Toxicity of PCB-126 in European flounder ( Platichthys flesus ) with emphasis on histopathology and cytochrome P4501A induction in several organ systems

Abstract

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.

PCBs and the energy cost of migration in the European eel (Anguilla anguilla L.)

“…In fish the m ost im portant organs in the immune function are the head kidney, thym us and spleen. In European floun der (Platichthysflesus) exposed to 50 mg PCB-126/kg (Grinwis et al, 2001) thym us atrophy was reported suggesting an impact on the specific resistance against infectious diseases (viral, bacterial, and parasitical) in the field situation. The reported effects of PCBs on the immunologically im portant spleen (Taysse et al, 1998) can be quite different, as in some studies a reduction of the spleen w eight is observed (Nakata et al, 2002) w hile in other studies a spleen hyper trophy was reported (Greichus et al, 1975).…”

Respiratory Surveillance and Ca²⁺-ATPase Enzyme Activity Studies of <i>Clarias gariepinus </i>Exposed to Acute Toxicity of Cyanide

“…Dube and Hosetti (2010) stated that pronounced secretion of mucus layer over the gill lamellae observed during cyanide stress curtails the diffusion of oxygen, which ultimately reduce the oxygen uptake by the animal. Also, it was said that if gills were destroyed due to xenobiotic chemicals (Grinwis et al, 1998) or the membrane functions are disturbed by a changed permeability (Hartl et al, 2001), oxygen uptake rate would rapidly decrease. Thus, it can be inferred that decrease oxygen consumption observed might be as a result alteration in membrane or damage to gills membrane by potassium cyanide molecules of exposed fish specimens.…”

Effects of sublethal levels of tributyltin chloride on a new toxicity test organism, Liza saliens (osteichthyes, mugilidae): a histological study

“…The organs possess immune Speciation Analysis and Environment and hematopoietic functions, and are essential for fish health. Grinwis et al 37 noted a significant reduction of thymus induced by TBTO in Platichthys flesus. Thymus atrophy by TBTO has been demonstrated in Poecilia reticulata and Oritias latipes.…”