The acute toxicity of Mercury and Copper on C. africanus and T. fuscatus and the bio-accumulation potentials of the metals were investigated in laboratory experiments employing standard bio–assay techniques. On the basis of LC50 values, both metals had similar magnitudes of toxicity against C. africanus. However, Mercury was more toxic than Copper when tested against T. fuscatus. Against either of the test metals, C. africanus was more susceptible than T. fuscatus by orders of magnitude that varied between 6 and 23. Under sub-lethal concentrations (0.00038 - 0.08 mg L-1 for either Copper or Mercury against C. africanus; 0.0088 - 1.08 mg Cu L-1 and 0.0025 - 0.25 mg Hg L-1 against T. fuscatus), C. africanus and T. fuscatus were shown to bioaccumulate these test metals in amounts that increased with time of exposure as well as dosage. Computed bioaccumulation factors for Mercury and Copper against C. africanus, at the same test concentration were 313 and 20974 respectively. Against T. fuscatus however, the bioaccumulation factors for Mercury and Copper after 28 days of exposure under the test conditions were 7.6 and 153 respectively; indicating that C. africanus was a much more efficient bioaccumulator of these metals than T. fuscatus. The implications of these findings for ecosystem viability, environmental management and public health considerations are discussed.
Key words: Acute toxicity, Bioaccumulation, Public Health, Ecosystem viability, Environmental management.
Journal of Aquatic Sciences Vol.18(2) 2003: 75-84