Aqueous potentially ecotoxic metal(loid)s in a tropical mining-affected river system: sources and environmental and human health risks.

Water contamination poses threats not only to aquatic life but also to human health. Understanding mining-related potentially ecotoxic metal(loid) (PEM) contamination in a tropical environment is vital for regulation and management. The study aimed to examine the concentrations, sources, and environmental and human health risks of PEMs in tropical river systems. Using the mining-impacted River Nyamwamba in Southwestern Uganda as an exemplar case study, 19 water samples along the River Nyamwamba and its tributaries, and Lake George were collected. The samples were analysed with ICP-MS. Concentrations decreased in the order Co > Mn > Fe > Cu > Ni > Al > Zn > Mo > As > Pb > Cd = Cr. Cobalt, Mn, and Ni concentrations exceeded safe drinking water standards. Multivariate statistical analysis revealed that mining contributed to the presence of As, Co, Cu, Mn, Mo, Ni, and Zn. Pollution load index and potential ecological risk index indicated severe ecological risks. Health risk assessment showed that both carcinogenic and non-carcinogenic risks were posed to human health, with children being the most vulnerable. Up to 2 in 10 children and 3 in 100 adults were at risk of developing excess cancer from PEMs exposure in the river water. The study highlights the importance of preventing untreated aqueous and mine waste discharge into tropical river systems, and recommends that the local government sensitise the community and restrict the use of River Nyamwamba water in favour of other sources (shallow wells, boreholes, springs, and rainwater harvesting), while regularly monitoring water quality.