Assessment of Heavy Metal and Hydrocarbon Contamination in Sediment and Water of Oguta Lake, Imo State, Nigeria

Abstract

This study assessed the levels of Total Petroleum Hydrocarbons (TPH) and selected heavy metals (Pb, Cr, Cd, Ni, and Fe) in the sediments and waters of Oguta and Abadaba Lakes between April 2023 and February 2024, with Abadaba Lake serving as a comparative reference. 144 composite samples of water and sediment were analysed using an Atomic Absorption Spectrophotometer and a Gas Chromatography-flame Ionisation Detector (GC-FID), following American Public Health Association (APHA, 1999) standards. pH results revealed that Oguta sediments remained acidic (< 7.0) throughout the study, while Abadaba sediments shifted from acidic to alkaline conditions after October 2023. In both lakes, water samples were alkaline across the period. TPH concentrations were significantly higher in Oguta sediments (36.43 – 49.95 mg/kg) compared to Abadaba sediments (1.40 – 2.67 mg/kg). Similarly, heavy metals were consistently more elevated in Oguta sediments, with peak levels recorded in February 2024 for Pb (0.194 mg/kg), Cr (0.198 mg/kg), Cd (0.116 mg/kg), and Fe (134.73 mg/kg). Water samples showed lower concentrations of TPH and metals than sediments, but Oguta waters still exhibited higher contamination than Abadaba waters. Comparisons with Nigerian Upstream Petroleum Regulatory Commission (NUPRC) standards revealed that TPH and metal concentrations were within permissible limits in both sediments and water. However, two-sample t-tests showed statistically significant differences (p < 0.05) in contaminant levels between Oguta and Abadaba Lakes, confirming higher pollution in Oguta. These findings underscore the impact of anthropogenic activities around Oguta Lake and emphasise the importance of ongoing environmental monitoring.