Determination of heavy metals in lates niloticus and caridina nilotica from winam gulf of Lake victoria using x-ray fluorescence

Abstract

Heavy metals have been recognised to be a major source of pollution in the aquatic ecosystems. Lates niloticus and its caridina nilotica feed, was selected as bioindicators because of their abundance in the gulf of Winam and their predator - prey relationship. The heavy metals determination was done by the x-ray fluorescence (XRF) analytical technique. For quality control Atomic Absorption Spectrophotometry (AAS) was also used for some samples. The analytical method was validated using International Atomic Energy Agency (IAEA) certified reference material MA-A-2 (Fish homogenate) on both the two techniques. The results agreed within acceptable range. The fish samples were collected within a period of six months with the bulk collected during a 10 day cruise aboard RV Utafiti on a trip sponsored by Lake Victoria Environmental Programme (LVEMP). A total of about 100 individuals of Lates niloticus and several caridina nilotica were collected from the Winam gulf of Lake Victoria. Prior to analysis the samples were digested in an aluminum block available at Kenya Marine and Fisheries Research Institute (K.M.F.R.I) laboratory in Kisumu and preconcentrated. The results of the study showed that the values obtained for Pb, Zn, Ni, Cu, Fe, and Mn were within the CAC and WHO guidelines. In the muscle tissue the heavy metals concentration levels ranged as follows: Pb, 0.1- 0.4 ug g"; Zn, 3.3- 5.9 ug g"; Ni, 0.1 - 0.6 Ilg g"; Cu, 0.2- 0.91lg g': Fe, 2.2 - 20.21lg g-l and Mn, 0.3 - 1.11lg g'. The results also showed a distinct variability in heavy metals in the different tissues of Lates niloticus. Liver presented the highest levels of iron with a mean of 41.21lg g-l and a range of 6.3 - 96.01lg g-l. Muscle tissue had substantial mean concentration of iron with a mean of 5.61lg s' and a range of2.2 - 20.2 ug g-l. III In terms of bioaccumulation of iron amongst the Lates niloticus tissues the order in descending order is as follows; Liver> Skin> Muscle tissue> Gills> Scales. Analysis of data showed a positive correlation (r = 0.61) between the concentration of heavy metals in caridina niloticus and Lates niloticus. This was expected since Caridina niloticus forms the bulk of Lates niloticus feed. Analysis of variance indicated that there is a significant variations in the heavy metal concentration in Lates niloticus tissues at p 0.05 significance level. Canonical correspondence analysis showed distinct variability in the elemental concentrations in Lates niloticus tissues and organs. Conductivity measurements of water results varied significantly from as low as 112 ms at the Mbita course way to 156 ms at the Asembo Bay. This indicated the difference in anthropogenic inputs across the Winam gulf of lake Victoria.