Effect of mussel reproductive status on biomarker responses to PAHs: Implications for large-scale monitoring programs

PAH residues and toxicity levels two years after an extensive oil spill on the northeast Brazilian coast

The most extensive oil spill ever recorded in tropical oceans occurred between August 2019 and March 2020, affecting approximately 3000 km of the Brazilian coast. This study assessed the chemical contamination and toxicity of sediments collected from affected reef areas during two sampling surveys conducted 17 and 24 months after the peak of oil slick inputs. Our results indicated that neither PAH levels nor measured toxicity showed a significant contribution from the spilled oil, with concentrations and biological effects indistinguishable from those in unaffected areas. Similarly, no differences were observed between seasons. Furthermore, there was no discernible relationship between sediment toxicity results and the measured PAH concentrations. Therefore, while biological responses indicated toxicity in most assessed areas, these responses are likely related to other local sources. This evidence suggests a natural oil attenuation process contributing to local environmental recovery. Nonetheless, further investigation is needed for other areas affected by oil spills.

Impact of Heavy Metal Exposure on Mytilus galloprovincialis Spermatozoa: A Metabolomic Investigation

Metabolomics is a method that provides an overview of the physiological and cellular state of a specific organism or tissue. This method is particularly useful for studying the influence the environment can have on organisms, especially those used as bio-indicators, e.g., Mytilus galloprovincialis. Nevertheless, a scarcity of data on the complete metabolic baseline of mussel tissues still exists, but more importantly, the effect of mussel exposure to certain heavy metals on spermatozoa is unknown, also considering that, in recent years, the reproductive system has proved to be very sensitive to the effects of environmental pollutants. In order to fill this knowledge gap, the similarities and differences in the metabolic profile of spermatozoa of mussels exposed to metallic chlorides of copper, nickel, and cadmium, and to the mixture to these metals, were studied using a metabolomics approach based on GC-MS analysis, and their physiological role was discussed. A total of 237 endogenous metabolites were identified in the spermatozoa of these mussel. The data underwent preprocessing steps and were analyzed using statistical methods such as PLS-DA. The results showed effective class separation and identified key metabolites through the VIP scores. Heatmaps and cluster analysis further evaluated the metabolites. The metabolite-set enrichment analysis revealed complex interactions within metabolic pathways and metabolites, especially involving glucose and central carbon metabolism and oxidative stress metabolism. Overall, the results of this study are useful to better understand how some pollutants can affect the specific physiological functions of the spermatozoa of this mussel, as well as for further GC-MS-based metabolomic health and safety studies of marine bivalves.

Effect of hexavalent chromium exposure on the reproductive status and biomarker responses of female Geloina erosa

Hexavalent chromium (Cr (VI)) is widely distributed in the marine environment of Hainan Province, China and poses a potential threat to its mangrove ecosystems. However, the mechanisms underlying Cr-induced stress and reproductive toxicity in clams remain largely unknown. In this study, the clams, Geloina erosa, were exposed to 4.34, 8.69, 17.38 and 34.76 mg/L Cr (VI) for 24, 48 and 72 h. The gonad-somatic index (GSI) was determined and histological alterations of the ovaries were quantified by light microscopy. The micronucleus test was performed which quantifies the genotoxic presence of small cytoplasmic bodies in eukaryotic cells. Enzymatic assays for catalase (CAT), glutathione reductase (GR), and malondialdehyde (MDA) activities were done. Quantitative real-time PCR (qRT-PCR) was used to quantify the expression of glutathione-S-transferase (GST), heat shock protein 70 (HSP70) and vitellogenin (Vtg) in ovaries of G. erosa. The results showed that the micronucleus frequency was significantly increased when clams were exposed to Cr (VI). Cr (VI) exposure induced the accumulation of MDA and affected CAT and GR enzyme activities. The high Cr (VI) concentration of 34.76 mg/L significantly increased the levels of GR activity, GST expression and HSP70 expression and inhibited Vtg expression and CAT activity. MDA content was significantly increased after 72 h at the high Cr (VI) exposure (34.76 mg/L). Therefore, Cr (VI) exposure may be toxic to the development of ovaries of G. erosa.

