De façon à maximiser leur valeur sélective, les individus doivent prendre différentes décisions qui doivent concorder aux conditions environnementales (se reproduire ou pas ? quand ? quel investissement parental ?). Ces décisions sont fortement influencées par la sécrétion de certaines hormones comme l’hormone lutéinisante (LH) déclencheur de la reproduction, l’hormone de stress (CORT) et la prolactine (PRL), pour l’expression des soins parentaux. Les contaminants chimiques et naturels sont omniprésents et ont même été retrouvés en zones polaires. De nombreux contaminants sont des perturbateurs endocriniens et pourraient altérer les décisions de reproduction, mais les preuves manquent pour la faune sauvage. Cette thèse vise donc à identifier les liens entre certains polluants organiques persistants dits ‘d’héritage’ (POPs : PCBs, pesticides organochlorés), le mercure (Hg) et les hormones LH, CORT et PRL chez plusieurs espèces d’oiseaux marins arctiques et antarctiques. Les résultats obtenus ont démontré que ces contaminants interagissent avec ces hormones, et de façon spécifique : le Hg réprimerait la sécrétion d’hormones hypophysaires (LH, PRL) tandis que les PCBs stimuleraient la production de CORT. Plus précisément, le Hg pourrait affecter la sécrétion de LH en réprimant l’apport de GnRH à l’hypophyse et les PCBs pourraient stimuler le nombre de récepteurs à l’ACTH au niveau des glandes surrénales. Le Hg et les PCBs peuvent donc altérer les décisions de reproduction et impacter la valeur sélective : des taux élevés de Hg sont associés à la suppression de la reproduction et à un moindre investissement parental, tandis que la présence de PCBs pourrait exacerber la susceptibilité au stress environnemental. Les conséquences à long terme de l’exposition des oiseaux marins à ces contaminants sont discutées dans le cadre des changements globaux qui affectent les pôles. / In order to maximise fitness, individuals will have to take several decisions that shall match with environmental conditions (whether to breed or not, when to breed, what level of parental investment). These decisions are mediated by hormones : such as luteinizing hormone (LH), a pituitary hormone involved in the onset of breeding, stress hormones (corticosterone, CORT) and prolactin (PRL) a pituitary hormone involved in the expression of parental care. Environmental contaminants are present world-wide, and also in Polar Regions. Since many contaminants are endocrine disruptors, they may impair breeding decisions, but evidences are scarce for wildlife. The aim of this thesis was to assess the relationships between some legacy persistent organic pollutants (POPs : PCBs, organochlorine pesticides), mercury (Hg) and hormones (LH, CORT, PRL) in different Arctic and Antarctic seabird species. Results show that POPs and Hg clearly interact with LH, CORT and PRL secretion. These contaminants appear to target different hormones : increasing Hg was related to decreasing pituitary hormone secretion (LH and PRL) ; whereas increasing PCBs were linked to an exacerbated CORT response to an acute stress. Hg disrupted LH secretion by probably suppressing GnRH input to the pituitary ; PCBs seem to act at the adrenal level by probably stimulating ACTH receptors. Legacy POPs and Hg are therefore able to disrupt reproductive decisions and to impact fitness : elevated Hg levels were linked to skipped reproduction and poor incubation behavior ; elevated PCB levels may make individuals more susceptible to environmental perturbations. The long-term consequences of contaminant exposure for seabirds are discussed in the context of the environmental challenges affecting polar regions.

