Application of a battery of biomarkers in mussel digestive gland to assess long-term effects of the Prestige oil spill in Galicia and Bay of Biscay: tissue-level biomarkers and histopathology

Nylon microfibers develop a distinct plastisphere but have no apparent effects on the gut microbiome or gut tissue status in the blue mussel, Mytilus edulis

Ingestion of microplastics (MP) by suspension-feeding bivalves has been well-documented. However, it is unclear whether exposure to MP could damage the stomach and digestive gland (gut) of these animals, causing ramifications for organism and ecosystem health. Here, we show no apparent effects of nylon microfiber (MF) ingestion on the gut microbiome or digestive tissues of the blue mussel, Mytilus edulis. We exposed mussels to two low concentrations (50 and 100 particles/L) of either nylon MF or Spartina spp. particles (dried, ground marsh grass), ca. 250-500 μm in length, or a no particle control laboratory treatment for 21 days. Results showed that nylon MF, when aged in coarsely filtered seawater, developed a different microbial community than Spartina spp. particles and seawater, however, even after exposure to this different community, mussel gut microbial communities resisted disturbance from nylon MF. The microbial communities of experimental mussels clustered together in ordination and were similar in taxonomic composition and measures of alpha diversity. Additionally, there was no evidence of damage to gut tissues after ingestion of nylon MF or Spartina spp. Post-ingestive particle processing likely mediated a short gut retention time of these relatively large particles, contributing to the negligible treatment effects.

The influence of temperature on the effects of lead and lithium in Mytilus galloprovincialis through biochemical, cell and tissue levels: Comparison between mono and multi-element exposures

Lead (Pb) and lithium (Li) are metals which have been detected in the environment and, at high concentrations, can induce toxic effects that disturb the growth, metabolism or reproduction of organisms along the entire trophic chain. The impacts of these metals have scarcely been investigated using marine bivalves, especially when acting as a mixture. The present study aimed to investigate the influence of temperature on the ecotoxicological effects caused by Pb and Li, acting alone and as a mixture, on the mussel species Mytilus galloprovincialis after 28 days of exposure. The impacts were evaluated under actual (17 °C) and projected (+4 °C) warming conditions, to understand the influence of temperature rise on the effects of the metals (both acting alone or as a mixture). The results obtained showed that the increased temperature did not influence the accumulation of metals. However, the biomarkers evaluated showed greater responses in mussels that are exposed to metals under increased temperature (21 °C). The IBR index showed that there is a comparable toxic effect of Li and Pb separately, while exposure to a mixture of both pollutants causes a significantly higher stress response. Overall, the results obtained revealed that temperature may cause extra stress on the mussels and exposure to the metal mixture caused the greatest impacts compared to each metal acting alone.

Integrated assessment of biological responses to pollution in wild mussels (Mytilus edulis) from subarctic and arctic areas in the Norwegian sea

North Atlantic and Arctic Oceans contain large amount of undiscovered oil and gas reserves. Therefore threat of oil spills and its hazardous ecological consequences are of great importance to the marine environment. Although mussels (Mytilus sp.) respond clearly to contaminants, biomarkers have shown variability linked to biological and environmental changes. In order to help avoiding misinterpretation of biological responses the aim of this study was to reveal the effect of natural variability in the responsiveness to pollution of a battery of cell and tissue-level biomarkers in mussels. Mussels were collected in relatively non-impacted and potentially impacted sites at ports and the vicinity of a waste water treatment plant in Trondheim and Tromsø in autumn of 2016. Although the battery of biomarkers used herein proved to be useful to discriminate impacted and non-impacted mussel populations, some confounding factors altering the biological responses were identified. Geographical/latitudinal factors seemed to be critical regarding the reproductive cycle, reserve material storage and the prevalence of parasites such as Gymnophallus cf. Bursicola trematodes. Mussels from the reference site in Tromsø displayed general stress responses at different levels, which could be influenced by the pathogenic effect of the Gymnophallus cf. Bursicola trematode and by a more advanced gametogenic developmental stage compared to the mussels from Trondheim, which could lead to misinterpretation of the reasons behind the measured stress levels in those mussels. Despite these confounding effects, the use of integrative tools such as IBR index helped to discriminate mussel populations from chemically impacted and non-impacted sites. Overall, this work serves as an anchor point both as a reference of the baseline level values of the analyzed endpoints in the studied geographical area and time of the year, and as an indication of the potential extent of the environmental confounding factors in monitoring programs causing stress on the analyzed mussel populations.

Fate and effects of graphene oxide alone and with sorbed benzo(a)pyrene in mussels Mytilus galloprovincialis

Graphene oxide (GO) has gained a great scientific and economic interest due to its unique properties. As incorporation of GO in consumer products is rising, it is expected that GO will end up in oceans. Due to its high surface to volume ratio, GO can adsorb persistent organic pollutants (POPs), such as benzo(a)pyrene (BaP), and act as carrier of POPs, increasing their bioavailability to marine organisms. Thus, uptake and effects of GO in marine biota represent a major concern. This work aimed to assess the potential hazards of GO, alone or with sorbed BaP (GO+BaP), and BaP alone in marine mussels after 7 days of exposure. GO was detected through Raman spectroscopy in the lumen of the digestive tract and in feces of mussels exposed to GO and GO+BaP while BaP was bioaccumulated in mussels exposed to GO+BaP, but especially in those exposed to BaP. Overall, GO acted as a carrier of BaP to mussels but GO appeared to protect mussels towards BaP accumulation. Some effects observed in mussels exposed to GO+BaP were due to BaP carried onto GO nanoplatelets. Enhanced toxicity of GO+BaP with respect to GO and/or BaP or to controls were identified for other biological responses, demonstrating the complexity of interactions between GO and BaP.

Biomarker responses in mussels (Mytilus trossulus) from the Baltic Sea exposed to water-accommodated fraction of crude oil and a dispersant at different salinities

Oil spills pose significant environmental risks, particularly in cold seas. In the Baltic Sea, the low salinity (from 0 to 2 up to 18) affects the behaviour of the spilled oil as well as the efficiency and ecological impacts of oil spill response methods such as mechanical collection and the use of dispersants. In the present study, mussels (Mytilus trossulus) were exposed under winter conditions (5 °C) to the water-accommodated fraction (WAF) of Naphthenic North Atlantic crude oil prepared by mechanical dispersion or to the chemically enhanced fraction (CEWAF) obtained using the dispersant Finasol OSR 51 at salinities of 5.6 and 15.0. Especially at the lower salinity, high bioaccumulation of polycyclic aromatic hydrocarbons was recorded in mussels in the CEWAF treatments, accompanied by increased biomarker responses. In the WAF treatments these impacts were less evident. Thus, the use of dispersants in the Baltic Sea still needs to be carefully considered.

Assessment of mercury and lead contamination using the bivalve Anadara tuberculosa (Arcidae) in an estuary of the Colombian Pacific

Buenaventura Bay is considered the main estuary on the Pacific coast of Colombia, because of port and industrial activities. Mining and agriculture are major sources of contamination in the estuary. This study used the bivalve Anadara tuberculosa to evaluate the presence of mercury and lead in the Dagua River estuary (Colombia), one of the main tributaries coming into the bay. Five samplings for sediments and six for tissues of A. tuberculosa were carried out between 2016 and 2017. Additionally, a series of bioassays were conducted to determine its ability to bioaccumulate metals. A mean mercury concentration of 0.57 ± 0.74 mg*kg^-1 and lead concentration of 0.87 ± 0.68 mg*kg^-1 in sediment were found. Bioassays allowed us to conclude that at low mercury exposure concentrations (0.25 mg*kg^-1), lesions are generated in animal tissue, mainly in sexual cells. The high concentrations of mercury found in organisms exceed the maximum permitted concentration established in Colombia. In addition, the contamination factors for mercury and lead were considered very high. This research aims at contributing to the use of Anadara tuberculosa, as prospective bioindicator for pollution biomonitoring in mangrove coastal ecosystems.

