The effects of contaminants in European eel: a review

Phagocytic cell responses to silica-coated dithiocarbamate-functionalized iron oxide nanoparticles and mercury co-exposures in Anguilla anguilla L

Immune system responses in fish are considered as suitable and sensitive biomarkers for monitoring aquatic pollution. However, a clear knowledge gap persists in the literture on the immunotoxic potential of engineered nanoparticles toward aquatic organisms such as fish. Employing major enzymatic- (glutathione reductase, GR; glutathione peroxidase, GPX; glutathione sulfo-transferase, GST; catalase, CAT) and thiol- (non-protein thiols, NP-SH; total glutathione, TGSH)-based defense biomarkers, this study assessed the response of phagocytes isolated from peritoneum (P-phagocytes), gill (G-phagocytes), head kidney (HK-phagocytes), and spleen (S-phagocytes) of European eel (Anguilla anguilla L.) to silica-coated magnetite particles (Fe3O4@SiO2/SiDTC, hereafter called IONP; size range: 82 ± 21 to 100 ± 30 nm; 2.5 mg L(-1)) alone and IONP and mercury (Hg; 50 μg L(-1)) concomitant exposures. Responses of previous biomarkers were studied in P-phagocytes, G-phagocytes, HK-phagocytes, and S-phagocytes collected during 0, 2, 4, 8, 16, 24, 48, and 72 h of exposures. Contingent to hour of exposure to IONP, Hg, and IONP + Hg GST, GPX, CAT, NP-SH, and TGSH exhibited their differential responses in all the phagocytic cells considered. In particular, under IONP exposure, the potential occurrence of the GSH-independent antioxidant defense was indicated by the observed herein inhibition in the enzymatic- and thiol-based defense in A. anguilla phagocytes. In contrast, the response of P-, G-, HK-, and S-phagocytes to the increasing Hg exposure period reflected an increased detoxification activity. Notably, the occurrence of an antagonism between IONP and Hg was depicted during late hours (72 h) under IONP + Hg concomitant exposure, where elevations in the defense biomarkers were depicted. Overall, the P-, G-, HK-, and S-phagocytic cells exhibited a differential induction in the studied enzymes and thiols to counteract impacts of IONP, Hg, and IONP + Hg concomitant exposures. Future studies on the fish immunotoxicity responses to IONP exposure in multi-pollution conditions can be benefited with the major outcomes of the present study.

Thyroid endocrine status of wild European eels (Anguilla anguilla) in the Loire (France). Relationships with organic contaminant body burdens

In teleost fish, thyroid function is involved in various critical physiological processes. Given the complexity of the hypothalamo-pituitary-thyroid (HPT) axis, a large number of genes and proteins can be the potential target of endocrine-disrupting compounds (EDCs). The aim of this study was to evaluate, in yellow and silver European eels (Anguilla anguilla), potential effects of EDCs on thyroid status by analyzing the associations between EDC body burdens and thyroid hormones (THs). In yellow individuals, greater free T3/T4 ratios (FT3/FT4) and lower plasma FT4 levels were associated with greater concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), as highlighted by significant correlations with many congeners. Few positive relationships with alkylphenols were noticed. In contrast, silver eels usually exhibited less significant correlations between THs and contaminant loads. Expression of a series of genes involved in the HPT axis was also investigated in the silver individuals. Concerning mRNA expression in silver females, some main correlations were noticed: thyroid-stimulating hormone (TSHβ) gene expression was significantly correlated to numerous PCBs, and hepatic mRNA levels of deiodinase 2 (Deio 2) were negatively correlated to 2-hydroxyfluorene (2-OHF) and 2-naphtol (2-OHNa). Thyroid receptor (TRα and TRβ) mRNA levels exhibited weak negative correlations with some PBDEs in silver females and males. Hepatic vitellogenin (Vtg) mRNA levels were detected in all silver males but at lower levels than in silver females. In males, Vtg mRNA levels were positively associated to FT4/TT4. In silver females, strong positive correlations were found between congeners of PCBs, PBDEs and PFAS suggesting potential estrogenic effects. Overall, the observed results indicate that several organic contaminants, mainly dl-, ndl-PCBs and PBDEs, could be associated with changes in thyroid homeostasis in these fish, via direct or indirect interactions with peripheral deiodination, metabolism of T4 and mechanisms involved in TSHβ, Deio 2 and Vtg gene transcription.

Detecting the exposure to Cd and PCBs by means of a non-invasive transcriptomic approach in laboratory and wild contaminated European eels (Anguilla anguilla)

Detecting and separating specific effects of contaminants in a multi-stress field context remain a major challenge in ecotoxicology. In this context, the aim of this study was to assess the usefulness of a non-invasive transcriptomic method, by means of a complementary DNA (cDNA) microarray comprising 1000 candidate genes, on caudal fin clips. Fin gene transcription patterns of European eels (Anguilla anguilla) exposed in the laboratory to cadmium (Cd) or a polychloro-biphenyl (PCBs) mixture but also of wild eels from three sampling sites with differing contamination levels were compared to test whether fin clips may be used to detect and discriminate the exposure to these contaminants. Also, transcriptomic profiles from the liver and caudal fin of eels experimentally exposed to Cd were compared to assess the detection sensitivity of the fin transcriptomic response. A similar number of genes were differentially transcribed in the fin and liver in response to Cd exposure, highlighting the detection sensitivity of fin clips. Moreover, distinct fin transcription profiles were observed in response to Cd or PCB exposure. Finally, the transcription profiles of eels from the most contaminated site clustered with those from laboratory-exposed fish. This study thus highlights the applicability and usefulness of performing gene transcription assays on non-invasive tissue sampling in order to detect the in situ exposure to Cd and PCBs in fish.

Histological and hormonal changes in the European eel (Anguilla anguilla) after exposure to environmental cocaine concentration

The aim of this study was the assessment of histological and hormonal changes induced in the European eel from environmental concentrations of cocaine. Silver eels were exposed to 20 ng L(-1) of cocaine during 50 days; at the same time, control, vehicle control and two post-exposure recovery groups (3 and 10 days) were made. The general morphology of the skin and the intestine, and the plasma levels of prolactin, cortisol and dopamine were evaluated. In the skin, cocaine decreased the number and size of mucous cells, increased the thickness of the epidermis and altered the club cells and the basal lamina. In the intestine, cocaine increased the thickness of the epithelium and the number of mucous cells and reactivated the structure of the intestine and of the intestinal musculature. Moreover, cocaine increased plasma prolactin, cortisol and dopamine levels. These results suggest that cocaine induced histological changes, directly and/or through the hormonal changes observed. Considering the complex life cycle of the eel, the changes induced by cocaine in the skin, the intestine and the endocrine system could threaten the ability of the eel to successfully migrate and reproduce.

A question of origin: dioxin-like PCBs and their relevance in stock management of European eels

The stock of European Eel (Anguilla anguilla L.) has reached an all-time low in 2011. Spawner quality of mature eels in terms of health status and fitness is considered one of the key elements for successful migration and reproduction. Dioxin-like Polychlorinated Biphenyls (dl-PCBs) are known persistent organic pollutants potentially affecting the reproductive capability and health status of eels throughout their entire lifetime. In this study, muscle tissue samples of 192 European eels of all continental life stages from 6 different water bodies and 13 sampling sites were analyzed for contamination with lipophilic dl-PCBs to investigate the potential relevance of the respective habitat in light of eel stock management. Results of this study reveal habitat-dependent and life history stage-related accumulation of targeted PCBs. Sum concentrations of targeted PCBs differed significantly between life stages and inter-habitat variability in dl-PCB levels and -profiles was observed. Among all investigated life stages, migrant silver eels were found to be the most suitable life history stage to represent their particular water system due to habitat dwell-time and their terminal contamination status. With reference to a possible negative impact of dl-PCBs on health and the reproductive capability of eels, it was hypothesized that those growing up in less polluted habitats have a better chance to produce healthy offspring than those growing up in highly polluted habitats. We suggest that the contamination status of water systems is fundamental for the life cycle of eels and needs to be considered in stock management and restocking programs.

Rescheduling the process of nanoparticle removal used for water mercury remediation can increase the risk to aquatic organism: evidence of innate immune functions modulation in European eel (Anguilla anguilla L.)

