Insights into the quality index of surface water from the Okpare Olomu River, Southern Nigeria

Abstract

This study evaluated the physicochemical characteristics, heavy metal contamination, and water quality of the surface water from the Okpare Olomu River in Ughelli South, Delta State, Nigeria. Water samples from four stations were analysed for physicochemical parameters, heavy metals (Fe, Pb, Cd, Cr, Cu, Zn, Mn), and the total hydrocarbon content (THC). The pH ranged from 5.71 to 5.86, indicating slightly acidic water. Electrical conductivity (17.23–24.23 µS/cm), total dissolved solids (6.18–13.46 mg/L), and total suspended solids (71.20–75.20 mg/L) were low, while dissolved oxygen (5.12–6.24 mg/L) and biochemical oxygen demand (3.34–7.43 mg/L) reflected moderate water quality. Heavy metal concentrations followed the order: Fe (0.86–2.35 mg/L) > Pb (0.00–0.23 mg/L) > Cd (0.02–0.07 mg/L) > Cr (0.06–0.12 mg/L) > Cu (0.06–0.09 mg/L) > Zn (0.13–0.16 mg/L) > Mn (0.01–0.02 mg/L), with Fe, Pb, and Cd exceeding the permissible limits established by NESREA, USEPA, and the WHO. THC ranged 2.85–3.62 mg/L. The Water Quality Index (WQI: 136.21–1113.24) classified all stations as Grade E and unsuitable for drinking, while the Comprehensive Pollution Index (CPI: 0.66–2.20) indicated station 2 as severely polluted, stations 1 and 3 as moderately polluted, and station 4 as slightly polluted. Health risk assessment revealed non-carcinogenic risk due to arsenic exposure (HI > 1), and integrated carcinogenic risk suggested a high potential for cancer among consumers. These findings highlight the urgent need for mitigation strategies, continuous monitoring, and public health interventions to reduce heavy metal contamination and protect communities dependent on the Okpare Olomu River.