Responses of microRNA in digestive glands of mussel Mytilus galloprovincialis exposed to polystyrene nanoplastics

Polystyrene nanoplastics (PS-NPs) are typical accumulated nanoplastics in the marine environment and organisms, and have strong potential risks to marine ecological environment and human health. MiRNAs could respond to and participate in the response process of environmental stressors. However, the response of miRNAs to nanoplastics has not been fully explored. In this study, miRNA responses of digestive glands in mussels Mytilus galloprovincialis treated by 200 nm PS-NPs (20, 200, 2000 μg/L) for 7 days were characterized by BGISEQ-500 deep sequencing and bioinformatics analysis, along with histopathological quantification with planimetric parameters on hematoxylin and eosin (H&E) staining. Results showed that one novel miRNA (novel_mir63) and seven known miRNAs (miR-34_2, miR-34_5, miR-281_8, let-7-5p_6, miR-10, miR-124, miR-29b-3p) were significantly (adjusted P-value < 0.05) differentially expressed after PS-NPs treatments, and most of them were down-regulated expect for novel_mir63 and miR-34_2. Function analysis of target genes corresponding to these differentially expressed miRNAs indicated that PS-NPs disturbed the process related to metabolism, aging, cardiac function, neural excitation, and repairment. Among them, acetyl-CoA C-acetyltransferase and purine metabolism pathway played vital connection roles. Meanwhile, significantly morphology changes of digestive tubes obtained from H&E stained sections also implied severely disrupted metabolic capability in digestive glands, reflected by significantly increased mean diverticular radius (MDR) and mean luminal radius (MLR) values and the ratio of MLR to mean epithelial thickness (MET), and significantly decreased MET value and MET/MDR. Overall, these findings have revealed new characterization of miRNAs and their target genes in mussel M. galloprovincialis under PS-NPs stress, and provide important clues to further elucidate the toxicity mechanisms of PS-NPs.

Gender influences molecular and histological biomarkers in mature oysters Crassostrea gasar (Adanson, 1757) after pyrene exposure

Oysters are frequently used as sentinel organisms for monitoring effects of contaminants due to their sessile, filtering habits and bioaccumulation capacity. These animals can show elevated body burden of contaminants, such as pyrene (PYR). PYR can be toxic at a molecular level until the whole oyster, which can show reproductive and behavioral changes. Considering that biologic parameters, such as gender or reproductive stage can interfere in the toxic effects elicited by contaminants uptake, the aim of this study was to evaluate some molecular and histological responses in females and males of oyster Crassostrea gasar exposed to PYR (0.25 and 0.5 μM) for 24 h at the pre-spawning stage. PYR concentrations were analyzed in water and in tissues of female and male oysters. Gene transcripts related to biotransformation (CYP3475C, CYP2-like, CYP2AU1, CYP356A, GSTO-like, GSTM-like, SULT-like), stress (HSP70), and reproduction (Vitellogenin, Glycoprotein) were quantified in gills. In addition, histological analysis and histo-localization of CYP2AU1 mRNA transcripts in gills, mantle and digestive diverticulum were carried out. Females and males in pre-spawning stage bioconcentrated PYR in their tissues. Males were more sensitive to PYR exposure. CYP2AU1 transcripts were higher in males (p < 0.05), as well as tubular atrophy was observed only in males exposed to PYR (p < 0.05). As expected, vitellogenin transcripts were lower in males (p < 0.05). Given these results, it is suggested that levels of CYP2AU1 be a good biomarker of exposure to PYR in oyster C. gasar and that it is important to consider the gender for the interpretation of biomarker responses.

Toxicopathic effects of lithium in mussels

The rising use of lithium (Li) in industrial processes, modern technology and medicine has generated concerns in the scientific community, in particular its potential impact on the environment. Unfortunately, there is only scarce information concerning the toxicity of lithium in marine organisms. The objective of this study is to determine the toxicity of Li using Mytilus galloprovincialis as model organism, based on acute and sublethal toxicity tests. In the first experiment, mussels were exposed for 9 days to a range of acute concentrations of Li (0, 2, 5, 13, 34, 89, 233 and 610 mg/L Li) in order to find the median lethal concentration. In the sublethal experiment, mussels were exposed to environmentally relevant concentrations of Li (0, 0.1, 1, 10 mg/L Li) for 21 days. Digestive gland and gonad samples were taken at day 0, 1, 7 and 21 for histopathological analysis. Samples of the whole mussels were taken for chemical analysis at day 0 and after 21 days. Results showed that M. galloprovincialis had a LC50 value of 153 mg/L Li after 9 days of exposure. Lower concentrations (environmentally relevant), led to Li bioaccumulation in a dose-dependent manner and histopathological effects in a time-dependent manner. Atrophy of the digestive alveoli epithelium and degeneration of the digestive gland were observed after 21 days of exposure. These findings open new perspectives for the understanding of the toxic effects of Li on marine organisms and evidence the need for further long-term research at different levels of biological organizations.

Variability and distribution of parasites, pathologies and their effect on wild mussels (Mytilus sp) in different environments along a wide latitudinal span in the Northern Atlantic and Arctic Oceans

Histopathological examination in mussels can provide useful information for the diagnosis of ecosystem health status. The distribution of parasites in mussels can be conditioned by several environmental factors, including mussels collecting sites or the presence/absence of other species necessary to complete the complex life cycle of certain parasites. Thus, these variables could not only govern the parasitic burden of mussels but also the presence of pathologies associated to parasitism. The aim of this study was to identify the histopathological alterations which could be indicative of a health status distress along a wide latitudinal span in the Northern Atlantic and Arctic Oceans in mussels of two size-classes sampled in clean and impacted sites. A latitudinal gradient is clearly observed in gamete developmental stages as northern and southern mussels presented different conditions at the same period. Furthermore, mussels of the same size in different latitudes presented differences in the reproductive cycle and the appearance of related pathologies, which probably meant the age of individuals was different. In addition, specific parasitic profiles ruled by latitudinal conditions and the settlement of mussels in the shore (horizontal/vertical) have been demonstrated to be significantly influential in the health condition of mussels. Furthermore, the present work provides the first histological description of Gymnophallus cf. bursicola parasite causing a considerable host response in Tromsø and Iceland plus the report of grave histopathological status that included high prevalence of granulocytomas in Scotland and Germany.

Accumulation, Depuration, and Biological Effects of Polystyrene Microplastic Spheres and Adsorbed Cadmium and Benzo(a)pyrene on the Mussel Mytilus galloprovincialis

Filter feeders are target species for microplastic (MP) pollution, as particles can accumulate in the digestive system, disturbing feeding processes and becoming internalized in tissues. MPs may also carry pathogens or pollutants present in the environment. This work assessed the influence of polystyrene (PS) MP size and concentration on accumulation and depuration time and the role of MPs as vectors for metallic (Cd) and organic (benzo(a)pyrene, BaP) pollutants. One-day exposure to pristine MPs induced a concentration-dependent accumulation in the digestive gland (in the stomach and duct lumen), and after 3-day depuration, 45 µm MPs appeared between gill filaments, while 4.5 µm MPs also occurred within gill filaments. After 3-day exposure to contaminated 4.5 µm MPs, mussels showed increased BaP levels whilst Cd accumulation did not occur. Here, PS showed higher affinity to BaP than to Cd. Three-day exposure to pristine or contaminated MPs did not provoke significant alterations in antioxidant and peroxisomal enzyme activities in the gills and digestive gland nor in lysosomal membrane stability. Exposure to dissolved contaminants and to MP-BaP caused histological alterations in the digestive gland. In conclusion, these short-term studies suggest that MPs are ingested and internalized in a size-dependent manner and act as carriers of the persistent organic pollutant BaP.

Assessment of seasonal and spatial variation responses of integrated biomarkers in two marine sentinel bivalve species: Agadir Bay (Southern of Morocco)

The present study aims to assess the effects of contamination of the Agadir bay coasts using bivalves as a biomonitoring sentinel species. Seasonal variations of biochemical composition in terms of total protein content and oxidative stress biomarkers including glutathione-S-transferase, malondialdehyde, catalase and acetylcholinesterase were evaluated in the soft tissues of Scrobicularia plana and Donax trunculus specimens. The latter were collected from two sites in Agadir bay during two-year span (2018-2020). The Integrated Biomarker Response Index (IBR) was performed to classify the stress response in both species and to assess the level of exposure to xenobiotics. The data showed maximum annual values of acetylcholinesterase and malondialdehyde for Donax trunculus in Agadir beach (AG) with 6.25 nmol/mn/mg and 3 nmol/mg of protein, respectively. Those of catalase and glutathione-S-transferase for Scrobicularia plana in Oued Souss estuary (OS) were of 4.41 μmol/mn/mg and 14.43 nmol/mn/mg of protein, respectively. The studied species are considered good indicators in aquatic ecosystems.

