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See detailApproaches for assessing the presence and impact of thyroid hormone disrupting chemicals in sea bass (Dicentrarchus labrax) from European coasts
Schnitzler, Joseph ULg

Doctoral thesis (2011)

Thyroid functional status of wild fish in relation with the contamination of their environment deserves further investigation. Polychlorinated biphenyls (PCBs) and organochlorine pesticides like Dichloro ... [more ▼]

Thyroid functional status of wild fish in relation with the contamination of their environment deserves further investigation. Polychlorinated biphenyls (PCBs) and organochlorine pesticides like Dichloro-Diphenyl-Trichloroethane (DDTs), Hexachlorocyclohexanes (HCHs), aldrin, dieldrin and trace elements (Cd, Cu, Se, Pb, Zn and Hg) were analysed in the muscle of sea bass (Dicentrarchus labrax) sampled in coastal regions near several important European river mouths (Gironde, Charente, Loire, Seine and Scheldt). We applied a multi-level approach of thyroid function assessment. Thyroxine (T4) and triiodothyronine (T3) concentrations in muscle were analyzed by radioimmunoassay. The activity of hepatic enzymes involved in extrathyroidal pathways of thyroid hormone metabolism, viz. deiodination, glucuronidation and sulfation were analyzed. Last, follicle diameter and epithelial cell heights were measured. We observed changes that lead to an increased conversion of T4 to T3 and lowered thyroid hormone excretion. The changes in the metabolic pathways of thyroid hormones can be interpreted as a pathway to maintain thyroid hormone homeostasis. The higher chlorinated PCBs seemed to be the most implicated in this perturbation. To gain a more integrated insight, we examined the effect of subchronic exposure to a mixture of Aroclor standards on thyroid hormone physiology and metabolism in juvenile sea bass. After 120 days of exposure, histomorphometry of thyroid tissue, muscular thyroid hormone concentration and activity of enzymes involved in metabolism of thyroid hormones were assessed. The results show that the effects of PCB exposures on the thyroid system are dose-dependent. Exposure to environmentally relevant doses of PCB (0.3 to 1.0 μg Σ7PCBs per g food pellets) increases thyroid hormone synthesis and stimulates hepatic T4 outer ring deiodinase and T4 sulfation. Thyroid hormone tissue levels were preserved thanks to the PCB induced changes in T4 dynamics. At 10 times higher concentrations (10 μg Σ7PCBs per g food pellets) an important depression of T3 and T4 levels could be observed which are apparently caused by degenerative histological changes in the thyroid tissue. We propose accurate interpretations, by reviewing the different stages of teleost thyroid function and regulation. [less ▲]

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See detailThyroid hormone disrupting chemicals in sea bass (Dicentrarchus labrax) from European coasts
Schnitzler, Joseph ULg; Michel, Loïc ULg; Klaren, Peter et al

Conference (2011, February 25)

Polychlorinated biphenyls (PCBs) and organochlorine pesticides like Dichloro-Diphenyl-Trichloroethane (DDTs), Hexachlorocyclohexanes (HCHs), aldrin, dieldrin and trace elements (Cd, Cu, Se, Pb, Zn and Hg ... [more ▼]

Polychlorinated biphenyls (PCBs) and organochlorine pesticides like Dichloro-Diphenyl-Trichloroethane (DDTs), Hexachlorocyclohexanes (HCHs), aldrin, dieldrin and trace elements (Cd, Cu, Se, Pb, Zn and Hg) were analysed in the muscle of sea bass (Dicentrarchus labrax) sampled in coastal regions near several important European river mouths (Gironde, Charente, Loire, Seine and Scheldt). These potential endocrine disrupting chemicals were present in European coastal waters. Even if their concentrations were well below the Maximum Residue Limits set by the governments, they induced alterations of the endocrine system. We established correlations between contaminant concentrations and effects on the thyroid system in sea bass. The contaminants induced modifications of the metabolic pathways of thyroid hormones and enhanced thyroid hormone synthesis. The activity of T4 Outer Ring Deiodinase was increased, that leads to an intensified conversion of thyroxine (T4) to its more biologically active form triiodothyronine (T3). Meanwhile, the activity of T4 sulfatation was reduced, that leads to a lowered biliary excretion of thyroid hormones. The modified metabolic pathways of the thyroid hormones can be interpreted as a tool to homeostatically maintain the thyroid hormone status. Of all tested compounds, the higher chlorinated PCBs seemed to be the most implicated in this perturbation. The nature of thyroid hormone synthesis, signalling and regulation is highly conserved among vertebrates. Although we cannot extrapolate thyroid toxicity data directly from one species to another, these environmental factors may well affect thyroid function in other species, including humans. [less ▲]

