Studies on levels of mercury, zinc and cadmium in soils and cassava in the vicinity of an alluvial goldmine at Dunkwa-On-Offin

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Studies on Hg, Zn and Cd in soils and cassava crop were carried out in the vicinity of Dunkwa-On-Offin where there is alluvial mine. The samples were collected from farms, the vicinity of the gold house and the dredge sites within 20 km by the shortest distance from the centre of Dunkwa-On-Offin. Flame - Atomic-Absorption Spectrophotometric technique was used to determine the levels of Cd and Zn while the cold vapour Atomic Absorption Spectrophotometric technique was used to determine the Hg levels. The range of the concentration of the metals in surface soils (0-5 cm) was as follows; Hg, 32.9 μgkg-1 to 274 μgkg-1 Cd, under no detectable limits of the analytical method to 4.75 mgkg-1. Zn ranges from 18.5 mgkg-1 to 75.6 mgkg-1. The zinc showed a decreasing concentration with depth in soil up to 30 cm zone while the Hg and Cd showed irregular trends with depth. For cassava tissues, the flesh, the leaves and the peels (the peridem and the cortex), showed different levels of the metals. The metal concentrations in the flesh were for most samples less than those in the peels and leaves. The peridem (outer peel) mostly showed higher metal concentrations than the cortex (inner peel) The leaves had the highest levels of Hg and Zn indicating that the source was aerial The range of the metals in the cassava tissues is as follows Hg, 3.06 μgkg-1 to 35.17μgkg-1 Zn, 10.6 mgkg-1 to 123.30 mgkg-1 Cd, 0.45 mgkg-1 to 4.08 mgkg-1
A Thesis Submitted to the Department Of Chemistry, College of Science, Kwame Nkrumah University of Science And Technology, Kumasi, in partial fulfilment of the requirements for the Degree of Master of Science (Analytical Chemistry), 2000