Joseph Schnitzler

Effects of persistent organic pollutants on the thyroid function of the European sea bass (Dicentrarchus labrax) from the Aegean sea, is it an endocrine disruption?

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 T(4) 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 T(4) levels) could be observed, which support the hypothesis that these compounds have an adverse impact on thyroid morphometry and function.

Organochlorine pesticides, polychlorinated biphenyls and trace elements in wild European sea bass (Dicentrarchus labrax) off European estuaries.

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.

POPs in free-ranging pilot whales, sperm whales and fin whales from the Mediterranean Sea: Influence of biological and ecological factors.

The pilot whale Globicephala melas, the sperm whale Physeter macrocephalus, and the fin whale Balaenoptera physalus are large cetaceans permanently inhabiting the Mediterranean Sea. These species are subjected to numerous anthropogenic threats such as exposure to high levels of contaminants. Therefore, selected persistent organic pollutants POPs (29 PCBs, 15 organochlorine compounds, 9 PBDEs and 17 PCDD/Fs) were analysed in blubber biopsies of 49 long-finned pilot whales, 61 sperm whales and 70 fin whales sampled in the North Western Mediterranean Sea (NWMS) from 2006 to 2013. Contamination profile and species feeding ecology were then combined through the use of stable isotopes. δ(13)C, δ(15)N values and POPs levels were assessed through IR-MS and GC-MS respectively. To assess the toxic potency of the dioxin-like compounds, the TEQ approach was applied. δ(15)N values were 12.2±1.3‰ for sperm whales, 10.5±0.7‰ for pilot whales and 7.7±0.8‰ in fin whales, positioning sperm whales at higher trophic levels. δ(13)C of the two odontocetes was similar and amounted to -17.3±0.4‰ for sperm whales and -17.8±0.3‰ for pilot whales; whilst fin whales were more depleted (-18.7±0.4‰). This indicates a partial overlap in toothed-whales feeding habitats, while confirms the differences in feeding behaviour of the mysticete. Pilot whales presented higher concentrations than sperm whales for ΣPCBs (38,666±25,731 ng g(-1)lw and 22,849±15,566 ng g(-1) lw respectively), ΣPBDEs (712±412 ng g(-1) lw and 347±173 ng g(-1) lw respectively) and ΣDDTs (46,081±37,506 ng g(-1) lw and 37,647±38,518 ng g(-1) lw respectively). Fin whales presented the lowest values, in accordance with its trophic position (ΣPCBs: 5721±5180 ng g(-1) lw, ΣPBDEs: 177±208 ng g(-1) lw and ΣDDTs: 6643±5549 ng g(-1) lw). Each species was characterized by large inter-individual variations that are more related to sex than trophic level, with males presenting higher contaminant burden than females. The discriminant analysis (DA) confirmed how DDTs and highly chlorinated PCBs were influential in differentiating the three species. Pollutant concentrations of our species were significantly higher than both their Southern Hemisphere and North Atlantic counterparts, possibly due to the particular Mediterranean geomorphology, which influences pollutants distribution and recycle. Dioxin-like PCBs accounted for over 80% of the total TEQ. This study demonstrated (1) an important exposure to pollutants of Mediterranean cetaceans, often surpassing the estimated threshold toxicity value of 17,000 ng g(-1) lw for blubber in marine mammals; and (2) how the final pollutant burden in these animals is strongly influenced not only by the trophic position but also by numerous other factors such as sex, age, body size and geographical distribution.

HARBOR PORPOISE THYROIDS: HISTOLOGIC INVESTIGATIONS AND POTENTIAL INTERACTIONS WITH ENVIRONMENTAL FACTORS

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.

Thyroid dysfunction in sea bass (dicentrarchus labrax): Underlying mechanisms and effects of polychlorinated biphenyls on thyroid hormone physiology and metabolism

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 μg Σ7PCBs per g food pellets) and higher (10 μg Σ7PCBs 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 (Σ7 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 μg Σ7PCBs per g food pellets) induced a larger variability of the follicle diameter and stimulated hepatic T(4) outer ring deiodinase. Muscular thyroid hormone levels were preserved thanks to the PCB induced changes in T(4) dynamics. At 10 times higher concentrations (10 μg Σ7PCBs per g food pellets) an important depression of T(3) and T(4) levels could be observed which are apparently caused by degenerative histological changes in the thyroid tissue.

Triclosan exposure results in alterations of thyroid hormone status and retarded early development and metamorphosis in Cyprinodon variegatus

Thyroid hormones are critically involved in somatic growth, development and metamorphosis of vertebrates. The structural similarity between thyroid hormones and triclosan, an antimicrobial compound widely employed in consumer personal care products, suggests triclosan can have adverse effects on the thyroid system. The sheepshead minnow, Cyprinodon variegatus, is now used in ecotoxicological studies that have recently begun to focus on potential disruption of the thyroid axis by endocrine disrupting compounds. Here, we investigate the in vivo effects of exposure to triclosan (20, 50, and 100μgL-1) on the thyroid system and the embryonic and larval development of C. variegatus. Triclosan exposure did not affect hatching success, but delayed hatching time by 6-13h compared to control embryos. Triclosan exposure affected the ontogenetic variations of whole body thyroid hormone concentrations during the larval phase. The T3 peak around 12-15 dph, described to be indicative for the metamorphosis climax in C. variegatus, was absent in triclosan-exposed larvae. Triclosan exposure did not produce any deformity or allometric repatterning, but a delayed development of 18-32h was observed. We conclude that the triclosan-induced disruption of the thyroid system delays in vivo the start of metamorphosis in our experimental model. We observed a global developmental delay of 24-45h, equivalent to 4-7% prolongation of the developmental time in C. variegatus. The costs of delayed metamorphosis can lead to reduction of juvenile fitness and could be a determining factor in the outcome of competitive interactions.