Muitas substâncias descartadas no meio ambiente não são totalmente degradadas, podendo assim persistir no ambiente. Diversos compostos são continuamente introduzidos no ambiente podendo afetar a biota e inclusive o homem. Os fármacos são alguns desses compostos que depois de descartados podem chegar nos corpos de águas naturais, e dentre eles merecem especial atenção os hormônios sintéticos utilizados em larga escala por mulheres em todo o mundo, na forma de contraceptivos orais. O hormônio sintético 17α-etinilestradiol é um micropoluente no ambiente aquático, que pode causar distúrbios na reprodução de diversos organismos atuando como um desregulador endócrino. O presente estudo teve como objetivo principal analisar o efeito do hormônio sintético 17α-etinilestradiol sobre o cladócero Daphnia magna, por meio de testes ecotoxicológicos. Testes de toxicidade crônica foram realizados em duas gerações consecutivas deste microcrustáceo (F0 e F1). Para os testes utilizaram-se neonatas com menos de 24 horas de idade, 6 concentrações do hormônio e dois controles. Foram estabelecidas 10 réplicas com 1 indivíduo por réplica. O ensaio foi realizado em incubadora com temperatura de 25 ± 1°C e fotoperíodo de 12h claro:12h escuro, com duração de 11 (F0) e 13 dias (F1), com término coincidindo com o nascimento das neonatas da terceira ninhada no controle. Os resultados evidenciaram que a exposição ao hormônio diminuiu a fecundidade de Daphnia magna nas quatro maiores concentrações de etinilestradiol na F0 e na concentração de 1000 μg L-1 da F1, revelando maior resistência ao contaminante na segunda geração. Na maior concentração do composto, o tempo para a produção das duas primeiras ninhadas foi maior na geração F1, quando comparada ao controle. Na concentração de 250 μg L-1 verificou-se a ocorrência de um indivíduo intersexo, apresentando tanto características de macho como de fêmea. Os resultados deste estudo evidenciaram que o 17α-etinilestradiol afeta a reprodução de Daphnia magna, e que também pode afetar a reprodução de diferentes invertebrados aquáticos, o que, a longo prazo pode causar danos às populações e comunidades aquáticas, diminuindo as populações e podendo até extingui-las eventualmente. / Many substances are discarded in the environment and not completely degraded, thus persisting in the environment. Some of these are continuously introduced in the environment, affecting the biota, including man. Pharmaceutical drugs are some of these compounds that after discarded can occur in natural water bodies and among them the synthetic hormones deserve special attention for being used in large scale by women world widely, as oral contraceptives. The synthetic hormone 17α-ethinyl estradiol is therefore a micropoluent in the aquatic environment, i. e. found in low concentrations that can cause deleterious effects in the reproduction of many organisms, acting as an endocrine disruptor. The present study had as main objective to analyze the effect of the synthetic estrogen 17α-ethinyl estradiol on the cladoceran Daphnia magna, by carrying out ecotoxicological tests. Chronic toxicity tests were performed on two consecutive generations of this microcrustacean (F0 and F1). In order to perform the tests, neonates aged less than 24 hours, 6 hormones concentrations and two types of controls were used. Ten replicates were established with one individual each. The test was performed in a growth chamber at the constant temperature of 25 ± 1°C and 12 h light:12 h dark photoperiod, had the duration of 11 and 13 days for the F1 and F0 generations, respectively, coinciding with the birth of the third brood in the control. The results evidenced that the exposition to the hormone decreased D. magna fecundity in the four highest of ethinyl estradiol in F0, and in the concentration 1000 μg L-1 for the F1, indicating resistance increase in the second generation. In the highest concentration of this compound the time for the production of the first two broods were higher in the F1 generation as compared with the controls. In the hormone concentration of 250 μg L-1 the occurrence of an intersex individual was verified, simultaneously presenting characteristics of male and female. The results of this study evidenced the 17α-ethinyl estradiol affect the reproduction of Daphnia magna, and can affect the reproduction of other aquatic invertebrates that at long term can cause damages to aquatic populations and communities by diminishing populations and eventually leading them to the extinction.

No description available.