Glutathione reductase, a biomarker of pollutant and stress in Pacific abalone

Abalone are frequently exposed to several environmental factors including heavy metal toxicity, thermal stress, H2O2-stress, starvation, viral and bacterial infection that can induce oxidative stress. Glutathione reductase is a vital enzyme in the antioxidant defense system that catalyzes the reduction of oxidized glutathione to reduced glutathione. The present study aimed to identify and localize glutathione reductase in Pacific abalone (Hdh-GR) and assess its potential role in stress physiology, heavy metal toxicity, immune response, gonadal development, and metamorphosis. The mRNA expression of Hdh-GR was upregulated in response to thermal stress, starvation, H2O2-stress, and cadmium-exposed toxicity. The induced mRNA expression was also quantified in immune-challenged abalone. Moreover, the Hdh-GR expression was significantly higher during metamorphosis. The Hdh-GR mRNA expression showed an inverse relationship with ROS production in heat stressed Pacific abalone. These results suggest that Hdh-GR has central role in the stress physiology, immune response, gonadal development, and metamorphosis of Pacific abalone.

Study of DNA methylation of hsd17β, er and reproductive endocrine disrupting effects in female Chlamys farreri under benzo[a]pyrene stress

Benzo[a]pyrene (B[a]P) is one kind of persistent organic pollutants (POPs) in the marine environment which has multiple toxic effects. However, epigenetic studies correlated with reproductive endocrine disruption in invertebrates have not been explored. In our study, Chlamys farreri in the mature stage were exposed to B[a]P (0, 0.4, 2 and 10 μg/L) for 5 and 10 d to explore the effects on reproductive endocrine and DNA methylation. The results proved that B[a]P stress significantly restrained the growth of mature oocytes, reduced the content of sex hormones, and affected the expression of genes related to ovarian development. Histological observation showed that the ovarian microstructure was damaged. The detection of SAM/SAH, dnmts, GNMT in the ovary showed that the level of global DNA methylation fluctuated. Significant hypermethylation of the hsd17β promoter region in the ovary was associated with a significant downregulation of its gene expression. In summary, our results suggested that exposure to B[a]P might affect DNA methylation to regulate key reproductive genes, interfere with the synthesis of sex hormones, and inhibit ovarian development. These findings provide a basis for a better understanding of how epigenetic mechanisms are involved in the response of marine invertebrates to POPs stress, opening up new avenues for incorporating environmental epigenetic approaches into marine invertebrate management and conservation plans.

Changes in metabolic profiles of amphipods Allorchestes compressa after acute exposures to copper, pyrene, and their mixtures

Amphipods are ideal indicators for biomonitoring and ecotoxicological studies of environmental contaminants because they are extensively distributed in aquatic environments, are easy to collect and are important in nutrient cycling. Marine amphipods (Allorchestes compressa) were exposed to two concentrations of copper and pyrene, and their mixtures, for 24 and 48 h. Changes in polar metabolites were assessed using Gas Chromatography Mass Spectrometry (GC-MS)-based untargeted metabolomics. Generally, limited metabolite changes were observed for copper and pyrene single exposures (eight and two significant metabolites, respectively), while 28 metabolites had changed following exposures to mixtures. Furthermore, changes were mainly observed after 24 h but had seemingly returned to control levels after 48 h. Multiple types of metabolites were affected including amino acids, Tricarboxylic acid (TCA) cycle intermediates, sugars, fatty acids, and hormones. This study highlights the sensitivity of metabolomics in assessing the impacts of low concentrations of chemicals compared to traditional ecotoxicological endpoints.

Active and passive biomonitoring of trace elements, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls in small Mediterranean harbours

Pollution particularly affects coastal ecosystems due to their proximity to anthropic sources. Among those environments, harbours are subjected to marine traffic but also to accidental and chronic pollution. These areas are thus exposed to complex mixtures of contaminants such as trace elements and organic contaminants which can impact marine species, habitats, and ecosystem services. The monitoring of these compounds is thus a crucial issue for assessment of environmental health. In this context, the aim of the present work was to evaluate the chemical contamination of harbours in Corsica (NW Mediterranean) by measuring the bioaccumulation of trace elements, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls in mussels, limpets, and sea cucumbers. The human health risks associated with seafood consumption were also assessed. Results reveal a relatively low contamination in the Corsican harbours studied compared to larger Mediterranean ports and suggest that the potential health risk for consumers eating seafood is low.

