Clean Water and Sanitation (SDG 6), Climate Action (SDG 13)
Toxic metals pollution and ecological risk assessment in coastal-urban rivers, Indian Ocean coast, Dar es Salaam, Tanzania Harieth Hellar-Kihampa* 1 , Zakaria Mhande 1 , Matobola Joel Mihale 1 , Natacha Brion 2 , Willy Baeyens 2 1 Faculty of Science, Technology and Environmental Studies, The Open University of Tanzania, Dar es Salaam, Tanzania 2 Department of Analytical, Environmental and Geo-Chemistry, Vrije Universiteit Brussel, Belgium Rivers located along coastal zones are normally subjected to various biogeochemical and climatic stressors, and when they are within urban vicinities, the impact is doubled. In this study, levels and seasonal trends of eleven selected toxic metals were evaluated in water and sediment samples from three coastal-urban urban rivers of Dar es Salaam city, along the Indian Ocean coast in Tanzania. Samples were seasonally collected from fifteen locations, treated as appropriate, and analyzed by High- Resolution Inductively Coupled Plasma Mass Spectrometer. The aim was to establish the current degree of contamination, identify hotspots and assess the ecological and human health risks. The analytical results indicated contamination of both water and sediment by various degrees. In the water samples, only Pb (0.7-24.0 mg/L) exceeded the Tanzania Bureau of Standards and the WHO limits, whereas the other metals were below these limits. In the sediment samples, metal concentrations ranged from 0.06 (Cd) to 92479 (Al) mg/kg dry-weight, and were higher during the dry season than the wet season. When compared to the local background, the metals Cd, Sn, Pb, Co, Cr, and Zn were found to be enriched in more than 50% of the sites. Further comparison with sediment quality guidelines also depicted levels that were unsafe for sediment-dwelling microorganisms. Both the water quality and the sediment quality suggested potential human health and ecological risks. Two hotspots that may require specific intervention were identified. These findings indicate that strategic measures to protect the rivers from further contamination are important in this area. Keywords: surface water; trace metals; coastal environment; ecological risk assessment
P04
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