Die vorliegende Arbeit befasst sich mit der Erweiterung des etablierten Stu-dienmodells Xenopus laevis zur Untersuchung der Wirkung von endocrine disruptors auf die Reproduktionsbiologie von Amphibien. Um einen Einblick in die grundlegenden Mechanismen der sexuellen Differenzierung von Amphibien zu gewinnen, wurden die Konzentrationen bestimmt, mit denen androgene und estrogene Sexualsteroide während der larvalen Entwicklung in verschiedenen Stadien von Xenopus vorliegen. Parallel wurde das Auftreten der korrespondierenden Rezeptoren im Verlauf der Entwicklung untersucht, über welche die hormonelle Wirkung vermittelt wird. Auf der Basis der gewonnenen Erkenntnisse konnte eine neue Hypothese zur sexuellen Differenzierung von Amphibien entwickelt und vorgestellt werden. Sie stellt das Enzym 5alpha-Reduktase, das die Umwandlung von Testosteron in das potentere und nicht weiter aromatisierbare Androgen Dihydrotestosteron (DHT) bewerkstelligt, in den Mittelpunkt des Prozesses der Geschlechtsdifferenzierung. Abhängig von der genetisch bedingten Expression dieses Enzyms kommt es zu einem höheren oder niedrigeren Auftreten des DHT und damit zu Unterschieden im Verhältnis von DHT zu Estradiol (E2). Der Charakter dieses Verhältnisses scheint der entscheidende Auslöser für die Entwicklung eines weiblichen oder männlichen Phänotyps zu sein. In einem zweiten, anwendungsorientierten Teil wurde untersucht, in wie weit die bislang auf Laboruntersuchungen beschränkte Arbeit mit X. laevis auf Feldstudien erweiterbar ist und ob sich auf diese Weise gewonnene Daten auf die Situation heimischer Amphibien übertragen lassen. Parallele Expositionen des Krallenfrosches einerseits und des Grasfrosches (Rana temporaria) andererseits gegenüber realen Medien unter Freilandbedingungen bestätigten die hervorragende Eignung des Studienmodells X.laevis zur Beurteilung endokriner Belastungssituationen. Darüber hinaus konnte gezeigt werden, dass sich durch die Verwendung von Festphasenextrakten die endokrinen Wirkungen komplexer Matrizes unter standardisierten Laborbedingungen charakterisieren lassen. Rezeptorbindungsstudien sowie Untersuchungen zur Genexpression spezifischer Marker, histologische Betrachtungen von Gonadengewebe und die Bestimmung von Geschlechterverhältnissen ermöglichten Aussagen auf vielfältigen Nachweisebenen. Auf diese Weise konnte das Potenzial, mit dem Proben jeder Art, sowohl durch kurz- als auch durch langfristige Exposition, adverse Effekte auf das amphibische Hormonsystem hervorrufen können, umfassend und differenziert analysiert werden. / The presented work aims to contribute to the various opportunities of studying the effects of endocrine disruption on sexual differentiation in amphibians provided by the well established model Xenopus laevis. In order to gain insight into the basic mechanisms underlying the sexual differentiation in amphibians, the concentrations of androgen and estrogen sexual steroids during several stages of the larval development of Xenopus were determined. In parallel, the ocurrence of the corresponding receptors, which mediate the effects of the respective hormones, was observed. Based on the results of the studies described, a new hypothesis regarding sexual differentiation in amphibians is presented, which assignes the enzyme 5alpha-reductase as the central element of sexual development. This enzyme converts the androgen testosterone into dihydrotestosterone, which can not be aromatized into estradiol. Depending on the genetic sex of the indivual, genexpression of 5a-reductase may differ and therefore lead to a characteristic ratio of androgens and estrogens. We suggest, that this ratio might be the essential trigger for amphibians to develop into a male or a female. A second part aimed to enlarge the Xenopus model to the use in field studies and to proof the transferability of such data to the situation of endemic amphibians. Exposure in parallel of Xenopus on one hand and the green frog Rana temporaria on the other to the effluent of a bavarian wastewater treatment plant revealed the exceeding suitability of the model to asess the endocrine charge of the environment. Furthermore, the use of solid phase extracts derived from natural samples allowed the characterization of the respective endocrine potential under standardized laboratory conditions. Rezeptor binding studies, detection of genexpression of specific biomarkers, histological examination of gonadal tissue and the determination of sex ratios provided the evaluation of effects on several levels of investigation. By this means the Xenopus model offers the opportunity to assess the ability of any kind of sample to cause endocrine impacts on amphibians after short time as well as after long time exposure in a broad and at the same time differentiated way.