Sex and gametogenesis stage are strong drivers of gene expression in Mytilus edulis exposed to environmentally relevant plasticiser levels and pH 7.7

Plastic pollution and changes in oceanic pH are both pressing environmental issues. Little emphasis, however, has been placed on the influence of sex and gametogenesis stage when investigating the effects of such stressors. Here, we examined histology and molecular biomarkers of blue mussels Mytilus edulis exposed for 7 days to a pH 7.7 scenario (- 0.4 units) in combination with environmentally relevant concentrations (0, 0.5 and 50 µg/L) of the endocrine disrupting plasticiser di-2-ethylhexyl phthalate (DEHP). Through a factorial design, we investigated the gametogenesis cycle and sex-related expression of genes involved in pH homeostasis, stress response and oestrogen receptor-like pathways after the exposure to the two environmental stressors. As expected, we found sex-related differences in the proportion of developing, mature and spawning gonads in histological sections. Male gonads also showed higher levels of the acid-base regulator CA2, but females had a higher expression of stress response-related genes (i.e. sod, cat, hsp70). We found a significant effect of DEHP on stress response-related gene expression that was dependent on the gametogenesis stage, but there was only a trend towards downregulation of CA2 in response to pH 7.7. In addition, differences in gene expression between males and females were most pronounced in experimental conditions containing DEHP and/or acidified pH but never the control, indicating that it is important to consider sex and gametogenesis stage when studying the response of mussels to diverse stressors.

Damages to biological macromolecules in gonadal subcellular fractions of scallop Chlamys farreri following benzo[a]pyrene exposure: Contribution to inhibiting gonadal development and reducing fertility

Benzo[a]pyrene (B[a]P), a representative polycyclic aromatic hydrocarbon (PAH) compound in marine ecosystem, has great potential for chronic toxicity to marine animals. It is becoming increasingly apparent that reproductive system is the major target of B[a]P, but the adverse effects of B[a]P on subcellular fractions in bivalve gonads have not been elucidated. Scallops Chlamys farreri are used as the experimental species since they are sensitive to environmental pollutants. This study was conducted to investigate how B[a]P affected the gonadal subcellular fractions, including plasma membrane, nucleus, mitochondria and microsome in scallops, and whether subcellular damages were related to reproductive toxicity. The results showed that mature gametes' counts were significantly decreased in B[a]P-treated scallops. Three biological macromolecules (viz., DNA, lipids and proteins) in gonadal subcellular fractions obtained by differential centrifugation suffered damages, including DNA damage, lipid peroxidation and protein carbonylation in B[a]P treatment groups. Interestingly, mitochondria and microsome were more vulnerable to lipid peroxidation and protein carbonylation than plasma membrane and nucleus, meanwhile males were more susceptible to DNA damage than females under B[a]P exposure. In addition, histological analysis showed that B[a]P delayed gonadal development in C. farreri. To summarize, our results indicated that B[a]P caused damages to biological macromolecules in gonadal subcellular fractions and then induced damages to gonadal tissues of C. farreri, which further inhibited gonadal development and ultimately leaded to reduction in fertility. This study firstly reports the impacts of PAHs on subcellular fractions in bivalves and their relationship with reproductive toxicity. Moreover, exposure of reproductive scallops to B[a]P leads to defects in reproduction, raising concerns on the possible long-term consequences of PAHs for natural populations of bivalves.

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

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

The influence of natural vs anthropogenic factors on trace metal(loid) levels in the Mussel Watch programme: Two decades of monitoring in the Spanish Mediterranean sea

