in other words, the biological health status of S2 was worse than S1 and S3. Moreover, the most suitable biomarkers to assess PAH pollution in Qingdao coastal areas proved to be DD mRNA expression and the F value in both the gills and digestive glands for the total PAHs, DD activity and PC contents or PC and MDA contents in the gills or digestive glands for 5 + 6 rings PAHs and DD mRNA expression in both the gills and digestive glands for 2 + 3 rings and 4 rings PAHs. Moreover, this study highlighted the possible use of the scallop Chlamys farreri for studying contamination due to PAHs and provided valuable information on environmental assessment.

Transcriptional changes in oysters Crassostrea brasiliana exposed to phenanthrene at different salinities

Euryhaline animals from estuaries, such as the oyster Crassostrea brasiliana, show physiological mechanisms of adaptation to tolerate salinity changes. These ecosystems receive constant input of xenobiotics from urban areas, including polycyclic aromatic hydrocarbons (PAHs), such as phenanthrene (PHE). In order to understand the influence of salinity on the molecular responses of C. brasiliana exposed to PHE, oysters were acclimatized to different salinities (35, 25 and 10) for 15days and then exposed to 100μgL^-1 PHE for 24h and 96h. Control groups were kept at the same salinities without PHE. Oysters were sampled for chemical analysis and the gills were excised for mRNA quantification by qPCR. Transcript levels of different genes were measured, including some involved in oxidative stress pathways, phases I and II of the xenobiotic biotransformation systems, amino acid metabolism, fatty acid metabolism and aryl hydrocarbon receptor nuclear translocator putative gene. Higher transcript levels of Sulfotransferase-like gene (SULT-like) were observed in oysters exposed to PHE at salinity 10 compared to control (24h and 96h); cytochrome P450 isoforms (CYP2AU1, CYP2-like1) were more elevated in oysters exposed for 24h and CYP2-like2 after 96h of oysters exposed to PHE at salinity 10 compared to control. These results are probably associated to an enhanced Phase I biotransformation activity required for PHE detoxification under hyposmotic stress. Higher transcript levels of CAT-like, SOD-like, GSTm-like (96h) and GSTΩ-like (24h) in oysters kept at salinity 10 compared to organisms at salinities 25 and/or 35 are possibly related to enhaced ROS production. The transcription of these genes were not affected by PHE exposure. Amino acid metabolism-related genes (GAD-like (24h), GLYT-like, ARG-like (96h) and TAUT-like at 24h and 96h) also showed different transcription levels among organisms exposed to different salinities, suggesting their important role for oyster salinity adaptation, which is not affected by exposure to these levels of PHE.

The detoxification responses, damage effects and bioaccumulation in the scallop Chlamys farreri exposed to single and mixtures of benzo[a]pyrene and chrysene

This study aimed to investigate the detoxification responses, damage effects and biotransformation in scallop Chlamys farreri exposed to benzo[a]pyrene (BaP) (0.1, 1μg/L), chrysene (CHR) (0.1, 1μg/L) and BaP+CHR (0.1+0.1, 1+1μg/L) for 15days. Results demonstrated that BaP and CHR concentration (BaP<CHR) in tissues increased rapidly in a time and dose effect. The mRNA expression of aryl hydrocarbon receptor (AhR), cytochrome P450 1A1 (CYP1A1), CYP1B1, multidrug resistance protein 1 (MRP1/ABCC1), breast cancer resistance protein (BCRP/ABCG2) and P-glycoprotein (P-gp) were induced especially in the mixtures of BaP and CHR. Heat shock protein 90 (HSP90) and aryl hydrocarbon receptor nuclear translocator (ARNT) mRNA expression was significantly elevated at days 1, 10 and 15. Detoxification enzymes of 7-ethoxyresorufin O-deethylase (EROD), uridine-diphosphate-glucuronyl-transferase (UGT) and sulfotransferase (SULT) were significantly induced and then became stable gradually while glutathione-S-transferase (GST) was inhibited in the mixtures of BaP and CHR at days 10 and 15. Superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and glutathione (GSH) were all stimulated especially in the mixtures of BaP and CHR. The levels of DNA strand breaks, lipid peroxidation (LPO) and protein carbonyl (PC) contents showed damage effects exposed BaP and CHR. All the results indicated that BaP and CHR have similar induced effect and a majority of the biomarkers pointed to a more toxic effect when BaP and CHR were mixed. These will provide a solid foundation for the study of PAHs detoxification mechanism in bivalves and valuable information for marine pollution monitoring.

