Comparisons of PAH-induced immunomodulation in three bivalve molluscs

Immunotoxicity of microplastics in fish

Plastic waste degrades slowly in aquatic environments, transforming into microplastics (MPs) and nanoplastics (NPs), which are subsequently ingested by fish and other aquatic organisms, causing both physical blockages and chemical toxicity. The fish immune system serves as a crucial defense against viruses and pollutants present in water. It is imperative to comprehend the detrimental effects of MPs on the fish immune system and conduct further research on immunological assessments. In this paper, the immune response and immunotoxicity of MPs and its combination with environmental pollutants on fish were reviewed. MPs not only inflict physical harm on the natural defense barriers like fish gills and vital immune organs such as the liver and intestinal tract but also penetrate cells, disrupting intracellular signaling pathways, altering the levels of immune cytokines and gene expression, perturbing immune homeostasis, and ultimately compromising specific immunity. Initially, fish exposed to MPs recruit a significant number of macrophages and T cells while activating lysosomes. Over time, this exposure leads to apoptosis of immune cells, a decline in lysosomal degradation capacity, lysosomal activity, and complement levels. MPs possess a small specific surface area and can efficiently bind with heavy metals, organic pollutants, and viruses, enhancing immune responses. Hence, there is a need for comprehensive studies on the shape, size, additives released from MPs, along with their immunotoxic effects and mechanisms in conjunction with other pollutants and viruses. These studies aim to solidify existing knowledge and delineate future research directions concerning the immunotoxicity of MPs on fish, which has implications for human health.

Mechanisms of Gills Response to Cadmium Exposure in Greenfin Horse-Faced Filefish (Thamnaconus septentrionalis): Oxidative Stress, Immune Response, and Energy Metabolism

Cadmium (Cd) pollution has become a global issue due to industrial and agricultural developments. However, the molecular mechanism of Cd-induced detrimental effects and relevant signal transduction/metabolic networks are largely unknown in marine fishes. Here, greenfin horse-faced filefish (Thamnaconus septentrionalis) were exposed to 5.0 mg/L Cd up to 7 days. We applied both biochemical methods and multi-omics techniques to investigate how the gills respond to Cd exposure. Our findings revealed that Cd exposure caused the formation of reactive oxygen species (ROS), which in turn activated the MAPK and apoptotic pathways to alleviate oxidative stress and cell damage. Glycolysis, protein degradation, as well as fatty acid metabolism might assist to meet the requirements of nutrition and energy under Cd stress. We also found that long-term (7 days, "long-term" means compared to 12 and 48 h) Cd exposure caused the accumulation of succinate, which would in turn trigger an inflammatory response and start an immunological process. Moreover, ferroptosis might induce inflammation. Overall, Cd exposure caused oxidative stress, energy metabolism disturbance, and immune response in greenfin horse-faced filefish. Our conclusions can be used as references for safety risk assessment of Cd to marine economic fishes.

Regulation of cellulase production via calcium signaling in Trichoderma reesei under PEG8000 stress

In this study, the effect of polyethylene glycol 8000 (PEG8000) stress on cellulase biosynthesis in Trichoderma reesei CICC2626 via calcium signaling was investigated, and a plausible mechanism by which intracellular Ca2+ regulates the transcription of cellulase genes was proposed. The results indicated that the total cellulase (filter paper-hydrolyzing activity [FPase]), endoglucanase (carboxymethyl cellulase activity [CMCase]), and β-glucosidase activities of the strain were 1.3-, 1.2-, and 1.3-fold higher than those of the control (no PEG8000 addition) at a final concentration of 1.5% (w/v) PEG8000. Moreover, the transcriptional levels of cellulase genes, protein concentrations, and biomass increased. With the synergistic use of commercial cellulase and T. reesei CICC2626 cellulase to hydrolyze alkali-pretreated rice straw, the released reducing sugar concentration reached 372.7 mg/g, and the cellulose content (22.7%, 0.32 g) was significantly lower than the initial content (62.5%, 1.88 g). Transcriptome data showed that 12 lignocellulose degradation-related genes were significantly upregulated in the presence of 1.5% PEG8000. Furthermore, the addition of Ca2+ inhibitors and deletion of crz1 (calcineurin-responsive zinc finger 1-encoding gene, which is related to the calcium signaling pathway) demonstrated that calcium signaling plays a dominant role in PEG8000-induced cellulase genes overexpression. These results revealed a link between PEG8000 induction and calcium signaling transduction in T. reesei CICC2626. Moreover, this study also provides a novel inducer for enhanced cellulase production. KEY POINTS: • Cellulase biosynthesis in Trichoderma reesei could be enhanced by PEG8000 • PEG8000 could induce a cytosolic Ca2+ burst in Trichoderma reesei • The activated calcium signaling was involved in cellulase biosynthesis.

The role of marine pollution on the emergence of fish bacterial diseases

Marine pollution and bacterial disease outbreaks are two closely related dilemmas that impact marine fish production from fisheries and mariculture. Oil, heavy metals, agrochemicals, sewage, medical wastes, plastics, algal blooms, atmospheric pollutants, mariculture-related pollutants, as well as thermal and noise pollution are the most threatening marine pollutants. The release of these pollutants into the marine aquatic environment leads to significant ecological degradation and a range of non-infectious disorders in fish. Marine pollutants trigger numerous fish bacterial diseases by increasing microbial multiplication in the aquatic environment and suppressing fish immune defense mechanisms. The greater part of these microorganisms is naturally occurring in the aquatic environment. Most disease outbreaks are caused by opportunistic bacterial agents that attack stressed fish. Some infections are more serious and occur in the absence of environmental stressors. Gram-negative bacteria are the most frequent causes of these epizootics, while gram-positive bacterial agents rank second on the critical pathogens list. Vibrio spp., Photobacterium damselae subsp. Piscicida, Tenacibaculum maritimum, Edwardsiella spp., Streptococcus spp., Renibacterium salmoninarum, Pseudomonas spp., Aeromonas spp., and Mycobacterium spp. Are the most dangerous pathogens that attack fish in polluted marine aquatic environments. Effective management strategies and stringent regulations are required to prevent or mitigate the impacts of marine pollutants on aquatic animal health. This review will increase stakeholder awareness about marine pollutants and their impacts on aquatic animal health. It will support competent authorities in developing effective management strategies to mitigate marine pollution, promote the sustainability of commercial marine fisheries, and protect aquatic animal health.

Toxicity assessment of environmental MPs and NPs and polystyrene NPs on the bivalve Corbicula fluminea using a multi-marker approach

Small plastic particles, microplastics (MPs) and nanoplastics (NPs) represent a major threat in aquatic environments. Freshwater organisms are exposed to MPs and NPs, particularly in industrial and urban areas. The present study aimed to compare the toxicity between polystyrene NPs (PS NPs) and environmental microplastics (ENV MPs) and nanoplastics (ENV NPs) generated from macro-sized debris collected in the Garonne River on the freshwater bivalve C. fluminea. The organisms were exposed to the different plastic particles at three environmentally relevant concentrations: 0.008, 10, and 100 μg L-1 for 21 days. The biological responses of organisms were assessed using a multi-biomarker approach from the sub-individual to the individual level. The results demonstrated that: i) ENV NPs triggered more effects on detoxification processes and immune response, confirming that using manufactured NPs for laboratory exposure can lead to misleading conclusions on the risks posed by plastic particles; ii) effects of ENV MPs were less marked than ENV NPs, emphasizing the importance of testing a size continuum of plastic particles from NPs to MPs; iii) some effects were only observed for the low and/or intermediate concentrations tested, underlining the importance of using environmentally relevant concentrations. In light of these results, laboratory studies should be continued by exposing aquatic species to environmental MPs and NPs. The properties of these particles have to be characterized for a better risk assessment of environmental plastic particles.

Effect of size continuum from nanoplastics to microplastics on marine mussel Mytilus edulis: Comparison in vitro/in vivo exposure scenarios

For several decades, plastic has been a global threat in terms of pollution. Plastic polymers, when introduce in the aquatic environment, are exposed to fragmentation processes into microplastics (MPs) and nanoplastics (NPs) which could potentially interact with living organisms. The objective of this work was to study the effects of plastic particles representative of those found in the environment, on the marine mussels Mytilus edulis, under two exposure scenarios: in vivo and in vitro. Whole mussels or cultured hemocytes were exposed for 24 h to NPs and MPs generated from macro-sized plastics collected in the field, but also to reference NPs, at concentrations found in the environment: 0.08, 10 μg and 100 μg·L^-1. Results showed that immune response was only activated when mussels were exposed in vivo. However, cytotoxicity (hemocyte mortality) and genotoxicity (DNA damage) parameters were induced after both types of exposure, but in a dose-dependent manner after in vitro hemocyte exposure to all tested plastic conditions. These results indicate that in vitro approaches could be considered as potential predictors of in vivo exposures.