The spatial distribution and temporal trends of trace metals (i.e. Cd, Cu, Hg, Pb and Zn) and a metalloid (i.e. As) along the Spanish Mediterranean coast from 1993 to 2013 are presented with a new estimation of their background levels monitored using wild mussels. Over a 20 years period, yearly mussel monitoring was undertaken with a rigorous field sampling protocol using 3 pooled samples strategy (3 x n = 80, with 8 mussels in the 3.0 to 3.9 size categories at each site), obtained in the pre-spawning period (May-June) to minimize biological factors and seasonal variability, which is a fundamental element of the international programme. Spatial distribution was characterized every 5 years and temporal trends were determined in 11 locations. The main aims of the present long term study are to evaluate the environmental status of different coastal locations regarding trace metal levels and follow the evolution of these levels over time after the implementation of regulatory measures. Regarding spatial distribution, the highest values for Cd, Cu, Hg and Pb were found close to known highly anthopogenic cities or shipyard areas. However, As and Zn did not strictly follow this pattern, showing natural increased concentrations in the Levantine Balearic and Strait of Gibraltar-Alboran Sea demarcations respectively. These distributions are associated with the conjunction of two geological formation inputs (Massif Central in France and Iberian Pyritic Belt in Spain) and the oceanographic conditions in the adjacent coastal area. In the case of temporal trends, metal concentrations decreased significantly over time in most stations, confirming the effectiveness of the regulatory measures and prohibitions established under European legislation. Concentrations of Pb were above the established thresholds for human consumption in only 12-14% of the sampling areas. With the information obtained for this study, we estimate background concentrations and propose new Background Assesment Criteria (BAC) for the Spanish Mediterranean coast as a threshold criterion: 1.62 mg/kg d.w. for Cd, 8.75 mg/kg d.w. for Cu, 0.202 mg/kg d.w. for Hg and 2.83 mg/kg d.w. for Pb. Exceptions should exist for As and Zn, for which there should be different levels in each demarcation, due to the geological, hydrological and oceanographic peculiarities of the Spanish coast. For the Levantine-Balearic demarcation, the proposed background concentrations are 117 mg/kg d.w. for As and 200 mg/kg d.w. for Zn., whereas in the Strait of Gibraltar-Alboran Sea demarcation, they are 27.5 mg/kg d.w. for As, and 471 mg/kg d.w. for Zn. This work demonstrates the vital importance of defining the background levels of metal(loid)s at a regional or subregional level because, for areas not affected by anthropogenic causes which have high values as the result of natural processes, this would avoid the risk of constantly surpassing the levels proposed in directives.

Integrated transcriptomics and metabolomics analyses reveal benzo[a]pyrene enhances the toxicity of mercury to the Manila clam, Ruditapes philippinarum

Mercury (Hg²⁺) and benzo[a]pyrene (BaP) are ubiquitous and persistent pollutants with multiple toxicities in bivalve molluscs. Here, the toxicological responses in the gills of Manila clams, Ruditapes philippinarum, to Hg²⁺ (10 μg L^-1), BaP (3 μg L^-1), and their mixture were analysed using transcriptomics and metabolomics approaches. Comparisons of the transcriptomes and metabolomes of Hg²⁺-and/or BaP-treated clams with control animals revealed the involvement of the detoxification metabolism, immune defence, energy-related pathways, and osmotic regulation in the stress response of R. philippinarum. Exposure to Hg²⁺ alone primarily enhanced the detoxification and energy metabolic pathways by significantly increasing the expression of genes associated with heat-shock proteins and oxidative phosphorylation. However, co-exposure to Hg²⁺ and BaP caused greater immunotoxicity and disrupted detoxification metabolism, the TCA cycle, glycolysis, and ATP generation. The expression levels of cytochrome P450 1A1 (CYP1A1), multidrug resistance-associated protein 1 (MRP1), and myosin (MYO), and the activity of electron transport system (ETS) in gills were detected, supporting the underlying toxic mechanisms of Hg²⁺ and BaP. We suggest that the presence of BaP enhances the toxicity of Hg²⁺ by 1) hampering the detoxification of Hg²⁺, 2) increasing the immunotoxicity of Hg²⁺, and 3) constraining energy availability for clams.

Comparative biomarker responses to urban pollution in three polychaete species: Perinereis cultrifera, Diopatra neapolitana, and Marphysa sanguinea from the lagoon of Tunis

Coastal lagoons are among the most vulnerable ecosystems as they are often exposed to different anthropogenic activities. The Polychaetes, which are dominant components in macrobenthic community, are particularly exposed to contamination. The current study was designed to assess and compare the sensitivity of different polychaetes species towards urban pollution. To do this, three polychaete species: Perinereis cultrifera, Diopatra neapolitana, and Marphysa sanguinea, were collected from the Tunis South Lagoon during summer 2013. A set of biomarkers indicative of genotoxicity (DNA damage), biotransformation, and oxidative stress (glutathione S-transferase, GST) as well as immune response (cyclooxygenase activity (COX), lysozyme activity, and nitric oxide level (NOx)), was used. The results revealed that D. neapolitana and P. cultrifera exhibited higher genetic alteration and GST activity and more prominent immune response when compared with M. sanguinea. These findings denote of the higher sensitivity of D. neapolitana and P. cultrifera to urban pollution and suggest their possible use in environmental biomonitoring programs.