Environmental factors affecting thyroid function of wild sea bass (Dicentrarchus labrax) from European coasts

Thyroid functional status of wild fish in relation with the contamination of their environment deserves further investigation. We here applied a multi-level approach of thyroid function assessment in 87 wild sea bass collected near several estuaries: namely the Scheldt, the Seine, the Loire, the Charente and the Gironde. Thyroxine (T(4)) and triiodothyronine (T(3)) concentrations in muscle were analyzed by radioimmunoassay. The activity of hepatic enzymes involved in extrathyroidal pathways of thyroid hormone metabolism, viz. deiodination, glucuronidation and sulfatation were analyzed. Last, follicle diameter and epithelial cell heights were measured. We observed changes that are predicted to lead to an increased conversion of T(4)-T(3) 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. From all compounds tested, the higher chlorinated PCBs seemed to be the most implicated in this perturbation.

The thyroid gland and thyroid hormones in sheepshead minnow (Cyprinodon variegatus) during early development and metamorphosis.

The sheepshead minnow is widely used in ecotoxicological studies that only recently have begun to focus on disruption of the thyroid axis by xenobiotics and endocrine disrupting compounds. However, reference levels of the thyroid prohormone thyroxine (T4) and biologically active hormone 3,5,3′-triiodothyronine (T3) and their developmental patterns are unknown. This study set out to describe the ontogeny and morphology of the thyroid gland in sheepshead minnow, and to correlate these with whole-body concentrations of thyroid hormones during early development and metamorphosis. Eggs were collected by natural spawning in our laboratory. T4 and T3 were extracted from embryos, larvae and juveniles and an enzyme-linked immunoassay was used to measure whole-body hormone levels. Length and body mass, hatching success, gross morphology, thyroid hormone levels and histology were measured. The onset of metamorphosis at 12-day post-hatching coincided with surges in whole-body T4 and T3 concentrations. Thyroid follicles were first observed in pre-metamorphic larvae at hatching and were detected exclusively in the subpharyngeal region, surrounding the ventral aorta. Follicle size and thyrocyte epithelial cell heights varied during development, indicating fluctuations in thyroid hormone synthesis activity. The increase in the whole-body T3/T4 ratio was indicative of an increase in outer ring deiodination activity. This study establishes a baseline for thyroid hormones in sheepshead minnows, which will be useful for the understanding of thyroid hormone functions and in future studies of thyroid toxicants in this species.

Size and shape variations of the bony components of sperm whale cochleae

Several mass strandings of sperm whales occurred in the North Sea during January and February 2016. Twelve animals were necropsied and sampled around 48 h after their discovery on German coasts of Schleswig Holstein. The present study aims to explore the morphological variation of the primary sensory organ of sperm whales, the left and right auditory system, using high-resolution computerised tomography imaging. We performed a quantitative analysis of size and shape of cochleae using landmark-based geometric morphometrics to reveal inter-individual anatomical variations. A hierarchical cluster analysis based on thirty-one external morphometric characters classified these 12 individuals in two stranding clusters. A relative amount of shape variation could be attributable to geographical differences among stranding locations and clusters. Our geometric data allowed the discrimination of distinct bachelor schools among sperm whales that stranded on German coasts. We argue that the cochleae are individually shaped, varying greatly in dimensions and that the intra-specific variation observed in the morphology of the cochleae may partially reflect their affiliation to their bachelor school. There are increasing concerns about the impact of noise on cetaceans and describing the auditory periphery of odontocetes is a key conservation issue to further assess the effect of noise pollution.

Mercury Stable Isotopes Discriminate Different Populations of European Seabass and Trace Potential Hg Sources around Europe

Our study reports the first data on mercury (Hg) isotope composition in marine European fish, for seven distinct populations of the European seabass, Dicentrarchus labrax. The use of δ202Hg and Δ199Hg values in SIBER enabled us to estimate Hg isotopic niches, successfully discriminating several populations. Recursive-partitioning analyses demonstrated the relevance of Hg stable isotopes as discriminating tools. Hg isotopic values also provided insight on Hg contamination sources for biota in coastal environment. The overall narrow range of δ202Hg around Europe was suggested to be related to a global atmospheric contamination while δ202Hg at some sites was linked either to background contamination, or with local contamination sources. Δ199Hg was related to Hg levels of fish but we also suggest a relation with ecological conditions. Throughout this study, results from the Black Sea population stood out, displaying a Hg cycling similar to fresh water lakes. Our findings bring out the possibility to use Hg isotopes in order to discriminate distinct populations, to explore the Hg cycle on a large scale (Europe) and to distinguish sites contaminated by global versus local Hg source. The interest of using Hg sable isotopes to investigate the whole European Hg cycle is clearly highlighted.