Screening of potential ecological risk of metal contamination in some Kenyan estuaries

Abstract

Sediment core samples from seven stations in three Kenyan estuaries were analysed for Al, Ni, Zn, Cu, Cr, Mn and Pb by atomic absorption spectrophotometry to determine the spatial contamination (vertical and horizontal) and to identify any potential ecological risks. Samples were analysed for total metal concentration and data normalised using regression model of metal/Ni. The data was further compared to toxicity based Sediments Quality Guidelines (SQG) [Effects Range Low (ERL) and Effect Range Median (ERM)] giving an indication of potential ecological risks.There was a general reduction in metals input into the Kenya estuaries as evident from depletion of a number of metals in surface samples as compared to the subsurface samples. Enrichment Factors (EF) ranged from 0.1-92.9 indicating low to extreme contamination. Low contribution of anthropogenic sources of metal and the existence of metals in acceptable risk levels in most of the sites was also observed. However, some sites had a few samples with moderate to significant anthropogenic contribution of metals with the associated moderate to significant potential risk to biota. This study recommends a site-specific evaluation of these sites in order to quantify the level of risk, identifysource of contamination and suggest relevant management and mitigation measures