First characterization of the ecotoxicity of paraffin particles: assessment of biochemical effects in the marine polychaete Hediste diversicolor

Plastics are a widespread environmental problem, particularly in the form of small particles or fragments (microplastics). With the purpose of gradually replacing the use of plastics in cosmetic products (primary microplastics), the use of paraffin in microspheres has recently been applied. Paraffin waxes are composed by organic molecules usually derived from petroleum, thus assumed to be chemically and biologically inert, having a lower (eco)toxicity and residence time compared with plastic particles. However, the low ecotoxicity of paraffin waxes may be somewhat questionable, because some paraffin constituents can be absorbed and catabolized, thus exerting biological effects. The main objective of this study was to understand the potential toxic effects of paraffin microparticles on key physiological processes of the polychaete Hediste diversicolor. To attain this objective, this work assessed the acute and chronic effects of three densities (5, 20, and 80 mg L^-1) of four size ranges of paraffin particles (from 100 to 1200 μm) on this epibenthic organism. Although paraffin wax can be generically considered innocuous, the present study was able to demonstrate a significant inhibition in the activity of acetylcholinesterase in acutely exposed organisms and an increase in the activity of glutathione peroxidase, catalase, and glutathione S-transferase under some specific scenarios.

Oxidative stress ecology on Pacific oyster Crassostrea gigas from lagoon and offshore Italian sites

Crassostrea gigas is a sentinel species along the Italian coast. In mussels, the levels of oxidative stress biomarkers can be modulated by several environmental pollutants or pathogens and also fluctuate in response to reproductive stages and seasonal changes. In this study, adult Crassostrea gigas were sampled during summer and autumn from two lagoon and two offshore sites along the Adriatic coast of Italy in order to investigate the influence of seasonality on oxidative stress biomarkers. Trace elements load of Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Se and Zn suggests low contamination for lagoon and offshore sites. Levels of total glutathione, superoxide dismutase, catalase, glutathione peroxidases, glutathione reductase and glutathione S-transferase were analyzed in digestive gland and gills of the Pacific oysters in June, July, September and October. OsHV-1 and Vibrio aestuarianus were detected in lagoon sites, but both pathogens did not affect the biomarkers levels in both tissues. Although several biological responses were found different among the four sites in the same month, principal component analysis revealed similar trend in biomarkers levels between sites during the whole sampling period. On the other hand, a different biochemical pattern through the months emerged, suggesting that the level of oxidative stress biomarkers in both tissues may be related to seasonal progress and biological cycle of oysters sampled from the two lagoons and offshore sites along the Italian coasts of the Mediterranean Sea.

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.

Oxidative Stress and Damage Biomarkers in Clam Ruditapes decussatus Exposed to a Polluted Site: The Reliable Biomonitoring Tools in Hot and Cold Seasons

In the present study, a multi-biomarker approach was used to assess the biological effects of metal pollution in the southern lagoon of Tunis, on clam Ruditapes decussatus both in "hot" (in summer) and "cold" (in winter) seasons. Clams were collected in August 2015 and February 2016 from three sites of the lagoon and from Louza considered a reference site. The concentrations of five trace metals (cadmium, copper, iron, lead, and zinc) in the soft tissues of R. decussatus were evaluated at the sampling sites. A core of biomarkers indicative of (a) neurotoxicity (acetylcholinesterase, AChE); (b) biotransformation (glutathione S-transferase, GST); (c) oxidative stress (catalase, CAT; total glutathione peroxidase, T-GPx; total glutathione peroxidase, T-GPx; selenium-dependent glutathione peroxidase, Se-GPx; glutathione reductase, GR; superoxide dismutase, SOD) (d) lipid peroxidation (malondialdhyde, MDA level), and (e) apoptotic process (caspase 3-like, CSP3) was selected for measurements of environmental effects on the populations of clams collected from the different sampling sites. The results of metal bioaccumulation in soft tissues of Ruditapes decussatus revealed a high pollution in the South Lagoon of Tunis with spatial variation and relatively high levels at the navigation channel. Anthropogenic pollutants in the lagoon led to the activation of antioxidant defense and biotransformation enzymes to oxidative damage of the membrane and activation of apoptosis, and revealed neurotoxicity. Among this core of biomarkers, the antioxidants enzymes (CAT, SOD, GR, and GPx) were very sensitive, allowing the discrimination among sites and pointing to the navigation channel as the most impacted site in the southern lagoon of Tunis. Moreover, a significant effect of season was recorded on biomarkers responses (e.g., CAT, GR, SOD, AChE, and CSP3 activities and MDA levels) with higher levels in winter than in summer, probably influenced by the reproductive stage and food availability. Finally, the measurement of the selected core of biomarkers in the whole soft tissues of clams was considered as an integrated indicator of environmental stress. Moreover, R. decussatus proved to be a remarkable sentinel species capable to establish a reliable diagnosis of the health status of the marine environment in different areas of the southern lagoon of Tunis, both in "hot" and "cold" seasons.