Background In some cross-sectional epidemiologic studies the shape of the association between serum concentrations of perfluoroalkyl acids (PFAAs) and lipids suggests departures from linearity. Objectives We used statistical approaches allowing for non-linearity to determine associations of prenatal exposures of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) with lipid concentrations. Methods PFAAs were measured in serum from pregnant women collected in 1991–1992 at enrollment in the Avon Longitudinal Study of Parents and Children and lipids in serum from their daughters at ages 7 (n = 111) and 15 (n = 88). The associations of PFAAs with lipids were first explored by cubic splines, followed by piecewise linear regressions by tertiles to obtain regression coefficients (β) and their 95% confidence limits (95% CL) (in mg/dL per 1 ng/mL). Results At age 7, total cholesterol was positively associated with prenatal PFOA concentrations in the lower tertile (β = 15.01; 95% CL = 2.34, 27.69) but not with PFOA concentrations in the middle (β = − 3.63; 95% CL = − 17.43, 10.16) and upper (β = − 1.58; 95% CL = − 4.58, 1.42) tertiles. At age 15, a similar pattern was noted as well. Positive associations between LDL-C and prenatal PFOA concentration in the lower tertile were observed in daughters at ages 7 (β = 14.91; 95% CL = 3.53, 28.12) and 15 (β = 13.93; 95% CL = 0.60, 27.26). LDL-C was not associated with PFOA concentrations in the middle or upper tertile at any age. Neither HDL-C nor triglycerides was associated with prenatal PFOA exposure. Non-linear patterns of association of total cholesterol and LDL-C with prenatal PFOS were less consistently noted. Conclusion Exposure to low levels of PFOA during prenatal development may alter lipid metabolism later in life. Given the small sample size further replication of the association in large independent cohorts is important.

Thyroid hormones (THs) are vital in the maintenance of homeostasis and in the control of development. One postembryonic developmental process that is principally regulated by THs is amphibian metamorphosis. This process has been intensively studied at the genomic level yet very little information at the proteomic level exists. There is also increasing evidence that changes in the phosphoproteome influence TH action. In addition, the disruption of TH-action by endocrine-disrupting compounds (EDC) is an emerging field and the developmental process of metamorphosis is a target as well as a model system for this research. This work identifies components of the proteome and phosphoproteome in TH-sensitive tadpole tissues that are altered during the initiation stages of TH-induced metamorphosis prior to the overt remodeling of the tissues. Proteomic analyses included two-dimensional (2D) gel electrophoresis for the assessment of differential protein/phosphoprotein expression, combined with mass spectrometry (MS) protein analysis for protein identification. Initial proteomic approaches in Xenopus laevis identified a number of proteins that are differentially expressed in the tadpole tail within 48 h of exposure of premetamorphic tadpoles to 3,5,3’-triiodothyronine (T3). Additionally, a time-course analysis of brain tissue within this 48 h period revealed alterations in phosphoproteins. The importance of phosphoproteome modulation in the process of metamorphosis was further revealed in the TH-induced tail of Rana catesbeiana tadpoles, where the inhibition of cyclin-dependent kinase activity which prevents tail regression, altered the tail phosphoproteome profile. Failure to identify the phosphoproteins involved in these initial studies led me to develop and apply new proteomic approaches. To this end, subcellular and protein fractionation methods were developed and combined with 2D gel electrophoresis and phosphoprotein-specific staining. Altered proteins were identified using MS. Here components of the proteome and phosphoproteome were identified in the tail fin that changed within 48 h of exposure of premetamorphic R. catesbeiana tadpoles to 10 nM T3. This approach allowed the identification of and led to the cloning of a novel Rana larval type I keratin, RLK I, which is a target for caspase-mediated proteolysis upon exposure to T3. In addition, the RLK I transcript level was reduced during T3-induced and natural metamorphosis, consistent with a larval keratin. Furthermore, GILT, a protein involved in the immune system, was changed in phosphorylation state which is linked to its activation. Using a complementary MS technique for the analysis of differentially-expressed proteins, isobaric