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See detailOrganisms as ecosystems engineers: the case of amphipod grazers from Posidonia oceanica meadows
Michel, Loïc ULg; Schnitzler, Joseph ULg; Dupont, Alessandra et al

Poster (2011, February 25)

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows shelter high biomasses and biodiversities of amphipod ... [more ▼]

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows shelter high biomasses and biodiversities of amphipod crustaceans. Moreover, It is now established that several species of these amphipods feed on the macro-epiphytes present on the leaves of the seagrass. Here, we performed in situ experiments to assess whether this grazing activity could impact the dynamics of the leaves’ epiphytic cover, and thus influence the functioning of the meadow as an ecosystem. We used microcosms containing monospecific populations of 3 amphipods taxa (Apherusa chiereghinii, Dexamine spiniventris and Gammarus spp.), and placed them directly in the meadow, at a depth of 10m. Biomasses of erected macroalgae and erected animals (hydrozoans, bryozoans) were lower in all grazed treatments. However, none of the studied taxa seemed to consume encrusting epiphytes, either vegetal or animal. This selective grazing pressure by amphipods may release encrusting epiphytes from competition for space, light and/or nutriments with the fast-growing erected algae, and could thus play an important role in the structuring of the epiphytic cover from P. oceanica leaves. Moreover, this top-down control might keep erected algae biomass to a normal, sustainable level, therefore also benefiting the seagrass itself. Our results also indicate that amphipod trophic activity caused nitrogen enrichment in both grazed (erected algae) and non-grazed (encrusting algae & seagrass leaves) vegetal tissues. A plausible interpretation could be that sloppy feeding and excretion by the grazers enhanced availability of this nutrient, which is typically limiting for photosynthesis in shallow P. oceanica meadows. This emphasizes the fact that grazing is not a simple negative interaction, but that it can also benefit the primary producers. Our results thus indicate that amphipods from P. oceanica meadows seem to be bound to the epiphytic cover of the leaves by complex and multilateral trophic interactions, and have an indirect influence on the seagrass itself. Amphipods may therefore play an important part in the functioning of the epiphyte/seagrass/grazer system of these meadows, and thus act as ecosystems engineers. This abstract is dedicated to the freshly born Adèle and Côme. [less ▲]

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See detailOrganochlorine pesticides, polychlorinated biphenyls and trace elements in wild European sea bass (Dicentrarchus labrax) off European estuaries
Schnitzler, Joseph ULg; Thomé, Jean-Pierre ULg; Lepage, Mario et al

in Science of the Total Environment (2011), 409(19), 3680-3686

Polychlorinated biphenyls (PCBs) and organochlorine pesticides like dichloro-diphenyl-trichloroethane (DDTs), hexachlorocyclohexanes (HCHs), aldrin, dieldrin and trace elements (Cd, Cu, Se, Pb, Zn and Hg ... [more ▼]

Polychlorinated biphenyls (PCBs) and organochlorine pesticides like dichloro-diphenyl-trichloroethane (DDTs), hexachlorocyclohexanes (HCHs), aldrin, dieldrin and trace elements (Cd, Cu, Se, Pb, Zn and Hg) were analysed in the muscle of European sea bass (Dicentrarchus labrax) sampled in Atlantic coastal regions near several important European river mouths (Gironde, Charente, Loire, Seine and Scheldt). High contamination levels were measured in the muscles of European sea bass sampled in the coastal regions near those river mouths (e.g. Σ ICES PCB=133–10,478 μg kg−1 lw and Hg=250–2000 μg kg−1 dw). The Scheldt and the Seine are still among the most contaminated estuaries in Europe. Each region presented their specific contamination patterns reflecting different sources due to the input of the respective rivers. As fish and fishery products are the main contributors of the total dietary intake of organochlorinated pollutants, regular consumption of European sea bass with the reported contamination levels may represent a significant exposure route for the general human population. [less ▲]