Comparative study of immunological biomarkers in the carpet shell clams (Ruditapes decussatus) from metal-contaminated sites in the South Lagoon of Tunis (Tunisia)

The South Lagoon of Tunis (Tunisia) is a Mediterranean lagoon adversely affected by industrial contaminants, harbour activity and untreated urban sewage. In this lagoon, the clam Ruditapes decussatus has been widely used as a biomonitor of seawater pollution through measurements of parameters related to oxidative stress and neurotoxicity. However, few studies have considered parameters of the immune system of this species in the South Lagoon of Tunis. Therefore, the aim of the present work was to evaluate several immune-related parameters in the cell-free haemolymph of carpet shell clams sampled during August and February from three polluted sites in the South Lagoon of Tunis (S1, S2 and S3) and one less polluted site as a reference site (RS) in order to identify suitable biomarkers for environmental quality assessments of this ecosystem. Concerning the immune-related parameters, seasonal factors modulated phenoloxidase, lysozyme, protease and esterase activity, with lower values measured for samples collected in August than for samples collected in February. In fact, bactericidal activity against two of the pathogenic bacteria tested and the activity of most immune-related enzymes were reduced in the cell-free haemolymph of clams collected from the most sampling sites in August compared to February one. In addition, values of abiotic parameters (temperature, salinity and pH) and metal (cadmium, copper, iron, lead and zinc) concentrations in the clams' soft tissues, previously obtained and published by the authors, as well as the values of immune-related parameters were integrated using principal component analyses. Results indicated that the values of all measured immune-related parameters were negatively correlated with the temperature values and the variations most of these parameters highlighted that the chemical industrial area (S3) was the most impacted location within the South Lagoon of Tunis. The present study illustrates that the immune-related parameters measured in carpet shell clam cell-free haemolymph represent suitable biomarkers for environmental quality assessments because they provide effective seasonal and spatial discrimination.

A review on polycyclic aromatic hydrocarbons distribution in freshwater ecosystems and their toxicity to benthic fauna

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds, found ubiquitously in all environmental compartments. PAHs are considered hazardous pollutants, being of concern to both the environmental and human health. In the aquatic environment, PAHs tend to accumulate in the sediment due to their high hydrophobicity, and thus sediments can be considered their ultimate sink. Concurrently, sediments comprise important habitats for benthic species. This raises concern over the toxic effects of PAHs to benthic communities. Despite PAHs have been the subject of several reviews, their toxicity to freshwater benthic species has not been comprehensively discussed. This review aimed to provide an overview on PAHs distribution in freshwater environments and on their toxicity to benthic fauna species. The distribution of PAHs between sediments and the overlying water column, given by the sediment-water partition coefficient, revealed that PAHs concentrations were 2 to 4 orders of magnitude higher in sediments than in water. The sediment-water partition coefficient was positively correlated to PAHs hydrophobicity. Toxicity of PAHs to benthic fauna was addressed through Species Sensitivity Distributions. The derived hazardous concentration for 5% of the species (HC₅) decreased as follows: NAP (376 μg L^-1) > PHE > PYR > FLT > ANT (0.854 μg L^-1), varying by 3 orders of magnitude. The hazardous concentrations (HC₅) to benthic species were inversely correlated to the hydrophobicity of the individual PAHs. These findings are pertinent for environmental risk assessment of these compounds. This review also identified future challenges regarding the environmental toxicity of PAHs to freshwater benthic communities, namely the need for updating the PAHs priority list and the importance of comprehensively and more realistically assess the toxicity of PAHs in combination with other stressors, both chemical and climate-related.

Histopathological alterations induced by marine environmental pollutants on the bivalve Cerastoderma glaucum (Bruguière 1789) from Temsah Lake, Suez Canal, Egypt

Bivalves are considered a main consumed matrix for coastal communities worldwide and classified as hyperaccumulators of pollutants. The present study aims to determine some micro-organisms, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and okadaic acid (OA) levels in Cerastoderma glaucum collected from Temsah Lake, Egypt, and their induction through histopathological damage and caspase-3 protein expression. During the autumn, it was found different types of biological and chemical pollutants, especially benzo[a]pyrene (BaP) that accumulated in C. glaucum soft tissues and exceeded the safety limit for shellfish consumption. Dioxin-like PCB3 was predominant in C. glaucum soft tissues during autumn, but the total levels of PCBs in these tissues have not exceeded the permissible limit. Chlorophyll-a (Chl. a), nutrient concentrations, and Prorocentrum lima dinoflagellates in the water significantly increased during autumn. High P. lima abundance was confirmed by high OA in the soft tissues during this season compared to the other seasons. The measured contaminants may render C. glaucum more susceptible to bacterial and fungal infections. The autumn season showed a significant increase in the colony-forming units (CFU). C. glaucum showed calcification abnormalities and adhering of abnormal brown organic material to the inner surface of the shell valves, which was related to poor water conditions and Vibrio infection. Damages or injuries on gills and digestive gland tissues indicated an impact of the pollutants on C. glaucum. Also, high expressions of caspase-3 were recorded in these tissues during all the seasons. So, C. glaucum cockles, collected from Temsah Lake, may induce serious diseases to consumers, especially when eaten raw or insufficient cooking.

Exopolysaccharide from Porphyridium cruentum (purpureum) is Not Toxic and Stimulates Immune Response against Vibriosis: The Assessment Using Zebrafish and White Shrimp Litopenaeus vannamei

Exopolysaccharides, or extracellular polysaccharides (EPS, sPS), represent a valuable metabolite compound synthesized from red microalgae. It is a non-toxic natural agent and can be applied as an immunostimulant. The toxicity test of exopolysaccharides from Porphyridium has been done in vivo using zebrafish (Danio rerio) embryonic model, or the ZET (zebrafish embryotoxicity test). The administration of extracellular polysaccharides or exopolysaccharides (EPS) from microalgae Porphyridium cruentum (synonym: P. purpureum) to shrimps Litopenaeus vannamei was investigated to determine the effect of this immunostimulant on their non-specific immune response and to test if this compound can be used as a protective agent for shrimps in relation to Vibrio infection. For immune response, exopolysaccharides were given to shrimps via the immersion method on day 1 and booster on day 8. Shrimp hemocytes were taken on day 1 (EPS administration), day 7 (no treatment), day 8 (EPS booster) and day 9 (Vibrio infection) and tested for their immune response on each treatment. The result shows that the EPS is not toxic, as represented by the normal embryonic development and the mortality data. In the Pacific white shrimps, an increase in the values of all immune parameters was shown, in line with the increasing EPS concentration, except for the differential hemocyte count (DHC). In detail, an increase was noted in total hemocytes (THC) value, phagocytotic activity (PA) and respiratory burst (RB) in line with the EPS concentration increase. These results and other previous studies indicate that EPS from Porphyridium is safe, enhances immune parameters in shrimp rapidly, and has the ability to act as an immunostimulant or an immunomodulator. It is a good modulator for the non-specific immune cells of Pacific white shrimps, and it can be used as a preventive agent against vibriosis.

Toxicological effects of microplastics and phenanthrene to zebrafish (Danio rerio)

The toxicology of microplastics in combination with other pollutants has attracted widespread attention. In this study, zebrafish were exposed to 3 mg/L polystyrene microplastic, 0.2 mg/L phenanthrene, and a combination of both. Zebrafish microplastic uptake, phenanthrene accumulation, antioxidant-associated enzyme activity and related gene expression, immune-associated gene expression, and the gut microflora were measured after 12 and 24 days of exposure. Phenanthrene and microplastic accumulation increased with exposure time and was also greater in the combined exposure group than in the single exposure group. Combined analysis of antioxidant enzyme activity and immune and antioxidant-related genes shows that exposure alone causes oxidative stress in zebrafish, ultimately increasing immunity and the expression of oxidative stress genes, while combined exposure exacerbates these changes. Fusobacteria decreased and Proteobacteria and Bacteroidetes increased in the three exposure groups of gut microorganisms. Overall, our study demonstrates that microplastics enhance the toxicity of phenanthrene and that the two have a synergistic effect.