tags for relative and absolute quantitation (iTRAQ) revealed 15 additional proteins whose levels were altered upon T3 treatment. The success in identifying proteins whose levels changed upon T3 treatment with iTRAQ was enhanced through de novo sequencing of MS data and homology database searching. These proteins are involved in apoptosis, extracellular matrix structure, immune system, metabolism, mechanical function, and oxygen transport. This study demonstrated the ability to derive proteomics-based information from a model species for postembryonic development for which limited genome information is currently available. The early appearance of caspase-cleaved RLK I in the TH-induced process led to its investigation as a contributor to apoptosis. Furthermore, the caspase-cleavage product of RLK I was used as a biomarker in the development of an assay for the detection of disruptors of TH-action based on ex-vivo multi-well culturing of R. catesbeiana tail fin biopsies. This assay was able to detect perturbations in TH-signalling within 48h of exposure demonstrating that it has utility as a novel system for screening of TH disrupting chemicals. The present study identified proteins whose levels and/or phosphorylation states are altered within 48 h of the induction of tadpole metamorphosis prior to overt tissue remodeling and provided important insight into the molecular mechanisms of this postembryonic development. In particular, I have identified a novel keratin that is a target for T3-mediated changes in the tail that can serve as an indicator of early response to this hormone and can be used for the detection of EDCs of TH-action in an ex vivo assay.

La pression toxique induite par les perturbateurs endocriniens sur l’environnement ainsi que sur la santé de l’homme a augmenté de manière significative durant les dernières décennies. Il est devenu urgent de mettre en place des outils pour détecter et surveiller les perturbateurs endocriniens et pour déterminer la possibilité de cause de perturbations endocriniennes pour les produits chimiques nouvellement introduits. Le développement de nouveaux tests biologiques in vivo en utilisant les larves d'organismes aquatiques tels que medaka (Oryzias latipes) ou Xenopus laevis semble être une stratégie adéquate pour identifier les perturbateurs endocriniens. Durant cette thèse, trois nouveaux modèles transgéniques à base de l’embryon de medaka ont été développés. Le modèle transgénique de medaka ChgH -gfp permet la détection rapide des œstrogènes et des inhibiteurs de l'aromatase en seulement 24 heures avec une sensibilité de 15 ng / L d’éthinylestradiol. Le modèle transgénique de medaka 42sp50-gfp_CgH-gfp montre une fluorescence dans le foie en réponse aux œstrogènes, en plus de la fluorescence émise dans les œufs en développement. C’est donc un système approprié pour étudier le lien entre la signalisation de l'axe ostrogénique et des aberrations de la détermination du sexe chez les poissons. Un embryon transgénique de medaka spiggin - GFP a aussi été développé pour détecter les androgènes et anti-androgènes dans un test de 96 heures avec une sensibilité de 1,5 ug / L de 17α–méthyl testostérone et 276 ug / L de flutamide. Les nouveaux modèles de medaka transgéniques rapporteurs développés dans cette thèse permettent une détection rapide, simple et fiable des perturbateurs d'axe ostrogénique, androgénique et de l’aberration de détermination du sexe chez le medaka. Ils ont été appliqués pour détecter les perturbateurs endocriniens dans les eaux de surface de l'environnement et pour évaluer le rôle potentiel des produits chimiques dans les perturbations endocriniennes. Cela a permis de démontrer l’applicabilité de ces embryons fluorescents comme outils biologiques dans la procédure de détection et la caractérisation des perturbateurs endocriniens. / The toxic pressure of endocrine disruptors on biodiversity and human health has increased significantly over recent decades. As a consequence tools are needed to detect and monitor endocrine disruptors in surface water and to determine the endocrine disrupting potential of newly introduced chemicals. Fish and amphibian larvae, notably the medaka (Oryzias latipes) and Xenopus laevis, offer multiple advantages in this context. In the research carried out in the context of this thesis, different novel medaka-based transgenic models were developed. First, transgenic ChgH-gfp medaka model was designed and optimized for the rapid detection of estrogens and aromatase inhibitors. The model shows significant response within 24 hours with a sensitivity of 15 ng/L