Assessment of Heavy Metal Concentrations in Groundwater and Climate Variability in Otukpo, Benue State, Nigeria

Groundwater is crucial for domestic and agricultural water needs in Otukpo, Nigeria, and its quality and sustainability could be affected by climate variability and heavy-metal pollution. The present study measured the concentrations of some of the heavy metals in groundwater and analyzed long-term climatic changes to offer integrated evidence of possible vulnerability of groundwater resources. The concentration of cadmium (Cd), nickel (Ni), lead (Pb), antimony (Sb), cobalt (Co), iron (Fe) and chromium (Cr) were measured by atomic absorption spectrophotometry (AAS) in groundwater samples from 20 locations during the rainy season. The concentrations of the metals were compared to the relevant drinking-water guidelines and relationships between concentrations of the metals and groundwater depth were assessed using Pearson correlation and Spearman correlation analyses. Climate data from 1990–2025 were retrieved from the NASA Prediction of Worldwide Energy Resources (POWER) database and the trends were analysed with ordinary least-squares regression and the Mann–Kendall test. The concentrations for Ni, Pb, Sb, Co, Fe and Cr were 0.952, 0.900, 10.143, 0.874, 5.317 and 4.884 mg/L, respectively, and were below the detection limit in all samples. There were a number of measured concentrations that were above applicable drinking-water guideline values, notably for Pb, Sb, Fe and Cr. Groundwater depth had a significant negative correlation with lead (Spearman's ρ = −0.527, p = 0.020) but no statistically significant relationship was found between groundwater depth and the other metals assessed. Climate analysis shows a significant warming, with mean, maximum and minimum temperatures showing warming rates of 0.0635 °C/year, 0.122 °C/year and 0.070 °C/year, respectively. The precipitation decreased at 0.0570 mm/day/year and the relative humidity decreased at 0.267 percentage points/year. The results will help support continued groundwater-quality monitoring, better wellhead protection, pollution control, and groundwater management that is informed by climate to increase water security and resource sustainability.