This study aimed to assess the mechanisms of innate immune function responses to silica-coated iron oxide nanoparticle functionalized with dithiocarbamate groups (IONP) exposure alone and its associated mercury (Hg) in European eel (Anguilla anguilla L.) phagocytes isolated from peritoneum (P-phagocytes), gill (G-phagocytes), head kidney (HK-phagocytes) and spleen (S-phagocytes). The study evaluated viability, phagocytosis, oxidative burst activity (OBA) and lipid peroxidation (LPO). Four groups were made: (1) 2 × 10(6) phagocytes + RPMI-1640 (control), (2) 2 × 10(6) phagocytes + IONP (2.5 mg L(-1)), (3) 2 × 10(6) phagocytes + Hg (50 μg L(-1)) and (4) 2 × 10(6) phagocytes + IONP + Hg. Samplings were performed at 0, 2, 4, 8, 16, 24, 48 and 72 h of exposure. A. anguilla P-, G-, HK- and S-phagocytes in vitro exposure to IONP alone revealed either increased (except HK-phagocytes at 16 h) or no change in viability, suggesting that the cells are metabolically active and resistant to IONP exposure alone. In terms of phagocytes overactivation and reactive oxygen species (ROS) production as an indirect mechanism of immunotoxicity, the phagocytes responded in the following manner: P- > S- > HK- = G-phagocytes for IONP exposure alone, S- > HK- > P- = G-phagocytes for Hg exposure alone and HK- > G- = S- > P-phagocytes for concomitant exposure. Overall, considering Hg as a surrogate for metals and its association with IONP, as well as the likelihood that it could pose a serious threat to aquatic organisms by modulating their immune defense mechanisms if accidentally discharged into the aquatic environment, current results suggest that the step of IONP-metal complex removal must not be underrated and should be processed without any more ado.

Field evidence of reproduction impairment through sperm DNA damage in the fish nase (Chondrostoma nasus) in anthropized hydrosystems

This work aims to explore in the field the relationship between the integrity of sperm DNA and the quality of offspring as a possible cause of the decline of a feral fish population through reproduction impairment. Mature nase (Chondrostoma nasus) were caught during the breeding season in three locations (A-C) of the Rhône River basin and gametes collected by stripping. Sampling locations were chosen according to the following gradient of contamination due to human activities on the watershed: A≤B<C. Samples of a pool of collected oocytes were fertilized with the sperm of individual males and then incubated individually back in the lab to study embryo-larval development as well as using sperm samples to assess DNA integrity. Genetic analysis clearly showed the absence of a difference in genetic structure between the three studied C. nasus populations from the Rhône basin. Sperm DNA integrity was significantly lower in males from station C compared to other ones while sperm biochemical characteristics and fertilization rate remained almost unchanged whatever the station. Mortality and abnormality rates measured at both hatching and at the end of yolk sac resorption stages followed the same trend as the sperm DNA damage, demonstrating an impact of river water quality on nase fitness through a loss of sperm DNA integrity. Since the level of both abnormalities and mortality measured in offspring of fish caught in the most contaminated area reached high values up to 15% and 80%, respectively, the hypothesis that the observed nase decline in Rhône River stemming through selection forces can be put forward.

Gonadal transcriptome analysis of wild contaminated female European eels during artificial gonad maturation

Since the early 1980s, the population of European eels (Anguilla anguilla) has dramatically declined. Nowadays, the European eel is listed on the red list of threatened species (IUCN Red List) and is considered as critically endangered of extinction. Pollution is one of the putative causes for the collapse of this species. Among their possible effects, contaminants gradually accumulated in eels during their somatic growth phase (yellow eel stage) would be remobilized during their reproductive migration leading to potential toxic events in gonads. The aim of this study was to investigate the effects of organic and inorganic contaminants on the gonad development of wild female silver eels. Female silver eels from two sites with differing contamination levels were artificially matured. Transcriptomic analyses by means of a 1000 candidate gene cDNA microarray were performed on gonads after 11weeks of maturation to get insight into the mechanisms of toxicity of contaminants. The transcription levels of several genes, that were associated to the gonadosomatic index (GSI), were involved in mitotic cell division but also in gametogenesis. Genes associated to contaminants were mainly involved in the mechanisms of protection against oxidative stress, in DNA repair, in the purinergic signaling pathway and in steroidogenesis, suggesting an impairment of gonad development in eels from the polluted site. This was in agreement with the fact that eels from the reference site showed a higher gonad growth in comparison to contaminated fish.

Toxic textile dyes accumulate in wild European eel Anguilla anguilla

Dyes are used to stain inks, paints, textile, paper, leather and household products. They are omnipresent, some are toxic and may threaten our environment, especially aquatic ecosystems. The presence of residues of sixteen dyes (triarylmethanes, xanthenes, phenothiazines and phenoxazines) and their metabolites was analyzed in muscle tissue samples of individual yellow-phased European eels (Anguilla anguilla) from 91 locations in Belgian rivers, canals and lakes sampled between 2000 and 2009 using ultra performance liquid chromatography-tandem mass spectrometry. Eel was contaminated by dyes in 77% of the sites. Malachite Green, Crystal Violet and Brilliant Green were present in 25-58% of the samples. Dye occurrence was related to the distribution of textile and dye production industries. This field study is the first large-scale survey to document the occurrence of artificial dyes in wildlife. Considering the annual amounts of dyes produced worldwide and the unintentional spillage during their use, our observations warrant additional research in other parts of the world. The presence of these highly toxic dyes in the European eel may form an additional threat to this critically endangered species. The contaminated eels should be considered as not suitable for consumption.

Maternal transfer of emerging brominated and chlorinated flame retardants in European eels

The European eel (Anguilla anguilla) is regarded as a critically endangered species. Scientists are in agreement that the "quality of spawners" is a vital factor for the survival of the species. This quality can be impaired by parasites, disease and pollution. Especially endocrine disrupting organic chemicals pose a potential threat to reproduction and development of offspring. To our knowledge, the findings in this publication for the first time describe maternal transfer of contaminants in eels. We analysed the concentrations of in total 53 polybrominated diphenyl ethers (PBDEs) and their halogenated substitutes in muscle, gonads and eggs of artificially matured European eels and in muscle and gonads of untreated European eels that were used for comparison. We found evidence that persistent organic pollutants such as PBDEs, as well as their brominated and chlorinated substitutes are redistributed from muscle tissue to gonads and eggs. Concentrations ranged from 0.001 ng g(-1)ww for sum Dechlorane metabolites (DPMA, aCL10DP, aCl11DP) to 2.1 ng g(-1)ww for TBA in eggs, 0.001 ng g(-1)ww for Dechlorane metabolites to 9.4 ng g(-1)ww for TBA in gonads and 0.002 ng g(-1)ww for Dechlorane metabolites to 54 ng g(-1)ww for TBA in muscle tissue. Average egg muscle ratios (EMRs) for compounds detectable in artificially matured eels from both Schlei Fjord and Ems River ranged from 0.01 for Dechlorane 602 (DDC-DBF) to 10.4 for PBEB. Strong correlations were found between flame retardant concentrations and lipid content in the analysed tissue types, as well as transfer rates and octanol-water partitioning coefficient, indicating that these parameters were the driving factors for the observed maternal transfer. Furthermore, indications were found, that TBP-DBPE, TBP-AE, BATE and TBA have a significant uptake from the surrounding water, rather than just food and might additionally be formed by metabolism or biotransformation processes. Dechloranes seem to be of increasing relevance as contaminants in eels and are transferred to eggs. A change of the isomer pattern in comparison to the technical product of Dechlorane Plus (DP) was observed indicating a redistribution of DP from muscle tissue to gonads during silvering with a preference of the syn-isomer. The highly bioaccumulative DDC-DBF was the most abundant Dechlorane in all fish of the comparison group even though it is not produced or imported in the EU. The aldrin related "experimental flame retardant" dibromoaldrin (DBALD) was detected for the first time in the environment in similar or higher concentrations than DP.