Effects of long-term exposure of Mytilus galloprovincialis to thiacloprid: A multibiomarker approach

Thiacloprid is a neonicotinoid insecticide widely exploited in agriculture and easily mobilized towards aquatic environments by atmospheric agents. However, little information about its toxicological effects on aquatic invertebrate bioindicators is available. In this study, specimens of the mussel Mytilus galloprovincialis were exposed to thiacloprid at environmental (4.5 μg L^-1) and 100 times higher than environmental (450 μg L^-1) concentrations for 20 days. Thiacloprid affected haemolymph biochemical parameters, cell viability in the digestive gland, antioxidant biomarkers and lipid peroxidation in the digestive gland and gills at environmentally relevant concentrations (4.5 μg L^-1). In addition, thiacloprid exposure caused histological damage to the digestive gland and gills. Interestingly, the pesticide was detected at levels equal to 0.14 ng g^-1 in the soft tissues of sentinels exposed for 20 days to 450 μg L^-1 thiacloprid in seawaterμ. Due to its harmful potential and cumulative effects after long-term exposure of M. galloprovincialis, thiacloprid may pose a potential risk to nontarget aquatic organisms, as well as to human health. This aspect requires further in-depth investigation.

Long-term exposure of marine mussels to paracetamol: is time a healer or a killer?

Pharmaceuticals pose a major threat to the marine environment, and several studies have recently described their negative effects on marine organisms. Pharmaceutical compounds are constantly being released into aquatic ecosystems, and chronic exposure, even at low concentrations, may have a major impact on marine organisms. The purpose of the present study is to evaluate the biological changes induced by one of the most widely used pharmaceuticals-paracetamol-in the blue mussel Mytilus edulis, after a long-term exposure at environmentally relevant concentrations. We present our data alongside and in comparison with results from a previous short-term exposure, to demonstrate the significance of exposure period on the effects of paracetamol in adult blue mussels. After 24 days of laboratory exposure, seven potential target genes were selected to examine toxicological effects in mussels' gonads and possible disruptive effects on reproductive processes. The results show the modulation of some important reproduction-related genes: estrogen receptor-2 (ER2), vitelline envelope zona pellucida domain-9 (V9), and vitellogenin (VTG). Variations in mRNA expression of four other genes involved in apoptosis (HSP70, CASP8, BCL2, and FAS) are also highlighted. Histopathological alterations caused by paracetamol, together with neutral red retention time response in mussels' hemocytes, are presented herein. Overall, this study highlights the exacerbated effects of low concentration of paracetamol after chronic exposure, similar to the damage induced by higher concentrations in a short exposure scenario, thus emphasizing the importance of length of exposure period when studying the effects of this substance. Additionally, this study also discusses the potential of paracetamol to inflict several major changes in the reproductive system of mussels and thus possibly affect the survival of populations.

Depicting an energetic chain involved in physiological responses of blue mussel Mytilus edulis coping with BDE-47 exposure

Depiction on an energetic chain in terms of assimilation, allocation and consumption as well as the linkage between energetic alteration and physiological process was performed in blue mussel Mytilus edulis coping with tetrabromodiphenyl ether (BDE-47) based on a 21-day bioassay to shed light on the possible mechanism from energetic perspective. The filtration was hindered along with BDE-47 concentration increment and the influence of digestion was suggested according to the combination of the digestive enzymatic activities' alteration and digestive gland tissue impairment, both of which decided the energy availability reduction. Energy consumption indicated by the electron transport system activity was firstly inhibited while was greatly increased with BDE-47 increment, and the cellular energy allocation and adenylate pool were decreased simultaneously. An energetic chain was thus depicted: it tended to reduce energy absorption, elevate the energy consumption and decrease the energy metabolism with BDE-47 exposure, and M. edulis adopted the energetic strategy with variation regarding to the stressing level, suggesting as the preference switched from protein utilization to lipid utilization with the concentration increment. A consistence was observed in index of growth and survival with the change of energy allocation, inferring the energetic involvement in sustaining the viability of the mussel.

Immunological Responses of Marine Bivalves to Contaminant Exposure: Contribution of the -Omics Approach

The increasing number of data studies on the biological impact of anthropogenic chemicals in the marine environment, together with the great development of invertebrate immunology, has identified marine bivalves as a key invertebrate group for studies on immunological responses to pollutant exposure. Available data on the effects of contaminants on bivalve immunity, evaluated with different functional and molecular endpoints, underline that individual functional parameters (cellular or humoral) and the expression of selected immune-related genes can distinctly react to different chemicals depending on the conditions of exposure. Therefore, the measurement of a suite of immune biomarkers in hemocytes and hemolymph is needed for the correct evaluation of the overall impact of contaminant exposure on the organism's immunocompetence. Recent advances in -omics technologies are revealing the complexity of the molecular players in the immune response of different bivalve species. Although different -omics represent extremely powerful tools in understanding the impact of pollutants on a key physiological function such as immune defense, the -omics approach has only been utilized in this area of investigation in the last few years. In this work, available information obtained from the application of -omics to evaluate the effects of pollutants on bivalve immunity is summarized. The data shows that the overall knowledge on this subject is still quite limited and that to understand the environmental relevance of any change in immune homeostasis induced by exposure to contaminants, a combination of both functional assays and cutting-edge technology (transcriptomics, proteomics, and metabolomics) is required. In addition, the utilization of metagenomics may explain how the complex interplay between the immune system of bivalves and its associated bacterial communities can be modulated by pollutants, and how this may in turn affect homeostatic processes of the host, host–pathogen interactions, and the increased susceptibility to disease. Integrating different approaches will contribute to knowledge on the mechanism responsible for immune dysfunction induced by pollutants in ecologically and economically relevant bivalve species and further explain their sensitivity to multiple stressors, thus resulting in health or disease.

What does the freshwater clam, Corbicula largillierti, have to tell us about chlorothalonil effects?

Chlorothalonil (CLT) is a broad spectrum, and non-systemic fungicide applied in foliar structures to prevent and treat pathogens. This compound reaches to aquatic environments and affects the biota. In this context, the main goal of this study was to assess the effects of CLT at biochemical, tissular, and individual levels of biological organization using the invasive bivalve Corbicula largillierti as a bioindicator species. Clams were exposed to different sublethal concentrations (0, 10, 20 and 50 µg. L^-1 CLT) for 96 h. At biochemical level, the enzymatic activity (Glutathione-s-Transferase, Catalase, Acetyl-, Butiryl- and Carboxyl-esterases) and lipid peroxidation were measured in gills and the visceral mass. Also, the digestive gland morphometry through quantitative histological indexes was registered at the tissular level. Finally, filtering activity and burial behavior at the individual level were measured. At the highest CLT concentration, the most significant changes were observed in enzymatic activity (except for butyrylcholinesterase), lipid peroxidation and in digestive gland morphometry. It was also registered increases of the filtering activity and the latency time to burial. Most of the biomarkers assessed showed significant responses under CLT exposure. Therefore, taking into account that C. largillierti was affected by CLT, it can be expected that other species could be in a potential risk if this fungicide is present in freshwater systems.

Cell and tissue level responses in mussels Mytilus galloprovincialis dietarily exposed to PVP/PEI coated Ag nanoparticles at two seasons

Silver nanoparticles (Ag NPs) are present in numerous consumer products due to their antimicrobial and other unique properties, thus concerns about their potential input into aquatic ecosystems are increasing. Toxicity of Ag NPs in waterborne exposed aquatic organisms has been widely investigated, but studies assessing the potential toxic effects caused after ingestion through the food web, especially at low realistic concentrations, remain scarce. Moreover, it is not well known whether season may influence toxic effects of Ag NPs. The main objective of this study was to determine cell and tissue level responses in mussels Mytilus galloprovincialis dietarily exposed to poly-N-vinyl-2-pirrolidone/polyethyleneimine (PVP/PEI) coated 5 nm Ag NPs for 1, 7 and 21 days both in autumn and spring. Mussels were fed every day with microalgae Isochrysis galbana exposed for 24 h to a low dose (1 μg Ag/L Ag NPs) in spring and to a higher dose (10 μg Ag/L Ag NPs) in spring and autumn. Mussels fed with microalgae exposed to the high dose accumulated Ag significantly after 21 days in both seasons, higher levels being measured in autumn compared to spring. Intralysosomal metal accumulation measured in mussel digestive gland and time- and dose-dependent reduction of mussels health status was similar in both seasons. DNA strand breaks increased significantly in hemocytes at both exposure doses along the 21 days in spring and micronuclei frequency showed an increasing trend after 1 and 7 days of exposure to 1 μg Ag/L Ag NPs in spring and to 10 μg Ag/L in both seasons. Values decreased after 21 days of exposure in all the cases. In conclusion, PVP/PEI coated 5 nm Ag NPs ingested through the food web were significantly accumulated in mussel tissues and caused adverse cell and tissue level effects both in autumn and in spring.

