Effects of anthracene on filtration rates, antioxidant defense system, and redox proteomics in the Mediterranean clam Ruditapes decussatus (Mollusca: Bivalvia)

Metabolic variation and oxidative stress responses of clams (Ruditapes philippinarum) perturbed by ofloxacin exposure

Ofloxacin (OFL), one of the most widely used fluoroquinolone antibiotics, has been frequently detected in marine environments. Nonetheless, researchers are yet to focus on the effects of OFL on the benthos. In the present study, marine clams (Ruditapes philippinarum) were exposed to OFL (0.5, 50, and 500 μg/L) for 14 d, followed by a 7 d depuration period. The accumulation of OFL, antioxidative defense responses, neurotoxicity, burrowing behavior, and metabolomic changes in clams were evaluated. The results indicated that OFL could accumulate in clams, albeit with a low bioaccumulation capacity. The intermediate (50 μg/L) and high (500 μg/L) levels of OFL induced significant antioxidative responses in the gills and digestive glands of clams, mainly manifesting as the inhibition of catalase activities and the induction of superoxide dismutase and glutathione S-transferase activities, which ultimately elevated the content of malondialdehyde, causing oxidative damage. Furthermore, the significant induction of acetylcholinesterase activities was observed, coinciding with a significant increase in burrowing rates of clams. The high level of OFL affected glycerophospholipid, arachidonic acid, steroid hormone biosynthesis, unsaturated fatty acids biosynthesis, and glycolysis/glycogenesis metabolism. In conclusion, this study has contributed to the understanding of the physiological and biochemical effects and molecular toxicity mechanisms of OFL to marine bivalves.

Integration approach of transcriptomics and metabolomics reveals the toxicity of Anthracene and its chlorinated derivatives on human hepatic cells

Polycyclic aromatic hydrocarbons (PAHs) and Chlorinated PAHs (Cl-PAHs) are ubiquitous environmental contaminants. The toxicological information of anthracene (Ant) and its chlorinated derivatives is quite limited. In this study, an integrated metabolomic and transcriptomic analysis approach was adopted to assess the toxic effects triggered by Ant and its chlorinated derivatives, 2-chloroanthracene (2-ClAnt) and 9,10-dichloroanthracen (9,10-Cl2Ant), at human-relevant levels on human normal hepatocyte L02 cells. The cell viability test showed no significant effects on the viability of L02 cells exposed to Ant, 2-ClAnt and 9,10-Cl2Ant at doses of 5-500 nM for 24 h. However, based on transcriptomic analysis, Ant, 2-ClAnt and 9,10-Cl2Ant exposure at human-relevant levels obviously perturbed global gene expression in L02 cells and induced the differential expression of several genes related to cancer development. As the number of genes related to cancer development altered by 9,10-Cl2Ant is the largest, 9,10-Cl2Ant posed greater risks of tumor development than Ant and 2-ClAnt did. Metabolomics analysis demonstrated that Ant, 2-ClAnt and 9,10-Cl2Ant caused significant metabolic perturbation in L02 cells. Pathway enrichment analysis indicated that Ant, 2-ClAnt and 9,10-Cl2Ant mainly perturbed the lipid metabolism and nucleotide metabolism pathway. However, 9,10-Cl2Ant caused a wider perturbation to metabolic pathways than Ant and 2-ClAnt did. In addition, dysregulation of nucleotide metabolism perturbed by Ant, 2-ClAnt and 9,10-Cl2Ant may be associated with the genomic instability and further carcinogenesis.

Anodonta cygnea, a freshwater swan mussel, exposed to diazinon: toxicity thresholds in behaviour and physiology

Swan mussels (Anodonta cygnea) have been suggested as suitable bioindicators for the presence of pollutants in the environment. Application of the physiological and behavioral markers in these sessile species can be beneficial for environmental monitoring. The present study aimed to investigate the relationship between the behavioral disorders of movement and siphoning associated with the inhibition of tissue Acetylcholinesterase (AChE). For experiments, overally 120 bivalves of Anodonta cygnea (mean total length 80.33 ± 6.7 mm) were transported from the agricultural drains and canals in Sari county (Mazandaran Province, Iran) to our laboratory. First, the LC50-96 h of diazinon was estimated according to the Organization for Economic Co-operation and Development (OECD 1992) guideline with static water conditions. The sub-lethal toxicity pesticide experiments were conducted on the basis of the lowest observed effect concentration (LOEC) and the maximum acceptable toxicant concentration (MATC). The LC50-96 h, LOEC, and MATC values of diazinon were 85.2, 42.1, and 8.5 mg L- 1, respectively. Based on the observations of mussels' movement, the burrowing and displacement decreased with the concentration of toxicant in water. Moreover, the presence of diazinon in water and its exposure to experimental animals significantly reduces their siphoning rate. The RDA showed that the AChE activity had a higher correlation with the siphoning behavior than the movement behavior. The comparison of enzyme activity at different exposure and recovery times showed that there was a significant difference among the groups affected by the consumed pesticide (p = 0.001, between contrasts). The most remarkable morphometric characteristic was the siphon opening that was inversely correlated with the enzymatic activity. Studies in bioethics might benefit from paying attention to these traits that are directly related to the level of toxicity and behavioral adaptations required for animal survival.

