Pesticide Residues and Levels of Some Metals in Soils and Cocoa Beans in Selected Farms in the Kade Area of the Eastern Region of Ghana

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The use of organochlorine pesticides for agricultural purposes has been banned for over 25 years now in some developing nations like Ghana. However, there are evidences of their continuous usage in many developing nations, such as Ghana, due to inadequate regulation and management on the production, trade and use of these chemicals. In addition, not much work has been done on organochlorine pesticides (OCPs) residues and metals in soils and beans from cocoa farms in Ghana. This study conducted an investigation into the occurrence and levels of organochlorine pesticide residues and metals in soils and cocoa beans from ten inorganic farms at Kade. Soil and cocoa beans samples were also collected from an organic cocoa farm from Kade to serve as a control. The soil samples were analysed for Al, As, Ca, K, La, Mn, Na, V, Fe, Cu, Zn, Pb, Cr, Ni, Cd and Co, using Instrumental Neutron Activation Analysis (INAA) and Atomic Absorption Spectrophotometer (AAS). The pesticide residues in the collected soil and beans samples were determined by gas chromatography with electron capture detector (GC-ECD). The metal pollution levels in the soil samples were quantified using pollution load index and geoaccumulation Index. In addition, the mean concentrations of Al, As, Ca, V, Fe, Cu, Zn, Pb, Cr, Ni, Cd and Co in the inorganic soils were below their respective concentrations in the control soil samples. However, the mean concentrations of K, La, Mn and Na in the inorganic cocoa farm soil samples were significantly (p<0.05) higher than the measured mean concentrations in the control samples. The generally low concentrations of the elements in the soil samples reflected in the overall pollution indices of the studied farms. The pollution load index (PLI) and geoaccumulation index analyses of the soil data revealed that the soils at Kade cocoa farms were not polluted with the measured elements. The low PLI values for all the inorganic farms (<1) may suggest that the agricultural activities in Kade have little impacts on the soil so far as the sixteen examined elements are concerned. The results from this study also show that the concentrations of Ca, Mg, Pb, Cr, Cd, Al, Co, As, La, K and V in the cocoa beans samples were less than the machine detection limits of 0.001 mg/kg. However, the mean detected concentrations of Fe, Mn, Zn and Ni in the cocoa beans samples collected from the inorganic cocoa farms were relatively higher than the measured amounts in the control samples. The recorded concentrations of Fe, Mn, Zn, Cu and Ni in the cocoa beans samples do not pose any health threat to consumers since they were all within the permissible levels of WHO and FAO. The study identified no organochlorine pesticide (OCPs) residue in the cocoa beans from Kade. In general, sixteen different pesticide residues were detected in the soil samples. These included the derivatives of HCH, DDT and its metabolites, aldrin, dieldrin, heptachlor, trans-heptachlor epoxide, cis-heptachlor epoxide, trans-nanochlor, and trans-chlordane. The total DDT and total HCH levels in the soils of each sampling site were lower than 200ng/g stipulated by WHO/FAO. The residue levels of HCHs and DDTs measured in the soils of this study would have little risk to ecological environment and human health. The results indicated that past agricultural application of OCPs might be the major source of OCP residues in the soils. The low concentrations or non-detectable levels of aldrin, dieldrin, heptachlor, trans-heptachlor epoxide, cis-heptachlor epoxide, trans-nanochlor, and trans-chlordane, indicate a possible phasing out of these persistent organic pollutants.
A thesis submitted to the School of Graduate 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 Environmental Science