Groundwater Contamination by Iron, Manganese, and Antimony in the Bangéli Canton (Northern Togo): Speciation, Seasonal Mobility, and Health Risk Assessment

Background: Borehole groundwater is the primary source of drinking water in Bangéli canton, northern Togo, but increasing contamination by iron (Fe), manganese (Mn), and antimony (Sb), partly linked to geological conditions and past mining activities, raises concerns about water quality and human health. Aims: This study investigated the speciation, mobility, seasonal variability, and health risks of antimony (Sb), iron (Fe), and manganese (Mn) in borehole groundwater from Bangéli canton, northern Togo. Methodology: Four contaminated boreholes were monitored during dry and rainy seasons from 2024 to 2025. Physicochemical parameters (pH and Eh) were measured in situ. Total concentrations of Fe, Mn, and Sb were determined using ICP-OES, while trace-level confirmation and analytical validation were performed using ICP-MS. Metal speciation was interpreted using hydrogeochemical conditions and Pourbaix diagrams. Groundwater quality and health risks were assessed using the Heavy Metal Pollution Index (HPI) and the USEPA risk assessment model. Results: Mean concentrations ranged from 1082.99 ± 685.38 to 1291.20 ± 980.42 µg/L for Fe, 184.21 ± 99.56 to 216.22 ± 133.15 µg/L for Mn, and 60.83 ± 21.57 to 248.49 ± 61.91 µg/L for Sb, exceeding WHO guideline values in most samples. Concentrations were generally higher during the rainy season, particularly for antimony. The dominant species were Sb(V), Fe²⁺, and Mn²⁺, indicating high mobility under prevailing hydrogeochemical conditions. Health risk assessment revealed significant non-carcinogenic risks, especially for children, with antimony as the major contributor. Hazard Index (HI) values exceeded acceptable limits. Conclusion: Groundwater contamination is mainly controlled by hydrogeochemical processes and past mining activities, highlighting the need for continuous monitoring and improved water management strategies.