The determination of some environmental pollutants in Obuasi and its environs

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The emergence of strange diseases among residents of Obuasi and its surrounding villages is attributed mainly to the mining activities of Ashanti Goldfields Corporation (A.G.C.).’ The extraction of gold by A.G.C. releases arsenic (III) oxide, sulphur (IV) oxide, selenium (IV) oxide and cyanide into the environment. Mercury is also introduced by small scale and illegal miners who use the metal for gold extraction. This work aimed at determining the levels of these pollutants in water, fish, food crops, vegetation and soil and to provide data on variation of pollutant levels’ with the seasons and distance from the P.T.P. Colorimetric methods were used to determine arsenic, selenium and cyanide; turbidimetric method for sulphate while atomic absorption spectrophotornetric and standard methods were used for mercury and general water quality, respectively. The results showed that the A.G.C. is the main contributor of arsenic, cyanide, selenium and sulphate to the environment of Obuasi as samples from villages affected by the flue gases and/or the effluent showed elevated levels of pollutants. Total arsenic, cyanide, selenium and sulphate concentrations in fern samples from Kwabrafoso were 78.7mg/kg, 13.1mg/kg, 12.3mg/kg and 520.0 mg/kg respectively. Samples from sites in the wind direction showed higher pollutant levels than those from the leeward side; selenium levels in top soil samples from the wind direction were 3.3-4.6mg/kg and 2.1-2.7mg/kg in samples from the leeward side. Samples from sites along the polluted rivers showed high levels of cyanide. The concentration of cyanide in fern was 8.6-13.5 and 0.6-1.2mg/kg in plantain samples. Mercury levels were generally high ranging from 0.1-9.4 mg/kg. Pollutants originating from the P.T.P showed decreasing levels with distance from the P.T.P. At Kokoteasua, sulphate concent.ration in elephant grass samples was 301.7mg/kg and 46.9mg/kg at Domeabra. Pollutant 1evels in polluted waters also decreased in the rainy season; cyanide concentration in polluted water samples from Ampunyase was 11.3mg/L in March but reduced to 6.0mg/L in August. Mercury levels did not however vary regularly with distance. Water quality analysis of the drinking waters showed that pollutant levels were within permissible limits. Those along the polluted rivers however, showed higher levels of arsenic from 0.06-0.08 mg/L.
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