Immune toxicity of phenanthrene and its combined effects of white spot syndrome virus on the survival of kuruma shrimp (Penaeus Japonicus)

Shrimp inhabiting coasts that are frequented by humans are exposed to various pollutants. Additionally, viral infections that cause serious damage to shrimp populations have been observed in these environments. The present study sought to evaluate the immunotoxic effects of phenanthrene (Phe), a pollutant detected in coastal environments, on kuruma shrimp (Penaeus japonicus). We further examined the survival of shrimp following combined exposure to Phe (30 or 300 μg/L) and white spot syndrome virus (WSSV). Results show that exposure to Phe for seven days decreased immune system-related parameters, including total hemocyte count and phenoloxidase activity in hemolymph (p < 0.05). However, these effects were not detected after three days of exposure. Moreover, a combined exposure assay revealed that shrimp mortality increased following exposure to 300 μg/L Phe and infection with WSSV. The number of WSSV gene copies was also observed to increase in these co-exposed shrimp. Taken together, these results indicate that long-term Phe exposure impairs the immune system of P. japonicus, resulting in fatal proliferation of WSSV. Hence, considering that combined exposure to Phe and WSSV leads to increased mortality of shrimp, it is imperative that the detrimental effects elicited by multiple stresses be considered, and controlled, in areas inhabited by kuruma shrimp.

Microplastic pollution as a grand challenge in marine research: A closer look at their adverse impacts on the immune and reproductive systems

Microplastic (MP) pollution of the marine environment is now a growing global concern posing a threat to a variety of species through the ingestion and transfer within food webs. This is considered a potential toxicological threat to marine species due to the chemical additives used to make many plastic products, or the persistent organic pollutants that may accumulate on them while residing in the environment. While the presence of MPs in the marine environment is widely documented, there are no other review articles providing a summary of published effect studies of MPs on the immune and reproductive systems of marine species. This manuscript reviews reproductive and immune-system changes in response to MPs in 7 and 9 species, respectively. Some species such as Mytilus galloprovincialis and oyster Crassostrea gigas were investigated in multiple papers. Most studies have been conducted on invertebrates, and only 3 studies have been performed on vertebrates, with exposure times ranging between 30 min and 60 days. A review of the literature revealed that the most common MPs types studied in relation to adverse impacts on immune system and reproductive success in marine species were polystyrene (PS) and polyethylene (PE). The immune system's responses to MPs exposure varied depending on the species, with altered organismal defense mechanisms and neutrophil function observed in fish and changes in lysosomal membrane stability and apoptotic-like nuclear alterations in phagocytes reported in invertebrate species. Reproductive responses to MPs exposure, varied depending on species, but included significant reduction in gamete and oocyte quality, fecundity, sperm swimming speed, and quality of offspring. The lack of published data means that developing a clear understanding of the impact across taxonomic groups with different feeding and behavioral traits is often difficult. Further work is required to better understand the risk MPs pose to the immune and reproductive systems of marine species in order to fully evaluate the impact these ubiquitous pollutants are having on marine ecosystems and the associated goods and services they provide.

Immunotoxicity of petroleum hydrocarbons and microplastics alone or in combination to a bivalve species: Synergic impacts and potential toxication mechanisms

Both the frequent occurrence of accidental petroleum spills and the ubiquitous presence of microplastics (MPs) in the sea may pose severe threats to marine species. However, the immunotoxic impacts of these two types of pollutants and the underlying toxication mechanisms still remain largely unknown in sessile filter-feeding bivalve mollusks. Therefore, the impacts of exposure to petroleum hydrocarbons and MPs alone or in combination on the total count, cell type composition, and phagocytic activity of hemocytes were investigated in the blood clam, Tegillarca granosa. In addition, the intracellular ROS content, cell viability, degree of DNA damage, and expression levels of genes from immune-, apoptosis-, and immunotoxicity-related pathways were analyzed to reveal the potential toxication mechanisms. The results demonstrated that exposure to petroleum hydrocarbons and MPs alone or in combination at environmentally realistic concentrations could exert significant immunotoxic impacts on the blood clam, which may be caused by alterations in a series of physiological and molecular processes. In addition, the immunotoxicity of petroleum hydrocarbons could be significantly aggravated by the copresence of MPs, which suggests that coexposure to these two pollutants deserves closer attention.

Realistic environmental exposure to microplastics does not induce biological effects in the Pacific oyster Crassostrea gigas

The aim of the present study was to evaluate the presence and potential toxic effects of plastic fragments (<400 μm) of polyethylene and polypropylene on the Pacific oyster Crassostrea gigas. Oysters were exposed to environmentally relevant concentrations (0, 0.008, 10, 100 μg of particles/L) during 10 days, followed by a depuration period of 10 days in clean seawater. Effects of microplastics were evaluated on the clearance rate of organisms, tissue alteration, antioxidant defense, immune alteration and DNA damage. Detection and quantification of microplastics in oyster's tissues (digestive gland, gills and other tissues) and biodeposits using infrared microscopy were also conducted. Microplastics were detected in oyster's biodeposits following exposure to all tested concentrations: 0.003, 0.006 and 0.05 particles/mg of biodeposits in oysters exposed to 0.008, 10 and 100 μg of particles/L, respectively. No significant modulation of biological markers was measured in organisms exposed to microplastics in environmentally relevant conditions.

Fluoxetine suppresses the immune responses of blood clams by reducing haemocyte viability, disturbing signal transduction and imposing physiological stress

The antidepressant fluoxetine (FLX), a selective serotonin reuptake inhibitor, is widely prescribed for the treatment of depression and anxiety disorders. Nowadays, measurable quantities of FLX have been frequently detected in the aquatic ecosystems worldwide, which may pose a potential threat to aquatic organisms. Although the impacts of FLX exposure on immune responses are increasingly well documented in mammals, they remain poorly understood in aquatic invertebrates. Therefore, to gain a better understanding of the ecotoxicological effects of FLX, the impacts of waterborne FLX exposure on the immune responses of blood clam, Tegillarca granosa, were investigated in this study. Results obtained showed that both cellular and humoural immune responses in T. granosa were suppressed by exposure to waterborne FLX, as indicated by total counts of haemocytes (THC), phagocytic rate, and activities of superoxide dismutases (SOD) and catalase (CAT), suggesting that waterborne FLX renders blood clams more vulnerable to pathogen challenges. To ascertain the mechanisms explaining how waterborne FLX affects immune responses, haemocyte viabilities, intracellular Ca²⁺ levels, in vivo concentrations of neurotransmitters, physiological stress conditions (as indicated by in vivo concentrations of cortisol), and expressions of key regulatory genes from Ca²⁺ and neurotransmitter signal transduction, as well as immune-related signalling pathways, were examined after 10 days of FLX exposure by blood clams via 1, 10 and 100 μg/L waterborne FLX. The results obtained indicated that immune response suppression caused by waterborne FLX could be due to (i) inhibited haemocyte viabilities, which subsequently reduce the THC; (ii) altered intracellular Ca²⁺ and neurotransmitter concentrations, which lead to constrained phagocytosis; and (iii) aggravated physiological stress, which thereafter hampers immune-related NFκB signalling pathways.

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.

Chlorothalonil induces oxidative stress and reduces enzymatic activities of Na+/K+-ATPase and acetylcholinesterase in gill tissues of marine bivalves

Chlorothalonil is a thiol-reactive antifoulant that disperses widely and has been found in the marine environment. However, there is limited information on the deleterious effects of chlorothalonil in marine mollusks. In this study, we evaluated the effects of chlorothalonil on the gill tissues of the Pacific oyster, Crassostrea gigas and the blue mussel, Mytilus edulis after exposure to different concentrations of chlorothalonil (0.1, 1, and 10 μg L⁻¹) for 96 h. Following exposure to 1 and/or 10 μg L⁻¹ of chlorothalonil, malondialdehyde (MDA) levels significantly increased in the gill tissues of C. gigas and M. edulis compared to that in the control group at 96 h. Similarly, glutathione (GSH) levels were significantly affected in both bivalves after chlorothalonil exposure. The chlorothalonil treatment caused a significant time- and concentration-dependent increase in the activity of enzymes, such as catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR), in the antioxidant defense system. Furthermore, 10 μg L⁻¹ of chlorothalonil resulted in significant inhibitions in the enzymatic activity of Na⁺/K⁺-ATPase and acetylcholinesterase (AChE). These results suggest that chlorothalonil induces potential oxidative stress and changes in osmoregulation and the cholinergic system in bivalve gill tissues. This information will be a useful reference for the potential toxicity of chlorothalonil in marine bivalves.

