Residues of organochlorine pesticides and heavy metal contamination at Akumadan, a vegetable growing centre in the Ashanti Region of Ghana

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A survey was conducted at Akumadan in the Ashanti Region of Ghana, to evaluate farmers’ perception, attitude and practice in the use of pesticides. The organochiorine pesticide residues and the heavy metals in water, sediments and soil were ascertained. The survey revealed the use of insecticides, fungicides, herbicides, fertilisers and other agrochemicals in this farming area. Of the insecticides, Karate (synthetic pyrethrum) 40%, Actellic (organophosphate) 15% and Thiodan (organochlorine) 10% were mostly used while Dithane (carbamate) and kocide were the fungicides of choice. Most of the farmers have had education only to the middle school leaving certificate level. Organochlorine pesticide residue analyses were performed on water and sediments from Afrancho, Nkotodwe, Ehuru, and Atwetwe rivers and on soil from cultivated fields about 50 m from each of the rivers as well as soils from old Akumadan Irrigation site and the Akumadan Irrigation extension site. The organochiorine detected were p p - DDT, HCB and α - Endosulfan. The mean residue levels of p p-DDT in the water of the rivers ranged from 0.232 to 0.522 μg/l and from 1.284 to 6.689 μg/1 for hexachlorobenzene (HCB) and lastly from 0.00 1 to 0.002 μg/l for α - Endosulfan. These values, with the exception of HCB, were well below the W.H.O. recommenced safe values in water. The mean residue level in sediments ranged from 0.001 to 0.002 μg/g for p p -DDT and from 0.002 to 0.015 μg/g for HCB. There were no measurable quantities of organochiorine pesticides in soil samples. Heavy metals residue levels of Pb, Zn, Cd, Cu, Hg and Ni were analysed in water, sediment and soil. The levels of the heavy metals in water ranged as follows. Pb, 0.1, 0.28 mg/l; Zn, 0.2- 0.21 mg/l, Cd. 0.03 - 0.08 mg/l; Cu, 0.14- 0.18 mg/l; Ni 0.02 - 0.09 mg/l and Hg, 0.00 - 0.01 mg/l. The mean Pb, Cd, and Hg levels exceeded the W.H.O. recommended safe values, while Zn and Cu were below the recommended safe values in the water. In the sediments under study, Pb, Zn and Cu levels were comparable to the levels reported from unpolluted sediments, while Cd and Hg far exceeded the safe levels. Heavy metal levels in soil in both 0 - 15 cm and 15 - 30 cm depth were also compared with levels reported for rural uncontaminated arable soil. Zn and Ni were within comparable limits while Pb, Cu and Hg (where it occurred) were above the levels reported for uncontaminated soil.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Science in Environmental Science, 1998