Assessment of heavy metal concentrations in water and sediment of dams in Central Namibia and bioaccumulation of copper in locally occuring crabs and fish
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Date
2015
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Abstract
Mining is a major contributor to water pollution, which can lead to accumulation of heavy metals in aquatic systems. Mining activities in the Karstveld, specifically in the Tsumeb-Grootfontein-Otavi area, may potentially result in heavy metal pollution of water sources. A seasonal study was conducted to assess the concentration of heavy metals in aquatic systems that receive water from the Karstveld aquifer. The potential of locally occurring fish and crab species as bio-indicators of copper pollution was also investigated. Water samples were collected from Omatako and Von Bach dams as well as along the Eastern National Water Carrier, while sediment samples were collected from the two dams. Concentrations of Copper, Lead and Zinc in sediment and water samples were measured with Inductive Coupled Plasma – Optical Emission Spectrometry (ICP-OES). No significant temporal difference (p > 0.05) in metal concentrations was found. Omatako dam had significantly (p < 0.05) higher concentrations of Copper (0.68 mg/L) and Zinc (1.0 mg/L) in the sediment than Von Bach dam. Water at the start of the canal had significantly (p < 0.05) higher Zinc concentrations (1.4 mg/L) compared to the canal’s mid-section (0.01 mg/L). Low copper and lead concentrations (< 0.1 mg/L) were found throughout the canal. An exposure study using Tilapia fish and freshwater crabs were done to determine at what concentrations and in which parts of the body bioaccumulation takes place. Organisms were exposed to different Copper concentrations (0, 20, 40 and 80 mg/L) for 8 weeks. Concentration of Cu in the gills, liver and muscle tissue in the fish and gills, muscle tissue and hepatopancreas in the crabs were determined by ICP-OES. Concentrations of up to 9.6 mg/L of Cu were found in liver tissue of the fish at 80 mg/L exposure. The gills in the crabs had the highest concentration of Cu of 2.6 mg/L. Muscle tissue in both the organisms had the lowest concentrations of Cu. Accumulation of Cu at a concentration of 80 mg/L was highest in the liver. Levels of Cu in the body of the organisms increased with higher exposure concentrations.
Description
A thesis submitted in fulfilment of the requirements for the Degree of Master of Science
Keywords
Heavy metals, Copper, Namibia, Pollution, Bioacccumulation, Sediment, Fish, Crabs