Impact of a phosphate fertilizer plant on the contamination of marine biota by heavy elements

Due to their toxicity, persistence, and bioaccumulation, metals are important marine environment pollutants, especially in low renewal rate water such as the Mediterranean Sea, receiving a lot of untreated industrial waste. The impact of a phosphate fertilizer plant on the marine biota metal contamination was studied. Several types of organisms: crabs, mussels, patella and fish were collected from two areas of the Lebanese coast, one subjected to the impact of the plant and another away from it; samples were analyzed for Zn, U, Cr, V, Mn, Ni, Co, Cu, As, Cd and Pb by ICP-MS. Higher accumulation was in crabs, patella, and mussels. Fish accumulated principally Zn, Cu, and Cd; a difference was observed between species and tissues. Cytosol metal fractionation using size-exclusion LC-ICP-MS showed principally Pb, As, Co, and Mn in the low molecular weight fraction (<1.8 Da); Cd, Zn, and Cu in the metallothionein fraction (1.8--18 k Da), and Ni in high molecular weight fraction (>20 kDa).

A global viability assessment of the European eel

The global European eel (Anguilla anguilla) stock is critically endangered according to the IUCN, and the European Commission has urged the development of conservation plans aimed to ensure its viability. However, the complex life cycle of this panmictic species, which reproduces in the open ocean but spends most of its prereproductive life in continental waters (thus embracing a huge geographic range and a variety of habitat types), makes it difficult to assess the long-term effectiveness of conservation measures. The interplay between local and global stressors raises intriguing cross-scale conservation challenges that require a comprehensive modelling approach to be addressed. We developed a full life cycle model of the global European eel stock, encompassing both the oceanic and the continental phases of eel's life, and explicitly allowing for spatial heterogeneity in vital rates, availability of suitable habitat and settlement potential via a metapopulation approach. We calibrated the model against a long-term time series of global European eel catches and used it to hindcast the dynamics of the stock in the past and project it over the 21st century under different management scenarios. Although our analysis relies on a number of inevitable simplifying assumptions and on data that may not embrace the whole range of variation in population dynamics at the small spatiotemporal scale, our hindcast is consistent with the general pattern of decline of the stock over recent decades. The results of our projections suggest that (i) habitat loss played a major role in the European eel decline; (ii) the viability of the global stock is at risk if appropriate protection measures are not implemented; (iii) the recovery of spawner escapement requires that fishing mortality is significantly reduced; and (iv) the recovery of recruitment might not be feasible if reproductive output is not enhanced.

Subcellular partitioning of non-essential trace metals (Ag, As, Cd, Ni, Pb, and Tl) in livers of American (Anguilla rostrata) and European (Anguilla anguilla) yellow eels

We determined the intracellular compartmentalization of the trace metals Ag, As, Cd, Ni, Pb, and Tl in the livers of yellow eels collected from the Saint Lawrence River system in Canada (Anguilla rostrata) and in the area of the Gironde estuary in France (Anguilla anguilla). Differential centrifugation, NaOH digestion and thermal shock were used to separate eel livers into putative "sensitive" fractions (heat-denatured proteins, mitochondria and microsomes+lysosomes) and detoxified metal fractions (heat-stable peptides/proteins and granules). The cytosolic heat-stable fraction (HSP) was consistently involved in the detoxification of all trace metals. In addition, granule-like structures played a complementary role in the detoxification of Ni, Pb, and Tl in both eel species. However, these detoxification mechanisms were not completely effective because increasing trace metal concentrations in whole livers were accompanied by significant increases in the concentrations of most trace metals in "sensitive" subcellular fractions, that is, mitochondria, heat-denatured cytosolic proteins and microsomes+lysosomes. Among these "sensitive" fractions, mitochondria were the major binding sites for As, Cd, Pb, and Tl. This accumulation of non-essential metals in "sensitive" fractions likely represents a health risk for eels inhabiting the Saint Lawrence and Gironde environments.

Swimbladder function and the spawning migration of the European eel Anguilla anguilla

The spawning migration of the European eel is an extensive journey over 5000 to 7000 km from the European coast to the Sargasso Sea. Eels do not feed during this journey and on-board fuels must be sufficient to support the journey of 3.5 to 6 month, as well as sexual maturation and the spawning activity. Swimming of eels appears to be quite energy efficient compared to other fish species, and elevated hydrostatic pressure has been shown to even reduce the costs of transport. Recent studies revealed, however, that during traveling eels perform extensive diurnal migrations and swim at a depth of about 100-300 m at night time, but go down to 600-1000 m at day time. At a depth of 200 m eels are exposed to a hydrostatic pressure of 21 atmospheres (2.13 MPa), while at 800 m hydrostatic pressure increases to 81 atmospheres (8.21 MPa). Accordingly, without any compensation at a depth of 800 m swimbladder volume will be reduced to about 25% of the volume established with neutral buoyancy at 200 m. Consequently, these diurnal changes in depth must be taken into consideration for a calculation of the energy requirements of the spawning migration. Without compensation a compression of the swimbladder will result in a status of negative buoyancy, which makes swimming more costly. Trying to keep the status of neutral buoyancy during descent by gas secretion into the swimbladder in turn requires metabolic activity to enhance swimbladder perfusion and for acid production of the gas gland cells to stimulate gas secretion. During ascent gas is passively removed from the swimbladder in the resorbing section and in the blood transported to the gills, where it is lost into the water. Accordingly, the swimbladder appears to be a crucial organ for the spawning migration. It can be assumed that an impairment of swimbladder function for example due to an infection with the nematode Anguillicola crassus significantly threatens the success of the spawning migration.

PCB and organochlorine pesticide burden in eels in the lower Thames River (UK)

Thirty-five European eels (Anguilla anguilla), caught in 2007 in the river Thames upstream and downstream of both London and the tidal limit, were analysed for PCBs and organochlorine pesticides. Most chemicals were detectable in every fish, although they have been banned or severely restricted for many years. In general, the tidal eels were more contaminated than upstream ones, which was related to their higher lipid contents. The ICES7 indicator PCB concentrations ranged overall from 4.2 to 124μgkg(-1) fresh weight with averages of 33 and 56μgkg(-1) for the upstream and tidal eels; 3.5-104μgkg(-1), average 26 and 48μgkg(-1) of that were ICES6 PCBs. Total DDT was on average 16μgkg(-1) (1.7-38μgkg(-1)) upstream and 18μgkg(-1) (8.6-35μgkg(-1)) downstream with about half of that provided by pp'DDE. Lindane (γ-HCH) was found at up to 2.8μgkg(-1) (averages 0.58 and 1.1μgkg(-1) upstream and downstream) and hexachlorobenzene (HCB) was on average 1.9 and 2.5μgkg(-1) in the two groups with a maximum of 6.4μgkg(-1) in each. Therefore all individuals passed the European Environmental Quality Standard (EQS) of 10μgkg(-1) for HCB. PCB contamination was fairly typical for recent UK eel data, whilst DDE and lindane concentrations were lower than most previous UK eel studies, perhaps reflecting a downward trend. Although not as highly contaminated as some eels from previous UK and European studies, the presence of so many of these chemicals, with their known health effects may represent a stress for the fish or higher predators, such as birds.

Transcriptome profile analysis reveals specific signatures of pollutants in Atlantic eels

Identifying specific effects of contaminants in a multi-stress field context remain a challenge in ecotoxicology. In this context, "omics" technologies, by allowing the simultaneous measurement of numerous biological endpoints, could help unravel the in situ toxicity of contaminants. In this study, wild Atlantic eels were sampled in 8 sites presenting a broad contamination gradient in France and Canada. The global hepatic transcriptome of animals was determined by RNA-Seq. In parallel, the contamination level of fish to 8 metals and 25 organic pollutants was determined. Factor analysis for multiple testing was used to identify genes that are most likely to be related to a single factor. Among the variables analyzed, arsenic (As), cadmium (Cd), lindane (γ-HCH) and the hepato-somatic index (HSI) were found to be the main factors affecting eel's transcriptome. Genes associated with As exposure were involved in the mechanisms that have been described during As vasculotoxicity in mammals. Genes correlated with Cd were involved in cell cycle and energy metabolism. For γ-HCH, genes were involved in lipolysis and cell growth. Genes associated with HSI were involved in protein, lipid and iron metabolisms. Our study proposes specific gene signatures of pollutants and their impacts in fish exposed to multi-stress conditions.

