Assessment of pesticide residues in fish and associated human health risks in Lake Ziway, Ethiopia

Lake Ziway, located in the Ethiopian Rift Valley, faces significant environmental pressure due to intensive agricultural and floriculture practices that heavily utilize pesticides. This study examined the concentrations, bioaccumulation, and health risks associated with 22 selected pesticides in four fish species: Oreochromis niloticus, Cyprinus carpio, Carassius carrasius, and Clarias gariepinus. A total of 48 fish, grouped by size into three sets for each species, were sourced from local fisheries and analyzed in duplicate. The dorsal muscle samples were extracted using a speed extractor, purified with florisil, and quantified using gas chromatography coupled with mass spectrometry (GC–MS/MS). Most compounds showed mean recoveries between 60 and 120%, except for dieldrin (51.33%) and bendiocarb (121.86%). Detection limits ranged from 0.01 to 2.6 μg kg−1. Positive pesticide residues, including Σ HCH, Σ DDTs, HCB, Σ heptachlor, chlorpyrifos, propoxur, and diazinon, were detected at concentrations between 0.010 and 66.44 μg kg−1. However, levels of β-HCH, γ-HCH, aldrin, dieldrin, endosulfan I, endosulfan sulfate, bendiocarb, profenofos, chlordane-trans, chlordane-cis, methoxychlor, and chlorpyrifos-methyl were below the detection limit. DDTs were the most prevalent contaminants, with concentrations ranging from 5.08 to 213.61 μg kg−1, likely due to historical contamination from past practice. The detection of newer pesticides points to ongoing agricultural pressure and inadequate pesticide management practices in the lake’s catchment area. These challenges underline the urgent need for integrated policy responses that combine stricter enforcement of existing bans on legacy POPs, strengthened monitoring systems to include emerging contaminants like carbamates, and improved farmer training and awareness programs to promote sustainable pesticide use. Prolonged consumption of pesticide-contaminated fish poses carcinogenic risks, also highlighting the need for enforcement of pesticide regulations.