DISTRIBUTION OF HEAVY METALS IN VARIOUS LAKE MATRICES; WATER, SOIL, FISH AND SEDIMENTS: A CASE STUDY OF THE LAKE NAIVASHA BASIN, KENYA

Abstract

Water, sediments, soil and fish, common carp (Cuprinus carpio), largemouth blackbass (Micropterus salmoides), tilapia (Oreochromis leucostictus) and mirror carp (Cyprinus spectacularlus) from the Lake Naivasha basin were analysed for lead (Pb), cadmium (Cd), zinc (Zn), copper (Cu) and nickel (Ni). Samples were collected from the Main Lake, Lake Oloidien, Crescent Lake, River Malewa, Naivasha Municipal Council Sewer entry point, flower farm discharge canals and the Kenya Wildlife Services (KWS) Sanctuary (Joan Roots Farm). Fish samples were bought from fishermen while still alive and identified by the Kenya Marine and Fisheries Research Institute (KEMFRI) staff. The heavy metal concentrations were determined using flame atomic absorption spectrophotometry (AAS). The mean sediment concentrations (in μg/g dry weight) were 62.5 ± 26.5 for Ni, 42.39 ± 17.95 for Zn, 32.71 ± 16.94 for Pb, 1.52 ± 0.87 for Cu and 1.65 ± 0.96 for Cd respectively, whereas those in soil (in μg/g dry weight) were 25.69 ± 10.62 for Pb, 2.56 ± 1.40 for Cd, 53.28 ± 19.41 for Zn, 52.05 ± 22.64 for Ni and 1.02 ± 0.57 for Cu respectively. The mean heavy metal contents in fish (in μg/g wet weight) were 1.7 ± 0.91 for Pb, 0.33 ± 0.30 for Cd, 8.03 ± 2.7 for Zn, 14.34 ± 4.4 for Ni and 0.3 ± 0.11 for Cu, whereas those in the water column (total content) were 16.56 ± 9.55 μg/L for Pb, 12.69 ± 9.54 μg/L for Cd, 1.34 ± 0.48 mg/l for Zn, 0.18 ± 0.13 mg/l for Ni and 5.68 ± 3.71 μg/L for Cu respectively. The study shows that the most important sources of heavy metals pollution in the Lake Naivasha basin are River Malewa, geochemical processes, flower farms and the Naivasha Municipal Council.