Occurrence of perfluorooctanesulfonate and perfluorooctanoic acid and histopathology in eels from north Italian waters

A perfluorinated alkylated substances (PFAS) biomonitoring study was conducted in European eel (Anguilla anguilla) in Italy for the first time. Perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA) concentrations were assessed in the organs of 35 wild eels from two locations, the highly impacted Po River and the Comacchio Lagoon along the north-western Adriatic coast. PFAS were extracted by ion-pairing liquid extraction procedure and measured using high performance liquid chromatography with electrospray ionization tandem mass spectrometry. There were no significant differences in mean PFAS concentrations (p>0.05) between samples from the two sites. PFOS and PFOA were detectable (>0.4ngg(-1) wet weight, w.w) in 73% and 31% of the total samples, respectively. PFOS concentrations ranged from <0.4 to 6.28ngg(-1)w.w and PFOA from <0.4 to 92.77ngg(-1)w.w. The highest PFAS levels were observed in blood and the lowest in muscle. Histology showed macrophage aggregates and hepatocytic vacuolation in some liver samples. No tissue anomalies were seen in the gonads, suggesting no reproductive impairment. The PFAS contamination levels observed were comparable to, or lower than, those reported in fish in other European countries, seeming to indicate that PFAS pollution of the study area is not remarkable.

Metabolic enzymes activity and histomorphology in the liver of whitefish (Coregonus lavaretus L.) and pike (Esox lucius L.) inhabiting a mineral contaminated lake

The effects of wastewater from a mining and ore-dressing mill on fish in Lake Kostomukshskoe, which is used as a cesspool of circulating water and for storage of industrial wastes produced by the Kostomuksha mining and ore-dressing mill in northwest Russia, were studied. The lake is characterized by heavy mineralization, high pH, elevated levels of K(+), Li(+), SO4 (2-), NO(2-), Cl(-), Li, Mn, and Ni, and the presence of a fine-dispersed mechanical suspension. To assess the impact of contamination on fish and determine the mechanisms of their adaptation, we investigated the biochemical indices and histology of the liver of whitefish (Coregonus lavaretus L.) and pike (Esox lucius L.) inhabiting Lake Kostomukshskoe, downstream Lake Koyvas (64° 47' 30° 59'), and Lake Kamennoe, which is located in a nature preserve and has not been affected by anthropogenic activity (64° 28' 30° 13'). Changes were detected in the activity of metabolic enzymes (cytochrome c oxidase (COX), lactate dehydrogenase, and glucose-6-phosphate dehydrogenase) in the liver. Specifically, the COX activity in the liver of both fish species from the contaminated lake decreased, indicating a low level of aerobic metabolism. Lipid infiltration was the most visible and widespread change observed in the liver of both fish species; therefore, it can be considered a marker of such long-term contamination. Lesions in pike liver demonstrated a wider range of severity than in those of whitefish. In summary, metabolic enzyme activity and histomorphology of the liver of whitefish and pike differed among lakes in a species-specific manner. The changes in enzyme activity and histomorphological alterations in fish that were observed can be applied for evaluation of freshwater systems that may be subjected to mineral pollution.

The occurrence of organic contaminants in European eel (Anguilla anguilla) in Poland: an environmental quality assessment

The objective of the present study was to provide information on the levels of pollutants in the tissues of eels caught in Polish waters. The contaminants included in the study are those which have not yet been widely studied in eel stocks, but which arouse concern in relation to the environment. An overview of the pollutant levels in eels caught in other European waters was also conducted. The results are evaluated in terms of environmental quality and consumer health. The mean concentrations of ΣPBDEs and ΣHBCDs in muscles of eels sampled in Polish waters were between 1 and 2 ng g(-1) ww. The mean TBT concentrations were between 2 and 4 ng g(-1)ww with the exception of samples from the Szczecin Lagoon, in which the mean TBT concentration was about tenfold higher.

PAH metabolites in European eels (Anguilla anguilla) as indicators of PAH exposure: different methodological approaches

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants of aquatic environments derived from pyrogenic and petrogenic sources. In fish, as in other vertebrates, PAHs are rapidly metabolized. However, the metabolites have been proven to induce multiple deleterious effects in fish. The concentrations of biliary polycyclic aromatic hydrocarbon metabolites in eels (Anguilla anguilla) caught in Polish waters were measured. The main objectives of the study were to provide information on the levels of PAH metabolites in eels inhabiting Polish waters and to discuss which methodological approach is appropriate for assessing PAH exposure in aquatic ecosystems. The non-normalized median concentration of 1-OH Pyr and 1-OH Phe measured in eels from Polish waters ranged from 11 to 1642 ng ml(-1) bile and from 83 to 929 ng ml(-1) bile, respectively, depending on the sampling site. Data normalization in relation to bile pigment content reduced inter-site variation, and the normalized median concentrations of 1-OH Pyr and 1-OH Phe ranged from 0.44 to 20.24 ng A(-1)380 and from 1.58 to 11.11 ng A(-1)380, respectively. Our study indicated that results were more consistent for the two species sampled in the same area (eel examined in the current study and flounder examined in our previous study) when the fluorescence response of diluted bile samples was compared than when concentrations of 1-OH Pyr determined with the mean of HPLC were compared.

Assessment of persistent brominated and chlorinated organic contaminants in the European eel (Anguilla anguilla) in Flanders, Belgium: Levels, profiles and health risk

Pooled yellow European eel (Anguilla anguilla (L.)) samples, consisting of 3-10 eels, collected between 2000 and 2009 from 60 locations in Flanders (Belgium) were investigated for persistent contaminants, such as polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDs), polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane and its metabolites (DDTs). The current study expands the knowledge regarding these contaminant concentrations, their patterns and distribution profiles in aquatic ecosystems. PBDEs, HBCDs, PCBs, and DDTs were detected in all eel samples and some samples had high concentrations (up to 1400, 9500, 41,600 and 7000ng/g lw, respectively). PCB levels accounted for the majority of the contamination in most samples. The high variability in PBDE, HBCD, PCB and DDT concentrations reported here is likely due to the variety in sampling locations demonstrating variable local pollution pressures, from highly industrialised areas to small rural creeks. Among PBDEs, BDE-47 (57% contribution to the sum PBDEs), -100 (19%) and -99 (15%) were the predominant congeners, similar to the composition reported in the literature in eel samples. For HBCDs, α-HBCD (74%) was predominant followed by γ-(22%) and β-HBCD (4%) isomers in almost all eel samples. CB-153 (19%) was the most dominant PCB congener, closely followed by CB-138 (11%), CB-180 (9%), CB-187 (8%) and CB-149 (7%). The contribution to the total human exposure through local wild eel consumption was also highly variable. Intake of PBDEs and HBCDs, through consumption of wild eel, was below the RfD values for the average population (consuming on average 2.9g eel/day). At 16 out 60 sites, eels exceeded largely the new EU consumption threshold for PCBs (300ng/g ww for the sum of 6 indicator PCBs). The current data shows an on-going exposure of Flemish eels to PBDEs, HBCDs, PCBs and DDTs through indirect release from contaminated sediments or direct releases from various industries.

How chemical pollution becomes a social problem. Risk communication and assessment through regional newspapers during the management of PCB pollutions of the Rhône River (France)

The case study of the polychlorinated biphenyl (PCB) pollutions of the Rhône River (France) offers the possibility of studying criteria for the construction of social problems that result from chemical pollution (2005-2010). We investigated the dynamics of competition that create and define pollution as a social problem and entail its decline. News outlets are crucial for determining how an environmental issue emerges locally or nationally; this study used newspapers to highlight the potential of new outlets as a data source to analyze discourse variability, science-policy-media connections and the hydrosphere. Media coverage was based on a content analysis and textual data analysis of 75 articles. Analytical frameworks such as the Downs Model and the Public Arena Model (Hilgartner and Bosk, 1988) that consider time and stakeholders were tested to determine how human alteration of the hydrosphere can become a social problem and to analyze different communication strategies held by stakeholders. In terms of management, we described the temporal dynamics of the social problem based on the case study and considered an explanation of the selections. We considered the organization of particular stakeholders who define the social problem from its beginning to end by focusing on their discourses, relationships, decision-making and political choices, and scientific studies. Despite some biases, newspapers are useful for retrospectively evaluating the emergence of a social problem in the public arena by describing it through discourse and then understanding the temporal patterns of information. Despite uncertainties and information flow, decisions are made and science is translated to the public.

