Determination of geochemical baseline and hydrogeochemical characterisation of groundwater in Lagos, Nigeria

This study investigated the baseline geochemistry, hydrogeochemical processes, and groundwater quality of Lagos, Southwest Nigeria, using 103 water samples collected from boreholes, hand-dug wells, and bottled water sources. Thirty-one parameters were determined, including physical, cations, anions and trace elements. ICP-MS was used to analyse trace elements and cations, while anions were analysed using ion chromatography Hydrogeochemical assessment revealed that groundwater chemistry is mainly influenced by silicate weathering, reverse ion exchange, and human activities from municipal, industrial, and agricultural sources. Piper plot classification indicated that the dominant geochemical facies are Ca–Mg–HCO₃ and Na–Cl types, reflecting both natural weathering and human impact. Water quality evaluation showed that levels of Ca, Mg, HCO₃, SO₄, SiO₂, Ba, B, Sr, Be, V, Cr, Cd, Ni, Cu, Zn, Se, and U were within permissible limits. However, exceedances occurred for pH (77%), EC (4%), TDS (5%), Na (4%), Fe (13%), Cl (3%), NO₃ (72%), NO₂ (5%), Mn (44%), Al (27%), Co (6%), F (100%), and Pb (6%), with hotspots in Kosofe, Shomolu, Mushin, and Igando/Iyana-Iba Local Government Areas. These findings highlight the urgent need for public health advocacy, especially concerning fluoride, nitrate, aluminium, manganese, and lead, and call for stronger policy measures to promote sustainable groundwater management in Lagos.