Bioaccumulation of polycyclic aromatic hydrocarbons, polychlorinated biphenyls and hexachlorobenzene by three Arctic benthic species from Kongsfjorden (Svalbard, Norway)

The predicted expansion of oil and gas (O&G) activities in the Arctic urges for a better understanding of impacts of these activities in this region. Here we investigated the influence of location, feeding strategy and animal size on the bioaccumulation of Polycyclic Aromatic Hydrocarbons (PAHs), Polychlorinated Biphenyls (PCBs) and Hexachlorobenzene (HCB) by three Arctic benthic species in Kongsfjorden (Svalbard, Norway). No toxicity was expected based on biota PAH critical body residues. Biota PCB levels were mainly below limit of detection, whereas samples were moderately polluted by HCB. PAH concentrations in biota and Biota Sediment Accumulation Factors (BSAFs) were generally higher in Blomstrandhalvøya than in Ny-Ålesund, which was explained by a higher abundance of black carbon in Ny-Ålesund harbour. BSAFs differed significantly among species and stations. We conclude that contaminant body residues are a less variable and more straightforward monitoring parameter than sediment concentrations or BSAFs in Arctic benthos.

Variability in antioxidant/detoxification enzymes of Sinonovacula constricta exposed to benzo[a]pyrene and phenanthrene

The purpose of this study was to investigate the toxic effects induced by benzo[a]pyrene and phenanthrene. For this purpose, a study was performed on the clam exposed to 0.0, 0.5, 4.5μgL(-1) B(a)P and PHE for 15days using parameters of antioxidant defenses and oxidative stress. Antioxidant biomarkers including ethoxyresorufin-O-deethylase, glutathione S-transferase, superoxide dismutase, and glutathione and rylhydrocarbon hydroxylasein gills of Sinonovacula constricta, were analyzed after a 1-, 3-, 9- and 15-day exposure to seawater containing B(a)P and PHE. Integrated biomarker response was calculated by combining multiple biomarkers into a single value. The results showed that the activity of all antioxidant biomarkers was induced throughout the exposure period, and different patterns of variations were detected with exposure time. In addition, the study showed that the two concentrations used caused the activation of different general detoxification mechanisms, and the same concentration at different two PAH compounds induced different toxicity responses.

Effect of diet quality on mussel biomarker responses to pollutants

The effect of the quality of two microalgal species on select biological and biochemical responses used as indicators of pollution were assessed. Mussels were conditioned for 6 weeks with the diatom Chaetoceros neogracile and the dinoflagellate Heterocapsa triquetra, chosen for being two clearly different types of primary production quality that differ in both biometric and biochemical characteristics. After dietary conditioning, the mussels were exposed to a polycyclic aromatic hydrocarbon, fluoranthene (FLU), for 1 week followed by 1 week of depuration. Results showed higher FLU accumulation in mussels fed on C. neogracile compared to those fed on H. triquetra. Concomitantly, a greater impact of this toxicant was observed in the biomarker responses of mussels fed on C. neogracile. These mussels showed an increase in the percentage of dead hemocytes, an activation of phagocytosis and ROS production of hemocytes after exposure. Some enzymatic activities also increased upon FLU exposure (superoxide dismutase -SOD-, catalase -CAT-, and glutathione reductases -GR-) and after depuration (glutathione-s-transferase -GST-). Results suggest that FLU exposure as well as food quality influence biomarker responses, with higher values of SOD, CAT and GR in non-exposed mussels fed on C. neogracile. In addition, upon exposure to the same FLU concentration, GR response varied according to dietary conditioning, suggesting that diet could act as a confounding factor in biomarker responses to pollution. Consequently, trophic conditions should be considered in marine pollution monitoring programs for a better interpretation of biomarker responses.