Brain glutathione redox system significance for the control of silica-coated magnetite nanoparticles with or without mercury co-exposures mediated oxidative stress in European eel (Anguilla anguilla L.)

This in vitro study investigates the impact of silica-coated magnetite particles (Fe3O4@SiO2/SiDTC, hereafter called IONP; 2.5 mg L(-1)) and its interference with co-exposure to persistent contaminant (mercury, Hg; 50 μg L(-1)) during 0, 2, 4, 8, 16, 24, 48, and 72 h on European eel (Anguilla anguilla) brain and evaluates the significance of the glutathione (GSH) redox system in this context. The extent of damage (membrane lipid peroxidation, measured as thiobarbituric acid reactive substances, TBARS; protein oxidation, measured as reactive carbonyls, RCs) decreased with increasing period of exposure to IONP or IONP + Hg which was accompanied with differential responses of glutathione redox system major components (glutathione reductase, GR; glutathione peroxidase, GPX; total GSH, TGSH). The occurrence of antagonism between IONP and Hg impacts was evident at late hour (72 h), where significantly decreased TBARS and RC levels and GR and glutathione sulfo-transferase (GST) activity imply the positive effect of IONP + Hg concomitant exposure against Hg-accrued negative impacts [vs. early (2 h) hour of exposure]. A period of exposure-dependent IONP alone and IONP + Hg joint exposure-accrued impact was perceptible. Additionally, increased susceptibility of the GSH redox system to increased period of exposure to Hg was depicted, where insufficiency of elevated GR for the maintenance of TGSH required for membrane lipid and cellular protein protection was displayed. Overall, a fine-tuning among brain glutathione redox system components was revealed controlling IONP + Hg interactive impacts successfully.

Modulation of glutathione and its dependent enzymes in gill cells of Anguilla anguilla exposed to silica coated iron oxide nanoparticles with or without mercury co-exposure under in vitro condition

The current study aimed to investigate the modulation of glutathione (GSH) and its dependent enzymes (glutathione reductase, GR; glutathione peroxidase, GPx; glutathione sulfotransferase, GST) from 0 to 72 h in the gill cells of Anguilla anguilla under in vitro condition exposed to silica coated iron oxide nanoparticles functionalized with dithiocarbamate (Fe₃O₄@SiO₂/SiDTC, hereafter called 'IONPs'; 100 nm; 2.5 mgL(-1)) with or without mercury (Hg) coexposure. Significantly decreased TGSH content under IONP alone exposure from 0 to 72 h indicated increased utilization of the TGSH in response to IONP stress. Significant increases in the activity of GR, GPx and GST were depicted when exposed to IONP alone. Lipid peroxidation (LPO), a membrane damage trait also significantly increased under IONP alone exposure indicating the efficient role of antioxidant induction abolishing the IONP-mediated enhanced reactive oxygen species. Under Hg exposure, gill cells displayed significantly increased activity of the studied enzymes (GR, GPx and GST) and LPO which was accompanied by significantly decreased TGSH content. Concomitant (IONPs+Hg) exposure displayed a synergistic response to that of individual responses of either IOPN or Hg which was evident by significant increases in GR, GPx, GST and LPO. Overall, our findings revealed a fine tuning among the GSH and its dependent enzyme modulation under IONP, Hg and its concomitant (IONPs+Hg) exposure in A. anguilla gill cells under in vitro condition.

Effects of chronic exposure to lead, copper, zinc, and cadmium on biomarkers of the European eel, Anguilla anguilla

Exposure to specific metallic compounds can cause severe deleterious modifications in organisms. Fishes are particularly prone to toxic effects from exposure to metallic compounds via their environment. Species that inhabit estuaries or freshwater environments can be chronically affected by persistent exposure to a large number of metallic compounds, particularly those released by industrial activities. In this study, we exposed yellow eels (European eel, Anguilla anguilla) for 28 days to environmentally relevant concentrations of four specific metals; lead (300, 600, and 1,200 μg/l), copper (40, 120, and 360 μg/l), zinc (30, 60, and 120 μg/l) and cadmium (50, 150, and 450 μg/l). The selected endpoints to assess the toxicological effects were neurotransmission (cholinesterasic activity in nervous tissue), antioxidant defense, and phase II metabolism (glutathione-S-transferase [GST] activity, in both gills and liver tissues), and peroxidative damage. The results showed an overall lack of effects on acetylcholinesterase for all tested metals. Lead, copper, and cadmium exposure caused a significant, dose-dependent, increase in GST activity in gill tissue. However, liver GST only significantly increased following zinc exposure. No statistically significant effects were observed for the thiobarbituric acid reactive substances assay, indicating the absence of peroxidative damage. These findings suggest that, despite the occurrence of an oxidative-based response after exposure to lead, copper, and cadmium, this had no consequence in terms of peroxidative membrane damage; furthermore, cholinergic neurotoxicity caused by lead, copper, and cadmium did not occur. The implications of these results are further discussed.

Dioxin-like, non-dioxin like PCB and PCDD/F contamination in European eel (Anguilla anguilla) from the Loire estuarine continuum: spatial and biological variabilities

To characterize the eel contamination by dioxin-like (dl) and non dioxin-like (ndl) polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), sixty-two eels from the Loire estuary (France) were analyzed. PCB contamination significantly increased from glass eel stage (3.71 ± 1.85 and 15.2 ± 4.2 ng g(-1) dw) to other life stages (for yellow eels: 62.8 ± 34.4 and 382 ± 182 ng g(-1) dw; for silver eels: 93.7 ± 56.3 and 463 ± 245 ng g(-1) dw respectively for dl and ndl-PCBs). An inter-site variability based on PCB levels and profiles was observed among the three studied sites. For glass eels, the profile was mainly characterized by less chlorinated PCBs contrary to the other eels, displaying a different bioaccumulation pathway. Overall, the contamination level in the eels from this estuary was shown to be low for PCDD/Fs and intermediate for dl and ndl-PCBs, compared to other international/national areas. However, more than 60% of the studied silver eels displayed higher values for PCDD/F and dl-PCB WHO2005 TEQ than the EU permissible level of 10 pg g(-1) ww. This statement suggests a potential exposure to PCBs through eel consumption, especially with silver eels, and also points out apparent contamination that could eventually affect the reproductive success of the species.

Bages-Sigean and Canet-St Nazaire lagoons (France): physico-chemical characteristics and contaminant concentrations (Cu, Cd, PCBs and PBDEs) as environmental quality of water and sediment

Environmental characteristics in water and sediments of two contrasted coastal Mediterranean lagoons, Bages-Sigean and Canet-St Nazaire, were measured over a three season survey. The urban pollution (treatment plant discharges) is very important in Canet-St Nazaire lagoon reflecting untreated sewages, while in Bages-Sigean, the northern part appears more impacted due to larger anthropogenic inputs. Dissolved Cd concentrations are on the whole similar in both lagoons, whereas Cu concentrations are by far higher in lagoon Canet-St Nazaire. Cu concentrations appear to be highly dependent on dissolved organic carbon whereas salinity seems to control Cd variations. Concerning the sediments, the confined northern part of lagoon Bages-Sigean shows organic carbon and total nitrogen enrichment whereas lipid concentrations are much higher in the Canet-St Nazaire lagoon. Cu complexation seems to be strongly related to organic matter as evidenced by the two significant positive relationships, on one hand between Cu and organic carbon, and on the other hand, between Cu and lipids. On the contrary, Cd concentrations appear to be mainly controlled by carbonates. PCBs and PBDEs were detected only in sediments and show relatively low concentrations compared to similar lagoon environments. Regarding the sediment quality guidelines, Cd, Cu and PCBs in both lagoons did not exceed any Probable Effect Concentration (PEC).

