Uptake and distribution of a copper, iron and zinc mixture in gill, liver and plasma of a freshwater teleost, Tilapia sparrmanii

Since polluted environments contain mixtures of different contaminants, the aim of this study was to investigate the time-integrated uptake of individ ual metals by a freshwater teleost, Tilapia sparrmanii following exposure t o a metal mixture containing Cu, Fe and Zn. The metal concentrations used d uring the bioassays were chosen to represent ecologically relevant concentr ations as found in the Olifants River, Kruger National Park, South Africa. The concentrations used in the bioassay were 0.16 mg.l(-1). 4.3 mg.l(-1) an d 1.003 mg.l(-1) for Cu, Fe and Zn respectively. Gill, plasma and liver wer e sampled at 0, 2, 4, 6, 12, 24, 24, 48, 72, 96 h and four weeks. Gill tiss ue is the initial site of accumulation of water-borne metals. Although the fish were exposed to a metal mixture. the interactions between metals and t he external gill surface, as well as the subsequent uptake rate, were assoc iated with the particular chemical properties of individual metals. The ten dency of the individual metals in the metal mixture to bind to the external gill surface via ionic bonds, and to Kill cytosolic compounds via covalent bonds, was Cu > Fe > Zn. The ensuing uptake rates into the extracellular c ompartment (blood) and intracellular compartment (liver tissue) were Zn > F e > Cu. The toxic effects of Cu and Fe were, therefore. primarily exerted o n the gill surface and in the gill cytosol, whereas the toxic action of Zn was primarily limited to the internal organs.