Bekele Afework (Professor)Megersa Negussie (PhD)Geta Selamawit2018-07-102023-11-092018-07-102023-11-092010-06http://etd.aau.edu.et/handle/123456789/7557The study had been carried out between July 2009 and June 2010 on the food chain components of Lake Ziway. Bioaccumilation and biotransference of heavy metals and organochlorine pesticides were measured and determined in tilapia (Oreochromis niloticus) and Abyssinian ground hornbill (Bucorvus abyssinicus) to evaluate ecological hazard levels. Heavy metals were determined using flame atomic absorption spectroscopy after digestion of the samples under reflux on kjeldhal hot plate apparatus using HNO3, HCLO4 and H2O2. Sample extraction for organochlorine pesticides analysis was carried out in a Soxhlet apparatus using mixtures of n-hexane and acetone (4:1) and clean up was carried out using SPE Cartridge (C-18 column). Gas chromatograph equipped with massspectrometer (GC-MS) was used for the detection and quantification of the organochlorine pesticides. Heavy metals; Cu, Zn, Cd and Pb were investigated with mean concentrations of 1.13 mg/kg, 27.13 mg/kg, 0.35 mg/kg and 0.28 mg/kg in tilapia and 8.91 mg/kg, 139.08 mg/kg, 0.225 mg/kg and 0.286 mg/kg in Abyssinian ground hornbill muscle tissue samples. The detected organochlorine pesticides were dieldrin, DDT and the metabolites of DDT (DDD and DDE). DDT and DDD are below the detection limit in tilapia and detected with mean concentration of 0.19ng/g and 0.14ng/g in Abyssinian ground hornbill samples. Dieldrin and DDE were detected in mean concentrations, 4ng/g and 0.45ng/g in tilapia and 11.8ng/g and 12.61ng/g in Abyssinian ground hornbill samples. Zn and Cu indicated biotransference up the food chain with 5 folds and 7.9 folds, respectively while Cd and Pb showed lower concentration in the predator bird. DDE and dieldrin were detected in the bird sample with 28 and 3 folds higher than the amount detected in the fish muscle tissue, respectively. From the detected heavy metals and organochlorine pesticides Zn, Cu, dieldrin, DDT and its metabolites indicated positive biotransference through the food chain. The concentrations of the detected heavy metals and organochlorine pesticides were compared with threshold limits set by international organizations and the levels are within the accepted limits. Key words; Organochlorine, Bioaccumulation, Contaminant, BiotransferenceenOrganochlorineBioaccumulationContaminantBiotransferenceThesis