Effect of low-dose cadmium exposure on DNA methylation in the endangered European eel

There is increasing evidence that epigenetics can play a key role in the etiology of diseases engendered by chronic pollutant exposure. Although epigenetics has received significant attention in the field of biomedicine during the last years, epigenetics research is surprisingly very limited in ecotoxicology. The aim of the present study was to investigate the possible effects of low-dose cadmium exposure on the DNA methylation profile in a critically endangered fish species, the European eel. Eels were exposed to environmentally realistic concentrations of cadmium (0.4 and 4 μg·L(-1)) during 45 days. The global CpG methylation status of eel liver was determined by means of a homemade ELISA assay. We then used a methylation-sensitive arbitrarily primed PCR method to identify genes that are differentially methylated between control and Cd-exposed eels. Our results show that cadmium exposure is associated with DNA hypermethylation and with a decrease in total RNA synthesis. Among hypermethylated sequences identified, several fragments presented high homologies with genes encoding for proteins involved in intracellular trafficking, lipid biosynthesis, and phosphatidic acid signaling pathway. In addition, few fragments presented high homologies with retrotransposon-like sequences. Our study illustrates how DNA methylation can be involved in the chronic stress response to Cd in fish.

Vg mRNA induction in an endangered fish species (Anguilla anguilla) from the Loire estuary (France)

Estuarine zones are extremely fragile due to increasing stress from anthropogenic activities. Among those, the Loire estuary (France) is potentially exposed to various contaminants including Endocrine Disruptors Compounds (EDCs) able to impact the reproduction physiology of fish. The European eel (Anguilla anguilla), endangered fish species, is apparently not relevant, in its yellow stage, to monitor the effects of endocrine disruption. Despite this weakly responsiveness, this study aimed to investigate whether European eel from the Loire estuary may still be the subject of estrogenic disruption quantifying the hepatic Vg gene expression according to gender and sexual stage. Vitellogenin (Vg) appears as a valuable biomarker of EDCs, as well as for exposure and effects. Quantitative real-time Reverse Transcription Polymerase Chain Reaction (q RT PCR) was used in this study to amplify responses of hepatic Vg transcripts. European eels were sampled in May 2009 (N=57) and November 2010 (during the downstream migration, N=10) in two sites of the Loire estuary with different ecological conditions and contamination pressures (upstream: Varades; downstream: Nantes). Reproductive (gender, sexual maturity stage) and biometric parameters of collected eels were determined. A laboratory exposure of silver male to steroid hormones (Testosterone (T), 11-KetoTestosterone (11-KT), Estradiol (E2)) was conducted in parallel to validate the q RT PCR approach on hepatic Vg mRNA. Results demonstrated the responsiveness of exposed silver male eels, since hepatic mRNA Vg induction was observed in E2 treated males compared to control specimens. In the field, results of female silver eels reflected large inter-individual differences in the activation of hepatic Vg at silvering. However, while only female silver eels should express hepatic Vg mRNA, quantifiable levels were also detected in a proportion of 38% of the other individuals sampled, normally not inclined to express it, those being undifferentiated eels, yellow females, yellow and silver males. According to each sexual stage, no difference of expression was observed between eels from the two sampling sites. Histological results as well as low Vg mRNA levels detected do not permit a conclusion as to a potential effect of endocrine disruption.

Influence of introduced vs. native parasites on the body condition of migrant silver eels

Because parasitism is among the reasons invoked to explain the collapse of Anguilla anguilla, we evaluated the parasitic constraint on body condition (BC) of migrant silver eels as a proxy of fitness with inter-site comparisons. Metazoan parasites were studied in 149 silver eels from five sites (northern Europe). In total, 89% were infected by 13 species including Myxozoa, Monogenea, Cestoda, Nematoda, and Acanthocephala. Anguillicoloides crassus was most common (56%), then Acanthocephalus clavula (30%), and Pseudodactylogyrus sp. (17%). BC, calculated for 58 females, was negatively correlated by abundance of the introduced Pseudodactylogyrus sp. but not by other parasite taxa. Nevertheless, the introduced A. crassus was considered as a severe pathogen based on previous data, whereas the native A. clavula was supposed to have limited impact. Parasite component communities and BC were different between sites. Silver eels from Stockholm Archipelago (Sweden) were the least parasitized (40% vs. 90-95% for other sites) with no parasites on the gills. Burrishoole (Ireland) differed by the absence of A. crassus and high prevalence of A. clavula (84%) but without consequences on BC. Gudenaa (Denmark), Corrib (Ireland), and Frémur (France) were close due to high prevalence of A. crassus (89-93%). Gudenaa and Corrib were the most similar because Pseudodactylogyrus sp. was also highly prevalent (respectively 71% and 60%) whereas absent in Frémur. Our results suggest that the fitness loss induced by the introduced parasites could affect the spawning success of migrant silver eels from Gudenaa and Corrib, and to a lesser extent from Frémur, but probably not those from Stockholm Archipelago and Burrishoole.

Polychlorinated biphenyls disrupt cell division and tip growth in two species of fucoid algae

Environmental contaminants, including poly-chlorinated biphenyls (PCBs), are enriched in coastal sediments, and despite a 1977 moratorium by the United States Environmental Protection Agency on the production of PCBs, levels remain high, more so near former industrial plants. The effects of these contaminants on sessile species in the intertidal zone, particularly nonanimal species such as the ubiquitous fucoid brown algae, are not well known. We investigated the developmental effects of chronic PCB treatment beginning at fertilization on two species of marine rockweed, Fucus vesiculosus Linnaeus and Silvetia compressa (J.Agardh) E.Serrão, T.O.Cho, S.M.Boo & Brawley. A mixture of the most widely used PCB congeners, Aroclors 1221, 1242, and 1254, was delivered at concentrations well below levels found in contaminated sediments, and resulted in severely delayed mitosis and cytokinesis in both species. In F. vesiculosus, this delay was accompanied by abnormal spindle morphology. PCB treatment also dramatically slowed or arrested rhizoid growth after 2-4 d, and by 7 d F. vesiculosus embryos were dead; in contrast, polar secretion of adhesive, germination, and photopolar germination were not affected. The dramatic delay in the first cell division and reduction in tip growth within the first week of development are likely to compromise S. compressa's ability to reproduce and establish new generations. Thus, the data presented here suggest that PCBs still present in coastal sediments may be inhibiting recruitment in these species. Moreover, as sediment dredging causes temporary spikes in PCB concentrations, these kinds of bioremediation steps may exacerbate the disruption of fucoid development.

Spatial trends of dioxin-like compounds in Atlantic anguillid eels

Several temperate freshwater eel stocks have experienced unsustainable declines, yet to be explained. The decline of lake trout (Salvelinus namaycush) in Lake Ontario has been linked to aryl-hydrocarbon receptor agonists such as polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), and polychlorinated naphthalenes (PCNs), and the question remains whether eels are affected similarly by these compounds. Concentrations of PCDD/Fs, dl-PCBs, and PCNs were determined in eels collected at seven locations in eastern Canada including L. Ontario, one location in New York, USA, and one location in Flanders, Belgium. Concentrations varied greatly among origins, indicating dissimilar historic loadings to local areas. The risk to eel reproduction was evaluated with 2,3,7,8-TCDD toxic equivalents, and increased by 10-fold from the least to most contaminated site. The risk to eel recruitment from dioxin-like compounds in American eel using available guidelines is low. The development of a more comprehensive model for eel recruitment risk assessment due to dioxin-like compounds, using eel-specific guidelines, is recommended. Toxic equivalents were 5-fold higher when based on mammalian toxic equivalency factors compared to fish values. About half of the eels captured in L. Ontario exceeded the Canadian guideline for fish consumption (20pg TEQ g(-1) ww), but there were no other exceedances in Canada. The current risk to eel consumers in Canada is low overall, except for highly urbanized and industrialized areas.