Contaminants of emerging concern in the Maumee River and their effects on freshwater mussel physiology

Contaminants of emerging concern pose a serious hazard to aquatic wildlife, especially freshwater mussels. The growing number of contaminants in aquatic systems requires scientists and managers to prioritize contaminants that are most likely to elicit a biological response for further monitoring and toxicological testing. The objectives of this study were to identify a sub-category of contaminants most likely to affect Pyganodon grandis and to describe alterations in metabolites and gene expression between various sites. Mussels were deployed in cages for two weeks at four sites along the Maumee River Basin, Ohio, USA. Water samples were analyzed for the presence of 220 contaminants. Hemolymph samples were collected for metabolomics and analyzed using mass spectrometry. Contaminants that significantly covaried with metabolites were identified using partial least-squares (PLS) regression. Tissue samples were collected for transcriptomics, RNA was sequenced using an Illumina HiSeq 2500, and differential expression analysis was performed on assembled transcripts. Of the 220 targeted contaminants, 69 were detected in at least one water sample. Of the 186 metabolites detected in mussel hemolymph, 43 showed significant differences between the four sites. The PLS model identified 44 contaminants that significantly covaried with changes in metabolites. A total of 296 transcripts were differentially expressed between two or more sites, 107 received BLAST hits, and 52 were annotated and assigned to one or more Gene Ontology domains. Our analyses reveal the contaminants that significantly covaried with changes in metabolites and are most likely to negatively impact freshwater mussel health and contribute to ongoing population declines in this group of highly endangered animals. Our integration of "omics" technologies provides a broad and in-depth assessment of the short-term effects of contaminants on organismal physiology. Our findings highlight which contaminants are most likely to be causing these changes and should be prioritized for more extensive toxicological testing.

Transcriptomic Profile of the Cockle Cerastoderma edule Exposed to Seasonal Diarrhetic Shellfish Toxin Contamination

Bivalves constitute an important source of proteins for human consumption, but some accumulate biotoxins such as diarrhetic shellfish toxins (DSTs), constituting a risk to human health. The cockle Cerastoderma edule is one of the most important species harvested in the Portuguese coast but also one of the most affected species due to recurrent DSTs exposure. However, little is known regarding the effects of the toxins produced by blooming dinoflagellates on C. edule. Herein, we explore the Differentially Expressed Genes (DEGs) of two tissues (gills and digestive gland) from wild cockles sampled in Portugal, through their whole transcriptomic response in two different seasons (exposed and not exposed to DSTs). The de novo transcriptome assembly returned 684,723 contigs, N50 of 1049, and 98.53% completeness. Altogether, 1098 DEGs were identified, of which 353 DEGs were exclusive for the digestive gland, 536 unique for the gills and 209 DEGs were common. Among DEGs were identified known DSTs-biomarkers including glutathione peroxidase, glutathione S-transferase, superoxide dismutase, cytochrome P450, ABC transporters, actin and tubulin-related proteins, Heat shock proteins and complement C1Q-like proteins. This study provides the first transcriptomic profile of C. edule, giving new insights about its molecular responses under different environmental conditions of DSTs exposure.

Effects of environmentally relevant levels of polyethylene microplastic on Mytilus galloprovincialis (Mollusca: Bivalvia): filtration rate and oxidative stress

The objective of the present study was to evaluate the potential toxic effects of polyethylene microplastics (PE-MPs) (40-48 μm) on the Mediterranean mussel Mytilus galloprovincialis in controlled laboratory conditions. The exposure was carried out for 14 days with three environmentally relevant PE-MPs concentrations of 1, 10, and 100 and a high concentration of 1000 μg/L. Effects of PE-MPs were assessed by evaluating the filtration rate (FR) after 7 and 14 days of exposure and by analyzing biochemical biomarkers of oxidative stress (catalase - CAT, glutathione S-transferase - GST, and the levels of lipid peroxidation - LPO) in the M. galloprovincialis digestive gland after 14 days of exposure. Results showed that M. galloprovincialis does not accumulate PE-MPs of 40-48 μm size in its whole tissues. The filtration rate was significantly reduced with the increase of PE-MPs concentrations. The biochemical biomarkers indicated that PE-MPs induced oxidative damage (LPO) at low concentrations (1 and 10 μg/L) with a significant reduction in females of 1000 μg/L treated group and inactivate antioxidative system (CAT and GST) in the digestive gland of both sexes at high concentrations (100 and 1000 μg/L). This study demonstrates that PE-MPs have biological effects on M. galloprovincialis at environmentally relevant concentrations thus brings new insights on the potential impacts of PE-MPs in marine bivalves.

