Environmental pollutants in biological and sediment samples from the mining environs of Obuasi, Ghana

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1993-09-03
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Drinking water from taps and deep wells, sediments of surface waters, fish, vegetables and cash crops were collected from Kwabrafoso, Wawaase, Kokoteasua, Nyamso, Dadwen, Pomposo, Diewuoso, Odurnase, Hia, Ayease, Domeabra, Akrofuom, Suhyenso and Ampunyase. The above-named samples were analysed for the levels of arsenic, sulphate, cyanide, selenium and mercury. Colorimetric methods were employed to determine arsenic, cyanide and selenium while turbidimetric and atomic absorption spectrophotometry methods were used to determine sulphate and mercury respectively. A’naiysis of the samples obtained from the above-named sites indicated that, the sediments, vegetables, oil palm fruits and fish contained high levels of arsenic, sulphate and selenium. At Kwabrafoso, cocoyam leaves have total arsenic level of 4.9-6.2mg/kg while sediments contain 132.4-269.5mg/kg. Cyanide levels in sediments collected from rivers carrying the effluent were also high. Levels in food crops and fish were however, within W.H.O. accepted limits. Cyanide levels in sediments were 13.0-30.0mg/kg at Kwabrafoso while garden eggs have a level of 1.3-3.9mg/kg. The analysis of food samples showed that the levels of mercury were all above the W.H.O. accepted limits as shown at Ampunyase with a level of 9.62-9.88 mg/kg in cocoyam leaves. The results also indicated that the levels of the pollutants decreased with increasing distance from the treatment plant. At Kwabrafoso, sulphate levels in sediments were 130.0-160.0mg/kg and 93.4-100.8 mg/kg at Ampunyase. The concentration of the pollutants increased during the rainy season; selenium concentration in oil palm fruits was 5.6mg/kg in December and 9.7mg/kg in June at Kokoteasua. Samples collected from villages in the prevailing wind direction however, showed higher levels of pollutants than those in the leeward side. Total arsenic levels in garden eggs were 1.5-4.3mg/kg in the wind direction and 1.2-1.5 mg/kg in the leeward side. The general water quality of tap and deep well waters showed that they were safe for drinking except the deep well at Kwabrafoso, which had arsenic level above the 0.O5ppm maximum limit of the W.H.O. Mercury levels in the borehole at Ampunyase and Nyamso were also higher than the W.H.O. maximum limit of 1.0ppb.
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A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Philosophy in Environmental Chemistry, 1993
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