Detecting genome-wide gene transcription profiles associated with high pollution burden in the critically endangered European eel

The European eel illustrates an example of a critically endangered fish species strongly affected by human stressors throughout its life cycle, in which pollution is considered to be one of the factors responsible for the decline of the stock. The objective of our study was to better understand the transcriptional response of European eels chronically exposed to pollutants in their natural environment. A total of 42 pre-migrating (silver) female eels from lowly, highly and extremely polluted environments in Belgium and, for comparative purposes, a lowly polluted habitat in Italy were measured for polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and brominated flame retardants (BFRs). Multipollutant level of bioaccumulation was linked to their genome-wide gene transcription using an eel-specific array of 14,913 annotated cDNAs. Shared responses to pollutant exposure were observed when comparing the highly polluted site in Belgium with the relatively clean sites in Belgium and Italy. First, an altered pattern of transcription of genes was associated with detoxification, with a novel European eel CYP3A gene and gluthatione S-transferase transcriptionally up-regulated. Second, an altered pattern of transcription of genes associated with the oxidative phosphorylation pathway, with the following genes involved in the generation of ATP being transcriptionally down-regulated in individuals from the highly polluted site: NADH dehydrogenase, succinate dehydrogenase, ubiquinol-cytochrome c reductase, cytochrome c oxidase and ATP synthase. Although we did not measure metabolism directly, seeing that the transcription level of many genes encoding enzymes involved in the mitochondrial respiratory chain and oxidative phosphorylation were down-regulated in the highly polluted site suggests that pollutants may have a significant effect on energy metabolism in these fish.

Spatial trends of organochlorinated pesticides, polychlorinated biphenyls, and polybrominated diphenyl ethers in Atlantic Anguillid eels

The bioaccumulation of lipophilic contaminants such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs) can result in a reduction in fitness and spawner quality in eels and may be a factor in Anguillid sp. population declines. Contaminant concentrations in eels have been studied extensively in Europe, but data for American eels are severely lacking. Concentrations of PCBs, OCPs, and PBDEs were determined in American eel from eastern Canada and New York, USA, along with European eel from Belgium. Principal component analysis revealed that eels captured in the St. Lawrence estuary were a mixture of upstream migrants from the St. Lawrence River watershed, and fish captured in local tributaries. Contaminant concentrations were dependent on origin, related to the local environment, and were lower than historic values. In Canada, concentrations of OCPs and PCBs in eel tissues were below the Canadian human consumption guidelines for contaminants in fish, indicating that the current risk to consumers is low. However, concentrations of PCBs, total DDT, and mirex in eels from L. Ontario and the upper St. Lawrence R. were above Great Lakes guidelines for the protection of piscivorous predators. Concentrations of penta-BDE homologs exceeded the Canadian guideline for environmental quality in over half of the eels in this study, but concentrations of the other homolog groups were below the guideline.

Gene transcription reflects poor health status of resident European eel chronically exposed to environmental pollutants

Understanding the effects of chronic exposure to pollutants on the genome and transcriptome of diadromous fish populations is crucial for their resilience under combined anthropogenic and environmental selective pressures. The catadromous European eel (Anguilla anguilla L.) has suffered a dramatic decline in recruitment for three decades, necessitating a thorough assessment of the transcriptional effects of environmental pollutants on resident and migrating eels in natural systems. We investigated the relationship between muscular bioaccumulation levels of metals (Hg, Cd, Pb, Cu, Zn, Ni, Cr, As and Se), PCBs and organochlorine pesticides (DDTs), the health status (condition factor and lipid reserves) and the associated transcriptional response in liver and gill tissues for genes involved in metal detoxification (metallothionein, MT) and oxidative metabolism (cytochrome P4501A, CYP1A) of xenobiotic compounds. In total 84 resident eels originating from three Belgian river basins (Scheldt, Meuse and Yzer) were analyzed along with five unpolluted aquaculture samples as control group. There was a large spatial variation in individual contaminant intensity and profile, while tissue pollution levels were strongly and negatively associated with condition indices, suggesting an important impact of pollution on the health of sub-adult resident eels. Gene transcription patterns revealed a complex response mechanism to a cocktail of pollutants, with a high variation at low pollution levels, but strongly down-regulated hepatic and gill gene transcription in highly polluted eels. Resident eels clearly experience a high pollution burden and seem to show a dysfunctional gene transcription regulation of detoxification genes at higher pollutant levels, correlated with low energy reserves and condition. To fully understand the evolutionary implications of pollutants on eel reproductive fitness, analyses of mature migrating eels and the characterization of their transcriptome-wide gene transcription response would be appropriate to unveil the complex responses associated with multiple interacting stressors and the long-term consequences at the entire species level. In the meanwhile, jointly monitoring environmental and tissue pollution levels at a European scale should be initiated, while preserving high quality habitats to increase the recovery chance of European eel in the future.

Contamination, parasitism and condition of Anguilla anguilla in three Italian stocks

In conjunction with habitat loss and overfishing, pollution and parasitism are believed to be relevant causes of collapse of Anguilla, as these can affect eel swimming ability and the development of gonads and embryos. The present study investigated Persistent Organic Pollutant (POP) concentrations, infection levels of Anguillicoloides crassus, lipid content and gonad abnormalities in eels sampled in 2007-2008 in three Italian water bodies (Caprolace Lake, Lesina Lagoon and Tevere River) that vary in salinity, trophic condition, contamination level and fishing pressure. Our analysis revealed that low-to-moderate levels of contamination and parasitism were not associated with gonad abnormalities in Caprolace Lake and Lesina Lagoon. On the contrary, POP concentrations and abundances of swim bladder nematodes were remarkably high in eels from the heavily urbanized Tevere River and were associated with significant gonad and swim bladder alterations. Contamination and infestation levels were so high to potentially impair spawner successful migration and reproduction. POP concentrations in Tevere eels also exceeded levels considered safe for food consumption. Though marginally contaminated, eels from the oligotrophic Caprolace Lake were in critical health condition: their lipid reserve was so low as to be considered insufficient to sustain the energetic costs of the transoceanic migration. Lesina eel stock was the only one displaying relatively good quality but here spawner abundance is likely limited by overfishing. Our results suggest that multiple stressors may potentially affect eel reproductive success. More definitive studies are needed to assess whether health effects caused by these multiple stressors are additive, compensatory or synergistic.

Biomonitoring of polychlorinated biphenyls (PCBs) in heavily polluted aquatic environment in different fish species

The distribution and concentrations of polychlorinated biphenyls (PCBs) were determined in fish species (European perch Perca fluviatilis, northern pike Esox lucius, pike perch Sander lucioperca, wels catfish Silirus glanus, common carp Cyprinus carpio, European eel Anguilla anguilla, freshwater bream Abramis brama, goldfish Carassius auratus, and roach Rutilus rutilus) in a heavily polluted water reservoir Zemplínska šírava (Slovakia). The study performed at two different time points 5 years apart (2004 and 2009) revealed serious PCB contamination of fish muscle tissue and significant interspecies as well as tissue-specific differences in PCB uptake by fish. Total PCBs broadly correlated with the trophic position of individual fish species within a food chain (P < 0.01). The concentrations were particularly high in predatory fish species, perch, pike, and pike perch (108.0, 90.1, and 113.0 mg kg(-1) lipid wt, respectively), but comparable PCB values were also found in non-predatory detrivorous freshwater bream (128.0 mg kg(-1) lipid wt). The lowest PCB values were surprisingly assessed in European eel (17.1 mg kg(-1) lipid wt). Tissue analysis showed the highest storage capacity of the liver (hepatopancreas in cyprinids) with maximum concentrations recorded found in northern pike (214.0 mg kg(-1) lipid wt) and freshwater bream (163.0 mg kg(-1) lipid wt). Negative correlations, mostly not significant, between the total PCB concentrations and fish weight were observed (P > 0.05). The study has shown that the kind of fish, its feeding habit, and specific conditions of the habitat are mutually interrelated factors that are responsible for significant variations in fish body burdens. A tendency to PCB biomagnification was also proved in some fish species of this water reservoir.

Surviving in a toxic world: transcriptomics and gene expression profiling in response to environmental pollution in the critically endangered European eel

BACKGROUND

Genomic and transcriptomic approaches have the potential for unveiling the genome-wide response to environmental perturbations. The abundance of the catadromous European eel (Anguilla anguilla) stock has been declining since the 1980s probably due to a combination of anthropogenic and climatic factors. In this paper, we explore the transcriptomic dynamics between individuals from high (river Tiber, Italy) and low pollution (lake Bolsena, Italy) environments, which were measured for 36 PCBs, several organochlorine pesticides and brominated flame retardants and nine metals.