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.

Can proteomics contribute to biomonitoring of aquatic pollution? A critical review

Aquatic pollution is one of the greatest environmental problems, and therefore its control represents one of the major challenges in this century. In recent years, proteomics has emerged as a powerful tool for searching protein biomarkers in the field of pollution biomonitoring. For biomonitoring marine contamination, there is a consensus that bivalves are preferred organisms to assess organic and inorganic pollutants. Thus, the bivalve proteome was intensively studied, particularly the mussel. It is well documented that heavy metal pollution and organic chemicals altered the structural proteins causing degradation of tissues of molluscs. Also, it is well known that proteins involved in stress oxidative such as glutathione and enzymes as catalase, superoxide dismutase or peroxisomes are overexpressed in response to contaminants. Additionally, using bivalves, other groups of proteins proposed as pollution biomarkers are the metabolic proteins. Even though other marine species are used to monitor the pollution, the presence of proteomic tools in these studies is scarce. Concerning freshwater pollution field, a great variety of animal species (fish and crustaceans) are used as biomonitors in proteomics studies compared to plants that are scarcely analysed. In fish species, proteins involved in stress oxidative such as heat shock family or proteins from lipid and carbohydrate metabolism were proposed as candidate biomarkers. On the contrary, for crustaceans there is a lack of proteomic studies individually assessing the contaminants. Novel scenarios, including emerging contaminants and new threats, will require proteomic technology for a systematic search of protein biomarkers and a greater knowledge at molecular level of those cellular pathways induced by contamination.

OMICs Approaches in Diarrhetic Shellfish Toxins Research

Diarrhetic shellfish toxins (DSTs) are among the most prevalent marine toxins in Europe's and in other temperate coastal regions. These toxins are produced by several dinoflagellate species; however, the contamination of the marine trophic chain is often attributed to species of the genus Dinophysis. This group of toxins, constituted by okadaic acid (OA) and analogous molecules (dinophysistoxins, DTXs), are highly harmful to humans, causing severe poisoning symptoms caused by the ingestion of contaminated seafood. Knowledge on the mode of action and toxicology of OA and the chemical characterization and accumulation of DSTs in seafood species (bivalves, gastropods and crustaceans) has significantly contributed to understand the impacts of these toxins in humans. Considerable information is however missing, particularly at the molecular and metabolic levels involving toxin uptake, distribution, compartmentalization and biotransformation and the interaction of DSTs with aquatic organisms. Recent contributions to the knowledge of DSTs arise from transcriptomics and proteomics research. Indeed, OMICs constitute a research field dedicated to the systematic analysis on the organisms' metabolisms. The methodologies used in OMICs are also highly effective to identify critical metabolic pathways affecting the physiology of the organisms. In this review, we analyze the main contributions provided so far by OMICs to DSTs research and discuss the prospects of OMICs with regard to the DSTs toxicology and the significance of these toxins to public health, food safety and aquaculture.

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.

Exposure to microplastics reduces attachment strength and alters the haemolymph proteome of blue mussels (Mytilus edulis)

The contamination of marine ecosystems with microplastics, such as the polymer polyethylene, a commonly used component of single-use packaging, is of global concern. Although it has been suggested that biodegradable polymers, such as polylactic acid, may be used to replace some polyethylene packaging, little is known about their effects on marine organisms. Blue mussels, Mytilus edulis, have become a "model organism" for investigating the effects of microplastics in marine ecosystems. We show here that repeated exposure, over a period of 52 days in an outdoor mesocosm setting, of M. edulis to polyethylene microplastics reduced the number of byssal threads produced and the attachment strength (tenacity) by ∼50%. Exposure to either type of microplastic altered the haemolymph proteome and, although a conserved response to microplastic exposure was observed, overall polyethylene resulted in more changes to protein abundances than polylactic acid. Many of the proteins affected are involved in vital biological processes, such as immune regulation, detoxification, metabolism and structural development. Our study highlights the utility of mass spectrometry-based proteomics to assess the health of key marine organisms and identifies the potential mechanisms by which microplastics, both conventional and biodegradable, could affect their ability to form and maintain reefs.

