Comparative evaluation of the concentrations of lead, cadmium and zinc in surficial sediments from two shallow tectonic freshwater lake basins, kenya

Abstract

Sources of metals in the environment are widespread and data on typical concentrations in the various media and environmental settings exits worldwide. Distribution and comparative concentrations of some selected metals in surface sediments of two shallow tectonic freshwater basins were assessed, as useful indicators of the level or magnitude of anthropogenic influences, as well as other aquatic processes, considering the increasing challenges in management of waste disposal. Concentrations of Pb, Cd and Zn in the sediments were detectable in all sites, albeit there were relatively lower levels reported in the column of alkaline waters. In dry weight basis, and in increasing order, the levels were Cd<Pb<Zn in both basins. Cd, Pb and Zn elements are all chalcophiles. However, using a student t-test, the concentrations of Cd and Pb in the sediments showed significant differences (p<0.05) between the two basins. Using freshwater sediment quality guidelines (ISQG) values, all the three metal mean contents in L. Baringo were above these values. Average levels of Zn and Cd were also above the ISQG values. However, all the mean concentrations of Zn, Cd and Pb in surficial sediments were found to be below the probable effect level, and above normal concentrations ranges found in sedimentary and igneous formations.  Concentrations of Pb and Zn found are comparable to other relatively large basins, with extensive  drainage basins and urban influences. Cadmium sediment levels are a concern, as the evaluation shows  increasing accumulation in sediments, with possible future exposure risks to aquatic organisms. Surface runoff, waste discharges and particulate deposition is thought to be significant in these basins, and to  understand overall impacts from anthropogenic deposition, it is important that background metal levels  are determined together with supporting chemical partitioning to reveal more information on available  metal contents.
 
Key words: Tectonic lake basins, surface sediments, concentrations, lead, zinc, cadmium.