Health risk evaluation of heavy metal-contaminated groundwater in unplanned settlements of Dar es Salaam,Tanzania

Deterioration of groundwater quality is an increasing global challenge threatening human health. This is highly exacerbated by the rapid urbanization mismatched with the planning of settlements and the provision of services. Many unplanned settlements are rapidly emerging with limited infrastructure for the management of environmental pollution sources. This has resulted in groundwater contaminations, which poses human health risks. This study was conducted to examine the risks associated with heavy metals (Pb, Cu, Cr, Cd and Zn) contamination in 75 boreholes used in 8 unplanned settlements of Dar es Salaam and the associated health risks. PerkingElmer, AAS-100 was used to analyze heavy metal concentrations in water samples. Risk assessment was established using the Hazard Quotient (HQ) and Chronic Daily Intake (CDI) using the United States Environmental Protection Agency (US EPA) Models. The results of CDI were in the order of Zn > Cr > Cu > Cd > Pb, and non-carcinogenic health risks were detected, particularly for Zn and Cr, with HQ > 1. The carcinogenic risks caused by cadmium and lead were above 1 × 10^-6 US EPA recommended standard. Pearson correlation indicated a weak to moderate correlation, indicating diversity of pollution sources. It is recommended to use alternative water sources for human consumption in the studied areas.