Occurrence of heavy metals in sediments, fish and oysters from Mtwapa, port Reitz, Makupa and Shirazi creeks along the Kenyan

Abstract

Prior to the present study, the Reitz-Kilindini Creek complex situated on the westerly and southwesterly boundaries of Mombasa Island (4.05°S, 39.65°E), was presumed to be contaminated with both inorganic and organic anthropogenic inputs from industrial and domestic effluents. Mtwapa Creek located about 20 km north of Mombasa town, was presumed contaminated mainly with organic inputs while Shirazi Creek situated 70 km south of Mombasa, was presumed to be relatively unpolluted. A comparative survey of the occurrence of heavy metals in the selected creeks was carried out to assess a possible anthropogenic activity influence in those ecosystems with respect to the trace element levels. Sediments, fish and oyster samples from various stations within the three sites were collected and analysed between the months of January and July 2001. A total of 106 sediment samples were digested using hydrochloric acid and hydrogen peroxide. Fish muscle from 158 individuals of 13 fish species were digested using nitric and sulphuric acids plus hydrogen peroxide. 81 groups, each of 1-12 oysters (Saccostrea cucullata) were digested in the same manner as fish muscle. Copper, zinc, lead and cadmium elemental concentrations in the digests were assessed by atomic absorption spectrophotometry (AAS). The method of analysis was validated using SOIL7, MA-M-2 (Mussel tissue) and MA-A-2 (Fish homogenate) International Atomic Energy Agency (IAEA) certified reference materials. These and a few experimental samples were also analysed using Energy dispersive X-ray fluorescence (ED-XRF) spectrometry. The data collected was analysed using Statistica and Excel software..