Evaluation of groundwater suitability in the Cretaceous Abeokuta Formation, Nigeria: Implications for water supply and public health

Abstract

The health implications of exposure to chemicals like cadmium and lead through the consumption of polluted groundwater have made monitoring groundwater sources imperative. This study evaluated the suitability of groundwater sources over the Cretaceous Abeokuta Formation, Ogun State, Nigeria, and mapped the distribution to identify the major pollution source. Abeokuta Formation was sectionalized into three regions (western, central, and eastern) to sample one hundred and seven groundwater sources. In-situ and detailed laboratory testing for physicochemical, anion, cation, metals and E-coli were carried out following the APHA standard procedure. Laboratory results were subjected to Water Quality Index (WQI), carcinogenic and non-carcinogenic risks of metals, spatial analysis using Kriging interpolation of ArcGIS, and several plots. Findings showed that the percentage of samples with a problematic pH concentration, chloride, bicarbonate, iron, lead, cadmium and coliform increased from western to central and recorded the highest percentage in the eastern region. Hydrogeochemical charts inferred that carbonate and silicate weathering were responsible for the enrichment of anions in the aquifer. WQI result indicates that all samples are within the acceptable range (<100). Although cancer risks for all samples were insignificant, 26.7%, 23.4%, and 56.7% of samples have significant non-carcinogenic risks (HI > 1) in western, central and eastern regions, respectively. Spatial analysis showed that the low elevation areas in the central and eastern regions have high non-cancer risks. The contribution of parameters to non-cancer risks were Cd > Cu > Pb > Zn > Fe > NO3− > Cr > Ni in central, and Cu > Cd > Pb > Zn > Fe > NO3− > Cr > Ni in eastern regions. This study, therefore, established that geogenic processes have severely polluted the groundwater aquifer in the eastern region, and groundwater in the area is unsuitable for consumption and poses a severe public health concern.