Use of multiple endpoints to investigate the ecotoxicological effects of abamectin and thiamethoxam on Theba pisana snails

The ecotoxicological effects of dietary exposure to sublethal concentration (1/20 LC₅₀) of abamectin (ABM) and thiamethoxam (TMX) for two weeks exposure and one week recovery on oxidative stress parameters; lipid peroxidation (LPO), reduced glutathione (GSH), catalase (CAT) and glutathione S-transferase (GST), Deoxyribonucleic acid (DNA) damage as well as immunological parameters; cell death, phagocytosis, lysosomal membrane stability (LMS), lectins, superoxide anion (O₂^-) generation, phenoloxidase (PO), peroxidase (POD) and hemocyanin (Hc) of the land snail, Theba pisana were examined. The results showed that both tested compounds significantly increased DNA damage, LPO content, the activity of CAT and GST, cell death, POD activity, Hc level, whereas, significantly declined in phagocytic activity, LMS, lectins level, O2^- generation, PO activity, and GSH content compared to the controls after two week exposure. After one week of recovery, the measured biochemical parameters of treated snails were slightly repaired but their levels were still less than that of the level of untreated animals. Overall, based on acute toxicity endpoints, ABM appeared to be more harmful than TMX against this animal. Indeed, the different patterns of endpoint responses could represent a useful picture to characterise exposure to these pesticides in the land snail, T. pisana. This battery of snail endpoints might be a promising option to biomonitor the health of the terrestrial ecosystem and to offer valuable insights to the pesticides toxicity mechanisms.

Using cell apoptosis, micronuclei and immune alternations as biomarkers of phenanthrene exposure in yellowfin seabream (Acanthopagrus latus)

In the present study, the apoptosis and tissue changes in the spleen, as well as humoral immune-related parameters, micronuclei (MN) induction in blood cells and Ethoxyresorufin-O-deethylase (EROD) activity were investigated in yellowfin seabream (Acanthopagrus latus) after short-term exposure to phenanthrene (Phe). The fish were intraperitoneally injected with different concentrations (2, 20 and 40 mg kg^-1) of Phe and tissue and blood samples were collected 1, 4, 7 and 14 days after injection. The concentrations of Phe in the fish liver increased 4 days after the experiment. EROD activity showed a pattern consistent with Phe concentration in the liver. Apoptotic index in the spleen increased dose dependently in Phe-exposed fish. Exposure to Phe caused significant decrease in the plasma level of immunoglobulin M, phagocytic and respiratory burst activity after 4 days of exposure. The frequency of MN in the erythrocytes of the treated fish was significantly higher than control. The main pathological alterations in the spleen included the increase in melanomacrophage centers (MMCs), destroyed red blood cell and hemorrhage. The degree of tissue changes in the spleen of the exposed fish ranged from slight to moderate damage. The size and number of MMCs in the spleen were significantly higher in Phe-treated fish compared to the control. Our results showed that Phe could suppress immune responses in fish, induce cell apoptosis, histological changes in the spleen and MN formation. This may suggest those parameters consider as useful biomarkers for monitoring of the health status of fish during exposure to Phe.

Effects of phenanthrene on early development of the Pacific oyster Crassostrea gigas (Thunberg, 1789)

Phenanthnere (PHE) is a polycyclic aromatic hydrocarbon continuously discarded in the marine environment and bioavailable to many aquatic species. Although studies about PHE toxicity have been documented for adult oysters, the effects on early developmental stages are poorly characterized in bivalves. In this study, the effects of PHE (0.02 and 2.0μg.L^-1) were evaluated on the embryogenesis and larval development of Crassostrea gigas. Toxicity bioassays, growth and deformities assessment, analysis of shell calcium abundance and transcript levels of genes related to xenobiotic biotransformation (CYP2AU2, CYP30C1), immune system (Cg-Tal) and tissue growth and shell formation (Ferritin, Insulin-like, Cg-Try, Calmodulin and Nacrein) were assayed in D-shape larvae after 24h of PHE exposure. At the highest concentration (2.0μg.L^-1), PHE decreased the frequency of normal development (19.7±2.9%) and shell size (53.5±2.8mm). Developmental deformities were mostly related to abnormal mantle and shell formation. Lower calcium levels in oyster shells exposed to PHE 2.0μg.L^-1 were observed, suggesting effects on shell structure. At this same PHE concentration, CYP30C1, Cg-Tal, Cg-Tyr, Calmodulin were upregulated and CYP2AU2, Ferritin, Nacrein, and Insulin-Like were downregulated compared to control larvae. At the lowest PHE concentration (0.02μg.L^-1), it was observed a minor decrease in normal larval development (89,6±6%) and the remaining parameters were not affected. This is the first study to provide evidences that exposure to PHE can affect early oyster development at the molecular and morphological levels, possibly threatening this bivalve species.

Combination of polycyclic aromatic hydrocarbons and temperature exposure: In vitro effects on immune response of European clam (Ruditapes decussatus)

Marine organisms are subjected to various biotic and abiotic factors such as changes of temperature and pollutants [e.g. polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and heavy metals, which may affect their defense mechanisms. In this context, the aim was to evaluate the combined effects of temperature (20 and 30 °C) and PAHs (fluorene, phenanthrene and pyrene) at two concentrations (10^-5 and 10^-3 mg mL^-1) on the immune responses of the European clam Ruditapes decussatus were after 24 h of in vitro exposure. Total haemocyte count, cell viability, phenoloxidase, lysozyme, alkaline phosphatase, esterase, antibacterial and agglutinating activities were measured. Exposure to high temperatures resulted in lower phosphatase alkaline activity and higher haemocyte viability and antibacterial and haemagglutinating activities, compared with the values recorded for clams maintained at low temperature. Only pyrene induced a significant decrease in haemocyte lysozyme (at 20 and 30 °C) and esterase (at 30 °C) activities. The total haemocyte count was increased by phenanthrene and pyrene at 20 °C and at 30 °C, respectively. Alkaline phosphatase activity increased when haemocytes were exposed to pyrene at 30 °C but decreased in the presence of fluorene at 20 °C. Furthermore, haemocyte viability was low in the presence of pyrene and fluorene at 20 °C and 30 °C, respectively, but was unaffected by phenanthrene. Antibacterial activity was significantly increased and no-significantly affected by the presence of pyrene and fluorene at 20 °C and 30 °C, respectively. The present study demonstrates the strong effect of PAHs and high temperature on haemocyte viability and other important immune functions, including phosphatase alkaline and antibacterial activities. Furthermore, changes in the immune parameters of European clam resulting from high temperatures may modulate the effects of PAHs and vice versa.

Hepatic gene transcription profiles in turbot (Scophthalmus maximus) experimentally exposed to heavy fuel oil nº 6 and to styrene

Oil and chemical spills in the marine environment, although sporadic, are highly dangerous to biota inhabiting coastal and estuarine areas. Effects of spilled compounds in exposed organisms occur at different biological organization levels: from molecular, cellular or tissue levels to the physiological one. The present study aims to determine the specific hepatic gene transcription profiles observed in turbot juveniles under exposure to fuel oil n °6 and styrene vs controls using an immune enriched turbot (Scophthalmus maximus) oligo-microarray containing 2716 specific gene probes. After 3 days of exposure, fuel oil specifically induced aryl hydrocarbon receptor mediated transcriptional response through up-regulation of genes, such as ahrr and cyp1a1. More gene transcripts were regulated after 14 days of exposure involved in ribosomal biosynthesis, immune modulation, and oxidative response among the most significantly regulated functional pathways. On the contrary, gene transcription alterations caused by styrene did not highlight any significantly regulated molecular or metabolic pathway. This was also previously reported at cell and tissue level where no apparent responses were distinguishable. For the fuel oil experiment, obtained specific gene profiles could be related to changes in cell-tissue organization in the same individuals, such as increased hepatocyte vacuolization, decrease in melano-macrophage centers and the regulation of leukocyte numbers. In conclusion, the mode of action reflected by gene transcription profiles analyzed hereby in turbot livers could be linked with the responses previously reported at higher biological organization levels. Molecular alterations described hereby could be preceding observed alterations at cell and tissue levels.

