Organochlorine Contaminants in Nile Tilapia, Oreochromis niloticus (Linnaeus 1758) in Densely Populated Areas of South-Western Kenya


Concentrations of OCP (Organochlorine Pesticide) residues were determined in cultured Nile tilapia (Oreochromis niloticus) fish in target stations within 1st order wetland of River Kuja, Kenya, between February-November, 2017. The aim was to assess the residue levels in wild and pond cultured fish within a heavily populated agricultural area of South Western Kenya. Biota samples were analysed for selected HCHs (Hexachlorocyclohexane) isomers, DDT (Dichlorodiphenyltrichloroethane) and metabolites and cyclodienes pesticide residues using GC-ECD (Gas Chromatography Equipped with Electron Capture Detector). Most of OCPs observed were BDL (Below Detection Limit) to detectable levels. Larger percentages (> 50%) of DDTs and HCHs were BDL and exhibited consistency, with significant (p < 0.05) differences in mean contamination levels in fish within the wetland, with average muscle tissue pesticides concentrate ranging between 0.229-2.541 g/kg for Nile tilapia. Most dominant isomer in target species was Lindane (-HCH) (3.417 ± 0.983 g/kg) and Endosulfans. Mean Endosulfan sulfate was 2.499 ± 0.071 g/kg d.w. and most frequently detected, and Methoxychlor (2.235 ± 1.459 g/kg), respectively. Mean Aldrin and Dieldrin was 2.028 and 0.574 g/kg d.w. Concentration for DDT and its metabolites was 0.27-3.71 g/kg for p, p’-DDE (DichlorodiphenylDichloroEthene), BDL-1.098 for p, p’-DDD (DichloroDiphenylDichloroEthane), and 0.105-3.518 g/kg for p, p’-DDT with significant differences in mean values and ranges whose levels were below the WHO (World Health Organization) maximum acceptable thresholds of 0.2, 2, 20 and 5.0 g/kg in fish and sea food.