Water contamination with heavy metals and trace elements from Kilembe copper mine and tailing sites in Western Uganda; implications for domestic water quality

•Kilembe tailings contain Co, Ni, Cu, and As which exceed world crust concentrations.•Kilembe mine contributed Co, Ni and Cu into river Nyamwamba, a public water source.•Geologic weathering appeared to contribute Fe, Al and Mn into public water sources.•Concentrations of Al, Fe and Co in some domestic water samples exceeded thresholds.

The mining and processing of copper in Kilembe, Western Uganda, from 1956 to 1982 left over 15 Mt of cupriferous and cobaltiferous pyrite dumped within a mountain river valley, in addition to mine water which is pumped to the land surface. This study was conducted to assess the sources and concentrations of heavy metals and trace elements in Kilembe mine catchment water. Multi-element analysis of trace elements from point sources and sinks was conducted which included mine tailings, mine water, mine leachate, Nyamwamba River water, public water sources and domestic water samples using ICP-MS. The study found that mean concentrations (mg kg−1) of Co (112), Cu (3320), Ni (131), As (8.6) in mine tailings were significantly higher than world average crust and were being eroded and discharged into water bodies within the catchment. Underground mine water and leachate contained higher mean concentrations (μg L−1) of Cu (9470), Co (3430) and Ni (590) compared with background concentrations (μg L−1) in un contaminated water of 1.9, 0.21 and 0.67 for Cu, Co and Ni respectively. Over 25% of household water samples exceeded UK drinking water thresholds for Al of 200 μg L−1, Co exceeded Winsconsin (USA drinking) water thresholds of 40 μg L−1 in 40% of samples while Fe in 42% of samples exceeded UK thresholds of 200 μg L−1. The study however found that besides mining activities, natural processes of geological weathering also contributed to Al, Fe, and Mn water contamination in a number of public water sources.