Heavy metal pollution level and risk assessment of river water receiving hospital effluent in Ekiti State, Nigeria

Abstract

Surface water contamination by heavy metals remains a significant environmental and public health concern in developing countries, particularly where untreated hospital effluents are discharged into natural water bodies. This study assessed the spatial and temporal distribution of selected heavy metals in river water receiving effluents from a teaching hospital in Ekiti State, Nigeria. Water samples were collected monthly for twelve months from three locations (upstream, midstream, and downstream) and analyzed for arsenic (As), manganese (Mn), chromium (Cr), nickel (Ni), lead (Pb), zinc (Zn), and copper (Cu) using atomic absorption spectrophotometry. Pollution and risk indices, including the Heavy Metal Pollution Index (HPI), Metal Index (MI), Risk Index (RI), and Cumulative Risk Index (CRI), were employed to evaluate contamination levels and potential ecological risks. Results showed that mean concentrations of As, Mn, Cr, and Pb frequently exceeded World Health Organization (WHO) guideline limits, particularly at the downstream sampling point, whereas Ni, Zn, and Cu were generally within permissible limits. The CRI values indicated moderate to very high contamination risk downstream (CRI = 103.38), compared to upstream (48.66) and midstream (45.91) locations. These findings highlight the environmental implications of untreated hospital effluent discharge and underscore the need for improved wastewater treatment, routine water quality monitoring, and public awareness to mitigate potential health risks.