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See detailThyroid dysfunction in sea bass (Dicentrarchus labrax): Underlying mechanisms and effects of polychlorinated biphenyls on thyroid hormone physiology and metabolism
Schnitzler, Joseph ULg; Celis, Niko; Klaren, Peter et al

in Aquatic Toxicology (2011), 105

The current study examines the effect of subchronic exposure to a mixture of Aroclor standards on thyroid hormone physiology and metabolism in juvenile sea bass. The contaminant mixture was formulated to ... [more ▼]

The current study examines the effect of subchronic exposure to a mixture of Aroclor standards on thyroid hormone physiology and metabolism in juvenile sea bass. The contaminant mixture was formulated to reflect the persistent organic pollution to which the European sea bass population could conceivably be exposed (0.3, 0.6 and 1.0 g 7PCBs per g food pellets) and higher (10 g 7PCBs per g food pellets). After 120 days of exposure, histomorphometry of thyroid tissue, muscular thyroid hormone concentration and activity of enzymes involved in metabolism of thyroid hormones were assessed. Mean concentrations of 8, 86, 142, 214 and 2279 ng g−1 ww ( 7 ICES PCB congeners) were determined after 120 days exposure. The results show that the effects of PCB exposures on the thyroid system are dose-dependent. Exposure to environmentally relevant doses of PCB (0.3–1.0 g 7PCBs per g food pellets) induced a larger variability of the follicle diameter and stimulated hepatic T4 outer ring deiodinase. Muscular thyroid hormone levels were preserved thanks to the PCB induced changes in T4 dynamics. At 10 times higher concentrations (10 g 7PCBs per g food pellets) an important depression of T3 and T4 levels could be observed which are apparently caused by degenerative histological changes in the thyroid tissue. [less ▲]

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See detailSTRATEGY FOR ASSESSING IMPACTS OF THYROID DISRUPTING CHEMICALS IN TELEOSTEANS
Schnitzler, Joseph ULg; Klaren, Peter; Celis, Niko et al

in Organohalogen Compounds (2011)

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See detailPolychlorinated Biphenyls affect Histological Appearance of European sea bass (Dicentrarchus labrax) Thyroids
Schnitzler, Joseph ULg; Klaren, Peter; Celis, Niko et al

Conference (2010)

Polychlorobiphenyls (PCBs) are well-described endocrine disrupters and of particular interest are effects on thyroid function. We propose here a thorough approach to assess effects of these compounds on ... [more ▼]

Polychlorobiphenyls (PCBs) are well-described endocrine disrupters and of particular interest are effects on thyroid function. We propose here a thorough approach to assess effects of these compounds on the thyroid function of European sea bass (Dicentrarchus labrax). An experimental exposure of sea bass to commercial PCB mixtures has been designed to understand underlying toxicity mechanisms and effects on the thyroid system. After 120 days of exposure histological appearance of thyroid tissue was assessed by light and electron microscopy. The follicle area, perimeter, diameter, length and with of every follicle cross section were interactively measured. The shape of the follicles was described with three dimensionless shape descriptors: roundness, form factor and aspect ratio. The histomorphometrical analysis showed a greater heterogeneity of thyroid follicle diameter and especially higher epithelial cell heights in sea bass exposed to environmental relevant doses of PCB (from 0.3 to 0.9 μg g-1 [7 ICES PCB]). Ultrastructural histological investigations showed that the epithelial cells surrounding the bigger follicles present an higher accumulation of colloid droplets. This was interpreted to be the result of increased stimulation of follicular cells. No differences in shape could be identified among the different treatment groups The size of the follicles and the form of the follicular cells gives an indication of the secretary activity of the gland. These observations support the hypothesis that the contamination of PCB mixtures can induce a hyperactivity of the thyroid tissue. These observations were confirmed by measurements of muscular thyroid hormone concentrations and activity thyroid hormone metabolism. [less ▲]

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See detailEffects of Polychlorinated Biphenyls on Thyroid Hormone Physiology and Metabolism of European sea bass (Dicentrarchus labrax)
Schnitzler, Joseph ULg; Klaren, Peter; Celis, Niko et al

