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Environmental pollutants capable of interfering with the thyroid hormone (TH) system increasingly raise concern for both human and environmental health. Recently, resorcinol has received attention as a compound of concern due to its endocrine disrupting properties. It is a known inhibitor of thyroperoxidase (TPO), an enzyme required in TH synthesis, and therapeutic use of resorcinol exposure has led to hypothyroidism in humans. There is limited evidence concerning ecotoxicologically relevant effects of resorcinol in fish. A set of adverse outcome pathways (AOPs) has recently been developed linking thyroid hormone system disruption (THSD) to impaired swim bladder inflation and eye development in fish. In the present study, these AOPs were used to provide the background for testing potential THSD effects of resorcinol in zebrafish eleutheroembryos. We exposed zebrafish eleutheroembryos to resorcinol and assessed TH levels, swim bladder inflation and eye morphology. As a TPO inhibitor, resorcinol is expected to affect TH levels and eye morphology but not swim bladder inflation during embryonic development. Indeed, thyroxine (T4) levels were significantly decreased following resorcinol exposure. In contrast to our hypothesis, swim bladder inflation was impaired at 5 days post fertilization (dpf) and no effects on eye morphology were detected. Therefore, in vitro assays were performed to identify potential additional thyroid hormone system disruption-related mechanisms through which resorcinol may act. Two new mechanisms were identified: TH receptor (TR) antagonism and transthyretin (TTR) binding inhibition. Both of these mechanisms can plausibly be linked to impaired swim bladder inflation and could, therefore, explain the observed effect. Overall, our study contributes to the knowledge of the THSD potential of resorcinol both in vivo in the zebrafish model as well as in vitro. • Resorcinol exposure significantly lowered T4 levels in zebrafish embryos. • Posterior swim bladder inflation was significantly impaired. • Larvae with uninflated swim bladders showed aberrant swimming behavior. • In vitro assays identified new mechanisms: TTR-binding inhibition and TR antagonism. [ABSTRACT FROM AUTHOR]

In this study the uptake of ZnO and CuO nanoparticles by Daphnia magna was tested. Daphnids were exposed during 48 h to acute concentrations of the nanoparticles and corresponding metal salts. The Daphnia zinc and copper concentration was measured and the nanoparticles were localized using electron microscopy. The aggregation and dissolution in the medium was characterized. A fast dissolution of ZnO in the medium was observed, while most CuO formed large aggregates and only a small fraction dissolved. The Daphnia zinc concentration was comparable for the nanoparticles and salts. Contrarily, a much higher Daphnia copper concentration was observed in the CuO exposure, compared to the copper salt. CuO nanoparticles adsorbed onto the carapace and occurred in the gut but did not internalize in the tissues. The combined dissolution and uptake results indicate that the toxicity of both nanoparticle types was caused by metal ions dissolved from the particles in the medium. [ABSTRACT FROM AUTHOR]

At four different aquatic sites in Flanders (Belgium) with different types and degrees of contamination, juvenile carp (Cyprinus carpio) were exposed in cages for 4 weeks. After exposure, metals, polychlorinated biphenyls (PCBs), and selected organochlorine pesticides (OCPs) were analyzed in the tissues of the carp. Besides pollutant accumulation, several effects were measured as well. Condition measures such as changes in weight, condition factor (CF), and hepatosomatic index (HSI) were assessed. In addition, activity of acetylcholinesterase (AChE) and a set of blood biochemical parameters were measured. At all sites, accumulation of metals in the fish tissues was observed. Levels of cadmium and lead at some of the exposure sites were higher than the levels at the start and comparable to levels in fish from moderately metal-contaminated sites. For most organic pollutants, however, levels were not significantly higher than at the start. Only for two PCB congeners, levels had slightly increased but were still lower than levels in carp captured at noncontaminated sites. Although food limitation probably caused some of the observed effects, significant relationships were found between metal load in tissues and CF, AChE, plasma osmolality and HSI. This study shows that caged carp might be useful for the assessment of bioaccumulation and some effects of micropollutants in aquatic ecosystems. [Copyright &y& Elsevier]