Surviving under pollution stress: Antibacterial and antifungal activities of the Oyster species (Magallana bilineata and Magallana cuttackensis)

Antibiotic effectively controls the bacterial and fungal infections. Pathogens developing multi-drug resistance are a global health concern, which necessitate developing new molecules to overcome the resistance dilemma. This study explores the intrinsic ability of marine oysters synthesizing bioactive compounds. The tissue extracts prepared in n-hexane from two oysters, Magallana bilineata and Magallana cuttackensis compared for broad spectral antimicrobial activates against the fungal, Gram positive and negative pathogens. Regardless, both the species tolerated the same pollution indices; the M. bilineata exhibits stronger antimicrobial activities as compared to M. cuttackensis. M. bilineata potentially inhibited the bacterial growth with minimal inhibitory concentration (0.75-20 μg/ml) and fungal pathogens (0.75-5 μg/ml) as compared to ciprofloxacin and miconazole. Inhibitory potential complimented with reduce bactericidal and fungicidal concentrations required to observed susceptible zone of inhibition (ZOI). The inhibition augmented with increased antimicrobial index (AMI) and total activity index (TAI) against the human pathogen than those of M. cuttackensis. It is widely acknowledged that there is a need to develop novel antimicrobial agents to minimize the threat of emerging multiple antimicrobial resistant pathogens. Therefore, the oysters surviving in the pollution stress modulate the physiological and immune response may exploit to develop potential antibiotics.

Sex and sex-related differences in gamete development progression impinge on biomarker responsiveness in sentinel mussels

In marine pollution monitoring, the biomarkers recorded in sentinel organisms are influenced by natural confounding factors that may jeopardise their interpretation. Among these confounding factors, little is known about the influence of sex along the annual reproductive cycle. The present investigation aims at contributing to understand how sex and sex-related differences in gamete development progression impinge on biomarker baseline values and on biomarker responsiveness to pollution in sentinel mussels. Mussels (Mytilus galloprovincialis) were collected from a relatively clean locality and from a chronically polluted site in the Basque Coast (Bay of Biscay) in January, April, August and November. Sex and gametogenesis stages were determined for each mussel. Tissue concentration of metals and PAHs was analysed. A battery of biomarkers was investigated: cytochrome c oxidase, pyruvate kinase and phosphoenolpyruvate carboxykinase enzyme activities; levels of protein carbonyls, malondialdehyde and 4-hydroxy-2-nonenal; lysosomal enlargement and membrane stability; intracellular neutral lipid accumulation; cell type composition and thinning of the digestive gland epithelium; and survival-in-air. Sex- and reproductive stage-related differences were found in bioaccumulation and in the values and responsiveness of most of the biomarkers. However, the patterns of sex-related differences were not consistent across all biomarkers. The differences in the biomarker responses between females and males also depended on the season, reflecting the progression of the gametogenesis cycle. Thus, selecting mussels of one specific sex does not seem to be a crucial requisite to carry out biomarker-based monitoring; yet, it is highly recommended to identify sex condition and gamete developmental stage of each mussel to test for the potentially confounding effects of sex, reproductive status and sex-related variability along the reproductive cycle.

Assessing the Effect of Contaminated and Restored Marine Sediments in Different Experimental Mesocosms Using an Integrated Approach and Mytilus galloprovincialis as a Model

The research presented here was conducted to ascertain the effectiveness of recovery technologies in remediating a compromised marine environment. The multidisciplinary approach aims to integrate traditional chemical-physical analysis and to assess the biological parameters of Mytilus galloprovincialis within different experimental mesocosms (W, G, and B). In particular, this system was designed to reproduce sediment resuspension in a marine environment, which is thought to be one cause of contaminant release. The study combined morphological and ultrastructural observations with DNA damage assessment and mRNA expression of those genes involved in cellular stress responses. The tissues of mussels maintained in the polluted mesocosm showed a higher accumulation of Pb and Hg than in those maintained in restored mesocosm. This observation correlates well with mRNA expression of MT10 and data on DNA damage. The outcome of the biological evaluation consolidates the chemical characterization and supports the concept that the remediation method should be evaluated at an early stage, both to analytically determine the reduction of toxic components and to assess its ultimate impact on the biological system.

Biomonitoring of Mimachlamys varia transplanted to areas impacted by human activities (La Rochelle Marina, France)

The development of human activities on French Atlantic coastlines (La Rochelle) lead to chronic pollution of the environment by organic (pesticides, hydrocarbons, agrochemicals) and inorganic (heavy metals) contaminants. These past years, several regulations have been implemented to preserve coastal environments. The purpose of this study was to perform biomonitoring of bivalve species using an outdoor caging technique. The goal of our work was to assess the impact of harbour's trace elements on the state of health of the marine bivalve Mimachlamys varia. First, various molecular defence biomarkers were measured: SOD (oxidative stress), GST (detoxification process), MDA (lipid peroxidation), and Laccase (immune reaction). Thus, in April 2016, scallops were collected at three caging sites, which differ by their levels of pollution, after transplantation into port areas (fairing, rainwater) and a control site (marsh). Bivalve samples were taken at three sampling dates (D0, D07, D21). Biomarker assays were performed in the digestive glands due to their bioaccumulation properties. The second aim was to explore the impacts of inorganic pollutants placed in environmental harbour's sites. After 21 days, the biomarker response of transplanted bivalves revealed a SOD decrease, Laccase and GST stimulations, higher concentrations in Cu, Fe, As, Co, Mn, Zn, Sn and no significant variation of MDA concentration. Our ecological relevance of biomarker approaches opens interesting perspectives to identify M. varia such as a pertinent marine sentinel species. The several selected biomarkers determined could confirm their ability to appraise the water quality of hydro-systems located in French coastlines, such as port areas.

Organotropism and biomarker response in oyster Crassostrea gigas exposed to platinum in seawater

Platinum (Pt) is a technology critical element (TCE) for which biogeochemical cycles are still poorly understood. This lack of knowledge includes Pt effects on marine organisms, which proved to be able to bioconcentrate this trace element. Oysters Crassostrea gigas were exposed to stable Pt isotope spiked daily in seawater for 35 days. Seawater was renewed daily and spiked (with Pt(IV)) to three nominal Pt concentrations (50, 100, and 10,000 ng L^-1) for two replicate series. Organotropism study revealed that gills, and to a lesser extent mantle, are the key organs regarding Pt accumulation, although a time- and concentration-dependent linear increase in Pt levels occurred in all the organs investigated (i.e., digestive gland, gonads, gills, mantle, and muscle). In oysters exposed to Pt concentrations of 10,000 ng L^-1, significant biomarker impairments occurred, especially at cellular levels. They reflect altered lipofuscin and neutral lipid contents, as well as intralysosomal metal accumulation. These observations were attributed to activation of excretion/detoxification mechanisms, including Pt elimination through feces and clearly support the importance of the digestive gland in the response to direct Pt exposure. Despite relatively constant condition index, the integrative biological response (IBR) index suggests a generally decreasing health status of oysters.

A multilevel response approach reveals the Asian clam Corbicula largillierti as a mirror of aquatic pollution

The endobenthic bivalves are widely used as a bioindicators since they inhabit the sediment-water interface and are able to accumulate a different kind of contaminants. In the present work, we evaluated wild Corbicula largillierti (Phillippi, 1844) as a bioindicator of water quality in the central region of Argentina. The responses at different levels of the biological organization were used. We measured organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) levels in water and clams tissues. The biomarkers selected were enzymatic activities (Glutathione S-Transferase, Catalase, Acetyl-, Butyryl-cholinesterase, and Carboxylesterase) morphometry of the digestive gland, condition index and morphology of valves. In order to integrate all the responses a multivariate analysis and integrated stress index were applied. Our results showed the presence of contaminants along the studied river and the ability of C. largillierti to bioaccumulate them. All the biomarkers selected varied according to the water quality gradient, although there was no specific correlation with OCPs and PCBs levels. At the most polluted sites, the detoxification and oxidative stress enzymes, the morphometric analysis of the digestive gland and the variation in the morphology of the valves indicated the water quality degradation. The multivariate analyses allowed to discriminate the sites according to the different biomarker responses. The IBR index also showed a variation pattern according to the environmental quality gradient along the basin. According to the responses shown by C. largillierti we suggest this species as an useful bioindicator of aquatic pollution.

