Metal Contamination in Sediments of Coastal Rivers around Dar es Salaam, Tanzania

Abstract

Sediments from coastal rivers of Kizinga, Mbezi, Msimbazi, and Mzinga were used to determine contamination levels of Cd, Pb, Cr, Ni, Cu, Al, Mn, Fe, and Zn metals. Sampling and sample preparation were done as appropriate and analysis was done using high resolution inductively coupled plasma–mass spectrometry (HR ICP-MS). Higher levels of Cd, Pb, Cr, Al, Mn, Fe, and Zn were mainly observed in Msimbazi river. Whereas higher levels of Ni and Cu were observed in Kizinga river, higher levels of Mn were observed in Mbezi river. Mzinga river had lowest levels of most metals except Mn. Lowest levels of Mn were observed in Kizinga river. Despite of enrichment factor indicating varied contamination status of metals in rivers, geo-accumulation index, contamination factor, degree of contamination, modified degree of contamination, potential contamination index and environmental toxicity quotient have indicated that sediments from these rivers are polluted, with Msimbazi and Kizinga river sediments being more polluted. Pearson correlation and hierarchical cluster analyses have revealed that Cd, Cu, Pb, and Zn were strongly correlated to each other (r²> 0.7, p < 0.05), indicating that they similar anthropogenic origin, while Fe, Mn, Ni, Cr, and Al were strongly correlated to each other (r²> 0.69, p < 0.05), indicative of similar natural origin. This implies that there might be metal-related anthropogenic activities around or close to rivers that pose environmental and health risks. Urgent river management strategies are needed to minimise the continuous metal pollution of these rivers.