Persistent organochlorine pollutants in Lake Bosomtwi and Weija Lake and their potential toxicological health implications

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March, 2015.
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This research work focused on the assessment of organochlorine pollutants in two water bodies and their health implications on aquatic species and humans. The research involved conducting systematic assessment of occurrence and burden of indicator polychlorinated biphenyls and organochlorine pesticides in water, sediment and fish samples.The main objective focused on the determination of persistent organochlorine pollutants as well as their bioaccumulation in fish species and their toxicological risk assessment on human population via drinking of water and dietary intake of fishes from the two water bodies. Lake Bosomtwi and Weija Lake were the study areas and investigations started from January 2012 to June 2014. Instrumental Neutron Activation Analysis (INAA) was used for determination of extractable organochlorines (EOCs) and bound organochlorines (BOCs). The EOCs were further characterized with Capillary Gas Chromatography equipped with Electron Capture Detector (GC - ECD). Hexane was used as extraction solvent for the extraction of OC pollutants from the water samples whiles, the sediment and fish samples were sonicated on ultrasonic bath using hexane/acetone (3:1) solvent system. The extracts were then cleaned up on a combined florisil-silica adsorbent packed in glass column. Ecotoxicological impact of sediments on aquatic species was assessed using two sediment quality guidelines. The impacts of OC pollution on humans was assessed by estimating daily exposure and cancer and non cancer hazard ratios on consumption of the studied fishes. ANOVA was applied to determine the differences in the mean concentration. The average levels of extractable organochlorine were 0.71 mg/L and 0.39 mg/L for the water samples from the Weija and Bosomtwi respectively. The sediment compartments had average extractable organochlorine content of 3.57 mg/kg from the Weija while that from Bosomtwi was 3.28 mg/kg. The average BOC content in the sediments were respectively, 0.48 mg/kg and 0.46 mg/kg for Weija and Bosomtwi samples. In the fish compartments, EOC composition varied from 6.89 mg/kg to 9.02 mg/kg for Weija species while those from Bosomtwi iv were from 3.99 mg/kg to 4.63 mg/kg. The concentrations range for the detected organochlorine pesticides (OCPs) were <0.01 µg/l to 4.30 µg/l, <0.01 µg/kg to 15.23 µg/kg, <0.01 µg/kg to 23.70 µg/kg for the water, sediment and fish samples respectively, while those for the PCBs were <0.01 µg/l to 4.72 µg/l for Lake water, <0.01 µg/kg to 7.55 µg/kg for sediments and <0.01 µg/kg to 32.40 µg/kg for the fish species. Statistically significant differences in the mean concentrations of the OCs were detected. The ecotoxicological impacts of measured organochlorine pollutants in the sediments to aquatic species showed that toxicity of ƩPCB, p,p'-DDT, P,P'-DDE and ƩDDT to aquatic species was below ERL Estimated daily intake (EDI) of organochlorine as a result of consumption of the studied fishes for children ranged from 0.002 µg/kg to 0.176 µg/kg and those for adults were from 0.0011 µg/kg to 0.0892 µg/kg. EDIs were however, far below reference doses (RFDs) recommended by United State Environmental Protection Agency (USEPA). Risk assessment in terms of carcinogenic and non-carcinogenic effects on humans on consumption of the fishes revealed that eating of Tilapia zilli, Tilapia nile and Tilapia galilaea from the Weija Lake present no risk of carcinogenic effect. However, more than one in a million of the consuming population on eating Clarias gariepinus can get cancer as a result of HCHs contamination. Consumption of fishes from the Lake Bosomtwi was found to present no carcinogenic effect. In general, the overall findings showed that levels of pollutants detected in the two water bodies posed minimum to no risk to communities that depend on the Lakes for livelihood.
A thesis presented to the Department Of Chemistry, College Of Science, in partial fulfilment of the requirements for the award Of Doctor of Philosophy degree in Environmental Chemistry, 2015