Influence of season-depending ecological variables on biomarker baseline levels in mussels (Mytilus trossulus) from two Baltic Sea subregions

For reliable mussel monitoring programmes based on biomarkers, regionally relevant reference values and their natural variability need to be known. The Baltic Sea exhibits high inter-regional and seasonal variability in physical factors such as salinity, temperature and primary production. The aim of this pilot study is to depict the effects of season-related environmental factors in a selected battery of biomarkers in two environmentally different subregions of the Baltic Sea to help establishing reference data for biochemical, cellular and tissue-level biomarkers. In order to achieve that, mussels were collected from reference sites in Kiel (Germany) and Tvärminne (Finland) during three seasons: summer and autumn 2016, and spring 2017. Finally, in order to characterize the ecological situation, analysis of the chemical tissue burden was performed and chlorophyll‑a and particulate organic carbon concentration and temperature changes were analyzed at each sampling locality using satellite remote sensing images. An integrated biomarker response index was performed to summarize the biomarker responses of each locality and season. The biochemical endpoints showed seasonal variability regulated by temperature, food supply and reproductive cycle, while among the cellular endpoints only lipofuscin accumulation and lysosomal structural changes showed slight seasonal variation. Seasonal changes in tissue level biomarkers were observed only at the northern Baltic Sea site Tvärminne, dictated by the demanding energetic trade-off caused by reproduction. In conclusion, the characterization of the ecological variables and physico-chemical conditions at each site, is crucial to perform a reliable assessment of the effects of a hypothetical pollution scenario in the Baltic Sea. Moreover, reference levels of biomarkers and their responses to natural environmental conditions must be established.

Impacts of dietary exposure to different sized polystyrene microplastics alone and with sorbed benzo[a]pyrene on biomarkers and whole organism responses in mussels Mytilus galloprovincialis

Due to their hydrophobicity and relatively large surface area, microplastics (MPs) can act as carriers of hydrophobic pollutants in the ocean and may facilitate their transfer to organisms. This study examined effects of dietary exposure to polystyrene MPs of 0.5 and 4.5 μm alone and with sorbed benzo[a]pyrene (BaP) on mussels Mytilus galloprovincialis in order to elucidate the effects of MP size and the presence of sorbed BaP on the organism. MPs were provided daily, mixed with algae, during 26 days at equivalent mass (0.058 mg/L), corresponding to 1000 particles/mL for 4.5 μm MPs and to 7.44 × 10⁵ particles/mL for 0.5 μm MPs. Effects were determined on early cellular biomarkers in hemocytes, structure and cell type composition of digestive tubules (DTs), histopathology and whole organism responses (condition index (CI), clearance rate (CR), food absorption efficiency (AE), respiration rate (RR) and scope for growth (SFG)). BaP concentrations in mussels increased with time, in particular when sorbed to smaller MPs. Large MPs were abundant in the lumen of stomach and DTs, but were also occasionally found within epithelial cells. Effects in all treatments increased with exposure time. MPs with sorbed BaP were more toxic than MPs alone according to hemocyte viability and catalase activity and to the quantitative structure of DT epithelium. Higher toxicity of small MPs compared to larger ones was recorded for DNA damage and cell composition of DTs. At tissue level a slight increase in prevalence of inflammatory responses occurred in all exposed groups. At whole organism level a compensatory effect was observed on absorption efficiency across MP treatments at day 26, resulting in increased SFG in mussels exposed to small MPs with sorbed BaP. This could be related to an increased energy need to deal with stress observed in biomarkers. Further work is required to understand the Trojan horse effect of a variety of plastic type, size, shape combinations together with a wide variety of pollutants.

Food-type may jeopardize biomarker interpretation in mussels used in aquatic toxicological experimentation

To assess the influence of food type on biomarkers, mussels (Mytilus galloprovincialis) were maintained under laboratory conditions and fed using 4 different microalgae diets ad libitum for 1 week: (a) Isochrysis galbana; (b) Tetraselmis chuii; (c) a mixture of I. galbana and T. chuii; and (d) a commercial food (Microalgae Composed Diet, Acuinuga). Different microalgae were shown to present different distribution and fate in the midgut. I. galbana (≈4 μm Ø) readily reached digestive cells to be intracellularly digested. T. chuii (≈10 μm Ø and hardly digestible) was retained in stomach and digestive ducts for long times and extracellularly digested. Based on these findings, it appeared likely that the presence of large amounts of microalgal enzymes and metabolites might interfere with biochemical determinations of mussel's biomarkers and/or that the diet-induced alterations of mussels' digestion could modulate lysosomal and tissue-level biomarkers. To test these hypotheses, a battery of common biochemical, cytological and tissue-level biomarkers were determined in the gills (including activities of pyruvate kinase, phosphoenolpyruvate carboxykinase and cytochrome c oxidase) and the digestive gland of the mussels (including protein, lipid, free glucose and glycogen total content, lysosomal structural changes and membrane stability, intracellular accumulation of neutral lipids and lipofuscins, changes in cell type composition and epithelial thinning, as well as altered tissue integrity). The type of food was concluded to be a major factor influencing biomarkers in short-term experiments though not all the microalgae affected biomarkers and their responsiveness in the same way. T. chuii seemed to alter the nutritional status, oxidative stress and digestion processes, thus interfering with a variety of biomarkers. On the other hand, the massive presence of I. galbana within digestive cells hampered the measurement of cytochemical biomarkers and rendered less reliable the results of biochemical biomarkers (as these could be attributed to both the mussel and the microalgae). Research to optimize dietary food type, composition, regime and rations for toxicological experimentation is urgently needed. Meanwhile, a detailed description of the food type and feeding conditions should be always provided when reporting aquatic toxicological experiments with mussels, as a necessary prerequisite to compare and interpret the biological responses elicited by pollutants.

In vitro toxicity testing in hemocytes of the marine mussel Mytilus galloprovincialis (L.) to uncover mechanisms of action of the water accommodated fraction (WAF) of a naphthenic North Sea crude oil without and with dispersant

Dispersants used in oil spills could result toxic to marine organisms and could influence the toxicity of oil compounds. The aim of this work was to uncover the mechanisms of action of the water accommodated fraction (WAF) of a naphthenic North Sea crude oil produced at 10, 15 and 20 °C without and with the dispersant Finasol OSR52 (WAF and WAFD, respectively) using hemocytes of the marine mussel Mytilus galloprovincialis. Primary cultures of hemocytes were exposed in glass-coated microplates to different WAF or WAFD dilutions (0.25, 2.5, 25, 50 and 100%) and to the dispersant alone at the same concentrations present in the WAFD dilutions (1.25, 12.5, 125, 250 and 500 mg/L). Of the two in vitro approaches tested, the second one was selected which involved exposure of hemocytes for 4 h to unfiltered WAF, WAFD and dispersant dilutions without cell culture media. WAF decreased hemocytes viability only at the highest dilution whereas WAFD and the dispersant alone were cytotoxic at the three highest concentrations. Temperature of production of WAF, WAFD and dispersant did not influence their cytotoxicity to hemocytes. WAF increased ROS production and MXR transport activity in hemocytes. Exposure to WAFD and dispersant increased ROS production, provoked plasma membrane and actin cytoskeleton disruption and decreased phagocytic activity. In conclusion, the dispersant tested was toxic to mussel hemocytes and it greatly increased the toxicity of WAFD. The present data could be useful for the environmental risk assessment of oil spills and their remediation strategies in the marine environment.

Multiple-biomarker approach in the assessment of the health status of a novel sentinel mussel Brachidontes rodriguezii in a harbor area

The objective of this study is to analyze whether a combination of biomarkers at different levels of biological complexity could be used to assess the health status of a population of Brachidontes rodriguezii associated to a harbor area in Mar del Plata, Argentina. A battery of biomarkers of general stress was measured in mussels collected from impacted and non-impacted areas. This included: condition index; shell analysis; histopathological alterations; atrophy and integrity of the digestive gland tissue; changes in cell type composition of the digestive gland, and glycogen accumulation. The studied biomarkers were integrated into the Integrative Biological Response (IBR/n) index. Overall, the IBR/n indicated a higher level of stress in mussels located in the harbor area. Thus, this biomarker index is a sensitive analytical tool that could be used to classify the ecotoxicological risk in coastal sites.