Assessment of the fitness of the mussel Mytilus galloprovincialis two years after the Hebei Spirit oil spill

In December 2007, >150km of the West coast of Korea were heavily polluted by crude oil leaked from the oil tanker Hebei Spirit, leading to mass mortality of bivalve mollusks on the intertidal areas. Two years after, mussels Mytilus galloprovincialis were collected from two impacted sites to investigate sub-lethal effects of the oil spill. Tissue content in polycyclic aromatic hydrocarbons (PAHs), hemocyte parameters, reproductive status and energetic reserves were analyzed. PAHs in tissues of mussels as well as hemocyte parameters were not different between impacted and control sites. Energetic reserves were altered in mussels from the impacted sites. Glycogen content remained low at polluted sites, whatever the season. Two years after the Hebei Spirit oil spill, mussels then presented altered energetic metabolism. Further investigations are thus warranted to monitor the sustainability of mussel populations on the oil spilled West coast of Korea.

Antiviral Activity of Myticin C Peptide from Mussel: an Ancient Defense against Herpesviruses

Little is known about the antiviral response in mollusks. As in other invertebrates, the interferon signaling pathways have not been identified, and in fact, there is a debate about whether invertebrates possess antiviral immunity similar to that of vertebrates. In marine bivalves, due to their filtering activity, interaction with putative pathogens, including viruses, is very high, suggesting that they should have mechanisms to address these infections. In this study, we confirmed that constitutively expressed molecules in naive mussels confer resistance in oysters to ostreid herpesvirus 1 (OsHV-1) when oyster hemocytes are incubated with mussel hemolymph. Using a proteomic approach, myticin C peptides were identified in both mussel hemolymph and hemocytes. Myticins, antimicrobial peptides that have been previously characterized, were constitutively expressed in a fraction of mussel hemocytes and showed antiviral activity against OsHV-1, suggesting that these molecules could be responsible for the antiviral activity of mussel hemolymph. For the first time, a molecule from a bivalve has shown antiviral activity against a virus affecting mollusks. Moreover, myticin C peptides showed antiviral activity against human herpes simplex viruses 1 (HSV-1) and 2 (HSV-2). In summary, our work sheds light on the invertebrate antiviral immune response with the identification of a molecule with potential biotechnological applications.

IMPORTANCE

Several bioactive molecules that have potential pharmaceutical or industrial applications have been identified and isolated from marine invertebrates. Myticin C, an antimicrobial peptide from the Mediterranean mussel (Mytilus galloprovincialis) that was identified by proteomic techniques in both mussel hemolymph and hemocytes, showed potential as an antiviral agent against ostreid herpesvirus 1 (OsHV-1), which represents a major threat to the oyster-farming sector. Both hemolymph from mussels and a myticin C peptide inhibited OsHV-1 replication in oyster hemocytes. Additionally, a modified peptide derived from myticin C or the nanoencapsulated normal peptide also showed antiviral activity against the human herpesviruses HSV-1 and HSV-2. Therefore, myticin C is an example of the biotechnological and therapeutic potential of mollusks.

A novel siglec (CgSiglec-1) from the Pacific oyster (Crassostrea gigas) with broad recognition spectrum and inhibitory activity to apoptosis, phagocytosis and cytokine release

Sialic acid binding immunoglobulin-type lectin (siglec) belongs to the immunoglobulin superfamily (IgSF), which acts as regulator involved in glycan recognition and signal transduction in the immune and nervous systems. In the present study, a siglec gene (designated CgSiglec-1) was characterized from the Pacific oyster, Crassostrea gigas. The cDNA of CgSiglec-1 was of 1251 bp encoding a predicted polypeptide of 416 amino acids. CgSiglec-1 was composed of two I-set immunoglobulin (Ig) domains, one transmembrane (TM) domain and two ITIM motifs, sharing a sequence similarity with vertebrate CD22 homologs. The mRNA expression of CgSiglec-1 could be detected in all the selected tissues, with the highest level in hemocytes and labial palps. The confocal analysis revealed that CgSiglec-1 mainly distributed on the cytoplasmic membrane of the oyster hemocytes. In addition, the mRNA transcripts of CgSiglec-1 in hemocytes increased significantly (4.29-fold to that of control group, p < 0.05) after Vibrio splendidus stimulation. The recombinant CgSiglec-1 protein (rCgSiglec-1) could bind to poly sialic acid (pSIAS), lipopolysaccharides (LPS) and peptidoglycan (PGN) in a dose-dependent manner. The blockade of CgSiglec-1 by specific polyclonal antibodies could enhance the LPS-induced cell apoptosis, phagocytosis towards V. splendidus and the release of cytokines, such as CgTNF-1, CgIFNLP and CgIL-17. The results collectively indicated that CgSiglec-1 could act as a bridge molecule between invader recognition and signal transduction cascade, and modulate the immune response by inhibiting various important processes of immunity in oyster.

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

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

Biological effects of marine diesel oil exposure in red king crab (Paralithodes camtschaticus) assessed through a water and foodborne exposure experiment

Shipping activities are expected to increase in the Arctic Seas. Today, the majority of vessels are using marine diesel oil (MDO) as propulsion fuel. However, there is a general lack of knowledge of how cold-water marine species respond to acute exposures to MDO. Arctic red king crabs (Paralithodes camtschaticus) were exposed to mechanically dispersed MDO in a flow-through exposure system for one week followed by three weeks of recovery. Observations of increased movements in exposed crabs were interpreted as avoidance behaviour. Further, glutathione peroxidase activity increased in high exposed crab, the catalase activity showed an insignificant increase with exposure, while no differences between groups were observed for lipid peroxidation and acetylcholinesterase activity. After three weeks of recovery in clean seawater, polycyclic aromatic hydrocarbons concentrations in the crabs were significantly reduced, with no specific biomarker responses in exposed groups compared to the control. The results suggest that effects from instantaneous MDO spill only will have short-term effects on the red king crab.

Detection of benzo[a]pyrene-induced immunotoxicity in orange spotted grouper (Epinephelus coioides)

This study aimed to investigate the effects of benzo[a]pyrene (BaP) on immune status of orange spotted grouper (Epinephelus coioides). Fish were injected with 2, 20 and 35 mg/kg-bw of BaP and were kept under laboratory conditions for 14 days. Blood samples were taken at days 1, 4, 7, and 14 and changes in total WBC and RBC, phagocytosis, lysozyme activity, lysosomal membrane stability, immunoglobulin M (IgM) level and antibacterial activity were evaluated. Also BaP bioaccumulation in fish muscle was measured. BaP concentration in the muscle of treated fish reached a maximum level after 4 days (P < 0.05). Exposure of fish to BaP resulted in a significant decrease of total RBC and WBC, lysozyme activity, lysosomal membrane stability, IgM level and antibacterial activity after 4 days and phagocytosis after 7 days of the experiment (P < 0.05). Totally, the results revealed BaP ability to suppress the fish immune function.

Interactive effects of copper exposure and environmental hypercapnia on immune functions of marine bivalves Crassostrea virginica and Mercenaria mercenaria

Estuarine organisms such as bivalves are commonly exposed to trace metals such as copper (Cu) and hypercapnia (elevated CO2 levels) in their habitats, which may affect their physiology and immune function. This study investigated the combined effects of elevated CO2 levels (∼800-2000 μatm PCO2, such as predicted by the near-future scenarios of global climate change) and Cu (50 μg l(-1)) on immune functions of the sediment dwelling hard clams Mercenaria mercenaria and an epifaunal bivalve, the eastern oyster Crassostrea virginica. Clams and oysters were exposed for 4 weeks to different CO2 and Cu levels, and tissue Cu burdens and immune parameters were assessed to test the hypothesis that hypercapnia will enhance Cu uptake due to the higher bioavailability of free Cu(2+) and increase the immunomodulatory effects of Cu. Exposure to Cu stimulated key immune parameters of clams and oysters leading to increased number of circulating hemocytes, higher phagocytosis and adhesion ability of hemocytes, as well as enhanced antiparasitic and antibacterial properties of the hemolymph reflected in higher activities of lysozyme and inhibitors of cysteine proteases. Lysozyme activation by Cu exposure was most prominent in normocapnia (∼400 μatm PCO2) and an increase in the levels of the protease inhibitors was strongest in hypercapnia (∼800-2000 μatm PCO2), but other immunostimulatory effects of Cu were evident in all PCO2 exposures. Metabolic activity of hemocytes of clams and oysters (measured as routine and mitochondrial oxygen consumption rates) was suppressed by Cu exposure likely reflecting lower rates of ATP synthesis and/or turnover. However, this metabolic suppression had no negative effects of the studied immune functions of hemocytes such as phagocytosis or adhesion capacity. Hypercapnia (∼800-2000 μatm PCO2) slightly but significantly enhanced accumulation of Cu in hemocytes, consistent with higher Cu(2+) bioavailability in CO2-acidified water, but had little effect on cellular and humoral immune traits of clams and oysters. These findings indicate that low levels of Cu contamination may enhance immunity of estuarine bivalves while moderate hypercapnia (such as predicted by the near future scenarios of the global climate change) does not strongly affect their immune parameters.