Biomarker response of Mediterranean mussels Mytilus galloprovincialis regarding environmental conditions, pollution impact and seasonal effects

The complexity of seasonally and spatially variable environments, coupled with complex biological interactions, makes it difficult to pinpoint biological responses to specific environmental stressors, including chemical pollution. To disentangle causative factors and reveal biomarker responses, we applied biomarker-based multivariate approaches to 15 native populations of Mediterranean mussel Mytilus galloprovincialis in spring and autumn. In addition, we used a subset of these populations in transplant experiments between clean and polluted environments in nature and in lab mesocosms. The extent of biomarker responses in native populations is affected by season, and significantly lower variability across seasons was observed among mussels from clean than from polluted sites. Results of paired block designed transplant experiment demonstrated both regional and pollution effect, with mussels uniformly exhibiting higher responses on more impacted sites in each of the Adriatic regions. Biomarker status of mussels varied among Adriatic regions in dependence on the set of environmental variables, and between clean and polluted sites in dependence on measured concentrations of metals in mussels' tissue. Results of the mesocosm experiment revealed distinctive biomarker responses of two populations of different origin when exposed to common conditions. Multivariate description of biomarker activity and application of specific experiments allowed us to link environmental condition, exposure to pollution and seasonality to mussels' biomarker responses.

Copper effect on the biomarker state of the Mizuhopecten yessoensis tissues in the prespawning period

The aim of this study was to investigate the sensitivity of the marine scallop Mizuhopecten yessoensis to different copper concentrations (10 and 30 μgl-1) in the prespawning period. Reaction of the scallop to this effect was evaluated by a set of biomarkers, including general metabolism enzymes (acid and alkaline phosphatase activities - AcPase, ALP), and oxidative stress parameters (catalase antioxidant enzyme activity - CAT and levels of damage for DNA, lipids and proteins). Experiment results show that when copper is accumulated in tissues, enzyme activity changes are similar and have phasic character. The dynamics of these changes depends on the copper accumulation levels in tissues. Unlike enzyme reaction to copper accumulation, oxidative damage of biologic molecules changes in tissues in different ways. Copper enters into a scallop's organism, mainly through the gills, where there is a more expressed reaction of biomarkers compared to the digestive gland.

Biomarkers responses in Manila clam, Ruditapes philippinarum after single and combined exposure to mercury and benzo[a]pyrene

Physiological and biochemical responses in bivalves exposed to pollutants have proved a valuable tool to assess the health of organisms in aquatic ecosystems. The single and combined effects of mercury (Hg²⁺, 2 and 10 μg/L) and benzo[a]pyrene (BaP, 3 μg/L) on physiological and biochemical biomarkers in Manila clam, Ruditapes philippinarum were evaluated. Results showed that significant higher oxygen consumption (OR) and ammonia-N excretion rates (NR) together with significant lower ingestion rates (IR) were observed for the 10 μg/L Hg²⁺ or 3 μg/L BaP treatments compared to controls (P < 0.05). However, clam NR decreased significantly in response to the binary mixtures of 10 μg/L Hg²⁺ and 3 μg/L BaP (P < 0.05). Moreover, the levels of superoxide dismutase (SOD), catalase (CAT), glutathione-s-transferases (GSTs), glutathione (GSH), acetylcholinesterase (AChE) and malondialdehyde (MDA) in the hepatopancreas of clams were induced substantially, whereas glycogen (GLY) contents were suppressed dramatically after Hg²⁺ and BaP exposure. Additionally, the integrated biomarker response (IBR) values measured showed significant increases in combination treatments and they were much higher than that in the Hg²⁺ treatment. This study will provide further information on the defense mechanism in the Manila clam after exposure to marine pollutants and may help evaluate the quality of the aquatic environment.