Prospective biomonitor and sentinel bivalve species for pollution monitoring and ecosystem health disturbance assessment in mangrove-lined Nicaraguan coasts

This research aims at contributing to the use of Polymesoda arctata, Anadara tuberculosa, and Larkinia grandis as prospective biomonitors and sentinels, surrogate of Crassostrea rhizophorae for pollution biomonitoring in mangrove-lined coastal systems. Localities were selected along the Nicaraguan coastline in the rainy and dry seasons during 2012-2013: A. tuberculosa and L. grandis were collected in the Pacific, and P. arctata in the Caribbean. The tissue concentration of metals, polycyclic aromatic hydrocarbons (PAHs) and persistent organic pollutants (POPs) were integrated into pollution indices (chemical pollution index -CPI- and pollution load index -PLI-) and biological endpoints (flesh-condition, reproduction, histopathology and stress-on-stress) were determined as biomarkers of ecosystem health disturbance. In the Caribbean, contaminant tissue concentration was low in P. arctata, with some exceptions. Ag, As, Cd, Hg, Ni and V were mainly recorded during dry season, and PAHs and POPs (HCHs, DDTs, AHTN, PCBs and BDE85) during rainy season. Metals and PAHs were not a major threat in the study area; in contrast, high levels of HCHs and DDTs and low-to-moderate levels of musk fragrances and PBDEs were recorded. Minor differences were found in biological parameters albeit during the rainy season the LT50 values were low and seemingly associated to high PLI and CPI values. In the Pacific, the main pollutants recorded in A. tuberculosa and L. grandis were HCHs, DDTs, AHTN and PDBEs in rainy season and Cd in dry season. Although basic research is needed to understand the general biology, ecology and diseases in these Pacific species, biological endpoints comparable to those used in other sentinel bivalves are seemingly suitable biomarkers of health disturbance. Overall, Caribbean P. arctata and Pacific A. tuberculosa and L. grandis seem to be potential target species for pollution monitoring and ecosystem health disturbance assessment in mangrove-lined Nicaraguan coastal systems. Their use together with C. rhizophorae would provide opportunities for common approaches to be applied in inter-ocean countries of the Mesoamerican region.

Bioaccumulation, tissue and cell distribution, biomarkers and toxicopathic effects of CdS quantum dots in mussels, Mytilus galloprovincialis

The bioaccumulation, cell, tissue distribution, and biological effects of 5 nm glutathione-capped CdS quantum dots (CdS QDs) in mussels was compared to bulk and aqueous Cd forms through a two-tier experimental approach. In the 1st tier, mussels were exposed for 3 d to 0.05, 0.5 and 5 mg Cd/l (QDs, bulk, aqueous), bioaccumulation, distribution and lysosomal responses were investigated. In the 2nd tier, mussels were exposed for 21 d to the same forms at the lowest effective concentration selected after Tier 1 (0.05 mg Cd/l), biomarkers and toxicopathic effects were investigated. Accumulation was comparable in QDs and aqueous Cd exposed mussels after 3 d. After 21 d, QDs exposed mussels accumulated less than mussels exposed to aqueous Cd and localised in the endo-lysosomal system and released to the alveoli lumen (21 d) after exposure to QDs and aqueous Cd. Intracellular levels of Cd increased on exposure to QDs and aqueous Cd, and to a lesser extent to bulk, and accompanied by the up-regulation of metallothionein 10 (1 d) and 20 (1, 21 d). Lysosomal membrane destabilisation depended on Cd²⁺ released by all forms but was marked after exposure to aqueous Cd (1 d). Toxicopathic effects (vacuolisation, loss of digestive cells and haemocytic infiltration) were evident after exposure to QDs (1 d) and aqueous Cd (21 d). Toxicity most likely depended on the ionic load resulting from Cd²⁺ release from the different forms of Cd; yet nanoparticle-specific effects of QDs cannot be disregarded.

Enhanced discrimination of basophilic cells on mussel digestive gland tissue sections by means of toluidine-eosin staining

Changes in the cell type composition of the digestive gland epithelium constitute a common and recognized biological response to stress in mussels. Usually, these changes are identified as alterations in the relative proportion of basophilic cells, determined in tissue sections stained with hematoxylin-eosin (H&E) and measured in terms of volume density of basophilic cells (Vv_BAS) after stereological quantification. However, the identification and discrimination of basophilic cells may be a difficult issue, even for a trained operator, especially when, in circumstances of environmental stress, basophilic cells lose their basophilia and the perinuclear area of digestive cells gains basophilia. Thus, the present study was aimed at exploring the best available practices (BAPs) to identify and discriminate basophilic cells on tissue sections of mussel digestive gland. In a first step, a thorough screening of potentially suitable staining methods was carried out; the final selection included several trichrome staining methods and some of their variants, as well as toluidine-based stains. Next, the sample processing (fixation/dehydration steps) was optimized. Toluidine-eosin (T&E) staining after fixation in 4% formaldehyde at 4 °C for 24 h was considered the BAP to identify and discriminate basophilic cells in the digestive gland of mussels. Using the mussel Mytilus galloprovincialis as a target organism, this approach was successfully applied to quantify Vv_BAS values after automated image analysis and compared with the conventional H&E staining in different field and laboratory tests. It is worth noting that Vv_BAS values were always higher after T&E staining than after H&E staining, apparently because discrimination of basophilic cells was enhanced. Thus, until more data are available, any comparison with Vv_BAS values obtained in previous studies using H&E staining must be done cautiously. Finally, the T&E staining was successfully used to discriminate basophilic cells in tissue sections of other marine molluscs of ecotoxicological interest, including Mytilus edulis, Mytilus trossulus, Crassostrea gigas and Littorina littorea.

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.

Effects of dietary Pb and Cd and their combination on lysosomal and tissue-level biomarkers and histopathology in digestive gland of the land snail, Cantareus apertus (Born, 1778)

The present study was aimed at determining cell and tissue-level biomarkers and histopathological alterations in the green garden snail, Cantareus apertus (Born, 1778), exposed to different nominal dietary concentrations of Pb (25, 100 and 2500 mg Pb/kg), Cd (5, 10 and 100 mg Cd/kg) and their combination (25 mg Pb + 5 mg Cd/Kg, 100 mg Pb + 10 mg Cd/kg and 2500 mg Pb + 100 mg Cd/ kg) for 1 and 8 weeks. Lead and Cd exerted histopathological effects on the digestive gland in a dose-dependent manner and related to lysosomal and tissue-level biomarkers. The biological responses observed included digestive cell vacuolisation and numerical atrophy, calcium cell hydropic degeneration, excretory cell hypertrophy, inflammatory responses, blood vessel congestion, and disruption of the blood vessel wall and the interstitial connective tissue. Lysosomal enlargement and transient intracellular accumulation of neutral lipids and lipofuscins were also observed, together with alterations in the cell type composition and thinning of the digestive gland epithelium and with diverticular distortion. This response profile fits well with the biological effects reported after metal exposure in gastropods from other regions, as well as with data obtained in parallel studies dealing with metal bioaccumulation and intralysosomal accumulation, mortality, feeding, growth, oxidative stress and neurotoxicity exerted elicited by Pb, Cd and their mixture in green garden snails under the present experimental conditions. Consequently, C. apertus seems to be a suitable model species for the biomarker-based assessment of the biological effects of Pb and Cd, alone or in combinations, thus providing a challenging opportunity to advance in identifying suitable sentinel species for metal pollution biomonitoring and ecosystem health assessment in soil ecosystems in Northern Africa.

Assessment of the Health Status of Mussels Mytilus galloprovincialis Along the Campania Coastal Areas: A Multidisciplinary Approach

The bivalve Mytilus galloprovincialis has a broad geographic distribution, represent an important species for the ecology of coastal waters, also constituting a major aquaculture species. In the present work, molecular and tissue biomarkers were examined in mussel populations (M. galloprovincialis) located in four different areas of the coastal water of the Campania Region. During an annual life cycle, we analyzed the expression patterns of several genes commonly used to estimate cellular stress response and damage, namely p53, p63, HSP70, MT-10, and MT-20, related tissue lesions (pathogens, inflammations, digestive tubules damage), oxidative stress indicators (H2O2, SOD specific activity) and associated environmental data. The computed Principal Component Analysis showed that the areas were discernible based on the environmental data and biomarker results. About animal health status, mussels from Gulf of Pozzuoli and Naples's harbor did show a thinnest epithelial cell of digestive tubules compared to mussels sampled from other sampling sites; moreover, high prevalence of cases of intersex in three of the examinated areas were observed. The presence of a potential zoonotic pathogen (Nocardia crassostreae) was identified, appearing as an important possible emerging disease. We also reported the OIE notifiable protozoa Marteilia refringens in three areas out of four. The likely impact of both observed pathogens on the mussel health and shellfish aquaculture needs to be urgently addressed. Results are discussed considering animal histopathological health parameters and biological effects.

