Assessment of Heavy Metals in a Rural River Receiving Agricultural Effluents: Ecological Health Implications

Abstract

Heavy metal contamination of freshwater ecosystems poses significant risks to aquatic organisms, human health and the sustainability of freshwater resources. This study assessed the concentrations, spatial variation, pollution status and potential ecological risks associated with selected heavy metals in the lower section of River Adofi, Delta State, Nigeria. Water samples were collected monthly from three sampling stations over nine months, from September 2025 to May 2026. Samples were analysed for copper (Cu), lead (Pb), silver (Ag), zinc (Zn) and cadmium (Cd) using atomic absorption spectrophotometry. Descriptive statistics, one-way analysis of variance, principal component analysis and hierarchical cluster analysis were employed to evaluate spatial patterns and relationships among the metals. Heavy Metal Pollution Index (HPI), Contamination Factor (CF), Pollution Load Index (PLI), ecological risk factor (Er) and Potential Ecological Risk Index (PERI) were used to assess pollution and ecological risk. Mean concentrations of Cu, Pb, Ag, Zn and Cd ranged from 0.5611–0.7533, 0.0299–0.0788, 0.4600–0.5867, 1.2167–1.6280 and 5.8633–6.0778 mg/L, respectively. Significant spatial differences were recorded for Pb (p = 6.2 × 10⁻⁶) and Zn (p = 0.00022), whereas Cu, Ag and Cd showed no significant differences among stations. The PLI values were 6.81, 5.36 and 5.65 for Stations 1, 2 and 3, respectively, indicating a substantial overall pollution load. HPI values were also extremely high at all stations, exceeding the critical value of 100. Cadmium exhibited exceptionally high contamination factors and was the principal contributor to the ecological risk, while Cu, Zn and Pb generally presented low individual ecological-risk values. The PERI values were 59,619.81, 58,650.23 and 60,800.87 for Stations 1, 2 and 3, respectively, indicating very high potential ecological risk. The findings demonstrate substantial heavy metal contamination of River Adofi, particularly from Cd, with implications for aquatic ecosystem integrity and human use of the river. Regular monitoring, pollution-source control and appropriate remediation measures are therefore required to protect the ecological functions and beneficial uses of the river.