Toxicity of TCDD in European Flounder (Platichthys flesus) with Emphasis on Histopahtology and Cytochrome P450 1A Induction in Several Organ Systems

Flounder taken from The Netherlands coast and estuaries had high incidence of lesions of the liver and lymphocystis virus. To elucidate the cause of these conditions, flounder were exposed oral doses of TCDD or extract of harbor sludge, followed by histopathological examination of several tissues. Cytochrome P4501A (CYP1A) induction, visualization of proliferation of hepatocytes, and thymus size were also monitored. After eight weeks of exposure to either substance increased CYP1A immunoreactivity in hepatocytes. Exposure to high doses of TCDD was associated with increases of endothelial CYP1A immunoreactivity in almost all organs and tissues. Mitotic activity was increased by exposure to 20 mu g/kg TCDD. Thymus size was reduced in fish exposed to the highest doses, but no obvious pathology was found in fish exposed to concentrations as high as 500 mu g/kg. Under laboratory conditions, flounder was not very sensitive to TCDD, but exposure to environmental levels may result in tumor promotion.promoter.