Geological Controls on the Distribution of Pharmaceutical Residues, Heavy Metals, and Hydrochemical Characteristics of Groundwater in Semi-Arid Communities of North-Central Nigeria

Abstract This study assessed geological controls on the distribution of pharmaceutical residues and associated contaminants in groundwater from semi-arid communities in North-Central Nigeria. Groundwater samples were collected from five locations representing contrasting lithological settings and analysed for pharmaceutical residues, physicochemical parameters, heavy metals, trace metals, and health-risk indices. Pharmaceutical residues were detected in all samples, with the highest concentrations recorded in fractured and weathered aquifer zones. Ciprofloxacin ranged from 1.74 ± 0.18 µg/L at G3 to 6.31 ± 0.62 µg/L at G4, while paracetamol reached 6.12 ± 0.56 µg/L and ibuprofen 5.74 ± 0.53 µg/L at G4. Physicochemical deterioration was also pronounced at G4, where EC, TDS, nitrate, chloride, phosphate, and BOD recorded 1564 ± 138 µS/cm, 984 ± 85 mg/L, 61.2 ± 5.8 mg/L, 301 ± 28 mg/L, 4.1 ± 0.4 mg/L, and 8.1 ± 0.8 mg/L, respectively. Heavy metals and trace metals, including Pb, Cd, Cr, Ni, Mn, As, and Hg, exceeded permissible limits at G2 and G4. Hazard index values were highest at G4 (3.42) and G2 (3.18), indicating potential non-carcinogenic health risks. The study concludes that fractured migmatite-gneiss and weathered granite gneiss formations enhance contaminant migration, whereas clayey sandstone provides greater natural protection. Routine groundwater monitoring and geology-guided borehole sitting are recommended. Keywords: Pharmaceutical residues, groundwater contamination, geological controls, trace metals, health risk, North-Central Nigeria.