Conference (2010)

Studies in the laboratory have shown that a number of synthetic and natural chemicals can interfere with the endocrine system in fish. Among them, organic compounds such as pesticides and ... [more ▼]

Studies in the laboratory have shown that a number of synthetic and natural chemicals can interfere with the endocrine system in fish. Among them, organic compounds such as pesticides and polychlorobiphenyls (PCBs) are well described endocrine disrupters. Of particular interest are effects on thyroid function, but data on effects of PCB exposure on these hormones and related metabolism has been lacking. We propose here a thorough approach to assess effects of these compounds on the thyroid function of European sea bass (Dicentrarchus labrax). An experimental exposure of sea bass to commercial PCB mixtures has been designed to understand underlying toxicity mechanisms and effects on the thyroid system. After 120 days of exposure, muscular thyroid hormone concentrations and the main metabolic pathways for thyroid hormones (deiodination, glucuronidation and sulfatation) were assessed. Exposure to environmental relevant doses of PCB (from 0.3 to 0.9 ppm [7 ICES PCB]). alters hepatic T4 outer ring deiodinase and T4 sulfatation whereas T4 glucuronidation was not affected. Owing to the extensive autoregulatory feedback at both central and peripheral levels, the thyroid hormone concentrations were preserved despite the PCB induced changes in thyroid hormone dynamics. At 10 times higher concentrations (10 ppm [7 ICES PCB]). an important depression of muscular T3 and T4 levels could be observed which are apparently caused by other mechanisms than metabolic pathways. Further analysis is required to evaluate thyroid gland function and secretion. These results support the observations made in our field study in wild sea bass (Dicentrarchus labrax) from coastal regions near several important European rivers mouths. [less ▲]

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See detailApproaches for assessing potential impacts of thyroid hormone disrupting chemicals in wild sea bass (Dicentrarchus labrax)
Schnitzler, Joseph ULg; Klaren, Peter; Thomé, Jean-Pierre ULg et al

Poster (2010)

Organic compounds such as pesticides and polychlorobiphenyls (PCBs) are well described endocrine disrupters; of particular interest are effects on thyroid function. To assess the ability of occurring ... [more ▼]

Organic compounds such as pesticides and polychlorobiphenyls (PCBs) are well described endocrine disrupters; of particular interest are effects on thyroid function. To assess the ability of occurring pollutants in European coastal areas to disrupt the thyroid system in sea bass, a field study in the major European estuaries, namely, the Scheldt, the Seine, the Loire, the Charente and the Garonne has been conducted. Several thyroid endpoints were simultaneously examined. Diameter of follicles and the epithelial cell heights give an indication on the production and secretion activity of the thyroid gland. The activity of enzymes involved in the metabolism (deiodination, glucuronidation and sulfatation) of thyroid hormones was analyzed. Finally thyroxine (T4) and triiodothyronine (T3) concentrations were analyzed in muscle by radioimmunoassay. The combined use of all those endpoints gives us an overview of the complex thyroid hormone system. PCB concentration in wild fish varied from 10 to 100 ng g-1 wet weight (ww) depending on length and location. Each region has its own contamination levels and profiles reflecting the contribution of pollutants from rivers. The contamination levels were as follows: the highest concentrations were measured in individuals collected from the coastal region near the Scheldt > Seine > Loire > Charente and the lowest levels were observed in sea bass from coastal regions near the Garonne. Measurements of metabolic activity revealed an altered hepatic T4 outer ring deiodinase whereas T4 sulfatation and T4 glucuronidation were not affected. Owing to the extensive autoregulatory feedback at both central and peripheral levels, the thyroid hormone concentrations were preserved despite the PCB induced changes in thyroid hormone dynamics. [less ▲]

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See detailPersistent organic pollutants in wild seabass (Dicentrarchus labrax) from the Northeast atlantic coastal regions and relationship with thyroid hormone levels
Schnitzler, Joseph ULg; Thomé, Jean-Pierre ULg; Das, Krishna ULg

Poster (2008, October 30)

