Toxicological effects of the widely used flame retardant, tetrabromobisphenol A (TBBPA) were assessed in a partial life-cycle test with zebrafish (Danio rerio). Exposure of adult fish during 30 days to water-borne TBBPA in nominal concentrations ranging from 0 (control) to 1.5 M was followed by exposure of the offspring in early life stages up to 47 days posthatching (dph) to the same concentrations. Adults exposed to 3 and 6 M showed severe disorientation and lethargy shortly after beginning of exposure and were euthanized. Because semistatic exposure resulted in fluctuating water concentrations, pooled fish samples were chemically analyzed for internal dose assessment. Egg production was decreased in fish exposed to TBBPA concentrations of 0.047 M and higher, and a critical effect level of 7.2 g/g lipid with a lower 5% confidence limit of 3.9 g/g lipid for 50% decreased egg production was calculated. Histology of adult ovaries indicated a relative increase of premature oocytes in two surviving females exposed to 1.5 M. Hatching of TBBPA-exposed larvae was decreased except in animals exposed to 0.375 M. In the highest exposure concentration, early posthatching mortality was high (81%) in larvae and the surviving juveniles showed a significant predominance of the female phenotype. Exposure of eggs from control parents up to 6 M TBBPA resulted in increasing malformation and pericardial fluid accumulation from 1.5 M; at higher concentrations, all embryos failed to hatch. The presented results indicate decreased reproductive success in zebrafish at environmentally relevant TBBPA concentrations.

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A series of experiments was set up to elucidate the effects of pollution on marine and estuarine fish health, since the European flounder (Platichthys flesus) has shown a relatively high prevalence of (pre)neoplastic liver lesions and lymphocystis virus disease in Dutch coastal and estuarine waters. The hypothesis of a causal relationship between pollution and the above-mentioned diseases was supported by results from semi-field experiments. Therefore several laboratory experiments were carried out to substantiate causality further and to identify the xenobiotics that may play a major role in the field. The present study focuses on polychlorinated biphenyls (PCBs). European flounders (Platichthys flesus) were orally exposed to a single dose of 0, 0.5, 5 or 50 mg PCB-126/kg body weight under controlled laboratory conditions. The effects on liver, gills, gastrointestinal tract, gonads, spleen and mesonephros were examined histologically after 16 days. Induction and localization of cytochrome P4501A (CYP1A) immunoreactivity, and effects on hepatocyte proliferation were visualized immunohistochemically. Effects on thymus size were examined by morphometric analysis of serial sections. Three out of five animals of the highest dose group showed haemorrhages in the fins and tail after 16 days. All animals showed reduced activity in the later stages of the experiment, and some animals of the highest dose group discontinued feeding 14 days after exposure. Strong and exposure-related induction of CYP1A immunoreactivity was noted in hepatocytes, endothelium in all organs examined, and epithelium of the digestive tract and mesonephros at PCB-126 levels of 0.5, 5 and 50 mg/kg. In addition, the strong induction of CYP1A immunoreactivity in a distinct population of haematopoietic cells in the mesonephros and in circulating blood is remarkable, and has not been described previously in other fish species. Furthermore, a morphometrically determined significant reduction in relative thymus size was noted in animals exposed to 50 mg PCB-126/kg. Although the functional implications for the immune system of this reduction need to be further investigated, an impact on the specific resistance against infectious diseases as observed in the field, e.g. viral lymphocystis disease, is not implausible. In addition, a significant increase in absolute liver weight, in hepatosomatic index, and in number of proliferating hepatocytes [measured as immunoreactivity against proliferating cell nuclear antigen (PCNA)] was noted in animals of the highest dose group. From these findings we suppose that PCB-126 (and related chemicals) may play a role in the promotion of tumour development in the liver of European flounders as observed in the field. The results of the present experiment show relatively stronger effects than effects previously reported from experiments with TCDD, suggesting that the TEF of 0.005 assigned to PCB-126 from early life stage mortality experiments in rainbow trout (Oncorhynchus mykiss), underestimates the toxic potential of PCB-126.

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