Assessment of ecosystem health disturbance in mangrove-lined Caribbean coastal systems using the oyster Crassostrea rhizophorae as sentinel species

This investigation was aimed at contributing to develop a suitable multi-biomarker approach for pollution monitoring in mangrove-lined Caribbean coastal systems using as sentinel species, the mangrove cupped oyster, Crassostrea rhizophorae. A pilot field study was carried out in 8 localities (3 in Nicaragua; 5 in Colombia), characterized by different environmental conditions and subjected to different levels and types of pollution. Samples were collected in the rainy and dry seasons of 2012-2013. The biological effects at different levels of biological complexity (Stress-on-Stress response, reproduction, condition index, tissue-level biomarkers and histopathology) were determined as indicators of health disturbance, integrated as IBR/n index, and compared with tissue burdens of contaminants in order to achieve an integrative biomonitoring approach. Though modulated by natural variables and confounding factors, different indicators of oyster health, alone and in combination, were related to the presence of different profiles and levels of contaminants present at low-to-moderate levels. Different mixtures of persistent (As, Cd, PAHs) and emerging chemical pollutants (musk fragrances), in combination with different levels of organic and particulate matter resulting from seasonal oceanographic variability and sewage discharges, and environmental factors (salinity, temperature) elicited a different degree of disturbance in ecosystem health condition, as reflected in sentinel C. rhizophorae. As a result, IBR/n was correlated with pollution indices, even though the levels of biological indicators of health disturbance and pollutants were low-to-moderate, and seasonality and the incidence of confounding factors were remarkable. Our study supports the use of simple methodological approaches to diagnose anomalies in the health status of oysters from different localities and to identify potential causing agents and reflect disturbances in ecosystem health. Consequently, the easy methodological approach used herein is useful for the assessment of health disturbance in a variety of mangrove-lined Caribbean coastal systems using mangrove cupped oysters as sentinel species.

Integrative biomarker assessment of the effects of chemically and mechanically dispersed crude oil in Pacific oysters, Crassostrea gigas

The impact of dispersed crude oil and dispersant on adult Pacific oysters, Crassostrea gigas, was evaluated through an integrative biomarker approach including (1) biochemical (plasma catecholase- and laccase-type phenoloxidase and superoxide dismutase), (2) histological (digestive cell lysosomal responses, digestive gland histopathology) and (3) physiological (flesh condition index) endpoints in the haemolymph and digestive gland. Adult oysters were exposed to non-contaminated water (control), chemically-dispersed oil (Brut Arabian Light), mechanically-dispersed oil and dispersant (FINASOL®) alone for 2days, and further depurated in non-contaminated water for 4weeks. After exposure to chemically and mechanically dispersed oil oysters exhibited induction of plasma laccase-type phenoloxidase and superoxide dismutase activities, enlargement of digestive cell lysosomes, lipofuscin accumulation, reduced neutral lipid content and atrophy of digestive gland diverticula; more markedly on exposure to chemically dispersed oil. From the studied biomarkers, only lysosomal biomarkers were significantly affected after exposure to the dispersant alone. This included lysosomal enlargement, neutral lipid depletion and lipofuscin accumulation in the digestive gland epithelium. A recovery of plasma enzyme activities was observed after 4weeks of depuration. The integrative biological response index indicated that chemically dispersed oil caused significantly higher stress to C. gigas than the mechanically-dispersed one or the dispersant alone; nevertheless, the response seems to be reversible after depuration.

Chronic environmental stress enhances tolerance to seasonal gradual warming in marine mussels

In global climate change scenarios, seawater warming acts in concert with multiple stress sources, which may enhance the susceptibility of marine biota to thermal stress. Here, the responsiveness to seasonal gradual warming was investigated in temperate mussels from a chronically stressed population in comparison with a healthy one. Stressed and healthy mussels were subjected to gradual temperature elevation for 8 days (1°C per day; fall: 16–24°C, winter: 12–20°C, summer: 20–28°C) and kept at elevated temperature for 3 weeks. Healthy mussels experienced thermal stress and entered the time-limited survival period in the fall, became acclimated in winter and exhibited sublethal damage in summer. In stressed mussels, thermal stress and subsequent health deterioration were elicited in the fall but no transition into the critical period of time-limited survival was observed. Stressed mussels did not become acclimated to 20°C in winter, when they experienced low-to-moderate thermal stress, and did not experience sublethal damage at 28°C in summer, showing instead signs of metabolic rate depression. Overall, although the thermal threshold was lowered in chronically stressed mussels, they exhibited enhanced tolerance to seasonal gradual warming, especially in summer. These results challenge current assumptions on the susceptibility of marine biota to the interactive effects of seawater warming and pollution.

Application of a weight of evidence approach utilising biological effects, histopathology and contaminant levels to assess the health and pollution status of Irish blue mussels (Mytilus edulis)

A weight of evidence (WOE) approach, integrating biological effects, mussel histopathology and tissue contaminant levels is proposed to evaluate mussel health and pollution status. Contaminant levels, histopathology and several biological effects (BEs) including Lysosomal membrane stability (LMS), acetylcholinesterase (AChe), metallothionein proteins (MT) and alkali labile phosphate (ALP), in Mytilus edulis are presented, improving the current knowledge base for these data. Potential links between histopathology, BEs and contaminants and ranking of sites are investigated with an integrated response (IR) indexing technique. Histopathological condition indices (Ih) in mussel digestive gland are used to calculate health indices. A spatial and temporal assessment is conducted at Irish coastal locations. Linear mixed effects modelling revealed effects of confounding factors such as reproductive condition on NRRT (gonad stage (p < 0.001)). Higher prevalence of inflammation, brown cells and epithelial thinning of the digestive gland was evident at Dublin and Wexford and this linked well with the Ih. Levels of contaminants were generally found to be low with few exceptions as were BE responses. Using the IR approach, Dublin was ranked as being most impacted while Shannon ranked the least impacted, this being consistent with the BE ranking.

Is there a direct relationship between stress biomarkers in oysters and the amount of metals in the sediments where they inhabit?

The effects exerted by metals in oysters are still a matter of debate and require more detailed studies. In this work we have investigated whether the health status of oysters are affected by the amount of metals present in the sediments of their habitat. Sediments and oysters were collected in the tidal part of the estuary of the Oka River (Basque Country), representative of other mesotidal, well mixed and short estuaries of the European Atlantic coast. The concentrations of 14 elements were determined in all the samples. Several biomarkers were also measured in the soft tissues of oysters. According to the concentrations found, the sediments were classified as non-toxic or slightly toxic. In good agreement, the histological alterations observed in oysters were not severe. Interestingly, in those sampling sites where the sediments showed relatively high metal concentrations, the metallic content in oysters was lower, and vice versa.

Nanoparticle size and combined toxicity of TiO2 and DSLS (surfactant) contribute to lysosomal responses in digestive cells of mussels exposed to TiO2 nanoparticles

The aim of this investigation was to understand the bioaccumulation, cell and tissue distribution and biological effects of disodium laureth sulfosuccinate (DSLS)-stabilised TiO2 nanoparticles (NPs) in marine mussels, Mytilus galloprovincialis. Mussels were exposed in vivo to 0.1, 1 and 10 mg Ti/L either as TiO2 NPs (60 and 180 nm) or bulk TiO2, as well as to DSLS alone. A significant Ti accumulation was observed in mussels exposed to TiO2 NPs, which were localised in endosomes, lysosomes and residual bodies of digestive cells, and in the lumen of digestive tubules, as demonstrated by ultrastructural observations and electron probe X-ray microanalysis. TiO2 NPs of 60 nm were internalised within digestive cell lysosomes to a higher extent than TiO2 NPs of 180 nm, as confirmed by the quantification of black silver deposits after autometallography. The latter were localised mainly forming large aggregates in the lumen of the gut. Consequently, lysosomal membrane stability (LMS) was significantly reduced upon exposure to both TiO2 NPs although more markedly after exposure to TiO2-60 NPs. Exposure to bulk TiO2 and to DSLS also affected the stability of the lysosomal membrane. Thus, effects on the lysosomal membrane depended on the nanoparticle size and on the combined biological effects of TiO2 and DSLS.