Polychlorinated biphenyls (PCBs) and organochlorine pesticides like Dichloro-Diphenyl-Trichloroethane (DDTs), Hexachlorocyclohexanes (HCHs), Aldrin and Dieldrin were analysed in the muscle of sea bass ... [more ▼]

Polychlorinated biphenyls (PCBs) and organochlorine pesticides like Dichloro-Diphenyl-Trichloroethane (DDTs), Hexachlorocyclohexanes (HCHs), Aldrin and Dieldrin were analysed in the muscle of sea bass (Dicentrarchus labrax) sampled in coastal regions near several important European river mouths (Garonne, Charente, Loire, Seine and Scheldt). These organochlorinated compounds are known to influence the endocrine system of many fish species and mammals and are thus qualified as endocrine disrupters. To highlight a potentially harmful effect of these compounds on the thyroid function of these fishes, we measured the muscular concentrations of thyroid hormones T3 and T4 by Radio-Immuno-Assay. The contamination levels were as follows: the highest concentrations were measured in individuals collected from the coastal region near the Scheldt > Seine > Loire > Charente and the lowest levels were observed in sea bass from coastal regions near the Garonne (from 2422 to 6188 ng.g-1 lw). The measured levels were generally higher than those reported in literature in sea bass from other regions in the Mediterranean Sea. Contamination patterns were different depending on the sampling area and thus the river input of pollutants. The multivariate statistical analysis revealed a significant relationship between the measured persistent organic pollutants and thyroid hormones in muscle. We cannot exclude the assumption that an endocrine disruption of the thyroid related to these pollutants could be the origin of these modifications of the thyroid hormone concentrations. [less ▲]

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See detailHarbour porpoise thyroids: Histological investigations and potential interactions with environmental factors
Schnitzler, Joseph ULg; Siebert, Ursula; Jepson, Paul et al

in Journal of Wildlife Diseases (2008), 44

The thyroid plays an important role in development and is of primary importance in metabolism and heat loss for cetaceans, including the harbor porpoise (Phocoena phocoena). Several studies have ... [more ▼]

The thyroid plays an important role in development and is of primary importance in metabolism and heat loss for cetaceans, including the harbor porpoise (Phocoena phocoena). Several studies have demonstrated that environmental contaminants can alter various aspects of thyroid function in mammals and may contribute to various histologic changes. The present study completes the data set of a 2006 study by Das et al., by performing histological and immunohistologic investigations on thyroids of 36 harbor porpoises from Belgian and United Kingdom waters. The number and mean diameter of follicles (µm) and the relative proportion of follicular, connective, and vascular tissue (%) were quantified in the thyroid gland of each individual. Interfollicular fibrosis has been observed in these thyroid glands, and the collective findings support the hypothesis of an endocrine disruption of thyroid function through organochlorinated compounds. Our study aimed also to reveal potential relationships between thyroid morphometric data and metal levels (Cd, Fe, Zn, Cu, Se, and Hg) using multivariate statistical analysis. The multiple regressions revealed statistically significant relationships between trace elements (cadmium, selenium, and copper) and thyroid fibrosis. The largely negative relationships are interesting findings but do not support the hypothesis that these elements have an adverse effect on thyroid morphometry. Further research is needed to understand the nature of any relationship between organochlorine and trace element exposure and thyroid gland morphology and function in harbor porpoises. [less ▲]

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See detailEffects of persistent organic pollutants on the thyroid function of the European sea bass (Dicentrarchus labrax) from the Aegean Sea, is it an endocrine disruption?
Schnitzler, Joseph ULg; Koutrarkis, Emmanuil; Siebert, Ursula et al

in Marine Pollution Bulletin (2008), 56(10), 1755-1764

We evaluated the alterations of organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) on the thyroid in wild ... [more ▼]

