Cytological alterations in the liver of rainbow trout Oncorhynchus mykiss after prolonged exposure to low concentrations of waterborne endosulfan

Abstract

In order to elucidate sublethal cytopathological alterations in hepatocytes, mature male rainbow trout Oncorhynchus mykiss were exposed to 1, 10, 50, and 100 ng 1-1 technical grade endosulfan (Thiodan™ 70 % α- and 30% β- isomers) for 28 d. Whereas stereological parameters, i.e. relative volumes and numbers of cell organelles, were unaffected, qualitative ultrastructural alterations were detectable from 10 ng 1-1 endosulfan. The No-Observed-Effect Concentration (NOEC) for cytological alterations was determined to be 1 ng 1-1 endosulfan, i.e. 3 orders of magnitude below the LC50 value. Cytological effects that were probably of an adaptive nature included proliferation of SER and circular arrays of RER indicating induction of mixed-function oxygenases (MFO) as well as an increase in lysosomal elements at 50 and 100 ng 1-1 endosulfan, probably due to enhanced cellular turnover. In addition, at ≥50 ng 11 endosulfan, degenerative effects such as dilation of intermembranous spaces in mitochondria, deformation of mitochondria, myelin formation in peroxisomes and cytoplasm, and vesiculation and dilation of RER cisternae were observed. Although there was no indication of specific sublethal modes of toxic action except, for MFO induction, the present study indicates that endosulfan has toxic impacts at concentrations of environmental relevance.