Exposure to phenanthrene and depuration: Changes on gene transcription, enzymatic activity and lipid peroxidation in gill of scallops Nodipecten nodosus

Understanding the mechanism of phenanthrene (PHE) biotransformation and related cellular responses in bivalves can be an important tool to elucidate the risks of polycyclic aromatic hydrocarbons (PAHs) to aquatic organisms. In the present study it was analyzed the transcriptional levels of 13 biotransformation genes related to cytochrome P450 (CYP), glutathione S-transferase (GST), sulfotransferase (SULT), flavin-containing monooxygenase and fatty acid-binding proteins by qPCR in gill of scallops Nodipecten nodosus exposed for 24 or 96h to 50 or 200μgL(-1) PHE (equivalent to 0.28 and 1.12μM, respectively), followed by depuration in clean water for 96h (DEP). Likewise, it was quantified the activity of catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione reductase (GR), glucose 6-phosphate dehydrogenase (G6PDH), GST and levels of lipid peroxidation. Increased transcriptional levels of CYP2UI-like, CYP2D20-like, CYP3A11-like, GSTomega-like, SULT1B1-like genes were detected in organisms exposed to PHE for 24 or 96h. In parallel, GR and GPX activities increased after 96h exposure to 200μgL(-1) PHE and G6PDH activity increased after 24h exposure to 50μgL(-1) PHE. This enhancement of antioxidant and phase I and II biotransformation systems may be related to the 2.7 and 12.5 fold increases in PHE bioaccumulation after 96h exposure to 50 and 200μgL(-1) PHE, respectively. Interestingly, DEP caused reestablishment of GPX and GR activity, as well as to the transcript levels of all upregulated biotransformation genes (except for SULT1B1-like). Bioaccumulated PHE levels decreased 2.5-2.9 fold after depuration, although some biochemical and molecular modifications were still present. Lipid peroxidation levels remained lower in animals exposed to 200μgL(-1) PHE for 24h and DEP. These data indicate that N. nodosus is able to induce an antioxidant and biotransformation-related response to PHE exposure, counteracting its toxicity, and DEP can be an effective protocol for bivalve depuration after PHE exposure.

Proteomic and metabolomic analysis on the toxicological effects of Benzo[a]pyrene in pearl oyster Pinctada martensii

Benzo[a]pyrene (BaP) is one of the typical toxic polycyclic aromatic hydrocarbons (PAHs) that are widely present in marine environment. BaP has diverse toxic effects, including teratogenic, carcinogenic, mutagenic effects and so on, in various organisms. In this work, we focused on the differential proteomic and metabolomic responses in the digestive gland of pearl oyster Pinctada martensii exposed to two doses of BaP (1 and 10μg/L). Metabolic responses revealed that the high dose of BaP (10μg/L) mainly caused disturbances in osmotic regulation and energy metabolism in the digestive gland. Proteomic responses indicated that both doses of BaP induced disturbances in energy metabolism, cytoskeleton, cell injury, oxidative stress and signal transduction based on the differential proteomic biomarkers. Overall, these results demonstrated a number of potential biomarkers that were characterized by an integrated proteomic and metabolomic approach and provided a useful insight into the toxicological effects on pearl oyster P. martensii.

Toxic effects upon exposure to polycyclic aromatic hydrocarbon (chrysene) in scallop Chlamys farreri during the reproduction period

This study aims to investigate potential toxic effects of chrysene (CHR) on mature scallop Chlamys farreri during the reproduction period, using indicators of antioxidant defences and oxidative stress. Scallops were exposed to 0.2, 0.8 and 3.2μg/L waterborne CHR for 21 days, at day 10 scallops were induced to spawn. At days 1, 3, 6, 10, 11, 15 and 21, aryl hydrocarbon hydroxylase (AHH), 7-ethoxyresorufin-O-deethylase (EROD), glutathione-s-transferase (GST), glutathione (GSH), superoxide dismutase (SOD), lipid peroxidation (LPO), protein carbonyl (PC) and DNA strand breaks in digestive glands were examined by separately analysing male and female scallops. During the pre-spawn period, Levels of enzymatic activities and oxidative stress were all induced by the exposure to CHR for females and males. GST activity presented a good time- and dose-dependent relationship only in males, and GSH content showed a dose-dependent manner in both sexes. During the post-spawn period, different trends were observed, while PC contents maintained growth in time- and dose-dependent manner. Overall, males were more sensitive than females to CHR exposure in enzyme activities, and correspondingly, females suffered from more serious oxidative damages. Both GSH and PC contents seemed to be potential biomarkers for PAH exposure. These results will offer the information on toxicity of CHR in this species, and ensure the influence of gender and reproductive status on PAH detoxification metabolism.

