Determination of levels of cyanide in soils, water and cassava at Bibiani- a gold mining town in Ghana

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Bibiani is a gold mining town in the Western Region of Ghana and the method of mining used is surface mining. The main leaching agent used is sodium cyanide which is toxic and when not properly managed could contaminate the soil, water and foodstuff which serve as the basis of livelihood for the natives living in the mining communities. Total cyanide concentrations in the soil, water and cassava samples from Bibiani were determined. Total cyanide concentrations were also determined in the soil, cassava and water samples from KNUST, Kumasi in the Ashanti Region to serve as control samples. Two analytical methods were adopted for cyanide determination of the samples. They are the argentometric method using potassium iodide as indicator and colorimetric method using pyridine-barbituric acid reagent as coupling agent and UV-Visible spectrophotometer to measure cyanide concentration. The research was conducted between October 2004 and May 2005 . Zinc, cadmium, copper and iron concentrations were determined in all the samples using the flame atomic absorption spectrometer. Sodium was also determined using the flame photometer. The mean total cyanide concentrations in raw cassava ranged from 84.74 to 149.99 mg/kg fresh weight using argentometric method and 82.45 to 142.91 mg/kg fresh weight using colorimetric method. The cassava peels had levels of cyanide ranging from 360 to 510 mg/kg for the argentometric method and 360.05 to 509.51 mg/kg for the colorimetric method. The cooked cassava had cyanide concentrations ranging between 6.79 and 24.91 mg/kg. The mean total cyanide levels in the soil samples ranged from 6.04 to 26.17 mg/kg and the mean total cyanide levels in water samples ranged from 2.17 to 7.83 mg/L. Sodium concentrations ranged from 998.1 to 1794.7 mg/kg in the soil, 25.94 to 29.92mg/L in the water and 114.7 to 159.6 mg/kg in the cassava samples. The concentration of iron in the soil samples ranged from 77.88 to 302.08mg/kg while in the cassava and water samples, iron was below detection limit. Copper concentrations ranged from 12.4 mg/kg to 115.4mg/kg in the soil, 4.6 to 6.0 mg/kg in the cassava and below detection in the water samples. The zinc concentrations ranged from 24.1 to 170.3 and 7;6 to 11.6 mg/kg. in soil and cassava samples respectively. Zinc was below detection in most of the water samples. however, two of the water samples had traces of it. Cadmium was generally low in all the samples. The pH of the soil, water and cassava samples ranged from 3.88 to 6.95, 3.14 to 7.44 and 5.42 to 5.60 respectively. The moisture content of the soil samples ranged between 2.47 and 35.40% and that of cassava. 56.08 to 56.87 %. Conductivity and total dissolved solids of water ranged from 34 to 155.5cm and 31 to 89mg/L respectively. The toxicological implications of these findings are discussed.
A thesis submitted to the College of Science in partial fulfilment for the requirements of Master of Science, 2005