Season-dependent effects of elevated temperature on stress biomarkers, energy metabolism and gamete development in mussels

In coastal areas, sessile species can be severely affected by thermal stress associated to climate change. Presently, the effect of elevated temperature on metabolic, cellular and tissue-level responses of mussels was determined to assess whether the responses vary seasonally with seawater temperature and reproductive stage. Mussels were collected in fall, winter and summer, and (a) maintained at 16, 12, and 20 °C respectively or (b) subject to gradual temperature elevation for 8 days (+1 °C per day; from 16 to 24 °C in fall, from 12 to 20 °C in winter and from 20 to 28 °C in summer) and further maintained at 24 °C (fall), 20 °C (winter) and 28 °C (summer) for the following 6 days. Temperature elevation induced membrane destabilization, lysosomal enlargement, and reduced the aerobic scope in fall and summer whereas in winter no significant changes were found. Changes at tissue-level were only evident at 28 °C. Gamete development was impaired irrespective of season. Since the threshold of negative effects of warming was close to ambient temperatures in summer (24 °C or above) studied mussel populations would be vulnerable to the global climate change.

iTRAQ-based quantitative proteomic analyses on the gender-specific responses in mussel Mytilus galloprovincialis to tetrabromobisphenol A

Tetrabromobisphenol A (TBBPA) accounts for the largest production of brominated flame-retardants (BFRs) along the Laizhou Bay in China and is the most widely used BFR in industrial products. It can induce diverse toxicities including hepatotoxicity, nephrotoxicity, neurotoxicity and endocrine disrupting effects in mammalian and fish models. In this work, we applied iTRAQ-based proteomics to investigate the gender-specific responses in mussel Mytilus galloprovincialis to TBBPA. Thirty-one proteins were differentially expressed in hepatopancreas between male and female mussels, which clearly indicated the biological differences between male and female mussels at the protein level. After exposure of TBBPA (18.4 nmol/L) for one month, a total of 60 proteins were differentially expressed in response to the TBBPA treatment in mussel hepatopancreas, among which 33 and 29 proteins were significantly altered in TBBPA-treated male and female mussel samples, respectively. Only two of the 60 proteins were commonly altered in both male and female mussel samples exposed to TBBPA. Based on KEGG analysis, these differentially expressed proteins of TBBPA-induced effects were assigned to several groups, including cytoskeleton, reproduction and development, metabolism, signal transduction, gene expression, stress response and apoptosis. Overall, results indicated that TBBPA exposure could induce apoptosis, oxidative and immune stresses and disruption in energy, protein and lipid metabolisms in both male and female mussels with different mechanisms. This work suggested that the gender differences should be considered in ecotoxicoproteomics.

Health status assessment through an integrative biomarker approach in mussels of different ages with a different history of exposure to the Prestige oil spill

A battery of cell and tissue-level biomarkers was applied in mussels of 6 size-classes collected from Galicia and the Basque coast in summer 2007 in an attempt to examine the health status of individuals affected as adults (mature before 2003), affected during their developmental or juvenile stages (2003-2004 offspring), or not directly affected by the Prestige oil spill (POS) exposure (presumably 2005-2006 offspring). This battery of biomarkers was akin to those formerly applied on mussels of 3.5-4.5 cm shell length for which there exist biomarker reference values in the studied geographical areas. The cause-effect relationship between biological responses and the different history of exposure to POS fuel oil was intricate for different reasons: (a) growth rate was dissimilar in mussels of the two studied localities and much lower than expected, (b) a chronological basis could not be directly associated to POS events (all mussels except the smallest from Galicia had been subjected to the direct POS impact at one or another stage of their life-cycle); and (c) some biomarkers and histopathology seemingly depended on size/age irrespectively of the locality and the POS chronology. As a whole, the present study gives a very useful set of reference values of biomarkers obtained for Mytilus galloprovincialis of different size-classes. Finally, it is recommended that Mussel Watch programmes should be designed by standardising the age of the sentinel mussels rather than their size, especially if the programme covers large or diverse geographical areas, if long-term trends are relevant or if significant pollution effects on growth are expected.

Short- and long-term responses and recovery of mussels Mytilus edulis exposed to heavy fuel oil no. 6 and styrene

Biomarkers have the potential to be used to assess the impact of anthropogenic discharges in marine waters. We have used a suite of biomarkers spanning from enzymatic to histopathological alterations and general stress responses to assess the short- and long-term impact on mussels Mytilus edulis of heavy fuel oil no. 6 and styrene. Mussels were exposed for 5 months, with a refilling of the exposure system, to a water soluble fraction of heavy fuel and, then, kept for a month in clean water for recovery. In a second experiment, mussels were exposed to styrene for 19 days and maintained in clean water for up to 4 months. Chemical body tissue levels reflected the weathering processes of these compounds. Acyl-CoA oxidase activity was induced in oil-exposed mussels after refilling, whereas styrene inhibited it after 19 days of exposure and after 2 weeks in clean water. Gamete development and alkali-labile phosphate levels suggest that neither oil nor styrene behaved as endocrine disruptors. Neutral red retention time was lower in treated groups than in controls. Lysosomal membrane stability was significantly reduced in exposed groups and recovered after withdrawal of oil but not after removal of styrene. Neither oil nor styrene exposure affected the condition index except for the reduction seen in mussels exposed to oil for 1 month. Biomarker response index discriminated exposed mussels, which showed higher values, and returned to control levels after recovery. Results obtained from these pilot experiments can help to identify relevant monitoring tools to assess the impact of oil and chemicals in marine spill scenarios.

Exposure-dose-response relationships of the freshwater bivalve Hyridella australis to cadmium spiked sediments

To understand how benthic biota may respond to the additive or antagonistic effects of metal mixtures in the environment it is first necessary to examine their responses to the individual metals. In this context, laboratory controlled single metal-spiked sediment toxicity tests are useful to assess this. The exposure-dose-response relationships of Hyridella australis to cadmium-spiked sediments were, therefore, investigated in laboratory microcosms. H. australis was exposed to individual cadmium spiked sediments (<0.05 (control), 4±0.3 (low) and 15±1 (high) μg/g dry mass) for 28 days. Dose was measured as cadmium accumulation in whole soft body and individual tissues at weekly intervals over the exposure period. Dose was further examined as sub-cellular localisation of cadmium in hepatopancreas tissues. The biological responses in terms of enzymatic and cellular biomarkers were measured in hepatopancreas tissues at day 28. H. australis accumulated cadmium from spiked sediments with an 8-fold (low exposure organisms) and 16-fold (high exposure organisms) increase at day 28 compared to control organisms. The accumulated tissue cadmium concentrations reflected the sediment cadmium exposure at day 28. Cadmium accumulation in high exposure organisms was inversely related to the tissue calcium concentrations. Gills of H. australis showed significantly higher cadmium accumulation than the other tissues. Accumulated cadmium in biologically active and biologically detoxified metal pools was not significantly different in cadmium exposed organisms, which suggests that H. australis has some tolerance to cadmium. The metallothionein like protein fraction played an important role in the sequestration and detoxification of cadmium and the amount sequestered in this fraction increased with increased cadmium exposure. The highest percentage of biologically active cadmium was associated with the lysosome+microsome and mitochondrial fractions. Cadmium concentrations in these two fractions of cadmium exposed organisms were significantly higher with respect to controls. Total antioxidant capacity decreased with increased cadmium exposure and tissue dose. Lipid peroxidation increased and lysosomal membrane stability decreased significantly with increased cadmium exposure and tissue dose. Based on exposure-dose-response analysis in this study, H. australis would be a suitable organism for assessing cadmium sediment exposure and toxicity.

Polycyclic aromatic hydrocarbon body residues and lysosomal membrane destabilization in mussels exposed to the Dubai Star bunker fuel oil (intermediate fuel oil 380) spill in San Francisco Bay

Following the spill of bunker fuel oil (intermediate fuel oil 380, approximately 1500-3000 L) into San Francisco Bay in October 2009, polycyclic aromatic hydrocarbon (PAH) concentrations in mussels from moderately oiled areas increased up to 87 554 ng/g (dry wt) and, 3 mo later, decreased to concentrations found in mussels collected prior to oiling, with a biological half-life of approximately 16 d. Lysosomal membrane destabilization increased in mussels with higher PAH body burdens.