Distribution of Heavy Metals in the Fosu Lagoon (Cape Coast)

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Mining and industrial processing are among the main sources of heavy metals contamination in the environment. Heavy metals concentration may accumulate to toxic level which can cause a potential risk to human health. Continuous discharge of industrial and residential waste water into the Fosu lagoon is a potential source of environmental pollution. Water, sediment and fish samples from the lagoon were used to assess the extent of heavy metals concentration in the lagoon. Heavy metal concentrations in the samples were measured using the Perkin-Elmer Atomic Absorption spectrophotometer. Some physicochemical parameters were also measured to know the level of the water quality. Twelve samples of water and sediment were collected from the lagoon at six different points to represents the wet and dry seasons. Results obtained for water samples were compared with USEPA National Recommended Water Quality Criteria. Geoaccumulation index was used to determine the extent of heavy metal pollution in the sediment samples whiles the heavy metal concentrations in fish samples were compared with US Food and Nutrition Board daily recommended intake levels. Pearson’s correlation was also used to determine how correlated the metals are to each other and their possible sources. The results obtained revealed that heavy metals concentrations were significantly higher during the dry season for both water and sediment samples but nutrients concentration in water samples were higher in the wet season. pH values for water and sediments revealed that the lagoon is neutral during the wet season but basic in the dry season. Only lead and cadmium were recorded in water samples for the wet season with lead concentration exceeding the USEPA threshold level of 3.0 mg/kg. The sediment samples contained high concentration of metals. Fe, Mn, Zn and Pb recorded mean concentrations of 1275.25 mg/kg, 236.72mg/kg, 22.72 mg/kg and 14.22 mg/kg for the dry season respectively. Geoaccumulation indices showed that the lagoon sediments were highly contaminated with iron, manganese, zinc and lead. Metal concentrations in fish samples were also detected and again, iron, manganese, zinc and lead recorded high concentrations. Examination of health of the fish by Fulton’s formula showed that all fish samples were in good condition. However, the presence of lead and cadmium in the fish samples is a health threat since these two metals are of no nutritional value and also have the tendency to bio accumulates in the fish and also be biomagnified along the food chain.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Science in Environmental Science, 2011