Heavy Metals in Wastewater and Fish Tissues from Waste Stabilization Pond and Human Health Risk Asseessment, Jimma, Ethiopia

Abstract

Introduction: Heavy metals are individual metals and metal compounds that can affect human health. These impurities are one of predominant type of water pollutants. Objective: The present study was conducted to determine concentration of heavy metals in wastewater and fish tissues from Kito Furdisa waste stabilization pond and to assess human health risk in Jimma, Ethiopia. Methods: Laboratory based cross-sectional study design was employed to determine the concentration of heavy metals in wastewater and fish tissues (gill, liver and muscle). A triplicate wastewater samples and a total of 32 fish samples (O. Niloticus) were collected from facultative and maturation ponds. A standard method of procedure was used to collect, digest and analyze samples. Micro Plasma Atomic Emission Spectrometry (Agilent 4210 MP-AES) and Hydride Generated Atomic Absorption Spectrometry (HGAAS, novAA 400P, Germany) were used to detect Cadmium, Lead, Arsenic and Mercury. SPSS version-26 was used for statistical analysis and a paired sample t-test at (p <0.01) was used to test for statistically significant variation of heavy metals concentration between sampling points. Results: From our findings, the mean concentration of heavy metals in wastewater were in the decreasing order of Cd>Pb >As>Hg, which ranged from (26.53µg/L to 27.66µg/L), (16.13µg/L to 20.67µg/L), (0.375µg/L to 0.387µg/L), (0.097µg/L to 0.346µg/L) in maturation and facultative pond, respectively. Among heavy metals, Hg in wastewater showed a statistically significant difference between sampling points (p = 0.023). The concentration of Arsenic (As) recorded in the muscles of fish under study was above the maximum permissible limits (MPL) recommended for human consumption by FAO/WHO which is 0.01 mg/kg. According to the non-carcinogenic and carcinogenic risk assessment, children were more susceptible to heavy metal exposure than adults. Conclusion: Due to the presence of high levels of these toxic heavy metals, the wastewater is not suitable for fishing purpose in order to avoid bioaccumulation. Generally, it was found that heavy metals showed tissues specific accumulation in this study. The target carcinogenic risk (TR) and THQ estimated in this study revealed that all metals were less than the safe limit. Our results are an indicative of heavy metal contaminations and regular biomonitoring studies in fish are essential in order to prevent excessive buildup of toxic heavy metals in the food chain and human body.