Histological responses and localization of the cytochrome P450 (CYP2AU1) in Crassostrea brasiliana exposed to phenanthrene

Phenanthrene (PHE) is an abundant polycyclic aromatic hydrocarbon (PAH), widely distributed in aquatic environment. The aim of this study was to evaluate the histological and molecular effects in the native oyster Crassostrea brasiliana(Lamarck, 1819) exposed to 100 and 1000 μg L(-1) PHE for 1, 5 and 10 days. Histological and chemical analyses were performed to evaluate, respectively, alterations in oyster tissues and bioaccumulation. In situ hybridization (ISH) was used to assess tissue distribution of CYP2AU1, a gene formerly identified as activated by PHE exposure in this species.Quantitative polymerase chain reaction (qPCR) in mantle was carried out to validate ISH data. Oysters bioaccumulated PHE increasingly along the exposure period in both exposure concentrations. Histologic changes, like tubular atrophy in digestive diverticula (digestive gland) and increased number of mucous cells in the mantle were observed in animals exposed to PHE for 10 days. ISH showed the presence of CYP2AU1transcripts in gills, digestive diverticula, mantle, intestine and gonads, but significant differences in transcript detection by ISH between treatments occurred only in gills, mantle and intestine. A positive and significant correlation between tubular atrophy and CYP2AU1hybridization signal was observed in digestive diverticula, suggesting that this gene product might be involved in energetic metabolism in C. brasiliana. Increased mucous cells and CYP2AU1transcript levels were observed in the mantle, where the inner and middle lobes showed higher intensity of hybridization signal. Mantle should be considered as a target organ for CYP2AU1 transcript evaluation and histological alterations in biomonitoring studies. CYP2AU1 signal in female gonads was observed in all follicular cells from different gonadic stages, while in male only the spermatic follicle cells of the wall in the pre-spawning stage showed this signal. ISH was an effective technique to evaluate the effects of PHE exposure and to locate CYP2AU1 transcripts in different tissues of oyster C. brasiliana.

Developmental abnormalities and differential expression of genes induced in oil and dispersant exposed Menidia beryllina embryos

Exposure of fish embryos to relatively low concentrations of oil has been implicated in sub-lethal toxicity. The objective of this study was to determine the effects of the exposure of Menidia beryllina embryos at 30-48h post-fertilization to the water accommodated fractions of oil (WAF, 200ppm, v/v), dispersants (20ppm, v/v, Corexit 9500 or 9527), and mixtures of oil and each of the dispersants to produce chemically enhanced water accommodated fractions (CEWAFs) over a 72-hour period. The polyaromatic hydrocarbon (PAH) and benzene, toluene, ethylene and xylene (BTEX) constituents of the 5X concentrated exposure solutions (control, WAF, dispersants and CEWAFs) were determined and those of the 1× exposures were derived using a dilution factor. PAH, BTEX and low molecular weight PAH constituents greater than 1ppb were observed in WAF and the dispersants, but at much higher levels in CEWAFs. The WAF and CEWAFs post-weathering were diluted at 1:5 (200ml WAF/CEWAF: 800ml 25ppt saltwater) for embryo exposures. Mortality, heartbeat, embryo normalcy, abnormality types and severities were recorded. The qPCR assay was used to quantify abundances of transcripts of target genes for sexual differentiation and sex determination (StAR, dmrt-1, amh, cyp19b, vtg and chg-L,), growth regulation (ghr) and stress response (cyp1a and Hsp90); and gapdh served as the housekeeping gene. Temperature was 21±1.5°C throughout the experimental period, while mortality was low and not significantly different (p=0.68) among treatments. Heartbeat was significantly different (0.0034) with the lowest heartbeats recorded in Corexit 9500 (67.5beats/min) and 9527 (67.1beats/min) exposed embryos compared with controls (82.7beats/min). Significantly more treated embryos were in a state of deterioration, with significantly more embryos presenting arrested tissue differentiation compared with controls (p=0.021). Exposure to WAF, dispersants and CEWAF induced aberrant expression of all the genes, with star, dmrt-1, ghr and hsp90 being significantly down-regulated in CEWAF and cyp19b in Corexit 9527. The cyp1a and cyp19b were significantly up-regulated in CEWAFs and WAF, respectively. The molecular endpoints were most sensitive, especially the expression of star, cyp19b, cyp1a, hsp90 and could therefore be used as early indicators of long term effects of Corexit 9500 and 9527 usage in oil spill management on M. beryllina, a valid sentinel for oil pollution events.

Immunotoxicological effects of environmental contaminants on marine bivalves

Coastal areas are complex environments frequently contaminated by numerous pollutants that represent a potential threat to marine organisms, especially bivalves. These pollutants may have major ecological consequences. Although effects of different environmental contaminants on the immune system in marine bivalves have been already reported, a few of reviews summarizes these effects. The main purpose of this chapter relies on summarizing recent body of data on immunotoxicity in bivalves subjected to contaminants. Immune effects of heavy metals, pesticides, HAP, PCB and pharmaceuticals are presented and discussed and a particular section is devoted to nanoparticle effects. A large body of literature is now available on this topic. Finally, the urgent need of a better understanding of complex interactions between contaminants, marine bivalves and infectious diseases is noticed.

Organic pollution and its effects in the marine mussel Mytilus galloprovincialis in Eastern Mediterranean coasts

Persistent chemicals and emerging pollutants are continuously detected in marine waters and biota. Out of these, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCs) are significant contaminants with decades of presence in the marine environment. The Mediterranean Sea is an ecosystem directly affected by a variety of anthropogenic activities including industry, municipal, touristic, commercial and agricultural. The Mediterranean mussel (Mytilus galloprovincialis) is a filter feeder, which presents wide distribution. In this regard, the specific organism was used as a biological indicator for the monitoring and evaluation of pollution in the studied areas with focus on the mentioned chemical groups. Pristine Turkish sites with minimum effect from anthropogenic activities, in contrast with Greek sites which were subjected to heavy industrial and shipping activity, were selected. A gas chromatographic tandem mass spectrometric method (GC-MS/MS) was developed and validated to monitor 34 compounds (16 EPA priority PAHs and 18 OCs). Analyses of mussel samples in 2011 from sites with the limited anthropogenic pollution shores have shown the occurrence of 11 pollutants (6 PAHs, 5 OCs), while in the samples from sites with intensive activity and expected pollution, 12 PAHs and 6 OCs were detected. Biochemical and biological responses studied only in mussels samples from the sites with the highest contamination showed a situation that was under strong seasonal influence. The intensity of the response was also influenced by deployment duration. Noteworthy correlations were detected among biochemical/biological effects and between mussel body burden and these effects. Continuous monitoring of priority pollutants of East Mediterranean Sea is vital both for ecological and human risk assessment purposes.

Metal-PAH mixtures in the aquatic environment: a review of co-toxic mechanisms leading to more-than-additive outcomes

Mixtures of metals and polycyclic aromatic hydrocarbons (PAHs) occur ubiquitously in aquatic environments, yet relatively little is known regarding their combined toxicities. Emerging reports investigating the additive mortality in metal-PAH mixtures have indicated that more-than-additive effects are equally as common as strictly-additive effects, raising concern for ecological risk assessment typically based on the summation of individual toxicities. Moreover, the current separation of focus between in vivo and in vitro studies, and fine- and coarse-scale endpoints, creates uncertainty regarding the mechanisms of co-toxicity involved in more-than-additive effects on whole organisms. Drawing from literature on metal and PAH toxicity in bacteria, protozoa, invertebrates, fish, and mammalian models, this review outlines several key mechanistic interactions likely to promote more-than-additive toxicity in metal-PAH mixtures. Namely, the deleterious effects of PAHs on membrane integrity and permeability to metals, the potential for metal-PAH complexation, the inhibitory nature of metals to the detoxification of PAHs via the cytochrome P450 pathway, the inhibitory nature of PAHs towards the detoxification of metals via metallothionein, and the potentiated production of reactive oxygenated species (ROS) in certain metal (e.g. Cu) and PAH (e.g., phenanthrenequinone) mixtures. Moreover, the mutual inhibition of detoxification suggests the possibility of positive feedback among these mechanisms. The individual toxicities and interactive aspects of contaminant transport, detoxification, and the production of ROS are herein discussed.