Gene expression and genotoxicity in Manila clam (Ruditapes philippinarum) modulated by sediment contamination and lagoon dynamics in the Po river delta

The lagoons of the Po River delta are potentially exposed to complex mixtures of contaminants, nevertheless, there is a substantial lack of information about the biological effects of these contaminants in the Po delta lagoons. These environments are highly dynamic and the interactions between chemical and environmental stressors could prevent the proper identification of biological effects and their causes. In this study, we aimed to disentangle such interactions focusing on Manila clams, previously exposed to six lagoons of the Po delta, adopting three complementary tools: a) the detailed description via modelling techniques of lagoon dynamics for salinity and water temperature; b) the response sensitivity of a number of target genes (ahr, cyp4, ρ-gst, σ-gst, hsp22, hsp70, hsp90, ikb, dbh, ach, cat, Mn-sod, Cu/Zn-sod, cyp-a, flp, grx, TrxP) investigated in clam digestive glands by Real Time PCR; and c) the relevance of DNA adducts determined in clams as markers of exposure to genotoxic chemicals. The lagoons showed specific dynamics, and two of them (Marinetta and Canarin) could induce osmotic stress. A group of genes (ahr, cyp4, Mn-sod, σ-gst, hsp-22, cyp-a, TrxP) seemed to be associated with overall lagoon characteristics as may be described by salinity and its variations. Lagoon modelling and a second group of genes (hsp70, hsp90, cat, ikb, ach, grx, Cu/Zn-sod) also suggested that moderate increases of river discharge may imply worse exposure conditions. Oxidative stress seemed to be associated with such events but it was slightly evident also under normal exposure conditions. DNA adduct formation was mainly associated with overwhelmed antioxidant defences (e.g. low Cu/Zn-sod) or seemingly with their lack of response in due time. In Po delta lagoons, Manila clam can be affected by chemical and environmental factors which can contribute to induce oxidative stress, DNA adduct formation and, ultimately, to affect clam condition and health.

Structural and functional responses of coastal marine phytoplankton communities to PAH mixtures

The toxicity of polycyclic aromatic hydrocarbons (PAHs) mixtures was evaluated on natural phytoplankton communities sampled from lagoons of Bizerte (South-western Mediterranean Sea) and Thau (North-western Mediterranean Sea). PAHs induced short-term dose and ecosystem-dependant decreases in photosynthetic potential. Chlorophyll a was negatively affected by increasing PAHs concentrations, together with dramatic changes in phytoplankton community composition. Size classes were strongly affected in the Bizerte compare to the Thau lagoon, with a decrease in nano- and microphytoplankton densities compare to picophytoplankton. In both locations, the diatom Entomoneis paludosa appeared favoured under PAH exposure as evidenced by increase in cell density, whereas autotrophic flagellates and dinophytes were strongly reduced. Smaller cells were more tolerant to exposure to highest PAHs concentrations, with persistent picophytoplankton carbon biomass at the end of the incubations. Apparent recovery of photosynthetic potential, accompanied with a regrowth of chlorophyll a under the lowest PAH doses, coincided with a significantly altered community composition in both lagoons. Furthermore, sensitivity to PAHs was not related to the phytoplankton cell size, and toxicity-induced modification of top-down control by grazers during the experiment cannot be excluded.

Semivolatile organic compounds in surface microlayer and subsurface water of Dianshan Lake, Shanghai, China: implications for accumulation and interrelationship

Semivolatile organic compounds (SVOCs) in surface microlayer (SML) and subsurface water (SSW) from Dianshan Lake were studied to investigate their occurrence, distributions, as well as enrichment and potential sources. A sample was concentrated by solid-phase micro-extraction (SPME). Identification and quantification were carried out by gas chromatography coupled to mass spectrometry (GC-MS). Total SVOCs concentrations ranged from 25.93 to 47.49 μg/L in SSW and 38.19 to 77.23 μg/L in SML. The phthalic acid esters (PAE) concentrations in both SSW and SML are the highest of the total SVOC. The enrichment factors (EFs) of total SVOCs ranged from 0.80 to 2.98, while the highest EF was found in benzyl phthalate and dibutyl phthalate, compounds of PAEs (4.06). The EFs values calculated in this study were consistent with the EFs reported for other water ecosystems. Compared with other place, the EF of PAHs were in the normal level (0.88-2.37). The results of correlation analysis, principal component analysis (PCA) suggested that at least three sources, i.e., agricultural residual pesticides, industrial sewage and miscellaneous sources, were responsible for the presence of SVOCs in Dianshan Lake examined, accounting for 94.16% of the total variance in the dataset. Environmental risk assessment revealed that a majority of SVOCs posed relatively low risks (the values of risk quotient were less than 0.1), while naphthalene, acenaphthene, 2,4-dinitrotoluene, and dibutyl phthalat exhibited moderate risks (values of risk quotient were more than 0.1 but less than 1fore) to aquatic organisms.