Ploidy-, gender-, and dose-dependent alteration of selected biomarkers in Clarias gariepinus treated with benzo[a]pyrene

Naturally-occurring and artificially-induced polyploids have been documented in various fish species but to date no comparison has been reported of the impacts of ploidy on fish biomarker responses to organic pollutants. This study describes effects of ploidy, gender, and dose on biliary fluorescent aromatic compound (FAC) concentrations, hepatic ethoxyresorufin-O-deethylase (EROD) and glutathione S-transferase (GST) activities in one of the most commonly cultured warm-water species, the African catfish Clarias gariepinus. Recently matured male and female diploid and triploid fish were intraperitoneally (i.p.) injected with 0, 5 or 25mg/kg benzo[a]pyrene (BaP) and liver and gallbladder were sampled 48hr later. No significant differences were found between ploidies in bile concentrations of 7,8 dihydrodiolbenzo[a]pyrene (7,8D BaP), 1-hydroxybenzo[a]pyrene (1-OH BaP) or 3-hydroxybenzo[a]pyrene (3-OH BaP). However, concentrations of the biliary FACs did differ between males and females at different dose of injection with generally higher concentrations in females at the low dose of BaP and higher concentrations in males at the higher BaP concentration. Hepatic EROD activity did not exhibit gender-dependent difference, whereas it was significantly higher in triploids than diploids. GST activities were not significantly influenced by any of the tested factors. This work advanced our understanding of the role of ploidy, gender, and dose in biotransformation of pollutants in fish.

Effect of nutritive status on Mytilus galloprovincialis pollution biomarkers: Implications for large-scale monitoring programs

Biomarkers have been extensively used in monitoring programs with the aim of assessing the biological effects of pollutants on marine organisms and determining environmental status. Data obtained from these programs are sometimes difficult to interpret due to the large amount of natural variables affecting biological processes, which could act as confounding factors on biomarker responses. The main aim of this work was to identify the effect of one of these variables, the food availability, and consequently, the mussel nutritive status, on biomarker responses. For that purpose, mussels (Mytilus galloprovincialis) were conditioned to three different food rations for 2 months in order to create three mussel nutritive statuses and afterwards, each status was exposed to three nominal concentrations of fluoranthene (FLU) for 3 weeks. A battery of biomarkers was considered in this study to cover a wide range of organism responses, both physiological (scope for growth - SFG) and biochemical (superoxide dismutase - SOD, catalase - CAT, glutathione reductase - GR, glutathione peroxidase - GPx, glutathione-S-transferase - GST and phenoloxidase - PO activities, and lipid membrane peroxidation - LPO). The results obtained, evidenced that most of the studied biomarkers (SFG, SOD, CAT, GPx, and PO) were strongly affected by mussel nutritive status, showing higher values at lower status, whereas the effect of toxicant was not always evident, masked by the nutritive status effect. This paper demonstrates that toxicants are not the only source of variability modulating pollution biomarkers, and confirms nutritive status as a major factor altering biochemical and physiological biomarkers.

Active and passive biomonitoring suggest metabolic adaptation in blue mussels (Mytilus spp.) chronically exposed to a moderate contamination in Brest harbor (France)

Brest harbor (Bay of Brest, Brittany, France) has a severe past of anthropogenic chemical contamination, but inputs tended to decrease, indicating a reassessment of its ecotoxicological status should be carried out. Here, native and caged mussels (Mytilus spp.) were used in combination to evaluate biological effects of chronic chemical contamination in Brest harbor. Polycyclic aromatic hydrocarbon (PAH) contamination was measured in mussel tissues as a proxy of harbor and urban pollution. Biochemical biomarkers of xenobiotic biotransformation, antioxidant defenses, generation of reducing equivalents, energy metabolism and oxidative damage were studied in both gills and digestive glands of native and caged mussels. In particular, activities of glutathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), NADP-dependent isocitrate dehydrogenase (IDP), pyruvate kinase (PK) and phosphoenolpyruvate carboxykinase (PEPCK) were measured and lipid peroxidation was assessed by malondialdehyde (MDA) quantification. In addition, a condition index was calculated to assess the overall health of the mussels. Moderate PAH contamination was detected in digestive glands of both native and caged individuals from the exposed site. Modulations of biomarkers were detected in digestive glands of native harbor mussels indicating the presence of a chemical pressure. In particular, results suggested increased biotransformation (GST), antioxidant defenses (CAT), NADPH generation (IDP) and gluconeogenesis (PEPCK), which could represent a coordinated response against chemically-induced cellular stress. Lipid peroxidation assessment and condition index indicated an absence of acute stress in the same mussels suggesting metabolic changes could, at least partially, offset the negative effects of contamination. In caged mussels, only GR was found modulated compared to non-exposed mussels but significant differences in oxidative stress and energy-related biomarkers were observed compared to native harbor mussels. Overall, these results suggested mussels chronically exposed to contamination have set up metabolic adaptation, which may contribute to their survival in the moderately contaminated harbor of Brest. Whether these adaptive traits result from phenotypic plasticity or genetic adaptation needs to be further investigated.

