Heavy metal contents of soil and citrus grown in selected districts of Ashanti Region, Ghana.
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Date
2011
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Abstract
Soil and edible citrus fruit samples from two mining districts (Obuasi and Asante Akim North) and two non-mining districts (Ejisu-Juaben and Sekyere West) of Ashanti Region, Ghana were assessed for their relative Zn, Cu, Fe, Cd, Pb and Mn contents and to ascertain whether citrus fruit heavy metal contents are within permissible limits. Representative areas were selected from these sites with sampling depending on the variability of the terrain. From each sampling unit, ten (10) soil cores/slice were taken from 0-15, 15-30 and 30-45 cm soil depths separately, each depth thoroughly mixed by hand in plastic bucket and sub-samples taken for laboratory analyses. Twenty-four edible citrus fruit samples were also taken from four trees at each sampling unit for laboratory analyses. A 0.1 M EDTA solution was used to extract the metals in soil. The citrus fruit pulp was digested in H2SO4/HCl mixture after evaporation to dryness. Mining activities, use of agrochemicals in agriculture production and vehicle exhaust fumes were proposed as the main sources of heavy metals. The accumulation of these metals in these municipalities were in the order Obuasi > Sekyere West > Asante Akim North > Ejisu-Juaben. There were significant differences of the selected metals levels in citrus fruits and soils from the four districts. Soils of low pH had higher citrus fruit uptake of heavy metals than those of moderate to high pH while soils of high organic matter content also had high metal content but low citrus uptake. There were either strong negative or positive correlations between soil and citrus fruit heavy metal contents.
Though the heavy metal load of soils from all the four municipalities were below the permissible limit set by the Dutch standards for soil contamination assessment, the levels of citrus fruit Zn and Pb of all the four districts were above the permissible limits set by FAO/WHO while Cd in citrus fruit of Obuasi, Asante Akim North and Sekyere West were above the permissible limit. Therefore, consumption of citrus fruit from the selected districts could pose health hazards to humans as at the time of the study.
Further research is required to determine the heavy metal content of soil and citrus fruit grown in other citrus-growing regions of the country as well as socio-economic and health status of neighbouring communities for sustainable citrus production in Ghana.
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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 Science in Soil Science