Abstract

Water pollution by heavy metals, especially chromium pollution from industrial sources can affect aquatic life, all ecosystems and human health directly or through food chain. This study aims to investigate the uptake of hexavalent chromium by a freshwater fish, (Tilapia, Oreochromis aureus). Short-term acute toxicity tests were performed over a period of 96 h providing the medium with various concentrations of potassium dichromate. Then the 96 h LC₅₀ value was found to be 91.51 mg l^-1 (Cr⁶⁺ as 32.35 mg l^-1). Five different concentrations of Cr⁶⁺ varying between 10, 15, 20, 25 and 30 mg l^-1were implemented for the uptake of this metal. The experiment was carried on for 28 days, meanwhile sampling fish weekly. With continued exposure, the accumulations were increased and fish progressively lost their ability to respond to this increase in exposure period.  The chromium concentration in different organs was in the following order gill > skin > muscles tissues (least). The concentration of Cr in the gill range from 3.11 - 45.23 µg g^-1 w.w, while the concentration accumulated in the muscle tissue of fish ranged from 0.86 to 12.34 µg g^-1 w.w.

Key words: Heavy metal, Cr toxicity, fish, Tilapia (Oreochromis aureus), accumulation.