Bioaccumulation and localization of exogenous cadmium in a teleost by electron microscopy (TEM) and its specific quantitation by electron probe X-raymicroanalysis (EPMA)

A cadmium bioconcentration study was carried out in a fresh water teleost, Colisa fasciatus, to study the bioaccumulation kinetics and fate of exogeno us cadmium (Cd) in biological tissues. Study shows that on exposure of the fish to a sublethal concentration of cadmium in test water, Cd uptake resul ts in its bioconcentration in gills, liver and muscle tissues. To explore w hether the accumulated Cd reaches the membranes or inside the cells, transm ission electron microscopy (TEM) of the thin sections of tissues was done a fter histochemical localization of Cd in cells by modified SST method. TEM studies of sections of gills, liver and muscle tissues showed the deposits of exogenous Cd (visualized as dense clouds) in biological cells. This sugg ests the presence of free or loosely bound Cd on the membranes and inside t he cells, which in the presence of Na2S is converted into insoluble metal s ulfides. Electron probe X-ray microanalysis (EPMA) studies confirmed the pr esence of Cd on the membrane surface as well as inside the cells of bioindi cator organs suggesting involvement of membrane transport of exogenous Cd i nside the cells and its deposition as loosely bound insoluble metal complex es. (C) 2000 Elsevier Science Ltd. All rights reserved.