Trace metal enrichment and sediment quality in coastal-urban rivers along the Indian Ocean coast, Dar es Salaam, Tanzania

This study investigated sediments quality in coastal-urban rivers of Dar es Salaam, Tanzania along the Indian Ocean coast, that are strongly influenced by human activities. Sediment samples were seasonally collected from fifteen sites and one control location, treated as appropriate, and analyzed by high-resolution inductively coupled plasma mass spectrometer for Cd, Sn, Pb, Cr, Co, Ni, Cu, Al, Mn, Fe, and Zn. Concentrations ranged from 0.06 (Cd) to 92,479 (Al) mg/kg dry weight. Levels were higher during dry season than wet season. Cd, Sn, Pb, Co, Cr, and Zn were enriched in > 50% of the sites. Comparison with risk-based regulatory sediment quality thresholds depicted considerable ecological risk in > 70% of the sites. Evaluation by sediment quality indices identified two hotspots that require intervention. The highest contributors to the Risk Index were Pb and Cd (> 60%). These findings indicate risks to human health and river ecology that call for measures to protect the rivers from further contamination.