We evaluated the alterations of organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) on the thyroid in wild and cultured sea bass (Dicentrarchus labrax) at environmental concentrations. These compounds influence the endocrine system of many fish species and are qualified as endocrine disruptors. The thyroid seems to be a target organ. Two alteration endpoints: the thyroid histology and the muscular thyroid hormone concentrations, were used simultaneously. High concentrations in PCBs and DDT were detected in muscles, supporting the idea that the Mediterranean fauna could be more polluted than the Atlantic fauna. The high abundance of DDE indicates a progressive degradation of remnant DDT load and the absence of new inputs in this area. Aquaculture sea bass shows a significant higher amount of pollutants on fresh weight basis (especially PCBs) in their muscles compared to the wild sea bass. Those differences may be related mainly to the contaminations of diet. Thyroid parameters vary between wild and aquaculture sea bass, wild sea bass were characterized by higher follicle diameters, epithelial cell heights and muscular T4 concentrations. A significant relationship between persistent organic pollutants (muscular PCBs and DDT concentration) and the different thyroid parameters (diameters of follicles, epithelial cell heights and muscular T4 levels) could be observed, which support the hypothesis that these compounds have an adverse impact on thyroid morphometry and function. [less ▲]

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See detailHarbour porpoises stranded on the Dutch coast in 2007: Impact of by cath and related lesions
Grondin, Alexia; Camphuysen, K.; Ghisbain, T. et al

Poster (2008)

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See detailCauses of death of harbor porpoises (Phocoena phocoena) stranded on the Dutch coast
Jauniaux, Thierry ULg; Bergerie, H.; Camphuysen, K. et al

in proceeding of the annual conference (2008)

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See detailEffects of persistent organic pollutants on the thyroid function of the sea bass (Dicentrarchus labrax), an endocrine disruption?
Schnitzler, Joseph ULg; Koutrakis, Emmanuil; Thomé, Jean-Pierre ULg et al

Conference (2007, May 23)

Organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) have the characteristic to influence the endocrine ... [more ▼]

Organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) have the characteristic to influence the endocrine system of many fish species and mammals and are thus qualified as endocrine disruptors. The objective of this project aims a better understanding of the effects of these compounds on the thyroid function of European seabass (Dicentrarchus labrax). Thyroid tissue and muscle of 46 seabass from the Aegean Sea in Greece (fished and aquaculture, n=15 and n=31, respectively) were sampled. The levels in PCBs, DDT and DDE were evaluated in the muscles of 30 individuals. The diameter of follicles and the epithelial cell heights were measured in each individual by optical microscopy. The concentration of the thyroid hormone T4 (thyroxin) was measured by Radio-Immuno-Assay (RIA). Finally, the potential relationships between these thyroid parameters and these organic compounds were investigated using factor analysis and multiple regressions. A significant relationship between persistent organic pollutants (muscular PCBs and DDT concentration) and the different thyroid parameters (diameters of follicles, epithelial cell heights and muscular T4 levels) could be observed. We cannot exclude the assumption that an endocrine disruption of thyroid gland related to these pollutants could be the origin of the modifications of these thyroid parameters. [less ▲]

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See detailLesions observed on harbor porpoises (Phocoena phocoena) stranded on the Dutch coast in 2006
Jauniaux, Thierry ULg; Bergerie, H.; Camphuysen, K. et al

(2007)

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See detailStudy of endocrine disruption in seabass (Dicentrarchus labrax)
Schnitzler, Joseph ULg; Koutrakis, Emmanuil; Thomé, Jean-Pierre ULg et al

Conference (2006, October 28)

Organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) have the characteristic to influence the endocrine ... [more ▼]

Organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) have the characteristic to influence the endocrine system of many fish species and mammals and are thus qualified as endocrine disruptors. The objective of this project aims a better understanding of the effects of these compounds on the thyroid function of European seabass (Dicentrarchus labrax). Thyroid tissue and muscle of 46 seabass from the Aegean Sea in Greece (fished and aquaculture, n=15 and n=31, respectively) were sampled. The levels in PCBs, DDT and DDE were evaluated in the muscles of 30 individuals. The diameter of follicles and the epithelial cell heights were measured in each individual by optical microscopy. The concentration of the thyroid hormone T4 (thyroxin) was measured by Radio-Immuno-Assay (RIA). Finally, the potential relationships between these thyroid parameters and these organic compounds were investigated using factor analysis and multiple regressions. A significant relationship between persistent organic pollutants (muscular PCBs and DDT concentration) and the different thyroid parameters (diameters of follicles, epithelial cell heights and muscular T4 levels) could be observed. We cannot exclude the assumption that an endocrine disruption of thyroid gland related to these pollutants could be the origin of the modifications of these thyroid parameters. [less ▲]

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