Assessment of heavy metals distribution in sediment and water, and their bioaccumulation in thumbprint emperor (lethrinus harak) in the msimbazi bay, Dar es salaam

This study aimed at investigating the distribution, influencing factors and concentration levels of cadmium (Cd), lead (Pb), zinc (Zn) and chromium(Cr) in marine sediments, seawater and fish (Lethrinus harak) in the Msimbazi Bay of the Dar es Salaam coast.The samples for heavy metals analysis were collected, prepared, digested accordingly and analyzed using AAS. The obtained results found that, marine sediments had higher levels of zinc (105.16 ±11.83 mg/kg) at sampling station OM (Mangrove creek) compared to other sampling stations in the bay and their concentration levels were found to be in the order of Zn > Pb > Cr > Cd. In the seawater, Pb and Zn were detected within the range considered as natural in the ocean and their concentrations were 1.84 and 19.35µg/L, respectively. Comparatively, concentration levels of heavy metals in sediments were higher than those of seawater. However, concentrations in both compartments were below the maximum permissible levels proposed by USEPA, CCME and, ANZECC and ARMCANZ with a decreasing concentration trend from the river mouth (mangrove creek) to offshore areas. Relationships were statistically observed between concentration of heavy metals in seawater and sediments against their physico-chemical characteristics. With emphasis on fish muscles as edible parts for human consumption, the concentration levels of heavy metals were; Zn (0.89 ± 0.18) > Pb (0.18 ± 0.09) > Cr (0.1 ± 0.04) > Cd (0.05 ± 0.012) µgg-1. Generally, concentration levels of heavy metals in all fish tissues examined (liver, gills, kidney and muscles) were below the permissible levels recommended by FAO and WHO.Despite the fact that the study findings on the levels of metals in all investigated samples were below permissible levels recommended by international organizations, there is still a need to put mechanisms in place to monitor contamination of heavy metals in the Msimbazi catchment area and it’s Bay.