Heavy metal concentration in indo-pacific bottlenose dolphins (Tursiops aduncus) and spinner dolphins (Stenella longirostris) from the coastal waters of Tanzania

Dolphins are marine mammals which commonly occur in coastal waters of Zanzibar, Tanzania. Liver, kidney and lung samples of Indo-Pacific bottlenose dolphins (Tursiops aduncus) and spinner dolphins (Stenella longirostris) incidentally caught in gillnet fisheries were analysed for the concentrations of heavy metals Cd, Cr, Cu, Pb and Zn. Atomic Absorption Spectrophotometry (AAS) and Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES) were used for measurement of heavy metal concentrations in the samples. The results obtained were in the range 0.10 - 476.9 \xglg dw for Cd, 0.08 - 3.20 ng/g dw for Cr, 1.14 - 87.87 M-g/g dw Cu, 0.051 - 1.93 |ag/g dw Pb and 13.6 - 221.7 (ig/g dw for Zn. Stenella longirostris dolphin were found to contain higher metal concentrations than Tursiops aduncus dolphin. Concentration of Cd was higher in kidney samples than other organs in all the two dolphin species. In Tursiops aduncus Cu and Zn concentrations were generally higher in liver followed by kidney and lowest in lung. Stenella longirostris had slightly high concentrations of Cu and Zn in kidney than in liver and lowest in lung. Cr and Pb concentrations were uniformly distributed in liver, kidney and lung of the two species of dolphin. The concentrations of Cr, Pb and Zn in Tursiops aduncus dolphin did not show significant correlation with the age or sex of the dolphin. However, Cu concentration was higher in immature T. aduncus whereas Cd concentration was higher in mature T. aduncus dolphins. For the Stenella longirostris dolphin no significant correlation was observed between metal concentration and age, length or sex of the dolphin.