ethinylestradiol. Second, a double transgenic 42sp50-gfp_ChgH-gfp medaka which exhibits fluorescence both in the liver in response to estrogens and in developing oocytes as a function of phenotypic sex. It is therefore a suitable model for studying the link between estrogen axis signalling and aberrations of sex determination in fish. Third, a novel spiggin-gfp medaka model was developed to detect androgens and anti-androgens. This model can be exploited in a 96-hour assay with a sensitivity of 1.5 μg/L 17α- methyltestosterone and 276 μg/L flutamide. The novel transgenic medaka models developed in this thesis allow rapid, simple and reliable detection of estrogen and androgen axis disruption and aberrations in medaka sex determination. They have been successfully applied to detect endocrine disruptors in environmental surface water and to assess chemicals with unknown endocrine disrupting potential. Taken together these results demonstrate the applicability of medaka reporter larvae as biological tools in the procedure of detection and characterization of endocrine disruptors.

Le maintien et le renouvellement des populations de poissons coralliens dépendent en grande partie du recrutement larvaire, c’est-à-dire de l’installation des larves pélagiques dans les habitats récifaux adultes, et de leur survie après s’être métamorphosées en juvéniles. De plus en plus d’études révèlent que les changements de composition de l’eau, causés par le changement climatique et la pollution, peuvent altérer les capacités sensorielles des poissons coralliens, diminuant leurs aptitudes à localiser des habitats propices (maximisant leur croissance et diminuant leur mortalité) lors de l’installation. Cependant, les mécanismes internes à l’origine de ces phénomènes sont méconnus. Lors de cette thèse, j’ai examiné le recrutement larvaire du poisson chirurgien bagnard Acanthurus triostegus et mis en évidence que les changements écologiques, morphologiques, physiologiques et comportementaux qui s’y déroulent correspondent à une métamorphose contrôlée par les hormones thyroïdiennes (HT). J’ai ensuite analysé comment des stress d’origine anthropique, tels que l’élévation des températures de surface et la pollution par un pesticide d’origine agricole, peuvent perturber sa métamorphose. Lors de cette étape clé de leur cycle de vie, ces perturbations diminuent les taux d’HT, altérant la maturation de leurs organes sensoriels, leurs capacités sensorielles, et augmentant leur mortalité. Cette thèse est donc une analyse holistique de l’impact des perturbations anthropiques sur les processus moléculaires, et les changements histologiques, anatomiques et comportementaux du recrutement larvaire des poissons coralliens. Elle souligne l’importance du système thyroïdien, et invite à une meilleure compréhension des processus endocriniens du recrutement larvaire, dans l’optique d’une amélioration de la conservation des récifs coralliens. / The persistence and sustainability of coral-reef fish populations depends on the continued larval recruitment, i.e. successful settlement by pelagic larvae into adult reef habitats and post-settlement survival through metamorphosis to a juvenile stage. There is growing evidence that changes to water conditions due to global change and waterborne pollution can impair coral-reef fish sensory abilities to locate settlement habitats that maximize growth while minimizing mortality risk. However, the inner mechanisms of such impairments remain unknown. In this thesis, I have examined the recruitment phase of the convict surgeonfish Acanthurus triostegus, and determined that the ecological, morphological, physiological and behavioral changes occurring at recruitment correspond to a metamorphosis mediated by thyroid hormones (TH). Then, I investigated whether this metamorphosis is prone to endocrine disruption under anthropogenic disturbances such as elevated sea water temperature and agricultural pesticide pollution. I demonstrated that such pressures can reduce TH levels at a critical developmental stage in coral-reef fishes, impairing their metamorphic processes such as intestine remodeling, sensory organ maturation, and sensory abilities acquisition, further increasing their mortality rates. Overall, this thesis is a holistic analysis that addresses molecular, histological, anatomical, and behavioral assays of multiple stressors affecting coral-reef fish recruitment. It indicates the importance of a proper endocrine function during coral-reef fish recruitment, highlighting the need for a better understanding of these processes for coral-reef conservation.