How does predation affect the bioaccumulation of hydrophobic organic compounds in aquatic organisms?

It is well-known that the body burden of hydrophobic organic compounds (HOCs) increases with the trophic level of aquatic organisms. However, the mechanism of HOC biomagnification is not fully understood. To fill this gap, this study investigated the effect of predation on the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs), one type of HOC, in low-to-high aquatic trophic levels under constant freely dissolved PAH concentrations (1, 5, or 10 μg L(-1)) maintained by passive dosing systems. The tested PAHs included phenanthrene, anthracene, fluoranthene, and pyrene. The test organisms included zebrafish, which prey on Daphnia magna, and cichlids, which prey on zebrafish. The results revealed that for both zebrafish and cichlids, predation elevated the uptake and elimination rates of PAHs. The increase of uptake rate constant ranged from 20.8% to 39.4% in zebrafish with the amount of predation of 5 daphnids per fish per day, and the PAH uptake rate constant increased with the amount of predation. However, predation did not change the final bioaccumulation equilibrium; the equilibrium concentrations of PAHs in fish only depended on the freely dissolved concentration in water. Furthermore, the lipid-normalized water-based bioaccumulation factor of each PAH was constant for fish at different trophic levels. These findings infer that the final bioaccumulation equilibrium of PAHs is related to a partition between water and lipids in aquatic organisms, and predation between trophic levels does not change bioaccumulation equilibrium but bioaccumulation kinetics at stable freely dissolved PAH concentrations. This study suggests that if HOCs have not reached bioaccumulation equilibrium, biomagnification occurs due to enhanced uptake rates caused by predation in addition to higher lipid contents in higher trophic organisms. Otherwise, it is only due to the higher lipid contents in higher trophic organisms.

Gender differences in detoxification metabolism of polycyclic aromatic hydrocarbon (chrysene) in scallop Chlamys farreri during the reproduction period

This study aims to investigate the effects of chrysene (CHR) on biotransformation and detoxification responses of mature scallop Chlamys farreri during the reproduction period. Scallops were exposed to 0.2, 0.8 and 3.2 μg/L CHR for 21 days; at day 10 scallops were induced to spawn. At days 1, 3, 6, 10, 11, 15 and 21, enzymatic activities of 7-ethoxyresorufin O-deethylase (EROD) and glutathione-s-transferase (GST), related mRNA expression levels of CYP1A1, GST-pi and P-glycoprotein (P-gp) in digestive glands and CHR bioaccumulation in tissues were examined by separately analyzing male and female scallops. During the pre-spawn period, CHR concentrations of the treated groups in tissues except the hemolymph increased rapidly. Levels of enzymatic activities and related gene expressions were all induced by the exposure to CHR for females and males. GST activity and GST-pi mRNA expression showed a good time- and dose-dependent relationship only in males, and P-gp mRNA expression exhibited a dose-dependent manner in both sexes. During the post-spawn period, spawning caused significant reductions of bioaccumulation in tissues but the gill and hemolymph. Enzymatic activities and related gene expressions were for females significantly depressed at day 21 at 0.8 or 3.2 μg/L CHR. Overall, females accumulated more CHR than males, while males were more sensitive than females to CHR exposure in gene expressions and enzyme activities. P-gp mRNA expression seemed to be a potential biomarker for PAH exposure. These results will offer the information on CHR biotransformation in this species, and ensure the influence of gender and reproductive status on PAH detoxification metabolism.