Determination of Bioaccumulation and Food Chain Contamination of Heavy Metals and Organochlorine Pesticides in Tilapia (Oreochromis niloticus) and Abyssinian Ground Hornbill (Bucorvus abyssinicus), Lake Ziway
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Date
2010-06
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Addis Ababa University
Abstract
The 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, Biotransference
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Keywords
Organochlorine, Bioaccumulation, Contaminant, Biotransference