Comprehensive study of sulfamethoxazole effects in marine mussels: Bioconcentration, enzymatic activities and metabolomics

Antibiotics accumulation in aquatic organisms may be of great concern from an ecological point of view but also from a human perspective, especially when they are accumulated in edible animals like marine mussels. In this work, mussels (Mytilus galloprovincialis) were exposed to sulfamethoxazole antibiotic (SMX) at 10 µg/L during 96 h, followed by 24 h of depuration. The experiment was carried out at summer and winter conditions. SMX showed a bioconcentration factor in mussel of 1.5 L/kg (dry weight) and 69% of the compound was eliminated from the organism in 24 h. The metabolomics approach revealed alterations in amino acids levels (aspartate, phenylalanine, valine and tryptophan) pinpointing disturbances in osmotic regulation and energy metabolism. Besides, the levels of some nucleotides (guanosine and inosine) and a carboxylic acid were also affected. However, SMX exposed mussels did not show any significant alteration in the enzymatic activities related to the xenobiotic metabolism and oxidative stress. Moreover, some of the changes observed in mussel's metabolites suggested alterations in mussel's organoleptic characteristics that can affect its quality as seafood commodity. Overall, our results showed that SMX exposure to marine mussels may have ecological implications by provoking sub-lethal effects to exposed organisms. Nevertheless, no risk for consumers derived from mussel ingestion is expected due to the low bioconcentration capacity of SMX and fast depuration in this seafood type.

The impact of ocean acidification on the gonads of three key Antarctic benthic macroinvertebrates

CO₂ atmospheric pressure is increasing since industrial revolution, leading to a lowering of the ocean surface water pH, a phenomenon known as ocean acidification, with several reported effects on individual species and cascading effects on marine ecosystems. Despite the great amount of literature on ocean acidification effects on calcifying organisms, the response of their reproductive system still remains poorly known. In the present study, we investigated the histopathological effects of low pH on the gonads of three key macroinvertebrates of the Terra Nova Bay (Ross Sea) littoral area: the sea urchin Sterechinus neumayeri, the sea star Odontaster validus and the scallop Adamussium colbecki. After 1 month of exposure at control (8.12) and reduced (7.8 and 7.6) pH levels, we dissected the gonads and performed histological analyses to detect potential differences among treatments. Results showed significant effects on reproductive conditions of A. colbecki and S. neumayeri, while O. validus did not show any kind of alteration. Present results reinforce the need to focus on ocean acidification effects on soft tissues, particularly the gonads, whose damage may exert large effects on the individual fitness, with cascading effects on the population dynamic of the species.

Seasonal and spatial variations in biomarker baseline levels within Arctic populations of mussels (Mytilus spp.)

Climate change and pollution resulting from human activities in the Arctic require reliable monitoring systems in sentinel species. Mytilus spp. are used as sentinel species all around the world. The use of Mytilus spp. in environmental monitoring requires knowledge about natural variations in pollution biomarkers. Seasonal variations in baseline levels of biomarkers were studied over a year in the mussels from both upper and lower littoral zones in Rakkfjorden, Norway, as they underwent their annual reproductive cycle. Spatial variations of these biomarker baseline levels were measured in five mussel populations within a 60-km radius from Rakkfjorden to investigate universality of the results from the specific population of Rakkfjorden at a regional scale. Seasonal variations in biomarker baseline levels were revealed and seemed to be related to the reproductive state of the mussels and the tidal zone. The mussels appeared to be more sensitive to oxidative stress during gametogenesis in autumn and winter, when having lower lysosome membrane stability and lower baseline levels of antioxidant biomarkers. An increase in baseline levels of these biomarkers was reported during spawning in spring, however, it was not possible to reveal whether these changes were due to spawning, or to a higher metabolic activity in mussels in response to elevated water temperature and food abundance. The differences between the tidal zones were reflected in reduced size of the mussels from the upper littoral zone, their late spawning in the season and increased baseline levels of antioxidant biomarkers during the coldest month, indicating a more challenging environment in the upper littoral zone. The spatial study indicated that the biomarker baseline levels measured in Rakkfjorden were no different from the levels measured in the mussels from five other sites and thus, are representative for mussels on a regional scale.