A light in the darkness: new biotransformation genes, antioxidant parameters and tissue-specific responses in oysters exposed to phenanthrene

Phenanthrene (PHE), a major component of crude oil, is one of the most abundant polycyclic aromatic hydrocarbons (PAHs) in aquatic ecosystems, and is readily bioavailable to marine organisms. Understanding the toxicity of PAHs in animals requires knowledge of the systems for xenobiotic biotransformation and antioxidant defence and these are poorly understood in bivalves. We report, for the first time, new transcripts and tissue-specific transcription in gill and digestive gland from the oyster Crassostrea brasiliana following 24h exposure to 100 and 1000μgL(-1) PHE, a model PAH. Six new cytochrome P450 (CYP) and four new glutathione S-transferase (GST) genes were analysed by means of quantitative reverse transcription PCR (qRT-PCR). Different antioxidant endpoints, including both enzymatic and non-enzymatic parameters, were assessed as potential biomarkers of oxidative stress. GST activity was measured as an indicator of phase II biotransformation. Rapid clearance of PHE was associated with upregulation of both phase I and II genes, with more pronounced effects in the gill at 1000μgL(-1) PHE. After 24h of exposure, PHE also caused impairment of the antioxidant system, decreasing non-protein thiols and glutathione levels. On the other hand, no change in antioxidant enzymes was observed. PHE treatment (100μgL(-1)) significantly decreased GST activity in the gill of exposed oysters. Both CYP and GST were transcribed in a tissue-specific manner, reflecting the importance of the gill in the detoxification of PAHs. Likewise, the antioxidant parameters followed a similar pattern. The data provide strong evidence that these genes play key roles in C. brasiliana biotransformation of PHE and highlight the importance of gill in xenobiotic metabolism.

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.

Effects of the antidepressant fluoxetine on the immune parameters and acetylcholinesterase activity of the clam Venerupis philippinarum

Fluoxetine is an antidepressant used worldwide for the treatment of depression and other psychological disorders. The occurrence of fluoxetine in aquatic environments has been demonstrated. However, there is a lack of information about the effects of fluoxetine on non-target species, such as bivalve molluscs. In the present study, the effects of fluoxetine on the immune parameters of the clam Venerupis philippinarum were evaluated for the first time. Clams were exposed to various sublethal concentrations of fluoxetine (0, 1, 5, 25, 125, 625 μg l⁻¹) for 7 days, and the effects on the total haemocyte count (THC), the diameter and volume of haemocytes, haemocyte proliferation, Neutral Red uptake (NRU), and lysozyme activity in cell-free haemolymph (CFH) were evaluated. In addition, acetylcholinesterase (AChE) activity was measured in clam gills as a biomarker of neurotoxicity. A significant increase in THC values was observed in clams exposed to 25 μg l⁻¹ compared with controls, whereas no significant variations were recorded in either the diameter or the volume of haemocytes. Haemocyte proliferation increased significantly in animals exposed to 25, 125 and 625 μg l⁻¹ compared with controls. NRU decreased significantly in the haemocytes of clams exposed to 1 or 5 μg l⁻¹, whereas NRU returned to control values in clams exposed to the highest fluoxetine concentrations tested (25-625 μg l⁻¹). No significant alterations were observed in CFH lysozyme activity, whereas gill AChE activity decreased significantly in clams exposed to 1 or 5 μg l⁻¹. Overall, the obtained results demonstrated that fluoxetine markedly affected immune parameters and AChE activity in clams.

Immune responses during the larval stages of Mytilus galloprovincialis: metamorphosis alters immunocompetence, body shape and behavior

We investigated the development of the immune system during the larval stages of the mussel Mytilus galloprovincialis. The ability of trochophore and veliger larvae to phagocytose foreign particles (Escherichia coli and zymosan) was measured. Phagocytosis was detected as early as 24 h post-fertilization (hpf) using flow cytometry and fluorescence microscopy. However, although there was a high basal production of reactive oxygen and nitrogen species (ROS and NRS), the phagocytosis of zymosan did not trigger an associated increase in radical production. In addition, a panel of immune-related mussel genes (Myticin B, Myticin C, Mytilin B, Mytimycin precursor 1, Macrophage migration inhibition factor, lysozyme, C1q, membrane attack complex protein and fibrinogen-related protein) was selected for expression profile analysis throughout the different developmental stages (trochophore, veliger, metamorphosis, post-settlement and spat). The expression of these genes increased during the transition from trochophore to spat, and the level of expression was higher in oocytes than in trochophores, suggesting that gene expression during the first larval stages might be maternal in origin. Metamorphosis was identified as a crucial stage when larvae increased the expression of immune-related genes and responded to environmental signals. Whole-mount in situ hybridization studies showed the mantle edge as an important area in the development of immunocompetence in bivalve larvae. Larvae responded to both live and heat-inactivated bacteria by modulating expression of immune-related genes. Altogether, our results support that during the early stages of M. galloprovincialis development, immune mechanisms emerge to aid larvae in managing infections.

Can ecological history influence immunomarker responses and antioxidant enzyme activities in bivalves that have been experimentally exposed to contaminants? A new subject for discussion in "eco-immunology" studies

Numerous studies have demonstrated that environmental parameters affect bivalve immunomarkers. In the present study, we tested the hypothesis that clams (Venerupis philippinarum) collected in sites with different environmental conditions respond differently to experimental contaminant exposure. Clams were collected at two sites within the Lagoon of Venice that are influenced differently by both anthropogenic impact and natural conditions: Marghera, which is characterised by relatively high contamination levels and restricted clam fishing, and Chioggia, which is inside a licensed clam culture area that is characterised by lower contamination levels. Total haemocyte count, haemocyte diameter and volume, lysozyme activity in both haemocyte lysate and cell-free haemolymph, superoxide dismutase and catalase activities in gills and digestive glands were measured at time 0 (clam sampling time), after 7 days of acclimation in the laboratory and after 1, 3 and 7 days of copper exposure. Interestingly, statistical analyses (three-way ANOVA and Canonical Correlation Analysis) revealed persistent differences in the biological responses of clams from the two sampling sites before and after copper exposure. Conversely, the influence of copper on cellular and biochemical parameters was negligible. Overall, the results obtained indicated that animals with a different ecological history respond differently to experimental contaminant exposure. In addition, this study suggested that immunomarkers and other biomarkers might be used to determine the origin of fishing products.

Comparative study of biochemical and immunological biomarkers in three marine bivalves exposed at a polluted site

A battery of biochemical and immunological biomarkers used for pollution assessment were measured for first time in the clams Venus verrucosa and Callista chione and were compared with those of the mussel Mytilus galloprovincialis, a well-established indicator organism utilized in numerous environmental monitoring programs. Clams and mussel were transplanted at a polluted and a reference site or maintained at the laboratory. Among biochemical biomarkers, acetylcholinesterase did not differ at the polluted site in all species, but there was a significant difference between the mussel and the clams, glutathione S-transferase showed a clear inhibition at the polluted site in all species and a significant difference between the two clams was also indicated, while catalase activities were increased only in V. verrucosa at the polluted site and not in mussel or the other clam. Immunological biomarkers responses were also pronounced at the polluted site. Lysozyme activity was species-dependent whereas respiratory burst activity measured as luminol-dependent chemiluminescence (CL) was site and stimulus dependent, and it was evident in M. galloprovincialis and V. verrucosa and not in C. chione. Further investigation focused on biochemical and immunological biomarkers related with the oxidative mechanisms in clams will strengthen and expand their use as bioindicators for pollution assessment.

In vivo exposure of Mytilus edulis to living enteric bacteria: a threat for immune competency?

