Environmental Risks of Pesticide Residues in the Lake Tana Sub-basin, Ethiopia: A Review

Lake Tana, Ethiopia's largest natural lake and the headwater of the Blue Nile, provides critical ecosystem services and socio-economic benefits. However, rapid agricultural expansion in the Lake Tana sub-basin has led to increased pesticide use, which raises serious environmental concerns. This systematic review synthesi zes information on agricultural pesticide use, their residues in fish, water, and sediments, and the associated ecological and human health risks. A total of 66 active ingredients were identified across 13 districts, with the highest pesticide use reported in Libokemkem, Fogera, and Gondar Zuria. Pesticide use was dominated by insecticides, including several WHO-classified hazardous compounds. Risk Quotients derived from fish body residues identified imidacloprid, oxamyl, and flazasulfuron as priority pesticides posing high to very high risks to Labeobarbus spp. In Lake Tana, legacy organochlorine pesticides (endosulfan, lindane, endrin, DDT, and dieldrin) posed high to very high risks to Oreochromis niloticus. Human health risk assessment based on fish consumption indicated negligible non-carcinogenic risks from both current-use and legacy pesticides. Potentially Affected Fraction (PAF) and multi-substance Potentially Affected Fraction (msPAF) analyses indicated severe ecological risks posed by the measured water concentrations across the Lake Tana sub-basin. Sediment-bound pesticides also posed consistently high ecological risks, particularly for persistent organochlorines (lindane, endrin, and dieldrin). Overall, these findings advocate the urgent need for improved pesticide regulation, better management of legacy contaminants, and the promotion of sustainable agricultural practices to protect the Lake Tana sub-basin and its vital ecosystem services.