Triclosan (TCS) and triclocarban (TCC) are antimicrobials found in U.S. surface waters. This dissertation assessed the effects of TCS and TCC on early development and investigated their potential to bioaccumulate using Xenopus laevis as a model. The effects of TCS on metamorphosis were also investigated. For 0-week tadpoles, LC50 values for TCS and TCC were 0.87 mg/L and 4.22 mg/L, respectively, and both compounds caused a significant stunting of growth. For 4-week tadpoles, the LC50 values for TCS and TCC were 0.22 mg/L and 0.066 mg/L; and for 8-week tadpoles, the LC50 values were 0.46 mg/L and 0.13 mg/L. Both compounds accumulated in Xenopus. For TCS, wet weight bioaccumulation factors (BAFs) for 0-, 4- and 8-week old tadpoles were 23.6x, 1350x and 143x, respectively. Lipid weight BAFs were 83.5x, 19792x and 8548x. For TCC, wet weight BAFs for 0-, 4- and 8-week old tadpoles were 23.4x, 1156x and 1310x. Lipid weight BAFs were 101x, 8639x and 20942x. For the time-to-metamorphosis study, TCS showed an increase in weight and snout-vent length in all treatments. Exposed tadpoles metamorphosed approximately 10 days sooner than control tadpoles. For the hind limb study, although there was no difference in weight, snout-vent length, or hind limb length, the highest treatment was more developed compared to the control. There were no differences in tail resorption rates between the treatments and controls. At relevant concentrations, neither TCS nor TCC were lethal to Xenopus prior to metamorphosis. Exposure to relatively high doses of both compounds resulted in stunted growth, which would most likely not be evident at lower concentrations. TCS and TCC accumulated in Xenopus, indicating that the compound has the potential to bioaccumulate through trophic levels. Although TCS may increase the rate of metamorphosis in terms of developmental stage, it did not disrupt thyroid function and metamorphosis in regards to limb development and tail resorption.

Endocrine-disrupting chemicals (EDCs) are known to cause endocrine disruption (ED), developmental neurotoxicity (DNT), infertility and impaired embryo development. EDCs do therefore impose a threat to humans, wildlife and the environment. The present study investigated the effects of the reference compounds dihydrotestosterone, estradiol, benzo(a)pyrene, rosiglitazone, as well as the EDCs bisphenol F and perfluorooctanesulfonic acid at various concentrations on zebrafish embryos. The scientific questions of the study were to investigate how these environmental pollutants impact the development of zebrafish, what their molecular mechanisms are and what the link between ED and DNT is. Zebrafish embryos were exposed for 5 days to the compounds and various parameters on development were collected at different time points. The expression of 41 genes (qPCR) related to ED and DNT, and the levels of 23 steroids (LC-MS/MS) were determined. Gene correlations were determined with Pearson’s correlation test and paired t-tests were used to determine significantly altered gene activities. The significant gene expression changes were further related to the pathways of steroids in order to connect how gene activity impacted steroid levels. Exposure to estradiol, dihydrotestosterone and bisphenol F induced cyp19a1b expression which can affect personality traits. Perfluorooctanesulfonic acid interferes with thyroid hormone transport by binding to TTR causing profound effects on neurodevelopmental processes and cognitive functions. The compounds influenced genes that can disrupt endocrine systems which can cause neurodevelopmental impairments.