Heavy Metal Contamination and Human Health Risk Assessment of Osin River, Ila-Orangun, Osun State.

Abstract

The present study assessed certain heavy metals contamination in water, sediment, and fish samples from the Osin River in Ila-Orangun, Osun State, along with the ecological and human health risks linked to these concentrations across five locations (L1–L5). Samples were collected at these strategic locations along the flow of the River and were analyzed for thirteen heavy metals using the inductively coupled plasma mass spectrometry (ICP-MS) (Agilent 7700 series, Agilent Technologies, USA).To assess health implications of heavy metals contaminations several indices such as Environmental water quality index (EWQI), lifetime cancer risk (LCR)were calculated. Water samples typically showed low or non-detectable (ND) concentrations of contaminants, with only trace amounts of Mn (0.05–0.09 mg/L), Fe (0.07–0.33 mg/L), Cu (0.02–0.05 mg/L), and Zn (0.10–0.16 mg/L), all adhering to U.S. Environmental Protection Agency (USEPA) and World Health Organization (WHO) guidelines. The fish samples showed the higher concentration of certain metals (Mn 5.42 - 16.40mg/kg; Fe 4.75 - 11.7mg/kg, Zn 7.05 - 21.75 mg/kg, and Se 3.52 -11.64mg/kg), exceeding the tolerable limit. The sediment sample revealed the highest concentrations of most metals relative to water and fish. EWQI demonstrated that the water quality was mostly good. Heavy metal pollution index (HMPI) and heavy metal toxicity index (HMTI) showed moderate to high contamination possibilities in sediments, with L5 as the most contaminated location. The hazard Index of adults ranged between 0.77 and 6.74, whereas that of children was between 0.03 and 0.72. LCR was within the acceptable range (10^-6 -10^-4), indicating a weak carcinogenic risk. However, the observed spatial variation in the sediment and fish concentration indicate the influence of localized anthropogenic activities which underscore the need for continuous environmental monitoring. Overall, the Osin River remains an important ecological and nutritional resource, however, regular risk assessments are essential to ensure its sustainable use.