Mussels are widespread in coastal environments and experience various physical, chemical, and bacteriological conditions. Owing to the increase of coastal urbanization, mussels are now commonly exposed not only to indigenous bacteria, but also to enteric bacteria originating from pulsed and chronic sewage discharges into coastal environments. Due to its broad resilience to environmental variations, the blue mussel Mytilus edulis is commonly used as an indicator of environmental quality in bio-monitoring programs. However, since mussel immune system capabilities may be affected by the presence of exogenous fecal bacteria in coastal seawater subjected to sewage discharges, we aimed to determine the effect of in vivo bacterial challenges on mussels' immune competency by using two exogenous enteric bacterial strains, Escherichia coli and Enterococcus faecalis, and an indigenous bacterial strain Vibrio splendidus (as control). Bacterial strains were tested individually, by injection into the posterior adductor muscle at three different cell densities (10(2), 10(3), and 10(4) cells). Unlike classic in vitro experiments using higher bacterial concentrations, neither the enteric bacteria nor the indigenous strain induced significant increase or decrease of either cell-mediated (phagocytosis, reactive oxygen species, and NO(x) production) or humoral components (prophenoloxidase-like, acid phosphatase, and L-leucine-aminopeptidase production) of the immune system. This study demonstrates that, at low concentrations, E. coli and E. faecalis do not represent an additional threat that could impair M. edulis immune competency and, as a consequence, its potential of survival in coastal areas subjected to sewage discharges.

An integrated environmental approach to investigate biomarker fluctuations in the blue mussel Mytilus edulis L. in the Vilaine estuary, France

Estuarine areas represent complex and highly changing environments at the interface between freshwater and marine aquatic ecosystems. Therefore, the aquatic organisms living in estuaries have to face highly variable environmental conditions. The aim of this work was to study the influence of environmental changes from either natural or anthropogenic origins on the physiological responses of Mytilus edulis. Mussels were collected in the Vilaine estuary during early summer because this season represents a critical period of active reproduction in mussels and of increased anthropogenic inputs from agricultural and boating activities into the estuary. The physiological status of the mussel M. edulis was evaluated through measurements of a suite of biomarkers related to: oxidative stress (catalase, malondialdehyde), detoxication (benzopyrene hydroxylase, carboxylesterase), neurotoxicity (acetylcholinesterase), reproductive cycle (vitelline, condition index, maturation stages), immunotoxicity (hemocyte concentration, granulocyte percentage, phagocytosis, reactive oxygen species production, oxidative burst), and general physiological stress (lysosomal stability). A selection of relevant organic contaminant (pesticides, (polycyclic aromatic hydrocarbons, polychlorobiphenyls) was measured as well as environmental parameters (water temperature, salinity, total suspended solids, turbidity, chlorophyll a, pheopigments) and mussel phycotoxin contamination. Two locations differently exposed to the plume of the Vilaine River were compared. Both temporal and inter-site variations of these biomarkers were studied. Our results show that reproduction cycle and environmental parameters such as temperature, organic ontaminants, and algal blooms could strongly influence the biomarker responses. These observations highlight the necessity to conduct integrated environmental approaches in order to better understand the causes of biomarker variations.

Modulation of immune-associated parameters and antioxidant responses in the crab (Scylla serrata) exposed to mercury

Organic and inorganic contaminants can suppress immune function in molluscs and crustaceans. It was postulated that metals could modulate immune function in marine crabs. To test this hypothesis, sublethal effects of mercury (Hg) on cellular immune and biochemical responses of crabs were determined. When crabs were exposed for 14 d to environmentally-relevant concentrations of Hg, changes in immune-associated parameters including, total haemocyte count, lysosomal membrane stability, phenoloxidase, super oxide generation and phagocytosis were observed. Oxidative stress, as measured by lipid peroxidation, antioxidant responses, including superoxide dismutase and catalase activities and glutathione-mediated antioxidant enzymes in serum, haemocyte lysate, gills, hepatopancreas and muscle were assessed in crabs exposed to Hg. Exposure to Hg resulted in significantly lesser immune-associated parameters in haemolymph and antioxidants in all tissues studied. Conversely, GST and phenoloxidase activity, were greater in crabs exposed to Hg. Responses of antioxidant parameters (SOD, CAT and GP(x)) were positively correlated with immune responses, including THC, superoxide and phagocytosis. These results were postulated to be due to an immediate response of antioxidant defense to oxygen radicals generated. Overall, the results suggest that 14 d exposure to environmentally realistic concentrations of Hg causes immunomodulation and potentially harmful lessened antioxidant defenses of crabs.

Hemocyte responses of Dreissena polymorpha following a short-term in vivo exposure to titanium dioxide nanoparticles: preliminary investigations

The widespread use of titanium-based nanoparticles and their environmental release may pose a significant risk to aquatic organisms within freshwater ecosystems. Suspension-feeder invertebrates like bivalve molluscs represent a unique target group for nanoparticle toxicology. The aim of this work was to investigate the short-term responses of Dreissena polymorpha hemocytes after in vivo exposure to titanium dioxide nanoparticles (TiO(2) NP). For this purpose, freshwater mussels were exposed to P25 TiO(2) NP at the concentrations of 0.1, 1, 5 and 25mg/L during 24h. Viability, phagocytosis activity and mitogen activated protein kinase (MAPK) phosphorylation level of ERK 1/2 and p38 in hemocytes extracted from exposed mussels were compared to those from control specimens. Results demonstrated an inhibition of the phagocytosis activity after exposure to TiO(2) NP at 0.1 and 1mg/L. Similar trends, albeit less pronounced, were reported for higher concentrations of NP. Transmission electron microscopy showed for the first time the internalization of TiO(2) NP into Dreissena polymorpha hemocytes. Besides, exposure to NP increased the ERK 1/2 phosphorylation levels in all treatments. Concerning the phosphorylation level of p38, only exposures to 5 and 25mg/L of NP induced significant p38 activation in comparison to that of the control. Finally, these short-term effects observed at environmentally relevant concentrations highlighted the need for further studies concerning ecotoxicological evaluation of nanoparticle release into an aquatic environment.

Immunomodulation in eastern oysters, Crassostrea virginica, exposed to a PAH-contaminated, microphytobenthic diatom

The trophic transfer of sediment-associated pollutants is a growing concern in shellfish harvesting areas. Previous studies have examined the role of phytoplankton in the transport of organic contaminants to bivalve species, but little information on microphytobenthic communities and their role as contaminant vectors exists. Polycyclic aromatic hydrocarbons (PAHs) are organic compounds formed during natural and industrial processes; they are termed "persistent organic pollutants" because they are only slowly degraded by natural processes. This study examined the transfer of PAH compounds (naphthalene, pyrene, and benzo(a)pyrene) by a microphytobenthic diatom to the eastern oyster, a commercially important shellfish species, to determine if dietary accumulation is a route of contaminant exposure capable of inducing physiological responses. PAH compounds were adsorbed to a diatom culture (Nitzschia brevirostris) in a range of concentrations (5, 125, 625, and 1000 μg L(-1)), and eastern oysters were exposed experimentally to the contaminated diatom cultures to assess possible effects upon oyster hemocytes and selected immune-defense functions. A preliminary experiment was designed to identify individual effects of several PAH compounds (naphthalene, pyrene, and benzo(a)pyrene) on hemocyte viability and phagocytic activity. Results from this experiment revealed that the most-toxic compound, benzo(a)pyrene, at the highest concentration, stimulated an increase in agranular hemocyte counts. A follow-up study examined the effects of benzo(a)pyrene on hemocyte viability, adhesion, phagocytosis, and reactive oxygen species (ROS). These studies showed the ability of this benthic diatom to transport PAHs to the eastern oyster and to cause immunomodulation. Hemocyte responses to dietary PAH exposure included an increase in circulating hemocytes and increased production of reactive oxygen species by these cells.

The nonsteroidal anti-inflammatory drug, ibuprofen, affects the immune parameters in the clam Ruditapes philippinarum

The effects of ibuprofen (IBU) on the immune parameters of the clam Ruditapes philippinarum were investigated after a 7-day exposure to sublethal IBU concentrations (0, 0 + ethanol, 100, 500, and 1000 μg/L). Total haemocyte count (THC), haemocyte diameter and volume, haemocyte proliferation and uptake of the vital dye Neutral Red (NR) were measured. The cytotoxicity (assessed by the lactate dehydrogenase assay, LDH) and the capability of IBU to induce DNA fragmentation (indicative of apoptosis) were also investigated. The exposure of clams to the highest IBU concentration significantly reduced their THC, whereas no significant changes were observed in either the diameter or volume of haemocytes. Significant increases in haemocyte proliferation were recorded in clams that were exposed to the two highest tested concentrations of IBU. Exposure of clams to 1000 μg IBU/L significantly reduced NR uptake and increased haemolymph LDH activity. Conversely, IBU did not induce DNA fragmentation in haemocytes. Although the IBU concentrations tested in this study were higher than those generally recorded in aquatic environments, results obtained indicate that exposure of clams to IBU induces significant alterations in the immune parameters and suggest potential immunosuppression in treated clams.