Metabolomic responses of mussel Mytilus galloprovincialis to fluoranthene exposure under different nutritive conditions

Biomarkers are useful tools to assess biological effects of pollutants that are extensively used in monitoring programs to assess ecosystem health. However, they are strongly affected by mussel physiological state, especially nutritive status, which has led to the search of new biological indicators of chemical pollutants exposition. Environmental metabolomics is an approach for examining the metabolic responses (measurement of low molecular weight endogenous metabolites) of an organism to both natural and anthropogenic stressors that can occur in its environment. The aim of the present work was to assess the effect of the polycyclic aromatic hydrocarbon fluoranthene (FLU) exposure on the metabolomic profiles of mussel digestive glands under different nutritive conditions. To achieve this objective, mussels were reared, for a period of 56 days, under three different food rations in order to obtain a gradient of nutritive status (negative, zero and positive energy balance), and after that, they were exposed, during 3 weeks, to a nominal concentration of 3 μg FLU L^-1. A total of 43 metabolites, including aminoacids (Ala, Val, Leu, Ile, etc.), energy metabolism related metabolites (ATP, AMP, etc.), organic osmolytes (taurine, etc.), redox metabolism (GSH, NADP+) and nucleotides, were identified and quantified in the digestive glands of the mussels. Principal Component Analysis (PCA) defined two principal components (PC1 and PC2) that explained 55.6% of the total variance, although the first component explains more than 80% of this variance, this being related to the mussel nutritive condition. The effect of the toxicant, explained by the PC2, is similar to that produced under conditions of food restriction, which masks the effect of the toxicant under these conditions. As the feeding conditions are more favorable, the toxic effect becomes more apparent. Therefore, the great influence of nutritive condition on mussel metabolome implies a handicap for the use of metabolomic biomarkers, as previously demonstrated for biochemical and other molecular biomarkers, in large-scale monitoring programs in which several food conditions coexist with pollution levels.

Using mussel as a global bioindicator of coastal microplastic pollution

The ubiquity and high bioavailability of microplastics have an unknown risk on the marine environment. Biomonitoring should be used to investigate biotic impacts of microplastic exposure. While many studies have used mussels as indicators for marine microplastic pollution, a robust and clear justification for their selection as indicator species is still lacking. Here, we review published literature from field investigations and laboratory experiments on microplastics in mussels and critically discuss the suitability and challenges of mussels as bioindicator for microplastic pollution. Mussels are suitable bioindicator for microplastic pollution because of their wide distribution, vital ecological niches, susceptibility to microplastic uptake and close connection with marine predators and human health. Field investigations highlight a wide occurrence of microplastics in mussels from all over the world, yet their abundance varies enormously. Problematically, these studies are not comparable due to the lack of a standardized approach, as well as temporal and spatial variability. Interestingly, microplastic abundance in field-collected mussels is closely related to human activity, and there is evidence for a positive and quantitative correlation between microplastics in mussels and surrounding waters. Laboratory studies collectively demonstrate that mussels may be good model organisms in revealing microplastic uptake, accumulation and toxicity. Consequently, we propose the use of mussels as target species to monitor microplastics and call for a uniform, efficient and economical approach that is suitable for a future large-scale monitoring program.

Single contaminant and combined exposures of polyethylene microplastics and fluoranthene: accumulation and oxidative stress response in the blue mussel, Mytilus edulis

The microplastic "vector effect" has received increasing attention. The aim of this study was to investigate the influence of polyethylene microplastic beads (PE MP) on accumulation and associated oxidative stress responses attributed to fluoranthene (Flu) in blue mussels, Mytilus edulis. Blue mussels were exposed for 96 h to four treatment groups: Flu-only, MP-only, Flu and MP coexposure, and Flu-incubated MP. Treatments were conducted at a low and high concentration (50 μg/L and 100  Flu μg/L and 100, and 1000 MP/mL). Results demonstrated that in both the gill and digestive gland, coexposure did not markedly affect Flu uptake, but this treatment significantly decreased tissue Flu concentrations. Antioxidant responses including activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (GPx), and levels of total glutathione (GSH) in both gills and digestive glands were significantly altered suggesting a perturbation of redox state induced by the exposure conditions. Although individual biomarkers varied, the biomarker profile enabled certain generalizations to be made. Antioxidant responses occurred more likely in gill tissue than in digestive gland. Individual contaminant exposures to Flu or MP led to varying responses, but coexposures and incubated exposures did not result in additive or synergistic effects. Exposure concentrations (i.e., low or high treatments) were not a consistent a predictor of response; and the internal Flu dose did not consistently predict outcome of various biomarkers. Importantly, MP-only exposure appeared to be capable of eliciting direct effects on the oxidative stress system as demonstrated by the activities of CAT and GPx. These findings warrant further investigation.

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.