RESULTS

To this end, we first (i) updated the European eel transcriptome using deep sequencing data with a total of 640,040 reads assembled into 44,896 contigs (Eeelbase release 2.0), and (ii) developed a transcriptomic platform for global gene expression profiling in the critically endangered European eel of about 15,000 annotated contigs, which was applied to detect differentially expressed genes between polluted sites. Several detoxification genes related to metabolism of pollutants were upregulated in the highly polluted site, including genes that take part in phase I of the xenobiotic metabolism (CYP3A), phase II (glutathione-S-transferase) and oxidative stress (glutathione peroxidase). In addition, key genes in the mitochondrial respiratory chain and oxidative phosphorylation were down-regulated at the Tiber site relative to the Bolsena site.

CONCLUSIONS

Together with the induced high expression of detoxification genes, the suggested lowered expression of genes supposedly involved in metabolism suggests that pollution may also be associated with decreased respiratory and energy production.

The xenometabolome and novel contaminant markers in fish exposed to a wastewater treatment works effluent

Organisms exposed to wastewater treatment works (WwTW) effluents accumulate complex mixtures of xenobiotics but there is a scarcity of information on the nature and impacts of these chemical mixtures. We applied metabolomics techniques as a novel approach to identify xenobiotics and their metabolites (the xenometabolome) that bioconcentrate in fish exposed to a WwTW effluent. Exposed juvenile rainbow trout (Oncorhynchus mykiss) accumulated surfactants, naphthols, chlorinated xylenols, and phenoxyphenols, chlorophenes, resin acids, mefenamic acid, oxybenzone, and steroidal alkaloids in the bile or plasma, and there were perturbations in the plasma concentrations of bile acids and lipids. Exposure of adult roach (Rutilus rutilus) to 50% or 100% concentrations of the same effluent resulted in dose-dependent increases in plasma concentrations of xenometabolites as well as cyprinol sulfate and taurocholic acid, lysophospholipids, and a decrease in sphingosine levels (a key component of cell membrane lipids). Our findings reveal the highly complex nature of xenobiotics accumulating in effluent-exposed fish, and the great potential of metabolomics for both identifying plasma marker (bio)chemicals for monitoring exposure to wastewater effluents, and for targeting studies on potential consequent impacts on fish health.

Perch and its parasites as heavy metal biomonitors in a freshwater environment: the case study of the Ružín water reservoir, Slovakia

Heavy metal concentrations were determined in 43 perches (Perca fluviatilis) and in two of its most common parasites, the acanthocephalan Acanthocephalus lucii and the cestode Proteocephalus percae, collected in the period 2009–2010 from Ružín, a seriously polluted water reservoir in Slovakia. Samples of muscle, liver, kidney, brain, male and female reproductive organs and adipose tissue of fish and both parasites were analyzed for As, Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn, by ICP-MS. Mean concentrations of individual heavy metals in all fish samples decreased in the order zinc > copper > manganese > mercury > arsenic > chromium > cadmium > nickel > lead. Zinc was found to be the dominant element and its antagonistic interaction with copper was confirmed. The kidney was a key target organ receiving the highest mean concentrations of all analyzed metals, but some metals showed specific affinity for particular tissues. In terms of human health, concentration of Hg in fish muscle, which exceeded more than two-times its maximum level admitted in foodstuffs in European countries, is of great importance and should be taken into account. Bioaccumulation factors (C_[parasite]/C_{[fish tissue]}) calculated for all elements indicated much higher detection skills of A. lucii and P. percae parasites than fish organs and hence, present results allow proposing both parasite models as useful tools to monitor aquatic environmental quality. Acanthocephalans, however, seem to be superior for heavy metal monitoring, also demonstrated under experimental conditions. Present results also indicate the decreasing heavy metal burden of the reservoir and its gradual recovery in the course of time.

The silvering process of European eel (Anguilla anguilla) influences PAH metabolite concentrations in bile fluid: consequences for monitoring

The stock of the catadromous European eel (Anguilla anguilla L.) continues to decline and there is growing evidence that poor health status due to contaminants might be a key element in this decrease. Organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) belong to the major threats to yellow eel in their growth habitat and their metabolites are detectable in the bile. Starting the silvering process eels undergo physiological and morphological changes including cessation of feeding and downstream migration back to their spawning grounds. Reduced feed intake results in a diminishment of bile production and induces accumulation of e.g. PAH-metabolites in bile. Therefore, the aim of the present study was to demonstrate the impact of silvering on biliary PAH metabolite concentrations and to utilize normalization procedures to overcome silvering related accumulation effects of PAH-metabolites in eel bile. We investigated the hydroxyl-metabolites of pyrene (1-OH Pyr) and phenantrene (1-OH Phen) in the bile of different maturation stages of eels (silvering index I-V) from nine German rivers. We detected increasing absolute PAH metabolite levels in bile during the silvering process. The highest rise could be observed at the transition from pre migration stage III to the migrating stage IV, suggesting the onset of cessation of feeding at this stage. A cessation bias in PAH metabolite measurement could be diminished by normalization of absolute values against bile pigments (A(380), biliverdin). In conclusion, we demonstrated the impact of silvering on PAH metabolite concentrations in eel bile and present suitable normalization procedures to overcome silvering related accumulation effects. Thus, for a future eel monitoring we recommend (1) to regularly monitor PAH metabolites in bile, (2) to determine silvering index of eel and (3) to normalize PAH metabolite values in bile based on maturation/silvering stages. The knowledge of the silvering stage is mandatory for an unbiased evaluation of PAH contamination of European eel towards an international harmonized eel monitoring program.

The European eel quality database: towards a pan-European monitoring of eel quality

The stocks of the European eel Anguilla anguilla are in decline and there is an increasing awareness that poor health status due to contaminants and/or diseases might be a key element in this decline and might be a hindrance to recovery. Many countries have started compiling data on the health status of eels in their water bodies. Objectives for these monitoring actions are diverse and there is a large amount of information collected by EU member countries. However, this information is widely scattered over Europe in agencies, institutes or universities. As there is a growing need to collect and report on data on the health status of the eel on international level, the Joint EIFAC/ICES Working Group on Eels initiated in September 2007 the set up of an European Eel Quality Database to collect recent data of contaminants and diseases over the distribution area of the eel. This paper describes the aim, the set up and future development of the database in order to give it greater publicity and to call on scientists or managers to submit data on eel health status. The database represents now the first comprehensive pan-European compilation of eel health data, including data from over 10,000 eels from approximately 1,200 sites over 14 countries. Preliminary work has indicated a number of shortcomings and future developments will be needed. Guaranteeing further development of the database, harmonisation of methods, quality assurance, and setting up harmonised eel monitoring strategies over Europe will be a great challenge and will need pan-European cooperative work.

Reproduction of European eel jeopardised by high levels of dioxins and dioxin-like PCBs?

Dioxins, furans and dioxin-like polychlorinated biphenyls (PCBs) were analysed in muscle tissue from yellow phased European eel (Anguilla anguilla) from 38 sites in Belgium. Dioxin concentrations in eel vary considerably between sampling locations, indicating that yellow eel is a good indicator of local pollution levels. Measured levels of dioxin-like PCBs are much higher than those of the dioxins and furans. In the majority of the sites, eel has levels considered to be detrimental for their reproduction. Field levels of dioxin and dioxin-like PCBs are therefore suggested as an additional causal factor contributing to the decline of the European eel. 42% of the sampling sites show especially dioxin-like PCB levels exceeding the European consumption level (with a factor 3 on average). Human consumption of eel, especially in these highly contaminated sites, seems unjustified.

River networks as biodiversity hotlines

For several years, measures to insure healthy river functions and to protect biodiversity have focused on management at the scale of drainage basins. Indeed, rivers bear witness to the health of their drainage basins, which justifies integrated basin management. However, this vision should not mask two other aspects of the protection of aquatic and riparian biodiversity as well as services provided by rivers. First, although largely depending on the ecological properties of the surrounding terrestrial environment, rivers are ecological systems by themselves, characterized by their linearity: they are organized in connected networks, complex and ever changing, open to the sea. Second, the structure and functions of river networks respond to manipulations of their hydrology, and are particularly vulnerable to climatic variations. Whatever the scale considered, river networks represent "hotlines" for sharing water between ecological and societal systems, as well as for preserving both systems in the face of global change. River hotlines are characterized by spatial as well as temporal legacies: every human impact to a river network may be transmitted far downstream from its point of origin, and may produce effects only after a more or less prolonged latency period. Here, I review some of the current issues of river ecology in light of the linear character of river networks.